Thumb Twitch Research Articles

A compressomyograph train of four monitoring device

The monitoring of the neuromuscular blockade is critical for patient's safety during and after surgery. The monitoring of neuromuscular blockade often requires the use of Train of Four (TOF) technique. During a TOF test two electrodes are attached to the ulnar nerve, and a series of four electric pulses are applied. The electrical stimulation causes the thumb to twitch, and the amount of twitch varies depending on the amount of neuromuscular blockade in patient's system. Current medical devices used to assist anesthesiologists to perform TOF monitoring often require free hand movement and do not provide accurate or reliable results. The goal of this work is to design, prototype and test a new medical device that provides reliable TOF results when thumb movement is restricted. A medical device that uses a pressurized catheter balloon to detect the response thumb twitch of the TOF test is created. An analytical model, numerical study, and mechanical finger testing were employed to create an optimum design. The design is tested through a pilot human subjects study. No significant correlation is reported with subjects’ properties, including hand size.

Train-of-four monitoring with the twitchview monitor electctromyograph compared to the GE NMT electromyograph and manual palpation.

The purpose of this study was to compare train-of-four count and ratio measurements with the GE electromyograph to the TwitchView electromyograph, that was previously validated against mechanomography, and to palpation of train-of-four count. Electrodes for both monitors were applied to the same arm of patients undergoing an unrestricted general anesthetic. Train-of-four measurements were performed with both monitors approximately every 5min. In a subset of patients, thumb twitch was palpated by one of the investigators. Eleven patients contributed 807 pairs of train-of-four counts or ratios. A subset of 5 patients also contributed palpated train-of-four counts. Bland-Altman analysis of the train-of-four ratio found a bias of 0.24 in the direction of a larger ratio with the GE monitor. For 72% of data pairs, the GE monitor train-of-four ratios were larger. For 59% of data pairs, the GE monitor train-of-four counts were larger (p < 0.0001). For 11% of data pairs, the GE monitor train-of-four count was 4 when the Twitchview monitor count was zero. When manual palpation of train-of-four count was compared to train-of-four count determined by the monitors, 70% of data pairs were identical between palpation and TwitchView train-of-four count, while 30% of data pairs were identical between palpation and GE train-of-four count. For 7% of data pairs, the GE monitor train-of-four count was 4 when the palpation count was 0. The GE electromyograph may overestimate the train-of-four count and ratio. The GE electromyograph frequently reported 4 twitches when none were actually present due to misinterpretation of artifacts.

Neurophysiological Assessment of Prolonged Recovery From Neuromuscular Blockade in the Neonatal Intensive Care Unit.

Objective: To evaluate recovery from neuromuscular blockade in infants using Train-of-Four nerve stimulation.Study Design: Ulnar nerve stimulation was used to evoke thumb twitch and reported as Train-of-Four ratio. Thumb twitch was also recorded visually in real-time. Primary outcome was time to near recovery of muscle function (Train-of-Four ratio >70%). Secondary analyses were time to greater degrees of recovery (Train-of-Four ratio >80, 90%), sensitivity of accelerometry vs. visual thumb-twitch and clinical variates to assess safety.Results: Patients were enrolled following rocuronium-boluses (n = 10) and vecuronium-infusions (n = 9). Median recovery time to Train-of-Four ratio >70% was 14 h following rocuronium-bolus dosing and 34 h following cessation of continuous vecuronium infusion. Median stimulus threshold for accelerometry was 27.5 mA and visual observation was 20 mA. There were no safety concerns.Conclusion(s): Neuromuscular monitoring using Train-of-Four nerve stimulation is feasible in infants. Some infants exhibited prolonged recovery from neuromuscular-blockade. These pilot data may facilitate future standardized pediatric protocols on neuromuscular monitoring for safer dosing.

