S. Nakatani-Enomoto

Postural tremor in X-linked spinal and bulbar muscular atrophy†

Postural tremor is a common initial symptom in spinal and bulbar muscular atrophy (SBMA), but its pathophysiological mechanisms remain to be studied. This study was undertaken to examine the physiological mechanisms underlying postural tremor in SBMA. For eight patients (36–63 years old) with genetically confirmed SBMA, we recorded surface electromyograms (EMGs) from the forearm muscles and hand movements with an accelerometer (ACC) while maintaining a posture with and without a weight load. We then analyzed their power spectra and coherence. The peak tremor frequency was 6–9 Hz in seven patients and 2–3 Hz in one patient. Oscillatory movements were associated with EMG activity in five patients, but not in three patients. Weight loads and postural changes affected the tremor frequency in all patients. Tremor was classified as “reflex tremor” in five patients and “mechanical tremor” in three patients. These results suggest that peripheral factors play important roles in tremor genesis in SBMA, although its clinical features resemble essential tremor. Subclinical sensory disturbance or a decrease of motor unit numbers might be candidates for such peripheral factors contributing to tremor genesis in SBMA.

Short-interval intracortical inhibition in Parkinson’s disease using anterior-posterior directed currents

Reduced short-interval intracortical inhibition (SICI) is reported in Parkinson’s disease (PD) and is considered to reflect abnormal GABAergic inhibitory system of the primary motor cortex in PD. We have recently shown, however, that SICI using anterior-posterior directed currents in the brain was normal in focal dystonia even though that using posterior-anterior currents was abnormal, indicating that the GABAergic system of the primary motor cortex is largely normal in dystonia. Here, we studied SICI in PD to clarify whether the GABAergic system is completely impaired in PD. We used paired-pulse transcranial magnetic stimulation to study SICI at interstimulus intervals of 3 and 4xa0ms with anterior-posterior or posterior-anterior directed currents in eight PD patients and ten healthy volunteers. The amount of SICI with posterior-anterior directed currents was reduced in PD patients compared with healthy volunteers; in contrast, SICI studied with anterior-posterior directed currents was normal in PD patients. These observations may be due to the difference in I-wave composition generated by the two directed currents and/or the difference in responsible inhibitory interneurons for the inhibition between the two current directions. We suggest that some or a part of inhibitory interneurons are not involved in PD. This discrepancy between SICI using posterior-anterior and anterior-posterior directed currents experiments may provide additional information about the circuits of the motor cortex.

Triad stimulation frequency for cortical facilitation in cortical myoclonus

Abnormally enhanced cortical rhythmic activities have been reported in patients with cortical myoclonus. We recently reported a new triad‐conditioning transcranial magnetic stimulation (TMS) method to detect the intrinsic rhythms of the primary motor cortex (M1). Triad‐conditioning TMS revealed a 40‐Hz intrinsic rhythm of M1 in normal subjects. In this investigation, we study the motor cortical facilitation induced by rhythmic triple TMS pulses (triad‐conditioning TMS) in patients with cortical myoclonus.

Forty-hertz triple-pulse stimulation induces motor cortical facilitation in humans

A single pulse of transcranial magnetic stimulation (TMS) can reset the 15- to 30-Hz beta-band oscillations in the motor cortex. These oscillations are known to influence the amplitude of corticospinal activity evoked by TMS. To garner further evidence for this resetting, we tested how electromyographic responses to motor cortex TMS were modulated by a preceding series of TMS pulses. We used a triad of conditioning TMS pulses at various interstimulus intervals (ISIs) in an attempt to drive cortical activity at the corresponding frequency. We then analyzed how the amplitude of motor-evoked potentials (MEPs) to a test pulse varied at different intervals after the conditioning triad. When conditioning pulses were given at an ISI of 25 ms, responses to the fourth (test) pulse were facilitated 25 ms later. Neither a single conditioning pulse nor triad of conditioning pulses separated by other ISIs enhanced responses to the test pulse at the expected timings. Triads of pulses at an ISI of 25 ms did not enhance subsequent MEPs to brainstem stimulation. Based on the intensity of the conditioning stimuli necessary to produce this effect and on the effective interval, we conclude that the facilitation at 25 ms differs from intracortical facilitation at 7-10 ms seen in the paired-pulse experiment originally reported by Kujirai et al. These results suggest that a triad of TMS pulses can enhance an intrinsic oscillatory rhythm of the motor cortex (40 Hz) and facilitate cortical activity at an ISI corresponding to the frequency of that rhythm.

