Polysomnographic scoring of sleep bruxism events is accurate even in the absence of video recording but unreliable with EMG-only setups.

PURPOSE: To determine the accuracy of scoring masticatory muscle activity (MMA) events in seven different polysomnography (PSG) setups. METHODS: Nineteen volunteers (13 females, 6 males, age 31.1 ± 12.9 years, 12 self-proclaimed bruxers) attended one-night PSG recording, supplemented with audio, video, and a separate frontal electroencephalography electrode set (FES). The same examiner scored the MMA events with seven different setups, with varying number of channels available: (1) one, (2) two, and (3) four EMG channels, (4) PSG without audio or video (PSG-N), (5) home PSG with FES and audio (FES-A), (6) PSG with audio (PSG-A), and (7) PSG with audio and video (PSG-AV). A subset (n = 10) of recordings was scored twice to determine intra-scorer reliability. MMA indices and accuracy of scoring the events in different setups were compared against PSG-AV. RESULTS: The intra-class correlation coefficient (ICC) between PSG-AV and PSG-A was high (0.940, p < 0.001) as well as for FES-A (0.927, p < 0.001), whereas for PSG-N, it was lower (0.835, p < 0.001); for setups with only EMG channels, coefficients were very low (ICC < 0.100 for all). Intra-examiner reliability was high (ICC > 0.939 for all setups), with the exception of PSG-N (ICC = 0.764, p = 0.002). When comparing against the MMA events scored in PSG-AV, the sensitivity of MMA event recognition for PSG-A was 78.5% and specificity 95.5%, which were substantially higher than sensitivity (52.0%) and specificity (87.2%) of PSG-N. CONCLUSIONS: MMA event scoring accuracy with PSG-A or FES-A is almost comparable to PSG-AV. Since precise event recognition is essential for accurate MMA scoring, it is evident that one cannot rely exclusively on EMG.

Home Polysomnography Reveals a First-Night Effect in Patients With Low Sleep Bruxism Activity.

STUDY OBJECTIVES: To examine the presence of a first-night effect (FNE) and the level of internight variability in sleep bruxism (SB) activity when a self-applicable electrode set is used in home polysomnography (PSG) in a sample of subjects with possible SB. METHODS: Fourteen females and two males aged 38.3 ± 9.1 years (mean ± standard deviation) with self-reported SB underwent home-PSG on three consecutive nights. The subjects applied PSG sensors themselves, including self-applicable electrode sets used to record sleep and masseter muscle activity. Repeated-measures analysis of variance was used to compare SB and sleep variables between the nights. RESULTS: Surprisingly, there were statistically significant elevations in the rhythmic masticatory muscle activity (RMMA) episode index (P = .009), burst index (P = .016), and bruxism time index (P = .049) throughout the course of 3 nights. More bruxers were diagnosed on the second (6 bruxers, ≥ 2 episodes/h) and third night (7 bruxers) compared to the first night (2 bruxers). Most subjects (14/16) had their highest RMMA index on the second or third night. The mean coefficient of variation for RMMA episode index was 50.7%. No statistically significant differences were detected in other sleep variables. CONCLUSIONS: The results indicate that a FNE may be present in SB activity, possibly lasting several nights in some subjects. Furthermore, FNE appears to be combined with high internight variability of SB activity without indications of internight changes in sleep macrostructure. To confirm the level of ongoing SB activity, several nights of PSG may be required, especially in subjects with low first-night SB activity. COMMENTARY: A commentary on this article appears in this issue on page 1281.

Success Rate and Technical Quality of Home Polysomnography With Self-Applicable Electrode Set in Subjects With Possible Sleep Bruxism.

