Event Details:
Wu Tsai Neurosciences Institute Seminar Series Presents
Stephen Lisberger, PhD
Professor of Neurobiology
Duke University
Host: Mu Zhou
Abstract
The cerebellum has long been implicated in motor and non-motor learning. Purkinje cells are the only output cells from the cerebellar cortex and they receive inputs over two pathways – mossy fibers and climbing fibers. In the simplest cerebellar learning theory, climbing fibers signal motor errors and cause learning in the simple-spike output of Purkinje cells; simple-spikes are driven by mossy fiber inputs to the cerebellar circuit and affect the firing in downstream circuits. Two neurophysiological observations motivate our model of cerebellar learning. First, a single instructive target motion is sufficient to cause neural learning in the simple spikes of Purkinje cells and behavioral learning, if and only if the instruction drives a climbing fiber response in the Purkinje cell. Second, the magnitude of learned simple-spike depression grows over about 200 instructive target motions and then shrinks even though behavioral learning continues to grow. Our circuit-level model is based on four principles: (1) early, fast acquisition is driven by climbing fibers at a site in the cerebellar cortex with poor retention; (2) learning gradually transfers from the cerebellar cortex to a site in the deep cerebellar nucleus with excellent retention, guided by Purkinje cells’ simple spike output; (3) functionally different neural signals are subjected to learning in the cerebellar cortex versus the deep cerebellar nuclei; and (4) negative feedback from the cerebellum to the inferior olive reduces the magnitude of the teaching signal in climbing fibers and limits learning. The model reproduces a large body of behavioral and neural data.