David Fitzpatrick

Research in the Fitzpatrick lab is focused on understanding the functional organization and development of circuits in primary visual cortex, an important component of the vast network of neural centers that are involved in processing visual information and the first site along the visual pathway where neurons exhibit selectivity for stimulus attributes such as the orientation of edges and the direction of motion of objects. Our research combines optical imaging, intracellular recording and neural tracing techniques to explore how stimulus features are represented in the activity of identified neural circuits. Our work on the development of visual cortex suggests that normal sensory experience is required to complete the maturation of properties that are first established by experience-independent mechanisms. In another series of experiments we are addressing how feedforward and recurrent circuits contribute to the orientation selective responses of individual neurons. Our results indicate a remarkable specificity in the spatial arrangement of the axonal arbors associated with these two systems, a specificity that imparts an axial bias to the way these neurons sample information from visual space both within and beyond their classical receptive field. In another set of experiments, we are exploring how different combinations of stimulus features such as orientation, direction of motion and speed are represented in the population response of visual cortical neurons. Contrary to the conventional view that activity patterns in visual cortex can be explained as the intersection between multiple stimulus feature maps, our results indicate that population activity is best explained as a single spatiotemporal transform in which orientation, direction of motion and speed are combined. Current efforts are directed at understanding the temporal dynamics of this spatiotemporal transform and the way in which it is altered by changes in luminance and contrast.