Biomedical subjects

H Pratt

Publications and source records attributed to H Pratt.

At least 55 records · Page 3Linked to original sources

PubMed1996

Electrophysiological evidence of a sound localizing binaural subsystem in the human auditory brainstem.

The binaural interaction components of auditory brainstem evoked potentials reflect electrical changes which are specific to binaural stimuli. Analysis of these components indicated that different click lateralizations result in spatially distinct distributions of activity in the pons, but not at more peripheral levels. The effects of ipsilateral and binaural masking on evoked activity indicated distinct binaurally- and monaurally-activated neural subsets in the human brainstem. These results on the effects of noise and the distinct distributions of pontine activity to different lateralizations provide the first electrophysiological evidence that the auditory system in the humans pons includes a subset which is specific to binaurally presented sounds and which is anatomically distributed according to the lateralization of the sound. These results suggest auditory spatial mapping, similar to other sensory systems. In contrast to other systems, in which mapping is according to receptor distribution in the periphery, auditory spatial mapping is achieved computationally at central levels of the pathway.

Acoustic Stimulation↗

PubMed1995

Short latency visual evoked potentials to flashes from light-emitting diodes.

Short latency visual evoked potentials (SVEPs) have been described in response to high-intensity, strobe flashes. High-intensity flashes can now be generated from goggle-mounted light emitting diodes (LEDs) and the SVEPs to such flashes have been shown to be reproducible across subjects, avoiding photic spread to the examination room and acoustical artifacts from the strobe stimulator. In this study, SVEPs from multichannel records are described in terms of normative latencies and amplitudes, as well as scalp distributions, to explore their generators. Potentials were recorded from 10 young male subjects, from 16 scalp locations, in response to flashes from goggle-mounted LEDs. Flashes were presented to each eye in turn, as well as binocularly. The latencies, scalp distributions and intersubject variabilities of the LED evoked SVEPs were similar to those obtained with strobe flashes. SVEP components were divided into 3 groups, according to their latency and the electrodes at which they were recorded with the largest amplitudes: periocular (under 40 msec latency), fronto-central (40-55 msec) and parieto-occipital (55-80 msec latency). The scalp distributions observed in this study suggest subcortical generators along the visual pathway, beginning at the retina. The use of goggle-mounted LEDs should promote routine evaluation of the integrity of the visual pathway between retina and cortex using SVEPs.

Adult↗

PubMed1995

Visual evoked potentials N75 and P100 latencies correlate with urinary delta-aminolevulinic acid, suggesting gamma-aminobutyric acid involvement in their generation.

Pattern reversal visual evoked potentials were recorded from 31 subjects who were occupationally exposed to lead and 54 non-exposed controls. No significant effects of lead were observed in the general subject population. However, when only non-smokers (17 lead-exposed and 27 controls) were evaluated, significant effects were found. The P100, but not the N75, latency was significantly prolonged in the lead-exposed group, and this correlated with both blood lead level and age. Nevertheless, both the N75 and P100 latencies correlated with the concentration of delta-aminolevulinic acid (delta-ALA) in urine and age. This, at least in part, could be due to elevated delta-ALA levels competing at gamma-aminobutyric acid (GABA) receptor neurons. This is consistent with the fact that GABA receptor neurons are involved along the entire length of the visual pathway. The results indicate that lead affects neural function even at permitted levels of exposure, and that this level should be reduced.

Aminolevulinic Acid↗

PubMed1995

The effect of lead exposure on target detection and memory scanning differs.

Visual event-related potentials were measured in lead-exposed and control subjects, while they were performing a target detection as well as a memory scanning task. Blood lead and urinary delta-aminolevulinic acid (delta-ALA) were determined in samples taken on the same day. Lead exposure did not affect the memory scanning P300 latency, but it did delay the target detection P300 latency in a dose-dependent fashion. The P300 amplitude of lead-exposed subjects was significantly reduced for both tasks, but not in a dose-dependent fashion. The target detection, but not the memory scanning, P300 latency correlated with urinary delta-ALA. No correlation of P300 with age was found, even though the subjects ranged from 20 to 60 years of age. The difference in the effect of lead exposure on the target detection and memory scanning P300 adds to the evidence that the P300 for the two tasks arises from different generators. The absence of a correlation of the measured P300 latency for each task with age in the present study raises the possibility that this extensively reported observation might, in part, be due to inappropriately matched younger and older subjects. This study indicates that evaluation of subjects exposed to toxic substances can increase our basic understanding of evoked potentials, as well as providing evidence of their toxic manifestations.

Analysis of Variance↗

PubMed1995

Spatio-temporal multiple source localization by wavelet-type decomposition of evoked potentials.

