Brain-stem auditory evoked potentials (BAEPs) from basal surface of temporal lobe recorded from chronic subdural electrodes

BAEPs were recorded from the basal surface of the temporal lobe by subdural electrodes chronically implanted in 6 patients who were evaluated for surgical management of intractable partial seizures. Near-field recordings were obtained by recording between the subdural electrode closet and most distant to the brain-stem. Far-field recordings were obtained by recording between the subdural electrodes and an indifferent electrode over the spinal process of the seventh cervical vertebrae. The recordings were compared with standard ear-vertex recordings.After ipsilateral ear stimulation, the subdural electrode closet to the brain-stem recorded large amplitude waves I and II, followed by less well-defined waves of longer latencies. Recordings to contralateral stimulation showed no clearly defined waves I and II and a large amplitude wave Vn. Waves III, IV, V, Vn and VI were of opposite polarity after ipsi- and contralateral stimulation. These findings indicate that waves I and II are generated ipsilaterally to the stimulation side, whereas wave Vn has a contralateral origin. Wave Vn may be generated in the brachium of the inferior colliculus, as suggested from latency and from dipole configuration studies. This conclusion is consistent with the classical anatomical observations that the supracollicular auditory pathways are predominantly crossed.     

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.     

The interaction between sex and click polarity in brain-stem auditory potentials evoked from control subjects of Oriental and Caucasian origin

Brain-stem auditory evoked potentials (BAEPs) were performed on 30 male and 30 female young normal Oriental subjects, using both condensation and rarefaction stimulation. The effects of sex and click polarity on the BAEP latencies and amplitudes were studied. Females had shorter absolute and interpeak latencies and higher absolute amplitudes than the males. These sex-related BAEP differences were independent of the click polarity. Rarefaction clicks produced shorter wave I latency and longer I–III interpeak latency, but the differences were significant in the female only. The polarity-related BAEP amplitude differences were essentially independent of the sex. BAEPs performed on 60 sex- and age-matched young Caucasian subjects produced similar results. The importance of establishing control BAEP values according to the sex and click polarity is emphasised.     

Age- and sex-related differences in brainstem auditory evoked potentials in secondary school students living in Northern European Russia

Brainstem auditory evoked potentials (BAEPs) were studied in 46 1st- to 11th-year students (22 boys and 24 girls) of a rural secondary school in Arkhangel’sk oblast. The objective of this work was to study age- and sex-related differences in BAEP characteristics in children and adolescents, living in the North and assess the BAEP characteristics as compared to reference values. In all three age groups of students, interpeak intervals I–III, III–V, and I–V characterizing the peripheral and central conduction times were shorter in girls than in boys. Interpeak interval III–V tended to increase with age only in boys (at puberty), with a significant increase in the latencies of waves I, III, and V. The BAEP characteristics in the subjects examined included a shorter peak latency and a greater amplitude of wave I (except senior students), relatively prolonged interpeak interval I–III, and more pronounced sex-related differences in BAEPs, especially at puberty. These findings show that it is necessary to revise regional reference values for BAEPs, differentiated by sex and age, including at puberty.     

Brainstem auditory evoked potentials in the fetal sheep, in utero

We studied brainstem auditory evoked potentials (BAEPs) in 8 fetal sheep in utero, ranging in gestational age from 105 to 142 days gestation (normal term 147 days). We could not elicit BAEPs prior to 117 days of gestation. After this age rapid maturation was seen, with three discernible peaks observed prior to 120 days and five peaks after 120 days. A significant (P less than 0.05) gestational age related fall in peak latencies and interpeak latencies was observed. The rate of stimulus presentation that could be tolerated without significant changes in wavepeak latency or amplitude also increased with advancing gestational age. In older fetuses (greater than 125 days), where a differentiated electrocorticogram (ECOG) was observed, differences were seen in latency and amplitude of several of the BAEP wavepeaks dependent upon the state. In high voltage ECOG states the amplitudes of wave IV and V were significantly (P less than 0.05) greater than in the low voltage ECOG state and the latencies of wave I, II and V were significantly (P less than 0.05) longer in low as compared to high voltage ECOG state. The BAEP, being obtainable over very short periods of time, appears to provide a useful indice of neural maturation for the sheep fetus in utero.     

