Hallowell Davis

The slow response of the human cortex to auditory stimuli: Recovery process ☆

Abstract The late, slow, non-specific diffuse cortical response (the “V potential”), recorded from the vertex relative to mastoid or ear, has been studied by the method of averaged responses in waking young adults. Filtered clicks (“tone pips”) were our usual stimuli, delivered in repeated cycles of one, two, three or four similar (or different) tone pips at various intervals within the cycle. The corresponding responses were collected and averaged separately. Responses earlier than 40 msec were disregarded because of contamination with myogenic components (the sonomotor reflex). The typical auditory V potential is a sequence of waves with the following latencies to peak: P 1 (vertex-positive) at 50–60 msec; N 1 (vertex-negative) at about 100 msec; P 2 at 170–200 msec; N 2 at about 300 msec, and often P 3 and N 3 also. P 2 may be double-peaked. Tactile responses have slightly longer latencies and show more prominent P 1 . Individual differences among subjects make exact descriptions impossible. As a first approximation the above latencies do not vary with the audio frequency, the intensity or the interval between the tone pips, although N 2 , P 3 and N 3 become small or disappear with short intervals. The latencies may be longer with very weak stimuli near threshold. The amplitude of the V potential is best measured from peak of N 1 to trough of P 2 . The amplitude increases slowly with the intensity of the pips. For maximal amplitude the intervals between stimuli must be over 6 sec and probably at least 10 sec. If the intervals are regular the average amplitude is about 1 2 maximal at 3 sec, 1 4 at 1 sec and 1 6 at 0.5 sec. If pairs of tone pips are employed the amplitude of the second response depends on the long interval between pairs as well as on the short interval between the members of the pair. Variability is considerable from test to test and across subjects but statistically the recovery function is smooth and reproducible.

Prospective Evaluation of Hearing Impairment as a Sequela of Acute Bacterial Meningitis

As part of a prospective study of acute bacterial meningitis in children, we studied for five years the hearing of 185 infants and children who had acute bacterial meningitis when they were more than one month of age. Nineteen (10.3 per cent) of the patients had persistent bilateral or unilateral sensorineural hearing loss. The incidence of hearing loss as determined by electric-response audiometry and conventional tests was 31 per cent with Streptococcus pneumoniae, 10.5 per cent with Neisseria meningitidis, and 6 per cent with Hemophilus influenzae infections. Transient conductive hearing impairment was found in 16 per cent of the sample, but in no case was there apparent improvement in a sensorineural deficit over time. The site of disease resulting in impaired hearing cannot be stated with certainty, but involvement of the inner ear or auditory nerve was suspected. The number of days of illness (symptoms) before hospitalization and institution of antibacterial treatment was not correlated with the development of sensorineural deafness.

Acoustic Relations of the Human Vertex Potential

The average amplitude of the slow, diffuse, nonspecific electrical response of the human cortex, called the V potential, evoked by tone pips or by tactile stimuli to thumb and forefinger, follows a power law with exponent about 0.24 (re sound pressure). The variability of the responses is great, across both trials and subjects. If auditory or tactile stimuli are judged equally strong, across frequency or modality, the V potentials tend to be equal. Both the latency and the amplitude of the V potential are independent of the rise time of a tone burst, at least up to 100 msec. The amplitude also remains nearly constant as the duration of the plateau of a burst, with rise and fall times of 5 msec, is varied from 2 to 320 msec. An off response that closely resembles the on response in waveform, latency, and amplitude appears at the end of any burst that is long enough, but an off response that follows an on response by 1 sec or less is much reduced in amplitude, and so is an on response that too closely follo...

Cochlear Responses to Acoustic Transients: An Interpretation of Whole‐Nerve Action Potentials

Intracochlear electrodes in the guinea pig are used to measure the relations among cochlear potentials in response to slow acoustic transients. The traveling wave of Bekesy is described in terms of cochlear‐microphonic (CM) voltage as functions of time and place along the cochlear partition. The results are consistent with previous observations in the ear and on models of the basilar membrane. Interpolations of wave velocity and wave amplitudes between places used for the measurements allow continuous representations of the traveling‐wave pattern of CM in either space or time. From these representations, it is clear that the duration of the stimulating phase of CM along the cochlear partition significantly exceeds the apparent duration of the whole‐nerve action‐potential (AP) response to these transients.Selective changes in the waveforms of the AP responses, as opposed to simple reductions in amplitude, are observed when the transients are accompanied by bands of noise and after local chemical or mechani...

