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Results for “Transcranial Direct Current Stimulation”

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PubMed2006

Safety of rTMS to non-motor cortical areas in healthy participants and patients.

OBJECTIVE: rTMS is increasingly being used for stimulation to non-motor areas, but available safety guidelines are derived from experience with motor cortex rTMS. We reviewed the literature and our own data to assess the safety of rTMS to non-motor areas. METHODS: We reviewed for adverse effects all articles published from January 1998 to December 2003 that applied rTMS to non-motor areas, and analyzed data from our own studies from January 1997 to December 2003. RESULTS: Adverse effects were infrequent and generally mild. Headache was the most common, occurring in 23% of the subjects and more frequent with frontal rTMS. More serious adverse effects were rare and consisted of two seizures and four instances of psychotic symptoms induced by rTMS to the dorsolateral prefrontal cortex in patients with depression. CONCLUSIONS: Overall, as currently applied rTMS to non-motor areas appears to be safe with few, generally mild adverse effects. In future studies, we recommend systematic reporting of adverse effects and careful documentation of machine type, coils used, and actual intensity as a function of maximum stimulator output. Phosphene threshold might be used to index stimulation intensity when rTMS is applied to the visual cortex, and research should be directed to identifying other indexes of intensity for TMS to other non-motor areas. SIGNIFICANCE: rTMS under the present guidelines is safe, with minimal adverse effects, when applied to non-motor areas.

Adult↗

PubMed2002

Transcranial magnetic stimulation: new insights into representational cortical plasticity.

In the last decade, transcranial magnetic stimulation (TMS) has been used increasingly as a tool to explore the mechanisms and consequences of cortical plasticity in the intact human cortex. Because the spatial accuracy of the technique is limited, we refer to this as plasticity at a regional level. Currently, TMS is used to explore regional reorganization in three different ways. First, it can map changes in the pattern of connectivity within and between different cortical areas or their spinal projections. Important examples of this approach can be found in the work on motor cortex representations following a variety of interventions such as immobilization, skill acquisition, or stroke. Second, TMS can be used to investigate the behavioural relevance of these changes. By applying TMS in its "virtual lesion" mode, it is possible to interfere with cortical function and ask whether plastic reorganization within a distinct cortical area improves function. Third, TMS can be used to promote changes in cortical function. This is achieved by using repetitive TMS (rTMS) to induce short-term functional reorganization in the human cortex. The magnitude and the direction of rTMS-induced plasticity depend on extrinsic factors (i.e. the variables of stimulation such as intensity, frequency, and total number of stimuli) and intrinsic factors (i.e. the functional state of the cortex targeted by rTMS). Since conditioning effects of rTMS are not limited to the stimulated cortex but give rise to functional changes in interconnected cortical areas, rTMS is a suitable tool to investigate plasticity within a distributed functional network. Indeed, the lasting effects of rTMS offer new possibilities to study dynamic aspects of the pathophysiology of a variety of diseases and may have therapeutic potential in some neuropsychiatric disorders.

Animals↗

PubMed1998

Localizing the site of magnetic brain stimulation by functional MRI.

In order to locate the site of action of transcranial magnetic stimulation (TMS) within the human motor cortices, we investigated how the optimal positions for evoking motor responses over the scalp corresponded to the hand and leg primary-motor areas. TMS was delivered with a figure-8 shaped coil over each point of a grid system constructed on the skull surface, each separated by 1 cm, to find the optimal site for obtaining motor-evoked potentials (MEPs) in the contralateral first dorsal interosseous (FDI) and tibialis anterior (TA) muscles. Magnetic resonance imaging scans of the brain were taken for each subject with markers placed over these sites, the positions of which were projected onto the cortical region just beneath. On the other hand, cortical areas where blood flow increased during finger tapping or leg movements were identified on functional magnetic resonance images (fMRI), which should include the hand and leg primary-motor areas. The optimal location for eliciting MEPs in FDI, regardless of their latency, lay just above the bank of the precentral gyrus, which coincided with the activated region during finger tapping in fMRI studies. The direction of induced current preferentially eliciting MEPs with the shortest latency in each subject was nearly perpendicular to the course of the precentral gyrus at this position. The optimal site for evoking motor responses in TA was also located just above the activated area during leg movements identified within the anterior portion of the paracentral lobule. The results suggest that, for magnetic stimulation, activation occurs in the primary hand and leg motor area (Brodmann area 4), which is closest in distance to the optimal scalp position for evoking motor responses.

