2023-2024 Psychology Department
Colloquium Speaker Series
presents
Lindsey Glickfeld
Associate Professor of Neurobiology
Duke University
Synaptic Mechanisms for Normalization
in the Visual Cortex
Normalization, or the rescaling of neural activity to account for the total input, is a fundamental computation that is performed at each stage of sensory processing to maintain activity within the appropriate dynamic range. While there is strong foundational knowledge about the kinds of normalization that occur in the visual system, the underlying circuit and synaptic mechanisms are largely unknown. In this talk I will discuss two fundamental forms of normalization: adaptation and contrast gain. First, we investigate the mechanisms underlying rapid adaptation in primary visual cortex (V1). Neurons in L2/3, but not in L4, are exquisitely sensitive to recent experience, such that even a 100 ms stimulus can suppress responses to similar stimuli for seconds. We find that these brief visual inputs drive a balanced reduction in both excitation and inhibition due to short-term depression at the L4 to L2/3 synapse. This mechanism allows for stimulus-specific input normalization in L2/3 that is engaged at short timescales, whereas a less selective output normalization is imposed after prolonged adaptation. Second, we investigate the circuit and synaptic mechanisms underlying contrast gain control in primary visual cortex. Inhibition stabilized networks have long been proposed to mediate gain control as sensory inputs increase, yet under what conditions these networks are recruited is unknown. Using a novel cell-type specific pharmacological approach to block AMPA receptors on somatostatin expressing interneurons, we find that inhibition stabilization increases as a function of both contrast and behavioral state. Together, these studies provide a mechanistic understanding of sensory normalization in V1.
Monday, January 22, 2024
12:30-1:45pm
390 Gilmer Hall