Using sleep laboratory polysomnography (PSG) is restricted for the diagnosis of only the most severe sleep disorders due to its low availability and high cost. Home PSG is more affordable, but applying conventional electroencephalography (EEG) electrodes increases its overall complexity and lowers the availability. Simple, self-administered single-channel EEG monitors on the other hand suffer from poor reliability. In this study, we aimed to quantify the reliability of self-administrated home PSG recordings conducted with a newly designed ambulatory electrode set (AES) that enables multichannel EEG, electrooculography, electromyography, and electrocardiography recordings. We assessed the sleep study success rate and technical quality of the recordings performed in subjects with possible sleep bruxism (SB). Thirty-two females and five males aged 39.6 ± 11.6 years (mean±SD) with self-reported SB were recruited in the study. Self-administrated home PSG recordings with two AES designs were conducted (n = 19 and 21). The technical quality of the recordings was graded based on the proportion of interpretable data. Technical failure rate for AES (both designs) was 5% and SB was scorable for 96.9% of all recorded data. Only one recording failed due to mistakes in self-applying the AES. We found that the proportion of good quality self-administrated EEG recordings is significantly higher when multiple channels are used compared to using a single channel. Sleep study success rates and proportion of recordings with high quality interpretable data from EEG channels of AES were comparable to that of conventional home PSG. Self-applicable AES has potential to become a reliable tool for widely available home PSG.

Screen-printed ambulatory electrode set enables accurate diagnostics of sleep bruxism.

Currently, definite diagnosis of sleep bruxism requires polysomnography. However, it is restrictedly available, and too cumbersome and expensive for the purpose. The aim of this study was to introduce an ambulatory electrode set and evaluate its feasibility for more cost-effective diagnostics of sleep bruxism. Six self-assessed bruxers (one male, five females; aged 21-58 years) and six healthy controls (four males, two females, aged 21-25 years) underwent a standard polysomnographic study and a concurrent study with the ambulatory electrode set. Bruxism events, cortical arousals and sleep stages were scored for the two montages separately in a random order, and obtained sleep parameters were compared. In addition, the significance of video recording and sleep stage scoring for the diagnostic accuracy of ambulatory electrode set was determined. Ambulatory electrode set yielded similar diagnoses as standard polysomnography in all subjects. However, compared with standard polysomnography the median (interquartile range) tonic bruxism event index was significantly higher in the control group [+0.38 (+0.08 to +0.56) events per hour, P = 0.046], and the phasic bruxism event index was significantly lower in the bruxer group [-0.44 (-1.30 to +0.07) events per hour, P = 0.046]. Exclusion of video recording and both video recording and sleep stage scoring from analysis increased overestimation of the tonic bruxism event index in the control group +0.86 (+0.42 to +1.03) and +1.19 (+0.55 to +1.39) events per hour, P = 0.046 and P = 0.028, respectively], resulting in one misdiagnosed control subject. To conclude, ambulatory electrode set is a sensitive method for ambulatory diagnostics of sleep bruxism, and video recording and sleep stage scoring help reaching the highest specificity of sleep bruxism diagnostics.

Assessment of the suitability of using a forehead EEG electrode set and chin EMG electrodes for sleep staging in polysomnography.

Recently, a number of portable devices designed for full polysomnography at home have appeared. However, current scalp electrodes used for electroencephalograms are not practical for patient self-application. The aim of this study was to evaluate the suitability of recently introduced forehead electroencephalogram electrode set and supplementary chin electromyogram electrodes for sleep staging. From 31 subjects (10 male, 21 female; age 31.3 ± 11.8 years), sleep was recorded simultaneously with a forehead electroencephalogram electrode set and with a standard polysomnography setup consisting of six recommended electroencephalogram channels, two electrooculogram channels and chin electromyogram. Thereafter, two experienced specialists scored each recording twice, based on either standard polysomnography or forehead recordings. Sleep variables recorded with the forehead electroencephalogram electrode set and separate chin electromyogram electrodes were highly consistent with those obtained with the standard polysomnography. There were no statistically significant differences in total sleep time, sleep efficiency or sleep latencies. However, compared with the standard polysomnography, there was a significant increase in the amount of stage N1 and N2, and a significant reduction in stage N3 and rapid eye movement sleep. Overall, epoch-by-epoch agreement between the methods was 79.5%. Inter-scorer agreement for the forehead electroencephalogram was only slightly lower than that for standard polysomnography (76.1% versus 83.2%). Forehead electroencephalogram electrode set as supplemented with chin electromyogram electrodes may serve as a reliable and simple solution for recording total sleep time, and may be adequate for measuring sleep architecture. Because this electrode concept is well suited for patient's self-application, it may offer a significant advancement in home polysomnography.

