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Non-hippocampal theta: mechanisms?

F. Frank LeFever flefever at ix.netcom.com
Fri Apr 16 11:48:02 EST 1999


Thanks.  From what I know of Buzsaki (he's right across the river, and
I used to see him pretty often when he was chair of the Academy's
Neuroscience section), he would be looking at hippocampal theta, but
I'll certainly ask.

F. LeFever





In <m7u2uglo8l.fsf at kaweah.i-have-a-misconfigured-system-so-shoot-me>
Bill Skaggs <skaggs at bns.pitt.edu> writes: 
>
>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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