On the estimation of silent period thresholds in transcranial magnetic stimulation

ObjectiveWe evaluated the induction of corticospinal silent period (SP) using transcranial magnetic stimulation (TMS) at stimulation intensities normalized to resting motor threshold (rMT) or silent period thresholds (SPTs). The aim was to reduce the characteristic inter-individual variation in SP measurements in healthy population to improve the sensitivity of such measurements.MethodsThe cortical representation area of the right hand musculature of 12 healthy subjects was stimulated with navigated TMS with varying stimulating intensities. Subsequently, the individual SPTs for eliciting SPs of 20, 30, and 50 ms in duration were determined from the input–output characteristics.ResultsWhile SPT for 20 and 50 ms SPs differed from rMT, the SPT for 30 ms was similar to rMT. Nevertheless, the inter-individual variation in SP duration was reduced significantly at 120% of SPT30 when compared with SP durations obtained at 120% of rMT.ConclusionsInter-individual variation in the SP duration decreases when applying TMS at stimulation intensities normalized to the individual SPTs instead to the rMT. This makes the SP duration more specific to inhibition and less affected by changes in cortical excitability.SignificanceUse of individual SPTs may improve the sensitivity of the SP measures in studies with inter-individual design.     

GABA and cortical inhibition in motor and non-motor regions using combined TMS–EEG: A time analysis

ObjectiveThe induction of long interval cortical inhibition (LICI) in motor cortex with paired pulse transcranial magnetic stimulation (ppTMS) is an established paradigm for the assessment of cortical inhibition, proposed to be related to GABA_B receptor inhibitory neurotransmission. This study aimed to further evaluate recent methods of the assessment of LICI in non motor regions with ppTMS and electroencephalography (EEG).MethodsppTMS was applied using a single coil to the motor and dorsolateral prefrontal cortex (DLPFC) in 14 healthy subjects, and in the parietal lobe in 5 of those subjects.ResultsIn the motor cortex, LICI resulted in significant suppression in mean cortical evoked activity on EEG between 75 and 250 ms following delivery of the test stimulus. Maximal inhibition was seen from 50 to 250 ms in DLPFC, and between 50 and 175 ms in the parietal lobe.ConclusionsppTMS may be used to produce LICI in several cortical regions with a time course similar to known GABA_B activity.SignificanceppTMS induction of LICI can be recorded by combining TMS with EEG and seems to relate to GABA_B activity.     

Neuromagnetic activation of primary and secondary somatosensory cortex following tactile-on and tactile-off stimulation

ObjectiveMagnetoencephalography (MEG) recordings were performed to investigate the cortical activation following tactile-on and tactile-off stimulation.MethodsWe used a 306-ch whole-head MEG system and a tactile stimulator driven by a piezoelectric actuator. Tactile stimuli were applied to the tip of right index finger. The interstimulus interval was set at 2000 ms, which included a constant stimulus of 1000 ms duration.ResultsProminent somatosensory evoked magnetic fields were recorded from the contralateral hemisphere at 57.5 ms and 133.0 ms after the onset of tactile-on stimulation and at 58.2 ms and 138.5 ms after the onset of tactile-off stimulation. All corresponding equivalent current dipoles (ECDs) were located in the primary somatosensory cortex (SI). Moreover, long-latency responses (168.7 ms after tactile-on stimulation, 169.8 ms after tactile-off stimulation) were detected from the ipsilateral hemisphere. The ECDs of these signals were identified in the secondary somatosensory cortex (SII).ConclusionsThe somatosensory evoked magnetic fields waveforms elicited by the two tactile stimuli (tactile-on and tactile-off stimuli) with a mechanical stimulator were strikingly similar. These mechanical stimuli elicited both contralateral SI and ipsilateral SII activities.SignificanceTactile stimulation with a mechanical stimulator provides new possibilities for experimental designs in studies of the human mechanoreceptor system.     

