Stimulating the deprived motor 'hand' area causes facial muscle responses in one-handers

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Selective modulation of interhemispheric connectivity by transcranial alternating current stimulation influences binaural integration

Brain connectivity plays a major role in the encoding, transfer, and integration of sensory information. Interregional synchronization of neural oscillations in the γ-frequency band has been suggested as a key mechanism underlying perceptual integration. In a recent study, we found evidence for this hypothesis showing that the modulation of interhemispheric oscillatory synchrony by means of bihemispheric high-density transcranial alternating current stimulation (HD-TACS) affects binaural integration of dichotic acoustic features. Here, we aimed to establish a direct link between oscillatory synchrony, effective brain connectivity, and binaural integration. We experimentally manipulated oscillatory synchrony (using bihemispheric γ-TACS with different interhemispheric phase lags) and assessed the effect on effective brain connectivity and binaural integration (as measured with functional MRI and a dichotic listening task, respectively). We found that TACS reduced intrahemispheric connectivity within the auditory cortices and antiphase (interhemispheric phase lag 180°) TACS modulated connectivity between the two auditory cortices. Importantly, the changes in intra- and interhemispheric connectivity induced by TACS were correlated with changes in perceptual integration. Our results indicate that γ-band synchronization between the two auditory cortices plays a functional role in binaural integration, supporting the proposed role of interregional oscillatory synchrony in perceptual integration

Phantom limbs and brain plasticity in amputees

Item does not contain fulltextPhantom sensations are experienced by almost every person who has lost their hand in adulthood. This mysterious phenomenon spans the full range of bodily sensations, including the sense of touch, temperature, movement, and even the sense of wetness. For a majority of upper-limb amputees, these sensations will also be at times unpleasant, painful, and for some even excruciating to the point of debilitating, causing a serious clinical problem, termed phantom limb pain (PLP). Considering the sensory organs (the receptors in the skin, muscle or tendon) are physically missing, in order to understand the origins of phantom sensations and pain the potential causes must be studied at the level of the nervous system, and the brain in particular. This raises the question of what happens to a fully developed part of the brain that becomes functionally redundant (e.g. the sensorimotor hand area after arm amputation). Relatedly, what happens to the brain representation of a body part that becomes overused (e.g. the intact hand, on which most amputees heavily rely for completing daily tasks)? Classical studies in animals show that the brain territory in primary somatosensory cortex (S1) that was "freed up" due to input loss (hereafter deprivation) becomes activated by other body part representations, those neighboring the deprived cortex. If neural resources in the deprived hand area get redistributed to facilitate the representation of other body parts following amputation, how does this process relate to persistent phantom sensation arising from the amputated hand? Subsequent work in humans, mostly with noninvasive neuroimaging and brain stimulation techniques, have expanded on the initial observations of cortical remapping in two important ways. First, research with humans allows us to study the perceptual consequence of remapping, particularly with regards to phantom sensations and pain. Second, by considering the various compensatory strategies amputees adopt in order to account for their disability, including overuse of their intact hand and learning to use an artificial limb, use-dependent plasticity can also be studied in amputees, as well as its relationship to deprivation-triggered plasticity. Both of these topics are of great clinical value, as these could inform clinicians how to treat PLP, and how to facilitate rehabilitation and prosthesis usage in particular. Moreover, research in humans provides new insight into the role of remapping and persistent representation in facilitating (or hindering) the realization of emerging technologies for artificial limb devices, with special emphasis on the role of embodiment. Together, this research affords a more comprehensive outlook at the functional consequences of cortical remapping in amputees’ primary sensorimotor cortex