Cortical Substrates of Working Memory for Visual Motion

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DESCRIPTION (provided by applicant): The ability to briefly retain visual information is fundamental to successfully executing visually guided behaviors. This is a renewal application to study the circuitry underlying the active maintenance of sensory representation, i.e. sensory working memory. The overriding goal is to provide a link between cortical areas traditionally associated with processing of visual motion and regions identified with working memory and cognitive control of visually guided behaviors. We will focus on cortical areas MT and MST, important for motion processing, and on prefrontal cortex (RFC) strongly associated with working memory and cognitive control. Our recent work revealed that during the performance of a memory for visual motion task, MT neurons carry memory-related signals and are affected by the demands of the behavioral task. Recordings from PFC also revealed memory related activity and of activity strongly modulated by the behavioral state of the animal. Furthermore, they revealed responses selective for visual motion, similar to those characteristic of neurons in areas MT & MST. The presence of memory signals and the similarity of sensory responses in motion processing areas and in PFC during the same behavioral task suggests a potential functional link between these 2 regions and their participation in the circuitry sub-serving the ability to remember visual motion. During the next grant period we will examine the nature of recently discovered memory-related directional motion signals in areas MT (Aim 1.1), MST (Aim 1.2) and PFC (Aim 2). We will also focus on the interactions between the 2 regions by determining whether PFC is a source of memory signals and modulation by task demands, recorded in MT and MST (Aim 3). For all experiments, we will use a task in which the monkeys compare the directions of 2 moving stimuli separated by memory delay. We will combine recordings of activity of single neurons and local field potentials, microstimulation and reversible inactivation with psychophysical measures of visual working memory. These studies will shed light on the involvement of neurons in PFC and in cortical areas processing sensory signals used in working memory and the way they coordinate their activity to support successful execution of memory tasks. The knowledge of the neural circuitry underlying short-term storage of sensory information will contribute to the understanding and treatment of diseases characterized by working memory impairments, such as Alzheimer's, Parkinson's and Schizophrenia.