Is the stimulation frequency of the repetitive nerve stimulation test that you choose appropriate?

The repetitive nerve stimulation test (RNST) has been a useful method in the diagnosis of myasthenia gravis (MG). In clinical practice, a short train of repetitive stimulation is usually given at 3 Hz. Although it was documented that lower stimulation frequencies could offer a greater sensitivity, no study has been done to testify the most sensitive stimulation frequency for RNST. To find out an optimal stimulation frequency, we performed RNST at 0.5, 1, 3, 5, 7, 10, 15 and 20 Hz in 15 MG patients and 5 healthy subjects. The results showed that the decremental response was most often seen at 7 Hz rather than at 3 Hz. To augment the sensitivity in the diagnosis of MG, RNST should be performed stimulation not only at 3Hz but also at other frequencies, preferably 7 Hz.     

Effects of repetitive facilitative exercise with neuromuscular electrical stimulation,vibratory stimulation and repetitive transcranial magnetic stimulation of the hemiplegic hand in chronic stroke patients

Aim: Repetitive facilitative exercise (RFE) is a developed approach to the rehabilitation of hemiplegia. RFE can be integrated with neuromuscular electrical stimulation (NMES), direct application of vibratory stimulation (DAVS) and repetitive transcranial magnetic stimulation (rTMS). The aims of the present study were to retrospectively compare the effects of RFE and NMES, DAVS with those of RFE and rTMS, and to determine the maximal effect of the combination of RFE with NMES, DAVS, rTMS and pharmacological treatments in stroke patients. Subjects and methods: Thirty-three stroke patients were enrolled and divided into three groups: 15 who received RFE with rTMS (4 min) (TMS₄ alone), 9 who received RFE with NMES, DAVS (NMES, DAVS alone) and 9 who received RFE with NMES, DAVS and rTMS (10 min) (rTMS₁₀ + NMES, DAVS). The subjects performed the Fugl-Meyer Assessment (FMA) and Action Research Arm Test (ARAT) before and after the 2-week session. The 18 patients in the NMES, DAVS alone and rTMS₁₀ + NMES, DAVS group underwent the intervention for 4 weeks. Result: There were no significant differences in the increases in the FMA, ARAT scores in the three groups. The FMA or ARAT scores in the NMES, DAVS alone and the rTMS₁₀ + NMES, DAVS group were increased significantly. The FMA and ARAT scores were significantly improved after 4 weeks in the NMES, DAVS alone group. Discussion: RFE with NMES, DAVS may be more effective than RFE with rTMS for the recovery of upper-limb function. Patients who received RFE with NMES, DAVS and pharmacological treatments showed significant functional recovery.     

“Slinky” coils for neuromagnetic stimulation

Future advances in neuromagnetic stimulation depend significantly on the design of coils with improved focality. Although in the absence of internal current sources, no true focusing of magnetically induced currents is possible, improvements in the focality of current concentrations passing through an area of biologic tissue are achievable through variations of the shape, orientation and size of neuromagnetic stimulating coils. The “butterfly” and the “4-leaf” coils are two examples of planar designs which achieve improved focality through centralization of the maximum coil current and peripheral distribution of the return currents. We introduce the “slinky” coil design as a 3-dimensional generalization of the principle of peripheral distribution of return currents and demonstrate its advantages over planar designs.     

