Effects of stimulus repetition rate on ABR threshold,amplitude and latency in neonatal and adult Mongolian gerbils

The ABR wave forms of 16-day-old and adult Mongolian gerbils were evoked by click stimuli presented at rates ranging from 1 to 80/sec. Wave I and wave IV thresholds were determined for each of 5 click rates. Amplitudes and latencies of waves I and IV were measured at each of 7 click rates and 3 intensity levels (15, 40 and 65 dB above threshold). Thresholds for waves I and IV in the adult gerbil and wave I in the 16 day gerbil were unaffected by changes in stimulus repetition rate. Neonatal wave IV thresholds were unaffected by click rate for rates below 25/sec but increased approximately 7 dB/decade increase in click rate when rate exceeded 25/sec. Increasing click rate produced greater reductions in ABR amplitude among neonates than adults for both waves I and IV. Decreases in amplitude due to increasing rate were independent of intensity level in both neonatal and adult subjects. Increasing rate produced similar increases in wave I latency among 16 day and adult subjects, but produced much greater increases in wave IV latency among neonates. Stimulus intensity level and click rate acted independently on wave I and wave IV latency in adult subjects and wave I latency in neonates. However, an interaction between rate and intensity was observed with respect to neonatal wave IV latency.     

The effect of click rate on latency and interpeak interval of the brain-stem auditory evoked potentials in children from birth to 6 years

Latency and interpeak interval of the brain-stem auditory evoked potentials at different click rates were measured in 80 healthy children from birth to 6 years, and 21 adults. Clicks were presented at 10, 30, 50, 70 and 90/sec, and 70, 40 and 20 db HL. At high stimulus intensity (70 dB SL), all latencies of waves I, III and V and the I–V, I–III and III–V intervals showed a progressive prolongation with increasing repetition rate. The latency- and the interval-rate functions were similar for all age groups but their slopes were slightly steeper in younger than in older. As click rate increased from 10/sec to 90/sec, the latencies of waves I, III and V at different age groups were prolonged by 4–10%, 9–13% and 12–15% respectively, and the intervals of I–V, I–III and III–V were prolonged by 15–16%, 8–16% and 14–24% respectively. The mean increments of wave V latency and I–V interval in different age groups were 0.404–0.575 and 0.332–0.526 msec respectively with increasing click rate from 10 to 50/sec, and 0.697–1.009 and 0.629–0.776 msec respectively with increasing click rate from 10 to 90/sec. The younger the age the larger the absolute increments for all these BAEP parameters, but the increasing rates for a BAEP measure were similar among different age groups, exhibiting no age-dependent differences. The III–V/I–III interval ration in most age groups was increased by 3–10% with increasing click rate from 10 to 90/sec, suggesting that the III–V interval was affected by stimulus rate slightly more than I–III interval.At moderate (40 dB HL) and low (20 dB SL) intensity, all waves and intervals showed similar latency- and interval-rate functions to those at high intensity. This demonstrates that the shifting latencies and interpeak intervals with increasing click rate appeared to be independent of the stimulus intensities.     

Brain-stem auditory evoked potentials in the rat: Effects of gender,stimulus characteristics and ethanol sedation

Rat BAEPs varied significantly as a function of gender and ethanol sedation as well as stimulus intensity and repetition rate. All BAEP wave latencies decreased and amplitudes increased with increasing stimulus intensity. Contrary to the prevailing view, the I–IV interpeak latency changed significantly as a function of stimulus intensity. In terms of repetition rate, all BAEP wave latencies increased and amplitudes decreased with increasing repetition rate. Male rats, compared to females, had significantly longer latencies for several BAEP components and interpeak latencies as well as smaller wave II amplitudes across a broad range of stimulus intensities. Males, compared to females, also had longer BAEP wave IV latencies and I–IV interpeak latencies at a slow stimulus repetition rate (8 clicks/sec) but shorter wave IV and I–IV latencies at a fast repetition rate (120 clicks/sec). These gender-dependent differences indicate that male and female rat BAEP data should not be combined indiscriminantly. Ethanol sedation had a statistically significant effect on the I–IV interpeak latency that was judged to be largely independent of core temperature changes. This finding suggests that while sedatives and anesthetics used to immobolize animals may have apparently minor temperature-independent effects on BAEP latencies, these effects can be statistically significant.     

