[evol-psych] Cerebral cortex cells may pulse electrical rhythm through the brain
- FOR RELEASE: 3 NOVEMBER 1999 AT 14:00 ET US
Cerebral cortex cells may pulse electrical rhythm through the brain
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
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