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Action Observation and Acquired Motor
Skills: An fMRI Study with Expert Dancers
B. Calvo-Merino
1
, D.E. Glaser
2
, J. Gre` zes
3
, R.E. Passingham
4
and P. Haggard
2
1
Institute of Movement Neuroscience, University College
London and Department of Basic Psychology, Faculty of
Psychology, Universidad Complutense, Madrid, Spain,
2
Institute of Cognitive Neuroscience and Department of
Psychology, University College London, 17 Queen Square,
London WC1N 3AR, UK,
3
Laboratoire de Physiologie de la
Perception et de l’Action, Centre National de la Reserche
Scientifique-College de France, Paris, France and
4
Wellcome
Department of Cognitive Neurology and Functional Imaging
Laboratory, Institute of Neurology, University College London
and Department of Experimental Psychology, University of
Oxford, Oxford, UK
When we observe someone performing an action, do our brains
simulate making that action? Acquired motor skills offer a unique
way to test this question, since people differ widely in the actions
they have learned to perform. We used functional magnetic
resonance imaging to study differences in brain activity between
watching an action that one has learned to do and an action that one
has not, in order to assess whether the brain processes of action
observation are modulated by the expertise and motor repertoire of
the observer. Experts in classical ballet, experts in capoeira and
inexpert control subjects viewed videos of ballet or capoeira actions.
Comparing the brain activity when dancers watched their own dance
style versus the other style therefore reveals the influence of motor
expertise on action observation. We found greater bilateral activa-
tions in premotor cortex and intraparietal sulcus, right superior
parietal lobe and left posterior superior temporal sulcus when expert
dancers viewed movements that they had been trained to perform
compared to movements they had not. Our results show that this
‘mirror system’ integrates observed actions of others with an
individual’s personal motor repertoire, and suggest that the human
brain understands actions by motor simulation.
Keywords: biological motion, expertise, intraparietal, mirror neurons,
motor repertoire, premotor cortex
Introduction
When we watch someone performing an action, our brains may
simulate performance of the action we observe (Jeannerod,
1994). This simulation process could underpin sophisticated
mental functions such as communication (Rizzolatti and Arbib,
1998), observational learning (Berger et al., 1979) and social-
ization (Gallese and Goldman, 1998). Thus it has a major
evolutionary benefit.
A specific brain mechanism underlying this process has been
suggested. Within the premotor and parietal cortices of the
macaque monkey, ‘mirror’ neurons have been recorded which
discharge both when the monkey performs an action, and also
when observing the experimenter or another monkey perform-
ing the same action (di Pellegrino et al., 1992; Gallese et al.,
1996; Gallese et al., 2002). A similar mirror system may exist in
corresponding areas of the human brain (Decety and Gre` zes,
1999; Gre` zes and Decety, 2001; Rizzolatti et al., 2001). Buccino
et al. (2001) found a somatotopic organization in premotor and
parietal cortex when observing movements of different body
parts. This somatotopy corresponded to that found when the
same body parts are actually moved. The network underlying
human action observation seen in functional magnetic reson-
ance imaging (fMRI) includes premotor cortex, parietal areas
and the superior temporal sulcus (STS) (Grafton et al., 1996;
Rizzolatti et al., 1996; Buccino et al., 2001; Iacoboni et al.,
2001), predominantly in the left hemisphere (Decety et al.,
1997; Iacoboni et al., 1999; Gre` zes et al., 2003). The supple-
mentary motor area and motor cortex are typically not
activated, unless an element of movement preparation is also
involved, for example in cases of action observation for delayed
imitation (Gre` zes and Decety, 2001). This might suggest that
action observation activates only high-level motor representa-
tions, at one remove from actual motor commands. However,
transcranial magnetic stimulation (TMS) studies suggest that
action observation can directly influence the final cortical stage
of action control in the motor cortex. When people observe
actions involving a particular group of muscles, responses to
transcranial magnetic stimulation (Fadiga et al., 1995; Strafella
and Paus, 2000; Baldissera et al., 2001) in those same muscles
are specifically facilitated. These results suggest a brain process
of motor simulation based on direct correspondence between
the neural codes for action observation and for execution.
Some previous studies have suggested that the mirror system
activity specifically codes motor actions of a biological agent.
