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Results for “Transcranial Direct Current Stimulation”

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PubMed2004

Brain stimulation for neurological and psychiatric disorders, current status and future direction.

Interest in brain stimulation therapies has been rejuvenated over the last decade and brain stimulation therapy has become an alternative treatment for many neurological and psychiatric disorders, including Parkinson's disease (PD), dystonia, pain, epilepsy, depression, and schizophrenia. The effects of brain stimulation on PD are well described, and this treatment has been widely used for such conditions worldwide. Treatments for other conditions are still in experimental stages and large-scale, well controlled studies are needed to refine the treatment procedures. In the treatment of intractable brain disorders, brain stimulation, especially transcranial magnetic stimulation (TMS), is an attractive alternative to surgical lesioning as it is relatively safe, reversible, and flexible. Brain stimulation, delivered either via deeply implanted electrodes or from a surface-mounted transcranial magnetic device, can alter abnormal neural circuits underlying brain disorders. The neural mechanisms mediating the beneficial effects of brain stimulation, however, are poorly understood. Conflicting theories and experimental data have been presented. It seems that the action of stimulation on brain circuitry is not limited to simple excitation or inhibition. Alterations of neural firing patterns and long-term effects on neurotransmitter and receptor systems may also play important roles in the therapeutic effects of brain stimulation. Future research on both the basic and clinical fronts will deepen our understanding of how brain stimulation works. Real-time computation of neural activity allows for integration of brain stimulation signals into ongoing neural processing. In this way abnormal circuit activity can be adjusted by optimal therapeutic brain stimulation paradigms.

Electric Stimulation↗

PubMed2005

Brain stimulation techniques in the treatment of obsessive-compulsive disorder: current and future directions.

Recent studies on the epidemiology of obsessive-compulsive disorder (OCD) estimate 50 million patients suffer from OCD worldwide, thus making it a global problem. The treatment of OCD has changed substantially over the last 2 decades following the introduction of selective serotonin reuptake inhibitors, which provide symptom improvement in approximately 60% of patients. However, some patients remain resistant to the standard pharmacologic and behavioral treatments. Although some treatment-resistant patients respond to pharmacologic augmentations, others do not, and there is evidence that some of the most severe cases benefit from treatment with neurosurgical interventions. Besides pharmacologic, behavioral, and neurosurgical approaches, different brain stimulation methods-transcranial magnetic stimulation, deep brain stimulation, and electroconvulsive therapy-have been investigated in treatment-resistant patients with OCD. However, available data about the use of these techniques in OCD treatment are quite limited in terms of sample size and study design, given the difficulty in conducting standard blinded trials for these procedures. In addition, none of the mentioned treatments have received Food and Drug Administration approval for the treatment of OCD. Nevertheless, promising findings regarding efficacy, tolerability, and non-invasiveness and/or reversibility of these techniques have increased interest in investigating their use in treatment-resistant OCD.

Deep Brain Stimulation↗

PubMedDate not supplied

Augmentation strategies in patients with refractory depression.

In the evaluation of treatment-resistant or treatment-refractory depression (TRD), true resistance to antidepressant therapy must be distinguished from inadequate dose, duration, or compliance with past antidepressant therapy. Reassessment of the diagnosis may reveal psychiatric comorbidity, the presence of depressive subtypes, or the possibility of a medical etiology. Management of TRD should consider patient-specific factors; drug therapy may be directed by depressive subtype or the presence of psychiatric comorbidity. Increasing the dose or duration of current antidepressant therapy is appropriate for patients who have received inadequate therapy in the past. Augmentation of tricyclic antidepressant (TCA) or selective serotonin reuptake inhibitor (SSRI) therapy with thyroid hormone (T3) or lithium has been shown to be effective in open and controlled trials. Efficacy of other strategies such as higher-dose antidepressant treatment, venlafaxine therapy, combined antidepressant therapy, electroconvulsive therapy (ECT), transcranial magnetic stimulation (TMS), or augmentation with pindolol or buspirone has been less well established, but emerging data from open studies and case reports are encouraging.

