The modulation of somatosensory evoked potentials during the foreperiod of a forewarned reaction time task

During the foreperiod of a forewarned reaction time (RT) task reflexes in the executing limb increase to a lesser extent than those in the contralateral limb. This is possibly due to input modulation. The present study investigates the possibility of cutaneous sensory modulation during motor preparation by studying the amplitudes of somatosensory evoked potentials (SEPs). Eighteen subjects performed a forewarned RT task with the same fingers as the ones which were electrically stimulated. SEPs evoked during the 4 sec preparatory period were compared to those evoked during movement execution and during the resting period after the motor response respectively. During response execution most SEP components showed smaller amplitudes, i.e., they were gated, which agrees with other studies. In the first part of the foreperiod no SEP modulation was observed. Towards the end of the foreperiod, 500 msec before the response stimulus (RS), the amplitude of the contralateral parietal N70-P100 was significantly decreased, while the P45-N70 showed a similar tendency. However, at the same time the P100-N140 was increased in amplitude. The decrease of the intermediate latency components towards the end of the foreperiod is discussed in terms of gating, while the increase in the long latency component is discussed with respect to a decrease in RT on trials where the fingers were stimulated just before the RS, pointing to the role of attentional mechanisms.     

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.     

Methods for determining auditory evoked brain-stem response thresholds in human newborns

Previous investigators have reported that newborn auditory evoked brain-stem responses (ABRs) are 20–30 dB higher than adult psychophysical thresholds to the same stimuli. These investigators reduced the intensity of the stimulus until they no longer reported an ABR to the stimulus. We adapted 2 widely used psychophysical methods, the up-down-transformed response (UDTR) method and the method of constant stimuli, for ABR threshold determination of human newborns. Response judgments were made blindly. ABR thresholds of healthy normal newborns by both procedures were no more than 10–15 dB higher than adult psychophysical thresholds. The differences between the newborn ABR thresholds we reported and those in the literature were probably explained by different procedures including the method used to estimate adult psychophysical thresholds. The correlations between ABR thresholds and suprathreshold ABR latencies and amplitudes and latency and amplitude/intensity functions were modest at best. In normal newborns suprathreshold ABR measurements are of little value in predicting ABR thresholds.     

Pain-related and cognitive components of somatosensory evoked potentials following CO2 laser stimulation in man

We recorded cortical potentials evoked by painful CO₂ laser stimulation (pain SEP), employing an oddball paradigm in an effort to demonstrate event-related potentials (ERP) associated with pain. In 12 healthy subjects, frequent (standard) pain stimuli (probability 0.8) were delivered to one side of the dorsum of the left hand while rare (target) pain stimuli (probability 0.2) were delivered to the other side of the same hand. Subjects were instructed to perform either a mental count or button press in response to the target stimuli. Two early components (N2 and P2) of the pain SEP demonstrated a Cz maximal distribution, and showed no difference in latency, amplitude or scalp topography between the oddball conditions or between response tasks. In addition, another positive component (P3) following the P2 was recorded maximally at Pz only in response to the target stimuli with a peak latency of 593 msec for the count task and 560 msec for the button press task. Its scalp topography was the same as that for electric and auditory P3. The longer latency of pain P3 can be explained not only by its slower impulse conduction but also by the effects of task difficulty in the oddball paradigm employing the pain stimulus compared with electric and auditory stimulus paradigms. It is concluded that the P3 for the pain modality is mainly related to a cognitive process and corresponds to the P3 of electric and auditory evoked responses, whereas both N2 and P2 are mainly pain-related components.     

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.     

Findings of somatosensory evoked potential to stimulation of the sciatic nerve in two different rat strains.

No comparative study about somatosensory evoked potentials (SEP) on different rat strains has been done yet. It is evident that comparative SEP studies are important since different rat strains have different physiological properties. We aimed to compare early latency SEP values from stimulation of sciatic nerve in Wistar (Wr) and Sprague-Dawley (SDr) rats which are frequently used rat strains in experimental studies. In Wr group, the mean of first far field potential (Ff1) latency was shorter and the mean Ff1 amplitude was lower than that of Sprague-Dawley rat group. Mean cortical potential latency in Wr group was longer than that of SDr group while amplitude was not different. Central conduction time (CCT) in Wistar rat group was found to be longer than that of SDr group. Shorter Ff1 latency in Wr group implies that afferent volley reaches cervical posterior fasciculus from sciatic nerve earlier than SDr group while longer CP latency implies that afferent volley reaches cortex later than SDr group. Similarity between the latencies of lumbar potentials implies that peripheral conduction velocity has no effect on the difference of Ff1 latencies.     

