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Biomedical subjects

H Pratt

Publications and source records attributed to H Pratt.

At least 19 recordsLinked to original sources
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

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

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↗
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↗
PubMed1994

Plasma cholesteryl ester transfer in patients with non-insulin dependent diabetes mellitus.

Plasma newly synthesised cholesteryl ester transfer (NCET) rates from high density lipoproteins (HDL) to very low density lipoproteins (VLDL) and low density lipoproteins lipoproteins (LDL) were measured in 26 patients with non-insulin dependent diabetes mellitus (NIDDM), 26 healthy subjects with closely matching plasma triglyceride (TG) levels and 10 normolipidaemic healthy individuals. In addition, insulin mediated glucose uptake was measured in the NIDDM patients and the normolipidaemic subjects. Rates of NCET were significantly (P < 0.05) elevated in NIDDM patients compared with healthy normolipidaemic individuals but were similar to rates in healthy subjects with closely matching TG levels. In all groups of subjects plasma NCET was significantly (P < 0.001) correlated with plasma TG concentration. In NIDDM patients correlations between NCET and plasma glucose (r = 0.489, P = 0.011) independently of plasma TG levels, and glycated haemoglobin levels (r = 0.430, P = 0.028) were also recorded. Insulin mediated glucose uptake was unrelated to plasma NCET rates in the study. These data suggest that in NIDDM patients under good diabetic control elevated plasma NCET rates are mainly due to hypertriglyceridaemia and a specific and possibly stimulatory effect of diabetes on these rates may be seen only in patients with poorly controlled diabetes.

Adult↗
PubMed1994

The effect of acute hyperinsulinemia on plasma cholesteryl ester transfer protein activity in patients with non-insulin-dependent diabetes mellitus and healthy subjects.

The effect of acute hyperinsulinemia on plasma cholesteryl ester (CE) transfer protein (CETP) activity was determined in 11 patients with non-insulin-dependent diabetes mellitus (NIDDM) and 10 healthy subjects. Plasma CETP activity was reduced significantly in NIDDM patients (-37 +/- 59 nmol/mL/h, P < .05) but not in healthy subjects (-7 +/- 37 nmol/mL/h) during insulin infusion. Saline infusion did not alter plasma CETP activity significantly. The change in plasma CETP activity was correlated significantly with the baseline plasma triglyceride (TG) concentration (r = -.523, n = 21, P = .01) and marginally with the concomitant decrease in these levels with acute hyperinsulinemia (r = .413, n = 21, P = .06) in NIDDM patients and healthy subjects combined. These data indicate that acute hyperinsulinemia reduces plasma CETP activity and probably plasma CETP concentration in NIDDM patients, and suggest coordinated regulation of CETP levels and TG metabolism by insulin.

Adult↗
PubMed1994

Absolute pitch--electrophysiological evidence.

People who have the ability to label or to produce notes without any reference are considered to possess Absolute Pitch (AP). Others, who need a reference in order to identify the notes, possess Relative Pitch (RP). The AP ability is assumed to reflect a unique, language-like representation of non-lexical musical notes in memory. The purpose of this study was to examine this assumption by comparing Event Related Potentials (ERP) of musicians with and without AP, to lexical and non-lexical representation of musical material. Subjects were eighteen young adult musicians. Seven were AP and eleven RP. Auditory stimuli, presented through earphones, were piano notes (non-lexical) or a voice saying the note's name (lexical). Visual stimuli, presented on a computer display were note symbols (non-lexical) or letters (lexical). Subjects performed a number of tasks, combining the two modalities (visual and auditory) and stimulus types (lexical and non-lexical), and reaction times (RT), performance accuracy and evoked potentials were recorded. The tasks forced the subjects to transfer mental representations of musical material from one mode to another. Our most important findings were the differences, between groups, in the scalp distribution of P300 amplitudes. We conclude that absolute pitch possessors use the same internal language as relative pitch possessors, when possible, but the distribution of the underlying brain activity is different between AP and RP subjects.

Acoustic Stimulation↗
PubMed1994

Machine scoring of somatosensory evoked potentials.

A machine-scoring algorithm was developed for automatic identification and measurement of the positive and negative peaks of short-latency somatosensory evoked potentials (SEPs). The algorithm enables objective and consistent identification and naming of specific components with minimal operator involvement, avoiding inaccuracies and variability resulting from differences in the criteria used by different operators, or by the same operator at different times. The algorithm is based on finite impulse response filtering of wave forms from 4 conventional recording channels at a bandpass of 90-240 Hz. The bandpass was based on the major lobe in power spectra of multiple records and was verified as effective by application to numerous wave forms. Peak identification is based on identifying the peak at its optimal channel and verifying its consistency with corresponding peaks in the other channels. The machine-scoring algorithm was validated on SEPs from 120 subjects. The machine-scored peak latencies obtained with this procedure were significantly correlated with their manually measured counterparts.

Adult↗