A Handy EEG Electrode Set for patients suffering from altered mental state.

Although electroencephalography (EEG) is an important diagnostic tool for investigating patients with unexplained altered mental state (AMS), recording of emergency EEG is not a clinical routine. This is mainly due to the cumbersome electrode solutions. A Handy EEG Electrode Set consists of ten EEG, two EOG, two ground and two commutative reference hydrogel-coated silver wire electrodes attached to a thin polyester carrier film. The clinical usefulness of the Handy EEG Electrode Set was tested in 13 patients (five females, eight males) with AMS. EEG recordings were conducted at the same time with a standard 10-20 electrode set. The registration in the first patient case without the behind-ear electrodes (T9 and T10), indicated that these electrodes are very crucial to provide clinically relevant information from posterior regions of brain. In following 12 cases, the sensitivity and specificity for detecting EEG abnormality based on the Handy EEG Electrode Set recordings were 83 and 100 %, respectively. The Handy EEG Electrode Set proved to be easy to use and to provide valuable information for the neurophysiological evaluation of a patient suffering from AMS. However, further studies with larger number of patients are warranted to clarify the true diagnostic accuracy and applicability of this approach.

Novel screen printed electrode set for routine EEG recordings in patients with altered mental status.

There is a growing need for an easy to use screening tool for the assessment of brain's electrical function in patients with altered mental status (AMS). The purpose of this study is to give a brief overview of the state-of-the-art in electrode technology, and to present a novel sub-hairline electrode set developed in our research group. Screen-printing technology was utilized to construct the electrode set consisting of ten electroencephalography (EEG) electrodes, two electrooculography (EOG) electrodes, two ground electrodes and two reference electrodes. Electrical characteristics of hydrogel-coated silver ink electrodes were found adequate for clinical EEG recordings as assessed by electrical impedance spectroscopy (EIS). The skin-electrode impedances remain stable and low enough at least two days enabling high-quality long-term recordings. Due to the proper material selection, thin ink layers and detachable zero insertion force (ZIF) - connector, electrode was observed to be CT- and MRI-compatible allowing imaging without removing the electrodes. Pilot EEG recordings gave very promising results and an on-going clinical trial with larger number of patients will show the true feasibility of this approach.

The severity of individual obstruction events is related to increased mortality rate in severe obstructive sleep apnea.

Obstructive sleep apnea (OSA) is linked to an increased mortality rate. However, the severity of individual obstruction events is rarely considered quantitatively in clinical practice. We hypothesized that OSA with especially severe obstruction events would predispose a patient to greater health risks than OSA with a similar apnea-hypopnea index (AHI), but lower severity of individual events. This hypothesis was tested in a follow-up (198.2 ± 24.7 months) of a population of 1068 men referred for ambulatory polygraphic recording due to suspected OSA. The recordings were analysed according to the guidelines of the American Academy of Sleep Medicine. Furthermore, a novel obstruction severity parameter was determined; this was defined as the product of duration of the individual obstruction event and area of the related desaturation event. Patients treated with continuous positive airway pressure (CPAP) were omitted. We identified 125 deceased patients from our original population and for 113 of these a matching alive patient with similar AHI, age, body mass index (BMI), smoking habits and follow-up time could be found. The deceased patients with severe OSA (based on conventional AHI) showed higher obstruction severity values than their AHI-matched alive controls. Based on the multivariate logistic regression analysis, obstruction severity was the only parameter which was related statistically significantly to mortality in the severe OSA category. Furthermore, 59% of all deceased patients and 83% of those who had severe OSA displayed higher obstruction severity than the AHI-matched alive counterparts. To conclude, the obstruction severity parameter provided valuable prognostic information supplementing AHI. The obstruction severity parameter might improve recognition of the patients with the highest risk.