Brain Mapping↗

PubMed1989

Functional organization of the trigeminal motor system in man. A neurophysiological study.

Transcranial stimulation (TCS) in intact human subjects was used to investigate the corticobulbar projections and the functional organization of the trigeminal motor system. Both electrical (with the anode overlying the face area of the motor cortex) and magnetic TCS (with the coil at the vertex) excite the upper motoneurons projecting to the trigeminal motor nucleus, evoking motor potentials (C-MEPs) in the jaw-closing and suprahyoid muscles, but only during voluntary contraction. At least 30% of jaw-closing motoneurons are reached by direct fast-conducting corticobulbar fibres; these projections are mainly crossed. Suprahyoid motoneurons are also reached by fast-conducting corticobulbar fibres; these projections are probably bilateral. In the masseter, electrical TCS also evokes an ipsilateral motor response (R-MEP), followed by a later wave (U), and bilateral inhibitory periods. The R-MEP is secondary to excitation of the motor trigeminal root; the U wave probably results from the simultaneous excitation of Ia afferents in the root and ipsilaterally projecting corticofugal fibres; the inhibitory periods are largely due to activation of exteroceptive afferents in the root. Magnetic TCS, avoiding spread of current to the trigeminal root, evokes C-MEPs but not R-MEPs or U waves. The masseter inhibitory period after magnetic TCS may be due to excitation of corticofugal inhibitory fibres and to mechanical activation of Golgi tendon organs.

Adolescent↗

PubMed2001

Interhemispheric facilitation of the hand motor area in humans.

1. We investigated interhemispheric interactions between the human hand motor areas using transcranial cortical magnetic and electrical stimulation. 2. A magnetic test stimulus was applied over the motor cortex contralateral to the recorded muscle (test motor cortex), and an electrical or magnetic conditioning stimulus was applied over the ipsilateral hemisphere (conditioning motor cortex). We investigated the effects of the conditioning stimulus on responses to the test stimulus. 3. Two effects were elicited at different interstimulus intervals (ISIs): early facilitation (ISI = 4-5 ms) and late inhibition (ISI > or = 11 ms). 4. The early facilitation was evoked by a magnetic or anodal electrical conditioning stimulus over the motor point in the conditioning hemisphere, which suggests that the conditioning stimulus for early facilitation directly activates corticospinal neurones. 5. The ISIs for early facilitation taken together with the time required for activation of corticospinal neurones by I3-waves in the test hemisphere are compatible with the interhemispheric conduction time through the corpus callosum. Early facilitation was observed in responses to I3-waves, but not in responses to D-waves nor to I1-waves. Based on these results, we conclude that early facilitation is mediated through the corpus callosum. 6. If the magnetic conditioning stimulus induced posteriorly directed currents, or if an anodal electrical conditioning stimulus was applied over a point 2 cm anterior to the motor point, then we observed late inhibition with no early facilitation. 7. Late inhibition was evoked in responses to both I1- and I3-waves, but was not evoked in responses to D-waves. The stronger the conditioning stimulus was, the greater was the amount of inhibition. These results are compatible with surround inhibition at the motor cortex.

Conditioning, Psychological↗

PubMed1991

Coil placement in magnetic brain stimulation related to skull and brain anatomy.

The influence of coil position on the size of electromyographic responses evoked by transcranial magnetic brain stimulation was systematically evaluated. The position of the stimulation coil (11.6 cm outer diameter, Novametrix) was recorded by constructing individual grids on the skull surface using extracranial bony landmarks and was then related to underlying cerebral sulci by analysis of magnetic resonance images of the brain and skull. The largest responses in the right first dorsal interosseus (FDI) muscle, when using anticlockwise coil currents as viewed from above, were found, on average (5 subjects), to occur with the coil centred 2 cm behind and left of the vertex. For the right tibialis anterior (TA) muscle the largest responses were obtained, on average, with the coil centred around a point 4 cm anterior to and 4 cm left of the vertex. Between individuals, the optimal coil position for responses in a particular muscle varied up to 2 cm. This variability could be explained by the variability in the relationship between the central sulcus and the extracranial bony landmarks of each individual. Responses could be obtained whenever the windings of the coil passed over the appropriate region of the motor cortex, providing evidence that magnetically evoked responses do originate from activation of the precentral gyrus. The size of the cortically evoked responses for a given stimulus intensity depended on the direction of the coil currents passing over the motor area. For FDI muscles, the largest responses were obtained when the coil currents passed over the lateral part of the motor strip from forwards behind and transversely to the central sulcus.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed2006

