Research in the Fitzpatrick lab focuses on the functional organization of neural circuits in primary visual cortex. 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. In one series of experiments we are addressing how feedforward and recurrent circuits contribute to the orientation selective responses of layer 2/3 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 series of experiments, we are exploring how individual stimulus features such as orientation, direction of motion and speed are represented in the spatial distribution of population activity. Our results force a significant revision of the conventional view that visual cortex is a collection of independent stimulus feature maps. Instead, we suggest that population activity in visual cortex does not specify individual stimulus features but a spatiotemporal transform in which multiple features are conflated. 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.
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