Binaural interaction and the effects of stimulus intensity and repetition rate in human auditory brain-stem

Binaural interaction (BI) components in brain-stem auditory evoked potential (BAEP) and their changes with stimulus intensity and repetition rate were examined in human adult. Seven BI components were identified, which occurred between the latency range of 5 and 11 ms and coincided consistently with the latency range of BAEP waves IV–VII. Waves DV and DVII, occurring at the downslopes of BAEP-waves V and VII, respectively, were the two most prominent and reproducible BI components. Wave DVII existed consistently at high, moderate and, in most cases, low stimulus intensities, suggesting that this component is neurogenic although acoustic cross-talk may account for a part of its waveform at high stimulus intensities. The latencies of all BI components increased as a function of decreasing stimulus intensity, while the interpeak intervals, especially DV–DVII, were essentially constant at different intensity levels. The amplitudes of BI components decreased slightly with decreasing intensity. As click repetition rate increased, BI wave latencies and interpeak intervals increased slightly and amplitudes decreased slightly. When repetition rate increased to above 20/s, BI components became poorly differentiated. Lower repetition rates, e.g. 10/s, are therefore preferred for routine derivation of the BI. The changes in the latency and amplitude of BI components with stimulus intensity and repetition rate were associated or concomitant with those of the corresponding BAEP components in monaural and binaural potentials. In view of the concomitant relationship between BI and BAEP latency, we designate BI components in association with the corresponding BAEP components.     

KILLER WHALE (ORCINUS ORCA) AUDITORY EVOKED POTENTIALS TO RHYTHMIC CLICKS

Temporal auditory mechanisms were measured in killer whales ( Orcinus orca ) by recording auditory evoked potentials (AEPs) to clicks. Clicks were presented at rates from 10/sec to 1,600/sec. At low rates, clicks evoked an AEP similar to the auditory brainstem response (ABR) of other odontocetes; however, peak latencies of the main waves were 3–3.7 msec longer than in bottlenose dolphins. Fourier analysis of the ABR showed a prominent peak at 300–400 Hz and a smaller one at 800–1,200 Hz. High-rate click presentation (more than 100/sec) evoked a rate-following response (RFR). The RFR amplitude depended little on rate up to 400/sec, decreased at higher rates and became undetectable at 1,120/sec. Fourier analysis showed that RFR fundamental amplitude dependence on frequency closely resembled the ABR spectrum. The fundamental could follow clicks to around 1,000/sec, although higher harmonics of lower rates could arise at frequencies as high as 1,200 Hz. Both RFR fundamental phase dependence on frequency and the response lag after a click train indicated an RFR group delay of around 7.5 msec. This corresponds to the latency of ABR waves PIII-NIV, which indicates the RFR originates as a rhythmic, overlapping ABR sequence. The data suggest the killer whale auditory system can follow high click rates, an ability that may have been selected for as a function of high-frequency hearing and the use of rapid clicks in echolocation.     

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.     

Auditory event-related potentials dissociate early and late memory processes

Event-related potentials (ERPs) to environmental sounds were recorded from 15 young control subjects in an auditory recognition memory task. Subjects listened to a continuous string of binaurally presented sounds, 20% of which were presented once and 80% were repeated. Of the repeated sounds, some repeated immediately after the initial presentation (2 sec; short delay repetition) while others repeated after 2–6 intervening sounds (4–12 sec; long delay repetition). Subjects were instructed to indicate whether they had heard the sounds before by pressing a “yes” or “no” button.The initial stimulus presentation and long delay repetition stimuli generated both an N4 component and a prolonged latency P3 component while the short delay repetition stimuli elicited no N4 component and an earlier latency P3 component. Subjects' responses were faster and more accurate for short delay repetition. All stimuli generated a sustained frontal negative component (SFN). These data indicate that auditory recognition memory for environmental sounds may involve two processes. The P3 generated by both short and long delay repetition stimuli may index activation of a neocortical template matching system. The N4 generated by initial stimulus presentations and long delay repetition is proposed to measure additional activation of limbic memory systems at long retention intervals.     

