The safety of transcranial magnetic stimulation with deep brain stimulation instruments

Objectives: Transcranial magnetic stimulation (TMS) has been employed in patients with an implanted deep brain Stimulation (DBS) device. We investigated the safety of TMS using Simulation models with an implanted DBS device. Methods: The DBS lead was inserted into plastic phantoms filled with dilute gelatin showing impedance similar to that of human brain. TMS was performed with three different types of magnetic coil. During TMS (I) electrode movement, (2) temperature change around the lead, and (3) TMS-induced current in various Situations were observed. The amplitude and area of each evoked current were measured to calculate charge density of the evoked current. Results: There was no movement or temperature increase during 0.2 Hz repetitive TMS with 100% stimulus intensity for 1 h. The size of evoked current linearly increased with TMS intensity. The maximum charge density exceeded the safety limit of 30 mu C/cm(2)/phase during Stimulation above the loops of the lead with intensity over 50% using a figure-eight coil. Conclusions: Strong TMS on the looped DBS leads should not be administered to avoid electrical tissue injury. Subcutaneous lead position should be paid enough attention for forthcoming Situations during surgery.ArticlePARKINSONISM & RELATED DISORDERS. 16(2):127-131 (2010)journal articl

Echoic memory: investigation of its temporal resolution by auditory offset cortical responses.

Previous studies showed that the amplitude and latency of the auditory offset cortical response depended on the history of the sound, which implicated the involvement of echoic memory in shaping a response. When a brief sound was repeated, the latency of the offset response depended precisely on the frequency of the repeat, indicating that the brain recognized the timing of the offset by using information on the repeat frequency stored in memory. In the present study, we investigated the temporal resolution of sensory storage by measuring auditory offset responses with magnetoencephalography (MEG). The offset of a train of clicks for 1 s elicited a clear magnetic response at approximately 60 ms (Off-P50m). The latency of Off-P50m depended on the inter-stimulus interval (ISI) of the click train, which was the longest at 40 ms (25 Hz) and became shorter with shorter ISIs (2.5∼20 ms). The correlation coefficient r2 for the peak latency and ISI was as high as 0.99, which suggested that sensory storage for the stimulation frequency accurately determined the Off-P50m latency. Statistical analysis revealed that the latency of all pairs, except for that between 200 and 400 Hz, was significantly different, indicating the very high temporal resolution of sensory storage at approximately 5 ms

Anterior horn damage in brachial multisegmental amyotrophy with superficial siderosis and dural tear: an autopsy case report

Abstract Background Patients with superficial siderosis (SS) rarely show brachial multisegmental amyotrophy with ventral intraspinal fluid collection accompanied with dural tear. Case presentation We describe spinal cord pathology of a 58-year-old man who developed brachial multisegmental amyotrophy with ventral intraspinal fluid collection from the cervical to lumbar spinal levels accompanied with SS, dural tear, and snake-eyes appearance on magnetic resonance imaging (MRI). Radiological and pathological analyses detected diffuse and prominent superficial deposition of hemosiderin in the central nervous system. Snake-eyes appearance on MRI expanded from the C3 to C7 spinal levels without apparent cervical canal stenosis. Pathologically, severe neuronal loss at both anterior horns and intermediate zone was expanded from the upper cervical (C3) to middle thoracic (Th5) spinal gray matter, and these findings were similar to compressive myelopathy. Conclusion Extensive damage of the anterior horns in our patient may be due to dynamic compression induced by ventral intraspinal fluid collection

Relationship between the Off-P50m latency and stimulus frequency.

<p>(A) The Off-P50m latency as a function of the ISI of the click train. The right column shows the latency difference of Off-P50m for each click sound relative to that for the 25-Hz train. Dotted lines indicate theoretical values. (B) Schematic illustration of the relationship between the latency of Off-P50m and ISI. Note that the delay in P50m latency reflects the click interval and the difference calculated by subtracting ISI from the P50m latency for each click is constant (right column).</p

Effects of the click frequency on the latency of Off-P50m.

<p>(A) Data from a representative subject. Equivalent current dipoles (ECDs) of the subject were superimposed on the subject’s own brain MR images. (B) Source strength as a function of time for the 200 Hz click train. (C) The off- and on-responses for 25 to 400 Hz click trains. The time course of each dipole is shown in the same color to that for the dipole location.</p

Grand-averaged source strength waveforms.

<p>(A) Grand-averaged waveforms for each click train obtained from seven subjects. The off-response was enclosed by gray lines. (B) Note that the peak latency of Off-P50m was delayed in parallel with the stimulus frequency.</p