P 193. Excitability modulation of the motor system induced by transcranial direct current stimulation

P 193. Excitability modulation of the motor system induced by transcranial direct current stimulation

Society Proceedings / Clinical Neurophysiology 124 (2013) e39–e187 series of the signal in selected regions of interest were extracted. The regions o...

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Society Proceedings / Clinical Neurophysiology 124 (2013) e39–e187

series of the signal in selected regions of interest were extracted. The regions of interest were selected in FSLview (FSLview, xxxx) as 4 mm-radius spheres around specific coordinates previously defined for circuits involved in motor-skill learning, which are both distinct and connected (Doyon et al., 2009): the cerebello-thalamo-cortical (CTC) loop and the striatio-thalamo-cortical (STC) loop. The integration within a circuit was defined as Ix = 1/2 lnjRxj and between circuits as Ix/y = 1/2 ln(jRxj. jRyj/jRxyj), where Rx is the correlation matrix of network X and jj stands for the determinant function (Merrelec et al., 2008). The integration was computed for each subject, each stimulation type, each time-point, and every combination of regions/circuits. Results: We have found that despite the lack of effect on the integration of the whole motor network, there were significant changes within and between sub-networks: an increase in integration from baseline to10 min after the intervention between the left corticocerebellar and the left and right cortico-striatal loops, as well as within the cerebello-thalamo-striatal loops bilaterally. All parameters returned to baseline levels at 60 min after the intervention. Conclusions: This demonstrates that inhibitory cerebellar stimulation is actively influencing the connectivity within the motor loops, involving both cortical and subcortical structures. It suggests that the stimulation of one area can potentially change the flow of information throughout the brain, and that the inhibition of cerebellar cortex in particular can enhance the strength of the communication between the cortical motor areas and the basal ganglia. References Popa et al. Cereb Cortex 2012. Huang et al. Neuron 2005. Popa et al. Brain Stim 2010. http://www.fil.ion.ucl.ac.uk/spm/software/spm5/. http://fsl.fmrib.ox.ac.uk/fsl/fslview/index.html. Doyon et al. Behav Brain Res 2009. Merrelec et al. Med Image Anal 2008. doi:10.1016/j.clinph.2013.04.268

P 192. Transcranial direct current stimulation modulates functional connectivity within and between motor cortices—B. Sehm, J. Kipping, A. Schäfer, A. Villringer, P. Ragert (Max Planck Institute for Human Cognitive and Brain Sciences, Neurology, Leipzig, Germany) Introduction: tDCS over the primary sensorimotor cortex (SM1) has been shown to induce changes in motor performance and learning. Recent studies indicate that tDCS is capable of modulating neural network properties within the whole brain. Objectives: To investigate the temporal evolution of online tDCS effects on functional connectivity within and between the stimulated sensorimotor cortices. Materials and methods: Two different tDCS montages were investigated: (i) unilateral tDCS (anode over right SM1, cathode over contralateral supraorbital region) and (ii) bilateral tDCS (anode over right and cathode over left SM1). In a randomized single-blinded crossover design, 12 healthy subjects underwent functional magnetic resonance imaging (fMRI) at rest before, during and after bilateral, unilateral or sham tDCS at rest. Seed-based analysis was used to investigate tDCS-induced changes in functional connectivity between SM1 and interconnected areas. Results: Both uni-and bilateral tDCS, induced dynamic and nonlinear changes in functional connectivity of both SM1 and interconnected brain areas. More specifically, tDCS induced decreases in functional connectivity between both SM1 as compared to sham in both conditions. This effect was more prominent during bilateral

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tDCS as compared to unilateral tDCS. Furthermore, only during bilateral tDCS, an increase in intracortical connectivity within right M1 was observed. Conclusion: Our results provide evidence that depending on the electrode montage, tDCS acts upon a modulation of either intracortical and/or interhemispheric processing of SM1. doi:10.1016/j.clinph.2013.04.269