Stochastic Properties of Discrete Waves of the Limulus Photoreceptor

In the dark-adapted photoreceptor of the horseshoe crab, Limulus, transient discrete depolarizations of the cell membrane, discrete waves, occur in total darkness and their rate of occurrence is increased by illumination. The individual latencies of the discrete waves evoked by a light stimulus often cannot be resolved because the discrete waves overlap in time. The latency of the first discrete wave that follows a stimulus can be determined with reasonable accuracy. We propose a model which allows us to make an estimate of the distribution of the latencies of the individual light-evoked discrete waves, and to predict the latency distribution of the first discrete wave that follows a stimulus of arbitrary intensity-time course from the latency distribution of the first discrete wave that follows a brief flash of light. For low intensity stimuli, the predictions agree well with the observations. We define a response as the occurrence of one or more discrete waves following a stimulus. The distribution of the peak amplitudes of responses suggests that the peak amplitude of individual discrete waves sometimes has a bimodal distribution. The latencies of the two types of discrete waves, however, follow similar distributions. The area under the voltage-time curve of responses that follow equal energy long (1.25 sec) and short (10 msec) light stimuli follows similar distributions, and this suggests that discrete waves summate linearly.     

Comparison in man of short latency averaged evoked potentials recorded in thalamic and scalp hand zones of representation

Recordings were performed in the thalamus of 13 patients suffering from either abnormal movements or intractable pain, with the aim of delimiting the region to be destroyed or stimulated in order to diminish the syndrome. In 11 of these patients averaged evoked potentials were recorded simultaneously from the scalp and specific thalamus (VP) hand area levels following median nerve stimulation. These recordings were done during the operation or afterwards when an electrode was left in place for a program of stimulation.The latencies of onsets and peaks on the scalp ‘P15’ were compared with those of the VP wave; a clear correspondence was found. Moreover, when increased stimulation was used, both waves began to develop in parallel. Thus in the contralateral ‘P15’ a component exists due to the field produced by the thalamic response. To explain the presence of an ipsilateral scalp ‘P15’ wave, we propose that a second wave having the same latency and a slightly shorter peak exists on the scalp due to a field produced by a brain-stem response. This double origin of ‘P15’ is also shown by the different changes which the ipsilateral and contralateral waves present during changes in alertness.The scalp ‘N18–N20’ is also composed of at least 2 components. The first peak appears on the scalp with a latency shorter than that of the negativity which develops in the thalamus. The N wave, moreover, increases in latency with rapid stimulus repetition. We propose with others that ‘N18’ is a cortical event reflecting the arrival of the thalamo-cortical volley. The second component, ‘N20,’ has a peak latency closely correlated to that of the thalamic negativity. This component was present alone in ‘N’ when rapid stimulation (> 4/sec) was used, which did not change the thalamic response. It must be a field produced by the thalamic negativity.     

Midlatency auditory evoked responses: Differential effects of sleep in the human

Middle latency responses (MLRs) in the 10–100 msec latency range, evoked by click stimuli, were studied in 14 adult volunteer subjects during sleep-wakefulness to determine whether such changes in state were reflected by any MLR component. Evoked potentials were collected in 500 trial averages during continuos presentation of 1/sec clicks during initial awake recordings and thereafter during a 2 h afternoon nap or all-night sleep session. Continuously recorded EEG, EOG and EMG were scored for wakefulness, stages 2–4 of slow wave sleep (SWS), and rapid eye movement (REM) sleep during each evoked potential epoch. The major components included in this study and their latency ranges, as determined by peak latency measurements from the awake records, were: ABR V, 5–8 msec, Pa, 30–40 msec, Nb, 45–55 msec, and P1, 55–80 msec. In agreement with previous reports, ABR V and Pa showed no amplitude changes from wakefulness to either SWS or REM. Not previously reported, however, was the dramatic decrease and disappearance of P1 during SWS and its reappearance during REM to an amplitude similar to that during wakefulness. This unique linkage between a particular evoked potential component and sleep-wakefulness indicates that its generator system must be functionally related to states of arousal. Relevant data from the cat model suggest that the generator substrate for P1 may be within the ascending reticular activating system.     