First, watching an artificial hand in action evoked much less
mirror system activity than watching real hand actions (Perani
et al., 2001; Tai et al., 2004). Second, biomechanically impos-
sible actions did not activate the mirror system (Stevens et al.,
2000). Finally, Buccino et al. (2004) carried out a study
comparing the actions of nonconspecifics, and found that
actions belonging to the motor repertoire of the observer
were mapped on the observer’s motor system. These results
suggest that the human mirror system might be sensitive to the
degree of correspondence between the observed action and the
motor capability of the observer.
However, it remains unclear whether a person’s action
observation system is precisely tuned to his or her individual
motor repertoire. Previous studies of the human mirror system
have used a very restricted set of simple actions, based on the
primate mirror neurons’ responses during grasping (Grafton
et al., 1996; Rizzolatti et al., 1996; Gre` zes et al., 2003). These
studies have reported mirror system activity during observation
of grasping, but have not directly tested whether the activity
while observing a particular action involves simulating the
corresponding motor programme for that action. However,
humans have a motor repertoire that far exceeds these simple
Ó Oxford University Press 2005; all rights reserved
Cerebral Cortex
doi:10.1093/cercor/bhi007
Cerebral Cortex Advance Access published December 22, 2004
object-oriented actions, and an apparently unlimited capacity to
acquire and perfect new motor skills. As a result, each person’s
motor repertoire is constrained not only by common musculo-
skeletal anatomy, but also by the acquired skills that person has
learned. A particular action may figure in the motor repertoire
of a trained expert but not in the motor repertoire of someone
who has not been so trained.
We therefore used acquired motor skills as a powerful way to
study the tuning of the brain’s mirror mechanisms. We studied
groups of people with different acquired motor skills to
investigate whether the brain’s system for action observation
is precisely tuned to the individual’s acquired motor repertoire.
If this were so, premotor and parietal cortex activity when
observing a given action should be stronger in individuals who
have learned to perform that action than in those who have not.
We tested this hypothesis using a factorial fMRI design in which
expert ballet and capoeira dancers watched videos of ballet and
capoeira movements. In this way, both groups of expert
subjects saw identical action stimuli, but only had motor
experience of the actions in their own dance style. We studied
these particular expert groups for several reasons. First, both
dance styles involve a well-established, distinctive set of move-
ments. Second, many male ballet and capoeira moves are
kinematically comparable. Third, dance involves arbitrary, in-
transitive movements of the whole body. Unlike the grasping
tasks previously used to investigate the mirror system in both
primate (di Pellegrino et al., 1992; Gallese et al., 1996, 2002) and
humans (Grafton et al., 1996; Rizzolatti et al., 1996; Gre` zes
et al., 2003), dance movements need not involve either external
objects or spatial targets locations. Therefore, any differences
between groups of dancers must reflect effects of expertise on
action observation, and not on the representation of the object
or location to which the action is directed. In other acquired
motor skills, such as ball games, action observation and object
representation might not be easily dissociable. A third group
of additional non-expert control subjects was also tested. If
differences in action observation activity between the two
groups of dancers are truly due to these groups’ expertise levels,
we predicted that non-expert control subjects should show
similar activity when watching either style of dance.
Materials and Methods
Subjects
Ten professional ballet dancers from the Royal Ballet, London, 9
professional capoeira dancers and 10 non-expert control subjects
participated. These dance styles were selected because of the kinematic
comparability of specific male ballet and capoeira moves. All subjects
were right-handed males aged 18--28 with normal vision and no past
neurological or psychiatric history. The professional dancers were
screened to ensure that they had no training in the other dance style.
All gave written informed consent and were paid for their participation.
The protocol was approved by the Ethics Committee of the Institute of
Neurology, London.
Stimuli and fMRI Task
Colour videos of standard classical ballet and capoeira movements were
recorded using a digital camera. The movements were performed by
ballet and capoeira professionals matched for body shape, appearance
and garments, in front of a neutral chromablue background. The
performers were naı¨ ve regarding the subsequent use of the videos. A
professional choreographer approximately matched the individual
capoeira moves to classical ballet moves, according to criteria of speed,
part of the body employed, body location in space and direction of
body movement. This process produced 12 pairs of 3 s video clips.
