Exploring the relationship between vagal tone and event-related potentials in response to an affective picture task

Abstract

The present study is the first to investigate the relationship between vagal tone level and event-related potentials (ERPs) in adults. Numerous studies have shown a relationship between vagal tone and the individual differences between a variety of psychophysiological, affective, and social outcomes. This suggests that vagal tone can be related to how people process relevant affective social information at the brain level. This study aimed to assess whether the ERP response varies between high and low vagal tone groups, in the face of salient affective information. In the experimental cohort, two groups were separated according to their vagal tone level. ERPs were recorded while individuals performed an affective picture task that included positive, neutral, and negative emotional stimuli. Differences between the high and low vagal tone groups were observed at the early posterior negativity for both positive and negative valences, and at the late positive potential for all the categories. It can be concluded that differences between high and low vagal tone levels are related to differences in the ERPs at early, middle, and late latencies. The results are discussed with respect to the effect of differences between the vagal tone conditions on various stages of information-processing.

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Exploring the relationship between vagal tone and event-related potentials
in response to an affective picture task
Michele Dufeya; Esteban Hurtado; Ana María Fernándezb; Facundo Manesc; Agustín Ibáñezd
a Universidad Diego Portales, Santiago, Chile b Universidad Diego Portales, and Universidad de
Santiago de Chile, Santiago, Chile c Institute of Cognitive Neurology (INECO) & Institute of
Neurosciences, Favaloro University, Buenos Aires, Argentina d Universidad Diego Portales, Santiago,
Chile, Institute of Cognitive Neurology (INECO) & Institute of Neurosciences, Favaloro University,
and National Scientific and Technical Research Council (CONICET), Buenos Aires, Argentina
First published on: 23 April 2010
To cite this Article Dufey, Michele , Hurtado, Esteban , Fernández, Ana María , Manes, Facundo and Ibáñez, Agustín(2011)
'Exploring the relationship between vagal tone and event-related potentials in response to an affective picture task',
Social Neuroscience, 6: 1, 48 — 62, First published on: 23 April 2010 (iFirst)
To link to this Article: DOI: 10.1080/17470911003691402
URL: http://dx.doi.org/10.1080/17470911003691402
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SOCIAL NEUROSCIENCE, 2011, 6 (1), 48–62
© 2010 Psychology Press, an imprint of the Taylor & Francis Group, an Informa business
www.psypress.com/socialneuroscience DOI: 10.1080/17470911003691402
PSNS Exploring the relationship between vagal tone
and event-related potentials in response to an
affective picture task
Vagal Tone and ERPS Michele Dufey
Universidad Diego Portales, Santiago, Chile
Esteban Hurtado
P. Universidad Católica de Chile, and Universidad de Santiago de Chile, Santiago, Chile
Ana María Fernández
Universidad Diego Portales, and Universidad de Santiago de Chile, Santiago, Chile
Facundo Manes
Institute of Cognitive Neurology (INECO) & Institute of Neurosciences, Favaloro University,
Buenos Aires, Argentina
Agustín Ibáñez
Universidad Diego Portales, Santiago, Chile, Institute of Cognitive Neurology (INECO)
& Institute of Neurosciences, Favaloro University, and National Scientific and Technical Research
Council (CONICET), Buenos Aires, Argentina
The present study is the first to investigate the relationship between vagal tone level and event-related potentials
(ERPs) in adults. Numerous studies have shown a relationship between vagal tone and the individual differences
between a variety of psychophysiological, affective, and social outcomes. This suggests that vagal tone can be
related to how people process relevant affective social information at the brain level. This study aimed to assess
whether the ERP response varies between high and low vagal tone groups, in the face of salient affective informa-
tion. In the experimental cohort, two groups were separated according to their vagal tone level. ERPs were
recorded while individuals performed an affective picture task that included positive, neutral, and negative
emotional stimuli. Differences between the high and low vagal tone groups were observed at the early posterior
negativity for both positive and negative valences, and at the late positive potential for all the categories. It can be
concluded that differences between high and low vagal tone levels are related to differences in the ERPs at early,
middle, and late latencies. The results are discussed with respect to the effect of differences between the vagal
tone conditions on various stages of information-processing.
Keywords: Vagal tone; ERPs; EPN; LPP; P1; IAPS; Affective social information; Peripheral–central relationship.
Correspondence should be addressed to: Agustín Ibáñez, Laboratory of Experimental Psychology & Neuroscience and Institute of Cogni-
tive Neurology (INECO) & CONICET Castex 3293 (CP 1425) Buenos Aires, Argentina. E-mail: aibanez@neurologiacognitiva.org
The authors would like to thank Ezequiel Gleichgerrcht for his help in reviewing the paper, and Rodrigo Ortega for his technical support.
Downloaded By: [University of California, Santa Barbara] At: 00:55 9 April 2011

VAGAL TONE AND ERPS 49
INTRODUCTION
In order to understand human behavior in its social
context, it is important to study how people extract and
process relevant information from their environment
through complex stimuli in order to make decisions
(San Martín et al., in press). Emotional information has
been shown to be robust and to have predictable effects
on cognition by providing specific cognitive strategies
that influence the selection of responses (Forgas, 1995;
Frith & Singer, 2008; Levenson, 1999; Riveros et al.,
2010) through the activation of bounded brain areas
(Eslinger et al., 2008; Harris & Fiske, 2007; Jabbi &
Keysers, 2008; Wager, Davidson, Hughes, Lindquist,
& Ochsner, 2008). Previous studies have identified and
characterized both central and peripheral responses to
incoming emotional information, with either positive or
negative hedonic valence (Bradley, Codispoti, Cuthbert,
& Lang, 2001a; Bradley, Codispoti, Sabatinelli, &
Lang, 2001b; Lang, Bradley, & Cuthbert, 1998a;
Schupp et al., 2000; Schupp, Junghöfer, Weike, &
Hamm, 2004a). This suggests that complex emotional
information provided by the social environment trig-
gers high-level cognitive processing not only through
structures and networks in the brain, but also by means
of the participation of peripheral organs in affective
self-regulation. This leads to a permanent feedback
loop between central and peripheral components
(Porges, Doussard-Roosevelt & Maiti, 1994) that is
coordinated by a central autonomic network (Thayer &
Lane, 2000). The present study represents an inquiry
into this kind of peripheral–central relationship that
occurs in response to affective social information.