Scalp recording of electrical events allows evaluation of human cerebral function, but contributions of the specific brain structures generating the recorded activity are ambiguous. This problem is ill-posed and cannot be solved without auxiliary physiological knowledge about the spatio-temporal characteristics of the generators' activity. In our source localization by model-based wavelet-type decomposition, scalp recorded signals are decomposed into a combination of wavelets, each of which may describe the coherent activity of a population of neurons. We chose the Hermite functions (derived from the Gaussian function to form mono-, bi- and triphasic wave forms) as the mathematical model to describe the temporal pattern of mass neural activity. For each wavelet we solve the inverse problem for two symmetrically positioned and oriented dipoles, one of which attains zero magnitude when a single source is more suitable. We use the wavelet to model the temporal activity pattern of the symmetrical dipoles. By this we reduce the dimension of inverse problem and find a plausible solution. Once the number and the initial parameters of the sources are given, we can apply multiple source localization to correct the solution for generators with overlapping activities. Application of the procedure to subcortical and cortical components of somatosensory evoked potentials demonstrates its feasibility.

Algorithms↗

PubMed1995

The origin of the human auditory brain-stem response wave II.

Auditory brain-stem responses (ABRs) were recorded from human subjects undergoing neurosurgical procedures which exposed the auditory nerve. Scalp recordings indicated that the latency of the negativity between waves I and II (In) and the latency of positive peak II (IIp) were shorter when the nerve was suspended in air than when the nerve was submerged in cerebrospinal fluid or saline, while earlier and later waves remained unaffected. These results could not be attributed to changes in stimulus or recording parameters or conduction velocity. Computational and somatosensory experimental evidence of stationary potentials generated by physical properties of the volume conductor, including changes in conductivity or geometry, are presented to develop a model of wave IIp generation. The results of this study suggest that wave IIp (and probably In) are manifestations of current flux asymmetries across conductivity boundaries created by the temporal bone-cerebrospinal fluid intradural space-brain-stem interfaces. The current flux asymmetries are generated as the propagating auditory nerve action potential crosses the conductivity boundaries. These results also indicate that the physical characteristics of the volume conductor and neural pathways must be considered when interpreting surface recorded evoked potentials.

Action Potentials↗

PubMed1995

P300 in response to the subject's own name.

The P300 component is influenced by task relevance which is typically achieved by employing an active task involving the evoking stimulus. This study explored the possibility of making use of the subject's name, which is innately relevant to the subject, to achieve stimulus relevance. Dependence of P300 amplitude on auditory presentation of the subject's name was assessed in two experiments in which no response was required: (1) a passive 2-word "oddball" paradigm where the low probability word was the subject's first name; (2) a passive 3-word "oddball" paradigm consisting of two low probability words, one of which was the subject's name, and a third, high probability word. In the first experiment, a typical active 2-word "oddball" paradigm, which did not include the subject's name, was compared with the passive paradigm. P300 amplitude was larger in response to the subject's name compared to the other word in the two-word paradigm, indicating that the name can be used to evoke P300 in a passive paradigm. It was also larger than either of the other two words in the 3-word paradigm, suggesting that stimulus relevance has an additional effect on P300 amplitude beyond rarity.

Adult↗

PubMed1995

Three-channel Lissajous' trajectory of the binaural interaction components of human auditory middle-latency evoked potentials.

Three-channel Lissajous' trajectories (3-CLTs) of the binaural interaction component (BI) of auditory middle latency evoked potentials (AMLEPs) were derived from 14 normally hearing adults by subtracting the response to binaural clicks from the algebraic sum of monaural responses. AMLEPs were recorded in response to 65 dB nHL, rarefaction clicks, presented at a rate of 3.3/s. A normative set of BI 3-CLT measures was calculated and compared with the corresponding measures of simultaneously recorded, single-channel vertex-left mastoid and vertex-neck derivations of BI and of AMLEP to binaural stimulation (B). 3-CLT measures included: apex latency, amplitude and orientation, as well as planar segment duration, orientation, size and shape. The results showed seven main apices and associated planar segments ('Be', 'Bf', 'Bg', 'Bh', 'Bi1', 'Bi2' and 'Bj') in the 3-CLT of BI. Apex latencies of the BI 3-CLT were comparable to peak latencies of the vertex-left mastoid and vertex-neck AMLEP and BI records, both in their absolute values and in intersubject variability. Durations of BI planar segments were approximately 5.0 ms. Apex amplitudes of BI 3-CLT were larger than the respective peak amplitudes of the vertex-mastoid and vertex-neck BI records, while their intersubject variabilities were comparable. The lateralization of BI components may indicate asymmetric processing of binaural auditory input, or may be connected with anatomical asymmetry such as skull thickness. Preliminary analyses did not reveal a clear correlation between the lateralization of the BI component 'Bi2' and the handedness of the subject. We suggest that BI components of AMLEP may be associated with the primary auditory cortex and subcortical ascending structures.

