Biomedical subjects

H Pratt

Publications and source records attributed to H Pratt.

At least 91 records · Page 5Linked to original sources

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↗

PubMed1991

Seismic communication in a blind subterranean mammal: a major somatosensory mechanism in adaptive evolution underground.

Seismic communication, through low-frequency and patterned substrate-borne vibrations that are generated by head thumping, and which travel long distances underground, is important in the nonvisual communication of subterranean mole rats of the Spalax ehrenbergi superspecies (2n = 52, 54, 58, and 60) in Israel. This importance pertains both intraspecifically in adaptation and interspecifically in speciation. Neurophysiologic, behavioral, and anatomic findings in this study suggest that the mechanism of long-distance seismic communication is basically somatosensory and is independent of the auditory mechanism. Seismic communication thus appears to be a channel of communication important in the evolution of subterranean mammals that display major adaptation to life underground.

Acoustic Stimulation↗

PubMed1991

Physiology of short-term verbal memory.

These studies document a series of brain events accompanying short-term memory functions. For auditory verbal material the sequence involves at least two different sites within auditory cortex subserving sensory and cognitive processes of memorization. During the scanning of the short-term store structures within the medial temporal lobes, presumably the hippocampus, are active. There is an inconsistency between these results and the clinical observations of the need for an intact dominant parietal lobe for auditory short-term memory to function normally. Magnetic recordings showed no focal dipolar source of activity in the parietal lobe during any aspect of auditory short-term memory. The discrepancy could be accounted for by considering the parietal lobe lesion as "disconnecting" the lateral temporal cortex from the deep medial hippocampal structures thereby impeding auditory short-term functions (Geschwind, 1965). These studies show that the physiological analysis of brain events in the msec range can provide information about relatively complex cognitive processes underlying short-term memory. The magnetic and electrical recording methods provide a noninvasive way to study human brain functions involved in cognition that can then be correlated with behavioral measures of specific cognitive activities.

Brain↗

PubMed1991

Event-related potential correlates of the serial position effect in short-term memory.

Event-related potential (ERP) correlates of the serial position effect in short-term memory were investigated using a memory scanning task. Nine normal young adults (18-39 years) indicated whether a probe item was a member of a previously presented 5-item memory set by pressing 1 of 2 reaction-time buttons. Three types of stimuli were used: verbal digits presented both auditorily and visually, and musical notes presented auditorily. The ERPs to the probes were separately averaged according to the serial position of the probe (1, 2, 3, 4 or 5) in the memory set. The ERPs to the memory set items in positions 1, 3 and 5 also were separately averaged. Both baseline-to-peak and average amplitudes of a late positive parietal potential to the probes were larger to probe items presented in the last position in the memory set than to probes presented in the middle positions (2, 3 and 4), showing a significant recency effect, but only for auditory digits. Reaction time reflected significant recency effects for both auditory digits and notes, but not for visual digits. Response accuracy (percent correct) showed a significant recency effect only for notes. For each stimulus type, both the baseline-to-peak and average amplitudes of a late frontal component to the memory set items became more negative (in the case of the visual digits, less positive) in the third and last serial position of the memory set compared to the first. These findings provide electrophysiological evidence of serial position effects in short-term memory, which, during memory scanning, are dependent on stimulus modality (auditory, visual) and type (verbal, non-verbal).

Adolescent↗

PubMed1991

Development of auditory brainstem evoked potentials in newborn infants: a three-channel Lissajous' trajectory study.

Auditory brainstem evoked potentials (ABEP) were recorded from 50 newborns (35-43 weeks gestational age), using three orthogonal differential electrode pairs, in addition to the widely used vertex-mastoid derivation. Potentials were evoked by alternating polarity, 75 dBnHL clicks presented monaurally at a rate of 10/s. From the records of the three orthogonal electrode pairs (nasion-inion; vertex-spinous cervical process VII; left-right mastoids), Three-channel Lissajous' trajectories (3CLT) were derived and analyzed. 3CLT point-by-point, as well as segmental descriptors were compared with peak latencies of the vertex-mastoid derivation. Point-by-point 3CLT descriptors included apex amplitude, latency and orientation. Segmental descriptors included planar segment beginning latencies, duration and orientation. The interpretation of these results in relation to developmental aspects of the auditory system, as well as to the question of ABEP generators, is enhanced by using 3CLT descriptors of ABEP, which are more comprehensive than their single-channel counterparts. 3CLT apices correlated well with the Vertex-Mastoid defined peaks. Both peak and apex latency changes indicate that at the developmental stages surveyed in this study, development takes place in the more central portions of the pathway, whereas the peripheral portion is already relatively mature. The results also indicate a maturational change in the relative contributions of constituent generators of ABEP components.