The dancers’ faces were blurred to ensure that subjects processed body
kinematics, rather than facial or emotional features (see Fig. 1 and online
Supplementary material for examples of the videos). The videos were
presented on a screen situated outside the scanner which the subject
viewed via a mirror (20
3 9 cm) located inside the scanner. During the
experiment, each video was repeated four times. Four null events (black
screen) were also presented. Stimulus order was randomized. Subjects
were instructed to indicate ‘how tiring’ they thought each movement
was by pressing one of three keys with three fingers of the right hand.
To avoid motor preparation, assignment of buttons to response
categories was randomized across trials. Previous training with this
response schedule was done outside the scanner with a second set of
dance videos.
Scanning and Data Analysis
The fMRI data were acquired on a 1.5 T Magnetom VISION system
(Siemens). Functional images were obtained with a gradient echo-planar
sequence using blood oxygenation level-dependent (BOLD) contrast,
each comprising 36 contiguous axial slices (2.5 mm thickness). Volumes
were acquired continuously with a repetition time (T
R
) of 3.24 s. A total
of 280 scans were acquired for each participant in a single session
(15 min), with the first five volumes subsequently discarded to allow for
T
1
equilibration effects. During fMRI scanning, eye position was
monitored on-line by an infrared eye tracker. The data were analysed
using a general linear model for event-related design in SPM2 (Wellcome
Department of Imaging Neuroscience, London; www.fil.ion.ucl.ac.uk/
spm) implemented in MATLAB 6.5 release 13. Individual scans were
realigned, slice time-corrected, normalized and spatially smoothed by
a 6 mm full width at half maximum Gaussian kernel using standard SPM
methods. The voxel dimensions of each reconstructed scan were 3
3
3 3 3 mm in the x, y and z dimensions, respectively.
Figure 1. Stimuli: Colour videos of standard classical ballet and capoeira movements
were performed by professional dancers. Twelve different moves of each style (a,
ballet; b, capoeira) were matched by a professional choreographer for kinematic
features (for examples see videos in the supplementary information online).
Page 2 of 7 Action Observation and Acquired Motor Skill
d
Calvo-Merino et al.
Event-related activity for each voxel, condition and subject was
modelled using a canonical haemodynamic response function plus
temporal and dispersion derivatives. Statistical parametric maps of the
t-statistic (SPM{t}) were generated for each subject and the contrast
images were stored.
In a second level random effects analysis, we used a 2
3 3 (stimulus
by group) ANOVA model. We constructed an F contrast to test for the
group by stimulus interaction, which indicates the extent to which the
difference between activity when viewing ballet and when viewing
capoeira may vary between groups. Plots of parameter estimates were
used to characterize whether the pattern of interaction constitutes
an effect of expertise. In order to correct for multiple comparisons in
interpreting these results, we used two strategies. First, for areas in the
action observation system about which we had a prior anatomical
hypothesis, a small volume correction (SVC) with a sphere of 10 mm
radius was used according to the coordinates of previous studies. We
used Buccino et al. (2001) for premotor and parietal and Gre` zes et al.
(2004) for posterior STS. Before using SVC, we transformed coordinates
given by Buccino et al. (2001) from Talairach space to MNI space (www.
mrc-cbu.cam.ac.uk). Second, to reveal unpredicted effects in other areas
outside the action observation system, we performed correction for
multiple comparisons over the whole brain, with a corrected signifi-
cance level of P
<
0.05. To characterize peak voxels within the activated
clusters of interest, we plot contrasts of parameter estimates for each
combination of the movement style and subject group. The surviving
activated voxels were superimposed on high-resolution magnetic re-
sonance (MR) scans of a standard brain (Montreal Neurological Institute,
MNI). In Table 1, we list clusters where SPM{F} for the interaction
reached P
<
0.001. We have additionally applied an extent threshold of
10 voxels to the data of Table 1, for the sake of brevity. Anatomical
identification was performed on cross-sections with reference to the
atlas of Duvernoy (1999).
Results
Functional images were analysed by statistical parametric
mapping (SPM2) using a general linear model applied at each
voxel across the whole brain. We localized those brain areas that
modulated their activity with expertise using an F-test. We de-
fined the expertise effect as the interaction between the three
subject groups and the two kinds of dance stimuli. That is, we
focused on voxels for which the difference between the re-
sponses to the two types of stimuli varied across the three
groups of subjects.