Self-Sustained Motor Activity Triggered by Interlimb Reflexes in Chronic Spinal Cord Injury, Evidence of Functional Ascending Propriospinal Pathways

The loss or reduction of supraspinal inputs after spinal cord injury provides a unique opportunity to examine the plasticity of neural pathways within the spinal cord. In a series of nine experiments on a patient, quadriplegic due to spinal cord injury, we investigated interlimb reflexes and self-sustained activity in completely paralyzed and paretic muscles due to a disinhibited propriospinal pathway. Electrical stimuli were delivered over the left common peroneal nerve at the fibular head as single stimuli or in trains at 2–100 Hz lasting 1 s. Single stimuli produced a robust interlimb reflex twitch in the contralateral thumb at a mean latency 69 ms, but no activity in other muscles. With stimulus trains the thumb twitch occurred at variable subharmonics of the stimulus rate, and strong self-sustained activity developed in the contralateral wrist extensors, outlasting both the stimuli and the thumb reflex by up to 20 s. Similar behavior was recorded in the ipsilateral wrist extensors and quadriceps femoris of both legs, but not in the contralateral thenar or peroneal muscles. The patient could not terminate the self-sustained activity voluntarily, but it was abolished on the left by attempted contractions of the paralyzed thumb muscles of the right hand. These responses depend on the functional integrity of an ascending propriospinal pathway, and highlight the plasticity of spinal circuitry following spinal cord injury. They emphasize the potential for pathways below the level of injury to generate movement, and the role of self-sustained reflex activity in the sequelae of spinal cord injury.

Cortex mapping of ipsilateral somatosensory area following anatomical hemispherectomy: A MEG study

A remarkable preservation of sensorimotor function is observed in patients with refractory epilepsy who were treated by hemispherectomy. Cortical regions in the remaining hemisphere or contralateral subcortical region contribute to the residual sensorimotor function. Somatosensory evoked field (SEF) is used to investigate the residual sensory function in hemispherectomized patients. The SEFs are usually recorded with magnetoencephalography (MEG). The objective is to investigate the ipsilateral cortical regions associated with residual sensory function in hemispherectomized patients using somatosensory evoked field techniques. Six patients with anatomical hemispherectomy were included. Ipsilateral and contralateral sensory functions were assessed by physical examination. Somatosensory evoked fields to electrical stimulation of the bilateral median nerves were recorded by MEG in the hemispherectomized patients and six control subjects. The stimulus intensity was adjusted to the minimum threshold that elicited a thumb twitch. The presumed neuronal source was identified as the equivalent current dipole. Six patients demonstrated different degrees of residual sensory function. Three patients had somatosensory evoked field activation in the ipsilateral cortex upon electrical stimulation of the hemiplegic hand. In these patients the locations of the ipsilateral sensorimotor cortex activation were in the primary somatosensory cortex (SI). The latency of the reliable somatosensory evoked field after stimulation of the median nerve was significantly longer for responses from the hemiplegic side compared with responses to stimulation of the median nerve from the normal side. In conclusion, ipsilateral sensory function has a time-locked relation to the cortical electromagnetic activation in the SI area of hemispherectomized patients.

Apparatus and simple method of monitoring neuromuscular function

The use of muscle relaxant is an integral part of anesthetic management in present-day practice. Clinically, the neuromuscular blockade is evaluated by determining the thumb twitching to train-of-four (TOF) ulnar nerve stimulation at elbow. 1–3 There are many ways for the assessment of twitch response, such as the use of electromyography 4,5 ; force displacement transducer techniques 2,6–9 ; and most recently, the acceleration transducer–based system of neuromuscular monitoring. 10–15 These equipments are, however, bulky, cumbersome, expensive, or time consuming for operation. Because of these limitations, the routine use of such monitors is impractical. The evaluation of neuromuscular blockade, at the present time, relies on either visual or manual (tactile) thumb twitch responses to the TOF nerve stimulation. Visual or tactile evaluation of neuromuscular blockade is subjective and involves uncertainty, especially in the recovery phase. Furthermore, in certain surgical procedures, such as those on the head and neck, both hands are tucked in the sides of the table and become inaccessible, rendering visual or tactile evaluation of the thumb twitch impossible. In such situation, muscle relaxant is often given in the light of guessing rather than on objective basis. Clearly, there is a need for a simple and practical way of measuring the twitch responses to TOF stimulation during anesthesia. Based on the current method of stimulation of the ulnar nerve over the ulnar groove at the elbow, which elicits a string thumb adduction (because of stimulation of the flexor carpi ulnaris muscle), a simple method that can objectively monitor and record the thumb twitch is developed. The unique features of the method or device are its simplicity and its ability to adapt to any pressure transducer to display the twitch response to TOF simultaneously with electrocardiogram, arterial, or central venous pressure.