Brain Stem↗

PubMed1991

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

Auditory brainstem evoked potentials (ABEP) were recorded from 16 awake cats to obtain 3-Channel Lissajous' Trajectories (3CLTs) using three orthogonal differential electrode configurations (nasion-midline nuchal ridge, left-right mastoids, vertex-midline under the mandible). Potentials, evoked by monaural 80 dBnHL (re, human threshold) clicks, were studied before, and up to 7 weeks 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 connecting these two structures. Neuronal lesions were induced by injection of kainic acid (KA), while myelin lesions were induced by injection of L-alpha-lysophosphatidylcholine (LPC). With CN neuronal lesions the major changes in 3CLT were in the time domain of 'b', 'c' and 'd' (components P2, P3 and P4 of single-channel ABEP). With SOC neuronal lesions the major changes were in 'c' and 'd' of 3CLT (P3 and P4 of ABEP). With trapezoid body lesions the major change was in 'c' (P3 of ABEP). The results are compatible with the peripheral generation of the first ABEP components (P1a and P1b). The second component (P2) is generated by ipsilateral CN neurones and their outputs. The third component (P3) is generated primarily by ipsilateral SOC neurones and their outputs, with the ipsilateral CN providing input. The The fourth component (P4) is generated bilaterally by the SOC neurones and their outputs, receiving their inputs from ipsilateral CN. The fifth ABEP component (P5) is generated by structures central to the SOCs and their immediate outputs. Neither focal neuronal nor myelin lesions were sufficient to produce obliteration of any component, consistent with a set of generators for each of the ABEP components, consisting of both cell bodies and their output fibers, that is distributed spatially in the brainstem.

Animals↗

PubMed1991

Three modality evoked potentials in Charcot-Marie-Tooth disease (HMSN-1).

Sixteen patients with dominant hereditary motor-sensory neuropathy type I (HMSN I), members of 5 families, underwent trimodality evoked potential studies. All patients had clinically normal optic nerves. History of deafness was present in 3 patients and sensory-neural hearing defect was found in 5 of 7 patients in whom audiometry was obtained. In 43.7 percent of the subjects significant prolongation of P100 of the VEP was found. Prolongation of N19 of the SEP was found in all 12 subjects examined. Significant bilateral prolongation of peak I of the ABEP was found in 37.5 percent of the subjects and in 50 percent of the ears examined: these findings indicated that in addition to peripheral nerves, the myelin of the optic and cochlear nerves is also affected in HMSN type I.

Adolescent↗

PubMed1991

Applications of three-dimensional analysis to the auditory P300.

Auditory Event Related Potentials (ERPs) to target stimuli were recorded by three orthogonal derivations from 18 normal subjects and were represented in three dimensional voltage-space (3-D), to produce Three Channel Lissajous' Trajectories (3CLTs). Target stimuli differed by pitch, phonemic or phonetic attributes. Assuming a central location, the orientation of the equivalent dipole moment was calculated for specific points (apices) along the trajectories. The apices roughly corresponded to the P300 peak in a voltage/time representation. The 3-D analysis resulted ina dipole pointing in a posterior-upward direction close to the mid-sagittal plane. Based on anatomical measures coupled with the behavioral role of the limbic system, we propose that a major contribution to the P300 to the stimuli tested derives from the outflows of the hippocampus and amygdala, i.e. fornix and stria terminalis. Orientation and laterality of the P300 dipole demonstrated clinical sensitivity beyond that of latency and amplitude measures in voltage/time representations.

Acoustic Stimulation↗

PubMed1991

On the limitation of brainstem auditory evoked potentials for indication of susceptibility to noise.

