Date: Tue, March 13, 14:00-16:00
Place: Room Dw601, D Block, IIS, The University of Tokyo

Invited Speaker: Dr. Kosuke HAMAGUCHI
                 (Université-René Descartes (Paris V))

Title: Inhibition-dominated network can explain multistability and
       highly irregular states in prefrontal cortex activity

Abstract:
The spike patterns of neurons in vitro in response to current injection
is typically very regular, however in vivo, from the sensory to
prefrontal cortex, the degree of spiking irregularity is known to be
high. In the prefrontal cortex, neurons seem to switch from a background
state to an active firing state during delayed response tasks and their
spikes trains are highly irregular in both types of states.

Although it is easy to obtain self-sustained states (bistability) with a
connectivity dominated by excitation, CV of spike trains typically
decreases when the firing rate increases. One robust mechanism to obtain
high spike irregularity is to balance the excitation and inhibition in
recurrent connections. In balanced or inhibition dominated networks,
firing patterns can be irregular depending on the parameters of the
network, however it is usually difficult to obtain bistability because
the mean input to the neuron is not depolarizing.

Here it remains unclear how to achieve simultaneously high firing rate
and high spike train irregularity. Here we focus on the possible firing
states in a spatial working memory model. More specifically, we
investigate the dynamics of sparsely interconnected spiking neurons
embedded in a ring structure. We construct a self-consistent theory of
the macroscopic variables of the system, and calculated the stable
states of the system. The activity of recurrent network of spiking
neurons have been studied by the mean-field approach. We found that the
network shows various patterns of activity, e.g.,  traveling wave,
oscillating wave, standing wave, uniform activity states, and quiescent
state.

In the seminar, I report that spatially localized activity (bump) states
can exist in inhibition dominated regions with sub-threshold external
input. In these region, multistability can be achieved thanks to
fluctuations of the recurrent input which provides localized positive
feedback. Similar fluctuation driven multistability might be relevant to
the spontaneous activity in the primary visual cortex.