More specifically, the purpose of this work is to
assess whether high and low vagal tone levels are
related to differences in the modulation of event-
related potentials (ERPs) evoked by emotional stim-
uli, categorized with positive, neutral, or negative
hedonic valence.
At the peripheral level, and from an affective regu-
lation standpoint, several studies have established
individual differences in responses to socially and
emotionally challenging situations as a function of
vagal tone. Vagal tone is a psychophysiological con-
struct that is often quantified by the amplitude of res-
piratory sinus arrhythmia (RSA), which is the result
of permanent increases and decreases in heart rate
(HR) coupled to the phase of inspiration and expira-
tion of the breathing cycle (Eckberg, 1983). There is a
considerable body of research that has shown that
vagal tone is related to affective, social and cognitive
variables, and therefore it has been proposed as an
index of emotional regulation (Appelhans & Luecken,
2006; Porges et al., 1994).
Various studies have shown that young children
with a high vagal tone level present more positive
psychophysiological, behavioral, and social perform-
ance in diverse experimental settings (Calkins, 1997;
Huffman et al, 1998; Linnemeyer & Porges, 1986;
Porter, Porges, & Marshall, 1988) as well as predic-
tive outcomes in mental, motor, and social skills
(Doussard-Roosevelt, McLenny, & Porges, 2001;
Doussard-Roosevelt, Porges, Scalon, Alemi, & Scalon,
1997), relative to children with lower vagal tone. In fact,
some studies have indicated that vagal tone and self-
regulation ability are related to children’s parental social-
ization (Calkins, Smith, Gill & Johnson, 1998; Haley &
Stansbury, 2003; Hastings et al., 2008; Katz, 2007).
Although not entirely consistent, these findings support
the idea that vagal tone can be related to differences
associated with individuals’ perceptions about their
own social environments.
Vagal tone in adults has been less extensively stud-
ied. It has been reported that high expression of vagal
tone predicts a superior level of self-control on self-
reports and a lower level of negative emotional
arousal towards moderate to high stress (Fabes &
Eisenberg, 1997). Similarly, a higher level of RSA is
associated with more intense emotional responses on
exposure to negative films (Demaree, Robinson,
Everhart & Schmeichel, 2004). Furthermore, evid-
ence suggests that individual differences in RSA are
predictive of increasing negative reactivity during face-
to-face interactions (Butler, Wilhem, & Gross, 2006; for
other results see Frazier, Strauss, & Steinhauer, 2004).
The divergent nature of these results could stem from
methodological differences in the experimental set-
tings used to evoke emotional responses in these stud-
ies. Nonetheless, the bulk of evidence suggests that
vagal differences are related to variations in affective
and emotional reactions. Reinforcing this idea, poor
vagal modulation has been related to affective disorders,
such as anxiety and depression (Light, Kothandapani, &
Allen, 1998; Lyonfields, Borkovec, & Thayer, 1995;
Rechlin, Weis, Spitzer, & Kaschka, 1994; Yeragani
et al., 1991), as well as higher levels of social anxiety
(Movius & Allen, 2004).
One particular aspect that has received little atten-
tion in the literature is the relationship between vagal
tone and brain activity. On one hand, a few studies
have evaluated variations in brain activity using neu-
roimaging, as well as variations of cardiac activity in
the high frequency (HF) domain, caused essentially
by parasympathetic (mainly vagal) influence on the
heart. While these studies illustrate the correlation
between the activity of specific brain structures and
autonomic parasympathetic activity towards cognitive
and emotional tasks, the variations according to vagal
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50 DUFEY ET AL.
tone and their relationship with brain activity
concerning emotional information have yet to be
established. On the other hand, only one study so far
has evaluated vagal tone and brain activity using the
electroencephalogram (EEG) in infants by employing
a mismatch negativity paradigm (MMN, Leppänen
et al., 2004). That study demonstrated that, among
other cardiac measures, vagal tone correlates signifi-
cantly with the ERP amplitude in some positions of
the scalp, which indicates a greater maturity of this
component.
An experimental strategy frequently used to study
the modulation of brain activity in response to emo-
tionally relevant stimuli is the presentation of images
with emotional valence that can be positive, negative,
or neutral, and with differing levels of arousal within
each hedonic category, obtained through the Interna-
tional Affective Picture System (IAPS; Lang, Bradley,
& Cuthbert, 2005). While such studies have not
assessed vagal activity, some have been able to char-
acterize the motivational aspects of attention
responses, at both the peripheral and brain levels (e.g.
ERPs). These studies are particularly relevant to the
search for correlates between peripheral and central
parameters in relation to how subjects react to psy-
chophysiological, adaptively relevant information.
At the peripheral level, exposure to emotional
stimuli is reflected through specific cardiac response
patterns, as well as facial muscle activity and electri-
cal conductance of the skin (Bradley et al., 2001a,
2001b; Lang et al., 1998a). At the brain level, it has
been reported that emotional stimuli modulate early
ERP latency components (e.g., P1), medial ERP
latency components (N2; P2; and early posterior neg-
ativity, EPN) and late ones (P300; late positive poten-
tial, LPP; and slow wave, SW). This modulation
depends on the nature of the task and its methodologi-
cal implementation. Specifically, emotional valence
seems to predominantly modulate early components
situated between 100 and 350 ms after the presenta-
tion of stimuli, while arousal appears to influence a
later time window (200–1000 ms after stimulus pres-
entation; Olofsson, Nordin, Sequeira, & Polich,
2008). In relation to the topographic distribution of
ERPs on the scalp, a greater positive modulation on
the posterior region is seen lateralized to the right
hemisphere, albeit inconsistently (Junghöfer, Bradley,
Elbert, & Lang, 1995; Schupp, Junghöfer, Weike, &
Hamm, 2003; Schupp et al., 2006).
The present research study stems from the fact that
little attention has been given to the relationship
between vagal tone and brain processing. Given the
individual differences in emotional vagal tone across
the normal adult population, expanding the knowledge
about this relationship would be instrumental in eluci-
dating the way in which people process relevant, emo-
tionally adaptive information at the central level. To
this end, we propose to evaluate the brain activity of
subjects who present either high or low vagal tone, by
employing an experimental paradigm with emotional
images portraying human social situations associated
with positive, negative, and neutral valence. This will
allow us to test whether vagal tone influences varia-
tions in ERPs induced by complex stimuli that are
adaptively relevant.