Neurovascular relationships in human sensorimotor cortex can be modulated by movement

Introduction: The interpretation of fMRl is critically dependent on understanding the relationship between observed blood flow responses and the underlying neuronal changes. We have established a linear nemovascular coupling relationship between fMRl BOLD and somatosensory evoked potential (SEP) amplitude in human sensorimotor cortex using changes in stimulus intensity. Finger movement during a stimulus is known to attenuate electrical SEP responses in somatosensory cortex (movement gating), however it is also a common method of inducing fMRl BOLD activity in sensorimotor cortex, suggesting that electrical and haemodynamic cortical responses diverge. Here we examined the effects of finger movement during sensory stimulation on fMIU BOLD and SEP amplitude in sensorimotor cortex, in order to establish whether movement can modulate this relationship. Methods: Normal volunteers were subject to 0.2 millisecond square-wave electrical pulses delivered to the median nerve at the wrist, at 50 - 175 % of predetermined motor threshold. SEPs were recorded from contra-lateral parietal cortex, Cp3/4, referenced to Fz, over 450 averages. Gradient-echo EPI BOLD imaging was performed on a 3.0 Tesla Bruker Medical S300 using a blocked design with TB 4 sec. Imaging was acquired for all intensities, which were pseudo-randomised, then the experiment was repeated with subjects performing a self-paced thumb twitch during the stimulus. Images were analyzed using SPM99. Results: Without movement, fMBI BOLD responses paralleled changes in SEP N20-P27 amplitude (pcO.05) as both increased with increasing intensity (pcO.05; pcO.05 respectively). However, thumb movement increased fMRl BOLD signal intensity change (pcO.05) but caused a significant decrease in SEP N20-P27 amplitude across all intensities in all subjects (pcO.05). Conclusion: SEP amplitudes increased with increasing stimulus intensity, as did fMFU BOLD signal intensity changes, consistent with a close neurovascular coupling relationship. However the effect of simultaneous movement is to reset this relationship by increasing the cerebral blood flow response and suppressing the electrical response. The apparent coupling relationship can therefore be modulated by movement.

Influence of task-related ipsilateral hand movement on motor cortex excitability

Objective: The time course of the right motor cortex excitability in relation to a task-related voluntary right thumb twitch was studied using sub-threshold transcranial magnetic stimulation (TMS) to the right motor cortex. Methods: Motor excitability was studied in 8 adult subjects who made a brief right thumb twitch to the predictable omission of every fifth tone in a series of tones 2.5 s apart. This paradigm avoided an overt sensory cue, while allowing experimental control of TMS timing relative to both movement and the cue to move. Motor excitability was characterized by several measures of motor evoked potentials (MEPs) recorded from the left thenar eminence in response to TMS over the right scalp with a 9 cm coil: probability of eliciting MEPs, incidence of MEPs and amplitude of MEPs. Results: All subjects showed suppression of motor excitability immediately following a voluntary right thumb twitch (ipsilateral response), and up to 1 s after it. However, two distinctly different effects on motor excitability were observed before the response: two subjects showed excitation, beginning about 500 ms before response until 300 ms after it, followed by the post-movement suppression; 6 subjects displayed pre-movement suppression, beginning about 600 ms before the response and persisting for the duration. Conclusions: The net effect of an ipsilateral response on motor cortex can be either inhibitory or excitatory, changing with time relative to the response. These findings are compatible with two separate processes, inhibitory and excitatory, which interact to determine motor excitability ipsilateral to the responding hand.