Exploration of Cochlear Potentials in Guinea Pig with a Microelectrode

The ac (“microphonic”) cochlear potential and the positive dc “endolymphatic” potential have been recorded simultaneously as the exploring electrode was introduced into scala media or as other parameters were varied. Negative intracellular de potentials were demonstrated in the cells of the organ of Corti. The zone of positive endolymphatic potential is bounded by the reticular lamina, not by the basilar membrane. The cochlear microphonic reverses phase as the exploring electrode penetrates the reticular lamina. A dc polarizing current with the positive pole in scala media (and negative in scala tympani) increases the cochlear microphonic just as it does when the positive pole is located in the scala vestibuli. These facts indicate that the source of the ac (microphonic) potential seems clearly to be at the hair‐bearing end of the hair cells and that the source of the dc endolymphatic potential is probably here also, while Reissners membrane is not the source of either the ac or the dc potential. No steady dc current flow outside scala media was found such as would be expected if stria vascularis were the dc source and if the hair cells modulated a dc current flow through them. The dc endolymphatic potential may be increased by as much as 10 percent if and while the basilar membrane is displaced toward scala vestibuli and may be decreased to 50 percent or less when and while it is displaced toward scala tympani. Isotonic solutions rich in potassium depressed the ac potential and nerve responses when introduced into scala tympani but not when in scala vestibuli only. The. dc potential, however, was not altered by high potassium concentration in scala tympani.

Effects of duration and rise time of tone bursts on evoked V potentials.

Tone bursts of 1000 Hz with linear on and off ramps and plateaus of various durations were used to evoke cortical (vertex) potentials in five adult subjects. With 30 msec rise time, the amplitude, from N1 peak to P2 trough, and the latency to either the N1 peak or P2 trough were all independent of duration of the plateau from 0 to 300 msec. With 3 msec rise time, the amplitudes were progressively reduced when the plateau was shortened from 30 msec to 10, 3, or 0 msec. With a long plateau, the amplitudes were nearly constant for rise times of 50 msec or less. The latency of the V potential was prolonged at intensities of 45 dB (ISO) or less and also in relation to the slope of the onset ramp. With very gradual slope [300 msec to reach 45 dB (ISO)], mean latency to N1 was 169 msec while with very steep slope [3 msec to reach 85 dB (ISO)], it was 109 msec. OFF responses showed similar relations but with smaller amplitudes and shorter (by 16 msec) latencies. For evoked‐response audiometry, the rise time of the test signal will not be critical if it is 30 msec or less and the plateau is at least 30 msec long, and any plateau of 30 msec or longer will be acceptable.

Acoustic Trauma in the Guinea Pig

The ears of anesthetized guinea pigs were exposed to intense tones of 135, 545, 2000, or 8000 cps at sound pressures (at the eardrum) from 138 to 148 db re 0.0002 microbar. The electrical output was recorded by differential intracochlear electrodes before, during, and after the exposures.The injury caused by 8000 cps centers in the basal turn, by 2000 cps in the second turn, by 500 and 185 cps in the third and fourth turns of the cochlea. No single tone, at the intensities and durations employed, injured all of the cochlea.The “threshold” and also the maximum voltage of the cochlear microphonic are valid indices of the anatomical injury seen under the microscope if the proper test frequencies and positions of electrodes are used.The destructiveness of a tone does not depend on its frequency. Equally severe (probably permanent) injuries were produced by a one‐minute exposure at all four frequencies tested when the intensity level was about 144 db at the eardrum.

