Dose response of somatosensory cortex repeated anodal transcranial direct current stimulation on vibrotactile detection: a randomized sham-controlled trial.

This randomized sham-controlled trial investigated anodal transcranial direct current stimulation (tDCS) over the somatosensory cortex contralateral to hand dominance for dose-response (1 mA, 20 min × 5 days) effects on vibrotactile detection thresholds (VDT). VDT was measured before and after tDCS on days 1, 3, and 5 for low- (30 Hz) and high-frequency (200 Hz) vibrations on the dominant and nondominant hands in 29 healthy adults (mean age = 22.86 yr; 15 men, 14 women). Only the dominant-hand 200-Hz VDT displayed statistically significant medium effect size improvement for mixed-model analysis of variance time-by-group interaction for active tDCS compared with sham. Post hoc contrasts were statistically significant for dominant-hand 200-Hz VDT on day 5 after tDCS compared with day 1 before tDCS, day 1 after tDCS, and day 3 before tDCS. There was a linear dose-response improvement with dominant-hand 200-Hz VDT mean difference decreasing from day 1 before tDCS peaking at -15.5% (SD = 34.9%) on day 5 after tDCS. Both groups showed learning effect trends over time for all VDT test conditions, but only the nondominant-hand 30-Hz VDT was statistically significant ( P = 0.03), although post hoc contrasts were nonsignificant after Sidák adjustment. No adverse effects for tDCS were reported. In conclusion, anodal tDCS at 1 mA, 20 min × 5 days on the dominant sensory cortex can modulate a linear improvement of dominant-hand high-frequency VDT but not low-frequency or nondominant-hand VDT. NEW & NOTEWORTHY Repeated weak anodal transcranial direct current stimulation (1 mA, 20 min) on the dominant sensory cortex provides linear improvement in dominant-hand high-frequency vibration detection thresholds. No effects were observed for low-frequency or nondominant-hand vibration detection thresholds.

Working memory training with tDCS improves behavioral and neurophysiological symptoms in pilot group with post-traumatic stress disorder (PTSD) and with poor working memory.

This pilot study investigated the feasibility of treating people suffering from both post-traumatic stress disorder (PTSD) and poor working memory by employing a combination of computerized working memory training and transcranial direct current stimulation (tDCS). After treatment, all four participants showed clinically significant improvements on a range of cognitive and emotional performance measures. Moreover, these improvements were accompanied by theoretically significant neurophysiological changes between pre- and post-treatment electroencephalographic (EEG) recordings. Specifically, the P3a component of participants' event related potentials (ERP) in response to novelty stimuli, characteristically abnormal in this clinical population, shifted significantly toward database norms. So, participants' initially slow alpha peak frequency (APF), theorized to underlie impaired cognitive processing abilities, also increased in both frequency and amplitude as a result of treatment. On the basis of these promising results, more extensive controlled studies are warranted.

Differential effects of peripheral vibration on motor-evoked potentials in acute stages of stroke.

OBJECTIVE: The excitability of sensorimotor cortex and spinal motoneurones can be modulated by afferent signals arising from the periphery. Low- and high-frequency vibrations activate separate classes of afferent units in the periphery. Low-frequency vibrations (2-100 Hz) activate the type I fast adapting afferent units (FA-I), whereas high-frequency vibrations (60-1000 Hz) preferentially activate the type II units (FA-II). Muscle spindles are also sensitive to high-frequency mechanical vibrations. Motor-evoked potentials (MEP) generated in response to transcranial magnetic stimulation (TMS) can be modulated by afferent signals. However, it is not clear whether these interactions take place at cortical or spinal cord levels. METHODS: Cerebrovascular attacks resulting in stroke generally affect both sensory and motor systems. In eight stroke patients with partial motor deficit in the first two weeks of the incident we studies the effects of low- (30 Hz) and high- (130 Hz) frequency mechanical vibrations on the MEPs obtained in response to TMS. Recordings from the abductor digiti minimi muscle were carried out by TMS of both lesioned and intact hemispheres. Six patients were tested again four to eight weeks after the initial assessment. The results also were compared with data obtained from eight control subjects. MEPs were evoked by 50% above threshold intensities and for each testing condition initially five control MEPs were recorded. This was followed by consecutive MEPs obtained during vibration (N= 5) and between vibrations (N= 5), and the traces were averaged and analyzed. RESULTS: In normal subjects both low- (30 Hz) and high- (130 Hz) frequency vibration resulted in shortening of MEP latencies. In patients, there was a similar effect on the affected side with 30 Hz, but not with 130 Hz. Stimulation of the intact hemisphere during high-frequency vibration in the second test revealed a latency shortening, which could be due to central reorganization. The amplitude of MEPs showed a stronger facilitation in the presence of low-frequency vibration in the early stage of stroke compared with normal subjects. However, in the second test the level of facilitation was reduced, indicating an effect at the cortical level. CONCLUSIONS: The results suggest that a cerebrovascular accident influences the modulatory effects of afferent inputs at both spinal and cortical levels, and in time, as reorganization takes place, these altered influences settle towards normal levels.

Neurophysiological measurements of affected and unaffected motor cortex from a cross-sectional, multi-center individual stroke patient data analysis study.

OBJECTIVES: Transcranial magnetic stimulation (TMS) has been used to measure cortical excitability as a functional measurement of corticomotor pathways. Given its potential application as an assessment tool in stroke, we aimed to analyze the correlation of TMS parameters with clinical features in stroke using data from 10 different centers. METHODS: Data of 341 patients with a clinical diagnosis of stroke were collected from studies assessing cortical excitability using TMS. We used a multivariate regression model in which the baseline cortical excitability parameter "resting Motor Threshold (rMT)" was the main outcome and the demographic, anatomic and clinical characteristics were included as independent variables. RESULTS: The variable "severity of motor deficit" consistently remained significant in predicting rMT in the affected hemisphere, with a positive ß coefficient, in the multivariate models after sensitive analyses and adjusting for important confounders such as site center. Additionally, we found that the correlations between "age" or "time since stroke" and the rMT in the affected hemisphere were significant, as well as the interaction between "time since stroke" and "severity of motor deficit". CONCLUSIONS: We have shown that severity of motor deficit is an important predictor for rMT in the affected hemisphere. Additionally, time since stroke seems to be an effect modifier for the correlation between motor deficit and rMT. In the unaffected motor cortex, these correlations were not significant. We discuss these findings in the context of stroke rehabilitation.

Somatosensory evoked potential and histopathological investigations in ischaemia-induced brain damage: effects of trimetazidine in rats.

We studied the protective effects of trimetazidine (TMZ) on brain damage by means of somatosensory evoked potentials (SEP) in rats. The TMZ group did not show any statistically significant difference from the control group with respect to SEPs. However, the percentage of cells with ischaemic cell damage in hippocampal regions was significantly smaller in the TMZ group than the control group. Trimetazidine reduced the number of damaged cells in the cerebral tissue during the ischaemia-reperfusion damage. It was suggested that higher doses of trimetazidine may further reduce the number of cells with ischaemic damage.