Transcranial alternating current stimulation of the primary motor cortex: intensity effects
Transcranial alternating current stimulation (tACS) can be used to modulate brain activity. tACS was shown to induce frequency-, state-, and phase- dependent effects which makes tACS a neurostimulation technique that provides a more valuable predictable outcome. However, the impact of different tACS intensities has not been systematically investigated yet. Here, we proposed to investigate the effects of tACS of the primary motor cortex (M1) delivered at different intensities.
There is a common assumption that application of stimulation for longer duration or for higher intensity leads to more reliable physiological and behavioral effects. However, previous studies performed using different transcranial electrical stimulation methods such as transcranial direct current stimulation (tDCS) and/or at high-frequency such as tACS at ripple range, showed non-monotonic effect of stimulation intensity. Nevertheless, tDCS and high-frequency tACS potentially rely on different mechanisms of neuromodulation with respect to conventional tACS delivered at EEG range (1 – 70 Hz).
In this study we applied 20 Hz tACS to the primary motor cortex (M1) to investigate potential non-monotonic effect of tACS intensities (ranging from 0.25 mA to 2 mA with 0.25 mA interval between conditions) on the M1 excitability measured as the peak-to-peak amplitude of TMS-induced motor evoked potentials (MEPs). As for control, we used 1 mA 10 Hz (alpha) tACS and a no stimulation condition.
Preliminary results (N = 9) showed increase of MEPs for higher intensities (1.5 mA, 2 mA) of stimulation. In addition, an interesting effect emerged for those subjects with a lower motor threshold which showed a higher MEPs modulation effect of beta-tACS
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Transcranial magnetic stimulation (TMS) is a modern non-invasive approach to study brain organization in humans. In TMS a time-varying magnetic fields generate induced electrical currents in the targeted brain regions with focal location of its maximum. Using of MRI navigation systems allows to fully realizing the advantages of TMS focality for brain mapping purposes. Due to this development, nowadays motor and speech nTMS mapping is becoming a routinely used procedure in neurosurgery. However, nTMS mapping for dynamic cortical assessment, for example, to study neuroplastic changes is still limited. An important reason for that is a lack of a standardized methodology for nTMS mapping results assessment. Here we propose TMSmap – a standalone graphical interface software for quantative analysis of the results of motor nTMS mapping (http://tmsmap.ru/), which allows considering both standard parameters like the size of the cortical muscle representation, the hotspot and the center of gravity location, as well as the additional ones such as the volume of the representation, the profile of the muscle cortical area and the overlap between the cortical representations and other user-defined parameters. The input data includes coordinates of the coil position and the response in each point of stimulation and individual structural MRI data.
Modern neuroimaging studies begin to explore neurobiological mechanisms of social norms enforcement. Several regions of frontal lobes and temporo-parieto-occipital cortex play a key role in decision making of social punishment of fairness’ norm violation. The cutting–edge methods of brain stimulation allow to change a frequency and intensity of social punishment in different economic tasks (games). The analysis of modern studies show that brain mechanisms of decision making to punish non–cooperative individual requires further investigation with brain stimulation methods to differentiate a role of frontal and temporo-parieto-occipital regions and clarify its interaction.
Despite being a routine technique for presurgical motor assessment, transcranial magnetic stimulation (TMS) mapping is underused for probing of neuroplastic brain changes. We investigated the test-retest reproducibility of the TMS cortical maps of several hand muscles using both standard and alternative parameters of the cortical representation.Pilot study results for four healthy right-handed male volunteers (19-33y.o.) are presented. Two TMS mapping sessions with the stimulation of the left motor cortex were performed within 5-10 days (Day1 and Day2). Day2 points repeated an exact order of the Day1. For quantative comparison of 3D profiles similarities earth mover's distance metrics was used. Analysis of nTMS maps was performed using custom-made software TMSmap (http://tmsmap.ru).The between-days difference in the area of cortical representation for four analyzed subjects was 14.5-30.4% for one and 3.9-11.2% for five repetitions of each cortical point. Considering 3D profiles of cortical representation, higher similarity was shown for the same muscles’ representations and their overlaps compared to the representations of the different muscles. The study is ongoing, further analyzed results will be present.
