Abstract
BackgroundGamma (γ) oscillations (30–50 Hz) have been shown to be excessive in patients with schizophrenia (SCZ) during working memory (WM). WM is a cognitive process that involves the online maintenance and manipulation of information that is mediated largely by the dorsolateral prefrontal cortex (DLPFC). Repetitive transcranial magnetic stimulation (rTMS) represents a non-invasive method to stimulate the cortex that has been shown to enhance cognition and γ oscillatory activity during WM.Methodology and Principal FindingsWe examined the effect of 20 Hz rTMS over the DLPFC on γ oscillatory activity elicited during the N-back task in 24 patients with SCZ compared to 22 healthy subjects. Prior to rTMS, patients with SCZ elicited excessive γ oscillatory activity compared to healthy subjects across WM load. Active rTMS resulted in the reduction of frontal γ oscillatory activity in patients with SCZ, while potentiating activity in healthy subjects in the 3-back, the most difficult condition. Further, these effects on γ oscillatory activity were found to be specific to the frontal brain region and were absent in the parieto-occipital brain region.Conclusions and SignificanceWe suggest that this opposing effect of rTMS on γ oscillatory activity in patients with SCZ versus healthy subjects may be related to homeostatic plasticity leading to differential effects of rTMS on γ oscillatory activity depending on baseline differences. These findings provide important insights into the neurophysiological mechanisms underlying WM deficits in SCZ and demonstrated that rTMS can modulate γ oscillatory activity that may be a possible avenue for cognitive potentiation in this disorder.
Highlights
Gamma (c) oscillations (30–50 Hz) are associated with working memory (WM)
We suggest that this opposing effect of Repetitive transcranial magnetic stimulation (rTMS) on c oscillatory activity in patients with SCZ versus healthy subjects may be related to homeostatic plasticity leading to differential effects of rTMS on c oscillatory activity depending on baseline differences
These findings provide important insights into the neurophysiological mechanisms underlying WM deficits in SCZ and demonstrated that rTMS can modulate c oscillatory activity that may be a possible avenue for cognitive potentiation in this disorder
Summary
WM involves the maintenance and manipulation of information [1] and has been shown to increase c oscillations with increases in WM load in healthy subjects [2], in the dorsolateral prefrontal cortex (DLPFC; [3]). Schizophrenia (SCZ) patients have marked deficits in WM [4] that has been attributed to altered c oscillatory activity. We demonstrated that SCZ patients compared to healthy subjects elicit excessive c oscillatory activity while performing the N-back task at all WM loads that was accompanied by impaired performance [5]. Gamma (c) oscillations (30–50 Hz) have been shown to be excessive in patients with schizophrenia (SCZ) during working memory (WM). Repetitive transcranial magnetic stimulation (rTMS) represents a non-invasive method to stimulate the cortex that has been shown to enhance cognition and c oscillatory activity during WM
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