New disposable forehead electrode set with excellent signal quality and imaging compatibility.

The use of emergency electroencephalography (EEG) in clinical practice is limited in part due to the lack of commercially available EEG monitoring sets that are suitable for rapid and simple use. The aim of this study was to develop a rapid and simple-to-use disposable forehead EEG electrode set for routine use that is also suitable for long-term monitoring. The EEG set we developed consists of 12 hydrogel-coated electrodes (10 recording electrodes, plus a reference and ground electrode) attached to a solid polymer film. The developed EEG set was compared to the full conventional 10-20 electrode setup in terms of the ability to detect epileptiform abnormalities in two critically ill patients. The technical quality of the EEG signal from the newly developed electrode set was excellent, and status epilepticus was reliably detected with this EEG set. Electric performance testing showed that the impedance spectra of the developed EEG electrodes were comparable to those of three commercially available, disposable electrodes, and the noise level was lower than that of the commercial electrodes. The developed EEG set is also MRI and CT compatible and lacks any signs of imaging artefacts or heat induction. These promising results provide a reason to expect that the developed EEG set may be applicable to situations in which the full, conventional 10-20 electrode setup is not available.

Human brain cortical correlates of short-latency afferent inhibition: a combined EEG-TMS study.

When linking in time electrical stimulation of the peripheral nerve with transcranial magnetic stimulation (TMS), the excitability of the motor cortex can be modulated to evoke clear inhibition, as reflected by the amplitude decrement in the motor-evoked potentials (MEPs). This specific property, designated short-latency afferent inhibition (SAI), occurs when the nerve-TMS interstimulus interval (ISI) is approximately 25 ms and is considered to be a corticothalamic phenomenon. The aim of the present study was to use the electroencephalographic (EEG) responses to navigated-TMS coregistration to better characterize the neuronal circuits underlying SAI. The present experimental set included magnetic resonance imaging (MRI)-navigated TMS and 60-channel TMS-compatible EEG devices. TMS-evoked EEG responses and MEPs were analyzed in eight healthy volunteers; ISIs between median nerve and cortical stimulation were determined relative to the latency of the individual N20 component of the somatosensory-evoked potential (SEP) obtained after stimulation of the median nerve. ISIs from the latency of the N20 plus 3 ms and N20 plus 10 ms were investigated. In all experimental conditions, TMS-evoked EEG responses were characterized by a sequence of negative deflections peaking at approximately 7, 44, and 100 ms alternating with positive peaks at approximately 30, 60, and 180 ms post-TMS. Moreover, ISI N20+3 ms modulated both EEG-evoked activity and MEPs. In particular, it inhibited MEP amplitudes, attenuated cortical P60 and N100 responses, and induced motor cortex beta rhythm selective decrement of phase locking. The findings of the present experiment suggest the cortical origin of SAI that could result from the cortico-cortical activation of GABAergic-mediated inhibition onto the corticospinal neurons modulated by cholinergic activation able to reducing intralaminar inhibition and promoting intracolumnar inhibition.

Does second-scale intertrial interval affect motor evoked potentials induced by single-pulse transcranial magnetic stimulation?

