Large-Scale EEG Neural Network Changes in Response to Therapeutic TMS

SOURCE: Brain Stimulation. 15(2):316-325, 2022 Mar-Apr.

AUTHORS: Gold MC; Yuan S; Tirrell E; Kronenberg EF; Kang JWD; Hindley L; Sherif M; Brown JC; Carpenter LL

BACKGROUND: Transcranial magnetic stimulation (TMS) is an effective therapy for patients with treatment-resistant depression. TMS likely induces functional connectivity changes in aberrant circuits implicated in depression. Electroencephalography (EEG) “”microstates”” are topographies hypothesized to represent large-scale resting networks. Canonical microstates have recently been proposed as markers for major depressive disorder (MDD), but it is not known if or how they change following TMS.

METHODS: Resting EEG was obtained from 49 MDD patients at baseline and following six weeks of daily TMS. Polarity-insensitive modified k-means clustering was used to segment EEGs into constituent microstates. Microstates were localized via sLORETA. Repeated-measures mixed models
tested for within-subject differences over time and t-tests compared microstate features between TMS responder and non-responder groups.

RESULTS: Six microstates (MS-1 – MS-6) were identified from all available EEG data. Clinical response to TMS was associated with increases in features of MS-2, along with decreased metrics of MS-3. Nonresponders showed no significant changes in any microstate. Change in occurrence and coverage of both MS-2 (increased) and MS-3 (decreased) correlated with symptom change magnitude over the course of TMS treatment.

CONCLUSIONS: We identified EEG microstates associated with clinical improvement following a course of TMS therapy. Results suggest selective modulation of resting networks observable by EEG, which is inexpensive and easily acquired in the clinic setting.