UC San Diego

The brain organizes information across multiple scales, from molecules to circuits to systems. Information is processed in stages, becoming increasingly refined and specialized at each level. We developed technologies to analyze information processing across multiple scales simultaneously. We answer several previously inaccessible questions about the structure and function of the mouse visual system (summarized in Chapter 1).

Direction of motion is first encoded by retinal ganglion cells (RGCs). We developed a method to image the responses of anatomically-identified neurons in the LGN. We found that LGN organizes direction information in a laminar pattern partially predicted by RGC inputs; only posterior and anterior directions are encoded in the superficial layer. This information is refined; direction-selective LGN neurons are more sharply tuned than RGCs. The superficial LGN integrates direction information, forming axis-of-motion selectivity for anterior-posterior motion (Chapter 2).

Understanding information integration by microcircuits requires novel technologies to study the structure and function of microcircuits in the intact brain. In Chapter 3, we developed a technology to target monosynaptic inputs to a single visual cortical neuron for gene manipulation and fine-scale cell labeling in vivo. We labeled inputs across the intact brain.

Single circuits in V1 and higher visual areas process signals from the LGN and other areas to compute increasingly specialized visual information. We developed methods to define visual cortical areas across the entire visual cortex down to single cell resolution in the same animal, within the same day (Chapter 4). We compared the response properties of populations of neurons from 7 visual areas. Extrastriate cortex processes motion information up to 3 times the temporal frequency than V1. A subset of areas maintains high spatial frequency tuning of V1, while another group prefers approximately half the spatial frequency. Extrastriate visual areas are more orientation selective and some are more direction selective.

We apply a novel rabies virus to measure the fine-scale structure and function of neurons in V1 providing monosynaptic input to an extrastriate visual area (Appendix). This technology may help integrate across the scales investigated in each chapter to understand how information is transformed at each processing stage by specialized microcircuits.