Kastytis Dapsys

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.

Closed eyes condition increases auditory brain responses in schizophrenia.

The 40-Hz auditory steady-state responses (ASSRs) of 14 medicated schizophrenic patients were recorded in eyes-open and eyes-closed conditions as previously done in healthy volunteers. Patients show significantly increased precision of the evoked response with eyes closed, and a significant increase of broad-band noise activity when eyes are open.

40 Hz auditory steady-state response in schizophrenia: Sensitivity to stimulation type (clicks versus flutter amplitude-modulated tones)

Auditory steady-state response (ASSR) at 40Hz has been proposed as a potential biomarker for schizophrenia. The ASSR studies in patients have used click stimulation or amplitude-modulated tones. However, the sensitivity of 40Hz ASSRs to different stimulation types in the same group of patients has not been previously evaluated. Two stimulation types for ASSRs were tested in this study: (1) 40Hz clicks and (2) flutter-amplitude modulated tones. The mean phase-locking index, evoked amplitude and event-related spectral perturbation values were compared between schizophrenia patients (n=26) and healthy controls (n=20). Both stimulation types resulted in the observation of impaired phase-locking and power measures of late (200-500ms) 40Hz ASSR in patients compared to healthy controls. The early-latency (0-100ms) 40Hz ASSR part was diminished in the schizophrenia group in response to clicks only. The late-latency 40Hz ASSR parameters obtained through different stimulation types correlated in healthy subjects but not in patients. We conclude that flutter amplitude-modulated tone stimulation, due to its potential to reveal late-latency entrainment deficits, is suitable for use in clinical populations. Careful consideration of experimental stimulation settings can contribute to the interpretation of ASSR deficits and utilization as a potential biomarker.

Pathological Imitative Behavior and Response Preparation in Schizophrenia

Introduction Pathological imitative behavior (ehopraxia) is occasionally observed in schizophrenia patients. However, only a severe form of echopraxia can be detected with the help of a direct observation. Therefore, our goal was to study a latent form of pathological imitative behavior in this disorder, which is indicated by an increase of imitative tendencies. Method In our study, 14 schizophrenia patients and 15 healthy subjects were employed in two tasks: (a) in an imitative task they had to copy a hand action seen on a screen; (b) in a counter-imitative task they had to make a different movement (which involves an inhibition of prepotent imitative tendency that is impaired in case of pathological imitative behavior). Imitative tendencies were assessed by an interference score - a difference between counter-imitative and imitative response parameters. We also studied a response preparation in both groups by employing precueing probabilistic information. Results Our results revealed that schizophrenia patients were able to employ probabilistic information to prepare properly not only the imitative, but also the counter-imitative responses, the same as the healthy subjects did. Nevertheless, we detected increased prepotent imitative tendencies in schizophrenia patients, what indicates the latent pathological imitative behavior in case of this disorder. Conclusions The obtained results suggest that in the case of schizophrenia problems with pathological imitative behavior more likely occurred in executive rather than in the preparatory stage of response. Our findings can help to detect a latent echopraxia in schizophrenia patients that cannot be revealed by direct observation.

Response preparation and intra-individual reaction time variability in schizophrenia

Background. It is important to prepare response in advance to increase the efficiency of its execution. The process of response preparation is usually studied using the precueing paradigm. In this paradigm subjects have to employ the preceding information about further imperative stimulus to perform proper response preparation, which shortens the reaction time of subsequent response execution. Previous studies detected the impairment of response preparation in schizophrenia only with the help of electroencephalographic parameters, but not with the assessing of reaction time. Therefore, in this study we attempted to find a behavioural parameter that could detect impairment in response preparation of schizophrenia patients. It was recently found that appropriate response preparation not only shortens the reaction time but also increases its stability, which is measured with the intra-individual reaction time variability. It was also revealed that response stability could better find cognitive dysfunction in some studies of schizophrenia disorder than classical behavioural parameters. Hence, the main goal of this study was to verify if intra-individual reaction time variability could detect the impairment of response preparation in schizophrenia patients. Materials and methods. In order to achieve the main purpose, we carried out a study with 14 schizophrenia patients and 14 control group subjects. We used precueing paradigm in our research, in which participants had to employ information about stimulus probability for the proper response preparation. Results. Our main result showed that despite the responses of schizophrenia patients were faster to the high-probability stimulus than to the low-probability one (F (1, 13) = 30.9, p < 0.001), intra-individual reaction time variability did not differ in this group between the responses to more and less probable stimuli (F (1, 13) = 0.64, p = 0.44). Conclusions. Results of the study suggest that people with schizophrenia were able to use precueing probabilistic information only to shorten their reaction time, but not to increase response stability. Therefore, it was found that intra-individual reaction time variability parameter could detect response preparation impairment in schizophrenia, and could be used in clinical purposes.

Effect of Electroconvulsive Therapy of Schizophrenia Spectrum Disorders and Affective Disorders on the Auditory Event-Related Potential P300

Auditory event-related potential (ERP) P300 is neurophysiological method of study of human cognitive functions, such as attention and working memory. Electroconvulsive therapy (ECT) is effective method of treatment of different, mainly affective, treatment-resistant psychiatric disorders. However the mechanisms of action of ECT are not clear and sometimes there are negative effects on the memory. The influence of ECT on P300 potential is poorly studied. The aim of this work was to evaluate the effect of ECT on the auditory ERP P300. 38 patients (21 female and 17 male) were studied. Average age was 44.5±13.5 years. Patients were divided into 2 groups according to diagnosis. First group consisted of patients with schizophrenia spectrum disorders (SSD), while the patients with affective disorders were included into the second group. 2 age-matched groups of healthy controls were also formed. ERPs were recorded two times – at the baseline and after the last procedure of ECT course at 3 electrode sites (Fz, Cz and Pz). The medication of patients has not changed during the course of ECT. Clinical symptoms were evaluated using PANSS scale in the case of SSD and HAMD and MADRS scales in the case of affective disorders. 4 parameters of P300 were measured: latency of N2, latency and amplitude of P300 and recognition time of target stimuli. Results have shown that the parameters of P300 potential of patients from both groups were abnormal in comparison with P300 of persons of control groups. The clinical symptoms of schizophrenia and depression have significantly improved after the course of ECT. ECT had positive effect on the P300 potential in the group of SSD – its amplitude has increased at all three sites of recording. In the case of affective disorders the positive changes of P300 potential were less marked. Article in Lithuanian doi:10.5200/sm-hs.2012.013

PTMS8 Transcranial magnetic stimulation effect on depression clinical symptoms and event-related potential P300

delivered at rest and during a sustained voluntary contraction of the target muscle. Results: Changes in the resting motor threshold (RMT), motor evoked potential (MEP) amplitudes and cortical silent period (CSP) duration were measured and compared in patients and healthy controls. Two of the 22 patients were re-tested after surgical removal of the parathyroid adenoma when serum calcium had normalized. In a subgroup of healthy subjects, changes in the rTMS parameters were tested before and after acute hypercalcemia. No significant between groups difference was found in the RMT values and MEP amplitude and CSP duration. During the course of 5 Hz-rTMS trains MEP size increased significantly less in hypercalcemia patients, than in healthy subjects, whereas the CSP duration lengthened to a similar extent in both groups. In the two patients studied after parathyroid adenomectomy, rTMS elicited a normal MEP amplitude facilitation. Conclusions: Our findings indicate that acute hypercalcemia significantly decreased the MEP amplitude facilitation possibly related to Ca2+dependent changes in synaptic plasticity.