Brain's motor cortex uses multiple frequency bands to coordinate movement

February 21, 2014
Figure 1: Typical slow gamma (left), fast gamma (center) and theta (right) brain-wave patterns measured during voluntary actions in rats. Credit: J. Igarashi et al.

Synchrony is critical for the proper functioning of the brain. Synchronous firing of neurons within regions of the brain and synchrony between brain waves in different regions facilitate information processing, yet researchers know very little about these neural codes. Now, new research led by Tomoki Fukai of the RIKEN Brain Science Institute reveals how one region of the brain uses multiple brain-wave frequency bands to control movement.

Control of movement requires activation of numerous muscle groups in correct sequence, a function achieved by the motor cortex. To investigate the contribution of to this process, Fukai and his colleagues inserted multi-channel electrodes into the motor cortex of rats to record brain-wave patterns as the animals learned to push, hold and then pull a lever to obtain a food reward. They also developed a machine-learning technique to extract spike sequences of individual neurons from the recorded waves.

Fukai and his colleagues found that brain waves of different frequencies appeared during distinct stages of the movements. Fast gamma waves, with frequencies of around 100 hertz, were most prominent when the rats pushed or pulled the lever, whereas slow gamma waves, with frequencies of 25–40 hertz, peaked when the rats held the lever to prepare for the next pull. Theta waves (4–10 hertz) peaked while the rats held the lever, and the initiation of the pulling movement coincided with a specific phase of these oscillations (Fig. 1).

Both frequencies of were coupled to the theta waves such that the peaks of all three brain-wave frequencies occurred at the same time. The activity of different types of nerve cells in different layers of the motor cortex was also synchronized with specific -wave frequencies. Importantly, cells encoding different stages of the sequential movements fired in distinct phases of the theta waves.

The results suggest that play an important role in coordinating the neuronal activity underlying the planning and execution of voluntary movement. Theta are known to be important for the processing of spatial information in the hippocampus, but this is the first time that a similar code has been observed in the motor cortex.

"We are currently using machine-learning techniques to study how phase-locked spikes in different layers of the encode motor information," says Fukai. "We are also studying whether a similar oscillatory coordination takes place in the prefrontal cortex during decision-making."

Explore further: Fluctuations in size of brain waves contribute to information processing

More information: Igarashi, J., Isomura, Y., Arai, K., Harukuni, R. & Fukai, T. "A θ–γ oscillation code for neuronal coordination during motor behavior." The Journal of Neuroscience 33, 18515–18530 (2013)

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not rated yet Feb 23, 2014
Great work, and i fully expect similar results will be found from prefrontal studies. More generally, i suspect that the hitherto loosely-defined bandwidths of brainwave spectra are in fact octave-bound; the current discrepancy from this median being due to the fluctuating nature of the net bandwidth, effectively a floating transposition of a four octave continuum.

I've outlined the reasons for this expectation here: http://medicalxpr...try.html ..and elsewhere wrt related articles.. suffice to say i would again expect factors of two between component freqs to represent 'zero' points in meta-information valuations.

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