Effect of repetition rate on middle latency auditory evoked potentials in humans

Middle Latency Auditory Evoked Potentials (MLAEPs) were recorded from 15 healthy subjects in order to evaluate the influence of different repetition rates on the latency and the amplitude of their main components Na, Pa and Nb. MLAEPs were obtained from Cz-ipsilateral ear lobe by averaging responses to 2000 monaural clicks delivered to both ears, at 65 dB SL of intensity, for each of 3 different repetition rates (1.1, 4.1, 8.1 Hz). Time base was 100 ms, analogical band-pass filter 5-1000 Hz (off-line digital bandpass: 20-100 Hz). The statistical analysis (repeated measures analysis of variance), demonstrated that, the latency and the amplitude of the Nb component were slightly influenced by repetition rate while Pa and Na were not. Moreover Nb showed the greatest interindividual variability (as already pointed out by other authors too); thus, we suggest that a stimulus rate of 8.1 Hz and the analysis of Na and Pa component only, can be regarded as the best assessment for MLAEPs evaluation when they are used for clinical purposes.     

Human middle-latency auditory evoked potentials: vertex and temporal components

We recorded middle-latency (20–70 msec) auditory evoked potentials (MLAEPs) to monaural and binaural clicks in 30 normal adults (ages 20–49 years) at 32 scalp locations all referred to a balanced non-cephalic reference. Our goal was to define the MLAEP components that were present at comparable latencies and comparable locations across the subject population. Group and individual data were evaluated both as topographic maps and as MLAEPs at selected electrode locations.Three major components occurred between 20 and 70 msec, two well-known peaks centered at the vertex, and one previously undefined peak focused over the posterior temporal area. Pa is a 29 msec positive peak centered at the vertex and present with both monaural and binaural stimulation, Pb is a 53 msec positive peak also centered at the vertex but seen consistently only with binaural and right ear stimulation. TP41 is a 41 msec positive peak focused over both temporal areas. TP41 has not been identified in previous MLAEP studies that concentrated on central scalp locations and/or used active reference electrode sites such as ears or mastoids.Available topographic, intracranial, pharmacologic, and lesion studies indicate that Pa, Pb and TP41 are of neural origin. Whether Pa and/or Pb are produced in Heschl's gyrus, primary auditory cortex, remains unclear. TP41 is probably produced by auditory cortex on the posterior lateral surface of the temporal lobe. It should prove of considerable value in experimental and clinical evaluation of higher level auditory function in particular and of cortical function in general.     

Gender differences in medium-latency acoustic evoked potentials

Medium-latency acoustic (auditory) evoked potentials (MLAEPs) were recorded in 30 men and 30 women. The MLAEPs recorded in the left and right mastoid derivations were found to be asymmetrical, the lateral differences depending on the sex: binaural stimulation and stimulation of the right ear yielded a higher total amplitude of the set of medium-latency components in the right derivation in men and in the left derivation in women. If the left ear was stimulated, there were no sex-related differences in MLAEP asymmetry. The data are discussed in terms of gender differences with respect to functional specialization of the cerebral hemispheres.     

Effect of monaural and binaural stimulation on cytoplasmic RNA content in cells of the central nucleus of the cat inferior colliculus

A cytophotometric study of sections stained with gallocyanin and chrome alum showed that monaural stimulation for 2 h and binaural stimulation for 1.5 h with rhythmic noise signals led to a marked increase in the cytoplasmic RNA content per cell in the principal and large multipolar neurons of the dorsal and ventral parts of the ventrolateral region of the central nucleus of the inferior colliculus. The increase in cytoplasmic RNA content in the principal cells of the ipsiand contralateral parts of this nucleus relative to the stimulated ear in the case of monaural stimulation and the increase in RNA content in response to binaural stimulation suggests a uniform distribution of bilaterally converging connections from the lower nuclei of the auditory system on the principal cells. The increase in cytoplasmic RNA in the large multipolar cells of the contralateral central nucleus in response to monaural stimulation is evidence of the predominantly contralateral projection to these cells. The results are evidence of convergence of binaural influences on the principal and large multipolar cells of the central nucleus of the inferior colliculus.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 10, No. 6, pp. 598–605, November–December, 1978.     

Brainstem auditory evoked potentials in the rabbit.

