Biomedical subjects

H Pratt

Publications and source records attributed to H Pratt.

17 recordsLinked to original sources

PubMed1992

Contralateral effects of cerebello-pontine angle exposure on human auditory brain-stem evoked potentials.

Auditory brain-stem evoked potentials (ABEPs) were recorded during surgical procedures which exposed the cerebello-pontine angle (CPA) in humans. Recordings made with the CPA contralateral to stimulus exposed were compared with those obtained with the skin sutured at the end of surgery. Single-channel as well as 3-channel Lissajous' trajectory (3-CLT) analyses were used to evaluate the effect of the surgical exposure on ABEP. The results suggest that exposure of the CPA contralateral to the stimulated ear did not affect dipole equivalent orientation nor magnitude, but did affect timing of the recorded activity being more pronounced for segments 'd'-'e' (corresponding to waves IV-V) than for 'a'-'b' (waves I-II). The results imply that the effects of disrupting the volume conductor may have been overwhelmed by other effects, such as local temperature changes. These changes, although not associated with clinical sequella, should be accounted for when analyzing subtle quantitative changes involving surgical exposures.

Acoustic Stimulation↗

PubMed1992

Auditory event related potentials during lexical categorization in the oddball paradigm.

Event related potentials (ERPs) and reaction times (RTs) were recorded from 18 subjects, performing lexical categorization of words and nonwords. Three sets of monosyllable utterances, differentiated in semantic and rhyming attributes, were presented using the "oddball paradigm." ERPs included a sustained negativity which began approximately 100 msec after stimulus onset and peaked at approximately 400 mses (SN4) poststimulus, in response to target as well as to nontarget word stimuli. Semantic effects on SN4 latency were observed only for target utterances. Nonmeaningful word targets were associated with longer SN4 peak latencies as well as slower RTs compared to meaningful word targets. It is suggested that these longer latencies are due to a longer time required for an exhaustive search in permanent memory before categorizing a stimulus as a nonmeaningful word.

Adult↗

PubMed1992

Brain correlates of hand dominance: the association between peripheral and cerebral asymmetries revisited.

Measures reflecting central processing of somatosensory stimulation were recorded in left- and in right-handed subjects in order to evaluate differences between the two handedness groups in the vertical, rather than lateral, axis of processing. Somatosensory evoked potentials were recorded in left- and right-handers following electrical stimulation of the median nerve at the wrist. The relative vertical balance of processing was probed by comparing the amplitudes of the underlying activity in early evoked potentials, presumably originating subcortically, with later, cortically originating potentials. Central conduction time (CCT) of the sensory volleys was also recorded. The data revealed higher amplitude ratios (ARs) between subcortical and cortical potentials, as well as shorter CCTs, in left-handers. These results demonstrate that transmission differences between the handedness groups may occur early in central nervous system (CNS) conductance. The results are further discussed in light of evidence suggesting that stronger reliance on a subcortical mode of processing may underlie phenomenon of left-handedness.

Adolescent↗

PubMed1992

Auditory event-related potentials among dyslexic and normal-reading children: 3CLT and midline comparisons.

Event-related potentials (ERP's) to verbal and non-verbal auditory stimuli were recorded from normal-reading and from dyslexic children while performing a target-detection task ("oddball" paradigm). Two methods of analysis were used: (1) Peak latency and amplitude measures of P3 recorded from 3 midline electrodes; (2) P3 apex latency, amplitude and orientation in the three-channel Lissajous' trajectory (3CLT) derived from 3 orthogonal pairs of electrodes. P3 peak amplitude was significantly attenuated in dyslexic children compared to normal-reading children and in response to verbal stimuli compared to non-verbal stimuli. P3 apex latencies were longer and apex amplitudes larger in response to non-verbal compared to verbal stimuli. The most striking finding involved P3 apex orientation, which pointed in an upward-posterior direction with a slight tilt to the left among normal readers, but with a tilt to the right in dyslexics.

Acoustic Stimulation↗

PubMed1979

Short latency mechanically evoked somatosensory potentials in humans.

Somatosensory potentials evoked by mechanical stimulation were recorded by surface electrodes over (1) the digital nerves in the index finger, (2) the median nerve at the wrist, (3) the median nerve near the axilla, (4) the brachial plexus, (5) the cervical cord at CII, (6) the scalp overlying the somatosensory cortex. Nerve conduction velocities varied inversely with age and ranged from 43 to 68 m/sec. Mechanically evoked potentials recorded from the electrodes overlying the digital nerves were an artifact of the finger movement. All other electrode configurations recorded potentials comparable to those evoked by electrical stimulation of nerves. These mechanically evoked potentials could prove useful in the assessment of clinical disorders of somatosensory function from receptor to cortex in man.

Adolescent↗

PubMed1979

Mechanically and electrically evoked somatosensory potentials in normal humans.