Behavioral evidence of a latency code for stimulus intensity in mormyrid electric fish

Mormryid electric fish (Gnathonemus petersii) respond to novel stimuli with an increase in the rate of the electric organ discharge (EOD). These novelty responses were used to measure the fish's ability to detect small changes in the amplitude and latency of an electrosensory stimulus. Responses were evoked in curarized fish in which the EOD was blocked but in which the EOD motor command continued to be emitted. An artificial EOD was provided to the fish at latencies of 2.4 to 14.4 ms following the EOD motor command.Novelty responses were evoked in response to transient changes in artificial EOD amplitude as small as 1% of baseline amplitude, and in latency as small as 0.1 ms. Changes in latency were effective only at baseline delays of less than 12.4 ms.The sensitivity to small changes in latency supports the hypothesis that latency is used as a code for stimulus intensity in the active electrolocation system of mormyrid fish. The results also indicate that a corollary discharge signal associated with the EOD motor command is used to measure latency.Abbreviations EOD electric organ discharge - ELL electrosensory lateral line lobe - epsp excitatory post synaptic potential     

Auditory brain stem responses in characterization of dolphin hearing

Summary Auditory brain stem responses (ABR) were recorded from the head surface of non-anesthetized and non-relaxed bottle-nosed dolphins, Tursiops truncatus. The region of best ABR recording was shown to be located 6–9 cm caudal to the blowhole. The threshold values were about 1 mPa for noise bursts and –3 dB re 1 mPa for tone bursts of the optimal frequency (80 kHz). The maximum frequency at which ABR could be evoked was 140 kHz. The duration of temporal summation reached 0.5 ms at intensities near the threshold and decreased with an increase in intensity. When the stimuli were paired clicks of the same intensity, the time to complete recovery from the second response was about 5 ms, while that to its 50% recovery was 0.7 ms. When the conditioning click exceeded the testing one in intensity, prolongation of the recovery period was observed. A 40-dB intensity difference led to an approximately 10-fold prolongation of this period.Abbreviations ABR auditory brain stem response - EP evoked potential     

Brain-stem,middle latency and late cortical evoked potentials in children with speech and language disorders

The topography of the brain-stem (ABR), middle latency (MLR) and cortical (ACR) evoked responses was investigated in chilfren with nornal speech and language development and those with either a language or motor speech disorder. The aim was to determine whether it is possible to discriminate between the groups of children in terms of the evoked potential characteristics.There were significant inter-group differences, particularly relating to the amplitude of the different responses. The ABR in both the language and motor speech groups exhibited smaller amplitudes for waves I, III and V than the control group, with no change in latency. Two explanations were suggested; firstly abnormal functioning of the peripheral hearing mechanism even though the hearing thresholds were normal which could be a secondary effect due to deprivation normal speech recording effects due to differences in the electrical conductivity of tissue and the distance separating the generator site and recording electrodes. The MLR in the motor speech group was significantly larger at the mastoid and temporal electrode sites than either the control or language groups. This was considered to be an enhanced myogenic response like the other exaggerated brain-stem reflexes seen in congenital suprabulbar paresis. Significantly larger amplitudes of the ACR were also recorded from the motor speech group at the Cz electrode site. This was thought to be due to underactivity of some normal cortical inhibitory system and not a direct result of increased MLR amplitude.The ACR in the language disordered children exhibited an abnormal left temporal hemispheric dominance and a more inverted or ‘dissimilar’ wave from at the T3 electrode site on the correlation analysis. These findings suggest impaired functioning of the left temporal cortex in our children who have failed to develop language normally. We feel that this has more significance for the language abnormality than the low amplitude ABRs which were observed in both the language and motor speech disordered children.     

Bioelectrical activity of the central nervous system among populations in a rare earth element area

Auditory brainstem electric response (ABR) and somatosensory evoked potential (SEP) of 21 subjects (41 ears) among villagers in a rare earth element (REE) area in Gan County, Jiangxi, China, were studied. No difference in ABR between the subjects from the REE area and the control group was noted. However, the conduction detected by SEP from the median nerve to the thalamus (P ₁₅) was shortened (P<0.05), especially to the first-grade primary somatosensory responsive region (S ₁) (P<0.01) and the amplitude of S₁ decreased (P<0.05), indicating that REE was difficult to accumulate in the brainstem, but it was susceptible to cerebral cortex, thus causing subclinical damage. This condition was confirmed in the animal experiment. It was suggested that the toxicity through long-term intake of small doses of REE might not be negligible, and the hazard of REE environments should be investigated.     

