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Results for “Transcranial Direct Current Stimulation”

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At least 181 records · Page 10Linked to original sources

PubMed2005

Investigation of the primary visual cortex using short-interval paired-pulse transcranial magnetic stimulation (TMS).

Previous studies using short-interval paired-pulse TMS have provided valuable insights into physiology of human motor cortex. Depending on the interstimulus interval (ISI) between the two pulses intra-cortical facilitation (ICF) or intra-cortical inhibition (ICI) can be observed. Similar patterns of inhibition and facilitation have also been demonstrated in prefrontal and parietal cortices. In order to prove whether principles that govern cortical excitability in the motor system also extend to the visual system and to further characterize possible neural correlates of phosphene generation, we applied short-interval paired-pulse TMS to the occipital cortex. In addition, we examined the effect of different coil orientations on perception of phosphenes induced by paired-pulse TMS. In all of 10 healthy subjects, a general facilitation of phosphene perception could be observed for interstimulus intervals of 2-12 ms (conditioning stimulus (CS) 90% and test stimulus (TS) 100% of subject's phosphene threshold) compared to TS alone. With CS intensity decreasing to 80% or less, the effect diminished. No significant changes occurred when TS intensity was increased to 110%. Phosphene perception was enhanced with an induced current direction from lateral to medial at an ISI of 12 ms. Inhibition was not observed in any condition. Our results indicate that the mechanisms underlying phosphene induction in the visual cortex are different from those underlying intracortical inhibition and facilitation in the motor cortex.

Adult↗

PubMed1990

[Masseteric responses following electrical stimulation of the scalp].

Electromyographic responses of the masseter muscles following electric transcranial stimulations by a conventional constant current stimulator were recorded with surface and needle electrodes. Ipsilateral motor evoked responses following both anodic and cathodic bipolar electrical stimulations performed at 7 and 11 cm laterally to the vertex on the biauricular line were recorded, with latencies ranging from 2 to 3.6 ms. Contralateral responses were not elicited. The ipsilateral responses to stimuli were ascribed to direct stimulation of the trigeminal nerve, probably its intracisternal portion.

Adult↗

PubMed2003

Brain polarization in humans: a reappraisal of an old tool for prolonged non-invasive modulation of brain excitability.

Direct current (DC) is very effective in modulating spontaneous neuronal firing. The history of electrophysiology starts with the discovery of the biological effects of DC and as early as two centuries ago scalp DC was used to treat mental disorder. Psychophysiological investigations suggested a possible effect of scalp DC in humans. More recently several studies assessed, with motor potentials evoked by transcranial brain stimulation, the motor-cortical excitability changes induced by scalp DC. Even weak DCs pass through the scalp and influence human brain activity. DCs delivered at relatively strong intensities (1 mA) and for long periods (10 min or so), not only influence (either increase or decrease) brain excitability during their application in normal subjects, but induce persistent changes in excitability after their offset that, at least in the motor cortex, can last for almost 1 h. Scalp DC might represent a non-invasive simple and valuable potential treatment for psychiatric and neurologic diseases with changes in brain excitability or focally abnormal (increased or decreased) function.

Brain↗

PubMed2004

Significance of coil orientation for motor evoked potentials from nasalis muscle elicited by transcranial magnetic stimulation.

OBJECTIVE: In transcranial magnetic stimulation (TMS) of the motor cortex, the optimal orientation of the coil on the scalp is dependent on the muscle under investigation, but not yet known for facial muscles. METHODS: Using a figure-of-eight coil, we compared TMS induced motor evoked potentials (MEPs) from eight different coil orientations when recording from ipsi- and contralateral nasalis muscle. RESULTS: The MEPs from nasalis muscle revealed three components: The major ipsi- and contra-lateral middle latency responses of approximately 10 ms onset latency proved entirely dependent on voluntary pre-innervation. They were most easily obtained from a coil orientation with posterior inducing current direction, and in this respect resembled the intrinsic hand rather than the masseter muscles. Early short duration responses of around 6 ms onset latency were best elicited with an antero-lateral current direction and not pre-innervation dependent, and therefore most probably due to stimulation of the nerve roots. Late responses (>18 ms) could inconsistently be elicited with posterior coil orientations in pre-innervated condition. CONCLUSIONS: By using the appropriate coil orientation and both conditions relaxed and pre-innervated, cortically evoked MEP responses from nasalis muscle can reliably be separated from peripheral and reflex components and also from cross talk of masseter muscle activation.

