Illustration:
Jose-Luis Olivares/MIT
Researchers discover neurons in the brain that weigh costs
and benefits to drive formation of habits.
(August 20, 2015) We
are creatures of habit, nearly mindlessly executing routine after routine. Some
habits we feel good about; others, less so. Habits are, after all, thought to
be driven by reward-seeking mechanisms that are built into the brain. It turns
out, however, that the brain’s habit-forming circuits may also be wired for
efficiency.
New research from MIT shows that habit formation, at least
in primates, is driven by neurons that represent the cost of a habit, as well
as the reward. “The brain seems to be wired to seek some near optimality of
cost and benefit,” says Ann Graybiel, an Institute Professor at MIT and also a
member of the McGovern Institute for Brain Research.
This study is the first to show that cost considerations are
wired into the learning of habits. The findings, which appear this week in the
journal Neuron, could also provide insights into neuropsychiatric disorders
that involve problems with repetitive behavior, such as Parkinson’s disease,
Huntington’s disease, obsessive-compulsive disorder, Tourette syndrome, and
autism spectrum disorder.
Graybiel and her
colleagues previously discovered clear beginning and ending signals in
the brain when
habits are performed. These signals appear in the striatum, a part
of the brain that,
among other things, coordinates body movements.
Image: Laura
Petersen/Okinawa Institute of Science and Technology
The anatomy of a
habit
Previous work by Graybiel and her colleagues discovered
clear beginning and ending signals in the brain when habits are performed.
These signals appear in the striatum, a part of the brain that, among other
things, coordinates body movements; the signals have been observed in mice,
rats, and monkeys that have been trained to perform specific tasks.
A few years ago, Graybiel and Theresa Desrochers, then a
doctoral student in her lab, decided to let two monkeys learn a habit on their
own, without training, as a way to mimic real-life learning. They also recorded
the activity of 1,600 neurons in the striatum during the learning period.
The primates learned, over several months, to visually
navigate a grid of dots on a screen in search of a randomly selected one that
has been “baited,” meaning that the monkey will receive a squirt of juice when
its eyes pass through it. When the monkey’s eyes land on the “baited” dot, the
color of the grid of dots changes, indicating that a reward is coming.