Middle Latency Components Research Articles

Habituation of the early and middle latency components of the auditory evoked potentials in freely moving cat

Habituation of the early and middle latency components of the auditory evoked potentials in freely moving cat

Auditory short, middle, and long latency responses in acutely comatose patients.

For assessing comatose patients, the combination of auditory short, middle, and long latency evoked potentials (auditory brain stem response [ABR], middle latency component [MLC], and slow vertex response [SVR] ) is more comprehensive than auditory brain stem response (ABR) only or ABR with slow vertex response (SVR). Fifty-four acutely comatose patients were studied. Thirty-four of the patients had severe head injury and others had coma of varied etiology. Within two months after admission, 25 patients survived, while 29 patients died. Auditory evoked response measurements were conducted usually within 48 to 72 hours after admission. For patients with normal SVR, MLC, and ABR, there was 100% survival; with absent SVR but normal MLC and ABR, survival was 91%; with absent SVR and MLC and normal ABR, it was 60%; with abnormal ABR, it was 10%; no patient survived whose ABR was absent. It is emphasized that a normal MLC is clearly a predictor of survival of comatose patients, but a normal ABR is not always a reliable indicator of survival.

Auditory evoked potentials (early, middle, late components) and audiological tests in Friedreich's ataxia

A functional assessment of the acoustic pathways in a group of 9 patients with Friedreich's ataxia was performed. In none of them was symptomatic auditory impairment noticeable. All patients were submitted to audiological tests and AEP recording. AEPs included early (BAEPs), middle (MLCs) and long (LLCs) latency components. The absence of one or more BAEP waves was observed in 5 out of 9 patients. N85 latency was significantly increased in all but one patient. MLCs, particularly P12, N15, P25 were often normal in amplitude and latency, scarcely showing a positive relationship with abnormalities of preceding and following waves. Pure tone audiometry revealed cochlear or neural impairment only in 2 patients. Speech audiometry showed deficits in all patients. These investigations, taken as a whole, showed a prevalent involvement of the brain-stem acoustic pathways, presumably at different levels, seldom associated with eighth nerve impairment. In some cases LLC ( N85 ) abnormalities could not be interpreted as a consequence of impaired function in peripheral and brain-stem acoustic sites and might suggest a cortical dysfunction. Major BAEP abnormalities were observed in patients with longer disease duration, while N85 changes were unrelated to the duration and the severity of the illness. The former may prove to be a reliable means of monitoring the progression of the disease, the latter could be employed as a complementary procedure in its early diagnosis.

Simultaneous recording of auditory evoked potentials. Relationships among the fast, middle and long latency components.

The whole pattern of the fast, middle and long latency auditory evoked potentials (AEP) was recorded simultaneously from the scalp surface of 13 normal-hearing adults. The individual responses were displayed on a nonlinear time axis in order to improve identification of the components. Stimulation consisted of 2048 unfiltered clicks, delivered monaurally at 80, 60, 40 dB HL with an ISI of 750 ms. Changes in mean latency and amplitude of each AEP component were statistically evaluated in relation to intensity and electrode montage (vertex-mastoid ipsi- and contralateral to the stimulated ear). The latencies of fast components I-VI and the slow P1 increase significantly with declining stimulus intensity. The amplitudes of the fast, I, II, III, V and the slow P1-N1, P2-N2 decrease significantly with intensity. As regards differences due to the electrode montage the contralateral recording causes significant changes in latency of the fast potentials up to wave IV, and changes in amplitude of the fast up to wave V, and of the slow P1-N1 and P2-N2. Therefore, as their latency and amplitude seem to be less closely related to the stimulus and electrode placement, the middle components behave differently, compared with the preceding and following components. Based on parametric comparisons of potentials ranging widely in latency, but each one evoked by an equal sensory input, this kind of AEP evaluation may be useful both for neurophysiological and clinical studies of the whole auditory pathway function.

Simultaneous Recording of Auditory Evoked PotentialsRelationships among the Fast, Middle and Long Latency Components

Simultaneous Recording of Auditory Evoked Potentials<i>Relationships among the Fast, Middle and Long Latency Components</i>

Frequency specificity of simultaneously recorded early and middle latency auditory evoked potentials

Early and middle latency auditory evoked potentials were recorded simultaneously with a 2-channel wide-band recording technique. Latency and amplitude distributions of components V, N a and P a were determined in 20 normal hearing adults for 3 different stimuli (click, plop, 500 Hz tone burst) presented at 70, 30 and 20 dB HL. Normative latency data of the middle latency components are presented. The detectability and amplitude of the N a-P a complex were considerably larger than those of wave V at 20 and 30 dB HL for the two low frequency stimuli. Ten ears exhibiting high frequency sensorineural hearing loss were examined. In these cases, only click-evoked N a and P a, but not wave V, were observed down to 20 dB HL. Also, the click latency-intensity function of N a-P a was found to be similar to the normal low frequency latency functions. The results consistently suggested that the low frequency contributions to wave V cancel in phase because of short duration, whereas the duration of the N a-P a complex allows for a positive superimposition of all frequency bands. Since these differences in frequency specificity of the EAEP and the MAEP affect latency, care is advised for the interpretation of inter-peak latencies.