Adult↗

PubMed1995

[Identification of motor area by transcranial magnetic stimulation using an "eight-figure" coil in patients with motor paralysis].

In patients with motor paralysis, we tried to identify the functional motor area by transcranial magnetic stimulation using an "eight-figure" coil designed by Ueno. Motor evoked potentials (MEPs) were recorded in 7 patients from 50 to 64 years old, and in 5 normal volunteers 26 to 45 years old. They were stimulated at 49 points over an unilateral hand motor area, and at 21 points over a foot motor area, and surface MEPs were recorded on their contralateral thenar muscle and abductor hallucis brevis muscle. In normal volunteers, the optimal eddy current for stimulating the hand motor area was directed anteriorly parallel to the midline, and for stimulating the foot motor area, it was postero-laterally directed with an angle of 45 degrees towards the midline. MEPs could be induced at their muscle contractions during which their thumbs and middle fingers softly touched each other, and their halluxes slightly flexed. In five patients two kinds of amplitude mappings reconstructed from MEPs were obtained at rest or at muscle contraction. A line connecting these two peaks on an amplitude mapping was regarded as an "MEP-motor area". A geographical difference between the MEP-motor area and MRI-motor area (identified by an MRI surface image) was studied at muscle contraction and at rest. In normal subjects the sites of the MEP-motor area and of the MRI-motor area coincided, whereas, in patients with space-occupying lesions near the central sulcus, the MEP-motor areas were located 1 to 2cm posterior to MRI-motor areas.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1991

Motor cortical representation of the diaphragm in man.

1. Transcranial magnetic stimulation was performed using a figure-of-eight-shaped coil over the right motor cortex with the aim of identifying those areas involved with activation of the diaphragm. 2. The response of the right and left hemi-diaphragms was recorded using surface electrodes in either the 7th or 8th intercostal spaces 3 cm lateral to the anterior costal margin on either side. 3. The compound muscle action potentials recorded over the left diaphragm in response to transcranial magnetic stimulation were maximal when the centre of the figure-of-eight coil was placed approximately 3 cm to the right of the mid-line and 2-3 cm anterior to the auricular plane. 4. The amplitude of the response recorded from the diaphragm depended upon the angulation of the figure-of-eight coil and hence the direction of the stimulating current. 5. The response of the inspiratory muscles to magnetic stimulation of one side of the brain was predominantly contralateral but a small response was seen on the ipsilateral side. Ultrasonic techniques confirmed that the diaphragm was responding contralaterally and not ipsilaterally.

Action Potentials↗

PubMed1990

Transcranial magnetic stimulation can influence the selection of motor programmes.

Transcranial magnetic stimulation is becoming increasingly popular to study the rapidly conducting output from the motor cortex. Little is known about the effects of such stimuli on other aspects of cortical function. In the study single magnetic stimuli, subthreshold for movement, produced significant preference for selection of one hand in a forced-choice task. The hand preference depended upon the direction of the induced current. It occurred when the coil was positioned over frontal but not occipital cortex and was not mimicked by weak DC stimulation. Single magnetic stimuli which do not evoke movement can alter high-level motor planning.

Electromagnetic Fields↗

PubMed2006

Monitoring of muscle motor evoked potentials during cerebral aneurysm surgery: intraoperative changes and postoperative outcome.

OBJECT: The authors in this study evaluated muscle motor evoked potentials (MMEPs) elicited by transcranial electrical stimulation (TES) and direct cortical stimulation as a means of monitoring during cerebral aneurysm surgery. The analysis focused on the value and frequencies of any intraoperative changes and their correlation to the postoperative motor status. METHODS: One hundred nineteen patients undergoing surgery for 148 cerebral aneurysms were included in the study. Muscle motor evoked potentials were elicited by a train of five constant-current anodal stimuli with an individual pulse duration of 0.5 msec and a stimulation rate of 2 Hz. Stimulation intensity was up to 240 mA for TES and up to 33 mA for direct cortical stimulation. The MMEPs were continuously recorded from the abductor pollicis brevis and tibialis anterior muscles bilaterally and from the biceps brachii and extensor digitorum communis muscles contralateral to the surgical side. The motor status was evaluated immediately after surgery and 7 days later. In 97% of the patients MMEPs were recordable for continuous neurophysiological monitoring of the vascular territory of interest throughout the surgery. In 14 patients significant intraoperative MMEP changes occurred, resulting in a transient motor deficit in one patient and a permanent motor deficit in six. The permanent loss of MMEPs in three patients was followed by a permanent severe motor deficit in one patient and severe clinical deterioration in the other two. CONCLUSIONS: Data in this study demonstrated that MMEPs are a useful means of intraoperative neurophysiological monitoring of motor pathway integrity and predicting postoperative motor status. The intraoperative loss of MMEPs reliably predicts both severe and permanent postoperative motor deficits.