Somatosensory-evoked potential modulation by quadripulse transcranial magnetic stimulation in patients with benign myoclonus epilepsy

OBJECTIVEnIn patients with benign myoclonus epilepsy (ME), giant sensory-evoked potential (SEP) reflects the hyperexcitability of the sensory cortex. The aim of this study was to compare the effect of quadripulse transcranial magnetic stimulation (QPS) on the median nerve SEP between ME patients and healthy subjects.nnnMETHODSnTen healthy volunteers and six ME patients with giant SEP participated in this study. QPSs at interpulse intervals (IPIs) of 5, 30, 50, 100, 500 and 1250 ms were applied over the left primary motor cortex (M1) for 30 min. The peak-to-peak amplitudes of N20 to P25 (N20-P25) and P25 to N33 (P25-N33) components were measured at the left somatosensory cortex.nnnRESULTSnIn healthy participants, the P25-N33 was bidirectionally modulated by QPS over M1, following the Bienenstock-Cooper-Munro (BCM) theory. The N20-P25 was not affected by any QPSs. In ME patients, the giant P25-N33 was potentiated after any QPSs. Furthermore, the N20-P25 was also potentiated after QPS at IPIs of 5, 30, 50 100 or 500 ms.nnnCONCLUSIONSnIn ME patients, the cascade for long-term depression-like effects may be impaired.nnnSIGNIFICANCEnThe giant SEP was furthermore enhanced by QPS.

Motor cortical epilepsia partialis continua in a patient with a localized sensory cortical lesion.

We describe a 33-year-old man with cyclosporine encephalopathy who showed continuous jerking in the left upper limb due to epilepsia partialis continua. Jerk-locked back averaging (JLA) of magnetoencephalogram disclosed a spike preceding the jerk localized at the hand motor area, whereas JLA of electroencephalogram revealed no premyoclonus spikes. The paired-pulse motor cortical transcranial magnetic stimulation revealed motor cortical hyperexcitability, while the paired-pulse somatosensory evoked potential showed no sensory cortical hyperexcitability. The brain MRI showed a high intensity lesion localized at the hand sensory area. These results suggest that the jerks were produced by discharges at the motor cortex probably disinhibited by the sensory cortical lesion.

O34: Short latency inputs from ventral premotor cortex to the primary motor cortex in healthy humans

s of Oral Presentations / Clinical Neurophysiology 125, Supplement 1 (2014) S1–S339 S39 We studied 10 DS, non epileptic patients (5 females and 5 males, mean age 24.5) and compared them with 10 age and sex-matched healthy individuals. In each individual we recorded resting motor threshold (RMT) of the APB as a measure of CE; ICI-ICF at 3, 5, 10 and 15 ms of interstimulus interval; and I-wave from 1.0 to 3.4 ms of interstimulus interval with increases of 0.2 ms. There were no significant differences in CE between the two groups. DS patients showed a statistically significant increase of facilitation in the ICI-ICF protocol both at 10 and 15 ms interval (Fig. 1). Concordantly they also showed a statistically significant increase of I-wave peaks almost at all intervals. Our results show that patients with DS present an increased intracortical facilitation that may be due either to the lack of inhibition through the GABAergic system, and/or to an incremented Glutamatergic interneuronal output. Unexpectedly these results point at a very different conclusion than that attained by animal models. Our study might suggest a malfunction of the GABAergic system since our results are similar to those reported in patients with a GABAA receptor mutation. Nonetheless further investigation is needed to solve this issue.

