Grouped SDE and <i>d</i>’ visualization.

<p>Responsivity and preference to each category for all subdural electrodes (SDEs) over ventral temporal cortex (VTC, <i>right</i>) and lateral occipital cortex (LOC, <i>left</i>), grouped across all 26 subjects (following surface-based normalization) and visualized on the MNI N27 template brain. Compass points denote SDE coordinates (Talairach space) and direction. SDE diameter reflects normalized BGA magnitude for each category (mean BGA divided by standard deviation), scaled by the largest normalized response across categories per region (VTC and LOC are scaled differently). SDE colors reflect their d’ values per category. Positive, significant <i>d’</i> indices (FDR corrected <i>q</i> ≤ 0.01) are represented by the category-specific color-code at the top of the color bar (e.g. SDEs with significant face <i>d’</i> colored red). Positive, non-significant <i>d’</i> indices are represented as intermediate color-scales specific for each category. Negative <i>d’</i> indices are represented by gray color-scale (darker = more negative values).</p

Experimental design and analysis.

<p>(A) Patients performed naming of 5 stimulus categories: faces, animate non-face (animals/body parts), places, tools, and words. Images were presented for 2 seconds followed by a jittered 3s inter-stimulus interval. Exemplar responses are indicated in red text. (B) Subjects were implanted with subdural electrodes (SDEs) in either the left (LH) or right hemisphere (RH). SDEs were localized to subject cortical surface models and represented as spheroids (white) centered on electrode coordinates. (C) Cortical activity was measured using electrocorticography (ECoG). (<i>Left)</i> ECoG data were spectrally decomposed to obtain percent-power change in the broadband gamma frequency range (BGA, 60 to 120 Hz; solid horizontal bars) relative to a pre-stimulus baseline window (-700 to -200 ms). The spectrogram depicts the response during face naming for a single SDE (black box) in the inferior occipital gyrus. (<i>Right)</i> For the same SDE, time-series representations of BGA are plotted per category. BGA for faces (red) is greatest compared to animate (orange), place (blue), tool (green), and word (cyan) stimuli. Shadings denote 1 SEM. Vertical dashed lines denote the time window (100 to 400ms; stimulus onset @ <i>t</i> = 0 ms) used to compute <i>d’</i> sensitivity indices.</p

Single subject analysis for category selectivity.

<p>Single subject category-selectivity determined using the <i>d’</i> sensitivity index. Five subdural electrodes (SDEs) were localized in this individual to the vicinity of the mid-fusiform sulcus (MFS, dark gray shading on cortical surface). Time-series representations of broadband gamma activity (BGA, 60–120 Hz) for face (red), animate (orange), place (blue), tool (green), and word (cyan) stimuli are depicted for each SDE. Vertical dashed lines denote the time window for <i>d</i>’ analysis (100 to 400 ms after stimulus onset). <i>p</i>-values per category and per SDE were determined against a null distribution (insets; <i>n</i> = 10,000 permutations). Colored vertical lines denote actual <i>d’</i> index per category (colors matched to tasks, asterisks denote <i>p</i>≤0.001). In this subject, all face-selective SDEs (<i>n</i> = 3; red spheres) are localized at or lateral to the MFS, while place and word selective SDEs are localized postero-medially and antero-medially, respectively.</p

Population coverage of higher-level visual cortex.

<p>Bilateral group-electrode coverage maps depict subdural electrodes (SDEs, white spheres) from all subjects (<i>n</i> = 26 subjects; LH <i>n</i> = 16; RH <i>n</i> = 10) on a common cortical surface (MNI N27 template brain aligned to Talairach coordinate space). A total of 3506 SDEs were implanted, from which 242 SDEs were localized to the lateral occipital cortex (LOC, top; LH <i>n</i> = 48, RH <i>n</i> = 35) and the ventral temporal cortex (VTC, bottom; LH <i>n</i> = 94, RH <i>n</i> = 64). Spatial transformation of individual SDE coordinates to Talairach space was performed in a surface-based fashion. Compass points denote SDE coordinates (Talairach space) and direction in each region. The VTC and LOC, and their respective boundaries, are highlighted (<i>Left</i>) using FreeSurfer’s automated gyral and sulcal parcellations and depicted on an inflated brain surface. The LOC consists of the middle occipital (MOG, pink) and inferior occipital gyri (IOG, blue), and lateral occipital sulcus (light purple, between IOG and MOG). The VTC consists of the fusiform gyrus (purple), occipitotemporal sulcus (cyan and orange), lingual gyrus (tan) and the posterior transverse collateral sulcus (teal).</p

Patient demographics.

<p>Patient demographics.</p

Spatial organization of category-selectivity.