Somatosensory potentials evoked by mechanical stimulation of the fingernail and electrical stimulation of the nerve in the finger and at the wrist were recorded by surface electrodes over; (1) the digital nerve in the index finger, (2) the median nerve at the wrist, (3) the median nerve at the axilla, (4) the brachial plexus at Erb's point, (5) the cervical cord at C2, and (6) the scalp overlying the somatosensory cortex. Nerve conduction velocities were computed for two portions of the median nerve. Conduction times along the somatosensory pathway between spinal cord and cerebral cortex were also defined. The mechanically evoked potentials had less temporal dispersion, were of lower amplitude, and occasionally consisted of fewer components than the electrically evoked potentials. Electrical stimulation of the nerve trunk at the wrist evoked some additional components not detected by the other stimulation methods. Nerve conduction velocities and conduction times were comparable among the three methods of stimulation.

Arm↗

PubMed1977

Research on infants.

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Blood Specimen Collection↗

PubMed1977

Research on infants.

Explore the source record for details and available documents.

Blood Specimen Collection↗

PubMed1977

Correlations between psychophysical magnitude estimates and simultaneously obtained auditory nerve, brain stem and cortical responses to click stimuli in man.

Responses from the auditory nerve, brain stem auditory nuclei and cortex, as well as subjective responses to click stimuli at 10 intensities, were recorded simultaneously in the same human subjects. For various measures of the responses, the power-law exponents of their intensity functions were calculated, along with their statistical significances. The electrophysiological and psycho-physical functions were compared for similarity. On average, the exponents of the intensity functions of amplitudes of the auditory nerve and earlier brain stem responses were highly significant, showing similarity across subjects and similarity with the exponents of the subjective estimates. However, a closer examination proved this similarity to be superficial, since magnitude estimates showed an appreciable intersubject and intersession variability while the auditory nerve and brain stem responses were approximately constant. All other electric response measures either had exponents which were not significant or showed even poorer correlation with the subjective response. It is proposed that the type of electrical activity recorded in this study may not be the proper set of neural parameters which give rise to the loudness estimate.

Acoustic Stimulation↗

PubMed1977

Identification and separation of acoustic frequency following responses (FFRS) in man.

Frequency following responses (FFRs) to monaural tone bursts were recorded in normal and hearing impaired subjects as the potential difference between an ipsilateral earlobe electrode and a scalp vertex electrode. Whenn the rubber tube coupler between the earphone and the subject's ear was clamped, a stimulus artefact FFR was occasionally recorded. The "biological" FFR had a latency of about 1 msec and an irregular wave form which was made more sinusoidal by the addition of white noise. When the responses to tone bursts of opposite onset phases were added together, a "double frequency" FFR was obtained which had a latency of about 6 msec and whose amplitude was appreciably reduced by white noise. In some hearing impaired subjects (with no neural responses to clicks), this longer latency double frequency component could not be recorded, while in those cases in which the cochlear microphonic potential could be recorded, the shorter latency FFR was also present. It is concluded that the FFR in normally hearing subjects is made up of a short latency cochlear microphonic component and a longer latency neural component.

Adolescent↗

PubMed1977

Sources of frequency following responses (FFR) in man.

In order to study the sources and pathways which are responsible for the frequency following response (FFR), records were made in control subjects and in patients with special types of lesion and response. It has already been shown that the FFR in normal subjects to tone bursts with single onset phases is made up of a short latency cochlear microphonic potential (CM) and a longer latency neural component (neural FFR). No neural FFR could be recorded in patients with upper brain-stem lesions (absence of click-evoked responses from the inferior colliculus along with clinical signs of such a lesion). Their FFR was exclusively a cochlear microphonic potential, thus demonstrating that the neural FFR with a latency of 6 msec is generated in the region of the inferior colliculus. Also in subjects with large post-auricular muscle (PAM) responses, the PAM can contribute to the FFR, with a latency of 10 msec. In patients with high-tone hearing loss due to acoustic trauma, no CM could be recorded while a neural FFR with a latency of 6 msec was present. This indicates that the CM recorded by this technique may be generated in the basal turn. It also demonstrates that the pathway of the neural FFR begins in the apical turn of the cochlea.

Adult↗

PubMed1976

Intensity and rate functions of cochlear and brainstem evoked responses to click stimuli in man.

The complex of five waves, which are the responses to click stimuli of the auditory nerve and the brainstem auditory nuclei, were recorded in ten human subjects by means of earlobe and scalp electrodes. The rate of the stimuli was varied from 5/s to 80/s and their intensity was varied over a 70 dB intensity range in order to study the rate and intensity functions of each of the response components. With increasing click intensity, the amplitude of the first wave (generated by the auditory nerve) increased proportionally while the amplitudes of the later waves (generated by the brainstem auditory nuclei) reached their maximum amplitudes at intermediate click levels (saturation), and at high intensities occasionally even decreased in amplitude. The latency of each of the waves decreased by similar amounts as the intensity was increased. With increasing click rates, the amplitude of the first wave decreased the most, while there were smaller effects on the amplitude of the later waves. There was no effect of click rate on the latency of the first wave, but the latency of the later waves increased with click rate, the effect being greater on the later waves. In the rate functions, the latency change of a wave was greater than that of the waves preceding it (accumulative effect). These results are explained by overlapping convergence and divergence in the ascending auditory pathway. These results support the notion that the principal component of each wave is activated by the principal component of the previous wave. These results may explain the relative ease with which several workers record the fourth wave of the complex, and their preference for this response.

