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P29-8 Do cortical rhythms influence the induction of plasticity in the human motor cortex by continuous theta burst stimulation?
29th International Congress of Clinical Neurophysiology P29-6 Imaging human brain cortical effective connectivity during single and paired pulse transcranial magnetic stimulation F. Ferreri1,2 , P. Pasqualetti3,5 , S. Maatta2 , D. Ponzo1 , F. Ferrarelli4 , G. Tononi4 , E. Mervaala2 , C. Miniussi6 , P.M. Rossini1,5 1 Department of Neurology, University Campus Biomedico, Rome, Italy, 2 Department of Clinical Neurophysiology, Kuopio University Hospital, University of Kuopio, Kuopio, Finland, 3 AFaR, Department of Neuroscience, Hospital Fatebenefratelli Isola Tiberina, Rome, Italy, 4 Department of Psychiatry, University of Wisconsin, Madison WI, USA, 5 IRCCS San Raffaele Pisana e Casa di Cura San Raffaele Cassino, Italy, 6 IRCCS San Giovanni di Dio, Hospital Fatebenefratelli, Brescia, Italy Objective: Intracortical inhibition (SICI) and facilitation (ICF) in the human motor cortex can be measured using a paired-pulse transcranial magnetic stimulation (ppTMS) protocol. Recently, a technical device has been introduced, which allows recording electroencephalographic (EEG) responses to TMS of a given scalp site. The latency, amplitude and scalp topography of such responses are considered a reflection of cortico-cortical connectivity and functional state. The aim of the present study is to better characterize the neuronal circuits underlying motor cortex connectivity as well as the mechanisms regulating its balance between inhibition and facilitation by means of EEG navigated-ppTMS coregistration. Methods: Sub-threshold and supra-threshold single and ppTMS of the left primary motor cortex were carried out during a multi-channel EEG recording on 8 healthy volunteers; the between-pulse intervals used in the paired-pulse trials were 3 (for SICI) and 11 ms (for ICF). Motor Evoked potentials (MEPs) from the opposite hand were simultaneously recorded. Results: Single and ppTMS induced EEG responses characterized by a sequence of negative deflections peaking at approximately 7, 18, 44, 100, 280 ms alternated with positive peaks at approximately 13, 30, 60 and 190 ms post-TMS. Moreover, ppTMS modulated both EEG evoked activity and MEPs. Amplitude variability of EEG responses was correlated with, and therefore might partially explain, amplitude variability of MEPs. Conclusion: EEG-ppTMS is a promising tool to better characterize the neuronal circuits underlying cortical effective connectivity as well as the mechanisms regulating the balance between inhibition and facilitation within the human cortices and the corticospinal pathway. P29-7 Evidence for surround inhibition in motor cortex contributing to a single finger contraction induced by training K. Sugawara1 , T. Higashi1 , S. Tanabe2 , T. Tsurumi1 , T. Kasai3 School of Rehabilitation, Kanagawa University of Human Services, Kanagawa, Japan, 2 School of Health Sciences, Hujita Health University, Japan, 3 Department of Rehabilitation of Locomotor System Dysfunction, Hiroshima University, Japan 1
Objective: Surround inhibition (SI) is a well known concept in sensory physiology. Recently, using transcranial magnetic stimulation (TMS), SI of human motor cortex has also been proposed and could play an essential role during motor skill learning. Although several studies using TMS have demonstrated an increase in excitability and an expansion of the cortical representation of finger muscles, neural mechanisms of SI are not clear. In particular, relationships between intracortical inhibitory (ICI) circuits and SI are not known. Previous reports indicated that ICI could contribute to volitional inhibition of motor activity. If that is the case, SI likely contributes to motor skill learning. That is, SI might be related to ICI and might play an important role for improvement and efficiency of motor skill performance. Methods: To address above-mentioned question, we used voluntary tonic index finger abduction (40%MVC) and monitored motor overflow activity in abductor digiti minimi (ADM). When subjects were performing index finger abduction, they were instructed to decrease EMGs activity of ADM as small as possible. Using single or paired pulse TMS, we examined preand post-motor training effects on M1 and ICI (ISI = 2 ms) activities. Motor evoked potentials (MEPs) were recorded using surface electrodes from ADM and first dorsal interosseous (FDI), simultaneously. MEP amplitudes after paired pulse were expressed as a ratio of MEP amplitudes induced by single TMS (inhibition ratio). Results and Conclusion: After training of tonic voluntary contraction of targeted FDI at 40%MVC, inhibition ratios of non-targeted ADM were decreased (i.e. increase of inhibition) but those in FDI were unaltered. These results suggest that functional changes of SI in non-targeted muscle