Adolescent↗

PubMed1996

Interaction between intracortical inhibition and facilitation in human motor cortex.

1. In seven normal subjects, subthreshold transcranial magnetic conditioning stimuli (using a figure-of-eight coil) were applied over the motor cortex in order to evoke activity in intracortical neuronal circuits. The net effect on cortical excitability was evaluated by measuring the effect on the size of EMG responses elicited in the abductor digiti minimi (ADM) muscle by a subsequent suprathreshold test stimulus. 2. A single conditioning stimulus suppressed the size of the test response at interstimulus intervals (ISIs) of 1-4 ms whereas the response was facilitated at ISIs of 6-20 ms. The facilitation could be augmented if pairs of conditioning stimuli were given. 3. Inhibition and facilitation appeared to have separate mechanisms. The threshold for inhibition (0.7 active motor threshold) was slightly lower than that for facilitation (0.8 active threshold). Similarly, the inhibitory effect was independent of the direction of current flow induced in the cortex by the conditioning shock, whereas facilitation was maximal with posterior-anterior currents and minimal with lateromedial current. 4. Direct corticospinal effects were probably not responsible for the results since facilitation of cortical test responses could be produced by conditioning stimuli which had no effect on the amplitude of H reflexes elicited in active ADM muscle. 5. Inhibition and facilitation appeared to interact in a roughly linear manner, consistent with separate inputs to a common neurone. 6. We suggest that subthreshold transcranial magnetic stimulation is capable of activating separate populations of excitatory and inhibitory interneurones in the motor cortex.

Adult↗

PubMed2002

Transcranial magnetic stimulation: a new investigational and treatment tool in psychiatry.

Transcranial magnetic stimulation (TMS) is a new investigational technique used to explore various neural processes and treat a variety of neuropsychiatric illnesses. The most notable advantage of TMS is its ability to directly stimulate the cortex with little effect on intervening tissue. Single-pulse stimulation techniques can measure cortical inhibition, facilitation, connectivity, reactivity, and cortical plasticity, providing valuable insights into the cortical physiology. Repetitive TMS (rTMS) is currently being used to investigate cognitive processes and as a treatment tool in disorders such as depression and schizophrenia. Both TMS and rTMS are safe and well tolerated. The most serious side effect of high-frequency rTMS is seizures. TMS represents an exciting new frontier in neuroscience research, providing insights into the pathophysiology and treatment of various neuropsychiatric disorders.

Brain↗

PubMed2004

The antinociceptive effect of transcranial electrostimulation with combined direct and alternating current in freely moving rats.

UNLABELLED: Transcranial electrostimulation (TES) has been reported to elicit significant analgesia, allowing a substantial reduction of intraoperative opioids. Acceptance of TES into clinical practice is hampered by lack of controlled clinical trials and inconclusive animal data regarding the TES antinociceptive action. This inconclusive data may be explained, in part, by failure in rat experiments to simulate the variables used in humans when TES electrodes are positioned on the skin. In this study we validated the TES antinociceptive effect in a novel animal model of cutaneously administered TES, when the stimulating conditions mimic the ones used in clinical practice. The antinociceptive effect was assessed by measuring nociceptive thresholds in the tail-flick and hot-plate latency tests in awake, unrestrained male rats. Data were analyzed by analysis of variance and mixed-effects population modeling. The administration of TES at 2.25 mA produced an almost immediate, sustained, frequency-dependent (40-60 Hz) antinociceptive effect, reaching approximately 50% of the maximal possible value. We conclude that an antinociceptive effect of cutaneously administered TES can be demonstrated in the rat. Some characteristics of the effect suggest an important role of the sensory nerves of the rat's scalp in mediating the TES antinociceptive response. IMPLICATIONS: Transcranial electrostimulation produces a significant, frequency-dependent antinociceptive effect that may be mediated by cutaneous nerves of the scalp.

Algorithms↗

PubMed2005

Recharging cognition with DC brain polarization.