Eight white New Zealand rabbits were submitted to auditory stimulation in order to obtain normative BAEP parameters. A monaural alternating 0.1 ms click stimulation at 20 Hz, 90 dB was used. Two series of 1000 responses were averaged (10 ms time-base, 160-3000 Hz band-pass) and highly reproducible peaks were obtained. Peaks P1, P2, P3, P4 were obtained in all ipsilateral recordings, whereas peak P5 was detectable in only 6 animals. In contralateral recordings P1 was absent and the following peaks were similar to those of ipsilateral recordings. Normative values of absolute and interpeak latencies, peak amplitudes and amplitude ratios were obtained. The procedure was repeated 24 hours after basal recordings and measures of test-retest variability were obtained.     

Evaluation of binaural interaction according to the characteristics of short latency acoustic evoked potentials in guinea pigs

Binaural interactions was evaluated in guinea pigs by plotting the difference between the algebraic sum of brainstem evoked potentials recorded during monaural stimulation of the right and left ears and those produced by binaural stimuli. This plot was distinguished by three peaks (N₁, P₁, and N₂) in the region of IV–IV wave latencies (short-latency acoustic evoked potentials) in the absence of masking noise, but using masking noise (signal-noise ratio: +20-0 dB), plots showed additional peaks No and Po in the region of wave III–III latencies. The amplitude of P₁N₂ in relation to that of wave IV of the summated potentials recording monaural stimulation of the right and left ear remains constant with an increase in the sound pressure level from 47 to 107 dB. This relationship grows with a decline in the signal-noise ratio when masking is used, while the P₁N₂ amplitude declines. It is postulated that binaural interaction pattern does not change when the clicking sound increases in intensity and that distinctive aspects of neurophysiological mechanisms underlying binaural interaction emerge during masking with a signal-noise ratio of +20-0 dB.Institute of Otolaryngology, Ministry of Public Health of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 19, No. 5, pp. 579–586, September–October, 1987.     

Evoked potentials recorded from brain-stem nuclei in awake cat: interaction of tone bursts and continuous tone

Previous work indicated that components of the auditory thalamocortical potential evoked by a brief binaural tone burst could be enhanced by certain stimulus combinations, e.g., a brief tone burst in the presence of a continuous tone. The principal questions of the present study were whether enhaced components could be obtained caudal to thalamocortex and whether monaural stimuli would be effective in producing enhancement. Eight cats received electrodes in cochlear nucleus and the nucleus of the inferior colliculus. Custom earmolds were made for each ear of each animal. The median attenuation produced by the earmolds was 35 dB and the use of a single earmold approximated monaural stimulation. Auditory evoked potentials were recorded from the electrodes while the animals were unanesthetized but comfortably restrained. Brief 6.25 kHz tone bursts were presented against a background of silence or of a 4.96 kHz continuous tone. In the presence of the continuous tone, enhanced components were obtained from a majority of the electrodes in inferior colliculus but from none of the electrodes in cochlear nucleus. The late negative component in the colliculus potential was increased in amplitude while other components were reduced in amplitude by the continuous tone. The latencies of all components from all electrodes were increased by the presence of the continuous tone. It was concluded that enhancement effects could be obtained at the level of inferior colliculus, and that binaural stimulation does not appear to be necessary to produce enhanced components.     

Effects of Low Frequency Prefrontal Repetitive Transcranial Magnetic Stimulation on the N2 Amplitude in a GoNogo Task

During the last decade, repetitive transcranial magnetic stimulation (rTMS) of the prefrontal cortex has become established as a treatment for various mental diseases. The rational of prefrontal stimulation has been adapted from the mode of action known from rTMS using motor-evoked potentials though little is known about the precise effect of rTMS at prefrontal sites. The objective of the current study is to investigate the inhibitory effect of prefrontal 1 Hz rTMS by stimulating the generators of event-related potentials (ERP) which are located in the prefrontal cortex. Thus, 1 Hz rTMS was applied offline over the left dorsolateral prefrontal cortex (DLPFC) and the medial prefrontal cortex (MPFC) in 18 healthy subjects who subsequently underwent a GoNogo task. Both active conditions were compared to sham rTMS within a randomized and counterbalanced cross-over design in one day. ERPs were recorded during task performance and the N2 and the P3 were analysed. After 1 Hz rTMS of the left DLPFC (but not of the MPFC), an inhibitory effect on the N2 amplitude was observed, which was related to inhibitory control. In contrast, after 1 Hz rTMS of the MPFC (but not at the left DLPFC) a trend towards an increased P3 amplitude was found. There was no significant modulation of latencies and behavioural data. The results argue in favour of an inhibitory effect of 1 Hz rTMS on N2 amplitudes in a GoNogo task. Our findings suggest that rTMS may mildly modulate prefrontally generated ERP immediately after stimulation, even where behavioural effects are not measurable. Thus, combined rTMS-ERP approaches need to be further established in order to serve as paradigms in experimental neuroscience and clinical research.     

