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Non-invasive modulation of spinal cord function with transcutaneous direct current (dc) stimulation
304
Abstracts
RT’s were analyzed by means of an ANOVA and post hoc T-test. Exp1: IT for phosphenes induced by O-TMS (36.5 ms) was about ten times slower than that for visually presented stimuli (4.96 ms). Exp2: IT for phosphenes induced by P-TMS and that obtained with visually presented stimuli were similar (4.95 ms) In sum, the present results show that phosphenes obtained by V1 TMS transfer via sparse callosal connections while those generated by parietal TMS transfer via widespread callosal connections. Interestingly, the latter transfer is similar to that of visually presented stimuli.
Movement Disorders Poster Only 203
Motor imagery in focal dystonia
Tyc F, Boyadjian A, Brasil-Neto JP, Allam N, Laboratoire plasticite´ & physio-patholog (Marseille Cedex, FR) Focal task-specific dystonias, such as writer’s cramp, are motor disorders with abnormalities of motor control mechanisms which impair fine coordination between muscles involved in specific tasks, often characterized by excessive involuntary muscular activation. We have used transcranial magnetic stimulation (TMS) to compare the effects of motor imagery (MI) on corticospinal excitability during coordination between proximal and distal muscles in 10 patients with focal hand dystonia and in 6 healthy controls. We applied single pulse TMS on the extensor carpi radialis (ECR) hot spot and recorded motor evoked potentials (MEPs) from contralateral upper limb muscles (ECR, medial deltoid MD, first dorsal interosseus FDI) in several conditions while subjects maintained a position of the arm and while the subjects imagined the movement. For the ‘‘overt movement’’ the subject had to maintain the position of the wrist by a tonic activation of the ECR muscle: 1) alone and 2) with the co-activation of the MD muscle. In the motor imagery, three conditions were proposed: 1) imagine the movement with the whole upper limb, 2) with the forearm only and 3) imagine the movement while the MD was contracted. Seven increasing intensities were applied in each condition. For each intensity, four stimulations were done and the MEPs were averaged to determine the excitability curves for the three recorded muscles. During motor imagery, the excitability curves of the controls showed lower plateau and smaller slope in the condition where MD was co-activated compared to the curves obtained during whole movement imagery. This was not the case in the dystonic patients where the MD activation facilitated the MEP in the ECR during MI. Furthermore, in patients but not in controls, the MEP amplitude in FDI increased when MD was activated during MI. Motor imagery seems to facilitate the three muscles MEPs in dystonic patients compared to control. This excessive facilitation extending to several muscles that are not facilitated in control seems to modify the coordination between muscles and seems to reveal an activation of the three muscles as a block. The global activation observed during overt movement and MI in dystonics may be interpreted as a dysfunction of the motor networks with an excess of excitability. Modifications in the neural networks implicated in coordination between the shoulder, the elbow and the wrist could be at the origin of an excess of activity observed in dystonic muscles.
TMS Poster Only 204
Time series analysis of ensemble motor unit discharge reveals I-wave periodicity (600 Hz) during skilled voluntary activity
Stewart M, Cracco R, Maccabee P, Amassian V, SUNY Downstate Medical Center (Brooklyn, US)
Single TMS pulses over parietal cortex generate a series of I-waves with periodicity w1.5 ms which reflect activation of corticospinal tract fibers by a vertically-organized neural network (Amassian & Stewart, Clin Neurophysiol 56 [Suppl]:119-142, 2003). Does this excitatory cortical network also function during voluntary activity? Searching for such activity was facilitated by recording from muscles with very short peripheral conduction times (w2 ms in extrinsic laryngeal muscles), and taking recordings during precisely timed voluntary activity (e.g. silently making plosive consonants like ‘‘T,’’ ‘‘P,’’ ‘‘priest’’). Surface EMG recordings of multiple single unit action potentials were made for 50-200 ms after their onset. Recordings were half-wave rectified and each negative deflection triggered a standard 100 or 200 `ıs pulse with subsequent 4 ms dead time. Multiple sweeps were accumulated to generate a histogram of motor unit ensemble activity, which permitted intervals shorter than 4 ms to occur. First, we searched for firing tendencies at different intervals using a variation of the expectation density (ED) function that was applied to the sum of the discriminated EMG sweeps. Secondly, a more precise measure of periodic tendencies was sought by computing the cross-channel ED (XED) between the EMG histogram and (a) a fixed period spike train, with periods adjusted from 1.0-2.0 ms (in 0.1 ms steps), or (b) random spike trains from radioactive decay. The ‘‘iterative ED’’ and XED functions revealed periodicity at 1.3.-1.6 ms and their harmonics. The periodic content of the XED was assessed by cross-correlating the XED with a sine wave having the same period as the fixed spike train. The magnitude of this correlation (maximum for all phases) was plotted as a function of period to detect and quantify tendencies in the EMG for particular frequencies. Significant tendencies for periodicity were identified by calculating the mean and 95 or 99% confidence intervals (two-tailed) at each frequency from randomly shuffled versions of the data (N 5 100-500 shuffled versions at each frequency). Summarizing, typical I-wave periodicities normally related to sTMS are now identified in skilled voluntary activity of motor neurons. Thus, the Iwave periodicity in not merely an artifact of powerful synchronous stimulation but reflects also a clock-like function favoring excitation within the cortex at coincidences occurring during computation.
