Using advanced imaging methods, we aim to understand how mouse primary visual cortex and superior colliculus encode visual stimuli and mediate visually-guided behaviors in awake behaving mice.
functional characterization of sensory encoding
Neurons within the primary visual cortex (V1) are densely packed into six layers, forming intricate circuits both within and across layers. Despite years of study, the connectivity and function of these layers are still largely unknown. For example, along dendrites projecting thousands of microns, a layer 5 neuron can receive inputs at ~10,000 synapses. What are these inputs and how does the neuron integrate them? We apply a synapse-resolving high-speed volumetric imaging method to these questions.
On the circuit level, each cortical layer receives a distinct yet little understood mixture of excitatory and inhibitory inputs. Without understanding the characteristics of these inputs, we cannot understand how they are processed in the cortex. By imaging the axon terminals from visual thalamus throughout L1 to L4 of V1, we discovered that about half of these thalamic inputs are already selective towards the orientation of visual stimuli, contrary to the longstanding belief of thalamic neurons lacking such selectivity. With adaptive optics allowing us to image neurons throughout mouse V1 with synaptic resolution, we are now addressing these questions by imaging these inputs directly in awake mice. Similar methodologies are being applied to mouse superior colliculus, the midbrain structure that is responsible for directing behavior responses toward specific sensory stimuli.
Unlike electronic circuits, whose properties do not change with repeated presentation of the same inputs, neural circuits possess plasticity, a phenomenon in which experience changes the responses to external stimuli via changes in strength of synapses and the excitability of neurons. How does learning-induced plasticity affect circuit dynamics? We are developing behavioral paradigms to study plasticity in head-fixed awake mice.