Abstract: Neuronal circuits are made of thousands of interconnected local networks containing thousands of neurons connected by millions of synapses. A precise understanding of these local circuits requires relating neuronal physiology with the underlying network structure. First, I’ll discuss work combining physiological imaging and large-scale electron microscopy (EM) to study structure-function relationships in a local network of pyramidal neurons in the mouse visual cortex. We found that pyramidal neurons are organized into subnetworks defined by connectivity, with more connections within groups than between them. Pyramidal cells are significantly more likely to be connected if they share the same orientation selectivity, despite the fact that axons and dendrites of all orientation preferences pass near (< 5 um) each other with equal probability. Neurons with similar orientation tuning formed larger synapses, potentially enhancing the net effect of synaptic specificity.
I will also touch on a second line of investigation - our more recent work reconstructing a feed-forward olfactory microcircuit. Over the last year, my group has reconstructed all the olfactory receptor neurons and central projection neurons of an antennal lobe glomerulus on both left and right sides of the Drosophila brain. My team focused on genetically identified neurons that have been intensely studied physiologically, so we were able to relate their physiology to connectivity. This circuit is conventionally thought of as highly stereotyped. Surprisingly, our results argue that there is a substantial amount of developmental stochasticity in this network’s architecture. Some effects of developmental noise are offset by compensatory wiring mechanisms, but other effects appear uncompensated, resulting in a sub-optimal wiring diagram that places important constraints on information content and downstream processing. A common emergent theme is that early sensory systems utilize functionally specific cell assemblies to generate fast, coherent, and robust representations of the external world. A logical next step is to unravel sensorimotor integration and computations guiding behavior.
About the presenter
Neurobiology, Harvard Medical School
Sponsored by Carnegie Mellon Biology Department