tDCS Poster Only 205
Non-invasive modulation of spinal cord function with transcutaneous direct current (dc) stimulation
Vergari M, Cogiamanian F, Pulecchi F, Marceglia S, Tadini L, Ferrucci R, Priori A, Fondazione IRCCS Ospedale Maggiore Policlinico,Dip. di Scienze Neurologiche, Universita` di Milano (Milano, IT) Objective: To evaluate whether transcutaneous direct current (DC) stimulation can modulate the function of the human spinal cord, we studied the after-effects of anodal, cathodal and sham transcutaneous spinal DC stimulation (tsDCS) delivered over the human thoracic spinal cord on the somatosensory evoked potentials (SEPs). Methods: tsDCS was delivered over the thoracic spinal cord (2.5 mA, 15 min.) in eleven healthy subjects. SEPs evoked by posterior tibial and by median nerve stimulation were recorded, before tsDCS and after tsDCS offset. Results: anodal tsDCS stimulation decreased significantly (44,3 6 8,7%; p 5 0,005) the amplitude of the cervico-medullary component of posterior tibial nerve SEPs (P30). Anodal tsDCS left median nerve SEPs unchanged. Sham and cathodal tsDCS failed to change the SEPs. Conclusions: tsDCS induces prolonged and focal changes of conduction along the human lemniscal pathway at spinal cord level. Our finding prompts to assess whether tsDCS can be an alternative to invasive spinal cord stimulation in patients.
Abstracts
RT’s were analyzed by means of an ANOVA and post hoc T-test. Exp1: IT for phosphenes induced by O-TMS (36.5 ms) was about ten times slower than that for visually presented stimuli (4.96 ms). Exp2: IT for phosphenes induced by P-TMS and that obtained with visually presented stimuli were similar (4.95 ms) In sum, the present results show that phosphenes obtained by V1 TMS transfer via sparse callosal connections while those generated by parietal TMS transfer via widespread callosal connections. Interestingly, the latter transfer is similar to that of visually presented stimuli.
Movement Disorders Poster Only 203
Motor imagery in focal dystonia
Tyc F, Boyadjian A, Brasil-Neto JP, Allam N, Laboratoire plasticite´ & physio-patholog (Marseille Cedex, FR) Focal task-specific dystonias, such as writer’s cramp, are motor disorders with abnormalities of motor control mechanisms which impair fine coordination between muscles involved in specific tasks, often characterized by excessive involuntary muscular activation. We have used transcranial magnetic stimulation (TMS) to compare the effects of motor imagery (MI) on corticospinal excitability during coordination between proximal and distal muscles in 10 patients with focal hand dystonia and in 6 healthy controls. We applied single pulse TMS on the extensor carpi radialis (ECR) hot spot and recorded motor evoked potentials (MEPs) from contralateral upper limb muscles (ECR, medial deltoid MD, first dorsal interosseus FDI) in several conditions while subjects maintained a position of the arm and while the subjects imagined the movement. For the ‘‘overt movement’’ the subject had to maintain the position of the wrist by a tonic activation of the ECR muscle: 1) alone and 2) with the co-activation of the MD muscle. In the motor imagery, three conditions were proposed: 1) imagine the movement with the whole upper limb, 2) with the forearm only and 3) imagine the movement while the MD was contracted. Seven increasing intensities were applied in each condition. For each intensity, four stimulations were done and the MEPs were averaged to determine the excitability curves for the three recorded muscles. During motor imagery, the excitability curves of the controls showed lower plateau and smaller slope in the condition where MD was co-activated compared to the curves obtained during whole movement imagery. This was not the case in the dystonic patients where the MD activation facilitated the MEP in the ECR during MI. Furthermore, in patients but not in controls, the MEP amplitude in FDI increased when MD was activated during MI. Motor imagery seems to facilitate the three muscles MEPs in dystonic patients compared to control. This excessive facilitation extending to several muscles that are not facilitated in control seems to modify the coordination between muscles and seems to reveal an activation of the three muscles as a block. The global activation observed during overt movement and MI in dystonics may be interpreted as a dysfunction of the motor networks with an excess of excitability. Modifications in the neural networks implicated in coordination between the shoulder, the elbow and the wrist could be at the origin of an excess of activity observed in dystonic muscles.