Somatosensory evoked potentials during natural and learned patterns of postural adjustment, accompanying limb movements in dogs]

A goal of the study was to investigate cortical reorganization corresponding to inhibition of innate motor patterns during motor learning. Functional changes in the sensorimotor cortex during learned rearrangement of the natural diagonal pattern of postural adjustment (PA) accompanying a hindlimb movement into a new one, the so-called unilateral pattern, were studied in dogs by testing somatosensory evoked potentials (SEP) in response to stimulation of a forelimb during PA immediately before the limb movement onset. During PA the latency and the amplitude of several SEP components decreased. In general, changes in SEP were less pronounced in the learned unilateral pattern of postural adjustment in comparison with the innate diagonal pattern, but the difference was significant only for some SEP components. The SEP late positivity in the learned postural pattern was replaced by a negativity. The SEP changes were similar independently of whether the test stimulus was applied on the forelimb loaded or unloaded during postural adjustment. The data suggest that changes in interrelations between different neuronal populations in the sensorimotor cortex during formation and realization of a learned motor program can be reflected in SEP changes.     

Evoked potential findings in Behçet's disease. Brain-stem auditory,visual, and somatosensory evoked potentials in 44 patients

We studied 54 patients with Behçet's disease, 41 males and 13 females, mean age 28 years. Forty-four patients had auditory brain-stem evoked potential (BAEP) recordings, 39 had pattern reversal visual evoked potentials (VEP), 27 had median nerve somatosensory evoked potential (SEP) recordings, and 25 tibial nerve SEPs. BAEPs were abnormal in 16 patients (52%) with neurological manifestations and in 4 (31%) without, because of decreased amplitude of wave V, prolonged I–III or III–V interpeak latencies, or uncertain/absent waves III and/or V. Eleven patients (40%) with neurological symptoms and 3 patients (25%) without, had abnormal VEPs. Absent potentials, decreased amplitude, with or without prolonged P100 latency, were found in 75% of the cases, the rest had prolonged P100 latency only. Median SEPs were abnormal in 8 patients (38%) with neurological manifestations. Four patients (21%) had abnormal tibial SEPs. Decreased amplitude with or without mild slowing in central conduction was the predominant SEP abnormality. SEPs were normal in all patients without neurological symptoms. In total, 84% of patients with, and 38% of patients without, neurological symptoms had abnormalities of one or more EP modality.When used cautiously, EP studies in Behçet's disease might be helpful to separate neuro-Behçet from other disorders with similar symptomatology, to disclose subclinical CNS involvement, to evaluate and monitor CNS disease activity, and to provide objective measures of treatment response.     

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.     

Changes in the somatosensory evoked potentials in the night sleep of healthy subjects under conditions of preceding emotional stress

Somatosensory evoked potentials (SEP) were studied in eight healthy subjects in a state of alertness, in different stages of night sleep and also in night sleep after previous emotional stress. Characteristic changes of SEP were revealed in the second stage of sleep in delta-sleep and in the phase of rapid sleep. In conditions of emotional stress changes in SEP characteristics in periods of alertness and of night sleep were observed, expressed in the amplitude increase of a number of components. Asymmetry was revealed with predominance of the amplitude increase in the right hemisphere in the phase of the rapid sleep testifying to different roles of the cerebral hemispheres in processing of emotionally significant information. SEP changes in different functional states after the influence of emotional stress were considered as the reflection of non-specific activation increase possibly due to activation of the limbic structures in response to stress-producing stimulus.     

Distribution of lumbar spinal evoked potentials and their correlation with stimulation-induced paresthesiae

In 7 awake patients with neuropathic lower extremity pain, spinal somatosensory evoked potentials (SEP) were elicited from the non-painful leg by electrical stimulation of the peroneal nerve and mechanical stimulation of the hallux ball. Recording was made epidurally in the thoraco-lumbar region by means of an electrode temporarily inserted for trial of pain-suppressing stimulation.In response to peroneal nerve stimulation, two major SEP complexes were found. The first complex consisted, as has been described earlier, of an initial positivity (P12), a spike-like negativity (N14), a slow negativity (N16) and a slow positivity (P23). The second complex consisted of a slow biphasic wave, conceivably mediated by a supraspinal loop. Both complexes had a similar longitudinal distribution with amplitude maxima at the T12 vertebral body.The SEP evoked by mechanical hallux ball stimulation had a relatively small amplitude, and there was no significant second complex. The relationship between stimulus intensity and SEP amplitude was negatively accelerating.The longitudinal distribution of spinal SEP was compated with the somatotopic distribution of paresthesiae induced by stimulation through the epidural electrode. It was found that stimulation applied at the level of maximal SEP generally induced paresthesiae in the corresponding peripheral region. Therefore, spinal SEP may be used as a guide for optimal positioning of a spinal electrode for therapeutic stimulation when implanted under general anesthesia.An attempt was made to record the antidromic potential in the peroneal nerve elicited from the dorsal columns by epidural stimulation. The antidromic response was, however, very sensitive to minimal changes of stimulus strength and body position of the patient, and was also contaminated by simultaneously evoked muscular reflex potentials.Thus, peripheral responses evoked by epidural stimulation appeared too unreliable to be useful for the permanent implantation of a spinal electrode for therapeutic stimulation.     