We predicted expertise effects in areas previously identified
within the human mirror system, namely the premotor cortex,
parietal cortex (intra-parietal sulcus, IPS), superior parietal lobe
(SPL) and superior temporal sulcus (STS). Accordingly, we
performed small volume corrections for multiple comparisons
using 10 mm spheres centred on these areas, as follows: we used
coordinates from Buccino et al. (2001) for premotor cortex, SPL
and IPS, and from Gre` zes et al. (2004) for STS. The results
showed bilateral activation in premotor cortex corresponding
to the expertise effect. We also found significant bilateral
activations in the intraparietal cortex /sulcus and right superior
parietal lobe (Fig. 2). Posterior parts of the STS were activated in
the left hemisphere. Although we show bilateral activations in
premotor and intraparietal cortex, the clusters for these
activations were larger in the left hemisphere than in the right.
These significant interactions were further investigated by
examining contrasts of parameter estimates (see Fig. 3). Experts
had greater activation when observing the specific movement
style that they could perform. This yielded a crossover pattern
of interaction between group and stimulus type. Moreover, the
same voxels in non-expert control subjects were essentially
insensitive to stimulus type, confirming that the interaction
depends on acquired motor skills, and not on visual properties
of the stimuli. Finally, no significant activations corresponding
to the main effects of expert group or stimulus type were found
in mirror system areas.
Beyond these predicted areas of interest, we also found other
expertise effects which survived correction for multiple com-
parisons over the whole brain (P
<
0.05). These included the
medial frontopolar gyrus, the cingulate gyrus extending from its
posterior part including the retrosplenial gyrus to its middle
part and the right parahippocampal gyrus (see Fig. 4). Further
activations are not discussed here since they were not specif-
ically predicted, and did not survive correction. These are, how-
ever, listed in Table 1 for information.
Discussion
Our results show that the brain’s response to seeing an action is
influenced by the acquired motor skills of the observer. Subjects
showed stronger BOLD responses in classical mirror areas
(Gre` zes and Decety, 2001; Rizzolatti et al., 2001), including
the premotor, parietal cortices and STS, when they observed
dance actions that were in their personal motor repertoire than
when they observed kinematically comparable dance actions
that were not in their repertoire. Thus, expert ballet dancers
showed greater activity in these areas when watching ballet
Table 1
Expertise effect s in action observation
Brain regions MNI coordinates Z-score
xyz
Predicted areas(SVC)
L superior precentral gyrus ÿ27 ÿ6 72 3.96
R superior precentral gyrus 30 ÿ6 69 3.35
R superior parietal lobe 24 ÿ69 63 4.15
L posterior intraparietal sulcus/superio r parietal lobe ÿ33 ÿ45 54 3.89
R intraparietal sulcus/postcentral sulcus 33 ÿ42 48 3.68
L precentral gyrus ÿ54 0 45 3.66
L Posterior Superior Temporal Sulcus ÿ39 ÿ66 36 4.04
Non-predicted areas (corrected P \ 0.05)
Retrosplenial gyrus 0 ÿ33 36 4.98
L posterior cingulate gyrus ÿ3 ÿ57 27 5.11
R Cingulate gyrus 3 15 27 5.08
Medial frontopolar gyrus 0 39 ÿ15 5.75
R parahippocampal gyrus 33 ÿ18 ÿ21 4.88
Non-predicted areas (uncorrected P \ 0.001)
L superior parietal lobe ÿ21 ÿ57 69 3.70
L precuneus ÿ15 ÿ54 51 3.88
R supramarginal gyrus 57 ÿ30 48 4.00
L ventral precentral gyrus ÿ48 3 27 4.17
R parieto-occipital fissure 21 ÿ60 27 3.79
R caudate nucleus 15 ÿ9 18 3.92
R inferior frontal gyrus 54 36 3 3.57
R head of caudate 9 12 ÿ6 3.45
R lateral occipital sulcus 63 ÿ48 ÿ9 3.97
R lateral occipital sulcus ÿ51 ÿ63 ÿ9 3.82
L occipital sulcus/middle temporal gyrus ÿ60 ÿ39 ÿ9 4.14
R lateral orbital frontal gyrus 33 36 ÿ18 3.92
L middle temporal gyrus ÿ60 ÿ12 ÿ 18 3.56
L lateral orbital frontal gyrus ÿ27 24 ÿ27 4.61
R anterior middle temporal gyrus 54 6 ÿ30 4.46
R anterior inferior temporal gyrus 54 --12 --36 3.68
The table shows transformed Z scores from an SPM{F} for the group by stimulus interaction.
