F. Pedace

Effects of repetitive cortical stimulation on the silent period evoked by magnetic stimulation

Abstract The effects of repetitive transcranial stimulation (rTMS) on brain activity remain unknown. In healthy subjects, we studied the effects of rTMS on the duration of the cortical silent period (SP). Repetitive stimuli were delivered with a Cadwell High Speed Magnetic Stimulator and a figure-of-eight coil placed over the hand motor area. rTMS was delivered in trains of 11 or 20 stimuli at frequencies of 3 and 5 Hz and at stimulation intensities of 110 and 120% of motor threshold. The SP was recorded from the forearm muscles during a voluntary contraction (20% of maximum effort). rTMS delivered at a frequency of 3 and 5 Hz and intensities of 110 and 120% motor threshold prolonged the duration of the SP, without modifying either the size or the latency of the muscle-evoked potentials (MEP). A conditioning train of 11 stimuli at 3 Hz had no effect on the duration of the SP evoked by a single magnetic shock delivered 600 ms after the train. These findings show that rTMS increases the duration of the cortical SP, but does so only during the train of stimuli. rTMS probably changes the duration of the SP by facilitating cortical inhibitory interneurons.

Cortical excitability in patients with essential tremor

We used transcranial magnetic stimulation in 10 patients with essential tremor and 8 matched healthy subjects. A round stimulating coil was placed over the vertex and electromyographic activity was recorded from the first dorsal interosseous muscle. Paired transcranial stimuli were delivered at interstimulus intervals of 3, 5, 20, 100, 150, and 200 ms. The intensity of the conditioning stimulus was 80% of motor threshold at short and 150% at long interstimulus intervals (ISIs). We also measured the silent period obtained after a single magnetic pulse delivered at 150% of motor threshold during a submaximal muscle contraction. Patients and controls had similar motor threshold and similar latencies. Paired magnetic stimuli given at short and long ISIs at rest, and during a voluntary muscle contraction, elicited similar responses in both groups. The silent period evoked by transcranial magnetic stimulation had a similar duration in patients with ET and controls. In conclusion, these findings suggest that patients with essential tremor have normal cortical motor area excitability.

Bladder filling inhibits somatic spinal motoneurones

OBJECTIVES Despite evidence that the activation of visceral afferents modulates spinal motoneurone activity in humans the responsible circuits remain unclear. We investigated changes in spinal motoneurone excitability during bladder filling in 8 healthy subjects and in 8 patients with spinal cord lesions and 5 patients with multi-infarct encephalopathy. METHODS Spinal motoneurone excitability was studied by analysing changes in H-reflex, F-wave and motor-evoked potential (MEP) size recorded from the calf muscles under different bladder filling conditions. RESULT In normal subjects, maximal bladder filling significantly suppressed the H-reflex, F-wave and MEPs; after bladder voiding these responses returned to normal. In patients with encephalopathy maximal bladder filling strongly reduced H-reflex size; similarly to normal subjects H-reflex returned to control value after bladder voiding. In patients with spinal cord lesions, activation of bladder afferents left the H-reflex unchanged. CONCLUSIONS These findings indicate that bladder distension induces post-synaptic inhibition of spinal motoneurones through a suprasegmental pathway, which is interrupted by rostral spinal cord lesions. This vesical-induced inhibition is probably mediated by the propriospinal system rather than by the diffuse noxious inhibitory control circuit.

Ia presynaptic inhibition after muscle twitch in the arm

Contraction of upper limb muscles in healthy subjects was used to investigate presynaptic inhibition at spinal level. The H reflex recorded in the forearm flexor muscles in response to median nerve stimulation was depressed in amplitude from 400 ms to 1 s after a muscle twitch induced by transcranial stimulation, root stimulation, direct biceps stimulation, and triceps tendon tap. Stimulation of the cutaneous branch of musculocutaneous nerve, ipsilateral triceps and contralateral biceps, and biceps tendon tap did not alter H‐reflex size. Forearm flexor H‐reflex amplitude is therefore related to changes in proprioceptive inflow secondary to the biceps muscle twitch. Root and direct muscle stimulation both failed to reduce the size of the motor evoked potential (MEP) after transcranial magnetic stimulation, suggesting that the inhibition acts at presynaptic level. Attenuation of H‐reflex amplitude was related to the size of the muscle twitch and was less pronounced during an isometric twitch than during free joint movement. Our results suggest that the biceps muscle twitch produces long‐lasting inhibition of the Ia afferents from forearm flexor muscles. This is an important and a simple mechanism for suppressing proprioceptive input during movement.

Spinal Nerves Schwannomas: Experience on 367 Cases—Historic Overview on How Clinical, Radiological, and Surgical Practices Have Changed over a Course of 60 Years

Background Spinal schwannomas are common benign spinal tumors. Their treatment has significantly evolved over the years, and preserving neurological functions has become one of the main treatment goals together with tumor resection. Study Design and Aims Retrospective review focused on clinical assessment, treatment techniques, and outcomes. Methods A retrospective study on our surgical series was performed. Clinical and operative data were analyzed. In regard to neurophysiologic monitoring, patients were retrospectively divided into two groups comparing the outcomes before and after introduction of routine intraoperative neurophysiology tests. Results From 1951 to 2010, 367 patients overall were treated. Diagnosis was obtained using angiography and/or myelography (pre-CT era), MRI, or CT scan. A posterior spinal approach was used for most patients; complex approaches were adopted for treatment of giant/dumbbell tumors. A trend of neurophysiology monitoring decreasing the rate of post-op neurological deficits was observed but was not statistically significant enough to draft evidence-based conclusions. Conclusions Clinical and radiological assessment of spinal schwannomas has markedly changed over the course of 50 years. Diagnostic tools have improved, and detection of recurrence has become way more sensitive. Neurophysiologic monitoring has become a useful intraoperative tool to guide resection and prevent post-op neurological impairment.

Hemiballism caused by a premotor cortex glioma

Ballism consists of violent flinging limb movements due to nvoluntary, arrhythmic proximal muscles contractions, usually nvolving only upper extremities of one side of the body (hemibalism). The arm is thrown into space and projected forward and ideways with flexion and rotation on its axis. Like the chorea, the emiballism generates phasic discharges and short synchronous otor unit potentials in the agonist muscles without activation of he antagonists. It is generally caused by injuries to the subthalamic ucleus of Luys or, more extensively, to the basal ganglia such as schemic or hemorrhagic infarctions, diencephalic tumors, inflamations and metabolic paraneoplastic syndromes [1]. Hemiballism esponds in part to neuroleptics. Primary or secondary cortical or subcortical brain tumors usully provoke seizures, focal neurological deficits, higher functions mpairments, or headache [2]. Cortical masses responsible for xtrapyramidal symptoms are not known in the literature. Rarely, arge intracranial lesions may cause movement disorders through mechanism of direct mechanical compression or torsion of the asal ganglia [1,2]. Two cases of small convexity meningiomas just bove the pre-motor cortex causing tremors which disappeared fter tumor removal have been reported [3].