Electrical direct current (DC) has been applied to the human head throughout history for various reasons and with claims of behavioral effects and clinical benefits. This technique has recently been rediscovered and its effects validated with modern quantitative techniques and experimental designs. Despite the very weak current used, DC polarization applied to specific brain areas can alter verbal fluency, motor learning and perceptual thresholds, and can be used in conjunction with transcranial magnetic stimulation. Compact and safe, this old technique seems poised to allow major advances cognitive science and therapy.

Cerebral Cortex↗

PubMed2004

The cortical silent period: intrinsic variability and relation to the waveform of the transcranial magnetic stimulation pulse.

OBJECTIVE: To assess the variability of the duration of the contralateral cortical silent period (CSP) between individuals and to assess the effect of different transcranial magnetic stimulation (TMS) pulse waveforms. METHODS: In Expt. 1, CSP duration, and the motor-evoked potential (MEP) amplitude and area were measured in the first dorsal interosseous muscle (FDI) of 11 subjects on 3 separate occasions using a TMS intensity of 150% active motor threshold (AMT). In Expt. 2, the stimulation intensity was varied between 100% AMT and 150% AMT. In both sets of experiments, 3 types of TMS pulse were used: monophasic posterior-anterior (PA) induced current in the brain, monophasic anterior-posterior induced current (AP), and biphasic PA/AP stimulation. RESULTS: Experiment 1: Between-subject variation in CSP duration was high. In addition, the duration after PA stimulation was significantly shorter than after AP or PA/AP stimulation. However, there was a good correlation between CSP duration and the area, or amplitude, of the MEP. This meant that calculating the ratio of duration/amplitude or duration/area reduced intersubject variability and eliminated differences between TMS pulses. Experiment 2: increasing stimulation intensity increased the mean value of all parameters, but with significantly lower values for PA than other forms of stimulation. The ratios of duration/amplitude or duration/area did not differ between current flow directions and were relatively constant for intensities 130-150% AMT. CONCLUSIONS: Between-subject variation in the duration of the CSP is high. A given intensity of stimulation (expressed in %AMT) produces a shorter CSP for PA stimulation than for AP or PA/AP stimulation. SIGNIFICANCE: If the ratio (CSP duration)/(MEP size) is calculated, then intersubject variability is reduced, and TMS pulse type differences are eliminated.

Adult↗

PubMed2000

Ultrasound contrast enhancing agents in neurosonology: principles, methods, future possibilities.

OBJECTIVES: Ultrasound of the brain supplying arteries is a standard diagnostic procedure in patients with suspected and definite acute and chronic cerebrovascular occlusive disease. Anatomical and pathological limitations led to the development of echocontrast agents which are able to survive pulmonary and capillary transit and improve the echogenicity of the flowing blood. MATERIAL AND METHODS: This article reviews present and future applications of echocontrast agents in conjunction with personal experiences. RESULTS: Currently, echocontrast is used for the differentiation of internal carotid artery occlusion and pseudoocclusion, better delineation of the maximal narrowing in high-grade stenoses, and better visualization of the extracranial vertebral artery and its collaterals. Transcranial applications include the insufficient foraminal or temporal window, assessment of arteriovenous malformations, thrombosis of cerebral veins and sinuses, and intracranial aneurysms. The use of echocontrast can have direct diagnostic and therapeutic consequences. Harmonic imaging, perfusion imaging, stimulated acoustic emission, and drug delivery are possible future domains of the technique. DISCUSSION: Besides the support of conventional neurovascular ultrasound in poor examination conditions due to the patients' anatomy or pathology, echocontrast agents may allow for novel applications in the diagnosis and treatment of cerebrovascular patients.

Carotid Artery Diseases↗

PubMed1999

Transcranial magnetic stimulation--a new tool for functional imaging of the brain.

Recent progress in the theory and technology of transcranial magnetic stimulation (TMS) is leading to novel approaches in brain mapping. TMS becomes a powerful functional brain mapping tool when other imaging methods are used to record TMS-evoked activity or when peripheral effects are observed as a function of stimulus location. TMS-evoked activity currently can be recorded by EEG, PET, and fMRI. In addition to providing indices of cortical excitability, these methods allow one to study brain connectivity directly, without the need for behavioral activations. When the coordinate systems in the different imaging modalities are combined, anatomical structures seen in MRI and activation sites determined by PET, fMRI, or MEG/EEG can be used for the selection of target areas in the brain. PET and fMRI can be used to map the spatial distribution of TMS-evoked activity. On the other hand, the combination of TMS and high-resolution EEG may often be the method of choice for basic neuroscience and for clinical diagnosis, for example, in the assessment of brain connectivity in patients suffering from neurodegenerative diseases or head injuries.