TMS Poster Only 204
Time series analysis of ensemble motor unit discharge reveals I-wave periodicity (600 Hz) during skilled voluntary activity
Stewart M, Cracco R, Maccabee P, Amassian V, SUNY Downstate Medical Center (Brooklyn, US)
Single TMS pulses over parietal cortex generate a series of I-waves with periodicity w1.5 ms which reflect activation of corticospinal tract fibers by a vertically-organized neural network (Amassian & Stewart, Clin Neurophysiol 56 [Suppl]:119-142, 2003). Does this excitatory cortical network also function during voluntary activity? Searching for such activity was facilitated by recording from muscles with very short peripheral conduction times (w2 ms in extrinsic laryngeal muscles), and taking recordings during precisely timed voluntary activity (e.g. silently making plosive consonants like ‘‘T,’’ ‘‘P,’’ ‘‘priest’’). Surface EMG recordings of multiple single unit action potentials were made for 50-200 ms after their onset. Recordings were half-wave rectified and each negative deflection triggered a standard 100 or 200 `ıs pulse with subsequent 4 ms dead time. Multiple sweeps were accumulated to generate a histogram of motor unit ensemble activity, which permitted intervals shorter than 4 ms to occur. First, we searched for firing tendencies at different intervals using a variation of the expectation density (ED) function that was applied to the sum of the discriminated EMG sweeps. Secondly, a more precise measure of periodic tendencies was sought by computing the cross-channel ED (XED) between the EMG histogram and (a) a fixed period spike train, with periods adjusted from 1.0-2.0 ms (in 0.1 ms steps), or (b) random spike trains from radioactive decay. The ‘‘iterative ED’’ and XED functions revealed periodicity at 1.3.-1.6 ms and their harmonics. The periodic content of the XED was assessed by cross-correlating the XED with a sine wave having the same period as the fixed spike train. The magnitude of this correlation (maximum for all phases) was plotted as a function of period to detect and quantify tendencies in the EMG for particular frequencies. Significant tendencies for periodicity were identified by calculating the mean and 95 or 99% confidence intervals (two-tailed) at each frequency from randomly shuffled versions of the data (N 5 100-500 shuffled versions at each frequency). Summarizing, typical I-wave periodicities normally related to sTMS are now identified in skilled voluntary activity of motor neurons. Thus, the Iwave periodicity in not merely an artifact of powerful synchronous stimulation but reflects also a clock-like function favoring excitation within the cortex at coincidences occurring during computation.
tDCS Poster Only 205
Non-invasive modulation of spinal cord function with transcutaneous direct current (dc) stimulation
Vergari M, Cogiamanian F, Pulecchi F, Marceglia S, Tadini L, Ferrucci R, Priori A, Fondazione IRCCS Ospedale Maggiore Policlinico,Dip. di Scienze Neurologiche, Universita` di Milano (Milano, IT) Objective: To evaluate whether transcutaneous direct current (DC) stimulation can modulate the function of the human spinal cord, we studied the after-effects of anodal, cathodal and sham transcutaneous spinal DC stimulation (tsDCS) delivered over the human thoracic spinal cord on the somatosensory evoked potentials (SEPs). Methods: tsDCS was delivered over the thoracic spinal cord (2.5 mA, 15 min.) in eleven healthy subjects. SEPs evoked by posterior tibial and by median nerve stimulation were recorded, before tsDCS and after tsDCS offset. Results: anodal tsDCS stimulation decreased significantly (44,3 6 8,7%; p 5 0,005) the amplitude of the cervico-medullary component of posterior tibial nerve SEPs (P30). Anodal tsDCS left median nerve SEPs unchanged. Sham and cathodal tsDCS failed to change the SEPs. Conclusions: tsDCS induces prolonged and focal changes of conduction along the human lemniscal pathway at spinal cord level. Our finding prompts to assess whether tsDCS can be an alternative to invasive spinal cord stimulation in patients.