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Quadripulse stimulation of the human motor cortex
242
Abstracts
treatment and to 33.6 after further two weeks of real treatment. Generally, tDCS was tolerated well and only minor side effects occurred. Conclusion: Though real tDCS did not appear to be superior to sham treatment and previous findings were not replicated in our therapy-resistant patients we observed differential effects in weeks 3 and 4 depending on the first condition. Thus, real tDCS may induce improvement continued over a prolonged period of time and extended trial protocols should further address this issue.
rTMS Poster Only 12
Effect of low frequency somatosensory rTMS on motor cortical excitability following mirror drawing practice
Kalyviotis M, Nowicky A, Lepoura A, Kapetan-Theologou E, Brunel University (Uxbridge, London, UK) Movement accuracy is impaired in mirror drawing due to visuo-proprioceptive conflict. Baslev et al. (2004) showed that low frequency (1Hz) repetitive transcranial magnetic stimulation (rTMS) over the somatosensory cortex improved mirror drawing. There was a reduction in proprioceptive feedback following rTMS which enhances visuo-motor task accuracy. Jones et al. (2001) have showed that following visuomotor practice, movement accuracy improves and is correlated with reduced muscle spindle firing. TMS studies of the motor cortex have also shown that motor practice can induce short and long term plasticity changes. We examined the possible interaction of mirror drawing practice and 1Hz rTMS over the somatosensory area. Healthy volunteers received either 1 Hz rTMS (n 5 7) or sham rTMS (n 5 7). One day before rTMS, participants received one hour of practice of the computerized mirror drawing task. Completion of the drawing task involved use of the right index finger to rotate the scroll ball of a pc mouse and trace a shape on a computer monitor. On the next day, fifteen minutes of 30 second trains of 1Hz rTMS or sham rTMS at 110% of resting motor threshold, was applied over the left somatosensory cortex (at 0.033Hz , 450 TMS pulses (biphasic, Magstim Rapid). Paired-pulse TMS was applied over the left motor cortex hotspot for the first dorsal interosseous (FDI) muscle and motor evoked responses were recorded by standard surface electromyography. We assessed both short-latency motor cortical intracortical inhibition (2ms, SICI) and facilitation (15ms, SICF), using the method of Kujirai et al (1993). Analysis of data compared two groups before and after rTMS treatment. Significant improvement of the task was observed following practice and remained 24 hours later. No differences were observed in baseline measures of performance and TMS motor evoked responses between the two groups. There were also no significant group or group x treatment changes in mirror drawing time or proprioceptive error following 1Hz rTMS. No significant changes in SICI or SICF were also observed. In our study, 1Hz rTMS over the somatosensory cortex did not improve mirror drawing once a practice-induced adaptation had already occurred. This may be due to possible neuroplasticity changes induced by mirror drawing practice and subsequent adaptation in visuoproprioceptive processing required for this task.
rTMS Poster Only 13
Quadripulse stimulation of the human motor cortex
Hamada M1, Terao Y1, Hanajima R1, Furubayashi T2, Ugawa Y2, 1The University of Tokyo (Tokyo, JP); 2Fukushima Medical University (Fukushima, JP) Objective: Homeostatic mechanisms have been shown to maintain synapses within a dynamic range of modifiability. A plausible explanation for homeostatic plasticity is the Bienenstock-Cooper-Munro (BCM)
theory. The BCM model might directly relate to the experimental observation which revealed the influence of the prior neuronal activity on the magnitude and direction of subsequent synaptic plasticity that is called metaplasticity. Here we demonstrate bidirectional long-term modification of MEPs elicited by a burst of four monophasic TMS pulses (quadripulse stimulation: QPS) separated by various inter-pulse intervals of 1.5-1250 ms, and its priming-dependent modulation to reveal metaplasticity of the human primary motor cortex. Methods: Conditioning protocols consisted of 360 trains of TMS pulses with inter-train interval (ITI) of 5 s (i.e., 0.2 Hz) for 30 min applied over the hot spot of hand muscle. Each train consisted of four magnetic pulses separated by a certain inter-stimulus interval. Then, one conditioning consisted of 1440 TMS pulses in total. Cortical changes after QPS were evaluated with MEPs, motor threshold (MT), short-interval intracortical inhibition (SICI), intracortical facilitation (ICF), and short-interval intracortical facilitation (SICF). Priming stimulation was performed prior to QPS conditioning. Results: The QPS at short intervals induced a long-lasting MEP facilitation, whereas QPS at long intervals induced a long-lasting suppression. MT which reflects postsynaptic neuronal membrane excitability was unaffected. SICF and ICF were enhanced after QPS at short intervals, whereas SICI remained unchanged. QPS-induced plasticity was altered by priming protocol conforming to the BCM theory: the stimulus-response function of QPS-induced plasticity shifted either leftward or rightward dependent on the priming protocol. Conclusions: We have demonstrated a novel and promising rTMS method for inducing bidirectional long-term plasticity of the human motor cortex in a systematic manner. Our investigation provides additional support for the hypothesis that a BCM-like mechanism is at work in the human primary motor cortex. It will open up a new possibility for understanding learning and memory of the human cerebral cortices and a potential for clinical application.
