Fig 6 - uploaded by Giulio Matteucci
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Examples of current source-density (CSD) patterns and corresponding visually evoked potential (VEP) profiles observed along the linear silicon probes. A: example of a superficial recording session, characterized by the presence of an inversion in the polarity of the VEPs (black curves), for which the peak from positive becomes negative, while moving downward from the base (channel no. 32) toward the tip (channel no. 1) of the probe. As a result of such inversion, the corresponding CSD pattern (color map) features the presence of a current source (yellow region) in the upper channels and a sink (blue region) in the lower ones. The sink is thought to be the signature of a stimulus-evoked barrage of synaptic input impinging on granular-layer neurons. B: example of a deep recording session, where neither the inversion of the VEP polarity nor the presence of a source region in the CSD pattern can be detected. On the other hand, a progressive change in the shape of the VEP deflection (more prolonged in time and with less positive rebound) can be observed moving downward along the probe. This change is reflected in the CSD pattern by a lengthening in time of the stimulus-evoked sink (blue region).
Source publication
In recent years, the advent of the so-called silicon probes has made it possible to homogeneously sample spikes and local field potentials (LFPs) from a regular grid of cortical recording sites. In principle, this allows inferring the laminar location of the sites based on the spatiotemporal pattern of LFPs recorded along the probe, as in the well-...
Contexts in source publication
Context 1
... ease the visual classification task, we overlaid the VEPs to the corresponding CSD pattern, a visual aid that is commonly applied to provide a richer picture of the stimulus-induced LFP response across the recording sites. Figure 6 shows the CSD pattern and the corresponding VEP profile for a representative superficial (Fig. 6A) and a representative deep session (Fig. 6B). As can be appreciated by comparing the two pictures, the inversion in the polarity of the VEPs, accompanied by an inversion of the polarity of the CSD, is visible only for the superficial recordings. ...
Context 2
... duration of the sink. To ease the visual classification task, we overlaid the VEPs to the corresponding CSD pattern, a visual aid that is commonly applied to provide a richer picture of the stimulus-induced LFP response across the recording sites. Figure 6 shows the CSD pattern and the corresponding VEP profile for a representative superficial (Fig. 6A) and a representative deep session (Fig. 6B). As can be appreciated by comparing the two pictures, the inversion in the polarity of the VEPs, accompanied by an inversion of the polarity of the CSD, is visible only for the superficial recordings. As a result, it is relatively easy to distinguish L2/3 from L4 in Fig. 6A, whereas it is ...
Context 3
... classification task, we overlaid the VEPs to the corresponding CSD pattern, a visual aid that is commonly applied to provide a richer picture of the stimulus-induced LFP response across the recording sites. Figure 6 shows the CSD pattern and the corresponding VEP profile for a representative superficial (Fig. 6A) and a representative deep session (Fig. 6B). As can be appreciated by comparing the two pictures, the inversion in the polarity of the VEPs, accompanied by an inversion of the polarity of the CSD, is visible only for the superficial recordings. As a result, it is relatively easy to distinguish L2/3 from L4 in Fig. 6A, whereas it is harder to discriminate the boundary between L4 ...
Context 4
... representative superficial (Fig. 6A) and a representative deep session (Fig. 6B). As can be appreciated by comparing the two pictures, the inversion in the polarity of the VEPs, accompanied by an inversion of the polarity of the CSD, is visible only for the superficial recordings. As a result, it is relatively easy to distinguish L2/3 from L4 in Fig. 6A, whereas it is harder to discriminate the boundary between L4 and L5 in Fig. 6B. Nevertheless, it is by inspecting this kind of plot that the manual annotation of layer boundaries is typically carried out. Fig. 5. Overall accuracy of the visually evoked potential (VEP) template-matching algorithm. A: distribution of absolute errors in ...
Context 5
... As can be appreciated by comparing the two pictures, the inversion in the polarity of the VEPs, accompanied by an inversion of the polarity of the CSD, is visible only for the superficial recordings. As a result, it is relatively easy to distinguish L2/3 from L4 in Fig. 6A, whereas it is harder to discriminate the boundary between L4 and L5 in Fig. 6B. Nevertheless, it is by inspecting this kind of plot that the manual annotation of layer boundaries is typically carried out. Fig. 5. Overall accuracy of the visually evoked potential (VEP) template-matching algorithm. A: distribution of absolute errors in estimating the depth of the recording sites using our method, as obtained by ...
Citations
Laminar electrode arrays allow simultaneous recording of activity of many cortical neurons and assignment to correct layers using current source density (CSD) analyses. Electrode arrays with 100-micron contact spacing can estimate borders between layer 4 versus superficial or deep layers, but in macaque primary visual cortex (V1) there are far more layers, such as 4A which is only 50-100 microns thick. Neuropixels electrode arrays have 20-micron spacing, and thus could potentially discern thinner layers and more precisely identify laminar borders. Here we show that CSD signals lack the spatial resolution required to take advantage of high density Neuropixels arrays and describe the development of approaches based on higher resolution electrical signals and analyses, including spike waveforms and spatial spread, unit density, high-frequency action potential (AP) power spectrum, temporal power change, and coherence spectrum, that afford far higher resolution of laminar distinctions, including the ability to precisely detect the borders of even the thinnest layers of V1.
Teaser
New analysis methods allow high-resolution cortical layer identification using data from high-density laminar electrode arrays.
Background
Cortical visual prostheses often use penetrating electrode arrays to deliver microstimulation to the visual cortex. To optimize electrode placement within the cortex, the neural responses to microstimulation at different cortical depths must first be understood.
Objective
We investigated how the neural responses evoked by microstimulation in cortex varied with cortical depth, of both stimulation and response.
Methods
A 32-channel single shank electrode array was inserted into the primary visual cortex of anaesthetized rats, such that it spanned all cortical layers. Microstimulation with currents up to 14 μA (single biphasic pulse, 200 μs per phase) was applied at depths spanning 1600 μm, while simultaneously recording neural activity on all channels within a response window 2.25–11 ms.
Results
Stimulation elicited elevated neuronal firing rates at all depths of cortex. Compared to deep sites, superficial stimulation sites responded with higher firing rates at a given current and had lower thresholds. The laminar spread of evoked activity across cortical depth depended on stimulation depth, in line with anatomical models.
Conclusion
Stimulation in the superficial layers of visual cortex evokes local neural activity with the lowest thresholds, and stimulation in the deep layers evoked the most activity across the cortical column. In conjunction with perceptual reports, these data suggest that the optimal electrode placement for cortical microstimulation prostheses has electrodes positioned in layers 2/3, and at the top of layer 5.
