Abstract
The neuromodulatory effects of brain stimulation therapies notably involving repetitive transcranial magnetic stimulation (rTMS) on nocturnal sleep, which is critically disturbed in major depression and other neuropsychiatric disorders, remain largely undetermined. We have previously reported in major depression patients that prefrontal rTMS sessions enhanced their slow wave activity (SWA) power, but not their sigma power which is related to sleep spindle activity, for electrodes located nearby the stimulation site. In the present study, we focused on measuring the spindle density to investigate cumulative effects of prefrontal rTMS sessions on the sleep spindle activity. Fourteen male inpatients diagnosed with medication-resistant unipolar or bipolar depression were recruited and subjected to 10 daily rTMS sessions targeting the left dorsolateral prefrontal cortex (DLPFC). All-night polysomnography (PSG) data was acquired at four time points: Adaptation, Baseline, Post-1 (follow-up after the fifth rTMS session), and Post-2 (follow-up after the tenth rTMS session). Clinical and cognitive evaluations were longitudinally performed at Baseline, Post-1, and Post-2 time points to explore associations with the spindle density changes. The PSG data from 12 of 14 patients was analyzed to identify sleep spindles across the sleep stages II–IV at four electrode sites: F3 (frontal spindle near the stimulation site), F4 (contralateral homologous frontal region), P3 (parietal spindle in the hemisphere ipsilateral to the stimulation site), and P4 (contralateral parietal region). Statistical analysis by two-way ANOVA revealed that spindle density at F3 increased at Post-1 but decreased at Post-2 time points. Moreover, the local and transient increase of spindle density at F3 was associated with the previously reported SWA power increase at F3, possibly reflecting a shared mechanism of thalamocortical synchronization locally enhanced by diurnal prefrontal rTMS sessions. Clinical and cognitive correlations were not observed in this dataset. These findings suggest that diurnal rTMS sessions transiently modulate nocturnal sleep spindle activity at the stimulation site, although clinical and cognitive effects of the local changes warrant further investigation.
Highlights
Sleep-related complaints that are most frequently accompanied by a depressive episode are symptoms and risk factors for mood disorders (Baglioni et al, 2011)
As reflected by the significant main effect of site, parietal spindles were more frequently observed than frontal spindles, which is compatible with the findings form previous studies (Nakamura et al, 2003)
Considering that the time-by-site interaction was significant, post hoc one-way analysis of variance (ANOVA) was performed for each electrode repetitive transcranial magnetic stimulation (rTMS)-Induced Changes of Spindle Density
Summary
Sleep-related complaints that are most frequently accompanied by a depressive episode are symptoms and risk factors for mood disorders (Baglioni et al, 2011). Even in partial or complete remission phase, 43% of patients suffer from insomnia, while residual insomnia is a risk factor for non-remission (Yoshiike et al, 2017, 2020). Sleep abnormalities observed in major depression are characterized by sleep fragmentation, disinhibition of rapid eye movement (REM) sleep, and inhibition of non-REM (NREM) sleep (Benca et al, 1997; Armitage, 2007). Sleep fragmentation comprises prolonged sleep latency, frequently interrupted sleep, and early-morning awakening. The disinhibition of REM sleep involves shortening of REM latency, increased REM density during the first REM period, and prolonged REM periods. Inhibition of NREM sleep implicates decreased stage II and slow wave sleep (stages III and IV), which can result in excessive daytime sleepiness
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