High frequency repetitive transcranial magnetic stimulation (rTMS) of the left dorsolateral cortex: EEG topography during waking and subsequent sleep.

Repetitive transcranial magnetic stimulation (rTMS) is a novel research tool in neurology and psychiatry. It is currently being evaluated as a conceivable alternative to electroconvulsive therapy for the treatment of mood disorders. Eight healthy young (age range 21-25 years) right-handed men without sleep complaints participated in the study. Two sessions at a 1-week interval, each consisting of an adaptation night (sham stimulation) and an experimental night (rTMS in the left dorsolateral prefrontal cortex or sham stimulation; crossover design), were scheduled. In each subject, 40 trains of 2-s duration of rTMS (inter-train interval 28 s) were applied at a frequency of 20 Hz (i.e. 1600 pulses per session) and at an intensity of 90% of the motor threshold. Stimulations were scheduled 80 min before lights off. The waking EEG was recorded for 10-min intervals approximately 30 min prior to and after the 20-min stimulations, and polysomnographic recordings were obtained during the subsequent sleep episode (23.00-07.00 h). The power spectra of two referential derivations, as well as of bipolar derivations along the antero-posterior axis over the left and right hemispheres, were analyzed. rTMS induced a small reduction of sleep stage 1 (in min and percentage of total sleep time) over the whole night and a small enhancement of sleep stage 4 during the first non-REM sleep episode. Other sleep variables were not affected. rTMS of the left dorsolateral cortex did not alter the topography of EEG power spectra in waking following stimulation, in the all-night sleep EEG, or during the first non-REM sleep episode. Our results indicate that a single session of rTMS using parameters like those used in depression treatment protocols has no detectable side effects with respect to sleep in young healthy males.

Mood effects of repetitive transcranial magnetic stimulation of left prefrontal cortex in healthy volunteers.

This study investigated the effect of high-frequency repetitive transcranial magnetic stimulation (HF-rTMS) of the left prefrontal cortex (LPFC) on mood in a sham-controlled crossover design. Twenty-five healthy male subjects received HF-rTMS of the LPFC in real and sham conditions. Forty trains (frequency 20 Hz, stimulation intensity 100% of individual motor threshold, train duration 2 s, intertrain interval 28 s) were applied in each session. Mood change from baseline was measured with five visual analog scales (VAS) for sadness, anxiety, happiness, tiredness and pain/discomfort. We were unable to demonstrate significant mood changes from baseline on visual analog scales after either sham or real stimulation of LPFC. There is insufficient evidence to support the general conclusion that HF-rTMS of LPFC has mood effects in healthy volunteers. Future studies should be sham-controlled, have larger sample sizes, and strictly stimulate one single region per session in order to exclude interaction effects with the previous stimulation.

The human vestibular cortex revealed by coordinate-based activation likelihood estimation meta-analysis.

The vestibular system contributes to the control of posture and eye movements and is also involved in various cognitive functions including spatial navigation and memory. These functions are subtended by projections to a vestibular cortex, whose exact location in the human brain is still a matter of debate (Lopez and Blanke, 2011). The vestibular cortex can be defined as the network of all cortical areas receiving inputs from the vestibular system, including areas where vestibular signals influence the processing of other sensory (e.g. somatosensory and visual) and motor signals. Previous neuroimaging studies used caloric vestibular stimulation (CVS), galvanic vestibular stimulation (GVS), and auditory stimulation (clicks and short-tone bursts) to activate the vestibular receptors and localize the vestibular cortex. However, these three methods differ regarding the receptors stimulated (otoliths, semicircular canals) and the concurrent activation of the tactile, thermal, nociceptive and auditory systems. To evaluate the convergence between these methods and provide a statistical analysis of the localization of the human vestibular cortex, we performed an activation likelihood estimation (ALE) meta-analysis of neuroimaging studies using CVS, GVS, and auditory stimuli. We analyzed a total of 352 activation foci reported in 16 studies carried out in a total of 192 healthy participants. The results reveal that the main regions activated by CVS, GVS, or auditory stimuli were located in the Sylvian fissure, insula, retroinsular cortex, fronto-parietal operculum, superior temporal gyrus, and cingulate cortex. Conjunction analysis indicated that regions showing convergence between two stimulation methods were located in the median (short gyrus III) and posterior (long gyrus IV) insula, parietal operculum and retroinsular cortex (Ri). The only area of convergence between all three methods of stimulation was located in Ri. The data indicate that Ri, parietal operculum and posterior insula are vestibular regions where afferents converge from otoliths and semicircular canals, and may thus be involved in the processing of signals informing about body rotations, translations and tilts. Results from the meta-analysis are in agreement with electrophysiological recordings in monkeys showing main vestibular projections in the transitional zone between Ri, the insular granular field (Ig), and SII.