OBJECTIVE: To determine whether a second-scale intertrial interval (ITI) of single-pulse transcranial magnetic stimulation (TMS) affects the measured amplitude of motor-evoked potentials (MEPs) representing individual corticospinal excitability. This was performed to challenge the common assumption of time invariance of such amplitudes. METHODS: Navigated TMS was used to map the dominant hemisphere of nine healthy subjects for the cortical representation focus of the contralateral thenar muscle, and resting motor threshold (MT) was determined. Single-trial MEP amplitudes were analyzed from trains of 30 responses induced at an intensity of 120% of the MT, and constant ITIs were investigated at 1, 2, 3, 5, and 10 seconds as well as randomized at ranges of 1-3 seconds, 3-5 seconds, and 5-10 seconds. MEP responses were divided into three blocks of 10 consecutive responses within each stimulation train. Repeated samples ANOVA was used to assess whether the individual characteristic MEP amplitudes were time invariant, i.e., not affected by the different ITIs and stimulus blocks. RESULTS: The individual single-trial MEP amplitudes were affected significantly (P < 0.05) by the ITI (8/8 subjects), block number (5/8 subjects), and ITI by block number interaction (6/8 subjects). One subject was excluded as the sphericity of the variances could not be confirmed. Consequently, the found time variant nature of the individual single-trial MEP amplitudes affected the estimates (means) of individual characteristic MEP amplitudes. This was also observed as a significant block number effect (P < 0.05) across all subjects. CONCLUSIONS: The individual characteristic MEP amplitudes are time variant, contrary to the common assumption. Hence, individual characteristic MEP amplitude estimates should be used cautiously, as erroneous conclusions could be made when assuming those as time invariant.

Motor cortical plasticity is impaired in Unverricht-Lundborg disease.

Patients with Unverricht-Lundborg disease, also referred to as progressive myoclonus epilepsy type 1, exhibit widespread motor symptoms and signs in addition to epileptic seizures, which suggest abnormal excitability of the primary motor pathways. To explore the plasticity of the sensory-motor cortex, we employed a modern neurophysiological method, the paired associative stimulation protocol, which resembles the concept of long-term potentiation of experimental studies. Seven patients with genetically verified Unverricht-Lundborg disease and 13 healthy control subjects were enrolled in the study to characterize cortical sensory-motor plasticity. In the study protocol, peripheral electric median nerve stimulation preceded navigated transcranial magnetic stimulation targeted to the representation area of thenar musculature on the contralateral primary motor cortex. The protocol consisted of 132 transcranial magnetic stimulation trials at 0.2 Hz, preceded by peripheral sensory stimulation at 25 ms. Motor-evoked potential amplitudes were analyzed at baseline and after the paired associative stimulation protocol at an intensity of 130% of the individual motor threshold. The patients with Unverricht-Lundborg disease exhibited an average decrease of 15% in motor-evoked potential amplitudes 30 minutes after paired associative stimulation, whereas in the control subjects, a significant increase (101%) was observed (P < .05), as expected. The results indicate a lack of normal cortical plasticity in Unverricht-Lundborg disease, which stresses the role of abnormal motor cortical functions or sensorimotor integration as possible pathophysiological contributors to the motor symptoms. The impaired cortical plasticity may be associated with the previously reported structural and physiological abnormalities of the primary motor cortex.

Corticospinal output and cortical excitation-inhibition balance in distal hand muscle representations in nonprimary motor area.

Transcranial magnetic stimulation (TMS) of the superior frontal gyrus in the non-primary motor area (NPMA) can evoke motor-evoked potentials (MEPs) at 20 ms latency range in contralateral distal hand muscles similar to stimulation of M1 and indicating monosynaptic corticospinal tracts. We compared the intracortical inhibitory and excitatory balance in primary motor cortex (M1) and in NPMA by navigated single- and paired-pulse TMS (ppTMS). We also evaluated the spatial stability of muscle representations in M1 and NPMA by remapping 11 healthy subjects one year after the initial mapping. Resting motor threshold (rMT) was higher in NPMA than in M1 as were the MEP amplitudes evoked by 120% rMT stimulation intensity of the local MT. Short-interval intracortical inhibition (SICI) was significantly weaker in NPMA than in M1 at ISI of 2 ms and conditioning stimulus (CS) 80% rMT. Our findings suggest that the cortical hand representations in NPMA 1) are connected to lower motoneurons monosynaptically, 2) are less strictly organized, i.e. motoneuron population representing a discrete hand muscle is sparser and less dense than in M1 and 3) have the capacity to generate powerful, rapid muscle contraction if sufficient number of motoneurones are activated. In NPMA, local intracortical inhibitory and excitatory activity is mainly similar to that in M1. The lower SICI in NPMA at an ISI of 2 ms may reflect less strict topographic organization and readiness to reorganization of neural circuits during motor learning or after motor deficits.