TMS Poster Only 14
Contraction-specificity of ipsilateral motor cortical (M1) responses to transcranial magnetic brain stimulation in humans
Hortoba´gyi T1, Howatson G2, Taylor M1, Rider P1, Solnik S1, DeVita P1, 1 East Carolina University (Greenville, US); 2St Mary’s University College (Twickenham, UK) Objective: Previous studies showed that responses to transcranial magnetic brain stimulation (TMS) of M1 are lower during lengthening compared with shortening muscle contractions performed with the contralateral limb. There is strong evidence to suggest that the ipsilateral M1 is also activated during a unilateral tasks. Here we examined the hypothesis that such ipsilateral M1 responses to TMS vary according to the type of muscle contraction. Methods: Twelve right-handed males (mean age 22) performed lengthening and shortening isokinetic contractions at 20 deg/s with the left wrist flexors at the same absolute force (20, 40, 60, 80, and 100% of concentric maximal voluntary force). During the contractions, TMS was delivered to the left (ipsilateral) M1 at 120% of resting motor threshold. Motor evoked potentials (MEP) were recorded from the resting right flexor carpi-radialis (FCR) using surface electrodes, amplified 1000x, band-passed at 10 to 500 Hz, sampled at 5 kHz, and recorded on a personal computer. MEPs were analyzed for peakto-peak amplitude with custom software. MEPs during contractions were expressed as a percent of control MEP amplitude recorded during rest. Results: Although the size of the ipsilateral MEPs was similar (p 5 0.132) during shortening (215 SE 6 17.4%) and lengthening (238% SE 6 18) contractions, there was a significant the contraction type (shortening, lengthening) by contraction intensity (20, 40, 60, 80,100%) interaction (p 5 0.025), indicating that M1 output increased more (p , 0.05) with contraction intensity during lengthening than shortening contractions at 80 and 100% MVC.
Abstracts
treatment and to 33.6 after further two weeks of real treatment. Generally, tDCS was tolerated well and only minor side effects occurred. Conclusion: Though real tDCS did not appear to be superior to sham treatment and previous findings were not replicated in our therapy-resistant patients we observed differential effects in weeks 3 and 4 depending on the first condition. Thus, real tDCS may induce improvement continued over a prolonged period of time and extended trial protocols should further address this issue.
rTMS Poster Only 12
Effect of low frequency somatosensory rTMS on motor cortical excitability following mirror drawing practice
Kalyviotis M, Nowicky A, Lepoura A, Kapetan-Theologou E, Brunel University (Uxbridge, London, UK) Movement accuracy is impaired in mirror drawing due to visuo-proprioceptive conflict. Baslev et al. (2004) showed that low frequency (1Hz) repetitive transcranial magnetic stimulation (rTMS) over the somatosensory cortex improved mirror drawing. There was a reduction in proprioceptive feedback following rTMS which enhances visuo-motor task accuracy. Jones et al. (2001) have showed that following visuomotor practice, movement accuracy improves and is correlated with reduced muscle spindle firing. TMS studies of the motor cortex have also shown that motor practice can induce short and long term plasticity changes. We examined the possible interaction of mirror drawing practice and 1Hz rTMS over the somatosensory area. Healthy volunteers received either 1 Hz rTMS (n 5 7) or sham rTMS (n 5 7). One day before rTMS, participants received one hour of practice of the computerized mirror drawing task. Completion of the drawing task involved use of the right index finger to rotate the scroll ball of a pc mouse and trace a shape on a computer monitor. On the next day, fifteen minutes of 30 second trains of 1Hz rTMS or sham rTMS at 110% of resting motor threshold, was applied over the left somatosensory cortex (at 0.033Hz , 450 TMS pulses (biphasic, Magstim Rapid). Paired-pulse TMS was applied over the left motor cortex hotspot for the first dorsal interosseous (FDI) muscle and motor evoked responses were recorded by standard surface electromyography. We assessed both short-latency motor cortical intracortical inhibition (2ms, SICI) and facilitation (15ms, SICF), using the method of Kujirai et al (1993). Analysis of data compared two groups before and after rTMS treatment. Significant improvement of the task was observed following practice and remained 24 hours later. No differences were observed in baseline measures of performance and TMS motor evoked responses between the two groups. There were also no significant group or group x treatment changes in mirror drawing time or proprioceptive error following 1Hz rTMS. No significant changes in SICI or SICF were also observed. In our study, 1Hz rTMS over the somatosensory cortex did not improve mirror drawing once a practice-induced adaptation had already occurred. This may be due to possible neuroplasticity changes induced by mirror drawing practice and subsequent adaptation in visuoproprioceptive processing required for this task.
