Prefrontal contributions to phase-dependent representation of visual information

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The function of rhythmic oscillations in brain activity has long been a subject of both speculation and research. Recent evidence supports theories than synchronization of such oscillations between brain areas can contribute to modulating the strength of their connectivity; such changes in coupling between areas have been reported during cognitive functions including attention and working memory. Information can also be encoded in the timing of neuron’s action potentials relative to these oscillations; indeed, such ‘phase coding’ can sometimes represent different information than is available in the firing rate alone. These experiments will determine whether phase coding is used to represent visual information during working memory and eye movements, and test the role of interactions between prefrontal and visual cortex in modulating this phase coding. The role of prefrontal signals in modulating phase coding in visual cortex will be tested using both correlative measures of synchronization between prefrontal and visual areas during memory maintenance, and pharmacological manipulation of prefrontal activity. Pharmacological activation will be used to test whether certain patterns of activity in visual cortex are sufficient to gate entry of a sensory signal into working memory. Lastly, the ability of a phase code to multiplex information around the time of eye movements, thus disambiguating the source of sensory signals and expanding the information capacity of the visual system will be directly examined. Understanding the contribution of phase coding to the visual representation, along with the role of interactions between prefrontal and visual cortex in modulating such representations, will provide a necessary comparison point for neurological disorders involving impaired prefrontal- sensory interactions, such as schizophrenia, Alzheimer’s disease, attention deficit hyperactivity disorder, and autism spectrum disorders.