Cortex Questions

ramesh at MV3600.BMEN.TULANE.EDU ramesh at MV3600.BMEN.TULANE.EDU
Fri Mar 12 13:23:34 EST 1993


In article <1993Mar9.193011.7855 at ringer.cs.utsa.edu>, nlawrenc at ringer.cs.utsa.edu (P. Nick Lawrence) writes:
>Could anyone direct me to answers to the following questions:
>
>(1) When the primary EEG frequency shifts, for example between and Alpha
>of (say) 8 Hz and a Beta of (say) 25 Hz, is the shift in fact a change
>in propagation rate or a change in wavelength?
>
>(2) Is there any experimental evidence that cortical neurons exist which
>function similar to the "sinus node" neurons found (eg) in the heart?
>How prevalent are they?
>
>Please answer by email.  Thanks!
>
>Nick L
>

The first question is a little confusing.  If propogation rate increases, or
more commonly velocity increases then certainly frequency increases, IF THE 
MECHANISM UNDERLYING THE TWO PROCESSES IS THE SAME.  In the EEG we have no 
theory that accounts for beta and alpha with the same mechanism.  

velocity=frequency*wavelength

Change in frequency and change in wavelength are just two different ways of
saying the same thing. 

Therefore when you suggest a change in wavelength, I will presume that velocity
stayed the same (600-900 cm/s in corticocortical fibres) and that for some
reason frequency has gone up from 8 to 25 Hz implying that wavelength went
down.

This is simply a statement of the facts, we don't really know why. 

With regards to the second question I think the answer must be no for the
following reason: the EEG is a gross estimate averaged over several cm of
cortex.  Using  the MEG which is a property of a unique point in space much
more power is recorded from 10-30 Hz even when the subject is putting out alpha
The dominance of alpha in EEG is simply a consequence of recording and 
measurement techniques: thus if such a cell existed, it would have to 
totally numerically dominate other cells in the cortex. Such a preponderance 
of cells has not been reported in the literature as far as I know. 

I hope this helps you out some. 


Ramesh



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