Abstract
BackgroundTranscranial 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. MethodsResting 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. ResultsSix 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. ConclusionsWe 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.
Highlights
Repetitive Transcranial Magnetic Stimulation is an effective therapy for treatment-resistant major depressive disorder (MDD)
3 Conclusions: We identified EEG microstates associated with clinical improvement following a course of Transcranial magnetic stimulation (TMS) therapy
We investigated microstates in treatment-resistant MDD patients undergoing a standard, six-week rTMS therapy course in a naturalistic setting to evaluate possible microstate changes associated with rTMS and Journal Pre-proof their relationship to treatment outcomes
Summary
Repetitive Transcranial Magnetic Stimulation (rTMS or “TMS”) is an effective therapy for treatment-resistant major depressive disorder (MDD). In addition to global effects, the repetitive pulses of TMS entrain stimulation-site cortical oscillations to the frequency of stimulation [3] These local dynamics appear relevant to TMS therapeutic mechanism of action, as the proximity of an individual’s endogenous peak alpha frequency to the stimulation frequency applied during TMS therapy is associated with better treatment response [4] [5]. While the efficacy of TMS therapy is robust for a population that has not benefitted from trials of standard antidepressant medications, only about 50% of patients who undergo TMS will see improvement from a six-week daily course [6] These outcome disparities likely reflect a heterogenous etiology within the broad depression diagnosis. Journal Pre-proof proposed as markers for major depressive disorder (MDD), but it is not known if or how they change following TMS
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