[Micropolarization of the brain: a noninvasive method for correction of morphological and functional disturbances in acute focal brain lesions and their consequences].

The paper is devoted to the use of small direct current in correction of morphological and functional disturbances of the human brain. Two hundred and one patients aged from 7 to 82 years have been studied. In patients with focal brain damages at the acute stage (1-2 days after stroke), the anode and cathode were placed in the projection of a damaged center. In patients in "autonomic status" condition, the anode was placed both in frontal and parietal projection of the right hemisphere cortex and the cathode--on a mastoid of the right hemisphere. Strength of the current used was 300-500 mcA, time of one procedure--30-40 min. The whole treatment course involved no more than 15 procedures. Before the treatment, after 3-5 procedures of micropolarization and at the end of the treatment course, patients underwent computer tomography and electroencephalographic study. Transcranial micropolarization exerts a cerebroprotective effect and has a selective-systemic character due to an increase of neuronal structures activity boht directly in the area of the impact that manifests with the absence of brain edema and the reduction of the destruction locus by 10-15% just after three procedures and as in the other brain regions that results in the decrease of intensity of general cerebral symptoms. The micropolarization promotes restoration of the broken functional connections in central regulatory systems caused by improvement of interaction between neurons, structures and systems the results finally in restoration of central regulation of body's functions.

Adult↗

PubMed2001

Investigation into non-monosynaptic corticospinal excitation of macaque upper limb single motor units.

There has been considerable recent debate as to relative importance, in the primate, of propriospinal transmission of corticospinal excitation to upper limb motoneurons. Previous studies in the anesthetized macaque monkey suggested that, compared with the cat, the transmission of such excitation via a system of C3-C4 propriospinal neurons may be relatively weak. However, it is possible that in the anesthetized preparation, propriospinal transmission of cortical inputs to motoneurons may be depressed. To address this issue, the current study investigated the responses of single motor units (SMUs) to corticospinal inputs in either awake (n = 1) or lightly sedated (n = 3) macaque monkeys. Recordings in the awake state were made during performance of a precision grip task. The responses of spontaneously discharging SMUs to electrical stimulation of the pyramidal tract (PT) via chronically implanted electrodes were examined for evidence of non-monosynaptic, presumed propriospinal, effects. Single PT stimuli (up to 250 microA; duration, 0.2 ms, 2 Hz) were delivered during steady discharge of the SMU (10-30 imp/s). SMUs were recorded from muscles acting on the thumb (adductor pollicis and abductor pollicis brevis, n = 18), wrist (extensor carpi radialis, n = 29) and elbow (biceps, n = 9). In all SMUs, the poststimulus time histograms to PT stimulation consisted of a single peak at a fixed latency and with a brief duration [0.74 +/- 0.25 (SD) ms, n = 56], consistent with the responses being mediated by monosynaptic action of cortico-motoneuronal (CM) impulses. Later peaks, indicating non-monosynaptic action, were not present even when the probability of the initial peak response was low and when there was no evidence for suppression of ongoing SMU activity following this peak (n = 20 SMUs). Even when repetitive (double-pulse) PT stimuli were used to facilitate transmission through oligosynaptic linkages, no later peaks were observed (16 SMUs). In some thumb muscle SMUs (n = 8), responses to PT stimulation were compared with those evoked by transcranial magnetic stimulation, using a figure-eight coil held over the motor cortex. Responses varied according the orientation of the coil: in the latero-medial position, single peak responses similar to those from the PT were obtained; their latencies confirmed direct excitation of CM cells, and there were no later peaks. In the posterio-anterior orientation, responses had longer latencies and consisted of two to three subpeaks. At least under the conditions that we have tested, the results provide no positive evidence for transmission of cortical excitation to upper limb motoneurons by non-monosynaptic pathways in the macaque monkey.