TMSmap software was developed for quantative analysis of the results of motor nTMS mapping, which allows to consider not only standard parameters like the size of the cortical muscle representation and hotspot and center of gravity location, but as well the volume of the representation considering the amplitude of MEPs in each stimulation spot, the shape of the area, the profile/landscape of the muscle cortical representation and the overlap between representations.
Adequate assessment of individual functional motor potentials is important for developing appropriate rehabilitation strategies in ischemic stroke . Microstructural changes in corticospinal tract (CST) and corpus callosum (CC) were repeatedly correlated to post-stroke outcome [2, 3]. However, relationship between them and functional recovery remains unclear. Here we investigated relationship between integrity of CST and CC assessed with diffusion tensor imaging (DTI) and brain functional state assessed with navigated transcranial magnetic stimulation (nTMS) in chronic ischemic supratentorial stroke.
Hand motor recovery prognosis in stroke patients is crucial to develop a realistic individual rehabilitation plan. The aim of this study was to perform a multimodal assessment in chronic ischemic stroke patients and to compare predictive role of corticospinal tract (CST) integrity measured by diffusion tensor imaging (DTI) and navigated TMS (nTMS), and functional condition of the motor cortex measured by functional MRI (fMRI) and multi-muscle nTMS cortical mapping for hand motor recovery.Total of 30 patients with the only chronic supratentorial ischemic stroke and various severity of hand paresis were enrolled (12 females, medium age 50,0±8,0). The assessment included fractional anisotropy FA (index, %) measurement in internal capsule (ic), cerebral peduncle (pc) and pons. Functional assessment included analysis of BOLD response induced by passive motor task, assessment of intracortical inhibition (SICI) and intracortical facilitation (ICF) phenomena in Abductor Pollicis Brevis (APB) and nTMS mapping of APB and Extensor Digitorum Communis (EDC) cortical representations in both hemispheres. A group of 14 healthy volunteers (7 females, mean age 36,6±15,2) completed fMRI and nTMS investigation. A strong correlation between clinical outcome and FA let to consider FA as an available clinical measurement for hand motor prognosis. Significantly higher disinhibition in the unaffected hemisphere (UH) in well recovered and normal SICI in the UH in poorly recovered patients allow to suppose that interhemispheric interaction might change extensively by chronic phase. A software for multi-muscle nTMS mapping was developed, though this approach need deeper exploration.
The distractive effects on attentional task performance in different paradigms are analyzed in this paper. I demonstrate how distractors may negatively affect (interference effect), positively (redundancy effect) or neutrally (null effect). Distractor effects described in literature are classified in accordance with their hypothetical source. The general rule of the theory is also introduced. It contains the formal prediction of the particular distractor effect, based on entropy and redundancy measures from the mathematical theory of communication (Shannon, 1948). Single- vs dual-process frameworks are considered for hypothetical mechanisms which underpin the distractor effects. Distractor profiles (DPs) are also introduced for the formalization and simple visualization of experimental data concerning the distractor effects. Typical shapes of DPs and their interpretations are discussed with examples from three frequently cited experiments. Finally, the paper introduces hierarchical hypothesis that states the level-fashion modulating interrelations between distractor effects of different classes.
This article describes the expierence of studying factors influencing the social well-being of educational migrants as mesured by means of a psychological well-being scale (A. Perrudet-Badoux, G.A. Mendelsohn, J.Chiche, 1988) previously adapted for Russian by M.V. Sokolova. A statistical analysis of the scale's reliability is performed. Trends in dynamics of subjective well-being are indentified on the basis the correlations analysis between the condbtbions of adaptation and its success rate, and potential mechanisms for developing subjective well-being among student migrants living in student hostels are described. Particular attention is paid to commuting as a factor of adaptation.