TWITCHER: a device to stimulate thumb twitch response to ulnar nerve stimulation.

To design and fabricate a device to simulate evoked thumb adduction in response to ulnar nerve stimulation. We implemented a computer-controlled, motorized thumb (TWITCHER) that responds to ulnar nerve stimulation by an unmodified peripheral nerve stimulator. Clinically realistic response patterns are generated for both depolarizing and non-depolarizing muscle relaxants and three modes of stimulation (single twitch, train-of-four, tetanus). The device has been used in a full-scale patient simulator for the last six years. TWITCHER has been well received by participants in simulation exercises including the use of neuromuscular blocking drugs.

Accelerated onset of vecuronium neuromuscular block with pulmonary arterial administration

The purpose of this study was to determine the onset times of vecuronium neuromuscular block administered into either the central circulation or a peripheral vein. One hundred and twenty adult patients with a pulmonary artery (PA) catheter were randomly divided into one of three groups with respect to the routes of vecuronium administration (n = 40 in each group). Anaesthesia was induced with midazolam 2.5 mg iv and fentanyl 10-50 micrograms.kg-1 iv and maintained with intermittent doses of fentanyl 50 micrograms iv and nitrous oxide 60-70% in oxygen. After immobilization of the forearm in a splint, the ulnar nerve was stimulated supramaximally every 12 sec. The resulting force of the evoked thumb twitch was recorded (Myograph 2000, Biometer, Denmark). The times from the injection to the first depression of twitch response (latent onset) in patients given vecuronium 0.08 mg.kg-1 into the pulmonary artery, the right atrium, and a peripheral vein on the hand were 58.0 +/- 19.5, 71.5 +/- 17.1, and 82.4 +/- 18.0 sec (mean +/- SD), respectively. The latent onset of neuromuscular block occurred sooner in patients given vecuronium into the central vein than when administered into a vein on the hand (P < 0.01). In comparing the patients given vecuronium into the central vein, the onset times to 95% twitch depression (onset) were 152.3 +/- 40.7 and 168.2 +/- 35.5 sec. The onset of block was found to be faster when vecuronium was administered into the pulmonary artery than into the right atrium (P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetics and pharmacodynamics of rocuronium in patients with cirrhosis.

Rocuronium, like other steroidal nondepolarizing muscle relaxants, may in part be eliminated by the liver. To determine the influence of liver disease on its neuromuscular blocking effect, we studied the pharmacokinetics and pharmacodynamics of rocuronium in patients with cirrhosis. Eighteen patients undergoing elective surgery, 10 with cirrhosis and 8 with normal liver function, were studied. Anesthesia was induced with intravenous thiopental 5-7 mg.kg-1 and maintained with 60% nitrous oxide in oxygen and repeated doses of fentanyl 2 micrograms.kg-1. The force of thumb adduction in response to supramaximal ulnar nerve stimulation was monitored and recorded. An intravenous bolus of rocuronium 0.6 mg.kg-1 was administered and venous blood sampled at frequent intervals for 6 h. Plasma concentrations of rocuronium was measured by high-pressure liquid chromatography. Data were fitted to both a pharmacokinetic and a pharmacodynamic model by using a two-compartment open model and an effect compartment model. Data were analyzed by least-squares regression. The onset of neuromuscular blockade was longer (P < 0.01) in patients with cirrhosis (158 +/- 56 s) than in normal patients (108 +/- 33 s). Recovery of the thumb twitch to 75 and 90% of its control value was 77 +/- 25 and 88 +/- 29 min in cirrhotic patients versus 57 +/- 11 and 64 +/- 13 min, respectively, in normal patients (P < 0.05). The central volume of distribution of rocuronium was 104 +/- 21 in cirrhotic patients and 78 +/- 24 ml.kg-1 in normal patients (P < 0.05). No significant difference in elimination kinetics was observed between the two groups. The elimination half-life was 87.5 +/- 17.5 min in normal patients and 96.0 +/- 36.8 min in cirrhotic patients (difference not significant). This increased onset time was linearly correlated to the increased central volume of distribution of rocuronium in cirrhosis. Rocuronium onset time is longer in cirrhotic patients than in those with normal liver function; this can be explained by an increase in the volume in which rocuronium initially distributes. Although elimination kinetics are unchanged in patients with cirrhosis, rocuronium recovery time is prolonged in cirrhotic patients.