Antidepressive Agents↗

PubMed2006

Hemispheric asymmetry in memory-guided pointing during single-pulse transcranial magnetic stimulation of human parietal cortex.

Dorsal posterior parietal cortex (PPC) has been implicated through single-unit recordings, neuroimaging data, and studies of brain-damaged humans in the spatial guidance of reaching and pointing movements. The present study examines the causal effect of single-pulse transcranial magnetic stimulation (TMS) over the left and right dorsal posterior parietal cortex during a memory-guided "reach-to-touch" movement task in six human subjects. Stimulation of the left parietal hemisphere significantly increased endpoint variability, independent of visual field, with no horizontal bias. In contrast, right parietal stimulation did not increase variability, but instead produced a significantly systematic leftward directional shift in pointing (contralateral to stimulation site) in both visual fields. Furthermore, the same lateralized pattern persisted with left-hand movement, suggesting that these aspects of parietal control of pointing movements are spatially fixed. To test whether the right parietal TMS shift occurs in visual or motor coordinates, we trained subjects to point correctly to optically reversed peripheral targets, viewed through a left-right Dove reversing prism. After prism adaptation, the horizontal pointing direction for a given visual target reversed, but the direction of shift during right parietal TMS did not reverse. Taken together, these data suggest that induction of a focal current reveals a hemispheric asymmetry in the early stages of the putative spatial processing in PPC. These results also suggest that a brief TMS pulse modifies the output of the right PPC in motor coordinates downstream from the adapted visuomotor reversal, rather than modifying the upstream visual coordinates of the memory representation.

Adaptation, Physiological↗

PubMed2006

Origin of facilitation of motor-evoked potentials after paired magnetic stimulation: direct recording of epidural activity in conscious humans.

A magnetic transcranial conditioning stimulus given over the motor cortex at intensities below active threshold for obtaining motor-evoked potentials (MEPs) facilitates EMG responses evoked at rest in hand muscles by a suprathreshold magnetic stimulus given 10-25 ms later. This is known as intracortical facilitation (ICF). We recorded descending volleys produced by single and paired magnetic motor cortex stimulation through high cervical epidural electrodes implanted for pain relief in six conscious patients. At interstimulus intervals (ISIs) of 10 and 15 ms, although MEP was facilitated, there was no change in the amplitude or number of descending volleys. An additional I wave sometimes was observed at 25 ms ISI. In one subject, we also evaluated the effects of reversing the direction of the induced current in the brain. At 10 ms ISI, the facilitation of the MEPs disappeared and was replaced by slight suppression; at 2 ms ISI, there was a pronounced facilitation of epidural volleys. Subsequent experiments on healthy subjects showed that a conditioning stimulus capable of producing ICF of MEPs had no effect on the EMG response evoked by transmastoidal electrical stimulation of corticospinal tract. We conclude that ICF occurs because either 1) the conditioning stimulus has a (thus far undetected) effect on spinal cord excitability that increases its response to the same amplitude test volley or 2) that it can alter the composition (but not the amplitude) of the descending volleys set up by the test stimulus such that a larger proportion of the activity is destined for the target muscle.

Adult↗

PubMed2002

Descending volleys evoked by transcranial magnetic stimulation of the brain in conscious humans: effects of coil shape.

