[Seminar]"Synaptic tenacity or lack thereof: Spontaneous remodeling of synaptic connections", by Professor Noam E. Ziv

Title

Synaptic tenacity or lack thereof: Spontaneous remodeling of synaptic connections

Abstract

Activity-dependent modifications to synaptic connections – Synaptic Plasticity – is widely believed to represent a fundamental mechanism for altering network function. This belief also implies, however, that synapses, when not driven to change their properties by physiologically relevant stimuli, should retain these properties over time. Otherwise, physiologically relevant modifications would be gradually lost amidst spurious changes and spontaneous drift. We refer to the expected tendency of synapses to hold on to their properties as "Synaptic Tenacity".
Imaging studies reveal that synapses are not truly structures; rather, they are better thought of as dynamic assemblies of molecules that move in, out and between synaptic sites. These innate dynamics, combined with the continual turnover of synaptic molecules and the logistics of supplying such molecules to remote synapses at appropriate amounts and stoichiometries, question the validity of the aforementioned expectations. Indeed, we find that synaptic properties do change spontaneously in manners that do not depend on particular activity forms, or for that matter, on activity at all. In fact, we find that less than half of the changes observed can be attributed to particular activity histories. Interestingly, however, we find that spontaneous changes to synaptic properties are governed by well characterized stochastic processes, which seem to be driven by the innate dynamics of synaptic molecules. These dynamics, and the spontaneous synaptic changes they generate, both shape and confine synaptic size distributions, continuously renormalize synaptic sizes but at the same time, continuously erode synaptic size configurations. These findings thus indicate that synaptic tenacity is inherently limited, and that synaptic properties – both at individual synapse and population levels – are governed by rules with very influential stochastic components.

Speaker:

Professor Noam E. Ziv