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Neural oscillations are rhythmic or repetitive neural activity in the central nervous system. In single neurons, it may display as periodic changes in the membrane potential below threshold, or a train of nerve impulses (Figure 34a). A population of neurons may also oscillate synchronously. The brain waves recorded by electroencephalography (EEG) are the results of synchronized oscillations. They play crucial roles in conscious perception and memory processing.

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Figure 34a. Examples of neural oscillations. The black and red curves represent subthreshold oscillations and nerve impulses (spikes), respectively.

An oscillation system has two essential physical parameters: frequency and amplitude.

  • Frequency is the inverse of the period. Its unit is hertz (Hz). 1 Hz = 1/second.
  • Amplitude is the maximum displacement.

If there are two or more oscillation systems, we should also consider the "phase" which refers to the time point in an oscillation cycle. If two oscillation systems are "in phase", they will arrive at the oscillation peak simultaneously. In this case, the two systems are "synchronized".

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Figure 34b. Illustration for the phase of oscillation systems. [Source: Wikipedia]

Synchronization

Figure 34c shows the difference between synchronization and non-synchronization. The oscillation of neuron A is synchronized with the oscillation of neuron B because both of them arrive at the peak simultaneously. They are not synchronized with the oscillation of neuron C.

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Figure 34c. Comparison between synchronization and non-synchronization.

EEG and MEG

Brain Waves

 

Author: Frank Lee
Posted on: 2020-08-25