NEW BRAIN PATHWAY THAT CONTROLS HAND MOVEMENT HAS BEEN IDENTIFIED 

Source: University of Pittsburgh.

Picking up a slice of pizza or sending a text message:

Scientists long believed that the brain signals for those and

related movements originated from motor areas in the

frontal lobe of brain, which control voluntary movement.

But that may not always be true. A new brain pathway has

been identified by neuroscientists at the University of

Pittsburgh School of Medicine and the University of

Pittsburgh Brain Institute (UPBI) that could underlie our

ability to make the coordinated hand movements needed to

reach out and manipulate objects in our immediate

surroundings. The discovery was made in a non-human

primate model, but researchers believe that a similar

pathway is likely to be present in humans as well.

The results, published this week in the journal Proceedings of

the National Academy of Sciences , show that the neural

pathway originates not from the frontal lobe, but from the

posterior parietal cortex (PPC), a brain region that scientists

previously thought was involved only in associating sensory

inputs and building a representation of extrapersonal space.

“The findings break the hard and fast rule that a furrow in

the brain called the central sulcus–a Mississippi River-like

separation–splits up the areas controlling sensory and motor

function,” said senior author Peter Strick, Ph.D., Thomas

Detre Professor of Neuroscience, Distinguished Professor and

chair of neurobiology, Pitt School of Medicine, and scientific

director of UPBI. “This has implications for how we

understand hand movement and may help us develop better

treatments for patients in whom motor function is affected,

such as those who have had a stroke. Our study also will

have a direct impact on the efforts of researchers studying

neural prosthetics and brain computer interfaces.”

More than three decades ago, renowned neuroscientist

Vernon Mountcastle proposed the presence of a movement

control center in the PPC and termed it a ‘command

apparatus’ for operation of the limbs, hands and eyes within

immediate extrapersonal space.

In the current study, Strick and his team confirm that such a

command apparatus exists and demonstrate a new pathway

that connects the PPC directly to neurons in the spinal cord

that control hand movement.

The research team conducted three separate experiments in

a non-human primate model to make the discovery. They

first showed that electrical stimulation in a region of the PPC

called “lateral area 5” evoked finger and wrist movements in

the animal. When they injected a protein marker into lateral

area 5, they found that the marker made its way to the

spinal cord and ended in the same location where the

neurons controlling hand muscles are known to be present,

suggesting a connection.

“The wiring and the connections from the PPC to the spinal

cord and the hand look extremely similar to those from the

frontal lobe that have been extensively studied. Similar form

suggests similar function in controlling movement,” said

Jean-Alban Rathelot, Ph.D., a research associate in Strick’s

laboratory and the lead author of the new study.

For their final experiment, they used a strain of rabies virus

as a ‘tracker’ since it has the ability to jump across

connected neurons. The team found that when they injected

the virus into a hand muscle, it was indeed transported back

to neurons in the same region of PPC where stimulation

evoked hand movements. This result demonstrated the

existence of a direct pathway from lateral area 5 to spinal

cord regions that control hand muscles.

“We know from previous research that individuals who have

suffered brain injuries in this area have trouble with

dexterous finger movements like finding keys in a bag

containing many other things, which strongly supports our

findings,” said Richard Dum, Ph.D., a research associate

professor in neurobiology and a co-author of the study.

Strick and his team believe that the multiple pathways for

controlling hand movement from the frontal lobe and the

PPC could work together to execute one complex hand task

or could work in parallel to speed up movement, much like

multiple processors in a computer can enhance efficacy.