Short- and intermediate-interval cortical inhibition and facilitation assessed by navigated transcranial magnetic stimulation.

OBJECTIVE: To characterize the behaviour of primary motor cortex and to determine appropriate measurement parameters for short-interval cortical inhibition (SICI) and intracortical facilitation (ICF) by paired-pulse transcranial magnetic stimulation (TMS) with the aid of MRI-based neuronavigation. METHODS: Paired-pulse TMS was targeted to the optimal cortical representation sites of the abductor pollicis brevis (APB) muscle in 48 healthy right-handed volunteers. Motor evoked potentials (MEPs) were recorded from the APB and abductor digiti minimi (ADM) muscles. The conditioning stimulus (CS) intensities were 80% and 90% and the test stimulus was 120% of the resting motor threshold (rMT). The interstimulus intervals (ISIs) were 3, 7, 13, 22 and 28 ms. RESULTS: Inhibition was observed at 3 ms with a CS of 80%. Facilitation emerged at ISIs of 7 and 13 ms with both CS intensities, more prominently with 90%. At ISI of 22 ms, facilitation was observed in ADM (p<0.01) but not in APB. No uniform amplitude change was observed at ISI of 28 ms. For both muscles, MEP latencies were shortened (p<0.01) at ISIs of 3 and 7 ms and prolonged (p<0.01) at 28 ms. CONCLUSIONS: Inhibition is most prominent at ISI of 3 ms and CS of 80% of rMT, whereas CS of 90% of rMT and ISIs of 7 and 13 ms are preferable for facilitation. Latencies appear to be stable and independent indicators of both phenomena should be taken into account. SIGNIFICANCE: Both the latency and amplitude of MEPs are important parameters when paired-pulse paradigms are used in clinical studies.

Evaluation of a novel ambulatory device for screening of sleep apnea.

The gold standard for diagnosis of obstructive sleep apnea (OSA) is the sleep laboratory polysomnography, which is technically demanding, labor-intensive, and time-consuming. Thus, screening of large undiagnosed population for OSA may be cost efficient only by means of ambulatory devices suitable for home recordings. The aim of our study was to evaluate the diagnostic and technical reliability of a novel ambulatory device (APV2, Remote Analysis Oy) introduced for sleep apnea diagnostics. APV2 records breathing movements, nasal and oral air flow, position, snore, blood oxygen saturation, and heart rate. The evaluation was done by comparing 10 simultaneous polygraphic recordings with APV2 and with commonly used clinical reference instrumentation (Embla, Embla Co.) at a sleep laboratory. Furthermore, the technical reliability of measurements was evaluated by analyzing the fraction of clinical APV2 and Embletta (Embla Co.) home recordings (n = 149 and n = 169, respectively) that were technically of diagnostically unacceptable quality. Similar diagnostic sensitivity in detecting OSA was found with the APV2 compared to the simultaneous reference recording with the Embla. Apnea-hypopnea indices and oxygen desaturation indices, recorded with APV2 and Embla, were closely correlated (r = 0.996-0.997, p < 0.0001). The quality of 90.0% of home recordings with APV2 was technically perfect and 96.0% of recordings were of diagnostically acceptable quality. As a comparison, the clinical evaluation of a widely used ambulatory polygraphy device (Embletta) showed that 77.2% of home recordings were technically perfect and 80.8% of recordings were diagnostically acceptable. In conclusion, the novel device was found clinically applicable, technically reliable, and sensitive for the diagnostics of OSA.

Altered cortical inhibition in Unverricht-Lundborg type progressive myoclonus epilepsy (EPM1).

