Columbia University in the City of New York

May 16, 20234:00 pm
Seminar

Columbia Neuroscience Seminar - Rainer Friedrich ( Fully Virtual )

Neuronal computations in a synaptically balanced memory network

May 16th, 4:00 pm – 5:00 pm at Online

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Rainer Friedrich, PhD
Associate Professor of Neuroscience and Mind Research

Friedrich Miescher Institute for Biomedical Research


Neuronal computations in a synaptically balanced memory network

Higher brain functions arise from the exchange of information between neurons in large networks. The function of such networks is determined to a large extent by their “wiring diagrams”, i.e. the specific synaptic connectivity between individual neurons. Moreover, information is assumed to be stored in specific modifications of synaptic wiring diagrams, both during evolution and over the lifetime of individuals. To understand mechanisms of neuronal computation we therefore established an approach referred to as “dynamical connectomics” that combines optical measurements of neuronal population activity with dense circuit reconstruction by electron microscopy. Using adult zebrafish as a model system allows us to reconstruct wiring diagrams of entire brain areas at synaptic resolution after measuring neuronal activity in the context of cognitive behaviors. We focus on neuronal computations in the olfactory bulb and telencephalic area Dp, the zebrafish homolog of piriform cortex. In the olfactory bulb, dynamical connectomics revealed that overlapping representations of structurally similar odorants are decorrelated by multisynaptic inhibitory interactions between specific cohorts of output neurons. Dp is a highly recurrent network that is thought to function as an autoassociative memory network. We found that Dp does not exhibit stable attractor dynamics, as proposed by classical autoassociative memory models, but enters a state of “precise synaptic balance” upon odor presentation. This state is characterized by strong and co-tuned excitatory and inhibitory synaptic input to individual neurons, giving rise to irregular, fluctuation-driven activity. Nonetheless, balanced networks can represent information accurately and efficiently. We further identified a brain area that contains joint representations of odor identity and valence. Associative conditioning of adult zebrafish remapped odor identity along the valence axis by a process that involves specific modifications of inhibitory interactions. Currently, we reconstruct neuronal wiring diagrams of the underlying circuitry in Dp. This work is driven by hypotheses derived from theoretical models and expected to provide mechanistic insights into neuronal computations involved in memory and cognition.


Host Information: Andrew Fink ([email protected]) Carl Schoonover ( [email protected] )

 

The Columbia Neuroscience Seminar series is a collaborative effort of Columbia's Zuckerman Institute, the Department of Neuroscience, the Doctoral Program in Neurobiology and Behavior and the Columbia Translational Neuroscience Initiative, and with support from the Kavli Institute for Brain Science.

 

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