Transcutaneous innervation zone imaging from high-density surface electromyography recordings.

OBJECTIVE: It is of great value to accurately localize innervation zones (IZs) to better diagnose and treat neuromuscular diseases, but it is challenging to do so noninvasively from surface electromyography (sEMG) recordings because of the blurring/distorting effect of the low conductive fat tissues. This study aimed to develop an innovative transcutaneous IZ imaging (TIZI) technique to precisely and efficiently localize the IZ distribution directly over the muscle surface in vivo from high-density sEMG recordings (HD-sEMG). APPROACH: The TIZI technique was implemented by incorporating HD-sEMG recording, signal decomposition, finite element analysis and inverse calculation. The performance of TIZI was evaluated on the flexor digitorum superficialis (FDS) muscle with simulated sEMG signal and experimental signal recorded from both healthy (n = 3) and stroke participants (n = 4). The accuracy of imaging was validated by both of the Pearson correlation coefficient (PCC) and localization error (LE) between the TIZI results and the 'true' IZ distribution. MAIN RESULTS: In the simulation study, results have shown PCCs of 99.85% ± 0.11%, 99.79% ± 0.08%, 99.63% ± 0.22% and 99.31% ± 0.54% at the depth of 10, 15, 20 and 25 mm and SNR of 25 dB. PCCs of 98.74% ± 1.78% and 97.82% ± 1.20% were respectively obtained for experimental signals acquired from the healthy and spastic FDS muscles. The TIZI provided smaller LEs of 1.4 ± 0.92 mm and 2.02 ± 1.3 mm, compared to LEs of 7.42 ± 2.29 mm and 7.8 ± 1.77 mm from skin observations in healthy and spastic FDS, respectively. SIGNIFICANCE: Results have demonstrated the high performance of the proposed TIZI technique by transcutaneous imaging of the IZ distribution of the skeletal muscles. The performance improvement can be attributed to the elimination of the blurring/distorting effect caused by the low conductive fat and high conductive skin tissues. TIZI may provide an advanced neurological tool for the clinical treatment of neuromuscular diseases, such as guiding botulinum neurotoxin injections in spasticity management.

Electrical stimulation-induced SSSEP as an objective index to evaluate the difference of tactile acuity between the left and right hand.

OBJECTIVE: The objective of this study is to propose an objective index to evaluate the difference of tactile acuity between the left and right hand based on steady-state somatosensory evoked potential (SSSEP). APPROACH: Two kinds of tactile sensations (vibration and pressure) with three levels of intensities (low/medium/high) were evoked on two finger areas of the left or right hand (thumb and index for healthy hands, thumb and index-projected areas for disabled hands) via transcutaneous electrical nerve stimulation (TENS). Three forearm amputees and 13 able-bodied subjects were recruited to discriminate the specific level and area of the applied stimulation. Electroencephalography was adopted to simultaneously record the somatosensory cortex response to TENS. We assessed the discrimination performance (discrimination accuracy rate (AR) and response time (RT)) to quantify the tactile acuity, while the evoked SSSEP was synchronously analyzed. Linear regression analyses were performed between the difference of SSSEP amplitudes and the difference of discrimination performance for the left and right hand stimulation. MAIN RESULTS: Frequency domain analysis revealed that SSSEP amplitude increased with the increase of the stimulation intensity. There were positive correlations between the difference of SSSEP amplitudes and the difference of ARs for the left and right hand stimulation in the sensations of vibration (R 2 = 0.6389 for able-bodied subjects, R 2 = 0.5328 for amputees) and pressure (R 2 = 0.6102 for able-bodied subjects, R 2 = 0.5452 for amputees), respectively. Significance The SSSEP amplitude could be used as an objective index to evaluate the difference of the tactile acuity between the left and right hand and has the potential to be applied in sensory rehabilitation for amputees or stroke patients.

An investigation into the magnitude of the current window and perception of transcutaneous electrical nerve stimulation (TENS) sensation at various frequencies and body sites in healthy human participants.