Auditory Pathways↗

PubMed1976

Recording of the cochlear microphonic potential with surface electrodes.

The cochlear microphonic potential was recorded in human subjects with surface electrodes (earlobe clip and scalp vertex disc) and an averaging procedure. Special precautions were taken to identify and separate artefactual, neural and microphonic components. These included shielding of the earphone, a rubber tube to introduce a time delay between artefact and biological response and white noise to mask the neural component. The cochlear microphonic potential was larger in amplitude in response to low frequency sounds and had a high threshold. Two clinical cases of cochlear hearing loss are presented, both lacking neural responses. The cochlear microphonic potential was present in one of them (i.e., neural hearing loss) and absent in the other (i.e., sensory hearing loss).

Adult↗

PubMedDate not supplied

Temporal correspondence of intracranial, cochlear and scalp-recorded human auditory nerve action potentials.

Conventional, vertex-ipsilateral ear records ('A'), as well as 3-channel Lissajous' trajectories (3-CLTs) of auditory brain-stem evoked potentials (ABEPs) were recorded from the scalp simultaneously with tympanic membrane electrocochleograms ('TME') and auditory nerve compound action potentials ('8-AP') recorded intracranially using a wick electrode on the auditory nerve between the internal auditory meatus and the brain-stem. The recordings were made during surgical procedures exposing the auditory nerve. The peak latency recorded from 'TME' corresponded to trajectory amplitude peak 'a' of 3-CLT and to peak 'I' of the 'A' channel ABEP. Peak latency of '8-AP' was slightly longer than the latency of peak 'II' of 'A' when '8-AP' was recorded from the root entry zone and the same or shorter when recorded from the nerve trunk. '8-AP' peak latency was shorter than trajectory amplitude peak 'b' of 3-CLT regardless of where the wick electrode was along the nerve. Peak latencies from all recording sites clustered into two distinct groups--those that included N1 from 'TME,' peak 'I' of the 'A' record and trajectory amplitude peak 'a' of 3-CLT, and those that included the negative peak of '8-AP' and trajectory amplitude peak 'b' of 3-CLT, as well as peak 'II' of the 'A' record, when present. In one case, the latency of peak 'II' and trajectory amplitude peak 'b' was manipulated by changing the conductive properties of the medium surrounding the auditory nerve.(ABSTRACT TRUNCATED AT 250 WORDS)

Acoustic Stimulation↗

PubMedDate not supplied

Surface-recorded cochlear microphonic potentials during temporary threshold shifts in man.

Cochlear microphonic potentials (CM) were recorded, by means of surface electrodes, before, during and after white-noise-induced temporary threshold shifts (TTS) in human volunteers. The behavioural threshold shift was not accompanied by a change in amplitude of CM. These findings indicate that in humans, the site affected by the noise exposure and which probably gives rise to the TTS is central to the site of generation of CM. In a previous study, the compound action potential generated in the auditory nerve was found to be of lower amplitude and longer latency during TTS, and it is thus proposed that the site affected is peripheral to the generation of conducted action potentials. The synapse between hair cells and the auditory nerve fibres is the most likely candidate to be the affected site.

Acoustic Stimulation↗

PubMedDate not supplied

Electrocochleography during noise-induced temporary threshold shifts.

The responses of the auditory nerve and brain stem auditory nuclei were recorded non-traumatically in human subjects by means of electrocochleography before, during and after exposure to white noise intensities which produced temporary threshold shifts. The largest decrement (amplitude decrease and latency increase) was seen in the response of the auditory nerve. Large intersubject variability was seen in the effects of the noise exposure on response amplitude, latency and recovery rates.

Acoustic Stimulation↗

PubMedDate not supplied

Comparison of hearing threshold determined by auditory pathway electric responses and by behavioural responses.

In order to evaluate their reliability for determing the hearing threshold, the cochlear microphonic potentials, the auditory nerve and brain stem neural evoked responses as well as the cortical evoked responses were compared with the behavioural hearing thresholds of the same subjects in the same session. The threshold for recording the cochlear microphonic potnetial was found to be appreciably higher than the behavioral threshold. The threshold for recording the auditory nerve and brain stem responses was within a few decibels of the behavioural threshold. The thresold of the cortical evoked response was several decibels higher. It is concluded that (1) the auditory nerve and brain stem neural evoked responses are the best indicators of hearing threshold; (2) the cortical evoked responses are usually comparable, and (3) all types of evoked responses are indispensable aids in the evaluation of hearing and the determination of site of lesion in the auditory system.

Audiometry↗