Cortico-Cortical Connectivity between Right Parietal and Bilateral Primary Motor Cortices during Imagined and Observed Actions: A Combined TMS/tDCS Study
Previous transcranial magnetic stimulation (TMS) studies showed functional connections between the parietal cortex (PC) and the primary motor cortex (M1) during tasks of different reaching-to-grasp movements. Here, we tested whether the same network is involved in cognitive processes such as imagined or observed actions. Single pulse TMS of the right and left M1 during rest and during a motor imagery and an action observation task (i.e., an index-thumb pinch grip in both cases) was used to measure corticospinal excitability changes before and after conditioning of the right PC by 10 min of cathodal, anodal, or sham transcranial direct current stimulation (tDCS). Corticospinal excitability was indexed by the size of motor-evoked potentials (MEPs) from the contralateral first dorsal interosseous (FDI; target) and abductor digiti minimi muscle (control) muscles. Results showed selective ipsilateral effects on the M1 excitability, exclusively for motor imagery processes: anodal tDCS enhanced the MEPs' size from the FDI muscle, whereas cathodal tDCS decreased it. Only cathodal tDCS impacted corticospinal facilitation induced by action observation. Sham stimulation was always uneffective. These results suggest that motor imagery, differently from action observation, is sustained by a strictly ipsilateral parieto-motor cortex circuits. Results might have implication for neuromodulatory rehabilitative purposes.
Increasing evidence suggests that neuronal communication is a defining property of functionally specialized brain networks and that it is implemented through synchronization between population activities of distinct brain areas. The detection of long-range coupling in electroencephalography (EEG) and magnetoencephalography (MEG) data using conventional metrics (such as coherence or phase-locking value) is by definition contaminated by spatial leakage. Methods such as imaginary coherence, phase-lag index or orthogonalized amplitude correlations tackle spatial leakage by ignoring zero-phase interactions. Although useful, these metrics will by construction lead to false negatives in cases where true zero-phase coupling exists in the data and will underestimate interactions with phase lags in the vicinity of zero. Yet, empirically observed neuronal synchrony in invasive recordings indicates that it is not uncommon to find zero or close-to-zero phase lag between the activity profiles of coupled neuronal assemblies. Here, we introduce a novel method that allows us to mitigate the undesired spatial leakage effects and detect zero and near zero phase interactions. To this end, we propose a projection operation that operates on sensor-space cross-spectrum and suppresses the spatial leakage contribution but retains the true zero-phase interaction component. We then solve the network estimation task as a source estimation problem defined in the product space of interacting source topographies. We show how this framework provides reliable interaction detection for all phase-lag values and we thus refer to the method as Phase Shift Invariant Imaging of Coherent Sources (PSIICOS). Realistic simulations demonstrate that PSIICOS has better detector characteristics than existing interaction metrics. Finally, we illustrate the performance of PSIICOS by applying it to real MEG dataset recorded during a standard mental rotation task. Taken together, using analytical derivations, data simulations and real brain data, this study presents a novel source-space MEG/EEG connectivity method that overcomes previous limitations and for the first time allows for the estimation of true zero-phase coupling via non-invasive electrophysiological recordings.
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.
Human societies crucially depend on social norms that specify appropriate actions in various situation. The effect of norms on collective behavior can break down if norm violations are not sanctioned. Social punishment is a form of behavior to enforce social norm compliance that relies on two key brain region: the “mentalizing network” (right temporo-parietal junction – rTPJ) evaluating individual responsibility and the “central-executive network” (right dorsolateral prefrontal cortex – rDLPFC) determining the final decision to punish norm violators. Here we further investigate the role of the brain network – rDLPFC-rTPJ – in third-party punishment. We used transcranial direct-current stimulation (tDCS) to disrupt the rDLPFC-rTPJ network of healthy subjects while they performed the Dictator Game. Our results suggests that the frequency of third-party punishment increased after the tDCS of the rDLPFC-rTPJ. To the best of our knowledge, this is the first study demonstrating the effect of simultaneous tDCS of the rDLPFC and rTPJ on the third-party punishment. We also show that personality traits modulate the effect of tDCS on the third-party punishment.
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.
The theory of cognitive dissonance suggests that individuals prefer new incoming information to be consistent with already existing knowledge. Conflicting or inconsistent information results in an emotionally uncomfortable state called cognitive dissonance. Cognitive dissonance theory suggests that a choice between two similarly valued alternatives creates psychological tension (cognitive dissonance) that is reduced by a post-decision re-evaluation of the alternatives. According to the action-based model of cognitive dissonance, activity in the posterior medial prefrontal cortex (pMFC) underlies the detection of cognitive conflicts and the reduction of the dissonance. Nevertheless, the neurocomputational foundation of cognitive dissonance remains unclear. In this study, for the first time we show that cathodal transcranial direct current stimulation (tDCS) of the pMFC significantly reduced post-decision re-evaluation of the alternatives. An ongoing follow-up study that applied anodal tDCS to the pMFC preliminarily showed a tendency to increase choice-induced preference changes. Our results suggest that cognitive dissonance, underlined by the activity of the prefrontal cortex, is a part of the performance-monitoring circuitry
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.
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.