Dopamine neurons control judgement of time
Sofia Soares from the Champalimaud Centre for the Unknown is presenting her work recently published in Science magazine. It touches upon the question why time is flying when you are having fun.
To guide adaptive behavior, animals must select which actions to take and when to perform them depending on the current state of their environment and their past experience. Since the consequences of an action are often delayed, animals must also be able to represent temporal information about when events and actions occur. Our sense of time, however, is not constant. Midbrain dopamine neurons have been implicated in interval timing. However, a direct link between signals carried by dopamine neurons and temporal judgments is lacking.
In this talk, I will present results from experiments where we measured and manipulated the activity of dopamine neurons in either the SNc or the VTA as mice judged the duration of time intervals. We measured dopamine neuron activity in the SNc and found that these neurons encode a reward prediction error signal that reflects both temporal expectation and the expected probability of reward.
Furthermore, we observed a horizontal shift of the psychometric curve toward long choices when SNc dopamine neuron activity was low, and the opposite horizontal shift when activity was high.
Additionally, we found that transient activation or inhibition of dopamine neurons in the SNc was sufficient to slow or speed time estimation, respectively. Interestingly, dopamine neurons in the VTA did not reflect nor control temporal judgments. Our data suggests that dopamine neuron activity in the SNc, but not in the VTA, reflects and can directly control the judgment of time. This difference may, in part, result from the parallel circuit architecture of the basal ganglia.
These findings provide a basis for a unifying view of dopamine neuron function in both reinforcement learning and interval timing.
Sofia Soares is a neuroscientist at the Champalimaud Centre for the Unknown in Lisbon, Portugal. Sofia obtained her undergraduate degree in molecular biology from the University of Lisbon in 2008, and joined the Paton lab in 2009 for her Masters and PhD training. During this time, Sofia has studied the role of basal ganglia nuclei in interval timing behavior.
Specifically, her work has shown how population activity in the striatum represents elapsed time, and how this population code scales with the interval being timed. Her recent work has looked into the basis of variability in subjective time estimates, and has shown how midbrain dopamine neurons represent and control subjective judgments of time.