PURPOSE: Progressive myoclonus epilepsies (PMEs) comprise a heterogeneous group of conditions characterized by an imbalance between excitatory and inhibitory neuronal mechanisms. The aim of this study was to assess the function of the motor cortex in Unverricht-Lundborg disease (ULD), progressive myoclonus epilepsy type 1 (EPM1). METHODS: Genetically verified EPM1 patients (n=24) were studied and compared with healthy subjects (n=24). MRI-navigated transcranial magnetic stimulation (TMS) was used to study the function of the motor cortex. Motor threshold (MT) and cortical silent period (SP) were used as parameters to evaluate cortical excitability. Peripheral muscle responses were recorded at the thenar and hypothenar using on-line electromyography (EMG). RESULTS: The normal shortening of SP duration with age was not evident in EPM1. Thus, older patients exhibited significantly prolonged SPs in comparison to healthy control subjects (p<0.05). The MTs, measured as both stimulator output percentage and induced electric field strength (EF), were significantly higher in EPM1 patients than in control subjects (p<0.001). The stimulation of the thenar caused a co-activation in the hypothenar with significantly higher amplitudes as compared to controls (p<0.05). CONCLUSIONS: The prolongation of the SPs with age in EPM1 patients suggests a prevailing inhibitory tonus of the primary motor cortex (M1) as possible reactive mechanism to the disease. Antiepileptic drugs may contribute to the increased MT but do not affect the SP. The results and methodology of this study can lead to a better understanding of the pathophysiology and progression of EPM1.

Comparison of navigated and non-navigated transcranial magnetic stimulation for motor cortex mapping, motor threshold and motor evoked potentials.

Transcranial magnetic stimulation (TMS) can be used for non-invasive assessment of cortical physiology and descending motor pathways. However, the focus/exact site of cortical activation is considerably widespread in traditional TMS. When combined with MRI-based navigation, it allows specific anatomical areas of the cortex to be stimulated. The peripheral muscle responses to TMS are commonly measured as motor evoked potentials (MEPs). We compared the accuracy of cortical mapping, as well as the congruity of the motor thresholds (MT) and MEPs between navigated and non-navigated TMS procedures. Eight volunteers were studied in two sessions. In each session both hemispheres were stimulated with and without navigation. Non-navigated TMS: Both hemispheres were mapped without navigation to find the representation area of the thenar muscles based on induced MEP amplitudes. MT was then determined at the optimum coil location. Navigated TMS: Individual MR-images were used for the on-line navigation procedure. The cortical representation area of the thenar musculature was mapped at the "hand knob". The optimum stimulus target was used for MT determination. The order of these two procedures was randomized. Following the MT determination, MEPs were recorded from 20 consecutive stimuli. The MTs were similar from session-to-session with no inter-hemispheric differences, and with and without navigation. The stimulus location was more spatially discrete in navigated TMS producing more stable MEPs with significantly higher amplitudes and shorter latencies. In summary, MEPs exhibit significant differences depending on whether navigation is used. However, the MTs are not significantly dependent on the discrete stimulation site.

Motor potentials evoked by navigated transcranial magnetic stimulation in healthy subjects.

Navigated transcranial magnetic stimulation (TMS) is a tool for targeted, noninvasive stimulation of cerebral cortex. Transcranial stimuli can depolarize neurons and evoke measurable effects which are unique in two ways: the effects are caused directly and without a consciousness of the subject, and, the responses from peripheral muscles provide a direct measure for the integrity of the whole motor pathway. The clinical relevance of the method has not always been fully exposed because localizing the optimal stimulation site and determining the optimal stimulation strength have been dependent on time-consuming experimentation and skill. Moreover, in many disorders it has been uncertain, whether the lack of motor responses is the result of true pathophysiological changes or merely because of unoptimal stimulation. We characterized the muscle responses from human primary motor cortex system by navigated TMS to provide normative values for the clinically relevant TMS parameters on 65 healthy volunteers aged 22 to 81 years. We delivered focal TMS pulses on the primary motor area (M1) and recorded muscle responses on thenar and anterior tibial muscles. Motor threshold, latencies and amplitudes of motor-evoked potentials, and silent period duration were measured. The correction of the motor-evoked potential latency for subjects' height is provided. In conclusion, we provide a modified baseline of TMS-related parameters for healthy subjects. Earlier such large-scale baseline material has not been available.