Joint Seminars in Neuroscience Lecture Series
Tuesday, February 21, 2017
Dr. Marshall Shuler, Ph.D.
Kavli Neuroscience Discovery Institute
Department of Neuroscience, Director of Admissions
Johns Hopkins University
"The Neural Genesis of Reward Timing and a Theory of Intertemporal Decision Making"
A central function of the brain is the ability to predict the timing of future events of behavioral importance based on past experience. This ability to appreciate the predictive qualities of environmental cues affords a means by which the organism may subsequently inform the timing of future actions, evaluate the relative worth of options, and govern future learning in response to changes in the statistics of the environment. By relating predictive neural activity to behavioral outcome, brain reinforcement systems are thought to mediate changes in synaptic efficacy underlying this ability to learn temporal expectations. Thus, understanding the means by which such reinforcement systems encode interval timing is a central question in the field. Exemplifying this process is the phenomenological observation of so-called “reward timing activity“ in the primary visual cortex (V1) of rodents, wherein pairing visual stimuli with delayed reward leads to stimulus-specific activity predicting the time of expected reward (Shuler and Bear 2006; Zold and Hussain Shuler 2015). Having modeled how reinforcement signaling can cause a network to learn to produce reward timing activity (Gavornik, Shuler et al. 2009; Huertas, Hussain Shuler et al. 2015), we tested and demonstrated that cholinergic innervation of V1 is necessary (Chubykin, Roach et al. 2013) and sufficient (Liu, Coleman et al. 2015) for cued-interval timing to form. We then show that such activity in V1 is behaviorally-relevant by demonstrating how spiking activity within V1 is predictive of visually-cued timing behavior, and how perturbation of V1 lawfully shifts the behavioral report of an interval’s expiration (Namboodiri, Huertas et al. 2015). Together, these observations advance a general understanding of reinforcement learning, that the cholinergic system can serve as a reinforcement signal, and that V1 can produce intervals informing the timing of visually-cued behaviors. Finally, a general theory of how time’s cost is assessed and incorporated into decision making is presented (Namboodiri, Mihalas et al. 2014; Namboodiri, Mihalas et al. 2014), rationalizing a number of well established, yet curious, observations.