PRIMING OF PANCURONIUM WITH MAGNESIUM

Magnesium inhibits the release of acetylcholine from the motor nerve terminal and thus potentiates the action of the non-depolarizing neuromuscular blocking drugs. We have examined the possibility that this effect might enhance the speed of onset of non-depolarizing block with pancuronium. Following the administration of pancuronium 100 micrograms kg-1, 95% depression of thumb twitch occurred in 68.3 (SD 25.9) s in magnesium-pretreated subjects and in 73.7 (19.5) s in a group given a priming dose (10 micrograms kg-1) of pancuronium. Tracheal intubation was performed after 97.8 (22.5) s in the magnesium group and in 121.0 (37.5) s in the control group (ns). It is concluded that pretreatment with magnesium does not usefully increase the speed of onset of action of pancuronium.

Method of Intraoperative Monitoring of Neuromuscular Function and Residual Blockade in the Recovery Room

We evaluated the method used intraoperatively to assess the degree of neuromuscular blockade prior to pharmacologic reversal to determine its role in preventing residual blockade in the postanesthesia care unit (PACU). We studied 38 patients who received a nondepolarizing muscle relaxant during general anesthesia for carotid endarterectomy or thoracotomy. The anesthesiologist assessed the degree of neuromuscular blockade intraoperatively prior to pharmacologic reversal either by the standard method of visually counting the number of evoked thumb twitches elicited by supramaximal train-of-four stimulation of the ulnar nerve (i.e., thumb train-of-four count), or by an alternative method such as 1) visually counting the number of evoked orbicularis oculi muscle twitches elicited by supramaximal train-of-four stimulation of the facial nerve, or 2) observing the patient for clinical evidence of partial recovery (e.g., swallowing or attempts to breathe). Residual blockade in the PACU was defined as 1) a train-of-four ratio less than 0.70 (measured by a mechanomyograph), or 2) the inability of the patient to perform clinical tests of neuromuscular function (e.g., a sustained head lift for 5 seconds) and evidence of neuromuscular weakness that was resolved following administration of edrophonium. Five of the 22 patients (23%) in whom one of the alternative methods was used had residual blockade in the PACU; none of the 16 patients with a thumb train-of-four count of 3 or 4 before pharmacologic reversal of NMB had residual blockade in the PACU (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Ketamine Potentiates Nondepolarizing Neuromuscular Relaxants in a Primate

Ketamine has many neuromuscular effects in vitro. Its neuromuscular effects in vivo have been controversial and inconsistent. To systematically examine its neuromuscular effects over a wide dose range and its interaction with all popular nondepolarizing neuromuscular relaxants, the effects of ketamine 2, 5, and 10 mg/kg IV were studied on a continuous but incomplete (50%) neuromuscular block preestablished by an IV infusion of d-tubocurarine, atracurium, vecuronium, and pancuronium. Indirectly stimulated adductor pollicis muscle response of monkeys anesthetized with 0.5-1.0% halothane in oxygen were quantified. Ketamine in the absence of a neuromuscular relaxant had no effect on the thumb twitch. In a dose-dependent manner, ketamine significantly enhanced the 50% depression of the thumb twitch preestablished by a constant IV infusion of each of the four muscle relaxants studied. Ketamine 2 mg/kg potentiated the neuromuscular relaxants in the following order of magnitude: vecuronium greater than atracurium greater than d-tubocurarine greater than pancuronium. However, with a 10 mg/kg dose of ketamine, pancuronium became as potentiated as was vecuronium, i.e., pancuronium = vecuronium greater than atracurium greater than d-tubocurarine. It is concluded that in the primate, ketamine potentiates all nondepolarizing muscle relaxants in a dose-dependent manner.

