All cognitive operations including perceptual and motor processes unfold in time, and actions lead to successful outcomes only when they are executed at appropriate times. However, controlling multiple actions and monitoring their outcomes over a relatively long temporal interval poses challenging computational problems for the brain. Moreover, the ability to utilize temporal information is impaired in various psychiatric and neurological disorders, including attention-deficit/hyperactivity disorder (ADHD), Parkinson's disease, and substance abuse. Despite such broad theoretical and clinical significance, previous neurobiological studies on timing behavior and temporal decision-making have focused narrowly on the brain functions related to a single temporal interval or a unitary reward. The main goal of this proposal is to gain novel insights into the neural mechanisms capable of concurrently monitoring multiple temporal intervals and evaluating the value of multiple outcomes in a sequence. First, we will investigate the anatomical specificity of timing signals in the medial and lateral areas of the primate prefrontal cortex using a task that requires the animal to plan different actions according to two concurrent temporal intervals. We will test the hypothesis that the medial prefrontal cortex plays a special role in creating the internal timing signals from transient sensory events and transforming them into motor responses. Second, we will study the mechanism in the fronto-parietal network for integrating the values of multiple rewards in a sequence while the animal chooses between two separate temporally extended reward sequences. Specifically, we hypothesize that the flexible transformation of signals related to reward magnitude between the posterior parietal cortex and prefrontal cortex underlies the process of integrating the values of individual rewards into a single decision variable. The results from these two experiments will advance our knowledge about how the brain handles the timing information about multiple events efficiently, and lay the foundation for understanding the nature of clinical conditions with impaired abilities to process temporal information.
Costs of mental illnesses to society are substantial, but the precise nature of underlying neural impairments responsible for cognitive and behavioral deficits remains unknown. In particular, many psychiatric disorders are characterized by impaired abilities to control behaviors temporally. Proposed studies will elucidate the cortical mechanisms for monitoring multiple temporal intervals and evaluating a sequence of multiple outcomes.
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