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Title: Three-dimensional shape selectivity in macaque prefrontal cortex
Authors: Michelet, Pascal ×
Verhoef, Bram-Ernst
Vogels, Rufin
Janssen, Peter #
Issue Date: 13-Oct-2012
Conference: Annual Meeting of the Society for Neuroscience edition:39 location:New Orleans, USA date:13-17 October 2012
Abstract: Horizontal binocular disparity is a powerful depth cue, both for relative and
absolute depth information. Sensitivity to binocular disparity is found in
various cortical areas in both the dorsal and the ventral visual stream. Previous
research has found a correlation between the neural activity in both the
Anterior Intraparietal area (AIP) and inferior temporal cortex (IT), and the
behavioral choices in a stereo discrimination task (Verhoef 2010). Both areas
have anatomical connections to area 46 of the prefrontal cortex (PFC).
Additionally, a previous awake monkey imaging study has hinted at the
existence of disparity-selectivity in area 46 (Joly et al. 2009). Our goal was to
examine the disparity selectivity of single neurons in area 46.
We recorded from 76 cells in area 46 (in the ventral bank of the principal
sulcus) of 1 macaque monkey using standard extracellular recording methods,
while the monkey passively fixated Random Dot Stereograms that depicted
curved 3D shapes, presented at the fixation point. Thirty-four out of 76 (45%)
responsive neurons tested showed significant disparity selectivity that could
not be accounted for by the monocular responses. These neurons were further
tested to determine the order of depth selectivity - zero-order (positionpositionin-
depth), or higher order - by presenting stimuli at different positions in depth.
Nineteen out of 34 neurons (56%) preserved their 3D-shape preference across
positions in depth, hence being considered as higher-order disparity selective.
Vergence eye movements were small (average 0.15 degrees) compared to
stimulus disparities (>=1 degree) and emerged on average 200 ms after
stimulus onset. The neural selectivity latency was remarkably long (median:
200 ms).
Higher order neurons were tested with approximations of the original smoothly
curved stimuli, portraying inclined surfaces (first-order stereo), linear approximations (second-order stereo, wedge), discrete approximations (three
separate planes at different positions-in-depth) and smoothly curved gradients
(second order stereo, curvature). We found that area 46 neurons could be either
first-order or second-order disparity selective, and could be selective for 3D
wedges or smoothly curved surfaces. The tuning for the amplitude of the
disparity variation (ranging from 0.03 to 1.27 degrees) was largely monotonic,
similar to previous findings in AIP. These data demonstrate that area 46
neurons can show disparity-defined 3D shape selectivity during passive
fixation. Further studies need to determine the contribution of these neurons to
3D shape categorization
Publication status: published
KU Leuven publication type: IMa
Appears in Collections:Laboratory for Neuro- and Psychofysiology
× corresponding author
# (joint) last author

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