[Eeglablist] Can amygdala activity be detected on the scalp?

[Richard Harner]

Teresa,
 
First off here is a list of some factors that contribute to the detection of
a signal deep in the brain:
 
1. magnitude of the generators--microvolts to millivolts
2. size of the field-- number of synapses, fibers, cells, regions
3. field type-- simple/mixed, open/closed, compact/distributed,
curved/planar
4. orientation of field to recording electrodes--perpendicular/parallel
5. distance from electrodes-- microns, millimeters, centimeters
6. frequency structure within bandpass of recording electrodes/amplifiers
7. signal/noise ratio-- temporal, spatial, frequency, statistical
8. stochastic properties--stationarity, gaussianity, etc
 
Anyone eel free to add or subtract or comment on this partial list. I am
sure Paul (Nunez) and others would have lots more to say, but even such a
short list suggests that addressing multiple factors can enhance the
likelihood of finding what you want, even deep in the brain.  EEG history is
full of examples of missing important signals because of inappropriate
selection of paradigm, electrode, montage or bandpass. 
 
Epileptic spikes from the amygdala are huge, have lots of connections
temporal cortex and may be easy to record and localize with surface
electrodes if field orientation is appropriate, as noted by others ( for
example see J. Ebersole). 

More relevant to the difficult problem you pose is the regularly successful
detection of extremely low amplitude auditory evoked potentials (AEP) from
the human pons and midbrain, using widely spaced electrodes, recording
bandpass 10-3000 Hz and averaging thousands of 10/sec very brief clicks.
This technique is now standardized and in clinical use for decades.

So, is it possible to record tiny, distant sources in the brain with surface
electrodes?  Unequivocally yes, if the contributing issues are addressed.
Easy in your circumstances?  Certainly not, without a fresh insight into
methodology.  Still, given

1) a clever protocol designed to give a large localized response, 
2) some external information  about the location of activated generators
(say fMRI) and 
3) some idea about the nature of the signal (say, by trying your protocol in
subjects who have intracranial electrodes for other purposes) it might be
worth a try.

Happy New Year!

Richard Harner 


-----Original Message-----
From: eeglablist-bounces at sccn.ucsd.edu
[mailto:eeglablist-bounces at sccn.ucsd.edu] On Behalf Of Mike Cohen
Sent: Friday, December 30, 2005 6:52 PM
To: eeglablist at sccn.ucsd.edu
Subject: Re: [Eeglablist] Can amygdala activity be detected on the scalp?

That's all true, but it's worth noting that the amygdala has a lot of
connections and interactions with other regions, such as prefrontal cortex,
that are measured by EEG. So while you probably can't measure amygdala
activity directly with scalp EEG, it doesn't mean that tasks that recruit
the amygdala won't generate scalp-recorded ERPs. You just have to be careful
about how exactly you interpret the results.


On 12/30/05, Bradley Voytek <semiconscious at gmail.com> wrote:
> Teresa--
>
> I'm sorry to say that the location of the amygdala in the anterior, 
> inferior, medial temporal lobe makes the attenuation due to distance 
> such that getting ERPs would be nearly impossible. Source localization 
> is limited because much of the signal from the amygdala is not being 
> recorded--it's on the ventral surface of the brain.
>
> The neurons in the amygdala are not as well aligned as in the cortex, 
> thus making dipole localization rather difficult: you'd get a lot of 
> cancelling effects due to different neuronal orientation.
>
> As for other limbic structures, the cingulate cortex has proven to be 
> a fairly reliable source of ERPs, so that is likely your best bet.
> Without depth-electrodes, I just don't think you're going to get 
> signal from other limbic regions (hippocampus, hypothalamus, amygdala,
> etc.)
>
> So, that's my impression.
>
> --brad voytek
>
> On 12/30/05, Teresa Wong <wongkwt at gmail.com> wrote:
> > Dear colleagues,
> >
> > I would like to hear your views on whether scalp ERPs can reflect 
> > activity of the amygdala.
> > Is it possible/valid to localize dipole sources (using 128-channel 
> > recordings, emotional faces as stimuli) in subcortical brain 
> > regions, limbic areas, amygdala, etc?
> >
> > Wishing you all a very happy and healthy 2006 with much success in
research!
> >
> > Teresa
> > --
> > Teresa Ka Wai Wong
> > PhD Student
> > Department of Psychiatry
> > The University of Hong Kong
> >
> > _______________________________________________
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--
Mike Cohen
UC Davis Psychology
Epilepsy and Psychiatry Clinics, Bonn, Germany
http://www.DynamicMemoryLab.org/mcohen

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