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Developmental Biology - Neural Brain Waves
Brain Waves Stimulate Muscle Movements
How waves in the motor cortex of our brain help initiate and regulate muscle movement...
For decades, scientists have wondered why specific cells in the brain fire when people simply plan or imagine moving their limbs, or even observe someone else making physical movements. It's long been known that when a person thinks about or plans a movement, neurons fire in the motor cortex and create a signal called a beta oscillation.
Now, University of Chicago scientists have discovered how other signals in the brain's motor cortex mediate muscle nerve responses. While the brain sees and interprets a visual act of muscle movement, it may send out similar signals to nerves to respond in kind, but also send signals to disrupt or slow down initiation of muscle response. The research is published in the journal Neuron.
"This work provides the first evidence that large-scale, spatially organized brain patterns are behaviorally relevant."
Nicho Hatsopoulos PhD, Neuroscientist, Professor of Organismal Biology and Anatomy, and senior author of the study.
Hatsopoulos likens the function of this series of signals to a clutch in a car with a manual transmission. The clutch assembly interrupts the power flow between the engine and the transmission. When you push in a clutch pedal you disengage the transmission, and the car doesn't move. If you press on the gas at the same time, the car engine will rev - but it can't move as the gears operating the wheels are not functioning.
Hopefully these findings will lead to interventions for people with Parkinson's disease, a muscle movement disorder, by helping initiate movement through stimulation of electrodes in their motor cortices.
Imagine moving your arm or observing someone else moving their arm. Signals in your motor cortex are maintained or even intensified - even if you don't move your arm. Only when you are ready to actually move your arm do the beta oscillation signals stop. Effectively that allows the engine (brain) to link to the transmission (muscle) which links to the wheels (arm) and you move your arm.
Hatsopoulos and his team have discovered that this "clutch" like signal in our motor cortex is not one, but multiple "clutches" that act in an organized pattern that begin at one end of the motor cortex and terminate at the other. Every time a movement is initiated, an organized wave of clutches - or groups of firing neurons - engages.
"While this clutch-like mechanism has been previously observed at single sites in the motor cortex, we've discovered that movement initiation is associated with a propagating wave of clutches across the cortical surface."
Nicho Hatsopoulos PhD.
To come to these conclusions, researchers studied three rhesus macaque monkeys, rewarded with juice each time they won a video game. The game required the monkeys use a joystick to move a cursor across a screen to a target. Electrodes implanted in the arm and hand area of their brain' motor cortices recorded neuronal activity of their arm movement in manipulating the joystick.
By electrically microstimulating multiple sites in the arm/hand area of the motor cortex to create waves of stimulation, researchers disrupted the monkeys' reaction time. When they applied stimulation in a way that followed the natural wave of brain clutches releasing, the monkey's initiation of movement remained unchanged. But when researchers stimulated nerve cells in the opposite direction of the wave, reaction time slowed.
The team is now studying whether similar patterns of signals occur in the motor cortex when moving the tongue, and whether movement initiation of the tongue can also be manipulated through micro stimulation.
Abstract Highlights
• Patterns of excitability propagate across M1 along the rostro-caudal axis
• Only stimulation against the natural propagating direction delays reaction time
• Functional connections among M1 units emerge along the same rostro-caudal axis
• Beta amplitude profiles along the rostro-caudal axis more accurately decode EMGs
Summary
Voluntary movement initiation involves the modulations of large groups of neurons in the primary motor cortex (M1). Yet similar modulations occur during movement planning when no movement occurs. Here, we show that a sequential spatiotemporal pattern of excitability propagates across M1 prior to the movement initiation in one of two oppositely oriented directions along the rostro-caudal axis. Using spatiotemporal patterns of intracortical microstimulation, we find that reaction time increases significantly when stimulation is delivered against, but not with, the natural propagation direction. Functional connections among M1 units emerge at movement that are oriented along the same rostro-caudal axis but not during movement planning. Finally, we show that beta amplitude profiles can more accurately decode muscle activity when they conform to the natural propagating patterns. These findings provide the first causal evidence that large-scale, propagating patterns of cortical excitability are behaviorally relevant and may be a necessary component of movement initiation
Authors
Karthikeyan Balasubramanian, Vasileios Papadourakis, Wei Liang, Kazutaka Takahashi, Matthew D. Best, Aaron J. Suminski and Nicholas G. Hatsopoulos.
Acknowledgements
The study, "Propagating Motor Cortical Dynamics Facilitate Movement Initiation," was supported by the National Institute of Neurological Disorders and Stroke at the National Institutes of Health (Grants R01 NS045853 and R01 NS111982). Additional authors include Vasileios Papadourakis, Wei Liang, Kazutaka Takahashi and Matt Best of the University of Chicago and Aaron Suminski of the University of Wisconsin.
Funding
The study was supported by the National Institute of Neurological Disorders and Stroke at the National Institutes of Health (Grants R01 NS045853 and R01 NS111982). Additional authors include Vasileios Papadourakis, Wei Liang, Kazutaka Takahashi and Matt Best of the University of Chicago and Aaron Suminski of the University of Wisconsin.
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.jpg) Waves of electrically stimulated neurons will slow or stop if a new wave is directed against the initial flow. CREDIT stock image/no copyright infringment intended
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