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Gamma oscillations
Gamma
oscillations and the cellular components of consciousness
Fiona
LeBeau,
Institute of Neuroscience, Newcastle University
In: - New Horizons in
the
Neuroscience of Consciousness – John Benjamins (2010)
Studies have
shown
that inhibitory interneurons using the GABA neurotransmitter are
essential to
generate gamma frequency oscillations in the brain. These neurons only
comprise
10-20% of the neurons in the cortex, but there is a great diversity
within this
type of neuron. Different types of interneuron are involved in varying
forms of
oscillatory activity. The neurons are distinguished by a variety of
calcium-binding proteins such as parvalbumin. This has been shown to be
particularly important in gamma activity, applying inhibitory input to
the somas
and the initial segment of the axons of pyramidal neurons. In this
chapter the
author places particular stress on the importance of interneurons with
parvalbumin.
Thus interneurons coordinate activity in large populations of pyramidal
cells. In
addition to synaptic connections, signalling via gap junctions between
interneurons and pyramidal cells is important for fast cortical
oscillations.
Singer and Gray (1995) were the first to identify the importance of
gamma
oscillations in the visual system, since when the gamma frequency has
been identified
in the other sensory cortices, the frontal cortex, the amygdala and the
hippocampus. The proposal was made that gamma synchrony could bind
together
spatially separate neuronal populations. In a study, an increase in
gamma
synchrony across multiple regions was demonstrated to occur when a word
was
consciously perceived, but not when it was masked and remained
unconscious.
Non-conscious processing has been suggested to be related to local
synchrony,
while conscious activity relates to synchrony between different areas of
the
brain. Gamma synchrony also seems to relate to different states of
consciousness
such as REM sleep and some hallucinations. Abnormal gamma activity has
been associated
with Alzheimer's, schizophrenia and autism.
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