INTRODUCTION: Strong nonpainful transcutaneous electrical nerve stimulation (TENS) is prerequisite to a successful analgesic outcome although the ease with which this sensation is achieved is likely to depend on the magnitude of current amplitude (mA) between sensory detection threshold (SDT) and pain threshold, that is, the current window. OBJECTIVES: To measure the current window and participant's perception of the comfort of the TENS sensation at different body sites. METHODS: A repeated measure cross-over study was conducted using 30 healthy adult volunteers. Current amplitudes (mA) of TENS [2 pulses per second (pps); 30 pps; 80 pps] at SDT, pain threshold, and strong nonpainful intensities were measured at the tibia (bone), knee joint (connective tissue), lower back [paraspinal (skeletal) muscle], volar surface of forearm (nerve) and waist (fat). The amplitude to achieve a strong nonpainful intensity was represented as a percentage of the current window. Data were analyzed using repeated measures analysis of variance. RESULTS: Effects were detected for body site and frequency for SDT (P<0.001, P=0.018, respectively), current window (P<0.001, P<0.001, respectively), and strong nonpainful TENS as a percentage of the current window (P=0.002, P<0.001, respectively). The current window was larger for the knee joint compared with tibia (difference [95% confidence interval]=12.76 mA [4.25, 21.28]; P=0.001) and forearm (10.33 mA [2.62, 18.40]; P=0.006), and for the lower back compared with tibia (12.10 mA [1.65, 22.52]; P=0.015) and forearm (9.65 mA [1.06, 18.24]; P=0.019). The current window was larger for 2 pps compared with 30 pps (P<0.001) and 80 pps (P<0.001). Participants rated strong nonpainful TENS as most comfortable at the lower back (P<0.001) and least comfortable at the tibia and forearm (P<0.001). CONCLUSIONS: TENS is most comfortable and easiest to titrate to a strong nonpainful intensity when applied over areas of muscle and soft tissue.

Cutaneous anesthesia of the forearm enhances sensorimotor function of the hand.

Temporary deafferentation of the upper limb, with ischemic or anesthetic nerve block, has rapid effects on sensorimotor cortex. Cutaneous anesthesia of the forearm has recently been found to improve sensory and motor function of the paretic hand in chronic stroke patients. However, the neurophysiological mechanisms are unknown. The aim of this study was to investigate the behavioral and neurophysiological effects of cutaneous forearm anesthesia. Twenty-five healthy right-handed adults participated in this double-blind, randomized study. Participants completed two sessions, with either a topical anesthesia cream (EMLA) or placebo applied to their left forearm in each session. Thresholds for cutaneous sensation and spatial acuity of the left hand were measured before and after the intervention. Transcranial magnetic stimulation was used to measure corticomotor excitability and short-interval intracortical inhibition in the left first dorsal interosseous and abductor digiti minimi muscles before and after the intervention. Manual dexterity was assessed with the grooved pegboard task after the intervention in each session. Left-hand dexterity improved to a greater extent after treatment with EMLA than placebo, and this was related to improved spatial acuity at the fingertips. Corticomotor excitability remained stable, and short-interval intracortical inhibition increased after EMLA treatment. We have confirmed and extended previous reports that cutaneous forearm anesthesia results in improved spatial acuity and manual dexterity of the ipsilateral hand. The neurophysiological mechanisms involve an increase in intracortical inhibition, which may improve the precision of voluntary movement. These results lend support to the therapeutic application of EMLA in movement rehabilitation.

Evaluation of sensation evoked by electrocutaneous stimulation on forearm in nondisabled subjects.

Few studies are available in the literature on the sensations artificially created by dual-channel electrocutaneous stimulation. This study assessed the effect of a set of selected stimulation parameters on the sensations evoked by single- or dual-channel electrocutaneous stimulation. The investigated parameters included the stimulation site, the number of pulses, the number of stimulating channels (single- vs dual-channel), and the interleaved time between two channels. The modality, quality, location, and magnitude of the sensations were evaluated when the stimulations were applied on the forearm skin in 16 nondisabled subjects. Tactile perception was found to be induced more easily on the median and ulnar aspect than the dorsal and radial aspect of the forearm. Stimulation site significantly affected the magnitude of the sensation (p < 0.01). Dual-channel stimulation significantly increased the sensation magnitude (p < 0.05) only when the two electrodes were positioned closely. Moreover, a higher number of pulses evoked a movement perception more frequently and the interleaved time showed no significant effect on the magnitude of the sensation. The findings are expected to be useful for sensory substitution and augmentation applications. The results may also help improve users' acceptance of hand prostheses.