Neurobehavioral Effects in Relation to Endocrine Alterations Caused by Exposure to Brominated Flame Retardants in Rats—Comparison to Polychlorinated Biphenyls

The widespread use of brominated flame retardants (BFRs) has led to increasing concentrations in environmental samples. Previous reports suggested endocrine activity of these compounds. Because thyroid hormones and sex steroids are known to regulate the development of the nervous system, we examined neurobehavioral and endocrine effects of gestational exposure to 2,2′4,4′,5-pentabrominated diphenyl ether (PBDE99) and lifetime exposure to tetrabromobisphenol A (TBBPA) or hexabromocyclododecane (HBCD) in rats. Treatment with PBDE99 (0, 1, or 10 mg/kg bw) reduced serum testosterone and estradiol in male offspring and affected sexual development in both sexes. Exposed males exhibited increased sweet preference, indicating feminization of this sexually dimorphic behavior. In TBBPA and HBCD experiments, a benchmark design was used with dose ranges of 0-3000 mg/kg bw/day and 0–100 mg/kg bw/day, respectively. Because thyroid hormones are critical for auditory development, brainstem auditory evoked potentials (BAEPs) were recorded in young adult offspring. TBBPA exposure elevated BAEP thresholds in females and prolonged latencies in both sexes. Benchmark doses were comparable for auditory effects and decreased plasma T4. HBCD increased BAEP thresholds and delayed BAEP waves only in males, but the relation to thyroid hormones remains to be determined. HBCD also reduced latencies in haloperidol-induced catalepsy, suggesting effects on the dopaminergic system.     

Effects of cocaine on the brain-stem auditory evoked potential in the Long-Evans rat

The present study examined the effects of an acute psychoactive dose of cocaine hydrochloride (HCl) in the rat, using the brain-stem auditory potential (BAEP) as an objective, quantitative measure of this substance's effects on brain and auditory electrophysiology. The animals were 8 adult Long-Evans rats (4 female, 4 male). BAEPs were recorded from skull screw electrodes during a baseline period as well as 30–90 min after cocaine HCl treatment (10 mg/kg, i.p.). Normothermia was maintained to control for possible temperature-related effects. Cocaine's effects on the BAEP were examined over a broad range of stimulus intensities (intensity profiles) and repetition rates (rate profiles). Cocaine prolonged latencies of several BAEP components at low stimulus intensities and shortened these latencies at high stimulus intensities. The average BAEP threshold was alos increased by cocaine treatment. These results were not strong, but were suggestive of a recruitment type change in auditory function. Cocaine treatment had no convincing effects on the BAEP as a function of stimulus repetition rate.     

Sex and ear differences of brain-stem acoustic evoked potentials in a sample of normal full-term newborns. Normative study

The present paper reports a normative study of the BAEPs recorded from 80 normal full-term newborns by using a rarefaction click at 70, 60, 40, 20 dB HL.Positive, negative peaks and the relative amplitudes were measured. Means, standard deviations and 95% and 99% confidence limits were calculated for each component, for positive and negative IPLs and amplitude ratios. A normality test distribution showed that each component had normal distribution except for wave PIII at 70 dB and at 60 dB HL beacause of its index of kurtosis and for IPLs PII-PIII and NII-NIII at 70 and 60 dB HL. MLRA was performed and significant statistical differences were found for sex, ears and intensities. Females had the latencies of waves PIII, PIV, PV, NII and NIV shorter than males. The BAEPs obtained from the left ear had shorter latencies for positive and negative peaks. Latencies, amplitude and morphology of the BAEPs vary with variations of the intensity. The IPLs PII-PV, PIII-PV and PIV-PV were not affected by changes of intensity.     

豚鼠耳蜗电图慢成分的研究

选用0.8-150Hz的带通滤波,从豚鼠圆窗记录出一负一正相慢电位.实验结果表明.其对0.5kHz短音的反应阈为729dB nHL.较耳蜗电图快成分低38.27dB nHL.通过离断听觉传导径路不同水平对该电位的观察,表明它是毛细胞及听神经电反应的慢成分.而且可能受听觉传出神经的调控.     