P 193. Excitability modulation of the motor system induced by transcranial direct current stimulation—M.C. Pellicciari a, D. Brignani a, C. Miniussi a,b (a IRCCS The Saint John of God-Fatebenefratelli, Cognitive Neuroscience Section, Brescia, Italy, b University of Brescia, Dept. of Clinical and Experimental Sciences, Neuroscience Section, Brescia, Italy) Question: Transcranial direct current stimulation (tDCS) is a noninvasive brain stimulation technique that modulates cortical excitability and activity in a polarity-dependent way. In the human motor system, such cortical modulations are inferred through changes in the amplitude of motor evoked potentials (MEPs). To directly evaluate tDCS-induced changes at the cortical level, we investigated polarity-dependent tDCS-induced effects on the motor system, evaluating changes in MEPs, TMS-evoked potentials (TEPs) and in the EEG oscillatory activity. Methods: Sixteen young healthy right-handed subjects participated in this study. Two experimental sessions were performed for each subject in randomized order: anodal and cathodal tDCS (aand c-tDCS). The EEG activity was recorded from 10 scalp electrodes while EMG activity was recorded from the right FDI. Corticospinal excitability and cortical reactivity were investigated through the recording of MEPs and TEPs, whereas the cortical state was evaluated through the acquisition of the EEG activity. All the measures were collected before tDCS, immediately and 30 min after tDCS, to evaluate short and long-lasting tDCS effects. The tDCS was applied for 13 min (1 mA) over the left primary motor cortex. The TEPMEP block consisted of 100 TMS pulses (intensity of 110% of the RMT), delivered with a random inter stimulus interval of 2–4 s. The EEG block consisted of 3 min of recording during a resting state. To determine the tDCS induced changes in the cortical evoked potentials, a local mean field power analysis was computed. To characterize tDCS-induced changes in cortical oscillatory activity, the EEG power density was estimated by means of the Fast Fourier transform. Results: The application of a- and c-tDCS over M1 induced respectively a short-term increase and decrease of MEPs amplitude. The MEPs changes persisted 30 min after a-tDCS but not after c-tDCS. The TEPs analysis highlighted short term changes induced by tDCS polarities. Particularly, we found a significant pattern of topographically specific and current-dependent changes. a- and c-tDCS induced consistent differences in cortical reactivity only on the stimulated area. The long lasting changes partially overlapped those observed in the short-term analyses. Finally, the EEG frequency analysis revealed a significant main effect only in the theta and alpha bands, suggesting a general increase in their power density after tDCS. These changes were reduced 30 min after stimulation. Conclusions: a-tDCS over primary motor cortex induced an enhancement of corticospinal excitability, whereas c-tDCS produced an excitability reduction. More interestingly, the cortical reactivity resulted increased after anodal stimulation whereas cathodal stimulation produced a decrease over the stimulated area. These cortical reactivity changes lasted for at least30 min. Moreover, a general increase in the power density of theta and alpha frequencies was also present over all scalp sites for both the stimulation polarities.

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Society Proceedings / Clinical Neurophysiology 124 (2013) e39–e187

These results shows direct evidence that tDCS induces polaritydependent changes on brain activity at cortical level. doi:10.1016/j.clinph.2013.04.270

P 194. The EEG correlates of the TMS induced EMG silent period in humans—F. Farzan a, M.S. Barr b, S. Hoppenbrouwers c, P.B. Fitzgerald d, R. Chen e, A. Pascual-Leone f,a, Z.J. Daskalakis b (a Harvard Medical School/BIDMC, Boston, United States, b University of Toronto/CAMH, Toronto, Canada, c Helmholtz Institute, Utrecht University, Department of Experimental Psychology, Utrecht, The Netherlands, d Monash Alfred Psychiatry Research Centre, The Alfred and Monash University Central Clinical School, Victoria, Australia, e University of Toronto/Toronto Western Research Institute, Division of Neurology, Toronto, Canada, f Institut Universitari de Neurorehabilitació Guttmann, Badalona, United States) Application of magnetic or electrical stimulation to the motor cortex can result in a period of electromyography (EMG) silence in a tonically active peripheral muscle. This period of EMG silence is referred to as the silent period (SP). The duration of SP shows intersubject variability and reflects the integrity of the cortical and corticospinal pathways. A non-invasive technique for assessing the duration of SP is the combination of Transcranial Magnetic Stimulation (TMS) with EMG. Utilizing TMS-EMG, several studies have reported on the shortening or lengthening of SP in neuropsychiatric disorders such as schizophrenia, bipolar disorder, depression, obsessive compulsive disorder, epilepsy, Parkinson’s disease, and stroke. However, cortical, corticospinal and peripheral components are difficult to disentangle from EMG alone. Here, we use the multimodal neuroimaging technique of TMS-EMG combined with concurrent electroencephalography (EEG) recording to further examine the cortical origin of SP and the cortical oscillatory activity that underlies SP genesis. We demonstrate that the duration of SP is related to the temporal characteristics of the cortical reactivity and the power of low frequency cortical oscillations (1–15 Hz) in both local and remote areas ipsilateral and contralateral to the stimulation site. We illustrate that, compared to EMG, the EEG indices of the SP provide additional information about the brain dynamics and propose that the EEG measures of SP may be used in future clinical and research investigations to more precisely delineate the mechanisms underlying inhibitory impairments. doi:10.1016/j.clinph.2013.04.271