Short-Latency Artifacts Associated with Concurrent TMS–EEG

BackgroundConcurrent transcranial magnetic stimulation and electroencephalography (TMS–EEG) is an emerging method for studying cortical network properties. However, various artifacts affect measurement of TMS-evoked cortical potentials (TEPs), especially within 30 ms of stimulation.Objective/hypothesisThe aim of this study was to assess the origin and recovery of short-latency TMS–EEG artifacts (<30 ms) using different stimulators and under different experimental conditions.MethodsEEG was recorded during TMS delivered to a phantom head (melon) and 12 healthy volunteers with different TMS machines, at different scalp positions, at different TMS intensities, and following paired-pulse TMS. Recovery from the TMS artifact and other short-latency artifacts were compared between conditions.ResultsFollowing phantom stimulation, the artifact resulting from different TMS machines (Magstim 200, Magventure MagPro R30 and X100) and pulse shapes (monophasic and biphasic) resulted in different artifact profiles. After accounting for differences between machines, TMS artifacts recovered within ～12 ms. This was replicated in human participants, however a large secondary artifact (peaks at 5 and 10 ms) became prominent following stimulation over lateral scalp positions, which only recovered after ～25–40 ms. Increasing TMS intensity increased secondary artifact amplitude over both motor and prefrontal cortex. There was no consistent modulation of the secondary artifact following inhibitory paired-pulse TMS (interstimulus interval = 100 ms) over motor cortex.ConclusionsThe secondary artifact observed in humans is consistent with activation of scalp muscles following TMS. TEPs can be recorded within a short period of time (10–12 ms) following TMS, however measures must be taken to avoid muscle stimulation.     

Inhibition of the anterior intraparietal area and the dorsal premotor cortex interfere with arbitrary visuo-motor mapping

ObjectiveThe contribution of the human anterior intraparietal area and the dorsal premotor cortex to arbitrary visuo-motor mapping during grasping were tested.MethodsTrained right-handed subjects reached for and pincer-grasped a cube with the right hand in the absence of visual feedback after the cube location had been displayed for 200 ms. During the reaching movements, the colour of the cube changed and visual feedback about the change of colour was provided for 100 ms at 500 ms after movement onset (at the time of peak grasp aperture). Depending on colour, subjects were instructed to either pincer-grasp the cube in a horizontal or vertical grasp position with the latter necessitating wrist rotation (experiment 1) or to pincer-grasp and transport the cube to either a left or right target position (experiment 2). Within two consecutive 200 ms time windows (TMS 1 and 2) starting 500 ms and 700 ms after movement onset, respectively, double pulses of supra-threshold transcranial magnetic stimulation (inter-stimulus interval: 100 ms) were delivered over (i) the left primary motor cortex (90° vertically angulated coil position, control stimulation), (ii) the left dorsal premotor cortex or (ii) the left anterior intraparietal area.ResultsCompared to control stimulation, stimulation of the anterior intraparietal area, but not of the dorsal premotor cortex, at TMS 1 delayed the times to wrist rotation (experiment 1) and hand transport (experiment 2). Compared to control stimulation, stimulation of the dorsal premotor cortex, but not of the anterior intraparietal area, at TMS 2 delayed both wrist rotation (experiment 1) and hand transport (experiment 2).ConclusionsWe contend that the anterior intraparietal area and the dorsal premotor cortex are both involved albeit at different phases during the mapping of arbitrary visual cues with goal directed grasp and transport movements.SignificanceThese data add to the current understanding of how human cortical areas work in concert during manual activities.     

Exercise-induced strengthening of inter-digital connections in musicians

ObjectiveTo investigate whether finger exercise affects surround inhibition in professional musicians as it was previously observed in non-musicians, we performed a transcranial magnetic stimulation (TMS) study in 13 healthy right-handed professional musicians.MethodsTMS was set to be triggered by self-initiated flexion of the index finger at 3 ms after electromyography onset (self-triggered TMS). Motor evoked potentials (MEPs) of the abductor digiti minimi (ADM) were measured before and at 0, 10, 20 and 30 min after ‘single’ (little finger abduction) and ‘dual’ (both index finger flexion and little finger abduction) exercise at 0.5 Hz for 30 min.ResultsControl and self-triggered MEPs were not different between the two exercise sessions. MEP enhancements were significantly greater in self-triggered TMS than control TMS after single exercise as well as dual exercise.ConclusionThis result demonstrates that MEP enhancement in self-triggered TMS was comparable between two exercise sessions in professional musicians, a result different from that observed in healthy non-musicians. Enhanced self-triggered MEPs after isolated finger exercise suggest that inter-digital cortical connections are strengthened in musicians, presumably due to previous musical training.SignificanceInter-digital cortical connections are strengthened in musicians and are not differently modulated by different types of short-term finger exercise.     