Acoustic Stimulation↗

PubMed1995

Brain stem auditory evoked potentials: effects of ovarian steroids correlated with increased incidence of Bell's palsy in pregnancy.

To investigate the effect of ovarian steroids on the brain stem during changes of estrogen and progesterone blood levels, we recorded brain stem auditory evoked potentials with increased stimulus rates from 26 women treated for sterility by menotropins (Pergonal and Metrodin). These women were divided into three groups according to their estrogen and progesterone blood levels. The brain stem auditory evoked potential results revealed a significant delay of peak III only, with an increased stimulus rate in the group with the highest estrogen level. Estrogen may cause a brain stem synaptic impairment, presumably because of ischemic changes, and thus also may be responsible for a higher incidence of Bell's palsy during pregnancy.

Adult↗

PubMed1995

Segmented matched filtering of single event related evoked potentials.

A fast segmentation-based Matched Filtering (MF) technique of single trial Evoked Potentials (EP's) is presented. MF improves the Signal-to-Noise Ratio of single EP's, reducing the number of repetitions necessary to obtain high quality signals by an order of magnitude. A computer simulation and analysis of experimental data of Movement Related Potentials and cognitive Event Related Potentials demonstrate the superior capabilities of MF compared to traditional Ensemble Averaging.

Algorithms↗

PubMed1995

Improved detection of auditory P3 abnormality in dementia using a variety of stimuli.

The purpose of this study was to test the improved sensitivity of P3 abnormality in the detection of dementia using a variety of auditory stimuli. Improved detection was obtained using auditory stimuli that differed in their cognitive attributes and by using several P3 measures. These measures included P3 latencies and amplitudes relative to pure tone evoked P3s. Fourteen demented patients (mean age 79.2 years) and a matched normative group were tested. Abnormality of P3 latency for pure tone targets was found in ten patients, equivalent to a hit-rate of 72%. The hit-rate could be further increased by using phonemically and phonetically different types of auditory stimuli, thought to vary in their cognitive attributes. These findings underscore the importance of using a variety of stimuli in testing demented patients.

Acoustic Stimulation↗

PubMed1995

Effects of myelin or cell body brainstem lesions on 3-channel Lissajous' trajectories of fast and slow components of feline auditory brainstem evoked potentials.

Auditory brainstem evoked potentials (ABEP) were recorded from 16 awake cats using three orthogonal differential electrode pairs before and during a week after inducing neuronal lesions localized to the cochlear nucleus (CN) or the superior olivary complex (SOC), or myelin lesions localized to the fibers of the trapezoid body. ABEPs were digitally filtered to include only the slow ('pedestal') component, or only the faster first to fifth components, and three-channel Lissajous' trajectories (3CLTs) of these fast and slow components of ABEP were obtained. Cell body lesions and myelin lesions induced effects on 3CLT measures of both fast and slow components of ABEP. The results suggest a primary contribution of cell body activity to the slow component, and a primary fiber tract contribution to the fast components. However, the results do not support exclusive generation of the pedestal by cell body and dendritic post-synaptic potentials and of the faster components by action potentials along fibers. The results are consistent with a set of generators for each of the slow and fast components of ABEP, consisting of both cell bodies and their output fibers, that are spatially distributed in the brainstem.

Analysis of Variance↗

PubMed1995

Source estimation of auditory brainstem evoked potentials: comparison of 3CLT and dipole localization.

The generators of auditory brainstem evoked potentials (ABEPs) are generally agreed to be located between the auditory nerve and upper pons. Thus, they are all located within a few cm from the center of the head. Three-channel Lissajous' trajectory (3CLT) provides the amplitude and orientation of a centrally located equivalent dipole of surface recorded activity. Volume conductor theory predicts decreased spatial resolution of source estimation the deeper the source. In this study we compared source estimates obtained with 3CLT, using three orthogonal differential channels, with those obtained with two other source estimation methods: i) setting the generators at their known anatomical coordinates and calculating orientation and magnitude of the source (dipole localization method--DLM); ii) estimation of all source parameters, including the number of sources by wavelet-type decomposition, without assumptions on the location of the sources (multiple source estimate--MSE). 3CLT, DLM and MSE all converged on magnitudes and orientations that were not significantly different from each other, and locations that were within a few cm of each other. In conclusion, although 3CLT can only estimate a single, centrally located equivalent dipole, in the specific case of ABEPs, it provides the same information available from the more demanding source estimate methods. In addition to the considerable saving in recording channels, 3CLT is reference-independent and thus avoids ambiguities resulting from the choice of reference.