The table is divided into three sections. In the first section, we show areas predicted that belong
to the action observation system and survive P \ 0.05 small volume correction using a 10 mm
sphere over coordinates from previous studies [Buccino et al. (2001) for premotor and parietal
cortex and Gre
`
zes et al. (2004) for pSTS]. In the second section, we present activations in areas
that were not predicted, but that surviv e correction for multiple comparisons across whole brain
at P \ 0.05. In the third section, we show areas for which no prediction was made, which are
significant at P \ 0.001 uncorrected. For the sake of brevity, only activations in excess of
10 voxels are listed in this section of the table. L/R: left and right hemispheres.
Cerebral Cortex Page 3 of 7
moves than when watching capoeira moves, while expert
capoeira dancers showed the opposite effect. Thus, while all
groups saw the same stimuli, the mirror areas of their brains
responded to the stimuli in a way that depended on the ob-
server’s specific motor expertise. This suggests that action
observation may recruit such mirror areas to the extent that the
observed action is represented in the subject’s personal motor
repertoire, i.e. if the subject has acquired the motor skills to
perform such actions. Further evidence linking action observa-
tion to specific motor representations comes from the param-
eter estimates in our normal subjects. For these individuals, who
had no motor experience of either ballet or capoeira, no such
differences were detected. Taken as a whole, our results suggest
that action observation in humans involves an internal motor
simulation of the observed movement.
In addition, these results clarify what kind of motor re-
presentation is engaged by action observation. First, significant
expertise effects suggest the mirror system codes complete
action patterns, not just individual component movements. The
dance styles studied here have quite similar components at the
muscle level (both involve jumping, for example). Even though
both groups of dancers could perform such primitive compon-
ent movements, our stimuli evoked mirror system activity
which varied with expertise. Previous studies emphasized
homology between muscle groups in observation and execu-
tion (Fadiga et al., 1995; Buccino et al. , 2001; Rizzolatti et al.,
2001). Our results suggest that the mirror system is also
sensitive to much more abstract levels of action organization,
such as those that differentiate dance styles. To borrow
a distinction from the motor control literature (Sanes and
Donohue, 2000), our results show that the mirror system is
concerned with observing skilled movements, not muscles.
Second, we find that mirror system representations are linked to
learned motor skills. A recent study of learning precisely timed
patterns of finger movements (Sakai et al., 2002) reported
premotor cortex activation associated with new learning of
such patterns. These activations were over and above the effects
of learning sequential order alone or temporal intervals alone.
Those results suggest that premotor cortex may encode de-
tailed action plans for complex movements. Our results suggest
such action plans may also be activated by action observation.
The experiment’s factorial design also excludes alternative
interpretations of these effects. First, our result cannot be due
to kinematic differences between ballet and capoeira stimuli,
since we defined expertise as the interaction of a factorial
design in which all groups of subjects saw both classes of
stimuli. We also carefully matched kinematics across the dance
two styles. Indeed, we found no main effect of stimulus type
within the mirror system, and parameter estimates of control
subjects showed similar activity in response to both kinds of
stimuli. This suggests that kinematics differences do not
contribute to our result. Second, our results are unlikely to
reflect differences between groups in purely perceptual pro-
cessing of the dance moves, since we found no evidence of
expertise effect in brain areas classically associated with
perceptual learning, such as the inferotemporal and occipital
cortices (Gauthier et al., 2000). Movement expertise did
modulate activity in middle temporal areas, perhaps reflecting
semantic categorization (Vandenberghe et al., 1996) of the
dance moves by experts but not by non-experts. However, this
effect did not survive correction for multiple comparisons.
Moreover, we suggest that any semantic categorization process
would be parallel to and independent of the motor simulation
conducted by the mirror system. Thus, Decety et al. (1997)
showed that meaningful and meaningless actions differed only
in the temporal and frontal activations evoked, while no
differences were seen in the classical action observation system.
We have suggested that the increased BOLD responses in
experts’ mirror systems reflected their motor expertise. How-
ever, dance performers generally see more of their own dance
style than of other dance styles. In particular, both classical ballet
and capoeira involve extensive practice with other dancers.
