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Joe Paton

 

Wednesday 31st August 2016

Time: 4.00pm

 

Ground Floor Seminar Room

25 Howland Street, London, W1T 4JG

 

Basal ganglia contributions to a time-based decision

 

Time is a fundamental dimension of experience, critical for extracting meaning from the environment and constructing behavior. However, the neural mechanisms that allow the brain to use information about time are poorly understood. We trained rats and mice to judge whether the duration of time intervals were longer or shorter than 1.5 seconds while recording and manipulating activity of neurons the dorsal striatum and dopamine (DA) neurons in the substantia nigra pars reticulata (SNc). I will describe how elapsed time, the critical decision variable in this task, is encoded by population dynamics of striatal neurons. This representation predicts the duration judgements produced by the animal. Strikingly, cooling striatal tissue led to underestimation of interval duration in a manner similar to that predicted by slower time estimates decoded from striatal populations, suggesting that striatal dynamics underlie animals’ timing behavior. But which endogenous mechanisms might cause striatal dynamics to fluctuate? DA neurons in the SNc receive input from and project densely to the dorsal striatum and have been implicated in timing. Using fiber photometry, we found that higher/lower dopaminergic activity within a trial predicted under/overestimation of interval duration. These signals were consistent with the predicted impact of variability in timekeeping on reward prediction error coding by DA neurons. Surprisingly, optogenetic activation caused underestimation of interval duration, indicating that midbrain DA neurons not only reflect variability in timing, but exert control over it. These data suggest that reciprocal interactions between dopamine neurons and striatal networks can cause variability in time estimation, with broad implications for reinforcement based decision-making.

Brief Bio: After university, Joe moved to California to work as a research technician at Stanford University in the laboratory of Dr. William Newsome, which studies neural mechanisms of vision and decision making. in 2001, Joe moved back to the east coast to start work towards his PhD at Columbia University in New York City in the laboratory of Dr. Daniel Salzman, where he studied the neural mechanisms that underly learning about positive and negative value. In 2008, Joe received his PhD and joined the Champalimaud Neuroscience Program as an independent fellow, and was promoted to principal investigator in 2012. His lab studies the neurobiology of time encoding in the brain and its relevance for learning using behavioral, electrophysiological, computational, and molecular techniques.