Over the last decade, an increasing number of studies using animal models have shown that the selectivity of visual cortical neurons can be modified by visual experience. However, not much is known about the more global changes that take place during learning. For instance, there is little information as to which underlying neuronal circuits are involved during the course of visual learning. The lack of this sort of information has been partly due to the poor global coverage provided by single cell recording. It is now possible to fill this gap by using imaging techniques such as fMRI, which provides excellent global coverage. Until now, fMRI has been extensively used to study the human brain, but applying it to monkeys has the additional advantage that it can be combined with other invasive techniques such as single cell recording and pharmacology. We propose to use fMRI on monkeys to characterize the effects of visual experience on cortical circuits involved in visual processing. Specifically, we will analyze changes in the topographic organization of early visual areas as a function of visual experience. Changes will be identified across single recording sessions both in anesthetized and awake-behaving animals. Initially, during the first mapping phase, the responses to visual stimuli placed at different retinotopic locations will be measured across the early visual areas such as V1, V2, V4 and MT. A training phase will follow during which specific combinations of the original mapping stimuli will be presented Subsequently, another mapping phase identical to the first one will be applied to characterize any changes induced by the recent visual experience. A number of such training phases with different combinations of stimuli will be carried out during the course of one experimental session. The training paradigm we propose is motivated by the well known hypothesis originated by Hebb, where learning is reflected in the strengthening of connections among neurons. It is thought that when cells, connected to each other are activated at the same time, then the connections between them are strengthened and therefore the selectivity of neurons ins modified in a way that reflects the temporal associations of stimuli in the environment.
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