Scientists have made a brain discovery that
could help lead to thought-
controlled machines. Recent experiments have shown that a little-
understood part of the brain that we use to process information about
objects also plays a role when we move a hand or other limb.
Researchers made the key discovery when they studied
the brain
activity of several patients with electrodes surgically implanted in
their brains.
The scientists found that an area of the brain called the ventrolateral
prefrontal cortex, located near our temples, processes spatial
information—information related to movements that we are about to make.
The study could aid the development of prosthetics that are
brain-controlled. One application might be a brain-machine interface
that helps paralyzed people to move and communicate simply by thinking.
"It had been thought that this area [of the brain] was
specialized for object processing [determining what an object is] and
did not contribute to spatial processing at all," said Daniel Rizzuto,
a postdoctoral neuroscience scholar at the California Institute of
Technology in Pasadena.
"This result opens up the possibility of using these spatial
signals to control a neural prosthetic device, which will eventually
help paralyzed people to move again."
Rizzuto led the study, which was reported last month in the online
edition of the research journal Nature Neuroscience.
Planting Electrodes
In the future, neural prosthetic devices could allow paralyzed
patients to move a computer cursor or a robotic arm using just their
thoughts.
To identify the brain areas that could best control such movements,
researchers have usually focused on the areas of the brain directly
responsible for the movement of body parts, not the planning stages of
the brain, such as the prefrontal cortex.
This brain region is thought to control goal-directed behavior.
It selects useful sensory information and integrates it with our
"goals" to direct our behavior.
To do so, it follows complex rules that helps us to act
appropriately in various situations, Rizzuto explained. "For example,
this area [of the brain] helps us to know not to pick up a ringing
phone in someone else's house."To find out exactly what happens in the
prefrontal
cortex, Rizzuto and his advisor, Richard Andersen, a Caltech
neuroscience professor, piggybacked on clinical work done by Adam
Mamelak, a neurosurgeon at Huntington Memorial Hospital in Pasadena.
Mamelak was treating three patients with severe
epilepsy. Trying to
identify the brain areas where the seizures occurred, the neurosurgeon
implanted electrodes into the patients' ventrolateral prefrontal
cortex.
"So for a couple of weeks these patients are lying there, bored,
waiting for a seizure," Rizzuto said. "I was able to get their
permission to do my study, taking advantage of the electrodes that were
already [surgically implanted] there."
The patients had to watch a computer screen for a flashing target, then
remember the target location for a short time, then reach to that
location on a touch screen.
Monitoring their brain activity, Rizzuto was able to show
conclusively that the ventrolateral prefrontal cortex is involved in
how we process spatial information.
"These findings were not surprising to our group, because we understand
that object and spatial processing do not necessarily require different
processing domains in the brain," Rizzuto said.
"There is more research showing that the brain areas dedicated
to object and spatial processing actually have a lot of
interconnections with each other," he added. "However, some scientists
still hold these traditional ideas of separate object and spatial
processing domains, and they may be surprised at our results."
Less Hardwired
Recent studies of monkeys have shown that neurons in the
monkeys' ventrolateral prefrontal cortex also carry spatial signals
when monkeys are planning movements.
"The monkey brain is a model for the human brain, and studies
like these provide critical evidence that there are indeed [structural
likenesses] between them, even at the highest levels of brain
processing," said Earl Miller, a neuroscience professor at the
Massachusetts Institute of Technology in Cambridge.
The Caltech research is important, Miller said, because it
identifies the ventral prefrontal cortex as a site where motor, or body
movement, planning takes place, meaning it could be used to drive
neural prosthetic devices.
"There may be big advantages to using the prefrontal cortex [for neural
prostheses] rather than [the] lower-level motor cortex, because the
prefrontal cortex seems less hardwired and specific to the details of
the movements than [the] primary motor cortex," Miller said. (The motor
cortex is a brain region that controls voluntary muscle movement.)
Movement-planning areas are also less susceptible to damage
than areas of the brain directly responsible for movement. In the case
of a spinal cord injury, for example, communication to and from the
primary motor cortex is cut off: For example, severed nerves might
prevent a person's brain from sending signals telling their legs to
step forward.
However, the brain still performs the computations associated with
planning to move. Scientists could, in theory, tap into these planning
calculations and decode where a person is thinking of moving.
"We believe that motor-planning areas will be more resistant to
pathological reorganization after spinal injury, as it is already known
that neurons in primary motor cortex die after such injuries," Rizzuto
said. In other words, neurons in motor-planning
parts of the brain are probably less likely to be "scrambled" after an
injury than they are in areas that are directly involved in carrying
out movement.
As the control center of the brain, the prefrontal cortex could
possibly be used to control multiple prosthetic devices simultaneously.
"For instance, a patient could navigate his wheelchair and use
an LCD interface to type a letter at the same time," Rizzuto said.
"This could be accomplished by having the patient learn different
neural codes, or contexts, for different devices."