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I am trying to better understand which brain waves are generated when the motor system (arms, legs, muscles of any kind) are activated.

According to Wikipedia, several types (Beta, Gamma, Mu) appear to be generated when motor movement is present, but it is not clear which muscle groups/movements/characteristics generate which types of waves.

Also, I see the certain waves (Alpha an Mu for instances) appear to have overlapping frequencies. If their frequencies are the same, then what makes them different?

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    $\begingroup$ EEG is a summation of all of the neural activity, and as such, it is difficult to attribute a certain wave type to something of the scope as activation of the movement center (primary motor cortex). fMRI scans are much more valuable in a clinical setting (in conjunction with other methods). It's a snapshot and sum of electrical activity. $\endgroup$ – MG_MD Feb 13 '16 at 1:44
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    $\begingroup$ I don't think that we know yet the exact answer of your question due to the reasons told by @MG_MD $\endgroup$ – another 'Homo sapien' Feb 15 '16 at 15:15
  • $\begingroup$ Thanks @aayushsrivastav (+1) - so if I'm reading that correctly, if I am hooked up to an EEG that is monitoring ALL waves, and have been sitting completely still for ~10 mins (to establish a baseline) and then immediately start doing a repetitive movement (say, blinking my eyes or opening/closing my right hand, etc.), you're saying that ALL the types (Alphas, Deltas, etc.) will start changing, and not just one particular type (say, only Alpha or only Delta)? Can you confirm/deny? Thanks again! $\endgroup$ – smeeb Feb 15 '16 at 15:38
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    $\begingroup$ @smeeb To put it in the simplest way possible, yes. You would have a baseline, then when you started to do all of these things you mentioned there would be a marked increase in many wave forms. You would be thinking about moving, actually moving, and perceiving the movement. These affect different areas of the brain and as such, the electrical output would increase. That's why EEGs are commonly used in a resting state (like sleep studies). Also depth comes into play when using EEG, as it is mainly superficial electronic activity, not deep within the brain. $\endgroup$ – MG_MD Feb 15 '16 at 20:15
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    $\begingroup$ Thanks @MG_MD (+1) - if you (or anyone else) can place this in an answer and provide citations that back up the claims, I will happily award you/them the check + bounty! $\endgroup$ – smeeb Feb 16 '16 at 2:32
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EEG signals can be broadly analyzed in two domains; the time domain and the frequency domain.

EEGs are often analyzed in the frequency domain, where signals are subjected to spectral analysis, by methods such as FFT. This is a classic type of analysis and is still used widely today. As you rightfully state in your question, EEGs are often analyzed in terms of frequency bands. In terms of voluntary motor activity, one study reports activity in the 15 – 30 Hz range when subjects performed wrist extensions and flexions (Halliday et al. 1998). This frequency range corresponds to the alpha (8 - 15 Hz) and beta (16 - 31 Hz) frequency bands in the EEG. Beta activity in general is associated with an alert state, alpha activity generally with a more relaxed state. Both make sense because the subjects were actively engaged in a task (alert), but the task was simple and likely kind of boring (relaxed). The authors conclude that the frequency range over the motor cortex represents (Halliday et al. 1998):

[...] [R]hythmic oscillations in the sensorimotor cortex [...] associated with voluntary motor tasks involving maintained muscle activation, such as position holding.

In the time domain a relatively straightforward response to record motor activity in the brain is asking a subject to perform a certain action, for example finger flexions. These events generate certain synchronized neuronal responses in the brain that can be measured on the scalp with EEG. However, a voltage response to a single event is typically swamped in background noise. A way top enhance the signal-to-noise ration is to repeatedly record the EEG in response to the same event. By time-locking the event with the EEG and averaging the individual event-related EEGs, the random background noise will be reduced (stochastic noise) and the event-related potential (or ERP) can be extracted from the EEG (Woodman, 2010). An example of an ERP to repeated index finger flexions is shown in Fig. 1.

motor ERP
Fig. 1. ERP to voluntary index finger flexions. Motor activity was recorded from the motor area. Source: Ball et al. (1999)

References
- Ball et al. NeuroImage (1999); 10: 682–94
- Halliday et al., Neurosci Letters (1998); 241: 5–8
- Woodman, Atten Percept Psychophys (2010); 72(8): 10.3758

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  • $\begingroup$ I think this is a part of the answer, not the full answer because the question is 'brain wave and motor movement co-relation', not 'how EEG works'. $\endgroup$ – another 'Homo sapien' Feb 17 '16 at 3:09
  • $\begingroup$ @aayushsrivastav - have you read the answer at all? Both sections are on movement and motor cortex. And I don't know how my answer even touches upon the workings of EEG O.o. $\endgroup$ – AliceD Feb 17 '16 at 7:30
  • $\begingroup$ the only thing in your answer that seems to be answering this question is "Beta activity in general is associated with an alert state, alpha activity generally with a more relaxed state. Both make sense because the subjects were actively engaged in a task (alert), but the task was simple and likely kind of boring (relaxed)." Can you please tell how time domain and frequency domain tells anthing about brain wave and motor movement co-relation? $\endgroup$ – another 'Homo sapien' Feb 17 '16 at 14:56
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As said by MG_MD:

You would be thinking about moving, actually moving, and perceiving the movement. These affect different areas of the brain and as such, the electrical output would increase.

Also, it is very rare that the brain produces only one type of waves as it is continuously processing millions of information, though we know the basic functions of all of those types (from here).

As to how EEG works:

The billions of nerve cells in your brain produce very small electrical signals that form patterns called brain waves. During an EEG, small electrodes and wires are attached to your head. The electrodes detect your brain waves and the EEG machine amplifies the signals and records them in a wave pattern on graph paper or a computer screen.

Source

EEG activity screenshot

Source of image

If you look at the image, th EEG has captured many waves of different types at the same time, which proves the staement of MG_MD.

For the "overlapping frequencies..." part:

For example there is the “mu rhythm” (which is actually alpha activity in the relevant sensory and motor cortical areas that happens when the arms/hands are not doing anything)...

Source

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    $\begingroup$ Interesting points, @Christiaan (+1) - it's not too late to weigh in with your own answer! $\endgroup$ – smeeb Feb 16 '16 at 12:51

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