Sensory stimuli are encoded by large neuronal populations that have to elaborate rapid and robust representation of the input image. This is a computational challenge since these inputs are ambiguous, dynamical, segmented into a myriad of piecewise cues and constantly influenced by frequent eye movements. To overcome this problem, our visual system must link sensory inputs with a priori knowledge at multiple spatial and temporal scales. One important candidate for these lateral interactions are the intra-cortical axons that dynamically links neurons separated by millimeters in the cortical tissue, the so-called �horizontal� connectivity. This connectivity functionally subtend lateral interactions within these cortical areas that are usually organized into cartographical functional maps. In the primary visual cortex, that possesses a retinotopic organization, the horizontal connectivity generates spreads of activity that links together cortical columns sensitive for displaced regions of the visual field (1, 2).

In this talk, I will present experimental evidences using optical imaging of voltage sensitive dye that suggests that lateral interactions in the primary visual cortex play indeed a key role in several key neural computations at the level of neuronal populations, ranging from input normalization to stimulus representation. First I will show that any local stimulus is dynamically normalized through lateral interactions as a function of the context in which it is embedded (3). In a second series of experiment, I will provide evidence that such spatio-temporal normalization can then lead to the emergence of motion signal in response to a sequence of static images, a cortical correlate of motion illusions (4, 5). These results suggest that lateral interactions within a cortical area plays a major role in shaping visual processing at the mesoscopic population scale, setting the conditions for an optimal decoding by downstream areas. 

1. V. Bringuier, F. Chavane, L. Glaeser, Y. Fr�gnac, Science 283, 695�699 (1999).

2. F. Chavane et al., Front Syst Neurosci 5, 1�26 (2011).

3. A. Reynaud, G. S. Masson, F. Chavane, Journal of Neuroscience 32, 12558�12569 (2012).

4. D. Jancke, F. Chavane, S. Naaman, A. Grinvald, Nature 428, 423�426 (2004).

5. F. Chavane, A. Reynaud, G. Masson, JOV 8, 226�226 (2008).