成对短声不同间隔对单、双耳听觉脑干反应的影响——衍生听觉脑干反应方法的应用

采用具有不同间隔(0～32ms)的65dB nHL(正常听力水平)的成对短声刺激,记录20名正常人的单侧耳和两耳交替刺激的听觉脑干反应(ABR)。用计算机从成对短声反应中减去单一短声反应以提取衍生ABR。结果表明,单、双耳的衍生ABR V波振幅在成对短声间隔为0.2～1.5ms时,受到明显影响。单耳的减小54％～65％(P<0.01),两耳的减少46％～53％(P<0.01),但单、双耳的衍生ABR I波振幅未显示显著差异(P>0.05)。该结果说明,高位脑干通路在成对短声间隔为0.2～1.5ms时,不但对同侧耳的第2个短声反应能力降低,而且对来自对侧耳的第2个短声也如此。从而推断,在两耳交替刺激的耳间短声间隔小于2ms范围时,在下丘部位可能存在两耳交互作用。结果还提示,临床检查ABR时,采用的短声刺激间隔至少不应小于30ms。     

Using Low Levels of Stochastic Vestibular Stimulation to Improve Balance Function

Low-level stochastic vestibular stimulation (SVS) has been associated with improved postural responses in the medio-lateral (ML) direction, but its effect in improving balance function in both the ML and anterior-posterior (AP) directions has not been studied. In this series of studies, the efficacy of applying low amplitude SVS in 0–30 Hz range between the mastoids in the ML direction on improving cross-planar balance function was investigated. Forty-five (45) subjects stood on a compliant surface with their eyes closed and were instructed to maintain a stable upright stance. Measures of stability of the head, trunk, and whole body were quantified in ML, AP and combined APML directions. Results show that binaural bipolar SVS given in the ML direction significantly improved balance performance with the peak of optimal stimulus amplitude predominantly in the range of 100–500 μA for all the three directions, exhibiting stochastic resonance (SR) phenomenon. Objective perceptual and body motion thresholds as estimates of internal noise while subjects sat on a chair with their eyes closed and were given 1 Hz bipolar binaural sinusoidal electrical stimuli were also measured. In general, there was no significant difference between estimates of perceptual and body motion thresholds. The average optimal SVS amplitude that improved balance performance (peak SVS amplitude normalized to perceptual threshold) was estimated to be 46% in ML, 53% in AP, and 50% in APML directions. A miniature patch-type SVS device may be useful to improve balance function in people with disabilities due to aging, Parkinson’s disease or in astronauts returning from long-duration space flight.     

A high-density EEG investigation into steady state binaural beat stimulation

Binaural beats are an auditory phenomenon that has been suggested to alter physiological and cognitive processes including vigilance and brainwave entrainment. Some personality traits measured by the NEO Five Factor Model have been found to alter entrainment using pulsing light stimuli, but as yet no studies have examined if this occurs using steady state presentation of binaural beats for a relatively short presentation of two minutes. This study aimed to examine if binaural beat stimulation altered vigilance or cortical frequencies and if personality traits were involved. Thirty-one participants were played binaural beat stimuli designed to elicit a response at either the Theta (7 Hz) or Beta (16 Hz) frequency bands while undertaking a zero-back vigilance task. EEG was recorded from a high-density electrode cap. No significant differences were found in vigilance or cortical frequency power during binaural beat stimulation compared to a white noise control period. Furthermore, no significant relationships were detected between the above and the Big Five personality traits. This suggests a short presentation of steady state binaural beats are not sufficient to alter vigilance or entrain cortical frequencies at the two bands examined and that certain personality traits were not more susceptible than others.     

