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Auditory P300 development from an active, passive and single-tone paradigms.

The P300 (P3) event-related brain potential (ERP) was elicited with auditory stimuli in order to compare three different tasks and to assess the effect of ageing from childhood to adolescence. Seventy-two subjects, ranging in age from 6 to 14 divided into three age groups, were selected for this study. In the active task, the subject was required to discriminate between standard and target tones (oddball); in the passive task condition, the subject did not respond to either the standard or target stimulus; in the single task, a target but not a standard tone stimulus was presented and the subject was required to react to the target tone. Our results show that the passive sequence and the single-tone paradigm yielded similar P300 waveform to those obtained from the active task. Separate age/ERP component latency and amplitude linear regression were computed. A significant negative correlation between age and P3 latency was found. The event-related potential P3 wave shows consistent and significant age-related changes in human cerebral function, regardless of the methodology used. These findings suggest that the passive and single-tone paradigms can be a useful way to elicit the P3 ERP component.

Filter effects and low stimulation rate on the middle-latency response in newborns.

Auditory middle-latency responses (MLR) have been recorded in 25 newborns at 60 dB nHL using two wide band-pass filter conditions and a slow stimulation rate of 2/s. With both types of filter, the MLR consisted in an initial positive wave followed by a negative component (Na) and a positive component (Pa). In newborns, this positive component appears in the vicinity of 45 ms and is more prolonged than the Pa of the MLR in adults. The probability of obtaining MLR after averaging only 500 signals was higher with a high-pass filter setting of 10 Hz (12 dB/octave), as compared with 5 Hz (12 dB/octave). No significant differences were found in the detectability rate of MLR between the two-filter band-pass settings. It is important to note that some MLR were unstable and not easily replicable. Therefore, the clinical application of these components is still doubtful.

The effects of age on human P3 latency.

103 subjects aged 6 to 78 years were studied in an "auditory oddball" event-related potential (ERP) paradigm. Linear regressions were computed for P3 latencies for the age groups 6-14, 12-24 and 18-78 years. In the first two groups a significant negative correlation between age and P3 latency was present. The age/P3 latency slope for the subjects under 15 was--19.00 msec/year versus -2.4 msec/year for the 12-24 year-olds. In contrast, there was a significant positive correlation in the 18-78 years group with an age/P3 latency slope of +1.25 msec/year. A significant age/P3 latency curvilinear relationship was found from 6 to 78 years old.

Auditory event-related potentials in well-characterized groups of children.

Sixty-eight subjects ranging in age from 6 to 23 years were studied in an 'auditory oddball' event-related potential (ERP) paradigm. Our results replicate other studies, finding P3 as the most consistent component of ERPs since childhood, although great variability of this component was found in the 6-year-old group. Separate age/ERP component latency and amplitude linear regressions were computed for subjects 6-14 and 6-23 years old. Our data show in both groups a significant negative and positive correlation between age and P3 latency and N1-P2 amplitude respectively. The age/P3 latency slope for the subjects under 15 years old was -19.00 msec/year versus 8.15 msec/year for all subjects (6-23 years old). Our results indicate that P3 latency during childhood decreases with age, reaching an asymptote after or during the second decade of life. No curvilinear relationship between age and P3 latency was found over the child groups, although a significant curvilinear relationship was found over the entire age range. This study showed no significant gender differences in latency at any age group. However, in the adult group females showed significantly larger amplitudes than males.

Auditory P3 development in childhood.

Fifty one subjects aged six to fourteen years old were studied in an "auditory oddball" event-related potential (ERP) paradigm. Our results found P3 as the most consistent component of ERPs since childhood, although a great variability in the latency of this component was found at six years old. An additional group of adults (19-23 years old) was included as a reference group. Separate age/P3 latency linear regressions were computed for subjects 6-14 and 6-23 years old. Our data shows in both groups a significant negative correlation between age and P3 latency. The age/P3 latency slope for the subjects under 15 years old was -19.00 msec/year, versus -8.15 msec/year for all the subjects (6-23 y/o). Our results indicate that P3 latency during childhood decreases with age reaching an asyntote after or during the second decade of life. A significant age/P3 latency curvilinear relationship was found from six to twenty three years old.

Middle latency and 40 Hz auditory evoked responses in normal hearing children: 500 Hz thresholds.