One advantage of using the previously described
affective task is that it offers a framework from which
to characterize the subject’s brain response in a way
that is comparable to previous evidence. Another
advantage is the fact that ERPs have a high temporal
resolution in the processing of the presented stimuli,
which ensures a substantial degree of accuracy in the
time window within which processing differences by
group may occur. If discrepancies in the brain
processing between the high and low vagal tone
groups are produced at early stages of the information
codifying, it is also predictable to find differences in
the modulation of the sign in the early components of
the ERPs. Otherwise, if differences occur at the later
stage of information-processing, then variations in the
amplitude of the sign will be reflected in the later
components of the ERPs. Alternatively, it is possible
that no differences at the early, middle or late compo-
nents of the ERPs exist between the high and low
vagal tone levels.
MATERIALS AND METHODS
Participants
A total of 32 undergraduate students were recruited
for the study. Data from four of them were discarded
due to artifacts in electrophysiological recording.
The final sample included 28 students (57%
females) ranging between 18 and 27 years of age,
with a mean of 21.56 years (SD = 2.56). Individuals
were screened to exclude any cardiac (e.g., arrhyth-
mia) or respiratory (e.g., asthma alterations) or drug
consumption that might affect any of the target vari-
ables. Visual acuity and handedness were controlled,
including only normal or corrected-to-normal indi-
viduals and right-handed participants (selected with
the Oldfield Inventory; Oldfield, 1971). All partici-
pants read and signed an informed consent approved
by the institutional ethical committee and in agree-
ment with the Declaration of Helsinki of 1975 before
the study.
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VAGAL TONE AND ERPS 51
Group selection
Vagal tone was operationalized as RSA. In order to
obtain this measure the electrocardiograms (ECGs) of
participants were recorded under resting conditions
while asking the subjects to remain comfortably
seated for 5 min. The ECG was registered continu-
ously and digitized online by the Biopac amplifier
MP100 and AcqKnowledge Software, using a Lead II
configuration for electrode placement. Sample fre-
quency was set at 250 Hz. Afterwards the heart period
(HP) was quantified offline from the ECG recording as
the time in milliseconds between consecutive R-wave
peaks. Results were analyzed with MxEdit software
(Porges, 1985) that computes the HP series for each
epoch of 30 s, which is then graphically displayed and
manually edited in order to remove artifacts. Then the
HP series are sampled in time, to obtain an instant
estimation of it on equally spaced intervals of 500 ms,
which allows further filtering by means of conven-
tional techniques. Sources of nonstationary tendencies
(aperiodicity and slow periodicity) are modeled and
removed from the HP by means of a 21-point moving
polynomial. Resulting HP stationary series are filtered
with a bandpass filter (0.12–0.40 Hz), in order to
exclude variance out of the range of respiratory
frequency that is typical in adults (e.g., 7–24 respira-
tions/min). Finally, the variance of the filtered data is
calculated and RSA is estimated by the natural loga-
rithm of the variance, to normalize its distribution,
varying the RSA values between 0 and 10, approxi-
mately (Spalding, Jeffers, Porges, & Hatfield, 2000).
According to the method proposed by Porges
(1985), RSA was calculated every 30 s for the resting
period. RSA scores for each subject (min. = 3.58,
max. = 8.88, mdn = 5.93) were considered in order to
divide the sample into a high (HVT, n = 13, 69%
females, mean age = 21.46, DE = 2.79) and a low
vagal tone group (LVT, n = 15, 47% females, mean
age = 21.64, DE = 2.44). After the conformation of
the HVT and LVT groups, age and gender differences
were analyzed in order to control the matching between
groups for those variables. No age, t(25) = .18, ns, or
gender differences, χ2 (1) = 1.45, ns, were found.
Finally, mean RSA values for the high and low vagal
tone groups were M = 7.18 (SD = 0.74) and M = 5.06
(SD = 0.74), respectively.
Stimulus validation
The stimuli presented in the affective picture process-
ing task were obtained from the IAPS (Lang et al.,
2005) and were initially selected according to their
arousal score (1 = low; 9 = high), and valence (1 =
negative; 9 = positive) following the IAPS’s norms
with a pilot sample of students (see below). The
images of the IAPS have been previously standard-
ized on US samples, showing test–retest reliability
coefficients and internal consistencies of r = .99, α =
.94 in valence, and of r = .97 and α = .93 in arousal
(Lang et al., 2005). From the standardized scores, a
total of 187 images representing people in different
social situations were selected. Some examples of the
selected images are, for the positive category: chil-
dren playing, couples in romantic situations; for the
neutral category: people walking on the street, inside
a house or standing up; and for the negative category:
people crying, situations of violence and obfuscation,
drugs and alcohol consumption.
Following the original standardization protocol
(Lang et al., 2005) a validation sample of 135 volun-
teers (mean age = 20.13, SD = 2.29) rated the stimuli
in valence and arousal. Finally, 20 images on each
affective category were intentionally obtained from
the above described contents (valence scores for pos-
itive M = 7.37, SD = 0.40; negative M = 2.66, SD =
0.44; neutral M = 4.64, SD = 0.44, and arousal scores
for positive M = 5.76, SD = 0.48; negative M = 6.02,
SD = 0.56, neutral M = 4.29, SD = 0.51).1
In order to calibrate valence and arousal values
between different categories of stimuli, it was
expected that all categories differed significantly from
the others, and that positive and negative categories
were similar in arousal values but different with
respect to the neutral one. Statistical analysis revealed
significant differences between all categories in
valence, F(2, 133) = 168.97; p = .001, and arousal dif-
ferences were also found between categories, F(2,
133) = 140.818, p = .001, with both positive and neg-
ative categories differing from neutral, p values =
.001, even though both showed similar arousal values
with no significant differences between the two of
them.
Experimental design and procedure
EEGs were assessed in both groups (HVT and LVT)
while subjects completed a processing task of affective
1 IAPS picture numbers for the pleasant category: 2070, 2071,
2152, 2208, 2209, 2216, 2311, 2340, 2345, 2530, 2550, 4574, 4599,
4607, 4623, 4660, 4689, 7325, 8490, 8496; neutral category: 2104,
2190, 2200, 2210, 2214, 2280, 2381, 2410, 2440, 2441, 2480, 2493,
2512, 2520, 2570, 2579, 2600, 2749, 2850, 9210; unpleasant cate-
gory: 2120, 2130, 2141, 2205, 2312, 2399, 2490, 2691, 2700, 2710,
2750, 2753, 2900, 3280, 4621, 6562, 6825, 9041, 9220, 9520.