P224: Cauda equina conduction time in GBS, CIDP, and MMN

Introduction: To investigate the conductions of proximal and distal parts of peripheral nerves in Guillain-Barré syndrome (GBS), chronic inflammatory demyelinating polyradiculoneuropathy (CIDP), and multifocal motor neuropathy (MMN), we measured cauda equina conduction time (CECT) and motor conduction velocity (MCV). Methods: Patients were 12 GBS (8 axonal and 4 demyelinating types), 14 CIDP, and 5 MMN patients. Compound muscle action potentials (CMAPs) were recorded from the abductor hallucis muscle. To measure MCV, electrical stimulation was conducted. To obtain CECT, magnetic stimulation was performed using a MATS coil (magnetic augmented translumbosacral stimulation coil). Results: CECT was normal in all axonal GBS patients but prolonged in all demyelinating GBS patients, whereas MCV was normal in all GBS patients. CECT was prolonged in 12 CIDP patients (85.7%), whereas MCV was delayed in 5 CIDP patients (35.7%). Both CECT and MCV were normal in all MMN patients. Conclusions: CECT is frequently prolonged in demyelinating GBS and CIDP, whereas it is usually normal in axonal GBS and MMN. MATS coil stimulation method can detect the conduction delay of cauda equina in some types of demyelinating polyneuropathy.

PTMS52 Normal SICI in Parkinson's disease: SICI using anterior posterior directed induced currents in the brain

phosphocholine [PCho] + glycerophosphocholine [GPC]) were measured bilaterally in primary sensorimotor cortex, lentiform nucleus, and the occipital region before and after 5 Hz TMS over the dominant motor cortex. Sixteen patients with upper limb primary dystonia were studied and compared to healthy volunteers. Results: At baseline, in patients with writer’s cramp, there was a higher GABA concentration bilaterally in the motor cortex as compared with controls. In controls but not patients, 5 Hz TMS over the left motor cortex induced an in situ-change in metabolite concentrations that depended on baseline concentration levels; i.e., increase for lower baseline levels and decrease for higher. Effects in basal ganglia were less consistent. Greater concentration decreases in NAA, mIns, and tCho were observed in the motor cortex of the patients after TMS. Conclusion: Together with previous results, our study points to a dysfunction of the GABAergic inhibitory system in dystonia. TMS-induced changes of NAA, mIns and tCho are interpreted in view of the maladaptive plasticity and abnormal membrane-related protein previously suggested in dystonia.

S17.5 Large click sounds influence near infrared spectroscopy (NIRS)

in healthy adults has been shown to modulate the attention towards threatening information, associated with decreased activation within the right DLPFC and increased activation in the right amygdala. Interestingly, as compared to the effects of HF-rTMS to the right DLPFC, it has been shown that healthy individuals with higher levels of anxiety portray similar dysfunctional attentional control and cortico-subcortical activation patterns. Objectives: The aim of this study in healthy volunteers was to investigate whether inter-individual differences in anxiety levels prior to the administration of HF-rTMS to the right DLPFC predicted dysfunctional attentional focus towards threatening information. Methods: We administered HF-rTMS to the right DLPFC to a group of 28 healthy female individuals. We measured mood and cognitive functioning before and after a SHAM controlled rTMS session. Results: As expected, a single session of HF-rTMS of the right DLPFC did not have an effect on mood but modified the attentional focus towards threatening information. Moreover, self-report measures of state anxiety (STAI-State) prior to stimulation correlated positively with the magnitude of the induced attentional bias. Specifically, we found that healthy individuals who scored higher on self-reports of state anxiety acquired more attentional focus towards threatening information after HF-rTMS. Conclusions: These findings have some important theoretical and clinical implications. Dysfunctional attentional control for threatening information and related decreased activation in the prefrontal cortex appear to be crucial underlying working mechanisms in the etiology of increased anxiety. Therefore, these findings might be especially germane in light of the existing therapeutic applications of multiple sessions of rTMS as a treatment for anxiety disorders.