Changes in RNA content in neurons of the superior olivary complex during monaural and binaural stimulation

The character of binaural competitive connections at the level of the superior olive was investigated cytospectrophotometrically in cats. As a result of monaural stimulation for 2 h or binaural stimulation for 1.5 h by rhythmic noise signal the RNA content in the neurons of the ipsilateral and contralateral medial and lateral nuclei increased significantly. The volume of functioning neurons in the nuclei studied either increased or remained the same as in the control. The increase in the RNA content in neurons of both the ipsilateral and contralateral medial and lateral nuclei suggests a uniform distribution of binaurally converging connections on the neurons of these nuclei. The results also suggest that the accumulation of cytoplasmic RNA takes place in response not only to excitation, but also to inhibition.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 10, No. 1, pp. 67–74, January–February, 1978.     

Response properties of auditory activated cells in the occipital cortex of the blind mole rat: an electrophysiological study

Previous studies have demonstrated that despite its blindness, the subterranean blind mole rat (Spalax ehrenbergi) possesses a noticeable lateral geniculate nucleus and a typical cyto-architectural occipital cortex that are reciprocally connected. These two areas, as revealed by the metabolic tracer 2-deoxyglucose, are activated by auditory stimuli. Using single unit recordings, we show that about 57% of 325 cells located within the occipital cortex of anesthetized mole rats responded to at least one of the following auditory stimuli — white noise, pure tones, clicks, and amplitude modulated tones — with the latter two being the most effective. About 85% of cells driven by either contralateral or ipsilateral stimulation also responded to binaural stimulation; about 13% responded only to binaural stimulation; and 2% were driven exclusively by contralateral stimulation. Comparing responsiveness and response strength to these three modes of stimulation revealed a contralateral predominance. Mean latency (±SD) of ipsilateral and contralateral responses were 48.5±32.6 ms and 33.5±9.4 ms, respectively. Characteristic frequencies could be divided into two distinct subgroups ranging between 80 and 125 Hz and between 2,500 and 4,400 Hz, corresponding to the most intensive spectral components of the vibratory intraspecific communication signals and airborne vocalizations.Abbreviations BMF best modulation frequency - CF characteristic frequency - 2-DG 2-deoxyglucose - dLGN dorsal lateral geniculate nucleus - IC inferior colliculus - LGN lateral geniculate nucleus - OC occipital cortex - MTF modulation transfer function - SAM sinusoidally amplitude modulation - SC superior colliculus     

Somatosensory evoked potentials by electrical stimulation of the third trigeminal branch in humans.

Somatosensory Evoked Potentials by stimulation of the trigeminal nerve (TSEPs) were recorded from 30 healthy subjects (15 males, 15 females; mean age: 45.2 years; range: 21-66 years) in order to assess normative data for clinical purposes. To elicit the TSEPs, electrical square pulses (duration: 0.1 msec; frequency: 3.3 Hz; intensity: 4-6 mA) were delivered by bipolar skin electrodes (cathode over the foramen mentale and anode on the middle of the chin, stimulating the trigeminal third branch). TSEPs were obtained from C3-Fpz and C4-Fpz by twice averaging 1000 responses. Time base was 100 msec; bandpass filter setting was 5-1500 Hz. In our normal subjects the TSEPs were composed of several components (N1, P1, N2, P2 and N3); the components, with the exception of N3, were always bilaterally detectable. Statistical analysis (repeated measures analysis of variance) demonstrated a dependence of TSEP latencies on sex; it did not demonstrate an analogous dependence on either side of stimulation or age. Finally, we propose some guidelines for the evaluation of TSEPs: consider N1, P1, N2 and P2 waves, base the judgement of normality on latencies rather on amplitudes, use differing normative data according to sex.     

