Seminar – Dissertation Defense
Functional architecture of cortical circuits: From synaptic clusters to orientation columns
Neural circuits in the neocortex represent higher-order sensory features, and their physical architecture has been thought to be at the core of these complex computations. Recent technological breakthroughs have allowed the structural and functional investigation of the basic computational units of neural circuits; individual synaptic connections. However, it reminds unclear how single cortical neuron achieves high selectivity to certain sensory features through integrating thousands of synaptic innervations supplied by many different brain structures. Here, I first describe how visual cortical circuits transform the elementary inputs supplied by the periphery into highly diverse, but also well-organized, feature representations. By combining and optimizing newly developed techniques to map the functional synaptic connections with defined sources of inputs, I show that the intersection between columnar architecture and dendritic sampling strategies can lead to the sensory properties of individual neurons. In the case of the canonical feedforward circuit, the basal dendrites of a pyramidal neuron utilize unique strategies to sample ON (light increment) and OFF (light decrement) inputs in the orientation columns to create the distinctive receptive field structure that is responsible for basic selectivity to visual space, orientation, spatial frequency, and phase. For long-range horizontal connections, apical dendrites unbiasedly integrate functionally specialized and spatially targeted inputs in different orientation columns, which generates specific axial surround modulation of the receptive field.