Could our results therefore reflect visual familiarity rather than
motor expertise? We suggest three arguments against this
Figure 2. Effects of motor expertise on brain responses to action observation defined as the group by condition interaction. Projections of the activation foci on the surface of
standard brain (Montreal Neurological Institute, MNI). Note that this projection renders onto the surface activity which may in fact be located in the sulci. Activations significant at
P \ 0.001 uncorrected are shown in red. For display purposes, an extent threshold of 10 voxels has been used. Arrows indicate predicted areas with activations significant at P \
0.05 after small volume correction using a 10 mm sphere. These are in the left hemisphere system ( A), in (1) ventral premotor, (2) dorsal premotor, (3) IPS and (4) pSTS. In the right
hemisphere (B) we show activations in (1) SPL and (2) IPS.
Page 4 of 7 Action Observation and Acquired Motor Skill
d
Calvo-Merino et al.
possibility. First, the expertise effects we observed within the
mirror system included areas classically considered as motor
areas, such as left premotor cortex. Second, we saw no expertise
effects in areas such as the fusiform gyrus, where effects of visual
familiarity and perceptual learning have been repeatedly re-
ported (Gauthier et al., 1999; Tarr and Gauthier, 2000). Finally,
preliminary evidence from another study suggests that motor
expertise has significant effects after effects of visual familiarity
are controlled for (Glaser et al., 2004). In classical ballet, some
moves are gender-specific, while others are performed by both
women and men. Since dancers train together, all dancers are
visually familiar with all moves. Female ballet dancers showed
lower left parietal BOLD responses when watching male-only
moves than when watching either female-only moves or moves
performed in common by either male or female performers.
The expertise effect showed two distinct activations — one
dorsal and one ventral — within the premotor cortex. The
dorsal premotor activation was found bilaterally, though with
a larger cluster size in the left hemisphere than in the right.
Ventral premotor activation was seen in the left hemisphere
only. Two distinct activations were also seen in the parietal
cortex, bilateral activity in the intraparietal sulcus and superior
parietal lobule in the right hemisphere only. Interestingly, we
also found SPL activation in the left hemisphere, but this did not
survive SVC using the coordinates of Buccino et al (2001). In
general, this pattern of activations fits well with previous studies
of somatotopic organization in premotor and parietal cortex.
Our dance stimuli obviously involved the whole body, with
large, proximal arm and leg movements. Primate studies suggest
that movements of each body part are coded in independent,
parallel parieto-frontal circuits that subserve somatotopically
organized motor representations of the different effectors
(Jeannerod et al., 1995; Rizzolatti et al., 1998). Thus, electrical
stimulation of the monkey premotor cortex elicited complex
postures (Graziano et al., 2002), with a dorsal-to-ventral
somatotopic organization for leg and foot, arm and hand and
finally face and mouth. A similar somatotopic organization for
Figure 3. Parameter estimates for the influence of motor expertise on action
observation in the central voxels of areas classically identified with the human mirror
system: (A) left precentral gyrus/dorsal premotor cortex (--24 --6 72), (B) left intra-
parietal sulcus (--33 --45 54), (C) left posterior superior temporal sulcus (--39 --66 36).
In all three areas, parameter estimates show that the effect of expertise is driven by
a crossover interaction between the two groups of expert dancers and the two
stimulus types. Stimulus type has minimal effects in control subjects. Black bars reflect
parameter estimates for ballet stimulus and white bars reflect capoeira stimulus.
Figure 4. Influence of motor expertise on brain responses to action observation:
saggital section showing activation after correction for multiple comparisons across
the whole brain at P \ 0.05. (1) ventro-medial frontopolar gyrus, (2) cingulate gyrus,
(3) posterior cingulate gyrus and (4) retrosplenial gyrus.
Cerebral Cortex Page 5 of 7
action observation was found in parietal and premotor cortex
when human subjects watched a moving hand or a moving foot
(Buccino et al., 2001). Our results are consistent this concept of
direct somatotopic matching between visual stimuli of body
parts and corresponding movements.
We also found a clear effect of expertise in a third element of
the human mirror system, the left posterior STS. This region is
functionally and anatomically distinct from other visual motion
areas such as MT (Watson et al., 1993) and the kinetic occipital
region (Van Oostende et al., 1997), because it does not respond
well to coherent, translational motion or kinetic boundaries.
