Biophysical cortical column model for optical signal analysis, in "Deuxième conférence française de Neurosciences Computationnelles, "Neurocomp08

We propose a biological cortical column model, at a mesoscopic scale, in order to better understand and interpret biological sources of voltage-sensitive dye imaging signal (VSD signal). This scale corresponds to one pixel of optical imaging: about 50 µm. Simulations are done with the NEURON software and visualization with the NEURO-CONSTRUCT software. This model confirms and quantifies the fact that the VSD signal is the result of an average from multiple components but shows surprisingly that inhibitory cells, spiking activity and deep layers likely participate more to the signal than initially though

Suppressive traveling waves shape representations of illusory motion in primary visual cortex of awake primate

How does the brain link visual stimuli across space and time? Visual illusions provide an experimental paradigm to study these processes. Whentwo stationary dots are flashed in close spatial and temporal succession,humanobservers experience a percept of apparent motion. Large spatiotemporal separation challenges the visual system to keep track of object identity along the apparent motion path, the so-called “correspondence problem.” Here, we use voltage-sensitive dye imaging in primary visual cortex (V1) of awake monkeys to show that intracortical connections within V1 can solve this issue by shaping cortical dynamics to represent the illusory motion. We find that the appearance of the second stimulus in V1 creates a systematic suppressive wave traveling toward the retinotopic representation of the first. Using a computational model, we show that the suppressive wave is the emergent property of a recurrent gain control fed by the intracortical network. This suppressive wave acts to explain away ambiguous correspondence problems and contributes to precisely encode the expected motion velocity at the surface of V1. Together, these results demonstrate that the nonlinear dynamics within retinotopic maps can shape cortical representations of illusory motion. Understanding these dynamics will shed light on how the brain links sensory stimuli across space and time, by preformatting population responses for a straightforward read-out by downstream areas