Effect of seduksen (diazepam) on cortical P300 potentials evoked by neutral and emotional words

The influence of seduxen (diazepam) on cortical potentials P300 evoked by neutral and emotional words was studied in adult subjects having life conflicts. The therapeutic dose of seduxen (10 mg) had no significant effect on the amplitude of the late positive cortical response P300 to neutral words. Seduxen depresses the emotional activation of the cerebral cortex; that is manifested in selective elimination of those changes in latency and amplitude of P300 wave which are observed in response to emotionally significant words. Under the action of seduxen, the interhemispheric difference in the latency of cortical response disappears due to latency increase in the right hemisphere.     

Auditory brainstem responses in Cope’s gray treefrog (Hyla chrysoscelis): effects of frequency,level, sex and size

Our knowledge of the hearing abilities of frogs and toads is largely defined by work with a few well-studied species. One way to further advance comparative work on anuran hearing would be greater use of minimally invasive electrophysiological measures, such as the auditory brainstem response (ABR). This study used the ABR evoked by tones and clicks to investigate hearing in Cope’s gray treefrog (Hyla chrysoscelis). The objectives were to characterize the effects of sound frequency, sound pressure level, and subject sex and body size on ABRs. The ABR in gray treefrogs bore striking resemblance to ABRs measured in other animals. As stimulus level increased, ABR amplitude increased and latency decreased, and for responses to tones, these effects depended on stimulus frequency. Frequency-dependent differences in ABRs were correlated with expected differences in the tuning of two sensory end organs in the anuran inner ear (the amphibian and basilar papillae). The ABR audiogram indicated two frequency regions of increased sensitivity corresponding to the expected tuning of the two papillae. Overall, there was no effect of subject size and only small effects related to subject sex. Together, these results indicate the ABR is an effective method to study audition in anurans.     

脑干缺血对听觉脑干反应影响的实验研究

目的 :探讨脑干缺血模型ABR变化特点及其在脑缺血早期诊断中的应用价值。方法 :阻断猫基底动脉不同部位血流 ,观察记录阻断血流后不同时间ABR变化特点及其规律。结果 :①夹闭基底动脉上、下段或小脑下前动脉 10min左右 ,ABRP3 ,P4振幅明显减小 (P <0 .0 1,P <0 .0 5 ) ,60min恢复夹前水平 ;②夹闭基底动脉上段 10～60minP5明显减小 (P <0 .0 5 ) ,直到 12 0min尚未恢复至夹前状态。结论 :①猫的ABRP3脑区的血供主要来自小脑下前动脉 ,P1,P2产生部位基本不依赖基底动脉供血 ;②轻度暂短性脑缺血时ABR振幅比潜伏期更敏感 ,振幅减小的程度与脑干缺血的程度密切相关 ;③ABR可用于脑缺血定位诊断及脑功能动态观察的电生理检测。     

对侧外周神经移位到损伤手臂引起的体感皮层功能动态重组

单侧肢体的外周神经损伤通常导致对侧体感皮层的功能重组. 然而,接受了对侧颈 7 (C7) 外周神经移位手术治疗单侧手臂臂丛全撕脱的病人,在术后早期当其患手被触摸时,只在其健手产生感觉. 在术后晚期,病人才逐渐恢复其患手和健手的正常、独立的功能. 我们在模拟对侧颈 7 (C7) 外周神经移位手术病例的大鼠模型上,用记录体感诱发电位的方法研究了患手和健手的体感代表区. 患手的体感和运动功能由于 C7 神经的再生而逐渐恢复. 术后第 5 个月始, 13 只大鼠患手的体感代表区只出现在其同侧的皮层,同时患手和健手的代表区在该皮层内是高度重叠的 (除掉一个例外),虽然刺激它们产生的体感诱发电位的潜伏期和反应幅度有很大的不同. 结果表明,移位到患手的对侧外周神经能够导致同侧体感皮层动态的功能重组,提示身体另侧感觉输入的介入激发了大脑显著的可塑性.     

Auditory evoked responses in tropical men during sojourn over the arctic region

The influence of an arctic environment on auditory evoked responses, both brainstem and cognitive, were evaluated in 10 Indian soldiers. They were first tested in Delhi and then flown to an arctic region where they were tested in the first week and again in the eighth week of their stay. Two migrants from Moscow, their usual place of residence, and six natives, born and brought up in the arctic, were also tested for comparison. The Indians, on their return to India, were tested again. The auditory evoked responses were recorded using the Nicolet (USA) Compact 4 Instrument. The Indians showed a delay in all the waves of the auditory brainstem response (ABR) during their induction in the arctic and these persisted even on their return to India whereas the migrants and the natives had relatively higher ABR latency values.