Instant gratification centre found?
Impulsive behaviour may be linked to a specific brain area.
25 May 2001
Would you rather have one slice of cake now, or a whole cake
later? Cambridge University researchers may have found the
brain region that makes this choice. The discovery could
aid our understanding of impulsiveness conditions such as
attention deficit/hyperactivity disorder (ADHD) and drug
Rudolf Cardinal and his team have found that rats with
lesions in an area of the forebrain involved in reward, the
nucleus accumbens core (AcbC), become more impulsive -- they
always chose a more immediate, smaller reward over a bigger,
later one1. The finding suggests that damage to this brain
area could contribute to behavioural disorders characterized
by the urge for instant gratification.
Drugs such as amphetamine and cocaine act on the AcbC,
altering levels of the neurotransmitter dopamine. The same
is true of Ritalin, the controversial drug widely used in
American schools to control hyperactive and inattentive
children. The researchers propose that a healthy AcbC is
required to fight off the urge for instant gratification2.
The group trained rats to chose between two levers. One
delivered a small food pellet immediately, the other a
larger pellet after a variable delay. The researchers then
gave trained rats lesions either in the AcbC or in an
unrelated part of the brain, as a control. Untreated and
non-AcbC-lesioned rats acted as expected, with the
likelihood of choosing the delayed reward decreasing as the
delay grew bigger. AcbC-lesioned rats only pressed for the
immediate reward, no matter how short the delay.
They also exhibited symptoms "quite parallel" to the
hyperactive/impulsive type of ADHD (ADHD-HI) -- they moved
more than usual and had short attention spans.
ADHD researcher Terje Sagvolden of the University of Oslo,
Norway, is enthusiastic about the research. "It suggests a
new animal model for ADHD-HI," he says. This could, he
believes, result in better treatment of impulsive disorders
in the future.
His praise is echoed by neurophysiologist Wolfram Schultz at
the University of Fribourg in Switzerland. The work is "a
major extension" of the idea that the AcbC is a reward
centre, and "the first associating it with impulsivity,"
Now Cardinal's team hope to investigate why the lesions made
the rats impulsive: did the animals not realize that the
delayed reward was available, or did they just not value the
delayed reward as much as the immediate one? The group also
intend to look at reward-related areas of the brain, such as
the amygdala, which is involved in fear.
1.Cardinal, R. et al. Impulsive choice induced in rats by
lesions of the nucleus accumbens core. Science 292 (2001).