Increased cortical excitability after selective REM sleep deprivation in healthy humans: A transcranial magnetic stimulation study

BackgroundREM sleep has antiepileptogenic properties whereas, its loss is known to have a proconvulsive role. However, the mechanisms underlying the proepileptogenic effects of REM sleep deprivation are yet not fully understood. The aim of our study was to evaluate the effects of selective REM sleep deprivation (SRD) on cortical excitability in healthy subjects by means of transcranial magnetic stimulation (TMS).MethodsTen normal subjects underwent three TMS sessions: (1) in baseline condition (BL), (2) after SRD by awakening them at each REM sleep onset and (3) after non-rapid eye movement sleep awakenings (NREM-A) as control for potential non-specific effects of interruptions. The TMS investigation included two protocols: (a) the evaluation of motor evoked potentials (MEPs) and silent period (SP) parameters, recorded in response to single pulse magnetic stimulation; (b) the evaluation of the time course of intracortical motor activity tested with paired-pulse TMS applied at inter-stimulus intervals of 1–10 ms.ResultsAfter SRD the principal finding observed using single pulse TMS was a significant reduction in the duration of SP whereas, a reduction of intracortical inhibition was found, using the paired-pulse TMS. TMS parameters did not show significant changes after NREM-A with respect to BL.ConclusionsSRD may influence cortical excitability with a reduction of inhibitory intracortical mechanisms, thus supporting the proconvulsant role of REM loss.     

Corticospinal activation confounds cerebellar effects of posterior fossa stimuli

ObjectiveTo investigate the efficacy of magnetic stimulation over the posterior fossa (PF) as a non-invasive assessment of cerebellar function in man.MethodsWe replicated a previously reported conditioning-test paradigm in 11 healthy subjects. Transcranial magnetic stimulation (TMS) at varying intensities was applied to the PF and motor cortex with a 3, 5 or 7 ms interstimulus interval (ISI), chosen randomly for each trial. Surface electromyogram (EMG) activity was recorded from two intrinsic hand muscles and two forearm muscles. Responses were averaged and rectified, and MEP amplitudes were compared to assess whether suppression of the motor output occurred as a result of the PF conditioning pulse.ResultsCortical MEPs were suppressed following conditioning-test ISIs of 5 or 7 ms. No suppression occurred with an ISI of 3 ms. PF stimuli alone also produced EMG responses, suggesting direct activation of the corticospinal tract (CST).ConclusionsCST collaterals are known to contact cortical inhibitory interneurones; antidromic CST activation could therefore contribute to the observed suppression of cortical MEPs.SignificancePF stimulation probably activates multiple pathways; even at low intensities it should not be regarded as a selective assessment of cerebellar function unless stringent controls can confirm the absence of confounding activity in other pathways.     

Methodology for intraoperatively eliciting motor evoked potentials in the vocal muscles by electrical stimulation of the corticobulbar tract

ObjectiveTo establish a methodology for recording corticobulbar motor evoked potentials (CoMEPs) from vocal muscles after transcranial electrical stimulation (TES) and direct cortical stimulation (DCS).MethodsTwenty-four patients were included in this study (22 for TES, 2 for DCS, 3 for TES plus DCS) that underwent different surgical procedures. We used two methods to elicit CoMEPs: (a) TES by stimulation over C3/Cz or C4/Cz and (b) DCS with a strip electrode placed over the primary motor area (M1) for laryngeal muscles. To record CoMEPs from vocal muscles we used two hook wire electrodes 76 μm of diameter passing through 27 gauge needle endotracheally placed in the vocal muscles after intubation.ResultsRecording of CoMEPs in the vocal muscles after TES was successfully performed in 22 patients. TES over the right or left hemisphere elicit responses bilaterally. The onset latencies for the right vocal muscle was 12.4 ± 3.1 ms (ipsilateral stimulation) and 12.7 ±2.2 ms (contralateral stimulation) while for the left vocal muscle, onset latency was 12.9 ± 2.3 ms (ipsilateral stimulation) and 14.1 ± 3.4 ms (contralateral stimulation). In five patients DCS elicited CoMEPs in right and left vocal muscle with latency of 16.6 ± 4.7 and 15.6 ± 3.7 ms, respectively.ConclusionThe method to elicit and record CoMEPs in vocal muscles shows reliable results and adds one more tool in the armamentarium of intraoperative neurophysiology.SignificanceThis method shows the ability to continuously monitor the functional integrity of corticobulbar pathways, vagal nucleus and laryngeal nerves.     