S275 occur dependent on ICI circuits. That is, SI in M1 for selective skilled movement might play an important role for non-needed muscles of motor activity. P29-8 Do cortical rhythms influence the induction of plasticity in the human motor cortex by continuous theta burst stimulation? S.M. McAllister1 , J.C. Rothwell2 , M.C. Ridding3 1 Discipline of Physiology, School of Medical Sciences, The University of Adelaide, Adelaide, Australia, 2 Sobell Department of Motor Neuroscience and Movement Disorders, Institute of Neurology, University College London, London, UK, 3 Neuromotor Plasticity and Development Research Group, The Robinson Institute, School of Paedeatrics and Reproductive Health, The University of Adelaide, Adelaide, Australia Objective: Plasticity can be induced in the human motor cortex using non-invasive brain stimulation techniques such as continuous Theta Burst Stimulation (cTBS). The response to these techniques is characterised by high variability; the reasons for this are not well-understood. One potentially important factor is the excitability of the cortex at the time of stimulation. The cortex exhibits dynamic rhythmical activity at a range of frequencies, which can be investigated using electroencephalography (EEG). We sought to investigate the relationship between subjects’ cortical rhythms at baseline and their responses to cTBS. Methods: Motor evoked potentials (MEPs) were recorded from the first dorsal interosseous (FDI) at baseline and 5 and 10 minutes following cTBS in fourteen healthy individuals. Two minutes of EEG was recorded over the motor cortex immediately prior to and 0 and 8 minutes following cTBS. Power spectra were computed from the EEG using the Fast-Fourier Transform algorithm. The power in the delta, theta, alpha and beta frequency bands was normalised to the 0 40 Hz power. The relationship between normalised power at baseline and changes in MEP amplitude following cTBS was investigated using regression analysis. Results: Mean MEP amplitude was significantly reduced to 77% of baseline five minutes following cTBS (ANOVA, p < 0.05). However, there was no significant correlation between normalised delta, theta, alpha or beta power and changes in MEP amplitude following cTBS (p > 0.05 for all). Conclusion: The results provide no support for an association between cortical oscillatory power and responses to cTBS. However, it is likely the motor cortical neurons involved in FDI control only make a very small contribution to the recorded EEG signal. Secondly, cortical oscillatory activity during rather than prior to cTBS may be more important. Thus a relationship between cortical rhythms and the induction of plasticity may indeed exist but was undetectable due to methodological constraints. P29-9 Neural connectivity origin and effects of M1 excitability variations: a TMS+EEG study F. Giambattistelli1 , L. Tomasevic2 , J.M. Melgari1 , C. Porcaro2,3 , F. Tecchio2 , P.M. Rossini1,4 1 Department of Clinical Neurology, University Campus Bio-Medico, Roma, Italy, 2 ISTC-CNR, Rome, Italy, 3 BUIC, Birmingham, United Kingdom, 4 Department of Neuroscience, AFaR, Osp. Fatebenefratelli, Isola Tiberina, Rome, Italy Objective and Methods: Transcranial magnetic stimulation-induced motor evoked potentials (MEPs) (amplitude/latency characteristics) allow the evaluation of the functional state of the corticospinal pathway. Amplitude is mainly related to corticospinal excitability; this parameter, however, shows high spontaneous variability. It has been clarified that it cannot be attributed to minor changes in coil position while it is effected by an actual change of M1 and spinal pools excitability; since literature indicated that neither background muscle tone nor the phase of the cardiac or respiratory cycles explain such excitability changes, aim of this study was to investigate whether transient changes of the cortico-cortical connectivity robustness can explain excitability variations. Combining navigated TMS and EEG, we analyzed the cerebral oscillatory activity (power spectral density, functional connectivity) during the few seconds before TMS stimuli (120% of resting motor threshold) over left and right First Dorsal Interosseous hot-spot in 10 healthy right handed volunteers. High and Low corticospinal excitability was classified on the basis of MEP amplitude above and below median value. Latency, amplitude and position of activated sources in the 300 ms after stimulus were compared
Objective: Surround inhibition (SI) is a well known concept in sensory physiology. Recently, using transcranial magnetic stimulation (TMS), SI of human motor cortex has also been proposed and could play an essential role during motor skill learning. Although several studies using TMS have demonstrated an increase in excitability and an expansion of the cortical representation of finger muscles, neural mechanisms of SI are not clear. In particular, relationships between intracortical inhibitory (ICI) circuits and SI are not known. Previous reports indicated that ICI could contribute to volitional inhibition of motor activity. If that is the case, SI likely contributes to motor skill learning. That is, SI might be related to ICI and might play an important role for improvement and efficiency of motor skill performance. Methods: To address above-mentioned question, we used voluntary tonic index finger abduction (40%MVC) and monitored motor overflow activity in abductor digiti minimi (ADM). When subjects were performing index finger abduction, they were instructed to decrease EMGs activity of ADM as small as possible. Using single or paired pulse TMS, we examined preand post-motor training effects on M1 and ICI (ISI = 2 ms) activities. Motor evoked potentials (MEPs) were recorded using surface electrodes from ADM and first dorsal interosseous (FDI), simultaneously. MEP amplitudes after paired pulse were expressed as a ratio of MEP amplitudes induced by single TMS (inhibition ratio). Results and Conclusion: After training of tonic voluntary contraction of targeted FDI at 40%MVC, inhibition ratios of non-targeted ADM were decreased (i.e. increase of inhibition) but those in FDI were unaltered. These results suggest that functional changes of SI in non-targeted muscle
