Safety study of high-frequency transcranial magnetic stimulation in patients with chronic stroke.

OBJECTIVE: Repetitive transcranial magnetic stimulation (rTMS) is a potential therapeutic tool to rehabilitate chronic stroke patients. In this study, the safety of high-frequency rTMS in stroke was investigated (Phase I). METHODS: The safety of 20 and 25 Hz rTMS over the motor cortex (MC) of the affected hemisphere, with intensities of 110-130% of the motor threshold (MT), was evaluated using surface electromyography (EMG) of hand and arm muscles. RESULTS: Brief EMG bursts, possibly representing peripheral manifestations of after discharges, and spread of excitation to proximal muscles are considered to be associated with a high risk of seizure occurrence. These events were recorded after the rTMS trains. Neither increased MC excitability nor improved pinch force dynamometry was found after rTMS. CONCLUSIONS: Stimulation parameters for rTMS, which are safe for healthy volunteers, may lead to a higher risk for seizure occurrence in chronic stroke patients. SIGNIFICANCE: rTMS at rates of 20 and 25 Hz using above threshold stimulation potentially increases the risk of seizures in patients with chronic stroke.

BOLD fMRI response to direct stimulation (transcranial magnetic stimulation) of the motor cortex shows no decline with age.

Previous studies using BOLD fMRI to examine age-related changes in cortical activation used tasks that relied on peripheral systems to activate the brain. They were unable to distinguish between alterations due to age-related changes in the periphery and actual changes in cortical physiology. Transcranial magnetic stimulation (TMS), which allows direct, noninvasive stimulation of cortical neurons, was interleaved with BOLD fMRI to study 6 young and 5 old subjects. Three different tasks were compared: direct stimulation by TMS, indirect active stimulation produced by a motor task, and indirect passive stimulation produced by hearing the TMS coil discharge. Direct neuronal stimulation by TMS produced similar fMRI signal increases in both groups, suggesting that cortical physiology itself may not necessarily decline with age.

Feasibility of vagus nerve stimulation-synchronized blood oxygenation level-dependent functional MRI.

RATIONALE AND OBJECTIVES: Left cervical vagus nerve stimulation (VNS) by use of an implanted neurocybernetic prosthesis (NCP) system is effective in treating epilepsy, with open data suggesting effectiveness in depression, yet the mechanisms of action are unknown. Our objective was to develop a methodology for performing VNS-synchronized functional magnetic resonance imaging (VNS-fMRI) and then to demonstrate its feasibility for studying VNS effects. METHODS: In nine patients implanted for treatment of intractable depression, a Macintosh computer was used to detect the signal from the implanted VNS stimulator and then to synchronize fMRI image acquisition with its regular firing. RESULTS: With our VNS-fMRI methodology, the blood oxygenation level-dependent response to VNS was shown in brain regions regulated by the vagus nerve: orbitofrontal and parieto-occipital cortex bilaterally, left temporal cortex, the hypothalamus, and the left amygdala. CONCLUSIONS: Vagus nerve stimulation pulses from an NCP system can be detected externally to determine its firing pattern, thus allowing VNS-fMRI studies of VNS-induced brain activity.

A low-cost system for monitoring skin conductance during functional MRI.

We built a low-cost system for monitoring human skin conductance responses (SCRs) in a clinical magnetic resonance (MR) scanner during functional imaging. The average scanner-induced conductance noise level was suppressed sufficiently to allow SCR measurements over the full range of SCR amplitudes, and functional image signal-to-noise ratio was unaffected by the skin conductance apparatus. The system may be useful for a variety of imaging studies.

BOLD-f MRI response to single-pulse transcranial magnetic stimulation (TMS).

Five healthy volunteers were studied using interleaved transcranial magnetic stimulation/functional magnetic resonance imaging (TMS/fMRI) and an averaged single trial (AST) protocol. Blood oxygenation level-dependent (BOLD)-fMRI response to single TMS pulses over the motor cortex was detectable in both the ipsilateral motor cortex under the TMS coil and the contralateral motor cortex, as well as bilaterally in the auditory cortex. The associated BOLD signal increase showed the typical fMRI hemodynamic response time course. The brain's response to a single TMS pulse over the motor cortex at 120% of the level required to induce thumb movement (1.0%-1.5% signal increase) was comparable in both level and duration to the auditory cortex response to the sound accompanying the TMS pulse (1.5% -2.0% signal increase).

[Transcranial magnetic stimulation in neurotic depression]. / Transkranial'naia magnitnaia stimuliatsiia pri nevroticheskoi depressii.

Transcranial magnetic stimulation (TMS) was applied in combination with psychotherapy in patients with neurotic depression, including 15 patients of the experimental group and 14 patients of the control one. 10 sessions of daily TMS for the patients from the experimental group (0.015 T, 40 pulses per sec) were performed at the same time for 20 min (twice for 10 min with 5-min interval) in a room which excluded any external stimulation. TMS was performed by contact method: 5 cm coil was applied to the left prefrontal area. The control group received the imitation of TMS-procedure stimulation. The improvement of mental state was in 13 patients of experimental group and in 3 of control one. The course of TMS resulted in a significant attenuation of depression by the Hamilton Depression Rating scale (from 22.9 to 8.6) and the Anxiety Inventory (from 39.4 to 26.6), that was significantly higher in comparison with the control. There weren't found any TMS-related changes in blood pressure and pulse rate as well as any pathological EEG symptoms.

[Conditioned reactions elaborated on the basis of reinforcement by hypothalamic stimulation]. / Osobennosti uslovnykh reaktsii, vyrabotannykh na osnove podkrepleniia razdrazheniem gipotalamusa.

The possibility of elaboration of conditioned emotional reactions on the basis of the stimulation of the hypothalamus, was studied in cats. Reinforcement of a sound (500 c/s) by electrical stimulation of the hypothalamus, which produced reactions of undirected rage, of fear with avoidance, of food search, led to the formation of a conditioned passive defensive reaction, analogous to that based on pain reinforcement. Elaboration of conditioned emotional reactions were blocked by switching off of the sensorimotor cortex by cold. A conclusion is made that during stimulation of the hypothalamus, the state of fear serves as the reinforcing factor and that the sensorimotor neocortical areas participate in the estimation of biological significance of the conditioned signal.

[Role of the frontal cortex in organizing emotional-behavioral reactions induced by hypothalamic stimulation and natural stimuli]. / Rol' frontal'noi kory v organizatsii émotsional'no-povedencheskikh reaktsii, vyzyvaemykh stimuliatsiei gipotalamusa i natural'nymi razdrazhiteliami.

Study of the effects of a functional switching off the sensorimotor neocortex area in cats by means of cooling reveals its inhibitory influence on emotional-behavioral reactions to hypothalamic stimulation. Multiple (up to 12) switchings off of the frontal neocortex are attended with a gradual compensation of its inhibitory function by the activity of other brain structures. On the other hand inactivation of the sensorimotor cortex reduces the ability of natural provoking stimuli to lower the thresholds of goal-directed rage which develops when these stimuli are combined with an electrical stimulation of the hypothalamus. A conclusion has been made on the participation of the frontal neocortex in the systemic organization of estimation of biologically significant stimuli.