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Robert Chen and Kaviraja Udupa

Several techniques that involve transcranial magnetic stimulation (TMS) can be used to measure brain plasticity noninvasively in humans. These include paired-associative stimulation (PAS), repetitive transcranial magnetic stimulation (rTMS) and theta burst stimulation (TBS). Some of these techniques are based the principle of use dependent plasticity or are designed to mimic protocols used to induce long-term potentiation or depression in animal studies. These studies have been applied to certain neurological and psychiatric disorders to investigate their pathophysiology. For example, PAS induced plasticity is enhanced in dystonia and stroke but is reduced in Huntington’s disease and schizophrenia. Furthermore, TMS may be used to modulate brain plasticity and has therapeutic potential in neurological and psychiatric disorders such as stroke, Parkinson’s disease, dystonia and depression.

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Y.L. Lo, H.H. Zhang, C.C. Wang, Z.Y. Chin, S. Fook-Chong, C. Gabriel, and C.T. Guan

In overt reading and singing tasks, actual vocalization of words in a rhythmic fashion is performed. During execution of these tasks, the role of underlying vascular processes in relation to cortical excitability changes in a spatial manner is uncertain. Our objective was to investigate cortical excitability changes during reading and singing with transcranial magnetic stimulation (TMS), as well as vascular changes with nearinfrared spectroscopy (NIRS). Findings with TMS and NIRS were correlated. TMS and NIRS recordings were performed in 5 normal subjects while they performed reading and singing tasks separately. TMS was applied over the left motor cortex at 9 positions 2.5 cm apart. NIRS recordings were made over these identical positions. Although both TMS and NIRS showed significant mean cortical excitability and hemodynamic changes from baseline during vocalization tasks, there was no significant spatial correlation of these changes evaluated with the 2 techniques over the left motor cortex. Our findings suggest that increased left-sided cortical excitability from overt vocalization tasks in the corresponding “hand area” were the result of “functional connectivity,” rather than an underlying “vascular overflow mechanism” from the adjacent speech processing or face/mouth areas. Our findings also imply that functional neurophysiological and vascular methods may evaluate separate underlying processes, although subjects performed identical vocalization tasks. Future research combining similar methodologies should embrace this aspect and harness their separate capabilities.

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János Négyesi, Menno P. Veldman, Kelly M.M. Berghuis, Marie Javet, József Tihanyi, and Tibor Hortobágyi

transfer-receiving hand. We supplemented the behavioral data with transcranial magnetic stimulation (TMS) measures to examine the potential underlying mechanisms involved in skill acquisition and its intermanual transfer. Materials and Methods Participants In total, 34 right-handed healthy adults (age 22

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Stephen P. Bailey, Julie Hibbard, Darrin La Forge, Madison Mitchell, Bart Roelands, G. Keith Harris, and Stephen Folger

improvement in performance is unclear; however, it is believed that the CHO MR enhances the excitability of the motor cortex via oral CHO receptors. Gant et al 3 provided supportive evidence for this premise when they found that the motor-evoked potential (MEP) response to transcranial magnetic stimulation

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Katherine G. Holste, Alia L. Yasen, Matthew J. Hill, and Anita D. Christie

The purpose of this study was to assess the effect of a cognitive task on motor cortex excitability and inhibition. Transcranial magnetic stimulation of the motor cortex was performed on 20 healthy individuals (18–24 years; 9 females) to measure motor evoked potentials (MEPs) and cortical silent periods at baseline, during, and following a secondary cognitive task. The MEP amplitude increased from 0.50 ± 0.09–0.87 ± 0.50 mV during a secondary cognitive task (p = .04), and returned to baseline (0.48 ± 0.31 mV; p = .90) posttask. The CSP duration also increased from 93.48 ± 28.76–113.6 ± 33.68 ms (p = .001) during the cognitive task, and returned to baseline posttask (89.0 ± 6.9 ms; p = .88). In the presence of a cognitive task, motor cortex excitability and inhibition were both increased relative to baseline. The increase in inhibition may help to explain the motor deficits experienced while performing a secondary cognitive task.