Sensory afferent inhibition within and between limbs in humans

ObjectiveTo examine the distribution and inter-limb interaction of short-latency afferent inhibition (SAI) in the arm and leg.MethodsMotor evoked potentials (MEPs) in distal and proximal arm, shoulder and leg muscles induced with ranscranial magnetic stimulation (TMS) were conditioned by painless electrical stimuli applied to the index finger (D2) and great toe (T1) at interstimulus intervals (ISIs) of 15, 25–35, 80 ms (D2) and 35, 45, 55, 65 and 100 ms (T1) in 27 healthy human subjects. TMS was delivered over primary motor cortex (M1) arm and leg areas. Electrical stimulus intensities were varied between 1 and 3 times the sensory perception thresholds. We also tested effects of posterior cutaneous brachial nerve (PCBN) stimulation on MEPs in arm muscles at ISIs of 18 and 28 ms.ResultsD2 but not PCBN electrical conditioning reduced MEP amplitudes in upper limb muscles at ISIs of 25 and 35 ms. SAI was more pronounced in distal as compared to proximal arm muscles. Also, SAI following D2 stimulation increased with higher conditioning intensities. D2 stimulation did not change lower limb muscles MEPs. In ontrast, T1 stimulation did not induce SAI in any muscles but caused MEP facilitation in a foot muscle at an ISI of 55 ms and in upper limb muscles at ISIs of 35 and 55 ms. Short interval intracortical inhibition (SICI) and intracortical facilitation (ICF) were not affected by electrical T1 conditioning.ConclusionD2 stimulation causes segmental SAI in upper limb muscles with a distal to proximal attenuation without affecting leg muscles. In contrast, toe stimulation facilitates motor output both in foot and upper arm muscles.SignificanceOur data suggest that cutaneo-motor pathways in arms and legs are functionally organized in a different way with cutaneo-motor interactions induced by toe stimulation probably relayed at a thalamic level. Abnormal cutaneo-motor interactions following electrical toe stimulation may serve as an electrophysiological marker of thalamic dysfunction, e.g. in neurodegenerative diseases.     

Bidirectional modulation of sensory cortical excitability by quadripulse transcranial magnetic stimulation (QPS) in humans

ObjectiveQuadripulse transcranial magnetic stimulation (QPS) is a newly designed patterned repetitive transcranial magnetic stimulation (TMS). Previous studies of QPS showed bidirectional effects on the primary motor cortex (M1), which depended on its inter-stimulus interval (ISI): motor evoked potentials (MEPs) were potentiated at short ISIs and depressed at long ISIs (homotopic effects). These physiological characters were compatible with synaptic plasticity. In this research, we studied effects of QPS on the primary sensory cortex (S1).MethodsOne burst consisted of four monophasic TMS pulses at an intensity of 90% active motor threshold. The ISI of four pulses was set at 5 ms (QPS-5) or at 50 ms (QPS-50). Same bursts were given every 5 s for 30 min. QPS-5 and QPS-50 were performed over three areas (M1, S1 and dorsal premotor cortex (dPMC)). One sham stimulation session was also performed. Excitability changes of S1 were evaluated by timeline of somatosensory evoked potentials (SEPs).ResultsQPS-5 over M1 or dPMC enhanced the P25–N33 component of SEP, and QPS-50 over M1 depressed it. By contrast, QPSs over S1 had no effects on SEPs.ConclusionsQPSs over motor cortices modulated the S1 cortical excitability (heterotopic effects). Mutual connections between dPMC or M1 and S1 might be responsible for these modulations.SignificanceQPSs induced heterotopic LTP or LTD-like cortical excitability changes.     

