Titre: What we see depends where we look: reference frames transformation in the primary visual cortex (V1) of awake monkeys
Conférencier: Andrzej Przybyszewski , University of Massachusetts Medical Center - Assistant Professor of Neurology
Lieu: École Polytechnique de Montréal, Dept. de génie électrique , Salle 6321, Pavillon Decelles
Date et heure: vendredi le 30 avril 2004 de 11:30 à 00:00

Résumé: Our behavior is mostly determined by what do we see. However, depends on their position objects may have different meanings. Helmholtz proposed that the copy of the motor commands affecting eye movements maybe send to the visual areas. More recently Andersen et al. proposed that modulation of the posterior parietal neurons by the eye position (EP) means coordinate transformation to non-retinocentric frame of references. Do cells in lower visual areas like V1 respond differently when the EP changes ? In order to answer this question, we have studied neuronal responses to moving bars in V1 of an alert monkey during different eye positions. Monkey was trained to fixate on the LED attached to the screen that was placed in the three positions: straight (0 position), 10 deg to the right (10R) or left (10L) in the horizontal plane. We have recorded contrast responses in V1 cells. Changing eye positions significantly influenced the maximum amplitude of the response in about 60% cells. In 7/17 cells in 0 position, in 5/17 cells in 10R position and in other 5/17 in 10L position, responses were larger than in other two positions. Contrast responses r(c) were fitted with the Naka-Rushton equation: r(c) = Rmax*(c^n/(c^n + c50^n)), where Rmax is the maximum response, c - contrast, c50 -contrast at the half of Rmax, n - nonlinearity. We have analyzed only those responses with a sufficiently good fit (estimated by the RMS). In most cases changing of the eye position had significant influence on Rmax. Therefore, we can reformulate the Naka-Rushton equation as r (c) = sEP * Rmax (cn/(cn + cn50), where sEP is signal related to the eye position (EP). This influence is like the Gain Field changes in the higher cortical areas. However, in most our cases the EP differently influenced the increment and decrement zones in the classical receptive field of V1 cells. It suggests that the visual information could be processed differently as a function of the EP

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