Subthalamic nucleus stimulation in Parkinson’s disease

OBJECTIVES: 1 - To assess the anatomical localization of the active contacts of deep brain stimulation targeted to the subthalamic nucleus (STN) in Parkinson's disease patients. 2 - To analyze the stereotactic spatial distribution of the active contacts in relation to the dorsal and the ventral electrophysiologically-defined borders of the STN and the stereotactic theoretical target. METHODS : Twenty-eight patients underwent bilateral high-frequency stimulation of the STN (HFS-STN). An indirect anatomical method based on ventriculography coupled to electrophysiological techniques were used to localize the STN. Clinical improvement was evaluated by Unified Parkinson's Disease Rating Scale motor score (UPDRS III). The normalized stereotactic coordinates of the active contact centres, dorsal and ventral electrophysiologically-defined borders of the STN were obtained from intraoperative X-rays images. These coordinates were represented in a three-dimensional stereotactic space and in the digitalized atlas of the human basal ganglia. RESULTS: HFS-STN resulted in significant improvement of motor function (62.8%) in off-medication state and levodopa-equivalent dose reduction of 68.7% (p < 0.05). Most of the active contacts (78.6%) were situated close to (+/- 1.6 mm) the dorsal border of the STN (STN-DB), while 16% were dorsal and 5.4% were ventral to it. Similar distribution was observed in the atlas. The euclidean distance between the STN-DB distribution center and the active contacts distribution center was 0.31 mm, while the distance between the active contacts distribution center and the stereotactic theoretical target was 2.15 mm. Most of the space defined by the active contacts distribution (53%) was inside that defined by the STN-DB distribution. CONCLUSION: In our series, most of the active electrodes were situated near the STN-DB. This suggests that HFS-STN could influence not only STN but also the dorsal adjacent structures (zona incerta and/or Fields of Forel).     

Therapeutic electrical stimulation. The transistorized placebo?

(1) Electrical stimulation therapy for patients suffering with labile signs and symptoms, and these include all varieties of acute and chronic pains, seizures and spasticity, has come into fashion and gone, and come again with each new technological advance for the past two hundred years. (2) A proportion of patients with chronic disease have their suffering made worse if they feel deprived of the latest therapy and may be relieved if they are given it in the right circumstances. In this group the relief will usually be temporary and the limited supply of such reactors will promote the cycle of fashion. In a group of 126 patients with chronic pain associated with organic disease who were offered transcutaneous stimulation, only 23 (18%) continued to use it one year after they started. (3) The cycling of therapeutic fashion is assisted not only because relief is often temporary, but also by the difficulty in establishing the normal range of variability from which significant change can be assessed and by the uncertain relationship between signs and symptoms and for the functions of daily living. For these reasons there is an inevitable tendency to temporary over-optimism and it seems impossible to counter this by the execution of a satisfactory clinical trial, since the patient cannot be "blind" and a significant variable is the enthusiasm with which a therapy is surrounded. (4) Electrical stimulation by cutaneous devices or implants can give much benefit to some patients in whom other methods have failed and there are indications, not only from anecdote and clinical impression but also now from experimental physiology, that it may benefit by mechanisms of interaction at the first sensory synapse. It is, however, an over-simplification to regard any therapy as either strictly physiological or simply fraudulent. Like other so-called placebos, physical methods of therapy can presumably act on hormonal systems associated with stress and the experience of pain.     

Vagus nerve stimulation: where are we?

Now nearly 5 years post-approval, vagus nerve stimulation has emerged as a major non-pharmacological treatment for epilepsy. The place of vagus nerve stimulation among antiepileptic drugs and other surgical therapies is still evolving. This review evaluates the role of vagus nerve stimulation in light of recently published research of its mechanism(s) of action, long-term efficacy, safety and tolerability, and application to other disorders besides epilepsy.     

Deep brain stimulation in Parkinson’s disease

Throughout the past decade, there has been a marked increase in surgical therapies, primarily deep brain stimulation (DBS), for the treatment of advanced Parkinson’s disease (PD). DBS of the thalamus has been shown to be effective in reducing parkinsonian tremor; however, it is not the treatment of choice for PD given the progression of other symptoms such as rigidity and bradykinesia. Stimulation of the globus pallidus or the subthalamic nucleus is safe and efficacious in the long-term treatment of all cardinal symptoms of PD, and they are currently the surgeries of choice. Serious adverse events with DBS can occur in 1% to 2% of patients, infection in 5% to 8% of patients, and hardware complications in approximately 25% of patients. Complications associated with DBS are related to the experience of the surgical center. Referring physicians and patients should be aware of the number of surgical procedures and complication rates of any prospective surgical center.     