OBJECTIVES: To directly compare the volleys evoked by figure-of-eight and circular magnetic coil stimulation of the motor cortex and to correlate the descending volleys with the EMG responses in distal hand muscles. METHODS: Descending corticospinal volleys were recorded from an electrode inserted into the cervical epidural space of two conscious human subjects after transcranial stimulation of the hand area of the motor cortex. We compared volleys evoked by stimulation with (a) a figure-of-eight coil inducing posterior-anterior or latero-medial currents in the brain, (b) a large circular coil centred at the vertex inducing clockwise currents in the brain, and (c) anodal electric pulses. RESULTS: For a given amplitude of EMG response in the first dorsal interosseous muscle, volleys were larger after stimulation with a circular than a figure-of-eight coil. In addition, the D wave evoked by circular coil stimulation had a longer latency than the anodal D wave, and increased in amplitude when stimulation was given during voluntary contraction. CONCLUSIONS: We conclude that stimulation with a large circular coil activates descending outputs less selectively than figure-of-eight coil stimulation and that it is capable of activating pyramidal neurones at the initial segment region.

Aged↗

PubMed1998

The first component of polyphasic motor evoked potentials is resistant to suppression by paired transcranial magnetic stimulation in humans.

The suppressive effect of paired transcranial magnetic stimulation on the different components of motor evoked potentials (MEPs) from the left first dorsal interosseous muscle (FDI) was investigated in ten healthy human subjects. Conditioning stimuli were delivered via a round coil centered on the vertex, and test stimuli via a figure-eight coil over the right motor area. The threshold stimulus intensity of the minimally contracted FDI was determined with each coil. The stimulus intensities of conditioning and test stimuli were 80% and 130-140% of the threshold intensity, respectively. The coil current direction at the intersection of the figure-eight coil was medio-lateral. The coil position for test stimuli was adjusted to evoke discretely polyphasic MEPs in the contracted FDI. Conditioning stimuli were followed by test stimuli at intervals of 1-10, and 15 ms. When the interstimulus intervals were less than 5 ms, the second negative phase of MEPs was suppressed compared to that of the unconditioned responses, whereas the first phase was not suppressed. The present results imply that the first phase reflects direct corticospinal volleys, which are resistant to cortico-cortical inhibition.

Adult↗

PubMed1998

Magnetic stimulation over different brain regions: no differential effects on the elicited sympathetic skin responses.

Peak latencies and amplitudes of sympathetic skin responses (SSRs) of the hand following magnetic stimulation at different sites with two or five consecutive 10-Hz stimuli were investigated with regard to safety aspects of repetitive transcranial magnetic cortex stimulation (rTMS). The amount of sympathetic activation as assessed by the amplitudes of the SSRs depended on the stimulation site and decreased in the following order: brachial plexus stimulation > nerve root stimulation > stimulation over the brain > activation by acoustic coil artefact. When stimulating over six different regions of the cortex (frontal, central, parieto-occipital, and both hemispheres), the elicited SSRs had similar amplitudes and peak latencies. The SSRs elicited by rTMS over the motor cortex were not related to the sum of the amplitudes of excitatory muscle compound responses. Currents with opposite directions over the motor cortex markedly influenced the size of the motor responses but not of the SSRs. The number of consecutive 10-Hz stimuli did not influence the latencies or amplitudes of the SSRs. It can be concluded that SSRs after magnetic stimulation over peripheral nerves or the brain are a correlate of an unspecific arousal reaction. A therapeutic application of short series of rTMS should not be limited by the amount of sympathetic activation.

Acoustic Stimulation↗

PubMed2005

Somatotopic blocking of sensation with navigated transcranial magnetic stimulation of the primary somatosensory cortex.

We demonstrate that spatially accurate and selective stimulation is crucial when cortical functions are studied by the creation of temporary lesions with transcranial magnetic stimulation (TMS). Previously, the interpretation of the TMS results has been hampered by inaccurate knowledge of the site and strength of the induced electric current in the brain. With a Navigated Brain Stimulation (NBS) system, which provides real-time magnetic resonance image (MRI)-guided targeting of the TMS-induced electric field, we found that TMS of a spatially restricted cortical S1 thenar area is sufficient to abolish sensation from a weak electric stimulation of the corresponding skin area. We demonstrate that with real-time navigation, TMS can be repeatably directed at millimeter-level precision to a target area defined on the MRI. The stimulation effect was temporally and spatially specific: the greatest inhibition of sensation occurred when TMS was applied 20 ms after the cutaneous test stimulus and the TMS effect was sensitive to 8-13 mm displacements of the induced electric field pattern. The results also indicate that TMS selectively to S1 is sufficient to abolish perception of cutaneous stimulation of the corresponding skin area.

