Download a high resolution image of the brain areas affected by hard-wiring.
NASHVILLE, Tenn. — When you grab a piece of food and put it in your
mouth, when you smile in response to the smile of a passerby or squint
and grimace in anger, the complex pattern of movements that you make
may be hard-wired into your brain.
Scientists have long known that many of the behaviors of lower
organisms are innate. In the insect world, for example, instinctive
behaviors predominate. Birds have a larger repertoire of fixed
behaviors than dogs.
In primates, voluntary or learned behavior predominates, so
neuroscientists have assumed that the hard-wiring in primate brains is
limited to simple movements, and complex behaviors are all learned.
Now, however, studies are finding that a number of surprisingly complex
behaviors appear to be built into the brains of primates as well. These
are “biologically significant” behaviors that appear likely to improve
the primate‘s ability to survive and reproduce. They include aggressive
facial patterns, defensive forelimb movements, and hand-to-mouth and
reaching-and-grasping movements.
Vanderbilt researchers, writing this week in the Proceedings of the National Academy of Sciences Online Early Edition,
report that they can elicit these complex behaviors by stimulating
specific areas in the brain of a small nocturnal primate called the
Galago or bush baby (Otolemur garnetti). Their results provide
significant new support for the proposition that all primate brains,
including our own, contain such a repertoire of innate complex
behaviors.
“We have now seen this feature in the brain of an Old World monkey and
New World prosimian. The fact that it appears in the brains of two such
divergent primates suggests that this form of organization evolved very
early in the development of primates. That, in turn, suggests that it
is characteristic of all primate brains, including the human brain,”
says Jon Kaas, the head of the research group, Distinguished Professor
of Psychology at Vanderbilt University and investigator at the
Vanderbilt Kennedy Center for Research on Human Development.
“These results explain why certain behaviors — such as defensive and
aggressive movements, smiling and grasping food — are so similar around
the world. It is because the instructions for these movements are
built-in and not learned,” he adds.
Over the last 20 years, neuroscientists have identified an area called
the primary motor cortex, which, when stimulated, triggers simple
muscle movements. The fact that they were able to produce only motions
by single muscles and other simple movements reinforced the idea that
only simple movements were hard-wired into primate brain circuitry.
Then, last year Michael Graziano at Princeton University pointed out
that previous stimulation experiments in the motor cortex — the area
that controls bodily motions — had been done using very short
electrical pulses that last less than a half-second. He further
suggested that longer pulses might stimulate more complicated motions.
Working with alert macaques, he and his colleagues found that applying
such long-duration signals did in fact elicit several of these complex
behaviors, much as they had predicted.
Kaas and his colleagues, research assistant professor Iwona Stepniewska
and doctoral student Pei-Chun Fang, decided to follow the Princeton
researchers‘ lead and try long-duration stimuli in the simpler brain of
the Galago. When they did, they also found that this type of stimuli
triggered complex behaviors. In fact, they were able to stimulate a
larger number of complex movements than the Princeton group had
reported, including aggressive facial patterns, defensive forelimb
movements, and hand-to-mouth and reaching-and-grasping movements.
The Princeton researchers stimulated areas in the motor cortex. The
Vanderbilt researchers found that they could also elicit these
behaviors by stimulating a nearby area of the brain called the
posterior parietal cortex. This area is heavily interconnected with the
motor cortex and had previously been associated with transforming data
from the eyes and other senses into a spatial map of the surrounding
environment. The new findings reveal that this brain area also plays an
important role in complex, innate behaviors.
The research was funded with a grant from the National Institutes of Health.
For more news about Vanderbilt research, visit Exploration, Vanderbilt‘s multimedia research magazine, at www.exploration.vanderbilt.edu.
Media contact: David F. Salisbury, (615) 343-6803
david.salisbury@vanderbilt.edu