Inconsistency of auditory middle latency and steady-state responses in infants

Auditory middle latency and steady-state responses (MLR/SSRs) were recorded in normal infants (aged 3 weeks to 28 months) and adults. SSR amplitudes were maximum using stimulus presentation rates near 40 Hz in adults. By contrast, the infant data showed no consistent amplitude maximum across the rates tested (9–59 Hz). With the exception of the brain-stem response wave V to MLR Na deflection, MLR components in infant's responses to 10.85 Hz clicks did not show any consistent pattern. To investigate the hypothesis that the 40 Hz SSR is derived from overlapping of the 10 Hz MLR components, 43.4 Hz SSRs were synthesized from the responses recorded at 10.85 Hz and compared with those recorded at 43.4 Hz. The predictive accuracy of the synthesized 43.4 Hz SSRs was significantly better in adults than in infants. The results of these studies indicate the presence of large age-related differences in the auditory MLR and SSR, and in the relationship between the two responses.     

Vocal communication in a neotropical treefrog, Hyla ebraccata: Advertisement calls

We studied the vocal communication of Hyla ebraccata in central Panama. The advertisement call of this species consists of a pulsed buzz-like primary note which may be given alone or followed by 1–4 secondary click notes. Primary notes are highly stereotyped, showing little variation within or0 among individuals in dominant frequency, duration, pulse repetition rate or rise time. Males calling in isolation give mostly single-note calls. They respond to playbacks of conspecific calls by increasing calling rates and the proportion of multi-note calls, and by giving synchronized calls 140–200 ms after the stimulus begins. Responses to conspecific advertisement calls are usually given immediately after the primary note of the leading call, but the primary note of the response often overlaps with the click notes of the leading call. Experiments with synthetic signals showed that males synchronize to any type of sound of the appropriate frequency (3 kHz), regardless of the fine structure of the stimulus. Playbacks of synthetic calls of variable duration showed that males do not synchronize well to calls less than 150 ms long, but they do to longer calls (200–600 ms). The variance in response latency increased with increasing stimulus duration, but modal response times remained at around 140–200 ms. Similar results were obtained in experiments withsynthetic calls having a variable number of click notes. Males showed no tendency to increase the number of click notes in their calls in response to increasing stimulus duration or increasing number of clicks in the stimulus. Females preferred three-note to one-note calls in two-choice playback experiments, whether these were presented in alternation, or with the one-note call leading and the three-note call following. Females showed no preference for leader or follower calls when both were one-note. When two-note calls were presented with the primary note of the follower overlapping the click note of the leader, females went to calls in which click notes were not obscured. Our results indicate that male H. ebraccata respond to other males in a chorus in ways which enhance their ability to attract mates.     

Unmasking of cortical SEP components by changes in stimulus rate: a topographic study

We performed topographic mapping of somatosensory responses to median nerve stimulation delivered at 2, 5 and 10 Hz. Parietal N20 was significantly attenuated in 10 Hz somatosensory evoked potentials (SEPs), while central P22 diminished between 2 and 5 Hz, remaining stable thereafter. The single component most affected by increasing stimulus rate was N30, which abated by more than 50% in 10 Hz SEPs, as compared with basal responses. N30 attenuation disclosed the existence of an earlier negative component, N24, which appeared as a notch on the N30 ascending slope in 2 Hz SEPs, but became a well-defined peak at higher stimulus rates. The N24 negativity was not significantly modified by stimulus rate; it had a parietal counterpart (P24) with the same peak latency and identical behavior during the experimental procedure. Both P24 and N24 could be differentiated from central P22 on the basis of topographical distribution and response to stimulus frequency. P22 topography could be the result of a radially oriented generator, while P24/N24 appeared as the two poles of a neural source tangential to the scalp. P27 was seen in 40% of the subjects only; it is suggested that P27 is itself a composite potential to which the generator of N30 could contribute in part. We conclude that there is no single “optimal” stimulation rate for SEP recording. On the contrary, combination of different frequencies of stimulation should enhance the diagnostic utility of this technique by allowing a more selective assessment of overlapping activities.     