Effect of proprioceptive and visual stimulation on brain stem auditory evoked potentials in the cat and in man

Proprioceptive effect on the activity of different levels of the auditory system was studied in cats under Nembutal anaesthesia and in humans, by means of recording brain stem auditory evoked potentials - BAEPs (in response to cliks), whose consecutive waves correspond to successive levels of the auditory system. BAEPs were compared when the head was in a straight position and when it was turned 45 degrees to one side. The turns elicited changes in amplitudes and latencies of all BAEP waves similarly in cats and humans but in different combinations and in different directions, which points to plurality and heterogeneity of proprioceptive effects at different auditory levels. Analogous effect on BAEPs was produced by photic stimulation - illumination of one eye in cats and of the experimental chamber in humans. The character of the effects suggests participation of the activity of descending auditory paths and the cerebellum.     

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.     

Brain-stem evoked potentials and noise effects in seagulls

Brain-stem auditory evoked potentials (BAEP) recorded from the seagull were large-amplitude, short-latency, vertex-positive deflections which originate in the eighth nerve and several brain-stem nuclei. BAEP waveforms were similar in latency and configurations to that reported for certain other lower vertebrates and some mammals. BAEP recorded at several pure tone frequencies throughout the seagull's auditory spectrum showed an area of heightened auditory sensitivity between 1 and 3 kHz. This range was also found to be the primary bandwidth of the vocalization output of young seagulls. Masking by white noise and pure tones had remarkable effects on several parameters of the BAEP. In general, the tone- and click-induced BAEP were either reduced or obliterated by both pure tone and white noise maskers of specific signal to noise ratios and high intensity levels. The masking effects observed in this study may be related to the manner in which seagulls respond to intense environmental noise. One possible conclusion is that intense environmental noise, such as aircraft engine noise, may severely alter the seagull's localization apparatus and induce sonogenic stress, both of which could cause collisions with low-flying aircraft.     

Evoked cochlear potentials in the barn owl

Gross electrical responses to tone bursts were measured in adult barn owls, using a single-ended wire electrode placed onto the round window. Cochlear microphonic (CM) and compound action potential (CAP) responses were evaluated separately. Both potentials were physiologically vulnerable. Selective abolishment of neural responses at high frequencies confirmed that the CAP was of neural origin, while the CM remained unaffected. CAP latencies decreased with increasing stimulus frequency and CAP amplitudes were correlated with known variations in afferent fibre numbers from the different papillar regions. This suggests a local origin of the CAP along the tonotopic gradient within the basilar papilla. The audiograms derived from CAP and CM threshold responses both showed a broad frequency region of optimal sensitivity, very similar to behavioural and single-unit data, but shifted upward in absolute sensitivity. CAP thresholds rose above 8 kHz, while CM responses showed unchanged sensitivity up to 10 kHz.     

Temperature-dependent hysteresis in somatosensory and auditory evoked potentials

Fourteen adult patients undergoing open heart surgery under induced hypothermia had median nerve, short-latency somatosensory evoked potentials (SSEPs) recorded during cooling (from 36°C to 19°C) and subsequent rewarming. Similar data on another group of patients who had brain-stem auditory evoked potentials (BAEPs) were also analyzed. Hypothermia produced increased latencies of the major SSEP and BAEP components and the latencies returned to normal with subsequent warming. The temperature-latency relationship during the cooling phase was significantly different from that during the warming phase. For SSEP components the temperature-latency relationship was linear during cooling and curvilinear during warming, whereas for BAEP it was curvilinear both during cooling and warming. Furthermore, the regression curves were different during the two phases of temperature manipulation, particularly for temperatures below 30°C both for SSEP and BAEP components. At the onset of warming there was an initial exaggerated warming response on the evoked potential (EP) latencies and amplitude of the EP components. The temperature-latency regression curves were uniformly less steep during the warming phase compared to those during cooling. These findings suggest the existence of hysteresis in the relationship between temperature and EP latencies. The latencies at a given temperature below 30°C depend on whether that temperature is reached during cooling or during warming.     

The human fetal auditory evoked potential

The brain-stem auditory evoked potential (BAEP), a sensitive test of the functional status of the neonatal brain, has not been studied in utero since no practical technique for human fetal recording is available. We have developed a simple recording technique which allows continuous monitoring of the fetal AEP during labor. Waves I, III and V of the fetal brain-stem AEP have been consistently identified. Wave form morphology, interpeak latencies, and latency-intensity relations are similar to postnatal recordings. Middle latency potentials have also been recorded, with wave forms that correspond to the neonatal middle latency AEP.     