Rather, the STS is involved in the perception of biological
motion (Bonda et al., 1996; Grossman and Blake, 2002) and of
hand, mouth and eye movements (Allison et al., 2000). As for
the premotor and the parietal cortex, the present study shows
an influence of motor expertise in a classically perceptual area
such as the STS.
Finally, we identified a second set of areas influenced by
expertise. This comprised the ventromedial frontal lobe, anterior/
middle and posterior cingulate and parahippocampal gyrus.
These areas did not form part of the initial hypotheses for the
study. However, they survive statistical correction for multiple
comparisons over the whole brain volume and are consistent
with other findings relating these areas to emotional experi-
ence. The activation in the ventromedial frontal cortex recalls
two previous theories of activation in this area. First, this area is
routinely activated in emotion processing (see Steele and
Lawrie, 2004, for a meta-analysis). In particular, it shows strong
responses to pleasurable and rewarding stimuli (O’Doherty et al.,
2003). Second, Decety and Chaminade (2003) have suggested
that this area contributes to social judgement and the regulation
of social behaviour. These two explanations are clearly not
mutually exclusive in the context of expertise effects. Experts
may show increased ventromedial frontal activation when
watching their own movement style because it is particularly
rewarding for them, or because they have a greater social
engagement with the person they observe. Our study cannot
distinguish between the emotional and the social-engagement
aspects of this activation, and indeed was not designed to do so,
though this would be a fruitful topic for future research.
The influence of expertise on cingulate, retrosplenial and
parahippocampal activation is also consistent with these areas’
role in episodic memory. Functional neuroimaging studies of
retrieving items from memory have shown effects of familiarity
on prefrontal activations, and also anterior and posterior
cingulate (Burgess et al., 2001). The posterior activations may
contribute to imagery and episodic recall from long-term storage
of allocentric information maintained in other areas of the brain.
The greater familiarity of experts with their own movement style
may lead to stronger activation of brain mechanisms of episodic
memory, even when watching another person.
The right parahippocampal region is involved in storing and
maintenance of stimulus representations across long delays, and
seems predominantly dedicated to visuospatial aspects of these
processes (Maguire et al., 2003; Small et al., 2003). Moreover, the
parahippocampal gyrus shows greater activity following when
viewing meaningful as compared to meaningless actions (Decety
et al., 1997). Actions that appear meaningless to inexpert sub-
jects may appear more meaningful to experts, and additionally
recruit circuits for semantic representation in the brain. The in-
fluence of expertise suggests that, taken together as a network,
activation of these midline areas reflects a combination of episo-
dic memory processes and the degree of engagement between
the viewer and the stimuli during action observation.
Conclusion
In summary, we have shown a clear effect of acquired motor
skills on brain activity during action observation. The network of
motor areas involved in preparation and execution of action was
also activated by observation of actions. Crucially this activation
was stronger when the subjects had the specific motor
representation for the action they observed. Therefore, the
parietal and premotor cortex mirror system does not respond
simply to visual kinematics of body movement, but transforms
visual inputs into the specific motor capabilities of the observer.
While all the subjects in our study saw the same actions, the
mirror areas of their brains responded quite differently accord-
ing to whether they could do the actions or not. We conclude
that action observation evokes individual, acquired motor repre-
sentations in the human mirror system. Our finding lends support
to ‘simulation’ theories (Gallese and Goldman, 1998), according
to which action perception involves covert motor activity
(Jeannerod, 1994; Gre` zes and Decety, 2001; Rizzolatti et al.,
2001). This activation of motor representations through mere
observation could have important applications in enhancing
skill learning and in motor rehabilitation.
Notes
We are grateful to Deborah Bull and Emma Maguire (Royal Ballet), Tom
Sapsford and Giuseppe Vitolo and Rodrigo Peres (Capoeira School,
London), and Opher Donchin for advice and assistance. This work was
supported by a Wellcome Trust Programme Grant and an EU Fifth
Framework Program (R.P., J.G.), EU Marie Curie Research Training
Site (B.C.), Leverhulme Trust Research Fellowship (P.H.) and MRC
Co-operative Group Grant to the Institute of Cognitive Neuroscience
(D.G.).
Address correspondence to Patrick Haggard, Institute of Cognitive
Neuroscience and Department of Psychology, University College
London, 17 Queen Square, London WC1N 3AR, UK. Email: p.haggard@
ucl.ac.uk.
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