Detection of simple and pattern regularity violations occurs at different levels of the auditory hierarchy

Auditory deviance detection in humans is indexed by the mismatch negativity (MMN), a component of the auditory evoked potential (AEP) of the electroencephalogram (EEG) occurring at a latency of 100-250 ms after stimulus onset. However, by using classic oddball paradigms, differential responses to regularity violations of simple auditory features have been found at the level of the middle latency response (MLR) of the AEP occurring within the first 50 ms after stimulus (deviation) onset. These findings suggest the existence of fast deviance detection mechanisms for simple feature changes, but it is not clear whether deviance detection among more complex acoustic regularities could be observed at such early latencies. To test this, we examined the pre-attentive processing of rare stimulus repetitions in a sequence of tones alternating in frequency in both long and middle latency ranges. Additionally, we introduced occasional changes in the interaural time difference (ITD), so that a simple-feature regularity could be examined in the same paradigm. MMN was obtained for both repetition and ITD deviants, occurring at 150 ms and 100 ms after stimulus onset respectively. At the level of the MLR, a difference was observed between standards and ITD deviants at the Na component (20-30 ms after stimulus onset), for 800 Hz tones, but not for repetition deviants. These findings suggest that detection mechanisms for deviants to simple regularities, but not to more complex regularities, are already activated in the MLR range, supporting the view that the auditory deviance detection system is organized in a hierarchical manner.     

Effect of stimulus rate on the cortical posterior tibial nerve SEPs: a topographic study

We performed topographical mapping of somatosensory evoked potentials (SEPs) in response to posterior tibial nerve stimulation delivered at 2, 5 and 7.5 Hz in 15 healthy subjects. P37 was significantly attenuated at 5 and 7.5 Hz and the N50 component attenuated only at 5 Hz, its amplitude remaining stable for further increases in stimulus frequency. Frontal N37 and P50 potentials showed no significant decrease when the stimulus repetition frequency was changed from 2 to 7.5 Hz. P60 showed an attenuation of the amplitude only at 7.5 Hz. Latency and scalp topographies of all cortical components examined remained uncharged for the 3 stimulus rates tested The optimal stimulus rate for mapping of tibial nerve SEPs was lower than 5 Hz. The distinct recovery function of the contralateral N37-P50 and ipsilateral P37-N50 responses suggests that these potentials arise from separate generators     

Auditory brain-stem (ABP) and somatosensory evoked potentials (SEP) in an animal model of a synaptic lesion: elevated plasma barbiturate levels

Experiments were conducted to determine whether a consistent pattern of auditory nerve brain-stem evoked potential (ABP) abnormalities could be demonstrated in the presence of a synaptic lesion model in cats (elevated levels of the barbiturate thiopental). The ABP in response to low (10/sec) and high (80/sec) stimulus rates was recorded. In order to differentiate between the effects of the elevated drug levels on axonal propagation and on synaptic transmission, the early components of the somatosensory evoked potential (SEP) were also recorded, with particular attention to the first SEP wave, which is solely an axonal event without any intervening synapse. Calculations showed that the effect on synapses was 3.0–9.5 times greater than the effect of the drug on axonal propagation. As the level of barbiturates increased (representing a more severe synaptic lesion), the interpeak latencies of the ABP and the SEP became progressively prolonged, more so than the dependence of the first waves of both the ABP and the SEP on drug level. In general, amplitudes were not affected. At progressively elevated drug levels, higher stimulus repetition rates did not have an increasingly greater effect than lower rates on evoked response latencies and amplitudes so that this study also shows that the use of elevated stimulus rates does not hold much promise in the diagnosis of synaptic lesions.     