Effects of spinal cord stimulation on the cortical somatosensory evoked potentials in failed back surgery syndrome patients

ObjectiveTo evaluate the functional activation of the somatosensory cortical regions in neuropathic pain patients during therapeutic spinal cord stimulation (SCS).MethodsIn nine failed back surgery syndrome patients, the left tibial and the left sural nerves were stimulated in two sessions with intensities at motor and pain thresholds, respectively. The cortical somatosensory evoked potentials were analyzed using source dipole analysis based on 111 EEG signals.ResultsThe short-latency components of the source located in the right primary somatosensory cortex (SI: 43, 54 and 65 ms) after tibial nerve stimulation, the mid-latency SI component (87 ms) after sural nerve stimulation, and the mid-latency components in the right (≈161 ms) and left (≈168 ms) secondary somatosensory cortices (SII) were smaller in the presence of SCS than in absence of SCS. The long-latency source component arising from the mid-cingulate cortex (≈313 ms) was smaller for tibial and larger for sural nerve stimuli during SCS periods compared to periods without SCS.ConclusionsSCS attenuates the somatosensory processing in the SI and SII. In the mid-cingulate cortex, the effect of SCS depends on the type of stimulation and nerve fibers involved.SignificanceResults suggest that the effects of SCS on cortical somatosensory processing may contribute to a reduction of allodynia during SCS.     

Synchronized measurement of simultaneous EEG–fMRI: A simulation study

ObjectiveThe quality of averaged gradient artifact subtraction from EEG recorded during fMRI is highly dependent on the accuracy of gradient artifact sampling. Even small sampling shifts (e.g. a single datapoint at 5 kHz) increase the variance of the sampled gradient artifacts because of very steep slopes in the signal time course. Hence, although principally gradient artifacts are invariant signals because of their technical origin, variance attributed to sampling errors attenuates the effect of artifact removal. Recently, it has been shown that synchronizing the EEG-amplifier clock to the MR-scanner control-device clock improves artifact reduction by subtraction.MethodsIn order to investigate the synchronized measurement of combined EEG–fMRI, we used simulated EEG by measuring function generator signals in the MR-scanner. Only the usage of known signals allows an assessment of the improvement in accuracy of artifact recording by synchronized compared to non-synchronized measurement, since the signal is identical in both conditions.ResultsAfter averaged gradient artifact subtraction synchronized recorded signals were apparently less distorted than non-synchronized recorded signals. Spectral analyses revealed that especially artifact frequencies above 50 Hz had less power in restored synchronized compared to restored non-synchronized recorded signals. Computed total signal variances were not always less in restored synchronized compared to restored non-synchronized recorded signals.ConclusionsTaken together, synchronizing simultaneous EEG–fMRI measurement is a useful enhancement for averaged gradient artifact subtraction although post-correction filtering is still necessary.SignificanceOur results support the recent finding that synchronization improves the quality of averaged gradient artifact subtraction. However, quantitatively we could not verify a systematic benefit of recording electrical signals during fMRI synchronously rather than non-synchronously to the MR-scanner control-device clock.     

Suppression of deep brain stimulation artifacts from the electroencephalogram by frequency-domain Hampel filtering

ObjectiveCurrently, electroencephalography (EEG) cannot be used to record cortical activity during clinically effective DBS due to the presence of large stimulation artifact with components that overlap the useful spectrum of the EEG. A filtering method is presented that removes these artifacts whilst preserving the spectral and temporal fidelity of the underlying EEG.MethodsThe filter is based on the Hampel identifier that treats artifacts as outliers in the frequency domain and replaces them with interpolated values. Performance of the filter was tested with a synthesized DBS signal and actual data recorded during bilateral monopolar DBS.ResultsMean increases in signal-to-noise ratio of 7.8 dB for single-frequency stimulation and 13.8 dB for dual-frequency stimulation are reported. Correlation analysis between EEG with synthesized artifacts and artifact-free EEG reveals that distortion to the underlying EEG in the filtered signal is negligible (r² > 0.99).ConclusionsFrequency-domain Hampel filtering has been shown to remove monopolar DBS artifacts under a number of common stimulation conditions used for the treatment of Parkinson’s disease.SignificanceApplication of frequency-domain Hampel filtering will allow the measurement of EEG in patients during clinically effective DBS and thus may increase our understanding of the mechanisms of action of this important therapeutic intervention.     

