No effects of offline high frequency transcranial magnetic stimulation to posterior parietal cortex on the choice of which hand to use to perform a reaching task
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Abstract The current study used a high frequency TMS protocol known as continuous theta burst stimulation (cTBS) to test a model of hand choice that relies on competing interactions between the hemispheres of the posterior parietal cortex. Based on the assumption that cTBS reduces cortical excitability, the model predicts a significant decrease in the likelihood of selecting the hand contralateral to stimulation. An established behavioural paradigm was used to estimate hand choice in each individual, and these measures were compared across three stimulation conditions: cTBS to the left posterior parietal cortex, cTBS to the right posterior parietal cortex, or sham cTBS. Our results provide no supporting evidence for the interhemispheric competition model. We find no effects of cTBS on hand choice, independent of whether the left or right posterior parietal cortex was stimulated. Our results are nonetheless of value as a point of comparison against prior brain stimulation findings that, in contrast, provide evidence for a causal role for the posterior parietal cortex in hand choice. Highlights High-frequency TMS applied to the left and right posterior parietal cortex, separately, did not produce reliable aftereffects on hand choice. Response times to initiate actions were significantly increased when reaching near the point in space where hand choice was equally probable.Keywords:
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Repetitive transcranial magnetic stimulation (rTMS) over primary motor cortex (M1) elicits changes in motor evoked potential (MEP) size thought to reflect short- and long-term forms of synaptic plasticity, resembling short-term potentiation (STP) and long-term potentiation/depression (LTP/LTD) observed in animal experiments. We designed this study in healthy humans to investigate whether STP as elicited by 5-Hz rTMS interferes with LTP/LTD-like plasticity induced by intermittent and continuous theta-burst stimulation (iTBS and cTBS). The effects induced by 5-Hz rTMS and iTBS/cTBS were indexed as changes in MEP size. We separately evaluated changes induced by 5-Hz rTMS, iTBS and cTBS applied alone and those induced by iTBS and cTBS delivered after priming 5-Hz rTMS. Interactions between 5-Hz rTMS and iTBS/cTBS were investigated under several experimental conditions by delivering 5-Hz rTMS at suprathreshold and subthreshold intensity, allowing 1 and 5 min intervals to elapse between 5-Hz rTMS and TBS, and delivering one and ten 5-Hz rTMS trains. We also investigated whether 5-Hz rTMS induces changes in intracortical excitability tested with paired-pulse transcranial magnetic stimulation. When given alone, 5-Hz rTMS induced short-lasting and iTBS/cTBS induced long-lasting changes in MEP amplitudes. When M1 was primed with 10 suprathreshold 5-Hz rTMS trains at 1 min before iTBS or cTBS, the iTBS/cTBS-induced after-effects disappeared. The 5-Hz rTMS left intracortical excitability unchanged. We suggest that STP elicited by suprathreshold 5-Hz rTMS abolishes iTBS/cTBS-induced LTP/LTD-like plasticity through non-homeostatic metaplasticity mechanisms. Our study provides new information on interactions between short-term and long-term rTMS-induced plasticity in human M1.
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Abstract The current study used a high frequency TMS protocol known as continuous theta burst stimulation (cTBS) to test a model of hand choice that relies on competing interactions between the hemispheres of the posterior parietal cortex. Based on the assumption that cTBS reduces cortical excitability, the model predicts a significant decrease in the likelihood of selecting the hand contralateral to stimulation. An established behavioural paradigm was used to estimate hand choice in each individual, and these measures were compared across three stimulation conditions: cTBS to the left posterior parietal cortex, cTBS to the right posterior parietal cortex, or sham cTBS. Our results provide no supporting evidence for the interhemispheric competition model. We find no effects of cTBS on hand choice, independent of whether the left or right posterior parietal cortex was stimulated. Our results are nonetheless of value as a point of comparison against prior brain stimulation findings that, in contrast, provide evidence for a causal role for the posterior parietal cortex in hand choice. Highlights High-frequency TMS applied to the left and right posterior parietal cortex, separately, did not produce reliable aftereffects on hand choice. Response times to initiate actions were significantly increased when reaching near the point in space where hand choice was equally probable.
