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Olga Parsons, Michele Rucci; A model of the possible influences of eye movements on the maturation of cortical direction selectivity. Journal of Vision 2003;3(9):365. doi: 10.1167/3.9.365.
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© ARVO (1962-2015); The Authors (2016-present)
Several features of the responses of cells in the striate cortex, such as orientation and direction selectivity, appear to develop before the exposure to pattern vision and are then refined by visual experience. It is a working hypothesis that the maturation of these neuronal characteristics relies on a Hebbian mechanism of synaptic plasticity that operates initially on spontaneous neural activity and later on visually induced responses.
To investigate whether the statistical structure of neural activity after eye opening may be compatible with a Hebbian refinement and maintenance of direction selective responses, neuronal activity was simulated in a computer model of the cat LGN and V1. Spatiotemporal filters were used to predict the responses of V1 and LGN cells while images of natural scenes were scanned in a way that replicated the oculomotor behavior of the cat. Kernels with inseparable spatial and temporal components were designed to replicate the initial directional bias of V1 neurons. The model of the LGN included neuronal populations with different timing characteristics as observed in the cat.
The specific patterns of correlated activity required for the maturation of direction selective cells were found during the periods of visual fixation when small eye movements occurred, but not when natural images were examined statically or scanned in the absence of fixational eye movements. In addition, simulations that replicated experiments in which kittens are reared under stroboscopic illumination produced a specific loss of direction selectivity, while preserving orientation selectivity, which is consistent with experimental findings. These results show that after eye opening a Hebbian mechanism of synaptic plasticity may account for the refinement of cortical direction selectivity and suggest a possible involvement of the oculomotor activity of visual fixation.
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