Spinal tracts producing slow components of spinal cord potentials evoked by descending volleys in man

Slow negative (N) and slow positive (P) waves are frequently produced in the posterior epidural space at the lumbosacral enlargement by epidural stimulation of the rostral part of human spinal cord. The production of these slow potentials are thought to be responsible for analgesia at the stimulated segment as well as below that level. In order to define the spinal tract which mediates these slow potentials, we stimulated directly or from the epidural space the dorsal, dorsolateral, lateral and ventral columns at the cervical or thoracic level, and epidurally recorded spinal cord potentials (des.SCPs) at the lumbosacral enlargement in 7 patients who underwent spine or spinal cord surgery. The des.SCPs recorded in the lumbosacral enlargement consisted of polyphasic spike potentials followed by slow N and P waves. At a near threshold level of stimulus intensity the slow N and P potentials were consistently elicited only by stimulation of the dorsal column. The slow waves were also produced by intense stimulation of other tracts, but remained significantly (P < 0.05−P <0.01) smaller than those evoked by dorsal column stimulation when compared at the same stimulus intensity. Moreover, the slow P wave could not be elicited even by intense stimulation (10 times the threshold strength for the initial spike potentials) of the ventral column. Thus, the results suggest that the slow N and P waves are mostly mediated by the antidromic impulses descending through the dorsal column.     

Neuromagnetic responses elicited by auditory stimuli in dichotic listening

We measured N1m and P2m components of the magnetic field responses that were elicited by random series of a tone burst given to the left ear and a monosyllabic speech sound given to the right ear. The magnetic responses had smaller amplitudes and/or longer peak latencies of the N1m and the P2m when the stimulus was preceded by a stimulus at the same ear than when preceded by a stimulus at the different ear. This reduction of the response by preceding stimulation of the same ear was significant over the hemisphere contralateral, but not ipsilateral, to the ear stimulated. The peak latencies of N1m and P2m were significantly longer in the response over the hemisphere contralateral than ipsilateral to the stimulated ear.     

Reappearance of brain-stem auditory evoked potentials after surgical treatment of a brain-stem hemorrhage: contributions to the question of wave generation

We report on a patient suffering a spontaneous hemorrhage primarily located in the right brain-stem; surgical correction of this led to a substantial improvement in clinical deficits. Brain-stem auditory evoked potentials (BAEPs) were recorded on postoperative days 18, 30, 55 and 205. Waves II through V were initially undetectable on stimulation of the damaged side, whereas the absence of peak V was the only abnormality seen on left-side stimulation. With the regression of the right lower mid-pontine deficits, the right waves gradually reappeared and normalized progressively. On the last recording, only a left wave V abnormality persisted. At that time, the patient had a moderate left hemisyndrome due to a circumscribed right upper pontine-midbrain lesion. Therefore, it can be suggested that the first 4 waves of BAEPs mainly originate in the ipsilateral pons, and the Vth in the contralateral higher regions.     

Development of brainstem auditory pathway in mallard duck embryos and hatchlings

Summary The development of the brainstem auditory evoked potential (BAEP) was studied in mallard duck (Anas platyrhynchos) embryos and hatchlings from 5–6 days before hatching through two days after hatching in response to tone pips of different frequencies. BAEPs showed a different time of onset and a different rate of development for low, middle, and high frequencies. Although auditory sensitivity in the mid-frequency range (1.0, 1.5, 2.0, and 3.0 kHz) appeared 1–2 days later than in the low-frequency range, development of the BAEPs in the mid-frequency range was almost complete by hatching. In contrast, the development of auditory sensitivity in the low- and high-frequency ranges continued to develop after hatching. Accelerated development of BAEPs to middle frequencies during the embryonic period and to high frequencies after hatching was correlated with the ducklings' exposure to their own mid-frequency and high-frequency vocalizations before and after hatching, respectively.Abbreviations BAEP brainstem auditory evoked potential - CM cochlear microphonic - CT contact-contentment call - DT distress call - EP evoked potential     

Correlation between a unilateral midbrain-pontine lesion and abnormalities of brain-stem auditory evoked potential

Brain-stem auditory evoked potentials (BAEPs) were evaluated over a 39 day period in a patient with a unilateral pontine-midbrain lesion verified by CAT scan and autopsy. Waves I, II and III were present on the side of lesion, whereas all 5 waves were present on the side opposite the lesion. The findings suggest that the BAEPs may be obtained with only an intact ipsilateral auditory pathway. Crossing fibers in the trapezoid body also appear to make contributions to the normal generation of wave V.