Date: Mon, July 31, 16:00-
Place: Room M203, Komaba Open Laboratory, The University of Tokyo
Invited Speaker: Dr. Kenji Morita (RIKEN)

Title: How is gamma frequency rhythmic firing of neocortical regular
       spiking neurons consistently shaped by recurrent inputs?

Abstract:
Gamma oscillations during neocortical sustained activity is thought to
be involved in a lot of neurocognitive functions. Many studies have
established that gamma oscillations can be generated and/or maintained
via recurrent connections in a self-organized manner. 
Recent work has shown that two major types of neurons, regular spiking
cells and fast spiking cells, fire with distinct phase distributions
with respect to the local field potential gamma oscillation during UP
states. We examined how recurrent connections shape such a phase
relationship by constructive in vitro experiments using the conductance
injection method. Gamma-modulated inhibitory and excitatory conductance
stimuli were synthesized from the observed spike phase distributions,
and used to drive firing in RS cells. We examined what are prerequisites
for recurrent inputs to RS cells for the observed spike phase
relationship to consistently hold. We found that strong, low-latency
input from FS cells to RS cells could well reproduce the observed spike
phase distributions, provided that it is accompanied with fluctuations
coming from stochastic neuronal firing. On the other hand, strong
excitatory recurrent inputs within the RS cell population were
inconsistent with the observed phase relationship unless they were so
dispersed in time that EPSPs in RS cells are only weakly
gamma-modulated. We examined if and how gamma-modulation of recurrent
excitation could be weakened to this expected extent by distributed
delays. Our results suggest that in RS cells during UP states, recurrent
inhibition from FS cells tends to maintain the gamma rhythmic drive.