Effects of water immersion on short- and long-latency afferent inhibition,short-interval intracortical inhibition,and intracortical facilitation

ObjectiveThe aim of the present study was to investigate the effect of water immersion (WI) on short- and long-latency afferent inhibition (SAI and LAI), short-interval intracortical inhibition (SICI), and intracortical facilitation (ICF).MethodsMotor evoked potentials (MEPs) were measured from the first dorsal interosseous (FDI) muscle of fifteen healthy males before, during, and after a 15-min WI at 30 °C up to the axilla. Both SAI and LAI were evaluated by measuring MEPs in response to transcranial magnetic stimulation (TMS) of the left motor cortex following electrical stimulation of the right median nerve (fixed at about three times the sensory threshold) at interstimulus intervals (ISIs) of 20 ms to assess SAI and 200 ms to assess LAI. The paired-pulse TMS paradigm was used to measure SICI and ICF.ResultsBoth SAI and LAI were reduced during WI, while SICI and ICF were not significantly different before, during, and after WI.ConclusionsWI decreased SAI and LAI by modulating the processing of afferent inputs.SignificanceChanges in somatosensory processing and sensorimotor integration may contribute to the therapeutic benefits of WI for chronic pain or movement disorders.     

The effect of modafinil on cortical excitability in patients with narcolepsy: A randomized,placebo-controlled,crossover study

ObjectiveTo investigate the effect of modafinil on cortical excitability in patients with narcolepsy using transcranial magnetic stimulation (TMS).MethodsNineteen drug-naïve narcolepsy patients with cataplexy (10 males, 9 females, and mean age 28.5 years) and 25 age- and sex-matched healthy controls were recruited. In this double-blind, randomized, crossover study, patients and controls received a single dose of 400 mg modafinil or placebo. Modafinil and placebo administrations were separated by a 2-week washout period. TMS parameters, such as resting motor thresholds (RMT), motor-evoked potential (MEP) amplitudes, cortical silent periods (CSP), short-interval intracortical inhibition (SICI), and intracortical facilitation (ICF), were measured before and 3 h after administering modafinil or placebo. The differences of TMS parameters were statistically tested between patients and controls and between before and after modafinil or placebo administration.ResultsNarcolepsy patients had significantly increased CSP durations compared to controls (independent t-test, P < 0.05), indicating decreased excitability of cortical networks in human narcolepsy. In patients after modafinil administration, MEP amplitudes, SICI, and ICF increased, and CSP duration shortened significantly, meaning enhanced motor excitability, whereas in controls modafinil did not change TMS parameters significantly. Placebo administration did not affect TMS parameters both in patients or controls.ConclusionsNarcolepsy patients with cataplexy showed decreased cortical excitability than normal healthy controls. Single dose modafinil significantly increased motor excitability in narcolepsy patients but had no effect in healthy controls.     

Increased motor cortical excitability after whole-hand electrical stimulation: A TMS study

ObjectiveTo examine the neuromodulatory effect of whole-hand mesh-glove (MG) stimulation on motor cortical pathways, we explored motor cortical excitability before and after suprathreshold whole-hand MG stimulation using transcranial magnetic stimulation (TMS).MethodsTwenty-eight healthy volunteers (14 controls) were studied at baseline, immediately post and 1 h post-MG stimulation for 30 min. Motor thresholds (MTs), motor evoked potentials (MEPs) recruitment curve, short intracortical inhibition (SICI) and intracortical facilitation (ICF) after paired magnetic stimuli were evaluated.ResultsAfter MG stimulation the MTs were significantly reduced and slope of MEP recruitment curve significantly increased; furthermore, the stimulation led to a sustained decrease of SICI and increase of ICF in the contralateral motor cortex. These effects lasted for at least 60 min and were stronger 1 h post-stimulation compared with testing immediately after stimulation. A sham group did not show any differences before and after MG stimulation.ConclusionsWe provide a first demonstration that MG whole-hand stimulation induces increases in motor cortical excitability lasting at least 1 h. Both the strength of the corticospinal projections and the inhibitory and facilitatory intracortical mechanisms are involved. Synaptic modifications such as long-term potentiation mechanisms may underlie this stimulation-induced cortical plasticity changes.SignificancePresent results prove the MG stimulation to be a promising tool in neurorehabilitation.     