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52 DUFEY ET AL.
images. Following the precedent of previous research
protocols (e.g., Schupp et al., 2000), the 60 images
were presented for 1500 ms, and each trial was pre-
ceded by a signaling image with a fixation point at the
center of the screen at 200 ms. The interval between
stimuli was randomized, ranging from 800 to 1500
ms. Images were presented four times each, with a
total of 240 trials, no stimulus being presented more
than twice for the same affective valence on each
sequence. The total set of 60 images appeared com-
pletely prior to the new sequence presenting them in a
different order.
Participants were instructed to carefully observe
each image, avoiding movements that could interfere
with the quality of the assessment (e.g., eye-blinks,
and eye or head movements). Then they had to rate
the valence of the image (positive, neutral, or nega-
tive) once it disappeared from the screen, using three
keys on a response keyboard placed in front of the
participant. The maximum response time was 2000
ms, during a period in which the screen went black
awaiting the participant’s response. The affective task
was run on a computer monitor situated approxi-
mately 80 cm away from the participant.
Once the EEG assessment was finished, partici-
pants were shown each image again, in order to evalu-
ate them on a behavioral task according to the valence
and arousal dimensions. For this purpose, the paper
and pencil version of the Self-Assessment Manikin
(SAM; Lang, 1980) was used. This is a language-free
scale that evaluates valence and arousal by presenting
graphical illustrations that represent nine varying lev-
els for each of these dimensions. The affective scores
of the SAM are highly correlated with longer instru-
ments that include language, such as the semantic
difference scale by Bradley & Lang (1994).
EEG acquisition and processing
Signals were recorded online using a GES300,
129-channel system with HydroCel Sensors from
Electrical Geodesic, Inc. with a DC coupling
amplifier, 24-bit A/D converter, 200 MΩ input
impedance, 0.7 μV RMS/1.4 μV pp noise, and
NetStationTM software. Analog filters were 0.1 and
100 Hz. A digital band pass filter between 0.5 and
30 Hz was applied offline to remove unwanted fre-
quency components. Signals were sampled at 500 Hz
and later resampled at 250 Hz to reduce the data size.
The reference was set by default to vertex, but then was
re-referenced offline to average electrodes. Two bipo-
lar derivations were designed to monitor vertical and
horizontal ocular movements (electrooculographs).
Stimulus-locked epochs were selected from the con-
tinuous data, beginning 200 ms prior to stimulus
onset. All epochs with eye movement contamination
were removed from further analysis, using an auto-
matic (Gratton, Coles, & Donchin, 1983) method for
removing eye-blink artifacts and visual procedures.
Artifact-free epochs were averaged to obtain the
ERPs. The analysis was done separately based on
group (HVT and LVT), category (positive, negative,
and neutral) and regions of interest (ROIs). ERP
waveforms were averaged separately for each experi-
mental condition. The EEGLAB Matlab toolbox and
T-Besp software were used for EEG offline process-
ing and analysis.
Data analysis
A mixed repeated-measures ANOVA was conducted
for the behavioral data from obtained offline record-
ings, with a between-subjects factor (Group: HVT and
LVT) and a within-subject factor (Category: positive,
neutral, negative). ROIs were used to represent and
analyze the scalp topography of the ERP components
as recommended for dense arrays, in order to avoid
loss of statistical power (Oken & Chiappa, 1986). The
ERP analysis was carried out based on the ROIs
chosen by visually checking each component. Each
ROI comprised three adjacent electrode sites centered
around the maxima: P1 (right: 96, 90, 83; left: 58, 65,
70); EPN (right: 96, 90, 83; left 58, 65, 70); and LPP
(anterior: 11, 16, 15; central: 129, 6, 55; posterior: 81,
72, 75). Although the figures show the ERP grand
averages for each group, all statistical calculations
were done using each participant’s individual data.
ERP amplitudes were quantified as the peak negative
or positive deflection occurring within a 115–125 ms
temporal window (P1); 220–290 ms temporal window
(EPN) and 350–500 ms temporal window (LPP).
For each component, a mixed repeated-measures
ANOVA with one between-subjects factor (Group:
HVT and LVT) and two within-subject factors (Cate-
gory: positive, neutral, negative) and ROI (left and
right P1; left and right EPN; and finally, anterior,
central and posterior LPP) were performed. Univariate
comparisons were done whenever necessary. Results
were corrected with the Greenhouse-Geisser and
Bonferroni methods to adjust the unvaried output of
the repeated-measures ANOVA for violations of
the compound symmetry assumption. All post-hoc
comparisons for both the behavioral and electrophysi-
ological data were performed with Tukey’s HSD
tests.
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VAGAL TONE AND ERPS 53
RESULTS
Behavioral data
Valence effects
A main effect for Category was observed, F(2,
25) = 505.07, p = .001. Post-hoc analysis (MS = 0.26,
df = 75.26) revealed that positive ratings (M = 6.47, SD
= 1.00) were significantly higher than neutral (M =
4.54, SD = 0.44), and neutral scores were signifi-
cantly higher than negative (M = 2.09, SD = 0.51)
scores, p values = .001. No significant effects for
Group, F(1, 26) = 1.32, ns, or Category × Group inter-
action F(2, 75) = 0.48, ns, were found.
Arousal effects
Similar to valence results, a significant Category
effect was found, F(2, 25) = 34.67, p = .001. The post-
hoc analysis (MS = 1.37, df = 77.20) showed that both
negative (M = 6.47, SD = 1.00) and positive (M =
5.18, SD = 1.44) categories significantly differed from
neutral (M = 4.28, SD = 1.00), p values = .001 and .01
respectively, but that there was no difference between
affective categories, ns. No main effect for Group,
F(1, 26) = 0.34, ns, or Category × Group interaction,
F(2, 25) = 0.87, ns, was observed.
ERPs
P1. A main effect on ROI’s variables was observed
F(1, 26) = 13.69, p = .001, in which the right ROI (M =
3.02, SD = 0.39), presented higher amplitudes than
the left ROI (M = 4.46, SD = 0.56; see Figure 1B).
There was also a main effect of Category, F(2, 52) =
3.49, p = .037. Post-hoc comparisons (MS = 0.42192,
df = 52.00) showed that only the negative category (M
= 3.56, SD = 0.41) was significantly distinguishable
from the positive (M = 3.88, SD = 0.49, p = .044).
Neither main effect nor interaction of the Group vari-
able was observed.
