CONTACT: JENNIFER CRONIN
2130 Medical Laboratories
Iowa City IA 52242
(319) 335-9917; fax (319) 335-8034
Release: August 3, 1999
UI Study Finds Types Of Decision-Making Deficiencies
Depend On Area Of Brain Damage
IOWA CITY, Iowa -- Decision making highly depends on
one's emotions. When a person cannot generate emotional responses to different
circumstances, which can happen when certain parts of the brain become damaged,
the person's ability to make good decisions may be disturbed. But, depending
on the location of the brain damage, how decision making is affected may
be different, according to findings from a recent University of Iowa Health
Researchers found that lesions of the amygdala disrupt
emotional conditioning, whereas lesions to the ventromedial prefrontal (VMF)
cortex cause an individual to have difficulty with conflict situations. These
results confirm the Somatic Marker Hypothesis, a theory advanced by Antonio
Damasio, M.D., Maurice Van Allen Professor and head of neurology. Damasio
had proposed that there is a neural circuit critical for processing emotional
signals. He predicted that lesions in any elements of that circuit would
result in defects in decision making.
"In essence, damage in either of the two structures
(the amygdala and VMF cortex) lead to impairments in decision making," said
Antoine Bechara, Ph.D., UI assistant professor of neurology and lead author
of the study that appears in the July issue of the Journal of Neuroscience. "However,
the underlying mechanisms responsible for the impairments are different.
In real life, the two types of patients exhibit two types of decision-making
Individuals with amygdala damage have trouble attaching
emotional significance to a previously neutral event. For example, walking
along a road is a neutral, routine event. However, if a person were mugged
while walking along this road, that person would inevitably experience fear
when he or she walked along the road again. Now, imagine that the individual
could not associate this particular road with fear. The person may decide
to continue to walk along the road and possibly subject himself or herself
to another harm in the future.
The decision-making difficulties for individuals with
VMF cortex damage are a bit more complex, Bechara said. These patients have
no trouble learning simple associations with emotions like the patients with
amygdala damage. The problems for the patients with VMF cortex damage arise
when they have to deal with conflict situations involving immediate reward
and distant consequence. Suppose a spy offered a bribe to sell government
secrets. On one hand, there is the thought of getting caught, being fired
and possibly going to jail. When confronted with this type of conflict, Bechara
and his colleagues believe that people generate two emotional signals a
positive signal triggered by the rewarding impact of money resulting from
the bribe, and a negative signal resulting from the fear of being caught.
If the negative/fear emotion is stronger than the positive/reward emotion,
the person will likely turn down the bribe. The UI study suggests that the
immediate effect of any action influences patients with VMF cortex damage,
regardless of whether the immediate effect is correct. In other words, patients
with VMF cortex damage would likely take the bribe in this situation.
"They are oblivious to any consequence that the action
may have in the future," Bechara said.
The decision-making deficit from VMF cortex damage is usually
confined to financial matters and social relationships. Patients with this
type of damage usually do not make decisions that lead to physical harm to
themselves or to others, Bechara explained. The patients with amygdala damage
have similar troubles to the VMF cortex patients, but in addition, they have
more profound problems that can cause harm to themselves and others, he said.
Bechara and his colleagues had two goals for their
study: to determine whether amygdala damage would interfere with decision
making and to find out whether there was a difference between the roles that
the amygdala and VMF cortex played in decision making.
Bechara and his colleagues based their findings on
a study of 23 subjects 13 individuals with no brain damage and 10
individuals with brain damage (five with amygdala damage and five with VMF
cortex damage). The study involved a computerized gambling task test. The
subjects saw four decks of cards on a computer screen. The goal of the game
was to win as much money as possible. If the subjects found themselves unable
to win, they needed to try to avoid losing as much money as possible. The
subjects were free to switch from one deck to another any time they wished.
The decks varied on the amount of overall wins and
losses. Using a mouse, the subjects could click on a card in any of the four
decks. The computer tracked the sequence of selected cards from the decks.
Every time the subjects chose a card, a green bar on the top of the computer
screen changed according to the amount of money won or lost after each selection.
The researchers attached electrodes to the subjects'
palms to measure skin conductance responses (SCRs) an index of emotional
state activation. Each time the subjects clicked the mouse, the action was
recorded as a mark on a polygram. The SCRs generated during the task were
divided into three categories: reward SCRs, which were generated after winning
a sum of money; punishment SCRs, which were generated after losing a sum
of money; and anticipatory SCRs, which were generated previous to turning
a card (i.e., when individuals were pondering from which deck to choose).
As the task progressed, the control group (people without
brain damage) gradually began choosing more from the good decks and less
from the bad decks. By contrast, both groups of patients with brain damage
failed to make the shift in behavior. They selected more cards from the bad
decks than from the good ones. However, the results of the polygram showed
that there was a difference between patients with VMF cortex damage and those
individuals with amygdala damage in the ability to generate SCRs after wins
(reward) or losses (punishment) were received. This physiological difference
reflects a difference in the contribution of each of the two brain structures
to the global process of decision making.
In addition to Bechara, the other researchers involved
in the study included Antonio Damasio; Hanna C. Damasio, M.D., UI Foundation
Distinguished Professor of Neurology; and Gregory P. Lee, from the section
of neurosurgery, Medical College of Georgia.
The UI-led study was supported by a grant from the
National Institute of Neurological Diseases.