CONTACT: JENNIFER BROWN
Iowa City IA 52242
(319) 335-9917; fax(319) 335-8034
Release: Dec. 28, 2000
UI study investigates human emotion processing at level
of individual brain cells
IOWA CITY, Iowa -- A region at the front of the brain's
right hemisphere, the prefrontal cortex, plays a critical role in how the
human brain processes emotions. Data from previous studies of brain lesions
(areas of damage that alter the brain's ability to generate normal emotions)
and data from functional brain imaging studies have delineated the extent
of the area involved. However, a recent University of Iowa study is the first
to investigate human emotion processing by the right prefrontal cortex at
the level of individual brain cells.
"This kind of single-cell study is very rarely performed
in humans," said Ralph Adolphs, Ph.D., assistant professor of neurology and
principal investigator on the study. The findings appear in the January issue
of the journal Nature Neuroscience.
A rare surgical situation allowed the UI Health Care
researchers to record the activity of individual brain cells, neurons, in
an awake, alert patient as he was shown images designed to elicit an emotional
The patient was undergoing neurosurgery to treat epilepsy,
which had not responded to medication. Usually, electroencephalogram (EEG)
electrodes placed on the scalp would be used to pinpoint where in the brain
the epileptic seizures are localized. However, in this case that approach
did not work, so for treatment purposes the surgeon implanted depth electrodes
into the patient's brain to monitor where the seizures originated.
"We used a custom-designed hybrid research-clinical
depth electrode, which provided the neurosurgeon with the clinical information
necessary to locate the area causing the seizures," explained Adolphs. "The
electrode also had a series of special contacts on its shaft, through which
we were able to isolate the activity of single brain cells. Recording the
activity of the neurons posed no additional risk to the patient."
Monitoring single neurons in the right prefrontal
cortex, the researchers found that these cells responded remarkably rapidly
to unpleasant images, which included pictures of mutilations and scenes of
war. Happy or neutral pictures did not cause the same rapid response from
To ensure that these neurons were not reacting to
pictures that were brighter or larger or had more of a particular color, the
researchers were particularly careful to make sure that the only difference
among these pictures was their emotional content.
"The changes in firing pattern of neurons responding
to the aversive visual stimuli happened within about 0.12 seconds, which is
very fast and probably prior to the patient consciously "seeing" the image,"
"The speed at which these cells change their firing
rates is surprisingly rapid. We thought it would take much longer for these
neurons to be able to extract information about an emotion category, which
is really a very high level cognitive function," Adolphs added.
Although the researchers were surprised by the speed
at which the neurons reacted to the aversive images, Adolphs indicated that
the findings are consistent with the idea that the brain has systems that
can respond extremely rapidly to potentially dangerous or threatening kinds
"It makes a lot of sense from an evolutionary point
of view," he said.
The UI study shows that neurons in the right prefrontal
cortex are able to distinguish, or categorize, emotional information from
visual stimuli very rapidly. Adolphs also indicated that it seems likely that
signals from these cells may serve to modulate visual information processing
by other regions of the brain.
"The area of the brain that we recorded from, the
prefrontal cortex, is only one component of a widely distributed neural system
for encoding this information," Adolphs said. "We think that another part
of that information is encoded in visual cortices. The visual cortices would
respond when the stimulus is seen, then those responses would be changed by
subsequent input from the prefrontal cortex."
Although the study involved only one patient who had
epilepsy, the region of the brain where the recording was performed was distant
from the site of the epileptic seizures. This meant that the tissue being
studied was essentially normal, healthy prefrontal cortex.
In addition to Adolphs, other UI investigators involved
in the study included Hiroto Kawasaki, M.D., post doctoral fellow in neurology,
Matthew A. Howard, M.D., associate professor of surgery and neurology and
Antonio R. Damasio, M.D., Maurice Van Allen Professor of Neurology and head
of the department.
The research was supported by grants from the Center
for Consciousness Studies, the EJLB Foundation, and the Klingenstein Fund.
University of Iowa Health Care describes the partnership
between the UI College of Medicine and the UI Hospitals and Clinics and the
patient care, medical education and research programs and services they provide.