EPN. The analysis of this posterior component
showed a main effect of Category, F(2, 52) = 34.11, p =
.001. The negative category presented a greater amplitude
(M = 5.95, SD = 0.44) followed closely by the neutral (M
= 5.65, SD = 0.38) and finally by the positive category,
with the lowest scores (M = 4.52, SD = 0.41). A main
effect of ROI was also observed, F(1, 26) = 27.26, p =
.001. Greater amplitude values were obtained on the right
scalp (M = 6.19, SD = 0.48) compared to the left scalp
(M = 4.56, SD = 0.37; see Figure 1).
Regarding the interactions, there was a significant
interaction between Group × ROI, F(1, 26) = 5.53, p =
.026. The HVT group presented greater lateralization
difference (right: M = 7.01, SD = 0.70; left: M = 4.64,
Figure 1. Early posterior negativity (EPN) effects. Left and right ROI waveforms (top) and difference waveforms (bottom, positive – nega-
tive subtraction); to the right are topographic maps showing the voltage difference (positive – negative) over the scalp for each group of partic-
ipants (HVT and LVT Groups).
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54 DUFEY ET AL.
SD = 0.54) than the LVT group (right: M = 5.37, SD
= 0.65; left: M = 4.48, SD = 0.51). Post-hoc compari-
sons (MS = 5.17, df = 33.76) confirmed that only in
the HVT group was the lateralization effect signifi-
cantly different, p = .001.
There was also a triple ROI × Category × Group
interaction, F(2, 52) = 3.86, p = .027. The greater dif-
ferences between categories and groups of participants
were observed on the right region (see Figure 2).
To compare differences in categories between
groups, a restricted ANOVA was conducted on the
ROI. Besides a main effect of Category, F(2, 52) =
20.93, p = .001, an interaction of Category × Group,
F(2, 52) = 3.19, p = .049 was observed. Post-hoc
comparisons (MS = 7.23, df = 32.73) showed that only
in the HVT group could the positive category (M =
5.49, SD = 0.79) be distinguished from the negative
(M = 7.94, SD = 0.77, p = .001) and neutral catego-
ries (M = 7.60, SD = 0.67, p = .001).
Difference waveforms analysis (EPN). Additionally,
an analysis of the wave differences was conducted.
Given that the above analysis showed that the largest
differences occurred between the negative and positive
categories, a subtraction of these (positive – negative)
was conducted, in order to compare the discrimination of
the emotional content through the wide gap between the
opposite valences in the two groups of participants. To
compare these results, an ANOVA of the different wave-
forms (positive – negative) was used on a design with a
within-subjects factor (ROI) and a between-subject fac-
tor (Group).
The ROI variable was significant, F(1, 26) = 4.95,
p = .034, demonstrating greater amplitudes in the
right region (M = –1.77, SD = 0.28), compared to the
left (M = –1.09, SD = 0.19). Although the Group fac-
tor was not significant itself, an interaction of ROI ×
Group, F(1, 26) = 6.63, p = .016 was observed, indi-
cating that, in the right region, differences between
positive and negative categories were greater in the
HVT group.
Because of this last interaction, a one-way ANOVA
(difference in waveform × Group) was performed, aim-
ing to compare the differences of positive – negative in
the right region, where the main differences between
groups showed up. This difference was significant, F(1,
26) = 6.13, p = .020, showing that the HVT group had a
greater difference between negative and positive cate-
gories (M = –2.45, SD = 0.40) than the LVT group
(M = –1.10, SD = 0.37).
LPP. There was a Group effect, F(1, 26) = 18.57, p =
.001, with the LTV group (M = –0.31, SD = 0.30)
obtaining lower amplitudes compared to the HVT group
(M = 0.96, SD = 0.22). A main ROI effect was observed,
F(2, 52) = 17.37, p = .001, showing different values for
the frontal (M = 0.61, SD = 0.38), central (M = –1.71,
SD = 0.41) and occipital (M = 2.08, SD = 0.50) LPP
(see Figure 3).
Figure 2. Triple interaction between the Regions of interest,
Group of participants and Category. The amplitude graph shows
that the greater differences between the groups of participants and
category type occurred mostly in the right hemisphere.
Figure 3. LPP component distribution on the midline and ERPs
corresponding to the LPP for each category and each group of
participants.
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VAGAL TONE AND ERPS 55
Also, a Category effect was evident, F(2, 52) =
3.40, p = .040. Post-hoc comparisons (MS = 0.73869,
df = 52.00) revealed that only the negative category
(M = 0.20, SD = 0.23) differed from the positive cate-
gory (M = 0.53, SD = 0.23, p = .040), but not from the
neutral category (M = 0.25, SD = 0.24).
Finally, there was an ROI × Category interaction,
F(4, 104) = 3.50, p = .010. Post-hoc comparisons (MS
= 0.79, df = 104.00) showed that in the central LPP,
the positive category (M = –1.12, SD = 0.34) was sig-
nificantly different from the negative (M = –2.04,
SD = 0.34, p = .004) and neutral categories (M = –1.97,
SD = 0.34, p = .013).
DISCUSSION
This is the first study to inquire into the relationship
between vagal tone level and brain affective informa-
tion-processing in an ERP task in an adult population.
Our results indicate that there are differences between
the ways in which high and low vagal tone groups
process emotional information at different ERP com-
ponents, suggesting that vagal tone level is accompa-
nied by particular strategies for information-
processing at middle and late latencies. In the EPN,
we observed a higher discrimination between emo-
tional categories in the right hemisphere for the HVT
group; however, both groups exhibited a lateralization
effect. Also, higher LPP modulation was evident in
the HVT group, regardless of the type of category.
Although the P1 component showed a valence effect,
there was no evidence for a group difference. In the
behavioral task, no differences could be observed
between the HVT and LVT groups, showing that
affective variations in picture processing among
groups can be more readily detected at an electro-
physiological level.
The P1 is an early visual component that has been
previously described at latencies similar to those
observed in this study at occipito-temporal sites. It is
modulated by face (Holmes, Vuilleumier, & Eimer,
2003) and body (Van Heijnsbergen, Meeren, Grèzes,
& de Gelder, 2007) emotional content, and it possibly
reflects an early visual mechanism for rapid emotion
detection based on rough visual cues of the body and
face (Van Heijnsbergen et al., 2007). These cues are
consistent with the kind of stimuli (i.e., human situa-
tions) used in the present study, although these are to
some extent more complex than the rough stimuli
used in previous studies by other authors. Also, later-
ality effects observed in the right hemisphere have
been previously described (Eger, Jedynak, Iwaki, &
Skrandies, 2003; Van Heijnsbergen et al., 2007).