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The current study used a high frequency TMS protocol known as continuous theta burst stimulation (cTBS) to test a model of hand choice that relies on competing interactions between the hemispheres of the posterior parietal cortex. Based on the assumption that cTBS reduces cortical excitability, the model predicts a significant decrease in the likelihood of selecting the hand contralateral to stimulation. An established behavioural paradigm was used to estimate hand choice in each individual, and these measures were compared across three stimulation conditions: cTBS to the left posterior parietal cortex, cTBS to the right posterior parietal cortex, or sham cTBS. Our results provide no supporting evidence for the interhemispheric competition model. We find no effects of cTBS on hand choice, independent of whether the left or right posterior parietal cortex was stimulated. Our results are nonetheless of value as a point of comparison against prior brain stimulation findings that, in contrast, provide evidence for a causal role for the posterior parietal cortex in hand choice.
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본 연구는 임상에서 적용되는 반복 경두개 자기 자극(repetitive transcranial magnetic stimulation, rTMS)의 구체적인 적용법을 알아보고자 하였다. rTMS는 저빈도 rTMS(low frequency, LF-rTMS), 고빈도 rTMS(high frequency, HF-rTMS), 세타 버스트 자극(theta burst stimulation, TBS), 쌍연관 자극(paired associative stimulation, PAS)의 4가지 방법으로 적용하여 사용할 수 있다. LF-rTMS와 continuous TBS(cTBS)는 대뇌피질의 흥분성을 억제하고 HF-rTMS와 intermittent TBS(iTBS)는 대뇌피질의 흥분성을 증가시키는 방법으로 사용되며 PAS는 구심성 감각 정보에 대한 자극과 r TM S 사이 가격에 따라 흥분성을 억제하거나 증가하는 방법이다. 본 연구에서 제시된 4가지 r TM S 적용법을 이해하고 임상에서 활용 근거로 사용되기를 기대한다.
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Aging is associated with reduced neuromuscular function, which may be due to central nervous system changes in corticospinal excitability and a reduced capacity of the human brain to re-organize the strength of its connections (neuroplasticity). PURPOSE: This symposium presentation will highlight two complementary studies that determined the influence of aging and physical activity (PA) on motor cortical excitability and neuroplasticity, elicited with Transcranial Magnetic Stimulation (TMS). METHODS: In study one, corticospinal excitability was assessed in 28 young (22.4 ± 2.2 yr; 14 women) and 50 old adults (70.2 ± 6.1 yr; 22 women) by measuring motor evoked potentials (MEPs) elicited in motor cortical areas and targeting the vastus lateralis (VL) muscle of the quadriceps. In the second study, the response to a continuous theta burst stimulation paradigm (cTBS) was assessed in 27 old adults (66.5 ± 4.5, 13 women) by measuring MEPs in the first dorsal interosseous (FDI) muscle elicited after a single and paired cTBS paradigm- targeting the primary motor cortex. PA was measured in both studies using accelerometry (Actigraph GT-3x or GENEActiv, respectively). RESULTS: In study 1, irrespective of age and sex, individuals who achieved >10,000 steps/day had reduced corticospinal excitability of the VL muscles (F[1.61, 85.6] = 3.49, p = 0.04). In study 2, when accounting for age and sex, more time engaging in PA was associated with a greater neuroplasticity response to the cTBS paradigm (r=-0.51, p=0.007). CONCLUSION: These studies provide evidence that PA in both young and old adults is associated with lower corticospinal excitability in the lower limb and an enhanced capacity of the motor cortex to re-organize the strength of its connections. Together these results suggest regular PA may protect against age-related movement decline through preservation of the inhibitory and excitatory networks within the primary motor cortex, resulting in maintenance of an optimal environment for neuroplasticity. Supported by NHMRC-ARC Dementia Research development fellowship awarded to Dr Ashleigh Smith (GNT 1097397) and NIH Grant R0I awarded to Dr Sandra K. Hunter.
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