P 195. TMS/EEG responses in epilepsy patients—E. ter Braack a, I. Silva Santos a,b, C. Eertman c, M. Putten van a,c (a University of Twente, Clinical Neurophysiology, Enschede, The Netherlands, b New University of Lisbon, Faculty of Sciences and Technology, Lisbon, Portugal, c Medisch Spectrum Twente, Clinical Neurophysiology, Enschede, The Netherlands) Introduction: Diagnosing epilepsy is often time-consuming, partially due to the limited sensitivity of the routine electroencephalogram (EEG). Therefore, there is a need for additional diagnostic measures. There is usually a small brain area responsible for the seizure onset, although it cannot always be localized. Transcranial magnetic stimulation (TMS) enables quantification of the brain’s excitability. Previous studies have shown an increased excitability in epilepsy patients (Badawy et al., 2010). When TMS is applied while recording EEG, a characteristic waveform-the TMS evoked potential (TEP)-is induced in the EEG. A previous study showed that TEP consists of an early part, which is always present, and a late part,

that was present in 9 out of 11 epilepsy patients, and not in healthy subjects (Valentin et al., 2008). Objectives: To investigate late TEP responses and the spread of induced activity over the cortex in healthy subjects and epilepsy patients. Materials and methods: TMS/EEG was recorded in healthy controls and adult epilepsy patients using a Magstim Rapid2 stimulator and a 64-channel EEG amplifier (ANT Neuro, Enschede). TMS was targeted at the left and right motor cortex. We administered 75 pulses at an intensity of 110% motor threshold for both targets. The TEP was obtained by averaging over all TMS pulses, and the baseline power was then subtracted from the late response power. The values for all trials before and after the TMS pulse were then compared using a student t-test. Increases in power of >1 lV in the 9 electrodes surrounding the stimulation point, with a significance level of p < 0.01, were regarded as a late response. Results: At present, 18 healthy subjects (11 males, mean age 28 years) and 10 epilepsy patients (3 males, mean age 24 years) have been included. Nine patients were taking anti-epileptic drugs. In all healthy controls and epilepsy patients we found an early TEP, and three patients and five healthy subjects showed a late response. Conclusion: Initial results show that the late responses are not sufficient to reliably differentiate between healthy subjects and epilepsy patients. We are currently analysing the activity spread data. In addition, more patient measurements have been scheduled. References Badawy et al. Ann Neurol 2010;67:64–73. Valentin et al. Epilepsia 2008;49:470–80. doi:10.1016/j.clinph.2013.04.272

P 196. Brain stem reflex abnormalities in patients with multiple sclerosis—F. Deriu a, G. Pilurzi a,b, I. Magnano b, F. Ginatempo a, M.P. Cabboi b, G.M. Pes b, M. Conti b (a University of Sassari, Biomedical Sciences, Sassari, Italy, b University of Sassari, Clinical and Experimental Medicine, Sassari, Italy) Introduction: Patients with multiple sclerosis (MS) often exhibit a brainstem (BS) involvement, which is sometimes undetected by conventional investigation. Recently, the vestibulocollic reflex (VCR) has been widely used in MS to assess vestibulospinal pathways. Besides VCR, other myogenic potentials can be used to explore BS circuits. Among these, the trigeminocollic reflex (TCR) has never been systematically studied in MS, while the vestibulomasseteric (VMR) and acousticmasseteric (AMR) reflexes have never been investigated in neurological diseases. Objectives: To perform a comprehensive evaluation of VMR, AMR, VCR and TCR in MS and compare frequency of abnormalities with those detected in controls; to correlate BSR data to those obtained from clinical examination, multimodal evoked potentials (EP) and conventional neuroimaging (MRI) assessment. Methods: Sixty patients (33.3 ± 8.3 years old) with diagnosis of relapsing-remitting MS and 60 age-and sex matched controls were studied. All participants underwent clinical examination and BSR recording. MS underwent additional mEP and MRI assessment. Group differences were tested with v2 test and Mann-Whitney U test. Spearman’s rank correlation coefficient was used for correlation analysis. Results: Patients had a mean illness duration of 8.2 ± 6.4 years and EDSS score of 1.78 ± 1.10 (with EDSS = 0 in 15.3%). Neurological examination showed symptoms and/or signs of BS involvement in 37.3% of cases. The frequency of altered BSR was significantly different (p = 0.00001) between controls and patients. In patients, the