Cerebral cortex cells may pulse electrical rhythm through the
brain
Brown University researchers have shown that some nerve
cells in the cerebral cortex use electrical connections to communicate.
Scientists had thought nerve cells in the cerebral cortex communicated
only through connections that use chemical signals. The new findings
appear in the Nov. 4 issue of Nature.
PROVIDENCE, R.I. � Like the steady synchronized blink of a string of
holiday lights, certain types of nerve cells in the cerebral cortex
communicate with each other through electrical connections, forming a new
type of brain circuitry described in the current Nature.
Until now, scientists thought nerve cells in the cerebral cortex, the
sinuous bumps on top of the brain, communicated only through chemical
signals.
The cerebral cortex contains two types of nerve cells � excitatory or
inhibitory. Each neuron � a nerve cell in the brain � communicates with
other neurons through chemical connections that fire off a tiny bit of
chemical that either inhibits or excites the next neuron. These
connections between neurons are called synapses.
While studying the chemical synaptic connections in the cerebral cortex
of rats, Brown University researchers found that two separate types of
inhibitory neurons were also using electrical synaptic connections to
communicate, but only within their specific groups.
The cerebral cortex is the biggest part of the brain. This large and
complicated neural circuit is involved in most of the brain�s highest
functions, such as memory, language and sight. Within each type of
excitatory or inhibitory cell, circuitry keeps neurons interconnected and
communicating to keep overall brain activity in balance. Too much
excitation and too little inhibition, for example, may lead to seizures.
The opposite may lead to a loss of consciousness, coma or death.
The presence of electrical synapses in the cerebral cortex allows each
network of inhibitory neurons to fire in a highly coordinated and direct
way, as if there were a wire directly connecting the cells, said Barry
Connors, professor of neuroscience and senior author of the study. �We
think the inhibitory cells are coordinating their activity through the
electrical synapses,� he said. The result is synchrony similar to the
steady blinking of Christmas lights.
One of the two circuits, dubbed LTS neurons, may be involved in
preventing runaway excitation among nerve cells in the cerebral cortex,
Connors said. The electrical synapses may allow these neurons to generate
activity over a large area of the brain, he said.
�It appears this one group is especially suited to regulating cortical
function,� he said. �Most of the time it is not doing anything. But it
becomes active when the brain�s activity increases to a high level. This
network of inhibitory neurons may act like the governor on the engine of
the cortex, keeping excitability from running away and becoming an
epileptic seizure.�
Some scientists have suggested that inhibitory neurons generate the
brain�s electrical rhythms. These rhythms offer clues to the brain�s
state. Rhythms are smaller and faster when one is awake and slower and
larger during sleep. LTS neurons may be the rhythms� source.
�As we continue this research, we do suspect that this group of
inhibitory cells may be the �pacemaker� for generating some of the brain�s
rhythmic electrical activity, the kind measured by an EEG,� Connors
said.
The other electrical network of inhibitory neurons described in the
study, called FS neurons, seems to be more directly involved in the
processing of sensory information, he said.
Connors and colleagues study epilepsy, an illness often controlled by
drugs that steady the brain�s chemical signals to keep cellular networks
in balance. Discovery of electrical interconnections among cells in the
cerebral cortex may one day provide another pathway for the treatment of
brain-based illnesses.
The study�s lead author is Jay Gibson, postdoctoral fellow. The other
author is graduate student Michael Beierlein. The National Institutes of
Health funded the research.
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