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Alex V. Nowicky, Alison H. McGregor, and Nick J. Davey

We used transcranial magnetic stimulation (TMS) to study corticospinal excitability to erector Spinae (ES) muscles during graded voluntary contractions in bilateral trunk extension (BTE) and forced expiratory breath holding (FEBH) in normal individuals. Motor evoked potentials (MEPs) could be produced in all subjects in the absence of voluntary activation. At maximum voluntary contraction, levels of surface electromyographic (EMG) activity were 4 times greater during BTE than FEBH. When EMG was normalized to maximum. MEP amplitudes increased in proportion to contraction in both tasks. MEPs in FEBH were compared with extrapolated values at similar EMG levels in BTE and were found to be larger. EMG and MEPs in left and right ES were symmetrical throughout the range of contractions in both tasks. ES muscles have a facilitation pattern similar to that previously shown in leg muscles, but subtle differences at low levels of EMG suggest that the facilitation is dependent on the task.

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Francesca Wightman, Suzanne Delves, Caroline M. Alexander, and Paul H. Strutton

Descending bilateral control of external oblique (EO) and latissimus dorsi (LD) was investigated using transcranial magnetic stimulation. Contralateral (CL) motor evoked potential (MEP) thresholds were lower and latencies were shorter than for ipsilateral (IL) MEPs. Hotspots for EO were symmetrical; this was not the case for LD. The volumes of drive to the left and right muscles were not different. The laterality index was not different between the left and right muscles. The average index for the EO muscles was closer to zero than that for LD, suggesting a stronger IL drive to EO. The symmetry of drive to each muscle did not differ; however, the symmetry of drive varies within a subject for different muscles and between subjects for the same muscle. The findings may be useful in understanding a number of clinical conditions relating to the trunk and also for predicting the outcome of rehabilitative strategies.

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Sukhvinder S. Obhi

Using more than one limb to perform functional, goal-directed actions is arguably one of the most important abilities that human beings possess. In many everyday tasks, the hands, in particular, must be used to accomplish all manner of goals. From buttoning a shirt to opening a jam jar and driving to work, good bimanual coordination is of great utility. In addition to the tasks mentioned above, there are also other tasks involving the functional use of more than one limb, including walking or cycling and typing a report. With a little thought, it becomes apparent that there is at least one important difference between these categories of coordination tasks. On one hand, in some tasks the effectors must perform markedly different motor outputs that are bound together in some functionally defined and usually object-oriented manner (e.g., buttoning a shirt) yet, in others, the effectors produce very similar motor outputs but in a specific temporal order, which may or may not repeat itself periodically (e.g., walking and cycling compared to typing or drumming). In this short article, I will argue that the second category of coordination task and, in particular, cyclical coordination, has been studied extensively and, at least at the level of behavior, is relatively well understood. In contrast the former category of bimanual task is seldom studied and, even at the descriptive level, is rather poorly understood. One of the reasons for this may be the complexity of such tasks and the technical difficulties involved in attempting to study them. By highlighting some key studies, I hope to illustrate that such tasks can be fruitfully studied in the laboratory. Last, since the neural control processes underlying both classes of coordination task are not yet well known, I aim to draw attention to the potential value of the interventional technique of Transcranial Magnetic Stimulation (TMS) as a tool for investigating the functions of brain regions contributing to bimanual coordination.

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Andrew Hooyman, Alexander Garbin, and Beth Fisher

Background Modulation of Intracortical Connectivity Current non-invasive brain stimulation (NIBS) paradigms, Repetitive Transcranial Magnetic Stimulation (rTMS) and Transcranial Direct Current Stimulation (tDCS), focus on changing behaviors through up or down regulation of a single cortical region

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David B. Copithorne, Davis A. Forman, and Kevin E. Power

The purpose of this study was to determine if supraspinal and/or spinal motoneuron excitability of the biceps brachii were differentially modulated before: 1) arm cycling and 2) an intensity-matched tonic contraction. Surface EMG recordings of motor evoked potentials (MEPs) and cervicomedullary motor evoked potentials (CMEPs) were used to assess supraspinal and spinal motoneuron excitability, respectively. MEP amplitudes were larger and onset latencies shorter, before arm cycling and tonic contraction when compared with rest with no intent to move, but with no difference between motor outputs. CMEP amplitudes and onset latencies remained unchanged before cycling and tonic contraction compared with rest. Premovement enhancement of corticospinal excitability was due to an increase in supraspinal excitability that was not task-dependent. This suggests that a common neural drive is used to initiate both motor outputs with task-dependent changes in neural excitability only being evident once the motor outputs have begun.