Adult↗

PubMed1998

Comparison of descending volleys evoked by transcranial magnetic and electric stimulation in conscious humans.

OBJECTIVES: The present experiments were designed to compare the understanding of the transcranial electric and magnetic stimulation of the human motorcortex. METHODS: The spinal volleys evoked by single transcranial magnetic or electric stimulation over the cerebral motor cortex were recorded from a bipolar electrode inserted into the cervical epidural space of two conscious human subjects. These volleys were termed D- and I waves, according to their latency. Magnetic stimulation was performed with a figure-of-eight coil held over the right motor cortex at the optimum scalp position, in order to elicit motor responses in the contralateral FDI using two different orientations over the motor strip. The induced current flowed either in a postero-anterior or in a latero-medial direction. RESULTS: At active motor threshold intensity, the electric anodal stimulation evoked pure D activity. At this intensity, magnetic stimulation with the induced current flowing in a posterior-anterior direction evoked pure I1 activity. When a latero-medial induced current was used, magnetic stimulation evoked both D and I1 activity. Using electric anodal stimulation, at a stimulus intensity of 9% of the stimulator output above the active motor threshold (corresponding approximately to 1.5 active motor threshold), a small I1 wave appeared only in subject 1. Using magnetic stimulation with a posterior-anterior induced current, at a stimulus intensity of 21% of maximum stimulator output above the active motor threshold (corresponding approximately to 1.8 times threshold in subject 1 and to two times threshold in subject 2), a small D wave appeared in subject 1 but not in subject 2. CONCLUSIONS: Present results demonstrate that, in conscious humans at threshold intensities, electric stimulation evokes D waves and magnetic stimulation (with a posterior-anterior induced current) evokes I waves, while magnetic stimulation (with a latero-medial induced current) evokes both activities.

Differential Threshold↗

PubMed2004

Excitability changes in human hand motor area dependent on afferent inputs induced by different motor tasks.

Using the technique of transcranial magnetic stimulation (TMS) with a figure-of-eight-shaped coil in 16 normal volunteers, we studied the extents of motor evoked potentials (MEPs) induced by remote facilitation of voluntary teeth clenching (VTC) and by motor imagery (MI). In particular, we examined whether different excitability changes in the primary motor cortex (M1) induced by both facilitation methods occur between early (I1 and I2) and late (I3 and I4) components of I-waves elicited from a first dorsal interosseous (FDI) muscle. Both components of I-waves were induced by anterior-medially (AM) directed currents or posterior-laterally (PL) directed currents. Our hypothesis was that facilitatory effects of VTC and MI on M1 differ because the neural pathways of these afferent inputs differ. The present results indicate that during MI MEP amplitudes of late components are significantly larger than those of early ones, although both MEP amplitudes are enhanced. On the other hand, during VTC MEP amplitudes of early components are significantly enhanced, but those of late ones are rather depressed. We conclude that recruitment of early and late components of I-waves differ depending on the afferent inputs to the motor cortex.

Adult↗

PubMed2003

Standardization of transcranial magnetic stimulation in the horse.

The influence of coil position on the peak-to-peak amplitude and onset latency of transcranial magnetic motor evoked potentials (MMEPs) in the extensor carpi radialis and cranial tibial muscles of horses was evaluated. Seven different stimulating coil positions were obtained by constructing a frame on the forehead. Two stimulation intensities (80% and 100% of maximal stimulator output) and two different coil currents (clockwise and counter-clockwise) were tested. For both recording sites MMEPs with the shortest onset latency and the largest peak-to-peak amplitude were detected when the coil was placed in the median of the forehead. There was no significant difference between left and right side recordings. The direction of the current flow in the coil had no influence on the onset latency of the MMEPs.