The EPN is a middle latency component that has
been associated with early and late stages of informa-
tion-processing, selectively for each affective cate-
gory (Schupp et al., 2004a, 2004b). Di Russo, Taddei,
Apnile, and Spinelli (2006) suggested that informa-
tion-processing within a 200–300 ms window would
reflect early discrimination and response selection
processes. Also, Schupp et al. (2004a) have stated that
processing indexed by the EPN is modulated by per-
ceptual features that facilitate further evaluation of
arousing stimuli. In the present study, the negative
category showed higher amplitude in the EPN, fol-
lowed by neutral and positive pictures.
Although a considerable number of studies have
found a similar modulation, differing from neutral, for
both emotional (pleasant, unpleasant) categories of
pictures, an increasing number of studies have
reported a differential modulation for the positive
stimuli when compared to both neutral and negative
in an early time window, such as the EPN. For
example, Cuthbert, Schupp, Bradley, Birbaumer, and
Lang (2000) observed that, within the time range of
the EPN (200–300 ms), responses to positive pictures
differed significantly from responses to both neutral
and negative ones; Keil et al. (2002) reported a similar
effect in the 120–150 ms time window and notably
also a lateralization pattern in the late P3 window,
with enhanced positivity for pleasant content. De
Cesarei & Codispoti (2006) found a larger positivity in
the early 150–300 ms window for both negative and
neutral pictures compared to positive; and finally, Pas-
tor et al. (2008) observed, in the same time window
(150–300 ms), that viewing of pleasant pictures
resulted in lower amplitude values over occipital sites
compared to neutral and negative pictures. The results
observed in our study are therefore consistent with this
body of evidence, as the positive category differed sig-
nificantly from both neutral and negative in our results.
Lateralization effects are in line with the literature
(De Cesarei & Codispoti, 2006; Junghöfer et al., 2001).
More interesting for the scope of this study are differ-
ences according to vagal tone in the EPN at the right
hemisphere, pointing to a higher affective discrimination
for the HVT in relation to LVT. Moreover, differences in
waveforms (positive – negative) further confirm this
finding, adding support to the hypothesis that a more
accurate discrimination between affective categories
exists for the HVT group when compared to the LVT
group, at early categorization stages of processing.
Consistently with lateralization findings, some
brain imaging studies have found a higher activation of
right-sided structures within associative visual cortices
in the processing of affective salient stimuli, when
compared to left-sided activation (Bradley et al.,
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56 DUFEY ET AL.
2003; Lang et al., 1998; Sabatinelli, Lang, Keil, &
Bradley, 2006). In light of our results, this evidence
suggests that differences in interhemispheric activity
between high and low vagal tone groups may in part
be due to variations in the engagement degree of vis-
ual cortices in face of high relevant affective informa-
tion, a process likely driven by interactions between
more anterior regions of the brain (e.g., the amygdala;
Davis & Whalen, 2001) and visual areas. It can be
added to this hypothesis that the higher recruitment of
right occipital areas in the HVT group might facilitate
the tuning of perceptual areas, thus allowing for a
more accurate discrimination between positive and
negative emotional stimuli, when compared to lower
levels of vagal tone. In sum, the lateralization effect sug-
gests a more accurate early modulation of EPN for the
HVT that is possible driven by a higher participation of
right visual cortices, which is specific for valence con-
tent and may reflect early encoding facilitated by emo-
tional content of visual stimuli (Schupp et al., 2003).
The LPP is a late component of the ERP that has
been well replicated in several studies (Cacioppo,
Crites, Gardner & Berntson, 1994; Crites, Cacioppo,
Gardner & Berntson, 1995; Schupp et al., 2000,
2004a, 2004b). It peaks typically around 300–400 ms
after the stimulus at medial sites, and is modulated by
affective content. Differences between the HVT and
LVT groups are generalized in this component, in
spite of the kind of hedonic category. The LPP has
been theoretically interpreted as a mandatory process
of initial semantic categorization, and is indicative of
the reflexive activation of the motivational neural net-
works that modulate emotional engagement (Pastor
et al., 2008). Furthermore, some evidence has shown
that this component (together with other late compo-
nents of the ERP, such as P300 and the SW) may be
involved in memory formation (Palomba, Angrilli, &
Mini, 1997). The group effects observed in the
present study show differential processing for all cate-
gories, suggesting that the HVT group had a greater
activation of the neural networks that underlie the
higher-order stages of information-processing.
The theoretical framework that accounts for the
differential processing of affective information claims
that the affect system has evolved from a bidimen-
sional organization, to being responsible for moti-
vated behavior (Cacioppo, Gardner, & Berntson,
1999; Lang, 1995). This can be further divided into
two motivational systems: an aversive system that
facilitates defensive and protective behaviors and an
appetitive system responsible for the approach to
pleasant stimuli when safety is perceived. The kind of
task used in the present study follows the line of
experimental paradigms that assume that unpleasant
and pleasant categories of pictures differentially acti-
vate the aversive or appetitive motivational systems,
respectively. This study is the first to account for dif-
ferences in the way that relevant affective stimuli are
processed differently by the brain, at diverse stages of
information-processing, according to vagal tone level.
Specifically, the early discrimination stages indexed by
the EPN component of the ERP show particular differ-
ences between the HVT and LVT groups for affective
categories. Thus, it can be stated that there is an adap-
tive value of more accurate stimuli discrimination
linked to differential engagement of the motivational
systems by affective stimuli for the HVT group, in
comparison to the LVT group. In fact, the organization
of successful behavioral strategies depends on the effi-
cient extraction of critical information from the envir-
onment (Öhman, Flykt &, Lundqvist, 2000).
The notion that vagal tone may be related to differ-
ences in the way the brain extracts relevant informa-
tion from the environment is concordant with research
on vagal tone and diverse affective variables (see
Beauchaine, 2001). At a theoretical level, the poly-
vagal theory of Porges (2003a, 2003b) emphasizes
the role of evolution in the organization of the
nervous system—particularly the vagus—and
social behavior, accounting for three different evo-
lutionary levels of the autonomic nervous system:
(1) a myelinated vagus linked to social communica-
tion, self-soothing, and calming; (2) a sympathetic-
adrenal system responsible for active avoidance by
mobilization; and (3) an unmyelinated vagus respons-
ible for immobilization, passive avoidance, and death
feigning. The first of these autonomic evolved levels is
well developed in mammals and particularly in pri-
mates, fostering what has been called the “social
engagement system.” One prediction of the polyvagal
theory is that individuals who exhibit higher cardio-
vagal tone levels would also express more social adap-
tive behaviors, and the opposite would be accompanied
by more difficulties in affective and social regulation.
