T&C Chen Center for Social and Decision Neuroscience Seminar
General. The neurobiology of decision-making is informed by neurons capable of representing information over time scales of seconds. Such neurons were initially characterized in studies of spatial working memory, motor planning (e.g., Richard Andersen lab) and spatial attention. For decision-making, such neurons emit graded spike rates, that represent the accumulated evidence for or against a choice. They establish the conduit between the formation of the decision and its completion, usually in the form of a commitment to an action, even if provisional. Indeed, many decisions appear to arise through an accumulation of noisy samples of evidence to a terminating threshold, or bound. Previous studies show that single neurons in the lateral intraparietal area (LIP) represent the accumulation of evidence when monkeys make decisions about the direction of random dot motion (RDM) and express their decision with a saccade to the neuron's preferred target. The mechanism of termination (the bound) is elusive. LIP is interconnected with other brain regions that also display decision-related activity. Whether these areas play roles in the decision process that are similar to or fundamentally different from that of LIP is unclear. I will present new unpublished experiments that begin to resolve these issues by recording from populations of neurons simultaneously in LIP and one of its primary targets, the superior colliculus (SC), while monkeys make difficult perceptual decisions.
More details. We use multi-contact linear probes to record simultaneously from retinotopically aligned populations of single neurons in LIP and SC as a monkey performed a choice-response time direction discrimination task. The population firing rates in LIP reveal diffusion dynamics on single trials, a feature formerly obscured by trial averaged firing rates. In contrast, the population firing of SC prelude neurons did not reflect evidence accumulation on single trials. They generated an all-or-none burst of activity immediately preceding the decision's report. In addition, the saccadic burst was often preceded by smaller, premature bump of activity, which resembled the dynamics of the saccadic burst but with lower amplitude. These bumps are also obscured by trial averaged firing rates. Both bumps and saccadic bursts were associated with a sharp increase in LIP activity. Saccadic bursts occurred when the sharp increase occurred on a higher firing rate. We hypothesized that this bursting mechanism could be a neural implementation of the decision threshold, and we found that focal inactivation of SC with muscimol increased the decision threshold associated with contralateral choices. We suggest that SC and LIP play fundamentally different roles in the decision process and present evidence that SC implements the terminating bound.
Collaborators: Gabriel Stine, Natalie Steinemann, Eric Trautmann, and Danique Jeurissen
For more information, or if you are interested in attending this online seminar, please contact Liz Schroeder by email at [email protected].