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Author Notes:

Correspondence should be addressed to either of the following: Michal T. Kucewicz, Mayo Clinic, 200 First Street SW, Rochester, MN 55902, E-mail: kucewicz.michal@mayo.eduk; or Gregory A. Worrell, Mayo Clinic, 200 First Street SW, Rochester, MN 55902, E-mail: worrell.gregory@mayo.edu.

M.T.K., B.M.B., G.A.W., Y.E., D.S.R., and M.J.K. designed research; M.T.K., B.M.B., G.A.W., S.M.S., M.R.S., B.C.J., K.A.D., R.E.G., B.L., J.M.S., R.E.G., B.H.B., P.W., and D.S.R. performed research; M.T.K., B.M.B., V.K. and J.M.S. analyzed data; M.T.K., B.M.B., L.R.M., F.K., and G.A.W. wrote the paper. M.T.K. and B.M.B. contributed equally to this work.

We thank Blackrock Microsystems Inc. for providing neural recording and stimulation systems.

Cindy Nelson and Karla Crockett provided technical and administrative assistance in patient testing and data collection at Mayo Clinic.

Isaac Pedisich provided programming and computational infrastructure for data analysis in the project.

Anastasia Lyalenko, Deborah Levy, Logan O'sullivan conducted data collection, storage, and reporting at the University of Pennsylvania (RAM coordinating site).

This work would not be possible without collaborations with local departments of neurosurgery radiology and neurology, nurses, EEG technicians, and without a dedicated effort and participation of patients and their families.

The authors declare no competing financial interests.


Research Funding:

This work was supported by the DARPA Restoring Active Memory (RAM) Program (Cooperative Agreement N66001-14-2-4032). V.K. was additionally supported by the Czech Technical University in Prague.


  • ECoG
  • brain stimulation
  • cognitive enhancement
  • high-frequency oscillations
  • intracranial EEG
  • γ-activity

Electrical Stimulation Modulates High γ Activity and Human Memory Performance

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Journal Title:



Volume 5, Number 1


Type of Work:

Article | Final Publisher PDF


Direct electrical stimulation of the brain has emerged as a powerful treatment for multiple neurological diseases, and as a potential technique to enhance human cognition. Despite its application in a range of brain disorders, it remains unclear how stimulation of discrete brain areas affects memory performance and the underlying electrophysiological activities. Here, we investigated the effect of direct electrical stimulation in four brain regions known to support declarative memory: hippocampus (HP), parahippocampal region (PH) neocortex, prefrontal cortex (PF), and lateral temporal cortex (TC). Intracranial EEG recordings with stimulation were collected from 22 patients during performance of verbal memory tasks. We found that high γ (62-118 Hz) activity induced by word presentation was modulated by electrical stimulation. This modulatory effect was greatest for trials with “poor” memory encoding. The high γ modulation correlated with the behavioral effect of stimulation in a given brain region: it was negative, i.e., the induced high γ activity was decreased, in the regions where stimulation decreased memory performance, and positive in the lateral TC where memory enhancement was observed. Our results suggest that the effect of electrical stimulation on high γ activity induced by word presentation may be a useful biomarker for mapping memory networks and guiding therapeutic brain stimulation.

Copyright information:

© 2018 Kucewicz et al.

This is an Open Access work distributed under the terms of the Creative Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by/4.0/).
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