The effects of 10 Hz repetitive transcranial magnetic stimulation on resting EEG power spectrum in healthy subjects.

10 Hz rTMS over the left prefrontal cortex may be useful in the treatment of depressive disorders. However, the effects of 10 Hz rTMS applied in potentially effective doses on electroencephalographic activity are not well studied. Using EEG, we aimed to investigate the neurobiological effects of the 10 Hz rTMS set of parameters currently used for depression treatment in a sample of healthy subjects. In 18 healthy subjects, either 10 Hz real rTMS or sham stimulation were given in a crossover design. Real rTMS stimulation was carried out with an intensity of 110% of motor threshold (MT) over the left dorsolateral prefrontal cortex. For the sham condition, the coil was angled over a parietotemporal position and the intensity was reduced to 90% of MT. EEG recordings were taken before and after a single rTMS session. EEG power spectrum was extracted using the complex demodulation method and changes in power were evaluated statistically. Real 10 Hz rTMS induced an overall increase in delta power. This increase prevailed throughout the sample, whereas effects on the power of the alpha, beta and theta EEG bands were highly variable. Sham stimulation had no substantial effects on the EEG power spectrum. Furthermore, no changes in EEG asymmetry were detected. Real 10 Hz rTMS applied at 2000 stimuli and 110% intensity may induce significant changes in resting EEG in healthy subjects.

Transcranial magnetic stimulation: the method and application.

Transcranial magnetic stimulation is a noninvasive method for stimulation of brain that is based on the ability of magnetic field to penetrate skull and brain meninges, subsequently inducing electric current in the brain tissues that produces neuronal depolarization and generation of action potentials. Moreover, transcranial magnetic stimulation has effects on neurochemical and synaptic processes in neurons. Due to its easy use and relatively fair side effects, nowadays, transcranial magnetic stimulation is widely used in neurosciences and medicine. The main areas of transcranial magnetic stimulation application are: 1) the investigation of cortical and spinal excitability, 2) the investigation of neuronal plasticity, 3) the investigation of neuronal connectivity, 4) functional mapping, and 5) the treatment of some neurological and psychiatric disorders. Transcranial magnetic stimulation alone or in combination with other noninvasive neuroimaging (PET--positron emission topography, MRI--magnetic resonance imaging) and neurofunctional (EEG--electroencephalography, ERP--event-related potentials, fMRI--functional magnetic resonance imaging) methods allows conducting research on brain functions. Thus, transcranial magnetic stimulation is suitable as a diagnostic tool in neurologic and neuropsychiatric brain research.

Does electroconvulsive therapy (ECT) affect cognitive components of auditory evoked P300?

Electroconvulsive therapy (ECT), as a treatment tool for psychiatric disorders, is believed to be safe and effective. Nevertheless, it has a negative impact on cognitive functioning, especially on memory, causing both retrograde and anterograde amnesia. However, ECT effects on more subtle stages of information processing are not studied enough. Event-related potentials, and especially P300, are thought to reflect physiology of cognition. Thus, we aimed to evaluate the effects of ECT treatment on parameters of endogenous components (N2, P3) of the P300 potential. Seventeen patients suffering from schizophrenia, schizoaffective disorder and recurrent depressive disorder participated at the study. After the course of ECT, significant increase of N2 amplitude in parietal midline region and prolongation of P3 latency in frontal midline region, of which the magnitude positively correlated with the number of ECT procedures, have been obtained.

Two discrete components of the 20 Hz steady-state response are distinguished through the modulation of activation level.

OBJECTIVE: To investigate the modulation of amplitude and phase precision of the auditory steady-state response (SSR) to 20 Hz stimulation in two conditions varying in the level of activation. METHODS: Click stimuli (20 Hz) were applied while subjects were sitting upright silently reading a book of interest (high activation level) and while subjects were sitting in a reclined position with eyes closed and the lights turned off (low activation level). Sixty-one channel EEG data was wavelet transformed, the amplitude and phase precision measures extracted and decomposed by the multi-subject non-negative multi-way factorization (NMWF). RESULTS: The NMWF decomposition of amplitude and phase precision measures resulted in the observation of two distinct components: a component at the frequency of stimulation--20 Hz SSR and a component emerging at 40 Hz--20 Hz SSR-related 40 Hz activity. Modulation by the activation level was observed only for 20 Hz SSR-related 40 Hz activity as increased amplitude and phase precision during low activation level. No such effects were observed for 20 Hz SSR. CONCLUSION: The discrete components of the 20 Hz SSR are distinguished through modulation of activation level, 20 Hz SSR-related 40 Hz being higher in low activation state. SIGNIFICANCE: The biological modulation of 20 Hz SSR-related 40 Hz activity by the level of activation points to a physiological nature of this activity beyond a mere periodic effect in relation to the 20 Hz activity.

The amplitude and phase precision of 40 Hz auditory steady-state response depend on the level of arousal.

The aim of this study was to investigate, in healthy subjects, the modulation of amplitude and phase precision of the auditory steady-state response (ASSR) to 40 Hz stimulation in two resting conditions varying in the level of arousal. Previously, ASSR measures have shown to be affected by the level of arousal, but the findings are somewhat controversial. Generally, ASSR is diminished in sleep but it may be increased in drowsiness. Besides, ASSR reduction has been observed in schizophrenia. However, schizophrenic patients are known to have a disturbance of arousal level, what makes it pertinent to know the effects of fluctuations in arousal on passive response to gamma-range stimulation. In nine healthy volunteers trains of 40 Hz click stimuli were applied during two conditions: in the "high arousal" condition subjects were sitting upright silently reading a book of interest; in the "low arousal" condition subjects were sitting in a reclined position with eyes closed and the lights turned off. The 64-channel EEG data was wavelet transformed and the amplitude and phase precision of the wavelet transformed evoked potential were decomposed by the recently proposed multi-subject non-negative multi-way factorization (NMWF) (Morup et al. in J Neurosci Methods 161:361-368, 2007). The estimates of these measures were subjected to statistical analysis. The amplitude and phase precision of the ASSR were significantly larger during the low arousal state compared to the high arousal condition. The modulation of ASSR amplitude and phase precision by differences in the arousal level during recording warrants caution when investigating oscillatory brain activity and interpreting the findings of reduced ASSR in schizophrenia. It also emphasizes the necessity of standardized recording procedures and monitoring the level of arousal during ASSR testing.