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  • 2005-2009  (3)
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  • 1
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: When we repetitively lift an object, our grip force is influenced by the mechanical object properties of the preceding lift, irrespective of whether the subsequent lift is performed with the same hand or the hand opposite to the preceding lift. This study investigates if repetitive high-frequency transcranial magnetic stimulation (rTMS) over the dominant primary motor cortex affects this relationship. After completion of 10 lifts of an object using the dominant hand, rTMS was applied over the dominant primary motor cortex for 20 s. On the first lift following rTMS, the peak grip force was significantly higher than on the lift preceding rTMS. Moreover, this measure remained elevated throughout the following set of lifts after rTMS. rTMS did not change the peak lift force generated by more proximal arm muscles. The same effect was observed when the lifts following rTMS over the dominant motor cortex were performed with the ipsilateral hand. These effects were not observed when subjects rested both hands on their lap or when a sham stimulation was applied for the same period of time. These preliminary data suggest that rTMS over the sensorimotor cortex disturbs predictive grip force planning.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Transcranial direct current stimulation (tDCS) of the primary motor hand area (M1) can produce lasting polarity-specific effects on corticospinal excitability and motor learning in humans. In 16 healthy volunteers, 〈inlineGraphic alt="inline image" href="urn:x-wiley:0953816X:EJN4233:EJN_4233_mu1" location="equation/EJN_4233_mu1.gif"/〉O positron emission tomography (PET) of regional cerebral blood flow (rCBF) at rest and during finger movements was used to map lasting changes in regional synaptic activity following 10 min of tDCS (± 1 mA). Bipolar tDCS was given through electrodes placed over the left M1 and right frontopolar cortex. Eight subjects received anodal or cathodal tDCS of the left M1, respectively. When compared to sham tDCS, anodal and cathodal tDCS induced widespread increases and decreases in rCBF in cortical and subcortical areas. These changes in rCBF were of the same magnitude as task-related rCBF changes during finger movements and remained stable throughout the 50-min period of PET scanning. Relative increases in rCBF after real tDCS compared to sham tDCS were found in the left M1, right frontal pole, right primary sensorimotor cortex and posterior brain regions irrespective of polarity. With the exception of some posterior and ventral areas, anodal tDCS increased rCBF in many cortical and subcortical regions compared to cathodal tDCS. Only the left dorsal premotor cortex demonstrated an increase in movement related activity after cathodal tDCS, however, modest compared with the relatively strong movement-independent effects of tDCS. Otherwise, movement related activity was unaffected by tDCS. Our results indicate that tDCS is an effective means of provoking sustained and widespread changes in regional neuronal activity. The extensive spatial and temporal effects of tDCS need to be taken into account when tDCS is used to modify brain function.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: High-frequency electrical stimulation through electrodes implanted in the subthalamic nucleus (STN) has been shown to reduce significantly the cardinal symptoms of Parkinson's disease (PD). Despite the success of this treatment, the mechanisms of action of stimulation are poorly understood. To elucidate further the mechanisms of action of deep brain stimulation and its effects on cortical activity, we recorded electroencephalographic potentials from 61 scalp-surface electrodes during low-frequency (5–10 Hz) bipolar stimulation in 11 patients with advanced PD (14 implanted electrodes were tested). In all electrodes tested, stimulation through at least one of the four contacts produced a medium-latency waveform with an average onset of 14 ± 3 ms and peak at 23 ± 4 ms. This potential typically increased in magnitude across contacts from ventral to dorsal. Within-subject comparisons of median nerve somatosensory evoked potentials demonstrated that the generator of the medium-latency potential was within the primary sensorimotor cortex or lateral premotor cortex ipsilateral to stimulation. The timing and topography of this potential were consistent with indirect activation of the cortex by excitation of pallido-thalamic axons that traverse the dorsal aspect of the STN. The potential evoked by stimulation through the contact used for optimal clinical effect was highly variable across electrodes and frequently different from the medium-latency potential described above, suggesting that the neuronal elements mediating the medium-latency potential were different from those that mediate the clinical effects.
    Type of Medium: Electronic Resource
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