Tuning of the ocular vestibular evoked myogenic potential to bone-conducted sound stimulation

Ocular vestibular evoked myogenic potentials (oVEMPs) are a recently described clinical measure of the vestibulo-ocular reflex. Studies demonstrating differences in frequency tuning between air-conducted and bone-conducted (BC) oVEMPs suggest a separate vestibular (otolith) origin for each stimulus modality. In this study, 10 healthy subjects were stimulated with BC stimuli using a hand-held minishaker. Frequencies were tested in the range of 50-1,000 Hz using both a constant-force and constant-acceleration method. Subjects were stimulated at the mastoid process and the forehead. For constant-force stimulation at both sites, maximum acceleration occurred around 100 Hz, in differing axes. Both forms of stimulation had low-frequency peaks of oVEMP amplitudes (constant force: mastoid, 80-150 Hz; forehead, 50-125 Hz; constant acceleration: mastoid, 100-200 Hz; forehead, 80-150 Hz), for both sites of application, despite differences in the magnitude and direction of evoked head acceleration. For mastoid stimulation, ocular responses changed from out of phase to in phase for 400 Hz and above. Our results demonstrate that BC stimuli show tuning around 100 Hz, independent of stimulus site, that is not due to skull properties. The findings are consistent with an effect on a receptor with a resonance around 100 Hz, most likely the utricle.     

Temporal resolution in olfaction III: flicker fusion and concentration-dependent synchronization with stimulus pulse trains of antennular chemoreceptor cells in the American lobster

To understand how chemoreceptor organs may extract temporal information from odor plumes, we investigated the frequency filter properties of lobster chemoreceptor cells. We used rapid stimulation and high-resolution stimulus measurement for accurate stimulus control and recorded extracellular responses from chemoreceptors in the lobster lateral antennule in situ. We tested 16 hydroxyproline-sensitive cells with a series of ten 100-ms pulses at 10, 100 and 1000 μmol l⁻¹ at stimulation frequencies from 0.5 Hz to 4 Hz. Receptor cell responses could accurately encode 10 μmol l⁻¹, but not 100 or 1000 μmol l⁻¹ pulses, delivered at rates of 4 Hz. Flicker-fusion frequency and synchronization with the stimulus pulse train were concentration dependent: performance rates above 1 Hz became poorer both with increasing pulse amplitude and frequency. Flicker fusion frequency was 3 Hz for 100 μmol l⁻¹ pulses and 2 Hz for 1000 μmol l⁻¹ pulses. Individual cells showed differences in their stimulus pulse following capabilities, as measured by the synchronization coefficient. These individual differences may form a basis for coding temporal features of an odor plume in an across-fiber pattern. Accepted: 7 July 1999     

CFTR displays voltage dependence and two gating modes during stimulation

The patch-clamp technique in conjunction with current noise analysis was employed to clarify the events underlying the regulation of the CFTR (cystic fibrosis transmembrane conductance regulator) during cAMP- dependent stimulation. 3T3 fibroblast cells expressing the CFTR were stimulated in cell-attached mode with forskolin. The number (N) of activated channels per patch ranged from 1 to approximately 100. In true single-channel recordings, CFTR's gating was best described by two open states (approximately 5 and approximately 100 ms) and three closed states (< or = 5, approximately 100, and approximately 1,000 ms). Current noise analysis resulted in spectra containing two distinct Lorentzian noise components with corner frequencies of 1.3 Hz and approximately 50 Hz, respectively. Single-channel time constants were dependent on voltage. The fastest closed state increased its contribution from 48% at +100 mV to 87% at -100 mV, and the medium open state reduced its length to one half, resulting in gating dominated by fast events. Similarly, the fast Lorentzian increased its amplitude, and its corner frequency increased from 44 Hz at +100 mV to 91 Hz at - 100 mV, while the slow Lorentzian was voltage independent. In multi- channel recordings N.Po (i.e., N times open probability) increased significantly, on average by 52% between -90 and +90 mV. Stimulation with forskolin increased Po of CFTR to approximately 0.5, which resulted from a decrease of the longest closed state while the faster open and closed states were unaffected. Neither corner frequency was affected during stimulation. Recordings from multichannel patches revealed in addition, unique, very long channel openings (high Po mode, average 13 s). Channels exhibiting high Po (i.e., Po approximately 1.0) or low Po (i.e., Po approximately 0.5) gating modes were both present in multichannel recordings, and CFTRs switched modes during stimulation. In addition, the switch to the high Po mode appeared to be a cooperative event for channel pairs. High forskolin concentration (i.e., 10 microM) favored transition into the high Po mode, suggesting a cellularly mediated regulation of model switching due to a fundamental change in configuration of the CFTR. Thus, during stimulation the CFTR increased its activity through two distinct effects: the reduction of the long closed state and modal switching to the high Po mode.     

