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Non-hippocampal theta: mechanisms?

Bill Skaggs skaggs at bns.pitt.edu
Fri Apr 16 07:54:34 EST 1999


flefever at ix.netcom.com(F. Frank LeFever) writes:
> The more I read about hippocampal theta (and perhaps thalamic
> oscillations in this range), the more it seems to me that (1) extrinsic
> factors may be fundamental (septal input for hippocampus; pontine for
> thalamus?), and (2) other kinds of theta, especially those associated
> with focal or diffuse pathologies, may be based on quite different
> mechanisms.

Both of these conclusions are probably correct.  One should remember
(it's easy to forget) that "theta" (and for that matter "alpha",
"beta", etc) only refer to a frequency range, not to a specific
cellular mechanism.  Incidentally, there really is no clear evidence
that hippocampal theta exists at all in humans, except in a few cases
of epilepsy that Halgren et al have reported.

> I haven't been able to find relevant work in recent literature, but
> maybe it is to be found in older lit (an editorial in J. Clin.
> Neurophysiol last year pointed out that there has been a dearth of
> really fundamental EEG research in the past 20 years).

I don't agree with this.  There was some early fundamental research,
by people like Nicholson, aimed at understanding how synaptic currents
combine to give rise to EEG waves.  That problem was essentially
solved a long time ago.  Beyond this, there was a lot more early
research into EEG but it was mostly phenomenology, and led to a lot of
correlations but little understanding of mechanisms.  Fundamental
research means trying to understand neural oscillators and neural
population dynamics, and there's a lot of that going on now.  It's a
hard problem.  In any case, you certainly won't find any stunning
insights into theta in the early literature.  There was a lot of
useful work, particularly in the area of pharmacology, but it didn't
come close to explaining the basic mechanisms.  It's too much to
expect: after all, back then they didn't even know that glutamate is a
neurotransmitter.

> Will be grateful for any references or ideas about cellular basis of
> diffuse or focal slowing, "theta bursts" or "paroxysmal slowing".

Sorry, not my area.  I believe Buzsaki has done some work on these
sorts of questions recently.

	-- Bill



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