Brain↗

PubMed1997

Tongue motor responses following transcranial magnetic stimulation of the motor cortex and proximal hypoglossal nerve in man.

Surface recordings of EMG responses were performed bilaterally from the tongue following transcranial magnetic cortex (TCS) and nerve stimulation (TNS) to characterize the activated corticonuclear pathways and to obtain normative data for a diagnostic use. TCS over the face-associated motor cortex with 1.3 times the response threshold for relaxed muscles produced bilateral tongue responses with similar latencies and amplitudes for ipsi-(8.3 +/- 1.1 ms, 1.3 +/- 0.7 mV) and contralateral responses (8.5 +/- 1.0 ms, 1.7 +/- 0.8 mV, n = 20, 10 subjects). In individual subjects maximal ipsilateral and contralateral responses were elicited by stimulation over about the same cortex area which lay 2-4 cm lateral and 0-2 cm anterior to the center of the hand motor representation area. Magnetic stimulation of the hypoglossal nerve with 70% of the maximal stimulator output and a circular coil placed over the posterior lateral skull produced a more proximal nerve excitation than electrical stimulation at the mandible, as reflected by the response latencies (3.4 +/- 0.9 ms vs. 2.1 +/- 0.7 ms). The effect of magnetic TNS was independent of the direction of the coil currents. Central motor latencies as calculated by subtracting the response latencies after TNS from the overall latency after TCS were 4.8 +/- 1.2 ms and 5.0 +/- 1.1 ms for ipsi- and contralateral responses, respectively. The findings suggest the existence of a direct and fast conducting connection between motor cortex and brainstem tongue motor nuclei on both sides in man.

Adult↗

PubMed1991

Study of central and peripheral motor conduction in normal subjects.

Motor potentials to transcranial and cervical magnetic stimulation and F-wave were recorded in 37 arms of 25 normal subjects. Clockwise and anticlockwise cervical stimulation were performed over C5, C7 and T2 spinous processes. A significant correlation was found between height and measurements of central and peripheral motor conduction. Peripheral motor conduction measured by F-wave derived techniques (Kimura formula) was 0.5 msec higher as compared with responses to cervical magnetic stimulation. The site and current flow direction of cervical magnetic stimulation influenced the amplitude of responses but not their latency: responses were larger in the right arm when the centre of the coil was placed over the C5 spinous process and clockwise stimuli were used. The same results were obtained in the left arm when the coil was reversed.

Adolescent↗

PubMed1994

Transcranial electrostimulation effects on rat opioid and neurotransmitter levels.

A specific form of Transcranial Electrostimulation Treatment (TCET) has been shown to induce analgesia, alleviate symptoms of opiate withdrawal and alter nociceptive responses in neurons in the midbrain and hypothalamus of rats. TCET consists of a 10Hz, charge balanced, 10 mu A current passed for 30 minutes between electrodes placed in the ears. Both serotonin (5HT) and endogenous opioids have been strongly implicated in TCET responses. This study directly measured brain levels of several neurotransmitters and their metabolites in anesthetized rats stimulated with either 10 mu A TCET or 0 mu A (Sham). Neurotransmitters measured in selected homogenized brain areas by high performance liquid chromatography were 5HT and its metabolite, 5-hydroxyindolacetic acid (5HIAA); norepinephrine (NE) and its metabolite, 3-methoxy-4-hydroxyphenethyleneglycol (MHPG); and dopamine (DA). Levels of NE and DA were significantly higher in the hypothalamic region of TCET rats than of control rats. The midbrains of TCET rats contained significantly elevated levels of DA, MHPG, 5HT and 5HIAA. In the hindbrain no significant differences were observed. Thus, TCET appears to cause an increase in the synthesis or release of 5HT, DA and NE in the midbrain and DA and 5HT in the hypothalamus. In a separate experiment, beta-endorphin-like immunoreactivity was measured in blood plasma taken from rats at intervals before, during and after a 30 minute TCET treatment, but no demonstrable TCET effect was observed. The lack of change in serum endorphin levels suggests that TCET-induced opioid activity may be confined to the central nervous system, a reasonable theory because the current passes only through the head.

Animals↗