If the differences seen in this study in the way HVT and
LVT brains extract and process information are taken
into account, the adaptive value of a high vagal func-
tion, as the polyvagal theory states, can be supported.
Possible neural sources that underlie the emotional
modulation of the ERPs are suggested by previous
imagery studies. On one hand, an increased activity in
visual cortices occurs when viewing pleasant and
unpleasant stimuli when compared to neutral ones
(Bradley et al., 2003; Lane, Reiman, Ahern, &
Schwartz, 1997; Lang et al., 1998a, 1998b; Sabatinelli
et al., 2006), which has been confirmed with ERP
modulations for the EPN and LPP components
(Schupp et al., 2003). As well, several studies have
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VAGAL TONE AND ERPS 57
shown that emotional content triggers specific
responses in the amygdala, which in turn activates sen-
sory cortical areas and therefore allows for a more accu-
rate perceptual processing when affective stimuli are
presented (Armony & Dolan 2002; Lang et al., 1998a;
Morris et al., 1998). On the other hand, positive correla-
tions have been observed among parasympathetic car-
diac HF domain measures and the activity of different
limbic-related structures, such as the insular and ventro-
medial prefrontal cortex (Gianaros, Van Der Veen, &
Jennings, 2004) or the anterior and ventral cingulate
cortex (Matthews, Paulus, Simmons, Nelesen & Dims-
dale, 2004; O’Connor, Gündel, McRae, & Lane, 2007)
in cognitive tasks, and in the medial prefrontal cortex,
the caudate nucleus, the periaqueductal gray and the
mid-insular area in response to emotional stimuli (Lane
et al., 2009). Taking this evidence together with laterali-
zation effects, it can be hypothesized that limbic and
cortical structures participating in functional networks
that are activated by emotional stimuli may be differen-
tially recruited in the high and low vagal tone conditions
(see also Ibañez, Gleichgerrcht, & Manes, in press;
Thayer & Lane, 2000).
Since the two groups were not significantly different
in terms of age or gender, and all participants belonged
to a similar educational level (undergraduate students),
differences cannot be explained in terms of socio-demo-
graphic variability between groups. In fact, groups were
equivalent in relevant variables that affect ERPs, except
for vagal tone level, excluding the possibility of ERP dif-
ferences between groups secondary to other variables.
The goal of our study was to assess the participation of
the body and peripheral organs (measured by vagal tone)
in relation to central processing (measured by ERPs). Our
report is the first to show a peripheral–central relationship
occurring in response to affective social information in
adults. This is a new branch of research and our study
does have some limitations, to be addressed in future
studies. Although numerous studies on IAPS/ERPs have
already been performed, showing an occipito-temporal
EPN and centro-parietal LPP, those components are
altered by several aspects of the design such as stimulus
features (i.e., complexity, size, color, frequency), gender
of participants, and type of task (Cano, Class, & Polich,
2009; Codispoti, Ferrari, De Cesarei, & Cardinale, 2006;
Delplanque, N’diaye, Scherer, & Grandjean, 2007; Lang
et al., 1998b; Rozenkrants, Olofsson, & Polich, 2008;
Rozenkrants & Polich, 2008). Paradigm-dependent
effects must be specifically addressed in future studies of
vagal tone group differences.
In the same line, although pleasant and unpleasant
pictures are usually associated with lower (more neg-
ative) occipito-temporal positivity compared to neu-
tral pictures (Codispoti, Ferrari & Bradley, 2007; Keil
et al., 2002; Schupp et al., 2004a), the reported effects
are not always in the same direction. Therefore, specific
effects (task or stimuli-dependent) on early components,
EPN and LPP relation to valence and the influence of
arousal should be studied in further vagal tone research.
Regarding early components (e.g., P1), the controver-
sies found throughout the literature result from differ-
ences on task and recording methodology. When studies
use dense arrays and short time windows for stimulus
presentation (i.e., 200 ms), P1 effects are present
(Carretié, Mercado, Hinojosa, Martin-Loeches, &
Sotillo, 2004; Junghöfer et al., 2001; Schupp et al.,
2003). Dense arrays allow for the consideration of sev-
eral different possible ROIs in order to better detect
valence category differences. In addition, fast presenta-
tion times enhance early components generation. Most
classic studies of IAPS used stimulus durations longer
than 500 ms, reducing the magnitude of early effects,
but when time presentation is around 120–300 ms, early
effects are reliable (Schupp et al., 2003, 2004a, 2006).
In our results, a weakness in the LPP category
modulation can be observed, since stimuli selected
were moderate in arousal. It is well known that the
LPP is more sensitive to arousal than to emotional
content. Arousal is the primary determinant of LPP,
and valence minimally influences LPP amplitude (Cano
et al., 2009; Rozenkrants et al., 2008; Rozenkrants &
Polich, 2008), which is consistent with our LPP
results showing a small emotional effect of valence.
As presented in our data, valence effects are typically
observed for early and EPN (100–300 ms), and
arousal effects are observed for later (300–800 ms)
components, with only a small effect of valence cate-
gory in this time window (Codispoti et al., 2007;
Olofsson et al., 2008; Rozenkrants & Polich, 2008).
Because our explicit goal was to look at the valence of
emotional effects and not arousal effects, we chose
stimuli that did not possess high arousal values.
Future studies may address other effects, such as
arousal, presentation time or task-dependent effects
and their possible interaction with emotional content
in the differences between LVT and HVT groups in
the P1, EPN, and LPP time windows. These studies
will be important to further elucidate the nature of
stimuli response, as recent studies have started to
describe the distinct underlying brain systems that
may mediate valence and arousal of affective stimuli
differently (Nielen et al., 2009).