Failure of the Tourniquet-Twitch Test as a Diagnostic or Screening Test for Malignant Hyperthermia

We have performed the tourniquet-twitch test of Roberts and Ryan in normal and in malignant hyperthermia (MH) patients and relatives. This test measures the ratio of electrically induced thumb twitches noted after 10 min of ischemia with those noted immediately prior to the ischemia. We found no significant differences in this ratio between normal subjects and those who have had MH reactions, or relatives of such individuals. Furthermore, we have observed no significant differences in tourniquet-twitch ratios between those with normal caffeine-halothane contractures and persons with caffeine-halothane contractures tests positive for MH. These findings do not agree with those of Roberts and Ryan, who reported that tourniquet-twitch ratios were higher in MH patients than in normal patients. We have, however, determined that subjects with tourniquet-twitch ratios greater than or equal to 1.8 are substantially younger than those with tourniquet-twitch ratios less than or equal to 1.0. Therefore we do not believe that the tourniquet-twitch test is useful as a diagnostic, or even as a screening test for MH.

Anaesthetic management of a child with dermatomyositis

A two years, ten months old male with dermatomyositis was anaesthetized with enflurane, nitrous oxide and oxygen by mask followed by intravenous succinylcholine to facilitate endotracheal intubation. The evoked thumb twitch in response to succinylcholine demonstrated an abnormal, short-lived contracture. The depression, duration and return to control of muscle twitch tension and a transient rise in serum potassium concentration followed a normal pattern.

Decreased Sensitivity to Metocurine in Patients with Upper Motoneuron Disease

Responses to the nondepolarizing muscle relaxant, metocurine, were studied in eight hemiplegic and eight unmatched patients with normal motor strength during the general anesthetic given for various neurosurgical operations. Metocurine, 0.3 mg/kg, was administered intravenously, and indirectly evoked thumb twitch tensions were measured on both sides in the hemiplegic patients, and on one side in the normal patients. Arterial blood samples were obtained as twitch tension was recovering, and serum metocurine concentrations were determined using a specific radioimmunoassay. Percentage of paralysis was plotted as a function of log [metocurine] and the data were compared by analysis of covariance. For the normal motor strength patients, r = 0.84; for the unaffected arm of the hemiplegic patients, r = 0.69; and for the affected arm of the hemiplegic patients, r = 0.86, all significant at P less than 0.001. The mean plasma metocurine concentrations at 20, 25, 50, 75, and 80% paralysis were significantly different for all groups (P less than 0.001). The regression lines, in turn, did not overlap and were significantly different, each from the other (P less than 0.005). We were, however, unable to detect any significant deviation from parallelism among the three regression lines. We also measured time to 50% return of single twitch height for each data group as follows (mean +/- SEM: for NMS patients, 242 +/- 73 min; for the unaffected arm of hemiplegic patients, 116 +/- 60 min; and for the affected arm of hemiplegic patients, 59 +/- 36 min. By ANOVA and the Bonferroni test, each value was different from the other at P less than or equal to 0.01.(ABSTRACT TRUNCATED AT 250 WORDS)

Antagonism of d-tubocurarine-induced neuromuscular blockade with a mixture of 4-aminopyridine and neostigmine in man.