Animals↗

PubMed1996

[Intracranial blood flow parameters in cerebral functional changes and cognitive cerebral performance].

Extensive studies have revealed a close relationship between neuronal activity and regional cerebral blood flow. However, SPECT and PET, the technologies most commonly used in these studies, are of limited value for assessment of the dynamics of cerebral blood flow changes at different states of functional brain activity. The introduction of transcranial Doppler sonography and the extended application of stimuli presentation and perception have now been added to the investigator's armamentarium. Simple sensory stimulation (visual, acoustic and tactile) and complex mental tasks (viewing of complex pictures, tactile differentiation of objects) changed the blood flow velocity in the basal intracranial arteries. These changes corresponded to the current concepts of functional cortical organization. The magnitude of the flow velocity increases upon visual stimulation was dependent on the complexity of the stimuli used, and was up to 38% in our studies. The introduction of continuous and bilateral simultaneous Doppler recordings, the calculation of mean flow velocity from cardiac cycle to cardiac cycle and a specially designed averaging method for data analysis allowed effective elimination of non-specific influences and made it possible to demonstrate rapid changes of perfusion in both middle cerebral artery territories in direct response to hemisphere-specific tasks. These changes were correlated with known functional cerebral asymmetries. A language task, for instance, was associated with a significantly larger flow velocity increase in the middle cerebral artery of the dominant hemisphere than in the corresponding artery of the non-dominant hemisphere (5.2 +/- 1,8% vs 3.0 +/- 1.8%, p < 0.001). The excellent time resolution of this technology made it possible to record hemodynamic changes taking place in response to modifications of neuronal activity within less than 1 s. The shortest time interval between stimulus presentation and the first significant increase in flow velocity was on average 717 +/- 191 ms. The latency of less than 1 s suggest that the coupling between alterations of neuronal activity and the regional cerebral blood flow response is mediated by an remarkably rapid mechanism.

Arousal↗

PubMed1991

Physiological studies of electric and magnetic stimulation of the human brain.

It is suggested that transcranial electric stimulation can activate pyramidal tract projections both directly and indirectly in a manner similar to that described after direct stimulation of the exposed cortex in the monkey. This produces both D- and I-waves in the pyramidal tract. At high intensities of stimulation, the stimulus can spread into the brain and activate pyramidal tract axons several centimeters below the cortical surface. Magnetic stimulation at moderate intensities produces electromyographic (EMG) responses with latencies 1-2 msec longer than those after electric stimulation. Two possible explanations have been put forward to account for this effect: (1) because of the difference in the direction of electric current flow induced in the brain by the 2 forms of stimulation, magnetic stimulation preferentially excites pyramidal tract cells indirectly, and hence evokes only I-waves in the pyramidal tract. (2) Electric stimulation (even at threshold) activates pyramidal axons deep in the white matter, whereas magnetic stimulation activates the pyramidal cells in the gray matter, probably at their initial segment. There is one interesting consequence common to both explanations. Whether magnetic stimulation activates the pyramidal neurons transsynaptically or at their initial segment, the size of the descending volley evoked will depend on the level of excitability of the motor cortex. In contrast, the response to electric stimulation will be less affected, since a proportion of the descending volley is initiated directly at the axon of the pyramidal cell. This differential effect of cortical excitability on the responses to electrical and magnetic stimulation can be useful in describing excitatory or inhibitory influences on motor cortex from other structures.

Action Potentials↗

PubMed1993

Transcranial electric and magnetic stimulation of the leg area of the human motor cortex: single motor unit and surface EMG responses in the tibialis anterior muscle.