The Audiometric Utility of Brain Stem Responses to Low-Frequency Sounds

The human scalp-recorded vertex-positive brain stem response to a click or high-frequency tone pip is an excellent audiometric indicator. Its latency of 6-9 ms is practically independent of the polarity of the stimulus but is inversely related to intensity. With a 4,800- or 2,400-Hz tone pip (filtered click) its threshold of detectability is usually at or below 10 dB SL. With a 500-Hz tone pip, with rise and fall of 2-3 ms, the response at 30 dBSL is low in amplitude, rounded in wave form, and has a latency of about 10 ms. When the polarity of the stimulus is reversed, the latency shifts by 1 ms. At and above 40 dB, this late response is obsured by a larger and earlier response. High-pass (1,500 Hz) masking noise does not affect the low-level response but the earlier high-level response is reduced in amplitude and delayed by about 1 ms. The large early response seems to be initiated by stimulation of the basal turn of the cochlea by the low-frequency transient. The frequency-following response (FFR) to a 500-Hz tone burst with a 2-ms rise time has a threshold at about 40 dB SL. Its relatively short latency is appropriate to the basal turn. A later low-amplitude apically generated response can sometimes be detected, either at a lower stimulus level or in the presence of high-pass masking noise. The usual FFR often has complex wave forms and some individuals show only an onset response, even at 70 dB SL. It is almost impossible to edentify with certainty the first individual waves of FFR as they relate to the individual waves of the tone burst and as they change amplitude with intensity. The audiometric usefulness of the high-threshold responses to 500 Hz that are initiated in the basal turn is doubtful. The low-threshold responses initiated in the apical turn are so difficult to identify with certainty that they are not likely to be of clinical value unless high-pass masking noise can be used to clarify them.

Slow vertex potentials: Interactions among auditory, tactile, electric and visual stimuli

Abstract Slow V potentials (Cz−M1:N100−P200) were evoked from 8 adult human subjects by filtered clicks (1200 c/sec), electric shocks to left median nerve, vibration of left middle finger or binocular flashes of light. The strengths of the stimuli were adjusted to be comfortably strong and to give equal magnitudes of sensation among the various modalities. Stimuli of the same or of different modality were paired, with an intra-pair interval of 0.5 sec. The amplitude of the responses to the second stimulus was much less than that of a reference single response about 5.0 sec after a previous response. The reduced amplitude of the second response of a pair, expressed as a percentage of its corresponding reference response, measures the interaction. The average depression of a response to a second stimulus in the same modality, after 0.5 sec, was significantly less (5% level of confidence) for flashes than for clicks or shocks, and for shocks it was significantly less than for clicks or vibration. The average intramodal second response, across all modalities, subjects and conditions was 39% of reference. Depression was significantly less with cross-modal than with intramodal pairs. The second responses averaged 64% of the reference response. With subjectively equated stimuli the depressions did not differ significantly among click-shock, shock-click, click-vibration, vibration-click, shock-vibration, vibration-shock, flash-click, click-flash, flash-shock and shock-flash. Although both shock and vibration activate the same cortical sensory projection area, the cross-modal shock-vibration interactions were less than intramodal shock-shock or vibration-vibration and they did not differ significantly from cross-modal shock-click or vibration-click. The general rules for intramodal and cross-modal effects hold true for the individual subjects in nearly all cases, although within-subject variability was considerable and the responses of one particular subject tended to be quite erratic.

Prospective evaluation of treatment of Hemophilus influenzae meningitis

Fifty children with Hemophilus influenzae meningitis have been enrolled in a prospective study. Patients were randomly assigned chloramphenicol or ampicillin treatment; there were no significant differences between groups in other respects. Countercurrent immunoelectrophoresis proved to be a valuable tool for rapid diagnosis of the causative agent even in pretreated patients. Increasing quantities of capsular polyribosephosphate antigen detected in the initial cerebrospinal fluid correlated significantly (r=0.62419; p less than 0.01) with early and late sequelae of meningitis. None of the patients died. Severe and persistent neurologic or intellectual deficits were noted in four (8%) of the children, and an additional 14 (28%) had IQ scores between 70 and 90. The presence of bactericidal antibody in serum was not protective. Anti-PRP antibody generally was not present in acute serum specimens and irrespective of the quantity of antigenic stimulus provided by the disease was nondetectable in 21 of 24 children less than 17 months of age following recovery.