Anesthesia↗

PubMed2003

Investigating human motor control by transcranial magnetic stimulation.

In this review we discuss the contribution of transcranial magnetic stimulation (TMS) to the understanding of human motor control. Compound motor-evoked potentials (MEPs) may provide valuable information about corticospinal transmission, especially in patients with neurological disorders, but generally do not allow conclusions regarding the details of corticospinal function to be made. Techniques such as poststimulus time histograms (PSTHs) of the discharge of single, voluntarily activated motor units and conditioning of H reflexes provide a more optimal way of evaluating transmission in specific excitatory and inhibitory pathways. Through application of such techniques, several important issues have been clarified. TMS has provided the first real evidence that direct monosynaptic connections from the motor cortex to spinal motoneurons exist in man, and it has been revealed that the distribution of these projections roughly follows the same proximal-distal gradient as in other primates. However, pronounced differences also exist. In particular, the tibialis anterior muscle appears to receive as significant a monosynaptic corticospinal drive as muscles in the hand. The reason for this may be the importance of this muscle in controlling the foot trajectory in the swing phase of walking. Conditioning of H reflexes by TMS has provided evidence of changes in cortical excitability prior to and during various movements. These experiments have generally confirmed information obtained from chronic recording of the activity of corticospinal cells in primates, but information about the corticospinal contribution to movements for which information from other primates is sparse or lacking has also been obtained. One example is walking, where TMS experiments have revealed that the corticospinal tract makes an important contribution to the ongoing EMG activity during treadmill walking. TMS experiments have also documented the convergence of descending corticospinal projections and peripheral afferents on spinal interneurons. Current investigations of the functional significance of this convergence also rely on TMS experiments. The general conclusion from this review is that TMS is a powerful technique in the analysis of motor control, but that care is necessary when interpreting the data. Combining TMS with other techniques such as PSTH and H reflex testing amplifies greatly the power of the technique.

Electromagnetic Fields↗

PubMed2006

Intraoperative motor-evoked potential monitoring in scoliosis surgery: comparison of desflurane/nitrous oxide with propofol total intravenous anesthetic regimens.

STUDY DESIGN: A prospective, randomized study in a large general hospital setting. BACKGROUND: During spinal surgery, monitoring motor-evoked potentials (MEPs) is a means of assessing the intraoperative integrity of corticospinal pathways. However, MEPs are known to be sensitive to the effects of anesthetic agents. OBJECTIVE: To compare the use of desflurane or total intravenous anesthetic regimens (TIVA) with multipulse cortical stimulation for intraoperative monitoring (IOM). METHODS: Twenty consecutive patients (10 in each arm) undergoing scoliosis correction surgery were randomly assigned to 2 equal groups receiving desflurane or TIVA. Inhalational anesthesia was maintained using 66% nitrous oxide in oxygen and a mean end-tidal desflurane concentration of 3.4%. For TIVA, continuous intravenous infusion of propofol was used. For analgesia, fentanyl and morphine were given when required for both groups. Cortical stimulation was achieved with 2 bipolar direct current stimulators connected in parallel by jumper cables. Five equivalent pulses 0.5 ms in duration at 4 ms intervals were delivered at C1C2 positions. MEP recordings were made in the abductor hallucis (AH) and tibialis anterior (TA) with needle electrodes. RESULTS: Reproducible MEPs were obtained throughout the operation in all 20 cases, with up to 80 mA per stimulator. Before insertion of pedicle screws, mean MEP amplitudes (SD) obtained were 85 (19) and 21.7 (10.8) mV for AH and TA, respectively, using desflurane. With TIVA, amplitudes were 56.7 (28.4) and 59.1 (24.5) mV, respectively. Both muscle MEP amplitudes were significantly different using different anesthetic regimens (P < 0.05 for all). AH MEP amplitudes obtained with desflurane were significantly larger than TA amplitudes (P < 0.0001). No complications were reported intraoperatively and postoperatively. CONCLUSIONS: This is the first study comparing the use of desflurane and TIVA showing that both anesthetic regimens allowed successful intraoperative monitoring useage throughout the procedures. For MEP recording, the AH was the preferred muscle with a desflurane anesthetic regimen.

Adolescent↗