Effects of therapeutic pentobarbital coma on multimodality evoked potentials recorded from severely head-injured patients

We sought to determine whether pentobarbital (PB) coma compromises the use of evoked potentials (EPs) in the assessment of brain dysfunction and of the prognosis of severely head-injured patients. Therefore, the effects of therapeutic PB on somatosensory (SEPs, BSEPs), visual (VEPs), and auditory (BAEPs) evoked potentials recorded from 20 patients early after injury were analyzed. Seventeen head-injured patients served as controls. EP studies were obtained shortly after admission (Mean Day 2, PB present) and approximately 2 weeks after injury (Mean Day 15, PB absent). The mean serum level of PB in the treatment group was 1.9 mg/100 ml. The drug effect was assessed by comparisons between the PB and the control groups. Statistical analyses were based on differences observed between two studies in the same patient. Analyses of covariance (F tests) were performed on data from all modalities. Wave form complexity was minimally affected by the drug. Middle and long latency components of the SEP were depressed by PB, and latencies of BSEP peaks and the early components of the SEP were delayed. The amplitude of some VEP peaks was reduced by PB. The BAEP was not significantly altered. All of the observed effects of PB were determined to be due to the hypothermia exhibited by PB-treated patients (mean temperature, 36.1ºC), which was not seen in the control group (mean, 37.8ºC). It is concluded that, with appropriate interpretation, EPs can be used to monitor brain function in head-injured patients when PB therapy is used. (Neurosurgery 12:613-619, 1983)

Effects of therapeutic pentobarbital coma on multimodality evoked potentials recorded from severely head-injured patients.

We sought to determine whether pentobarbital (PB) coma compromises the use of evoked potentials (EPs) in the assessment of brain dysfunction and of the prognosis of severely head-injured patients. Therefore, the effects of therapeutic PB on somatosensory (SEPs, BSEPs), visual (VEPs), and auditory (BAEPs) evoked potentials recorded from 20 patients early after injury were analyzed. Seventeen head-injured patients served as controls. EP studies were obtained shortly after admission (Mean Day 2, PB present) and approximately 2 weeks after injury (Mean Day 15, PB absent). The mean serum level of PB in the treatment group was 1.9 mg/100 ml. The drug effect was assessed by comparisons between the PB and the control groups. Statistical analyses were based on differences observed between two studies in the same patient. Analyses of covariance (F tests) were performed on data from all modalities. Wave form complexity was minimally affected by the drug. Middle and long latency components of the SEP were depressed by PB, and latencies of BSEP peaks and the early components of the SEP were delayed. The amplitude of some VEP peaks was reduced by PB. The BAEP was not significantly altered. All of the observed effects of PB were determined to be due to the hypothermia exhibited by PB-treated patients (mean temperature, 36.1 degrees C), which was not seen in the control group (mean, 37.8 degrees C). It is concluded that, with appropriate interpretation, EPs can be used to monitor brain function in head-injured patients when PB therapy is used.

Auditory middle-latency responses in humans.

Middle-latency responses (MLR) in humans were studied using an unconventional recording technique with wide bandpass filters. Such filtering permitted simultaneous recording of the auditory brain stem response (ABR) thus facilitating comparisons between the two responses. Effects of sedation (chloral hydrate and diazepam), stimulus-related properties and the coronal distribution of MLRs were examined. Mild sedatives did not appear to affect either MLRs or ABRs. MLRs differed from ABRs in their stimulus-related properties, implying that the neuronal mechanisms underlying their generation are not the same. The amplitude of the MLR component, Pa, was largest at the vertex and symmetrically distributed over the temporal lobes. MLR components Na and Pa and ABR wave V were reliably obtained in all subjects at moderate and high stimulus intensities. At low stimulus levels, however, the detectability of wave V was more robust than the middle-latency components. Thus ABR appears to be the test of choice when hearing sensitivity is in question. MLRs are likely to be most clinically useful in patients with neurological or central auditory processing disorders.