Comparison between local and regional anesthesia in arteriovenous fistula creation.

PURPOSE: Assessment of the effectiveness of brachial plexus block (BPB) via axillary approach compared to regional anesthesia for arteriovenous fistula surgery in patients affected by end-stage renal disease. METHODS: We compared forty patients randomly divided into two groups. Group A underwent BPB procedure with 15 mL ropivacaine 1% and 10 mL of saline (0.9% NaCl) via axillary approach. Group B received local anesthesia with lidocaine 2%. The forearm blood vessels were assessed by Doppler ultrasonography before and after the intervention. RESULTS: BPB performed on Group A was associated with a considerable venous dilation and a significant decrease (48.7%, P<.05) in pulsatility index (PI) measured by Doppler ultrasound. In Group B, PI and venous dilation remained unaltered in the postoperative phase. No complications such as thrombosis or occlusion were encountered among patients who underwent BPB. CONCLUSIONS: The axillary-approached BPB was more advantageous than local anesthesia. Its effectiveness was because of venous dilation and the decrease in the PI, consequent to the reduction in peripheral resistances and the increase in local blood flow, thus offering an ideal background for fistula creation and short-term patency.

Changes of excitability in M1 induced by neuromuscular electrical stimulation differ between presence and absence of voluntary drive.

The aim of this study is to investigate excitability changes in the human motor cortex induced by variable therapeutic electrical stimulations (TESs) with or without voluntary drive. We recorded motor-evoked potentials (MEPs) from extensor and flexor carpi radialis (FCR) muscles at rest and during FCR muscle contraction after the application of TES on FCR. TES application conditions were changed intensities, frequencies, and trains. In addition, to evaluate the contribution of M1 inhibitory circuits to the effects of TES application, we also recorded MEPs using paired-pulse transcranial magnetic stimulation. In resting muscle states, an increase in TES intensity resulted in an increase in MEP ratio in both the muscles. In contrast, when TES was applied to FCR during contraction, MEP ratios of both the muscles decreased with increased number of pulse trains. However, under both the states, MEP ratios decreased induced by paired-pulse transcranial magnetic stimulation in extensor carpi radialis to which TES was not applied. Excitability changes in M1 induced by TES application were reversibly modulated depending on the presence or absence of voluntary drive. This study showed that the therapy and the voluntary drive of the target muscles act together, and complement the effects of each other, which may be beneficial for optimizing the rehabilitation if the therapy accompanies voluntary drive.

The effect of long-term TENS on persistent neuroplastic changes in the human cerebral cortex.

The long-term effect of daily somatosensory stimulation with transcutaneous electrical nerve stimulation (TENS) on reorganization of the motor cortex was investigated in a group of neurologically intact humans. The scalp representation of the corticospinal projection to the finger (APB, ADM) and forearm (FCR, ECR) muscles was mapped by means of transcranial magnetic stimulation (TMS) before and after a 3-week intervention period, using map area and volume, and topographical overlaps between the cortical motor representations of these muscles as primary dependent measures. Findings revealed a significant increase in cortical motor representation of all four muscles for the TENS group from pre to posttest (all, P ≤ 0.026). No significant changes in cortical motor representations were observed in the control group. The present observations highlight the potential benefit of sensory training by means of TENS as a useful complementary therapy in neurorehabilitation.

The hyperthermic effect of a distal volar forearm nerve block: a possible treatment of acute digital frostbite injuries?

BACKGROUND: The authors have observed that carpal tunnel surgery nerve blocks consisting of subfascial distal volar forearm injection of 10 cc of 1% lidocaine with epinephrine result in fingers that appear hyperemic, warm, and numb in both median and ulnar nerve distributions. The purposes of this study were to (1) determine whether forearm nerve blocks in patients undergoing carpal tunnel releases result in an objective increase in finger temperature, and (2) document the location and duration of finger anesthesia. METHODS: Thirty-nine patients undergoing unilateral carpal tunnel release were studied prospectively. An infrared thermometer was used to measure the temperature in the fingers of operative and nonoperative hands before and after injection of local anesthetic. The distal volar forearm block was performed using 10 cc of 1% lidocaine with 1:100,000 epinephrine deep to the forearm fascia between the median and ulnar nerves 1 cm proximal to the wrist crease. Before and after carpal tunnel release, bilateral finger temperatures were measured at hourly intervals. Statistical analysis included a one-sample test of proportions. RESULTS: The finger temperature of the operative hand was significantly warmer than the unoperated hand over the first 2 hours after the nerve block. Seventy-four percent of patients had a statistically significant increase in temperature. On average, the nerve block lasted 6.27 hours in the median nerve distribution and 5.78 hours in the ulnar nerve distribution. CONCLUSIONS: Forearm nerve blocks produce a chemical sympathectomy that provides a significant increase in skin temperature as a result of vasodilatation in most patients. They also provide prolonged finger numbness. This could be of clinical benefit in patients with acute finger frostbite injuries.

