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

Wed Jan 18 20:51:26 PST 2006

Hi all, 

Interesting discussion...just wondered whether the distance of the source
from the electrodes would play a significant factor in detecting a signal?
Given that intracerebral currents summate instantaneously at every point
within a conductive medium (cranium). I had always thought that distance (or
far field) effects are not observed in EEG/ERP recordings?

Would appreciate being corrected if I'm misguided here!

Also, type of activity would also play a major role..probably due to a
combination of Richard's points 2 and 3 below, but I think there is some
acceptance that compound action potentials contribute very little to EEG/MEG
and that it is postsynaptic or slow graded potentials that are primarily
responsible for the potential changes observed at the scalp.

Cheers

	-Bill  

> -----Original Message-----
> From: eeglablist-bounces at sccn.ucsd.edu [mailto:eeglablist-
> bounces at sccn.ucsd.edu] On Behalf Of Richard Harner
> Sent: Thursday, 5 January 2006 11:23 AM
> To: eeglablist at sccn.ucsd.edu
> Subject: RE: [Eeglablist] Can amygdala activity be detected on the scalp?
> 
> 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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> >
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> 
> 
> --
> Mike Cohen
> UC Davis Psychology
> Epilepsy and Psychiatry Clinics, Bonn, Germany
> http://www.DynamicMemoryLab.org/mcohen
> 
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