Simultaneous recording and separation of early and middle latency auditory evoked potentials

A method, consisting of wideband (1–5000 Hz) recording, dual artifact rejection (for both EEG and muscle artifacts) and separation of the EAEP by digital high-pass filtering of the averaged signal, is proposed for the simultaneous recording of early and middle latency auditory evoked potentials. The high-pass was realized by a simple recursive filter. The middle (MAEP) latency components were derivable directly from the wideband averaged signal without further filtering, thus avoiding wave form distortions. Through this method additional information on the afferent auditory system can be gained, and auditory threshold determination can be considerably improved. The proposed procedure is implementable on any computer-based EP system and does not require extra amplifiers, filters or separate test runs for the acquisition of the MAEP.

Middle latency components of the auditory evoked response: lateral differences and changes by mental tasks.

Middle latency components in response to stimulation of both ears with 50 dB SL clicks at a rate of 10/sec were recorded in young healthy subjects from the left mastoid-nose tip and right mastoid-nose tip. All were right-handed. 1) Lateral differences were found in most subjects. As to the largest peak-to-peak amplitude, the amplitude on the right side was larger than that on the left in 18 subjects, but the reverse was found in 11. Only two showed little differences. 2) The amplitudes on the right side during addition were larger than those when merely looking at numerals. The amplitudes during multiplication were larger than those during addition.

Effects of Anesthesia on the Middle Latency Components in Cat

The influence of the anesthetics (secobarbital, pentobarbital and α-chloralose) on the auditory middle latency response (MLR) was studied in adult cats. The results were as follows:1) These three anesthetics caused great variations in both the peak latency and the amplitude of Pa component.2) The early components of M. L. R. were comparatively stable, while the late components of M. L. R. were greatly influenced by these anesthetics.3) The generator of Na component seems not to be the same as that of Pa component.4) Special attention should be paid to the anesthetic condition in the discussion on the late component of M. L. R.

Effects of rise time on simultaneously recorded auditory-evoked potentials from the early, middle and late ranges.

The view that the effects of stimulus rise time are qualitatively different for early brain stem components, middle latency components and late vertex components of the auditory-evoked responses was reexamined. The amplitudes and latencies of the brain stem response (Jewett's wave V), middle latency components Na and Pa, and vertex potentials P1, N1 and P2, evoked by tone burts of various rise times, were analyzed. Increases in rise time were associated with smaller peak amplitudes and longer peak latencies for all of the components measured. These effects were comparable in magnitude for all the components. The results are interpreted in terms of a delayed and less synchronized neural discharge from the cochlea as rise time is extended.

Effects of number and interstimulus interval of tone pips on fast responses.

Effects of stimulus number and interstimulus interval on auditory-evoked fast responses (BSR: Jewett's V, and middle-latency components: Na, Pa and Nb) were studied by using 1000- and 500-Hz tone pips in 6 normal human adults. At a stimulus intensity of 50 dB SL, 500 stimuli evoked BSRs and the middle-latency components in all cases. At a stimulus intensity of 30 dB SL, 1000 stimuli were necessary to evoke BSRs and Na in all 6 subjects. Even 4000 stimuli were not sufficient for identifying Pa in 1 subject and Nb in 3 subjects. The largest mean peak-to-peak amplitude was the Na-Pa amplitude, but, differences across subjects were large. On the other hand, the BSR-Na amplitude showed relatively small differences across subjects. The BSR latencies were highly stable across subjects. These characteristics indicate that the BSR-Na component is more suitable as an indicator for objective audiometry than either the Na-Pa or Pa-Nb component. The BSR-Na amplitude did not show a decrease as the interstimulus interval was decreased from 104 to 32 ms. On the other hand, the Na-Pa amplitude significantly decreased as the interstimulus interval was decreased from 104 to 42 ms, and the Pa-Nb amplitude also significantly decreased as the interstimulus interval was decreased from 104 to 73 ms. Therefore, because of its resistance to the effects of high rates of stimulation, the BSR-Na component appears to be a suitable audiometric index in the clinical situation where time constraints are a consideration.

Human auditory evoked potentials. I: Evaluation of components

Fifteen distinct components can be identified in the scalp recorded average evoked potential to an abrupt auditory stimulus. The early components (I–VI) occuring in the first 8 msec after a stimulus represent the activation of the cochlea and the auditory nuclei of the brainstem. The middle latency components (N o, P o, N a, P a, N b) occuring between 8 and 50 msec after the stimulus probably represent activation of both auditory thalamus and cortex but can be seriously contaminated by concurrent scalp muscle reflex potentials. The longer latency components (P 1, N 1, P 2, N 2) occuring between 50 and 300 msec after the stimulus are maximally recorded over fronto-central scalp regions and seem to represent widespread activation of frontal cortex.