Role of the caudate nucleus in differentiating spatially separated acoustic signals in the dog

In tests on dogs the influence has been studied of bilateral electrolytic lesion of the caudate nuclei heads on realization of acquired conditioned instrumental defensive reactions to spatially separated sound signals (clicks series) under dichotic stimulation. It is shown that caudatectomy does not influence the dogs differentiation of the side of monaural sound stimulation, but leads to their absolute disability for a long time to differentiate right- and left-side positions of the sound image, modelled by changes in interaural difference in time of sound signal arrival at binaural stimulation.     

Neuromagnetic index of hemispheric asymmetry prognosticating the outcome of sudden hearing loss

The longitudinal relationship between central plastic changes and clinical presentations of peripheral hearing impairment remains unknown. Previously, we reported a unique plastic pattern of "healthy-side dominance" in acute unilateral idiopathic sudden sensorineural hearing loss (ISSNHL). This study aimed to explore whether such hemispheric asymmetry bears any prognostic relevance to ISSNHL along the disease course. Using magnetoencephalography (MEG), inter-hemispheric differences in peak dipole amplitude and latency of N100m to monaural tones were evaluated in 21 controls and 21 ISSNHL patients at two stages: initial and fixed stage (1 month later). Dynamics/Prognostication of hemispheric asymmetry were assessed by the interplay between hearing level/hearing gain and ipsilateral/contralateral ratio (I/C) of N100m latency and amplitude. Healthy-side dominance of N100m amplitude was observed in ISSNHL initially. The pattern changed with disease process. There is a strong correlation between the hearing level at the fixed stage and initial I/C(amplitude) on affected-ear stimulation in ISSNHL. The optimal cut-off value with the best prognostication effect for the hearing improvement at the fixed stage was an initial I/C(latency) on affected-ear stimulation of 1.34 (between subgroups of complete and partial recovery) and an initial I/C(latency) on healthy-ear stimulation of 0.76 (between subgroups of partial and no recovery), respectively. This study suggested that a dynamic process of central auditory plasticity can be induced by peripheral lesions. The hemispheric asymmetry at the initial stage bears an excellent prognostic potential for the treatment outcomes and hearing level at the fixed stage in ISSNHL. Our study demonstrated that such brain signature of central auditory plasticity in terms of both N100m latency and amplitude at defined time can serve as a prognostication predictor for ISSNHL. Further studies are needed to explore the long-term temporal scenario of auditory hemispheric asymmetry and to get better psychoacoustic correlates of pathological hemispheric asymmetry in ISSNHL.     

Wide-pulse-width, high-frequency neuromuscular stimulation: implications for functional electrical stimulation.

Electrical stimulation (1-ms pulses, 100 Hz) produces more torque than expected from motor axon activation (extra contractions). This experiment investigates the most effective method of delivering this stimulation for neuromuscular electrical stimulation. Surface stimulation (1-ms pulses; 20 Hz for 2 s, 100 Hz for 2 s, 20 Hz for 3 s) was delivered to triceps surae and wrist flexors (muscle stimulation) and to median and tibial nerves (nerve stimulation) at two intensities. Contractions were evaluated for amplitude, consistency, and stability. Surface electromyograph was collected to assess how H-reflexes and M-waves contribute. In the triceps surae, muscle stimulation produced the largest absolute contractions (23% maximal voluntary contraction), evoked the largest extra contractions as torque increased by 412% after the 100-Hz stimulation, and was more consistent and stable compared with tibial nerve stimulation. Absolute and extra contraction amplitude, consistency, and stability of evoked wrist flexor torques were similar between stimulation types: torques reached 11% maximal voluntary contraction, and extra contractions increased torque by 161%. Extra contractions were 10 times larger in plantar flexors compared with wrist flexors with muscle stimulation but were similar with nerve stimulation. For triceps surae, H reflexes were 3.4 times larger than M waves during nerve stimulation, yet M waves were 15 times larger than H reflexes during muscle stimulation. M waves in the wrist flexors were larger than H reflexes during nerve (8.5 times) and muscle (18.5 times) stimulation. This is an initial step toward utilizing extra contractions for neuromuscular electrical stimulation and the first to demonstrate their presence in the wrist flexors.