We compared single motor unit and surface EMG responses in the active right tibialis anterior following anodal electrical or magnetic stimulation of the motor cortex over the vertex. Magnetic stimulation used a monophasic current pulse through a circular coil centred 3 cm anterior to the vertex. Lowest threshold magnetic stimulation occurred when the current in the coil flowed from the left to the right side at the posterior rim of the coil. Such stimulation produced single unit and surface EMG responses which had the same latency as those produced by anodal electric stimulation. If the direction of the magnetic stimulating current was reversed, response latencies became more variable from unit to unit, and on average they occurred 1.0 +/- 0.5 msec later. In single motor units anodal and magnetic post-stimulus time histogram (PSTH) peaks had the same duration. This was similar to the duration of the PSTH peaks produced by a single low intensity stimulus given to the common peroneal nerve. We conclude that magnetic stimulation can produce direct activation of corticospinal neurones to the tibialis anterior if the direction of induced current flow is optimal. This projection is likely to be either monosynaptic or oligosynaptic.

Adult↗

PubMed2000

[The influence of transcranial micropolarization on convulsive manifestations in children].

Eighteen patients with infantile cerebral paralysis and organic brain damage underwent to therapeutical sessions of transcranial micropolarization directed to decrease the incidence of convulsive fits. Transcranial micropolarization of the posterior temporal and parietal areas caused a marked decrease in the incidence of convulsive fits and made the electroencephalographic pattern normal. This effect was caused by the target exposure of the structures responsible for the formation and regulation of brain convulsive activity to constant current through the respective morphofunctional linkages of the cortical areas.

Brain↗

PubMed2006

Direct evidence for a prefrontal contribution to the control of proactive interference in verbal working memory.

Controlling the effects of proactive interference (PI), the deleterious effect of prior mental activity on current memory representations, is believed to be a key function of the prefrontal cortex. This view is supported by neuroimaging evidence for a correlation between the longer reaction times caused by high PI conditions of a working memory task and increased activity in left inferior frontal gyrus (IFG) of the prefrontal cortex. An alternative that has never been ruled out, however, is that this left IFG effect may merely reflect sensitivity to such nonspecific factors as difficulty and/or time on task. To resolve this confound, we applied the interference methodology of repetitive transcranial magnetic stimulation (rTMS) to the left IFG and two control regions while subjects performed delayed letter recognition. rTMS was guided with high-resolution magnetic resonance images and was time-locked to the onset of the memory probe. The effect of rTMS, a disruption of accuracy restricted to high-PI probes, was specific to the left IFG. These results demonstrate that unpredictable, phasic disruption of the left IFG selectively disrupts control of responses to high-conflict verbal working memory probes, and they conclusively reject nonspecific alternative accounts.

Female↗

PubMed2003

Effect of transcranial magnetic stimulation on single-unit activity in the cat primary visual cortex.

Transcranial magnetic stimulation (TMS) has become a well established procedure for testing and modulating the neuronal excitability of human brain areas, but relatively little is known about the cellular processes induced by this rather coarse stimulus. In a first attempt, we performed extracellular single-unit recordings in the primary visual cortex (area 17) of the anaesthetised and paralysed cat, with the stimulating magnetic field centred at the recording site (2 x 70 mm figure-of-eight coil). The effect of single biphasic TMS pulses, which induce a lateral-to-medial electric current within the occipital pole of the right hemisphere, was tested for spontaneous as well as visually evoked activity. For cat visual cortex we found that a single TMS pulse elicited distinct episodes of enhanced and suppressed activity: in general, a facilitation of activity was found during the first 500 ms, followed thereafter by a suppression of activity lasting up to a few seconds. Strong stimuli exceeding 50 % of maximal stimulator output could also lead to an early suppression of activity during the first 100-200 ms, followed by stronger (rebound) facilitation. Early suppression and facilitation of activity may be related to a more or less direct stimulation of inhibitory and excitatory interneurons, probably with different thresholds. The late, long-lasting suppression is more likely to be related to metabotropic or metabolic processes, or even vascular responses. The time course of facilitation/inhibition may provide clues regarding the action of repetitive TMS application.

Action Potentials↗