Multi-locus transcranial magnetic stimulation—theory and implementation

Background

Transcranial magnetic stimulation (TMS) is a non-invasive brain stimulation method: a magnetic field pulse from a TMS coil can excite neurons in a desired location of the cortex. Conventional TMS coils cause focal stimulation underneath the coil centre; to change the location of the stimulated spot, the coil must be moved over the new target. This physical movement is inherently slow, which limits, for example, feedback-controlled stimulation.

Regional specificity of cathodal transcranial direct current stimulation effects on spatial–numerical associations: Comparison of four stimulation sites

Neuromodulation with transcranial direct current stimulation (tDCS) is an increasingly popular research tool to experimentally manipulate cortical areas and probe their causal involvements in behavior, but its replicability and regional specificity are not clear. This registered report investigated cathodal tDCS effects on spatial–numerical associations (i.e., the SNARC effect), the numerical distance effect (NDE), and inhibitory control (i.e., stop-signal reaction time; SSRT). Healthy adults (N = 160) were randomly assigned to one of five groups to receive sham tDCS or 1 mA cathodal tDCS to one of four stimulation sites (left/right prefrontal cortex [PFC], left/right posterior parietal cortex) with extracephalic return. We replicated that cathodal tDCS over the left PFC reduced the SNARC effect compared to sham tDCS and to tDCS over the left parietal cortex. However, neither NDE nor SSRT were modulated in the main analyses. Post hoc contrasts and exploratory analyses showed that cathodal tDCS over the right PFC had a time-dependent effect by delayed practice-related improvements in SSRT. Math anxiety moderated changes in the NDE in the groups receiving tDCS to the right parietal cortex. With few exceptions, the replicability and regional specificity of tDCS effects on behavior were weak and partially moderated by individual differences. Future research needs to characterize the parameter settings for effective neuromodulation.     

Transcranial magnetic stimulation downregulates β-adrenoreceptors in rat cortex

Summary Recently, a method for transcranial magnetic stimulation (TMS) of the brain has been developed. Thus, it is possible to explore neurochemical and behavioral effects of TMS in rats. Repeated TMS (9 days) reduced -adrenergic receptor binding in cortex, as does electroconvulsive shock (ECS) and other antidepressant treatments. Thus TMS appears to be a potential antidepressive treatment.     

Rapid rate transcranial magnetic stimulation – a safety study

We assessed the safety of repeated short trains (4 stimuli) of rapid-rate transcranial magnetic stimulation (rrTMS) over the left motor cortex in 6 healthy normal subjects. rrTMS involved two separate blocks of 50 consecutive trains of 4 stimuli at a frequency of 20 Hz and an intensity of 5–10% above active motor threshold. We monitored EEG, and assessed aspects of neurological (balance, gait, two-point discrimination, blood pressure, pulse rate), cognitive (attention, memory, executive function) and motor function (speed of movement initiation and execution and manual dexterity) before and after the two blocks of rrTMS. EMG was also recorded from a number of hand, forearm and arm muscles contralateral to the site of stimulation. Two blocks of repeated rrTMS at 20 Hz and 5–10% above active motor threshold did not produce any adverse effects. Measures of neurological, cognitive and motor function showed no change following rrTMS. From the EMG recording there was evidence of increase in the amplitude of the motor evoked potentials (MEPs) recorded from the biceps in one subject during the first block of rrTMS, but this did not occur in the second block. A similar magnification of MEPs was also observed in another subject only during the second block of stimulation. When applied using parameters falling within published guidelines (Pascual-Leone et al., 1993; Pascual-Leone et al., 1994), repeated rrTMS is a relatively safe technique in healthy normal subjects. As rrTMS allows disruption of cortical function for a longer period, it has the potential of becoming a particularly useful tool for the study of cognitive function as well as sensory or motor function.