Midlatency auditory evoked responses: Differential effects of sleep in the cat

Middle latency responses (MLRs) in the 10–100 msec latency range, evoked by click stimuli, were studied in 8 adult cats during sleep-wakefulness to determine whether such changes in state were reflected by any MLR component. In particular, we wanted to determine whether the 20–22 msec positivity recorded at the vertex, ‘wave A,’ shown in previous studies to reflect a generator substrate within the ascending reticular formation, was tightly linked to changes in sleep-wakefulness, as reported for single neurons in the ascending reticular activating system. Evoked potentials were collected in 100 trial averages during continuous presentation of 1/sec clicks during initial awake recordings and thereafter during all-night sleep sessions. Continuously recorded EEG, EOG and EMG were scored for wakefulness, slow wave sleep (SWS), and rapid eye movement (REM) sleep during each evoked potential epoch. Recordings were obtained from electrodes implanted at the vertex and overlying the primary auditory cortex referenced to frontal sinus or to neck. In agreement with others, components of the auditory brain-stem response and the 12 msec primary cortical response showed no change in amplitude from wakefulness to either SWS or REM. Only wave A, among the components evaluated in the 1–100 msec range, decreased and disappeared during SWS and dramatically reappeared during REM to an amplitude equal to that during wakefulness. These data lend particular support to a functional relation between wave A and the ascending reticular activating system and suggest that this potential may provide a unique and dynamic probe of tonic brain activity. Moreover, this animal model provides a hypothetical basis for expecting a similar surface recorded potential in the human, a potential which has consequently been discovered.     

Responses of auditory brainstem neurons in the grassfrog to clicks

Single unit recordings were made in the dorsal medullary nucleus and in the torus semicircularis of the immobilized grassfrog. The natural calls have a periodic pulsatile structure. To investigate the coding of pulse repetition rate periodic click trains with varying pulse repetition rate and an ensemble of clicks distributed randomly in time were used as stimuli. In the dorsal medullary nucleus strong time-locking to clicks was found. Most units showed an activation followed by suppression response. Some units showed a preference for pulse repetition rates matching their low-frequency sensitivity. In the torus semicircularis part of the units showed responses similar to dorsal medullary nucleus units. Other response types were activation irrespective of pulse repetition rate, and suppression followed by activation. The responses to the two stimulus ensembles were more compatible in the dorsal medullary nucleus than in the torus semicircularis.     

Short latency vestibular evoked potentials (VsEPs) to linear acceleration impulses in rats

In this study, short latency (t<12.7 ms) vestibular evoked potentials (VsEPs) in response to linear acceleration impulses were recorded in 37 rats. A new technique (based on a solenoid) was used for generating linear force impulses that were delivered to the animal's head. The impulse had a maximal peak acceleration of 12 g. During the impulse, the displacement was 50 μm (at 4 g) and the rise time was 1.0 ms. A stimulation rate of 2/s was usually used. The VsEPs (averaged responses to 128 stimulations, digital filter: 300–1500 Hz) were recorded with electrodes on pinna and vertex, and were composed of 4–6 clear waves with mean amplitudes (for a 4 g stimulus) of 1–5 μV. The VsEPs were resistant to white noise masking, and were significantly suppressed (P<0.05) following bilateral application of a saturated KCl solution to the inner ear, showing that contributions of the auditory and somatosensory systems are negligible. The latency of the response decreased as a power law function of stimulus magnitude, and the amplitude of the first wave increased as a sigmoid function of stimulus magnitude. VsEP responses were still present at the lowest intensities attainable (0.06–0.4 g) and reached saturation at 9 g. The amplitude of the later components was reduced when stimulus rate was elevated to 20/s. These results suggest that VsEPs in response to linear accelerations are similar in their nature to VsEPs in response to angular acceleration impulses that were previously recorded. These VsEPs to linear accelerations are most likely initiated in the otolith organs.     

Effects of hypothermia on auditory brain-stem and somatosensory evoked responses. A model of a synaptic and axonal lesion

Auditory nerve brain-stem (ABR) and somatosensory evoked responses (SER) were recorded in cats as body temperature was uniformly lowered from 37 to 27°C. Analysis of the results showed that the alterations in the evoked responses were due to disturbances induced both in axonal propagation and synaptic transmission by the hypothermia. By studying the first wave of the SER, which is solely an axonal event, and by assuming reasonable values for the total synaptic delay and axonal propagation times along the ABR pathway, it was concluded that this lesion model induced an effect on synaptic transmission 1.3–1.7 times greater than that on axonal propagation. There was a strong inverse correlation between wave latency and body temperature, with slightly steeper slopes for the longer latency waves. Wave amplitudes were not correlated with temperature. Furthermore, the wave latencies and amplitudes were generally not dependent on stimulus rate.