State-dependent effects of transcranial oscillatory currents on the motor system: what you think matters.
Imperceptible transcranial alternating current stimulation (tACS) changes the endogenous cortical oscillatory activity in a frequency-specific manner. In the human motor system, tACS coincident with the idling beta rhythm of the quiescent motor cortex increased the corticospinal output. We reasoned that changing the initial state of the brain (i.e., from quiescence to a motor imagery task that desynchronizes the local beta rhythm) might also change the susceptibility of the corticospinal system to resonance effects induced by beta-tACS. We tested this hypothesis by delivering tACS at different frequencies (theta, alpha, beta, and gamma) on the primary motor cortex at rest and during motor imagery. Motor-evoked potentials (MEPs) were obtained by transcranial magnetic stimulation (TMS) on the primary motor cortex with an online-navigated TMS-tACS setting. During motor imagery, the increase of corticospinal excitability was maximal with theta-tACS, likely reflecting a reinforcement of working memory processes required to mentally process and "execute" the cognitive task. As expected, the maximal MEPs increase with subjects at rest was instead obtained with beta-tACS, substantiating previous evidence. This dissociation provides new evidence of state and frequency dependency of tACS effects on the motor system and helps discern the functional role of different oscillatory frequencies of this brain region. These findings may be relevant for rehabilitative neuromodulatory interventions
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.
Neuronal oscillations have been shown to be associated with perceptual, motor and cognitive brain operations. While complex spatio-temporal dynamics are a hallmark of neuronal oscillations, they also represent a formidable challenge for the proper extraction and quantification of oscillatory activity with non-invasive recording techniques such as EEG and MEG. In order to facilitate the study of neuronal oscillations we present a general-purpose pre-processing approach, which can be applied for a wide range of analyses including but not restricted to inverse modeling and multivariate single-trial classification. The idea is to use dimensionality reduction with spatio-spectral decomposition (SSD) instead of the commonly and almost exclusively used principal component analysis (PCA). The key advantage of SSD lies in selecting components explaining oscillations-related variance instead of just any variance as in the case of PCA. For the validation of SSD pre-processing we performed extensive simulations with different inverse modeling algorithms and signal-to-noise ratios. In all these simulations SSD invariably outperformed PCA often by a large margin. Moreover, using a database of multichannel EEG recordings from 80 subjects we show that pre-processing with SSD significantly increases the performance of single-trial classification of imagined movements, compared to the classification with PCA pre-processing or without any dimensionality reduction. Our simulations and analysis of real EEG experiments show that, while not being supervised, the SSD algorithm is capable of extracting components primarily relating to the signal of interest often using as little as 20% of the data variance, instead of > 90% variance as in case of PCA. Given its ease of use, absence of supervision, and capability to efficiently reduce the dimensionality of multivariate EEG/MEG data, we advocate the application of SSD pre-processing for the analysis of spontaneous and induced neuronal oscillations in normal subjects and patients.
We investigated the time-course of cortical activation during comprehension of literal and idiomatic sentences using MEG and anatomically guided distributed source analysis. Previous fMRI work had shown that the comprehension of sentences including action-related words elicits somatotopic semantic activation along the motor strip, reflecting meaning aspects of constituent words. Furthermore, idioms more strongly activated temporal pole and prefrontal cortex than literal sentences. Here we show that, compared to literal sentences, processing of idioms in a silent reading task modulates anterior fronto-temporal activity very early-on, already 150-250 ms after the sentences' critical disambiguating words ("kick the habit"). In parallel, the meaning of action words embedded in sentences is reflected by somatotopic activation of precentral motor systems. As neural reflections of constituent parts of idiomatic sentences are manifest at the same early latencies as brain indexes of idiomatic vs. literal meaning processing, we suggest that within ¼ of a second, compositional and abstract context-driven semantic processes in parallel contribute to the understanding of idiom meaning.
We here investigate whether the well-known laterality of spoken language to the dominant left hemisphere could be explained by the learning of sensorimotor links between a word's articulatory program and its corresponding sound structure. Human-specific asymmetry of acoustic-articulatory connectivity is evident structurally, at the neuroanatomical level, in the arcuate fascicle, which connects superior-temporal and frontal cortices and is more developed in the left hemisphere. Because these left-lateralised fronto-temporal fibres provide a substrate for auditory-motor associations, we hypothesised that learning of acoustic-articulatory coincidences produces laterality, whereas perceptual learning does not. Twenty subjects studied a large (n=48) set of novel meaningless syllable combinations, pseudowords, in a perceptual learning condition, where they carefully listened to repeatedly presented novel items, and, crucially, in an articulatory learning condition, where each item had to be repeated immediately, so that articulatory and auditory speech-evoked cortical activations coincided. In the 14 subjects who successfully passed the learning routine and could recognize the learnt items reliably, both perceptual and articulatory learning were found to lead to an increase of pseudoword-elicited event-related potentials (ERPs), thus reflecting the formation of new memory circuits. Importantly, after articulatory learning, pseudoword-elicited ERPs were more strongly left-lateralised than after perceptual learning. Source localisation confirmed that perceptual learning led to increased activation in superior-temporal cortex bilaterally, whereas items learnt in the articulatory condition activated bilateral superior-temporal auditory in combination with left-pre-central motor areas. These results support a new explanation of the laterality of spoken language based on the neuroanatomy of sensorimotor links and Hebbian learning principles.
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.
In 2006, Russia amended its competition law and added the concepts of ‘collective dominance’ and its abuse. This was seen as an attempt to address the common problem of ‘conscious parallelism’ among firms in concentrated industries. Critics feared that the enforcement of this provision would become tantamount to government regulation of prices. In this paper we examine the enforcement experience to date, looking especially closely at sanctions imposed on firms in the oil industry. Some difficulties and complications experienced in enforcement are analysed, and some alternative strategies for addressing anticompetitive behaviour in concentrated industries discussed.
The results of research of different areas of personality of homeless men: values, life attitudes, activity, homelessness area is presents. The data indicate the presence of a number of characteristics inherent in varying degrees all homeless people. The data obtained can be used to build an effective program of psychological re-socialization of homeless people.