The LPP observed in the IAPS tasks has been
recently identified as P300 (Cano, Class, & Polich, 2009;
Rozenkrants, Olofsson, & Polich, 2008; Rozenkrants &
Polich, 2008; see a review in Olofsson et al., 2008). The
P300 is now thought to be composed of several proc-
esses that reflect attentional and memory-engaged
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58 DUFEY ET AL.
mechanisms. In particular, the integrated view of
P300 as assessed by Polich (2007) can orient future
studies of vagal tone differences and ERP/IAPS
designs. This view assesses two components (P3a and
P3b) with differences in scalp localization (more ante-
rior and more posterior, similar to those obtained in our
LPP results) and in function. In this view, P3a origi-
nates from stimulus-driven frontal attentional mecha-
nisms during task processing (focal attention), whereas
P3b originates from temporal-parietal activity associ-
ated with attention and subsequent memory processing
(context maintenance). Since there are topographic and
functional features related to P300, further studies can
test the integrated theory of P300 as a potential back-
ground for highlighting the ERPs differences and relat-
ing subjacent mechanisms observed in each group-
specific pattern with different vagal tone levels.
As an alternative hypothesis, it can be proposed
that RSA might influence only the ERPs amplitude
(modulator variable) rather than the emotional dis-
crimination process. However, our data seem not to
support this notion, since higher amplitude of the
ERPs in the HVT group can only be observed in some
temporal windows and this effect is not generalized to
all components. On one hand, the early P1 component
did not show group differences, so an absolute ERP
amplitude difference cannot be assumed. On the
other, the EPN window does not support the alternat-
ive hypothesis either. Although there is a general
higher amplitude in this group restricted to right hem-
isphere, the most relevant finding is actually the
higher differentiation of positive and negative stimuli
by the HVT group, in the ERP as well as in the differ-
ence waveforms (positive – negative). This finding is
indicative of a more accurate discrimination between
positive and negative categories of stimuli in the HVT
group. This effect cannot be accounted for by higher
ERP amplitude alone. Finally, the general higher
modulation of the LPP in the HVT group is the only
result that does not contradict the alternative hypothe-
sis of the RSA as a moderator effect over the ERPs.
LPP does not show valence affects but a general
group effect. Since the LPP component is mainly sen-
sitive to arousal levels of the stimuli (instead of
valence effects, Hurtado, Gonzalez, Haye, Manes, &
Ibanez, 2009; Olofsson et al., 2008) it could be the
case that higher levels of RSA influence higher levels
of arousal in the HVT group, giving rise to the general
higher amplitude effect. If that were the case, it would
imply a different explanation from the alternative
hypothesis. In sum, ERP modulation seems to be dif-
ferentially modulated according to valence and arousal
parameters of the stimuli within each group, rather than
being a consequence of a general amplitude effect for
the HVT group. However, future studies should
address this topic by implementing precise experimen-
tal designs to determine whether specific aspects of
emotional information (such as valence or arousal) are
influencing different components of the ERPs and how
those relate to vagal tone, or whether vagal tone moder-
ates the sensitivity of the ERP to affective stimuli.
Finally, it is important to highlight the fact that
HVT and LVT differences in response to stimuli were
found only at the electrophysiological level, with no
significant group differences observed on the behav-
ioral task, a finding that has been previously reported
in IAPS studies (e.g., Hot, Yasuhiko, Mandai, Kobayashi,
& Sequeira, 2006). Reporting ERP changes without
overt behavioral differences is not a new topic in the
ERP literature (Gray et al., 2004; Ibáñez, Haye,
González, Hurtado, & Henríquez, 2009; Ibañez,
Lopez, & Cornejo, 2006; Ibáñez, Manes, Escobar,
Trujillo Andreucci, & Hurtado, 2010; Ibáñez, San
Martin, Dufey, Bacquet, & Lopez, 2008a; Ibáñez, San
Martin, Hurtado, & López, 2008b; Kotchoubey,
2006), and even more so in psychiatric populations
(Guerra et al., 2009). This finding is crucial for sev-
eral reasons that have direct theoretical and clinical
implications. First, it reveals that physiological
responses may dictate essential aspects of human
social interactions (e.g., the way we react to someone
else’s behavior) that may not necessarily reach con-
sciousness or explicit behavior. In this sense, the
results of this study can be useful in debating specific
aspects of behavioral models in social neuroscience
(e.g., the somatic marker hypothesis; see Ibáñez et al.,
2009). As well, electrophysiological measures of this
caliber may contribute to the identification of relevant
affective response patterns that may help distinguish
the behavioral phenotype of several neuropsychiatric
disorders and, ultimately, complement differential
diagnosis, which is otherwise established through
clinical, functional, and neuropsychological assess-
ment. In addition to its potential contribution to diag-
nosis, electrophysiological measures like the ones
employed in the present study may also help in the
design of therapeutic approaches for a wide variety of
conditions. For example, patients with chronic fatigue
syndrome have been shown to exhibit reduced vagal
tone (Sisto et al., 1995), suggesting that interdiscipli-
nary treatment of psychiatric conditions could also
focus on the modulation of autonomic functioning as
part of comprehensive treatment programs, or even
use electrophysiological measures as an indicator of
treatment evolution and effectiveness.
One limitation of this study is that only baseline
vagal tone was assessed. It would be of great interest
to introduce dynamic measures of vagal reactivity,
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VAGAL TONE AND ERPS 59
since it points to behavioral and attentional regulation
that facilitates orientation to stimuli (for a discussion
see Santucci et al., 2008). ERP technique poses a
challenge for simultaneous assessment of both cere-
bral and physiological activity, as most affective para-
digms require briefer periods of stimuli presentation
than physiological recordings. Van Hecke et al.
(2009) have implemented a design that allows for the
joint assessment of both RSA and continuous EEG
(although they did not evidence any relationship
between the two variables); however, it is important
to consider that quantitative EEG and ERPs estimate
different aspects of brain activity. Future works
should consider the study of baseline vagal tone,
vagal reactivity and emotional processing in a single
experiment, either implementing a modified ERP
design that considers both cerebral and peripheral
recording time requirements or exploring other brain
activity measures such as quantitative EEG.
In conclusion, this is the first report that inquires
into the relationship between vagal tone level and the
cerebral response to affective salient information
assessed by ERPs. The results show that differences
between high and low vagal tone levels are related to
differences in the ERPs at middle and late latencies.
The HVT group showed a clear differentiation
between pleasant and unpleasant categories at the
EPN component on the right hemisphere, when com-
pared to the LVT. This would imply that a higher
vagal tone is associated with a more accurate strategy
to encode and discriminate affective relevant informa-
tion in relation to a lower vagal tone, which may
foster further processing at higher order levels (e.g.,
of semantic categorization or memory storage), as the
LPP differences between groups suggest. Future repli-
cation is necessary to assess the stability of these find-
ings and their generalization.
Manuscript received 21 October 2009
Manuscript accepted 28 January 2010
First published online 23 April 2010
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