Infraclavicular brachial plexus block for regional anaesthesia of the lower arm.

BACKGROUND: Several approaches exist to produce local anaesthetic blockade of the brachial plexus. It is not clear which is the technique of choice for providing surgical anaesthesia of the lower arm although infraclavicular blockade (ICB) has several purported advantages. We therefore performed a systematic review of ICB compared to the other brachial plexus blocks (BPBs). OBJECTIVES: To evaluate the efficacy and safety of ICB compared to other BPBs in providing regional anaesthesia of the lower arm. SEARCH STRATEGY: We searched CENTRAL (The Cochrane Library 2008, Issue 3), MEDLINE (1950 to September 22nd 2008) and EMBASE (1980 to September 22nd 2008). We also searched conference proceedings (from 2004 to 2008) and the www.clinicaltrials.gov registry. No language restriction was applied. SELECTION CRITERIA: We included any randomized controlled trials (RCTs) that compared ICB with other BPBs as the sole anaesthetic techniques for surgery on the lower arm. DATA COLLECTION AND ANALYSIS: The primary outcome was adequate surgical anaesthesia within 30 minutes of block completion. Secondary outcomes included sensory block of individual nerves, tourniquet pain, onset time of sensory blockade, block performance time, block-associated pain and complications related to the block. MAIN RESULTS: We identified 15 studies with 1020 participants, of whom 510 received ICB and 510 received other BPBs. The control group intervention was the axillary block in 10 studies, mid-humeral block in two studies, supraclavicular block in two studies and parascalene block in one study. Three studies employed ultrasound-guided ICB. The risk of failed surgical anaesthesia and of complications were low and similar for ICB and all other BPBs. Tourniquet pain was less likely with ICB (risk ratio (RR) 0.47, 95% CI 0.24 to 0.92, P = 0.03). When compared to a single-injection axillary block, ICB was better at providing complete sensory block of the musculocutaneous nerve (RR for failure 0.46, 95% CI 0.27 to 0.60, P < 0.0001) and the axillary nerve (RR of failure 0.37, 95% CI 0.24 to 0.58, P < 0.0001). ICB was faster to perform than multiple-injection axillary (mean difference (MD) -2.7 min, 95% CI -4.2 to -1.1, P = 0.0006) or midhumeral blocks (MD -4.8 min, 95% CI -6.0 to -3.6, P < 0.00001) but this was offset by a longer sensory block onset time (MD 3.9 min, 95% CI 3.2 to 4.5, P < 0.00001). AUTHORS' CONCLUSIONS: ICB is a safe and simple technique for providing surgical anaesthesia of the lower arm, with an efficacy comparable to other BPBs. The advantages of ICB include a lower likelihood of tourniquet pain during surgery, and more reliable blockade of the musculocutaneous and axillary nerves when compared to a single-injection axillary block. The efficacy of ICB is likely to be improved if adequate time is allowed for block onset (at least 30 minutes) and if a volume of at least 40 ml is injected. Since publication of many of the trials included in this review, it has become clear that a distal posterior cord motor response is the appropriate endpoint for electrostimulation-guided ICB; we recommend it be used in all future comparative studies. There is also a need for additional RCTs comparing ultrasound-guided ICB with other BPBs.

Electric pulse frequency and magnitude of perceived sensation during electrocutaneous forearm stimulation.