The antagonistic properties of a mixture of 4-aminopyridine (4-AP) 3 mg X ml-1 and neostigmine 0.2 mg X ml-1 (in three patient groups) administered at 90 per cent d-tubocurarine block were compared with those of plain neostigmine (in three patient groups) in thirty-six patients during thiopentone-fentanyl-nitrous oxide-oxygen anaesthesia. The recovery variables included thumb twitch height, thenar e.m.g. peak-to-peak amplitude, and train-of-four ratio in response to supramaximal ulnar nerve stimulation. In addition, mean arterial pressure, heart rate, apnoea time and time to responsiveness to verbal command after nitrous oxide was turned off at 20 minutes of recovery were examined as circulatory and central nervous system responses to antagonism. The addition of 4-AP 30 mg to neostigmine 2 mg enhanced the recovery of train-of-four ratio from 54.2 +/- 5.2 to 80.2 +/- 5.2 per cent at 20 mins of antagonism (mean +/- SEM; p less than 0.01) while adding 4-AP 45 mg to neostigmine 3 mg increased the train-of-four ratio from 67.7 +/- 2.3 to 92.3 +/- 2.4 per cent (p less than 0.01) when compared with plain neostigmine. No statistically significant difference could be found between the groups in the recovery of twitch height or e.m.g. amplitude. The antagonism of d-tubocurarine block with 4-AP 30 mg plus neostigmine 2 mg was at least as effective as with neostigmine 3-4 mg. Mean arterial pressure increased in the group receiving 45 mg 4-AP plus 3 mg neostigmine.(ABSTRACT TRUNCATED AT 250 WORDS)

Cortical activation during somatosensory stimulation and voluntary movement in man: A regional cerebral blood flow study

Regional cerebral blood flow (rCBF) changes were measured by a 254-channel dynamic gamma camera in 7 human subjects during peripheral nerve stimulation and during voluntary movement. Normal somatosensory evoked potentials (SEPs) were recorded simultaneously from the scalp over the primary cortical projection areas when contralateral digital or ipsi- or contralateral median nerve was stimulated electrically. The voluntary movement was an imitation of the passive thumb twitch which occurred during median nerve stimulation. Focal rCBF increases were observed during nerve stimulation and during voluntary movement in the same area within the middle part of the contralateral central region. This area of cortical activation was localized over the sensory and motor projection areas of the hand and thus involved both the precentral and postcentral gyri. During voluntary movement additional focal increases of rCBF were observed in the upper premotor region, including the supplementary motor area. This area was also activated during contralateral median nerve stimulation. Focal rCBF increases were also observed during contralateral nerve stimulation in the lower central region, just anterior to the primary auditory cortex. This area appears to correspond to the second sensory area (SII) in man. During ipsilateral median nerve stimulation no focal increases of rCBF were observed and also no SEPs were recorded within the analysis time of 200 msec. It is concluded that activation of the contralateral primary cortical sensory and motor areas, as well as the SII area, as shown by focal rCBF increases, reflects generation of the early components of the SEP. The activation of the upper premotor region during median nerve stimulation and during voluntary movement is more likely to be involved in the generation of the later components of the evoked potential and the electrical activity preceding voluntary movement. The same extents of the focal rCBF activation in the contralateral sensorimotor area during peripheral nerve stimulation and during voluntary movements confirm that the precentral gyrus is involved in sensory perception and, similarly, that sensory feedback to the post-central gyrus is a normal component of the execution of voluntary movement.

Short-latency somatosensory evoked potentials.

Short-latency components of the somatosensory evoked potential (SEP) were studied in 20 subjects who had median nerve stimulation using knee, forehead, and ear reference recordings. Six potentials were identified (P10, P12, P14, N19, P20, P23). Potential P10 seems to originate in the brachial plexus, P12 most likely is generated in dorsal column nuclei and medial lemniscus, P14 is probably thalamic in origin but is frequently bilobed and may have a second generator source, and N19 may originate in sensory radiation or cortex. The origin of P20 is unclear, and P23 appears to be generated in the contralateral somatosensory cortex. Clinically, we recommend using right, left, and bilateral median nerve stimulation at 4 Hz. Intensity of stimulus should produce at least a small thumb twitch, it was only with knee reference recording that all early potentials were seen.