[Eeglablist] Source localization and hippocanpus

[Kevin Spencer]

I see a lot of papers, mainly MEG, that use forward solutions from beamformers and claim to be measuring activity in subcortical structures with no measure of forward model errors or cross-validation with other modalities. It seems to me that if you can't localize a pattern of activity using an inverse method, you can't just generate a forward solution from a region of interest and assume your results are valid.

There are old papers (late 80s - 90s) from when people first started using dipole localization to measure activity in auditory subcortical structures (MGN, IC, etc.). Those data seemed reasonable to me because of the SNR of the input data, the spatial separation between cortical and putative subcortical sources, and the comparison of different dipole models to establish validity.

Kevin
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Kevin M. Spencer, Ph.D.
Research Health Scientist, VA Boston Healthcare System
Associate Professor of Psychiatry, Harvard Medical School
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On Thursday, January 15th, 2026 at 12:05 AM, Joseph Dien via eeglablist <eeglablist at sccn.ucsd.edu> wrote:

> We made a good case that the Feedback Negativity (FN) originates from
> the striatum (Foti, Weinber, Dien, & Hajcak, 2011, 2011). It's not a
> claim to be made lightly. The cortex is a strong candidate as far-field
> generators because it is rich on pyramidal neurons, which have
> asymmetrical dendrites and tend to be oriented in the same direction,
> but that does not mean it is the only possible source. To make a case
> for a subcortical generator, you have to be able to demonstrate
> convergent validity with data from methods like intracranial EEG
> recordings. See our papers for arguments and references.
> 
> The hippocampus, on the other hand, is the classic example of a
> structure that is likely to be a closed field generator because it is in
> the form of a tube, wherein the field from a given neuron is likely to
> be canceled out by the field from a neuron pointing the opposite
> direction on the other side of the tube, resulting in a net zero voltage
> field when measured from outside the tube. No amount of electrodes or
> computational sophistication is going to help with that. Of course,
> it's all complicated because the entire tube isn't necessarily equally
> active. Also, the adjoining parahippocampal cortex isn't a tube. There
> seems to be a lot of discussion going on right now about what can be
> measured. But yeah, making a plausible claim for a hippocampal
> generator would require very strong evidence. As John says, it's easy
> to put a equivalent dipole in the hippocampal region and get non-zero
> results, so not strong evidence by itself. But I'd also be wary of
> making sweeping generalizations.
> 
> Joe
> 
> Foti, D., Weinberg, A., Dien, J., & Hajcak, G. (2011). Event-related
> potential activity in the basal ganglia differentiates rewards from
> nonrewards: Temporospatial principal components analysis and source
> localization of the feedback negativity. /Hum Brain Mapp/, /32/(12),
> 2207–2216. https://urldefense.com/v3/__https://doi.org/10.1002/hbm.21182__;!!Mih3wA!F6lfB756tGdH_QFKwL5mIWetNG672s_aafnqgyt9T8wO7nrcuWuqfT_GvDz4sGND_j85H6f_kjzDtWSplqI$
> 
> Foti, D., Weinberg, A., Dien, J., & Hajcak, G. (2011). Event-related
> potential activity in the basal ganglia differentiates rewards from
> nonrewards: Response to commentary. /Hum Brain Mapp/, /32/(12),
> 2267–2269. https://urldefense.com/v3/__https://doi.org/10.1002/hbm.21357__;!!Mih3wA!F6lfB756tGdH_QFKwL5mIWetNG672s_aafnqgyt9T8wO7nrcuWuqfT_GvDz4sGND_j85H6f_kjzDCIoX_BY$
> 
> On 1/14/26 18:52, Richards, John via eeglablist wrote:
> 
> > The hippocampus, caudate, putamen, amygdala, sometimes are classified with "cortex" as gray matter and people might try to do source analysis. However, only the cortex has the perpendicular pyramidal structure that conducts current to the scalp, and the "subcortical" brain areas do not have the correct structure to generate current on the scalp. If you put source locations in these areas and do source analysis you will get "something", likely due to activity in other brain areas, noise, or other non-neuron activity.
> > 
> > I think that a couple of the "internal" cortex ROIs, like the insula, have the cortex structure to generate current. But its possible that it cannot be measured because the area is relatively far from the scalp and any current would be small.
> > 
> > John
> > 
> > ***********************************************
> > John E. Richards
> > Carolina Distinguished Professor
> > Department of Psychology
> > University of South Carolina
> > Columbia, SC 29208
> > Dept Phone: 803 777 2079
> > Fax: 803 777 9558
> > Email:richards-john at sc.edu
> > https://urldefense.com/v3/__https://jerlab.sc.edu/__;!!Mih3wA!ETNTEAJ6TN4Jy-leSX_wNE4oEjcJRGEvhvPv9VUow0FLXB7TonoRBJczbLfGx7O-lhiZ8zLs-rOV6e3nqjWwi01tM5J3lQ$
> > ***********************************************
> > 
> > -----Original Message-----
> > From: eeglablisteeglablist-bounces at sccn.ucsd.edu On Behalf Of Cedric Cannard via eeglablist
> > Sent: Wednesday, January 14, 2026 3:43 PM
> > To: EEGLAB Listeeglablist at sccn.ucsd.edu
> > Subject: [Eeglablist] Source localization and hippocanpus
> > 
> > Hi everyone,
> > 
> > My understanding is that it is impossible to reliably pick up activity from the hippocampus when doing any form of source localization/reconstruction from 64 channels EEG data (or more?). Is that still correct or are there solutions I am not aware of?
> > 
> > Thanks,
> > 
> > Cedric
> > 
> > Sent from Proton Mail for iOS.
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> 
> --
> --------------------------------------------------------------------------------
> 
> Joseph Dien, PhD
> Senior Research Scientist
> Department of Human Development and Quantitative Methodology
> University of Maryland, College Park
> E-mail:jdien at umd.edu
> https://urldefense.com/v3/__http://joedien.com__;!!Mih3wA!F6lfB756tGdH_QFKwL5mIWetNG672s_aafnqgyt9T8wO7nrcuWuqfT_GvDz4sGND_j85H6f_kjzDInHV-ww$
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