OBJECTIVES: To investigate the effect that electric pulse frequency has on the perceived magnitude of sensation and to quantify the relationship between electric pulse frequency and perceived magnitude of sensation during low-intensity electrocutaneous stimulation. DESIGN: A repeated-measures research design was applied to evaluate the effect of electric pulse frequency on the perceived magnitude of electrocutaneous stimulation. SETTING: Electrocutaneous agents laboratory. PARTICIPANTS: University students (N=26) with normal hearing and normal sensation were recruited for the study. INTERVENTIONS: Electrocutaneous stimulation was applied to the forearm at 10 electric pulse frequencies. MAIN OUTCOME MEASURES: A cross-modality matching procedure was used in which stimulation intensity was matched with the level of loudness. Pairwise comparisons with 2 degrees of freedom at a power of 80% was performed. Statistical significance was set at P equal to .05. RESULTS: Electric pulse frequency had a significant effect on the perceived magnitude of sensation, with the perceived sensation growing between 0 and 120Hz (F=36.02; P<.001). The relationship between the 2 variables was strong (r(2)=.99; P<.01). CONCLUSIONS: Increasing the electric pulse frequency of electrocutaneous stimulation increases the perceived magnitude of the resulting sensation. This has implications for the use of electrocutaneous stimulation for both analgesia and muscle stimulation.

Perforation of the median nerve with an acupuncture needle guided by ultrasound.

In an experiment on one of the authors, we used ultrasound to visualise an acupuncture needle completely perforating the median nerve at the acupuncture point PC6. During this procedure only a slight sensation occurred, and no pain. We conclude that, in individual cases, the median nerve might be perforated without causing pain or neurological problems.

Regimen and results of physiotherapy in patients following surgical treatment of ulnar nerve injury.

BACKGROUND: Ulnar nerve injuries are the most common cause of damage to the nerves of the hand. Diverse mechanisms of injury may be involved, the most frequent being injuries to various areas within the forearm, usually lacerations. In such cases, surgery followed by physiotherapy is a treatment of choice. The aim of the study was to estimate the efficacy of physical therapy following surgical treatment of ulnar nerve injuries. MATERIAL AND METHOD: The study group initially comprised 33 patients. Twelve patients with additional damage to the median nerve were excluded and further analyses concerned a group of 21 patients with ulnar nerve injuries who underwent physiotherapy at the Malopolska Regional Hand Rehabilitation Centre in Cracow. Treatment outcomes were evaluated on the basis of measurements of hand function including the range of motion, function tests as well as sensation and dynamometric tests. RESULTS AND CONCLUSIONS: Range of motion data were used to assess movement impairment according to Swanson's method. The measurements were taken on two occasions before and after the physiotherapy. Analysis of the results revealed significant efficacy of the physiotherapy regimen.

[Low minimal stimulating current improves infraclavicular brachial plexus block efficacy].

OBJECTIVE: To investigate if low minimal stimulating current used in nerve stimulator localizing is associated with a greater likelihood of infraclavicular block success. METHODS: 188 patients, aged 14 to 64, of ASA physical status class I - II, and scheduled for surgical procedures below elbow were assigned to low current group (Group A, n = 118) or regular current group (Group B, n = 70) according to the last figure of admission number. The infraclavicular plexus block was performed using the Wilson's approach 2 cm medial and caudal to the coracoid process guided by nerve stimulator with 30 ml of 0.5% ropivacaine after eliciting distal motor responses. The minimal stimulating current (I) was adjusted to 0.1 mA < or = I < 0.3 mA in Group A or 0.3 mA < or = I < 0.5 mA in Group B. The 2 groups were further sub-divided into 2 subgroups: lateral cord subgroup when motor responses of wrist and finger-flexion and pronation of forearm were induced, and posterior subgroup when extension of wrist and finger was induced. Anesthesia efficacy was assessed 5, 10, 20 and 30 min after the local anesthetic injection. A successful blockade was defined as analgesia in all dermatomes of the five nerves (median nerve, musculocutaneous nerve, radial nerve, ulnar nerve, and medial antebrachial cutaneous nerve). RESULTS: The success rate of Group A was 84.7%, significantly higher than that of Group B (67.1%, P < 0.05). When divided into posterior and lateral cord subgroups, The success rate of the posterior subgroup of Group A was 96.5%, significantly higher than that of the posterior subgroup of Group B (78.9%, P < 0.05). CONCLUSION: Minimal stimulating current lower than 0.3 mA, significantly lower than the recommended value (0.5 mA), improves the efficacy of infraclavicular brachial plexus block, especially when the posterior cord is stimulated.