S275 occur dependent on ICI circuits. That is, SI in M1 for selective skilled movement might play an important role for non-needed muscles of motor activity. P29-8 Do cortical rhythms influence the induction of plasticity in the human motor cortex by continuous theta burst stimulation? S.M. McAllister1 , J.C. Rothwell2 , M.C. Ridding3 1 Discipline of Physiology, School of Medical Sciences, The University of Adelaide, Adelaide, Australia, 2 Sobell Department of Motor Neuroscience and Movement Disorders, Institute of Neurology, University College London, London, UK, 3 Neuromotor Plasticity and Development Research Group, The Robinson Institute, School of Paedeatrics and Reproductive Health, The University of Adelaide, Adelaide, Australia Objective: Plasticity can be induced in the human motor cortex using non-invasive brain stimulation techniques such as continuous Theta Burst Stimulation (cTBS). The response to these techniques is characterised by high variability; the reasons for this are not well-understood. One potentially important factor is the excitability of the cortex at the time of stimulation. The cortex exhibits dynamic rhythmical activity at a range of frequencies, which can be investigated using electroencephalography (EEG). We sought to investigate the relationship between subjects’ cortical rhythms at baseline and their responses to cTBS. Methods: Motor evoked potentials (MEPs) were recorded from the first dorsal interosseous (FDI) at baseline and 5 and 10 minutes following cTBS in fourteen healthy individuals. Two minutes of EEG was recorded over the motor cortex immediately prior to and 0 and 8 minutes following cTBS. Power spectra were computed from the EEG using the Fast-Fourier Transform algorithm. The power in the delta, theta, alpha and beta frequency bands was normalised to the 0 40 Hz power. The relationship between normalised power at baseline and changes in MEP amplitude following cTBS was investigated using regression analysis. Results: Mean MEP amplitude was significantly reduced to 77% of baseline five minutes following cTBS (ANOVA, p < 0.05). However, there was no significant correlation between normalised delta, theta, alpha or beta power and changes in MEP amplitude following cTBS (p > 0.05 for all). Conclusion: The results provide no support for an association between cortical oscillatory power and responses to cTBS. However, it is likely the motor cortical neurons involved in FDI control only make a very small contribution to the recorded EEG signal. Secondly, cortical oscillatory activity during rather than prior to cTBS may be more important. Thus a relationship between cortical rhythms and the induction of plasticity may indeed exist but was undetectable due to methodological constraints. P29-9 Neural connectivity origin and effects of M1 excitability variations: a TMS+EEG study F. Giambattistelli1 , L. Tomasevic2 , J.M. Melgari1 , C. Porcaro2,3 , F. Tecchio2 , P.M. Rossini1,4 1 Department of Clinical Neurology, University Campus Bio-Medico, Roma, Italy, 2 ISTC-CNR, Rome, Italy, 3 BUIC, Birmingham, United Kingdom, 4 Department of Neuroscience, AFaR, Osp. Fatebenefratelli, Isola Tiberina, Rome, Italy Objective and Methods: Transcranial magnetic stimulation-induced motor evoked potentials (MEPs) (amplitude/latency characteristics) allow the evaluation of the functional state of the corticospinal pathway. Amplitude is mainly related to corticospinal excitability; this parameter, however, shows high spontaneous variability. It has been clarified that it cannot be attributed to minor changes in coil position while it is effected by an actual change of M1 and spinal pools excitability; since literature indicated that neither background muscle tone nor the phase of the cardiac or respiratory cycles explain such excitability changes, aim of this study was to investigate whether transient changes of the cortico-cortical connectivity robustness can explain excitability variations. Combining navigated TMS and EEG, we analyzed the cerebral oscillatory activity (power spectral density, functional connectivity) during the few seconds before TMS stimuli (120% of resting motor threshold) over left and right First Dorsal Interosseous hot-spot in 10 healthy right handed volunteers. High and Low corticospinal excitability was classified on the basis of MEP amplitude above and below median value. Latency, amplitude and position of activated sources in the 300 ms after stimulus were compared