The 500 Hz tone burst thresholds were obtained by four independent judges from recorded middle latency responses (MLR) and 40 Hz event related potentials (40 Hz ERP) in a group of children ranging in age from 5-12 years old. The thresholds obtained from the two electrophysiological methods were compared to each other and to behavioural pure-tone thresholds by means of a paired t-tests. The general trend was for the MLR thresholds to be lower than 40 Hz ERP thresholds. However, the statistical analysis indicated that the differences between the two electrophysiologic thresholds and pure-tone audiometric thresholds were not significant. It was concluded that MLR and 40 Hz ERP under the conditions in which this study was done are not suitable electrophysiological measurements in order to estimate the low frequency thresholds in children.

Middle latency response to a 500-Hz tone pip in normal-hearing and in hearing-impaired subjects.

Measurement of middle latency responses (MLR) appears to be one of the most useful ways of determining low-frequency auditory threshold. It is known that analog filtering can drastically affect MLR and since most laboratories use different recording characteristics, we carried out these measurements with a number of filter configurations. Ten subjects with normal hearing sensitivity were tested. The stimuli were 500-Hz tone pips (alternating in polarity) with a 4-ms rise-fall time and a plateau of 2 ms, presented at the rate of 9.3/s. The MLR were recorded with filter settings of 10-100, 10-250, 10-1,500, 10-3,000, 30-100 and 30-250 Hz at 12 dB per octave roll-off with a time base of 100 ms. MLR threshold was found between 8.0 and 11.5 dB nHL. The Wilcoxon statistical test showed that mean MLR thresholds did not differ significantly at the various bandpass configurations. An additional objective of this study was to compare hearing sensitivity based on MLR threshold to tone pips at 500 Hz and behavioural results obtained by conventional pure-tone audiometry. Although the correlation coefficient between the behavioural and electrophysiological measurements was statistically significant (r = 0.85), further studies are required in order to determine the real magnitude of the predicted errors obtained, before this electrophysiological measure can be applied clinically.

Brainstem response audiometry as subjective and objective test for neurological diagnosis.

This investigation is a preliminary report in which the auditory brainstem response (ABR) cross-correlation evaluation method is applied to a group of patients with a definite diagnosis of multiple sclerosis. The analysis of the results shows that the cross-correlation procedure is able to detect the ABR abnormalities with at least the same degree of accuracy as the abnormality identification made by visual inspection. Furthermore, discriminant analysis of the cross-correlations results shows that by using the Z-maximum correlation from only two derivations it is possible to separate the multiple sclerosis group from the normal group with only two failures. Since the cross-correlation procedure allows the evaluation of the ABR waveform, avoiding the unsatisfactory limitations of subjective identification, this contribution supports the idea that the cross-correlation procedure can be a clinically promising method for objective evaluation of the ABR.

Evaluation of ipsilateral and contralateral brainstem auditory evoked potentials in multiple sclerosis patients.

Brainstem auditory evoked potentials (BAEP) were recorded simultaneously between the vertex and the mastoid ipsilateral and contralateral to the ear stimulated in 30 patients with multiple sclerosis (MS) and compared with the responses in a control group of 30 normal hearing adults. The control group showed that significant latency differences exist between ipsilateral and contralateral recording. Definitions of abnormalities were based on interwave separation and the wave V amplitude ratio. No case was found among the MS patients with an abnormal contralateral but normal ipsilateral response.

Audiometric study of the neonate: impedance audiometry. Behavioural responses and brain stem audiometry.

The following clinical measurements of acoustic impedance were carried out successfully on 25 neonates. Average compliance was 0.48 cm3, with a range from 0.28 to 0.81 cm3. Tympanometry showed a high percentage of maximum compliance curves with positive pressures. In a notably high percentage, the stapedial reflex was combined with generalized body movements and was therefore considered a behavioural response. Behavioural responses of the child were also observed separately. Ipsilateral stimulation did not evoke a measurable stapedius reflex in any of the cases, but with contralateral stimulation some babies did show this reflex. The most intense behavioural responses occurred when white noise was used as the stimulus. Of the 25 children studied with impedance audiometry, 10 were evaluated audiologically by brain stem electric potentials. The latency of wave V was within the normal range in all the cases. Electric response audiometry could be a promising method for audiological evaluation of the neonate.