Electrodes↗

PubMed1995

The precision level of the objective hearing tests.

A comparative study was performed with 51 patients, using the stapedial reflex (ART), early auditory brain-stem responses (ABR), later auditory evoked potentials (SN10) and the audiogram, to assess the value of objective tests in the evaluation of the auditory level. The ABR and the SN10 are valid to determine the level of hearing. The ART s of limited value.

Audiometry↗

PubMed1994

Intra- and extra-uterine development of neonatal 3-channel Lissajous' trajectory of auditory brainstem evoked potentials.

This study compared intra- and extra-uterine maturation of the auditory pathway, using auditory brainstem evoked potentials (ABEPs), recorded with three orthogonal differential electrode configurations. From the three records of each subject, 3-channel Lissajous' trajectories (3CLTs) were derived and analyzed. 107 newborns were compared at the same gestational and post-conceptional (gestational+postnatal) age, from 29 weeks (wks) up to 43 wks. In addition, we explored the effects and neurophysiological consequences of early exposure to extra-uterine life, on the peripheral and central portions of the auditory pathway. Our findings indicate that exposure of premature infants to the extra-uterine environment is associated with advanced peripheral development, but slower central conduction compared to intra-uterine development.

Analysis of Variance↗

PubMed1994

Lexicality and modality effects on evoked potentials in a memory-scanning task.

Event-related potentials, as well as reaction times and performance accuracies, were recorded from normal young adults during the performance of a memory-scanning task, in response to the first and second items of the memorized set and to the probe. Stimuli included computer-generated digits, presented by earphones as speech (lexical auditory) or on a screen (lexical visual), meaningless voices (nonlexical auditory) with precisely the same frequency contents as the digits, or meaningless shapes with the very same colors and contours as the digits (nonlexical visual). The evoked potentials' late positivity (P3) to memorized items was earlier to auditory than to visual stimuli. P3 to memorized items and to probes was earlier to lexical than to nonlexical stimuli. P3 amplitudes to both memorized items and probes were smaller with auditory stimuli. Assuming P3 latency to reflect processing time and amplitude to reflect attentional allocation (effort) to the task-relevant stimuli, the results support phonological representations during processing in short-term memory, with nonauditory and nonlexical stimuli requiring more processing time and effort. A significant electrode x modality x lexicality interaction may suggest that stimuli of different modalities and lexicality involve variations in the relative contributions of the brain structures involved in their processing.

Adult↗

PubMed1994

A multidisciplinary study of lead-exposed subjects. I. Delayed target detection P-300 latency, an electrophysiological parameter, correlates with urinary delta-ALA.

Visual event-related potentials, generated while performing a target detection (oddball) task, were successfully evaluated in 21 out of 34 individuals occupationally exposed to lead and 40 out of 56 nonexposed controls who were examined. The blood lead level of the lead-exposed subjects ranged from a mean of 29 to 53 micrograms Pb/dl blood in three exposed subgroups, while that of the control group was 7.7 micrograms Pb/dl blood. The latencies of the N2 and P300 components of the visual event-related potential were significantly longer in the lead-exposed subjects. Both the N2 and P300 latencies significantly correlated with the blood lead levels of the subjects. In addition, the P300 latency correlated with the concentration of delta-aminolevulinic acid (delta-ALA) in urine. This in part could be due to elevated delta-ALA levels interacting with gamma-aminobutyric acid (GABA) receptor neurons. The results indicate that lead affects mental function even at permitted levels of exposure. They strengthen the conclusion, based on biochemical and hematological assays, that the maximum permitted blood lead level of 50 micrograms Pb/dl blood is not safe and should be reduced.

Adult↗

PubMed1994

Unsupervised clustering of evoked potentials by waveform.

A procedure for clustering evoked potentials (EPs) according to their waveforms is presented. Clustering is performed without a priori selection of basis waveforms, the number of basis waveforms or the number of clusters. The method uses the principal-component-analysis coefficients of EP records as features for unsupervised optimal fuzzy clustering (UOFC) of the records. The validity of the procedure is demonstrated in two instances: visual evoked potentials (VEPs) and cognitive event-related potentials (ERPs) from humans in a memory-scanning task. In the clustering of VEPs, the procedure differentiates between waveforms judged to be clinically normal and abnormal. In the clustering of ERPs, the procedure correctly differentiates between waveforms evoked by the same stimuli which differ in their context to the performance of a memory-scanning task (memorised items against probes). Within this classification, the procedure detects two subgroups to probe-evoked waveforms, which are not obvious from visual inspection of the waveforms. The advantage of the procedure, which conducts clustering by UOFC, is the adaptive and machine-learning nature of its operation.

Evoked Potentials↗