Neurophysiologic markers in laryngeal muscles indicate functional anatomy of laryngeal primary motor cortex and premotor cortex in the caudal opercular part of inferior frontal gyrus

ObjectiveThe aim of this study was to identify neurophysiologic markers generated by primary motor and premotor cortex for laryngeal muscles, recorded from laryngeal muscle.MethodsTen right-handed healthy subjects underwent navigated transcranial magnetic stimulation (nTMS) and 18 patients underwent direct cortical stimulation (DCS) over the left hemisphere, while recording neurophysiologic markers, short latency response (SLR) and long latency response (LLR) from cricothyroid muscle. Both healthy subjects and patients were engaged in the visual object-naming task. In healthy subjects, the stimulation was time-locked at 10–300 ms after picture presentation while in the patients it was at zero time.ResultsThe latency of SLR in healthy subjects was 12.66 ± 1.09 ms and in patients 12.67 ± 1.23 ms. The latency of LLR in healthy subjects was 58.5 ± 5.9 ms, while in patients 54.25 ± 3.69 ms. SLR elicited by the stimulation of M1 for laryngeal muscles corresponded to induced dysarthria, while LLR elicited by stimulation of the premotor cortex in the caudal opercular part of inferior frontal gyrus, recorded from laryngeal muscle, corresponded to speech arrest in patients and speech arrest and/or language disturbances in healthy subjects.ConclusionIn both groups, SLR indicated location of M1 for laryngeal muscles, and LLR location of premotor cortex in the caudal opercular part of inferior frontal gyrus, recorded from laryngeal muscle, while stimulation of these areas in the dominant hemisphere induced transient speech disruptions.SignificanceDescribed methodology can be used in preoperative mapping, and it is expected to facilitate surgical planning and intraoperative mapping, preserving these areas from injuries.     

Movement-related cortical potentials in patients with Machado-Joseph disease.

ObjectiveMovement-related cortical potentials (MRCP; nomenclature of MRCP components according to Shibasaki and Hallett (Shibasaki H, Hallett M. What is the Bereitschaftspotential? Clin Neurophysiol 2006;117:2341–56) were studied in patients with Machado–Joseph disease (MJD) to elucidate the pathophysiology of voluntary movement.MethodsWe studied nine genetically proven MJD patients and eight age-matched healthy subjects. Multi-channel electroencephalogram (EEG) recordings were obtained during self-paced fast extensions of the wrist. EEG epochs were time-locked to electromyography (EMG) onset or offset of the voluntary EMG burst and averaged.ResultsIn the MJD patients, the early Bereitschaftspotential (early BP, −1500 to −500 ms) was not affected but the late BP was reduced over the central midline area and contralaterally to the movement side. The amplitude of the fpMP, a post-movement MRCP component, was also reduced. In addition, the offset cortical potential in the first 500 ms after EMG offset (Moff + 500) was attenuated bilaterally over a wide cortical area.ConclusionsFindings suggest that cortical activations associated with the initiation and termination of a voluntary movement are impaired in MJD patients.SignificanceAbnormalities of pre- and post-movement MRCP components provide researchers with pathophysiological insight into voluntary motor dysfunction in MJD.     

When is electrical cortical stimulation more likely to produce afterdischarges?

ObjectiveTo study when afterdischarges (ADs) are more likely to occur during cortical stimulation.MethodsWe examined 6250 electrical stimulation trials in 13 patients with subdural electrodes, studying whether AD occurrence during a trial was influenced by electrode pair stimulated or AD occurrence during the previous trial. In total 545 electrodes were stimulated, 119 frontal (pre-perirolandic), 289 perirolandic, 36 parietal (post-perirolandic), 95 temporal, and 6 occipital.ResultsWhen the same electrode pair was stimulated as the prior trial, 19% produced ADs compared to 5% of trials when a different electrodes pair was stimulated (p < 0.0001). When trials showed ADs, and the next trial stimulated the same electrode pair, ADs occurred in 46% of cases, compared to 13% of trials following trials without ADs (p < 0.0001). AD probability decreased with increased inter-trial interval length only when the prior trial was at the same electrode pair and had produced an AD (p = 0.001). AD probability increased with stimulation duration, whether the trial followed a trial with (p < 0.001) or without (p < 0.0001) an AD.ConclusionsADs were more likely to occur when an electrode pair showed ADs and was stimulated again, especially when stimulating after short inter-trial intervals or for longer duration.SignificanceWhen ADs occur, waiting about a minute before resuming stimulation might lessen the likelihood of AD recurrence.