DEPARTMENT OF NEUROBIOLOGY & BEHAVIOR
Ph.D. DISSERTATION DEFENSE
Dr. Gandhi’s Lab
Functional specialization of eye-specific visual pathways into higher visual cortex
Tuesday, November 19th, 2019
Dale Melbourne Herklotz Conference Center, Center for Neurobiology of Learning and Memory
Abstract: The brain is able to construct a visual representation of the world by parallel processing of cortical neurons that prefer increasingly complex stimuli. For example, its has been demonstrated that primary visual cortex (V1) sends functionally distinct information to higher visual areas (HVAs), which are more specialized in their processing of spatiotemporal information. Inherently coupled to this process is the convergence of eye-specific inputs in visual cortex. Shifting the eye-specific tuning of neurons in V1 by monocular deprivation in early life is known to disrupt tuning for spatial frequency in adulthood. To understand if eye-specificity could be linked to tuning properties important for the specialization of HVAs, we characterized eye-specific spatiotemporal tuning of layer 2/3 excitatory neurons within the binocular zone of V1 and two HVAs grouped into the putative ventral and dorsal streams, LM and PM, using two-photon GCaMP6s imaging of awake mice. An asymmetry was found at the level of V1, such that responses driven primarily by the contralateral eye were biased towards high spatial frequencies, low speeds, cardinal directions, and were more direction selective than binocular or ipsilateral eye-driven responses. This eye-specific functional specialization was also present in LM and PM, and could help explain their overall unique spatiotemporal selectivity. To determine if LM and PM receive eye-specific functionally distinct information from V1, we injected AAV-Syn-GCaMP6s into the binocular zone of V1 and imaged the afferents that targeted either LM or PM. We found that V1 afferents to LM and PM were distinct in their distributions for ocular dominance and spatial frequency preferences, suggesting that eye-specific projections from V1 may contribute to their functional specificity. If the functional specialization of HVAs depend upon eye-specific developmental mechanisms, depriving mice of visual experience through the contralateral eye (CMD) during the ocular dominance critical period (P19-33) may impair the spatiotemporal tuning of V1, LM and PM in adulthood. We found that CMD diminished the functional specificity of V1, LM and PM, resulting in areas without differentiated spatiotemporal preferences. CMD also reduced the functional specialization of neurons linked by eye-specificity. Altogether, our data demonstrates that the maturation of V1 and HVAs is dependent upon proper binocular visual experience and suggests that the functional specialization of eye-specific responses could be an efficient routing mechanism to differentiate higher visual areas.