Ultrasound measurements of the distance between acupuncture needle tip at P6 and the median nerve.

BACKGROUND: Pericard 6 (P6) is one of the most frequently used acupuncture points, especially in preventing nausea and vomiting. At this point, the median nerve is located very superficially. OBJECTIVES: To investigate the distance between the needle tip and the median nerve during acupuncture at P6, we conducted a prospective observational ultrasound (US) imaging study. We tested the hypothesis that de qi (a sensation that is typical of acupuncture needling) is evoked when the needle comes into contact with the epineural tissue and thereby prevents nerve penetration. SETTINGS/LOCATION: The outpatient pain clinic of the Medical University of Vienna, Austria. SUBJECTS: Fifty (50) patients receiving acupuncture treatment including P6 bilaterally. INTERVENTIONS: Patients were examined at both forearms using US (a 10-MHz linear transducer) after insertion of the needle at P6. OUTCOME MEASURES: The distance between the needle tip and the median nerve, the number of nerve contacts and nerve penetrations, as well as the number of successfully elicited de qi sensations were recorded. RESULTS: Complete data could be obtained from 97 cases. The mean distance from the needle tip to the nerve was 1.8 mm (standard deviation 2.2; range 0-11.3). Nerve contacts were recorded in 52 cases, in 14 of which the nerve was penetrated by the needle. De qi was elicited in 85 cases. We found no association between the number of nerve contacts and de qi. The 1-week follow-up showed no complications or neurologic problems. CONCLUSIONS: This is the first investigation demonstrating the relationship between acupuncture needle placement and adjacent neural structures using US technology. The rate of median nerve penetrations by the acupuncture needle at P6 was surprisingly high, but these seemed to carry no risk of neurologic sequelae. De qi at P6 does not depend on median nerve contact, nor does it prevent median nerve penetration.

Local and systemic vasodilation following hypnotic suggestion of warm tub bathing.

During hypnosis it is easy to induce hallucinations having, for the hypnotized subject, the characteristics and the concreteness of reality. This study was performed to put in evidence the physical effects of hypnotic suggestion of warm tub bathing. 18 volunteers screened for high hypnotizability were studied. They underwent suggestion of forearm in warm water (30 min), suggestion of body in warm water (30 min), and hypnosis without any thermal suggestion (30 min), while blood pressure, heart rate, body temperature, forearm flow and resistance, stroke volume, cardiac index and total peripheral resistance were monitored. During suggestion of forearm in warm water, local vasodilation was recorded, with decrease of forearm resistance (-18%, P<0.01) and increase of forearm blood flow (+43%, P<0.01) like in real local passive warming. During suggestion of whole-body in a warm water tub, there was a systemic vasodilation with decrease of total peripheral resistance (-29%, P<0.01) and increase of cardiac index (+54%, P<0.01), like in real total-body passive warming. Body temperature, arterial blood pressure and heart rate were unchanged. During simple hypnosis (sham procedure) no haemodynamic variations were observed. These results are in keeping with the possibility to induce through hypnotic suggestion of heat a physical pattern that is typical of hyperthermia, even without increase in body temperature.

Referred pain pattern of the pronator quadratus muscle.

Pain patterns of the myofascial trigger points (TrP) for most muscles of the forearm have been documented. However, there are no published reports on the referred pain patterns for the pronator quadratus (PQ) muscle. The purpose of this study was to determine the referred pain pattern of the TrP in the PQ. Thirty-five arms of 35 healthy adult volunteers with no history of neck pain, arm pain or paresthesia were studied. Following skin sterilization, a Teflon-coated syringe needle was inserted into the PQ of the non-dominant forearm under electromyographic guidance, and 0.3mL of 6% hypertonic saline was injected. Subjects drew in their pain areas on a pain diagram, and this drawing was transferred into the Pain Chart System for analysis. Two main pain patterns were observed. The most common pattern involved pain spreading both distally and proximally from the injection site, along the medial aspect of the forearm (57%). In half of these cases, the pain area extended to the medial epicondyle proximally and the fifth digit distally. The second main pattern revealed pain spreading distally to the third and/or fourth finger (29%). The pain patterns originating from the PQ resemble the C8-T1 dermatomes, and ulnar and median nerve sensory distributions. Thus, myofascial pain of the PQ should be considered as a possible cause of pain in the medial forearm and hand, especially when no other neurological abnormalities are present.

