Reinforcement learning is a powerful learning strategy in which random perturbations are made to an output and changes that lead to more successful outputs are reinforced. Animals learn to perform highly skilled tasks by trial and error, but how biological neural networks generate variability from trial to trial is not known. An ideal model for examining this relationship between variability and learning can be found in song learning by birds. Birds learn their songs by trial and error, and are able to adjust their songs into adulthood. In addition, the basic neural architecture of the learning circuit has been mapped out; some effects of behavioral context on variability are also known. How variability is generated, and how it is controlled, can thus be studied mechanistically.
This project will study two candidate mechanisms for the generation and control of variability: chaotic dynamics in a cortex-like area, and dynamical modulation of synchrony in a basal ganglia circuit. While generic neural networks are chaotic, this project will explore how such dynamics are modified in a cortical network of biophysically plausible neurons with structured connectivity based on the known topography of the learning circuit. Furthermore, the birdsong cortical area receives inputs generated by basal ganglia. How might this input influence the variability of the output? It is proposed that the ability of activity in basal ganglia to affect cortex may depend on the synchrony of basal ganglia outputs. The studies will be constrained by experimental data from these candidate areas through collaborations with two laboratories.
The work will contribute to a general understanding of variability in biological learning, and may suggest strategies for structuring noisy input during motor learning that can lead to efficient outcomes for robotics applications. Further, Dr Fairhall is developing materials for broad outreach programs that include a Massive Online Open Course to introduce concepts in computational neuroscience to a very diverse audience, and a workshop for middle school girls interested in mathematics applied to the life sciences.
