The Impact of Behavior on Plasticity: The Sleep/Wake Rules Governing Firing Rate Homeostasis

Summary

Date: 
July 14, 2015 - 1:30pm
Location: 
NW 243
About the Speaker
Name: 
Keith Hengen (Turrigiano Lab, Brandeis)

It is widely believed that homeostatic mechanisms stabilize neural circuit function by keeping neuronal firing rates within a set-point range. While the cellular and molecular processes involved in synaptic homeostasis have been widely investigated, little is known about neuronal homeostasis in the freely behaving animal. Some have speculated that sleep/wake states serve to gate homeostatic plasticity, with sleep permitting the homeostatic renormalization of excitability that was perturbed during wake learning. However, the notion that sleep promotes homeostatic plasticity remains controversial. To address this question, we developed tools to continuously record extracellular signals from ensembles of single neurons in freely behaving rats for hundreds of hours during the critical period for ocular dominance plasticity. With this approach, we can track cells across many iterations of naturally occurring activities, as well as during developmental changes that occur on very long time-scales. Here, we recorded activity from ensembles of cortical single units in juvenile rats continuously for 10 days during a monocular deprivation (MD) paradigm. When examining neurons that were “online” for the entire recording, firing rates dropped during early MD and then rebounded to baseline levels despite continued deprivation. We then examined the dynamics of the homeostatic rebound of spontaneous activity (during prolonged MD) as a function of sleeping and waking states. Our work provides direct physiological evidence that sleep/wake states can indeed gate firing rate homeostasis, but the relationship we observed between sleep and homeostatic plasticity in the visual cortex is precisely opposite what has been proposed: sleep inhibits, rather than promotes, firing rate homeostasis. These results raise the possibility of unanticipated interactions between animal behavior and the expression of homeostatic plasticity mechanisms.