Up
Previous
Next
Neural and synaptic mechanisms of the gamma rhythmic activity in local
cortical circuitry
Tomoki Fukai,1,3
Takeshi Takekawa,1
Masaki Nomura,3
and Toshio Aoyagi2
1Tamagawa University
2Kyoto University
3CREST, Japan Science and Technology (JST)
The activity of the brain engaging in cognitive process often exhibits
rhythmic oscillations. In particular, synchronization of neuronal
activity in the gamma band (20-70Hz) is considered to play significant
functional roles in sensory perception, motor control and higher
cognitive processes. Chattering neuron is a possible neocortical
pacemaker for the gamma oscillation (Gray & McCormick, 1996). Based on
our recent model of chattering neurons (Aoyagi et al., 2002), we
investigate computationally how the gamma-frequency bursting is
synchronized in small- and large-scale networks of chattering neurons.
In a weak-coupling range, the synchronized bursting of chattering
cells entrains activity of the regular spiking pyramidal cells in the
gamma band. However, synchronization occurs only slowly with a
transient time of about 500 ms. On the other hand, in a
strong-coupling range, the chattering cells can quickly synchronize,
but they do not entrain regular spiking cells. We find that both
transient and steady state properties of synchronization are greatly
improved by incorporation of short-term synaptic depression. In
addition, we investigate the synchronization phenomena in networks of
fast-spiking (FS) interneurons simultaneously interconnected by
electric and GABAergic synapses. Our model of FS interneurons is based
on the Kv3.1/3.2 type delayed potassium channels characteristic of
these neurons. We find that, in a physiologically reasonable range of
the intensity ratio between electric and GABAergic synapses, the
network of FS interneurons shows bistability between synchronous and
asynchronous firing states. How chattering neurons and fast-spiking
interneurons together govern the coherence of local cortical activity
is now under investigation.