Biology subjects

Kopec, C. D.

Publications and source records attributed to Kopec, C. D..

3 recordsLinked to original sources

bioRxiv2018

Collicular circuits for flexible sensorimotor routing

Historically, cognitive processing has been thought to rely on cortical areas such as prefrontal cortex (PFC), with the outputs of these areas modulating activity in lower, putatively simpler spatiomotor regions, such as the midbrain superior colliculus (SC). Using a rat task in which subjects switch rapidly between task contexts that demand changes in sensorimotor mappings, we report a surprising role for the SC in non-spatial cognitive processes. Before spatial response choices could be formed, neurons in SC encoded task context more strongly than neurons in PFC, and bilateral SC silencing impaired behavioral performance. Once spatial choices could begin to be formed, SC neurons encoded the choice faster than PFC, while bilateral SC silencing no longer impaired choices. A set of dynamical models of the SC replicates our findings. Our results challenge cortically-focused views of cognition, and suggest that ostensibly spatiomotor structures can play central roles in non-spatiomotor cognitive processes.

neuroscience↗

bioRxiv2018

Controlling for temporal discounting shifts rats from geometric to human-like arithmetic bisection

How our brains measure the passage of time is still largely open for debate. One behavioral task commonly used to study how durations are perceived is the Temporal Bisection Task, in which subjects categorize time durations as either \"short\" or \"long.\" The duration equally likely to be categorized as short or long is known as the bisection point. It has been consistently demonstrated that for humans, the bisection point is near the arithmetic mean of the longest and shortest durations the subject was trained on. In contrast, for non-human subjects it has been consistently found near the geometric mean. This difference implies that humans may process or represent temporal durations differently than other species. Here we present a behavioral model that reconciles the differences by demonstrating that rats performance on this task is driven not only by their noisy estimates of duration, but also by the temporally-discounted value of future rewards. The model correctly predicts shifts in the bisection point induced by unequal rewards and explains otherwise-paradoxical psychometric reversals documented three decades ago. Furthermore, as predicted by the model, we found that modifying the Temporal Bisection Task to eliminate the temporally-discounted reward component shifted the rats bisection point from the geometric mean to the arithmetic mean, thus bringing the rat results into line with the human results. We therefore propose that humans and rats (and perhaps other non-human subjects as well) process temporal information similarly, and that the difference between them in the Temporal Bisection Task may be simply due to rats weighing temporal discounting of future rewards more strongly than humans.

animal behavior and cognition↗

bioRxiv2017

Posterior parietal cortex represents sensory stimulus history and is necessary for its effects on behavior

Many models of cognition and of neural computations posit the use and estimation of prior stimulus statistics1-4: it has long been known that working memory and perception are strongly impacted by previous sensory experience, even when that sensory history is irrelevant for the current task at hand. Nevertheless, the neural mechanisms and brain regions necessary for computing and using such priors are unknown. Here we report that the posterior parietal cortex (PPC) is a critical locus for the representation and use of prior stimulus information. We trained rats in an auditory Parametric Working Memory (PWM) task, and found that rats displayed substantial and readily quantifiable behavioral effects of sensory stimulus history, similar to those observed in humans5,6 and monkeys7. Earlier proposals that PPC supports working memory8,9 predict that optogenetic silencing of this region would impair behavior in our working memory task. Contrary to this prediction, silencing PPC significantly improved performance. Quantitative analyses of behavior revealed that this improvement was due to the selective reduction of the effects of prior sensory stimuli. Electrophysiological recordings showed that PPC neurons carried far more information about sensory stimuli of previous trials than about stimuli of the current trial. Furthermore, the more information about previous trial sensory history in the neural firing rates of a given rats PPC, the greater the behavioral effect of sensory history in that rat, suggesting a tight link between behavior and PPC representations of stimulus history. Our results indicate that the PPC is a central component in the processing of sensory stimulus history, and open a window for neurobiological investigation of long-standing questions regarding how perception and working memory are affected by prior sensory information.

neuroscience↗