Circuits across the brain display correlated activity, in which the responses among neurons are coordinated at a level beyond that expected from the stimulus structure itself. What role does such correlated activity play in neural coding? The retina provides a strong opportunity for progress: widespread correlated activity is generated by key circuit mechanisms that recur throughout the brain. Moreover, the impact of these mechanisms can be studied in the context of stimuli with clear functional significance. Nevertheless, circuit-level nonlinearities at multiple locations cause retinal outputs to depend on stimuli in a manner that defies traditional filter-based models. This demands a tightly coupled computational and experimental approach: purely computational attacks will become lost in the combinatorics of all possible circuit configurations at the difficult "mesoscales" relevant to retinal computation, where averaging approaches fail; purely experimental strategies cannot predict and prioritize the most critical circuit mechanisms and stimulus parameters to explore. The investigators apply this interdisciplinary approach to the mechanisms producing correlated activity in directionally-selective (DS) ganglion cells. In particular, they determine how convergent and divergent pathways in the DS cell circuit interact to shape correlations and encoded information across the cell population, and asses the possible roles of recurrent coupling in modulating this process. These circuit features are the basis of correlated activity in many retinal pathways, and in circuits throughout the brain. Thus, our findings will guide studies of collective neural computation and dynamics currently under intense study in a variety of domains.
The brain translates the sensory environment into its own code, that of neural spikes distributed across vast numbers of neurons. Neuroscience seeks to understand the nature of this code -- what aspects of the spiking activity carry what information, how it is implemented by the cellular hardware of the brain, and how this process can fail in disease. A key puzzle is deciphering what it means when many neurons spike simultaneously -- is this just inevitable statistical coincidence, an artifact of neural hardware, or a key symbol in the code? The investigators take a direct approach to answering this question in the earliest stage of the visual pathway, the retina. Here, the team rigorously combines experiment and theory to connect biological circuit mechanisms and coding, and to identify principles that could be tested in other brain areas. Matching the interdisciplinary demands of this endeavor, investigators from Applied Mathematics and Physiology and Biophysics will unite, and will mentor a small team of undergraduate, graduate, and postdoctoral researchers with diverse backgrounds including both mathematics and biology. They will share their results with peers through an open, user-friendly database, and their most exciting findings with students in the interdisciplinary courses that they teach.