Proximal receptors and the mechanical stimulation of the fingers: a somatosensory evoked potential study.

OBJECTIVE: To characterize scalp responses to mechanical stimulation of the fingers and evaluate the contribution of different receptors. DESIGN AND METHODS: Somatosensory evoked responses to mechanical stimulation of the right third finger were recorded from a P3-P4 montage (n = 15) and from a F3-P4 montage (n = 9) as well as after electrical stimulation (n = 9). Responses after mechanical stimulation of the distal region of the finger, with the hand at different positions, were also recorded (n = 8). Complementary experiments in a small number of individuals included EMG and accelerometer recordings as well as anaesthesia of the finger. RESULTS: Scalp responses characterized by an initial sequence of waves, here called NI-PI-NII, were recorded from the P3-P4 montage. Mean peak latencies were 20, 23 and 26 ms, respectively; electrical stimulation of the same region evoked an initial negativity (mean peak latency 23 ms). EMG recordings suggested the involvement of different receptors in response to electrical and mechanical stimulation. Accelerometer recordings showed the spread of a sizable mechanical wave at the forearm. Anaesthesia did not change the responses to mechanical stimulation. CONCLUSIONS: Relatively small mechanical stimuli applied at distal phalanxes may activate proximal receptors which generate scalp recorded responses that may completely occlude the contribution of the distal receptors.

Magnetic stimulation of the human motor cortex evokes skin sympathetic nerve activity.

Single-pulse magnetic coil stimulation (Cadwell MES 10) over the cranium induces without pain an electric pulse in the underlying cerebral cortex. Stimulation over the motor cortex can elicit a muscle twitch. In 10 subjects, we tested whether motor cortical stimulation could also elicit skin sympathetic nerve activity (SSNA; n = 8) and muscle sympathetic nerve activity (MSNA; n = 5) in the peroneal nerve. Focal motor cortical stimulation predictably elicited bursts of SSNA but not MSNA; with successive stimuli, the SSNA responses did not readily extinguish (94% of discharges to the motor cortex evoked SSNA responses) and had predictable latencies [739 +/- 33 (SE) to 895 +/- 13 ms]. The SSNA responses were similar after stimulation of dominant and nondominant sides. Focal stimulation posterior to the motor cortex elicited extinguishable SSNA responses. In three of six subjects, anterior cortical stimulation evoked SSNA responses similar to those seen with motor cortex stimulation but without detectable movement; in the other subjects, anterior stimulation evoked less SSNA discharge than that seen with motor cortex stimulation. Contrasting with motor cortical stimulation, evoked SSNA responses were more readily extinguished with 1) peripheral stimulation that directly elicited forearm muscle activation accompanied by electromyograms similar to those with motor cortical stimulation; 2) auditory stimulation by the click of the energized coil when off the head; and 3) in preliminary experiments, finger afferent stimulation sufficient to cause tingling. Our findings are consistent with the hypothesis that motor cortex stimulation can cause activation of both alpha-motoneurons and SSNA.

The effects of ipsilateral forearm movement and contralateral hand grasp on the spastic hand opened by electrical stimulation.

The purpose of this study was to investigate the effects of ipsilateral arm movement and contralateral hand grasp on the spastic hand opened by open-loop electrical stimulation. The major problem of applying proper electrical stimulation is variable spasticity, the intensity of which changes with posture and movements of other parts of the body. Electrical stimulation was applied to extensor digitorum communis and ulnar nerve to open the affected hand. Different procedures were then used to assess the effects of moving the ipsilateral forearm and contracting the contralateral normal hand. Electrical stimulation opened the spastic hand in more than 95% of trials in all subjects, whether stimulation was applied before or after the movement of the forearm. Moving the ipsilateral forearm did have an effect on opening the hand, and making adjustment of stimulation intensities was necessary in all subjects. The stimulation opened the spastic hand during the contraction of the contralateral normal hand. Electrical stimulation could open the spastic hands most of the time, in the presence of ipsilateral forearm movement and contralateral normal hand contraction. If electrical stimulation was applied before the ipsilateral forearm was moved toward the target, stimulation intensities needed to be adjusted.