Network-Targeted, Multi-site Direct Cortical Stimulation Enhances Working Memory by Modulating Phase Lag of Low-Frequency Oscillations

Sankaraleengam Alagapan, Justin Riddle, Wei Angel Huang, Eldad Hadar, Hae Won Shin, Flavio Fröhlich, Sankaraleengam Alagapan, Justin Riddle, Wei Angel Huang, Eldad Hadar, Hae Won Shin, Flavio Fröhlich

Abstract

Working memory is mediated by the coordinated activation of frontal and parietal cortices occurring in the theta and alpha frequency ranges. Here, we test whether electrically stimulating frontal and parietal regions at the frequency of interaction is effective in modulating working memory. We identify working memory nodes that are functionally connected in theta and alpha frequency bands and intracranially stimulate both nodes simultaneously in participants performing working memory tasks. We find that in-phase stimulation results in improvements in performance compared to sham stimulation. In addition, in-phase stimulation results in decreased phase lag between regions within working memory network, while anti-phase stimulation results in increased phase lag, suggesting that shorter phase lag in oscillatory connectivity may lead to better performance. The results support the idea that phase lag may play a key role in information transmission across brain regions. Thus, brain stimulation strategies to improve cognition may require targeting multiple nodes of brain networks.

Keywords: brain stimulation; cortical oscillations; direct cortical stimulation; human neuroscience; intracranial eeg; phase lag; working memory.

Conflict of interest statement

DECLARATION OF INTERESTS

F.F. is the lead inventor of intellectual property filed on the topics of noninvasive brain stimulation by UNC. F.F. is the founder, chief scientific officer (CSO), and majority owner of Pulvinar Neuro LLC, which played no role in this research. The other authors declare no competing interests.

Copyright © 2019 The Author(s). Published by Elsevier Inc. All rights reserved.

Figures

Figure 1.. Schematic of Network-Targeted Stimulation
Figure 1.. Schematic of Network-Targeted Stimulation
(A) Intracranial EEG data from implanted electrodes, collected when participants performed WM tasks, are processed to identify functionally connected regions that are then targeted with direct cortical stimulation. (B) Sternberg WM task depicting the different epochs and timing of the components of each epoch. (C) The stimulation paradigms used in the study. Each vertical red line denotes a biphasic pulse. In-phase stimulation consists of pulses applied simultaneously to functionally connected regions without any phase offset (time delay). Anti-phase stimulation consists of pulses applied with a phase offset of 180° (time delay of half the inter-stimulus interval Ts). Dotted lines are provided for visual guidance.
Figure 2.. Functional Connectivity of Stimulation Electrodes
Figure 2.. Functional Connectivity of Stimulation Electrodes
(A) Mean dWPLI for the stimulation electrodes for the different cognitive loads and the different epochs. Shaded regions denote the jackknife estimate of SD. (B) The anatomical locations of the identified stimulation electrodes for the three participants. The beige-shaded regions denote WM regions identified from meta-analyses of functional neuroimaging studies. See also Figure S1.
Figure 3.. Effect of Network-Targeted Stimulation on…
Figure 3.. Effect of Network-Targeted Stimulation on WM Performance
In-phase stimulation increased accuracy relative to sham (top). Stimulation did not affect reaction time (bottom). See also Figure S2.
Figure 4.. Effect of Network-Targeted Stimulation on…
Figure 4.. Effect of Network-Targeted Stimulation on WM Network
(A) Pairwise difference of dWPLI between stimulation conditions. In-phase versus sham and anti-phase versus sham were significantly greater than 0. (B) Pairwise difference of coherence between stimulation conditions. All three pairwise differences were significantly greater than 0. (C) Circular histogram denoting the pairwise differences in phase lag across the three comparisons for the three participants. The black line denotes the mean phase lag difference for each comparison. *p

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