<p>All subdural electrodes (SDEs) with significant category-selectivity (FDR corrected <i>q</i>≤0.01) are visualized on the MNI N27 template brain (aligned to Talairach coordinate space) after surface based normalization. SDEs are color-coded by the category of preference (matched to image legends). Compass points denote SDE coordinates (Talairach space) and direction. Left: Pial surface maps of lateral occipital cortex (LOC, <i>top</i>) and ventral temporal cortex (VTC, <i>bottom</i>). Right: inflated surfaces for these regions with the lateral-occipital sulcus (LOS) and mid-fusiform sulcus (MFS) delineated by dark gray shades and white contours, and adjacent sulci delineated by lighter gray shades (TOS, transverse occipital sulcus; STS, superior temporal sulcus; p/aOTS, posterior/anterior occipito-temporal sulcus; CoS, collateral sulcus). In the LOC, all 13 face-selective (red; LH <i>n</i> = 8; RH <i>n</i> = 5) and 9 animate-selective (orange; LH <i>n</i> = 6; RH <i>n</i> = 3) SDEs are localized at or below the LOS, while all 12 place- (blue; LH <i>n</i> = 9; RH <i>n</i> = 3) and 3 tool-selective (green; LH <i>n</i> = 1; RH <i>n</i> = 2) SDEs are localized at or dorsal to the LOS. In the VTC, all 3 animate- (LH only) and 42/45 face-selective (LH <i>n</i> = 27/28; RH <i>n</i> = 15/17) SDEs are localized to-or-lateral to the MFS, while all 43 place- (LH <i>n</i> = 29; RH <i>n</i> = 14) and 9 tool-selective (LH <i>n</i> = 7; RH <i>n</i> = 2) SDEs are localized to-or-medial to the MFS. All 6 word-selective (cyan, LH only) SDEs are localized anteriorly at the intersection of the MFS and aOTS (arrow and black circle), interspersed with animate, tool, and anteriorly-localized face-selective SDEs.</p

Linear mixed effects model results.

<p>Linear mixed effects (LME) models computed to quantify relationship between <i>d’</i> sensitivity index (category-selectivity) and subdural electrode (SDE) coordinates (cortical topology) for each category per hemisphere in the ventral temporal cortex (VTC; left) and lateral occipital cortex (LOC; right). Tables provide coefficient estimates, standard errors, significance levels and number of observations (N_obs) for fixed effects predictors in each hemisphere per region. For face, animate, place, and tool LME models, the number of observations is consistent for each region and hemisphere, and thus listed once (under model results for faces). In the LOC, the fixed effects were: Z-Coord, Y-Coord, and Z*Y-Coord. In the VTC: X-Coord, Y-Coord, and X*Y-Coord. All SDE coordinates (in mm, aligned to Talairach space using surface-based normalization) were mean-centered prior to being entered into the models. Bold text denotes significant predictors, with significance levels denoted by the asterisks (legend at bottom).</p

Grouped SDE and <i>d</i>’ visualization.

<p>Responsivity and preference to each category for all subdural electrodes (SDEs) over ventral temporal cortex (VTC, <i>right</i>) and lateral occipital cortex (LOC, <i>left</i>), grouped across all 26 subjects (following surface-based normalization) and visualized on the MNI N27 template brain. Compass points denote SDE coordinates (Talairach space) and direction. SDE diameter reflects normalized BGA magnitude for each category (mean BGA divided by standard deviation), scaled by the largest normalized response across categories per region (VTC and LOC are scaled differently). SDE colors reflect their d’ values per category. Positive, significant <i>d’</i> indices (FDR corrected <i>q</i> ≤ 0.01) are represented by the category-specific color-code at the top of the color bar (e.g. SDEs with significant face <i>d’</i> colored red). Positive, non-significant <i>d’</i> indices are represented as intermediate color-scales specific for each category. Negative <i>d’</i> indices are represented by gray color-scale (darker = more negative values).</p

Network dynamics of human face perception

<div><p>Prevailing theories suggests that cortical regions responsible for face perception operate in a serial, feed-forward fashion. Here, we utilize invasive human electrophysiology to evaluate serial models of face-processing via measurements of cortical activation, functional connectivity, and cortico-cortical evoked potentials. We find that task-dependent changes in functional connectivity between face-selective regions in the inferior occipital (f-IOG) and fusiform gyrus (f-FG) are bidirectional, not feed-forward, and emerge following feed-forward input from early visual cortex (EVC) to both of these regions. Cortico-cortical evoked potentials similarly reveal independent signal propagations between EVC and both f-IOG and f-FG. These findings are incompatible with serial models, and support a parallel, distributed network underpinning face perception in humans.</p></div

Frequency distribution of differences in f-IOG vs. f-FG selectivity onset latencies, left hemisphere.

<p>Frequency distribution of differences in f-IOG vs. f-FG selectivity onset latencies, left hemisphere.</p