rTMS Poster Only 13
Quadripulse stimulation of the human motor cortex
Hamada M1, Terao Y1, Hanajima R1, Furubayashi T2, Ugawa Y2, 1The University of Tokyo (Tokyo, JP); 2Fukushima Medical University (Fukushima, JP) Objective: Homeostatic mechanisms have been shown to maintain synapses within a dynamic range of modifiability. A plausible explanation for homeostatic plasticity is the Bienenstock-Cooper-Munro (BCM)
theory. The BCM model might directly relate to the experimental observation which revealed the influence of the prior neuronal activity on the magnitude and direction of subsequent synaptic plasticity that is called metaplasticity. Here we demonstrate bidirectional long-term modification of MEPs elicited by a burst of four monophasic TMS pulses (quadripulse stimulation: QPS) separated by various inter-pulse intervals of 1.5-1250 ms, and its priming-dependent modulation to reveal metaplasticity of the human primary motor cortex. Methods: Conditioning protocols consisted of 360 trains of TMS pulses with inter-train interval (ITI) of 5 s (i.e., 0.2 Hz) for 30 min applied over the hot spot of hand muscle. Each train consisted of four magnetic pulses separated by a certain inter-stimulus interval. Then, one conditioning consisted of 1440 TMS pulses in total. Cortical changes after QPS were evaluated with MEPs, motor threshold (MT), short-interval intracortical inhibition (SICI), intracortical facilitation (ICF), and short-interval intracortical facilitation (SICF). Priming stimulation was performed prior to QPS conditioning. Results: The QPS at short intervals induced a long-lasting MEP facilitation, whereas QPS at long intervals induced a long-lasting suppression. MT which reflects postsynaptic neuronal membrane excitability was unaffected. SICF and ICF were enhanced after QPS at short intervals, whereas SICI remained unchanged. QPS-induced plasticity was altered by priming protocol conforming to the BCM theory: the stimulus-response function of QPS-induced plasticity shifted either leftward or rightward dependent on the priming protocol. Conclusions: We have demonstrated a novel and promising rTMS method for inducing bidirectional long-term plasticity of the human motor cortex in a systematic manner. Our investigation provides additional support for the hypothesis that a BCM-like mechanism is at work in the human primary motor cortex. It will open up a new possibility for understanding learning and memory of the human cerebral cortices and a potential for clinical application.
TMS Poster Only 14
Contraction-specificity of ipsilateral motor cortical (M1) responses to transcranial magnetic brain stimulation in humans
Hortoba´gyi T1, Howatson G2, Taylor M1, Rider P1, Solnik S1, DeVita P1, 1 East Carolina University (Greenville, US); 2St Mary’s University College (Twickenham, UK) Objective: Previous studies showed that responses to transcranial magnetic brain stimulation (TMS) of M1 are lower during lengthening compared with shortening muscle contractions performed with the contralateral limb. There is strong evidence to suggest that the ipsilateral M1 is also activated during a unilateral tasks. Here we examined the hypothesis that such ipsilateral M1 responses to TMS vary according to the type of muscle contraction. Methods: Twelve right-handed males (mean age 22) performed lengthening and shortening isokinetic contractions at 20 deg/s with the left wrist flexors at the same absolute force (20, 40, 60, 80, and 100% of concentric maximal voluntary force). During the contractions, TMS was delivered to the left (ipsilateral) M1 at 120% of resting motor threshold. Motor evoked potentials (MEP) were recorded from the resting right flexor carpi-radialis (FCR) using surface electrodes, amplified 1000x, band-passed at 10 to 500 Hz, sampled at 5 kHz, and recorded on a personal computer. MEPs were analyzed for peakto-peak amplitude with custom software. MEPs during contractions were expressed as a percent of control MEP amplitude recorded during rest. Results: Although the size of the ipsilateral MEPs was similar (p 5 0.132) during shortening (215 SE 6 17.4%) and lengthening (238% SE 6 18) contractions, there was a significant the contraction type (shortening, lengthening) by contraction intensity (20, 40, 60, 80,100%) interaction (p 5 0.025), indicating that M1 output increased more (p , 0.05) with contraction intensity during lengthening than shortening contractions at 80 and 100% MVC.