The efficiency of Brainstem Auditory Evoked Potentials (BAEP) as an indicator of susceptibility to hazardous noise was investigated. In earlier studies, subjects were exposed to very intense occupational noise and temporary threshold shift (TTS) was produced by high intensity noise of 115 dB. Correlations between experimental TTS and the BAEP changes were investigated. BAEP indices, which significant correlations with the eventual hearing loss, were found. Similar criteria, which were found significant in the earlier work, were investigated in 94 industrial workers with normal hearing, without past exposure to noise, using a more moderate TTS-producing noise of 110 dB SPL. Under these conditions, no significant correlation between the noise susceptibility index and BAEP changes during TTS was found. The results of this study demonstrate the limitation of determining individual susceptibility to noise-induced hearing loss using BAEP. TTS-producing noise levels must be high enough. Their predictive value holds only for hearing losses typical of high intensity occupational exposures.

Adolescent↗

PubMed1990

Three-channel Lissajous' trajectories of auditory brainstem evoked potentials: contribution of fast and slow components to planar segment formation.

Three-Channel Lissajous' Trajectories (3CLT) of Auditory Brainstem Evoked Potentials (ABEP) to clicks were obtained after finite impulse response filtering in three frequency bands. These bands were chosen to replicate the widely used passband (100-3000 Hz) and to selectively enhance the definition of the 'pedestal' (10-240 Hz) or the first, third and fifth components (240-483 Hz). Quantitative measures of 3CLT were calculated to describe apex latencies, planar segment orientations, durations, trajectory amplitude peaks and their latencies. In addition, dipole moments at the latencies of apical points along 3-CLT were calculated. The planarity of ABEP 3-CLT segments persisted after selective enhancement of the 'pedestal' or the first, third and fifth components. These results rule out the suggestion that planarity of ABEP segments results from the interaction of the 'pedestal' with the superimposed faster components. These results demonstrate summation of 3-CLT planar segments ('a' 'c' and 'e' with the 'pedestal') to form new segments (wide-band 'a', 'c' and 'e'). With the exception of 'c', planar segments and the equivalent dipole moments associated with apexes did not change orientations across passbands. The effects of passband on the orientation of planar segment 'c' and the dipole moment of its apex are explained by its superimposition on the 'pedestal' in the wide-band records. A similar analysis of ABEP to clicks as compared to low-frequency stimuli (high-pass masked clicks) revealed no change in planarity nor in plane parameters. These results are compatible with the suggestion that the generators of the first, third and fifth ABEP components are curved fiber tracts. The planarity of the slow 'pedestal' may be due to the summation of slow synaptic potentials in auditory brainstem nuclei. These findings indicate that the generators of ABEP are composites that may be separated by selective lesion studies.

Acoustic Stimulation↗

PubMed1990

Brainstem auditory evoked potential with increased stimulus rate in minor head trauma.

Fifteen Minor Head Trauma patients were investigated by Brainstem Auditory Evoked Potentials at 10/s and 55/s stimulus rate. The results were compared with those of the same patients at a second examination, two months later, as well as with a matched normal control group. Increasing the stimulus rate in MHT patients caused a significant but reversible delay in the central conduction time. No significant difference was found regarding the interpeak latency differences at a 10/s stimulus rate. The present study suggests that the primary lesion in MHT is ischaemic, affecting synaptic efficiency, and not axonal damage. These findings may be informative on the as yet obscure pathophysiological mechanism of minor head trauma.

Audiometry, Evoked Response↗

PubMed1989

Miniature fiber-optic pattern-reversal stimulator for determination of the visual evoked potential threshold; comparison with Snellen acuity.

In this report we recommend the estimation of visual acuity by detection of the visual evoked potential (VEP) threshold, defined by the smallest visual angle of a constant check size that evokes potentials. This approach was implemented using a fiber-optic pattern-reversal stimulator placed at measured, increasing distances from the examined eye. Snellen visual acuity as determined in 113 subjects was correlated with the VEP detection threshold. A highly significant correlation was found between visual acuity and the threshold visual angle of check size in subjects whose vision was impaired due to opacity in ocular media. For any given visual acuity a somewhat wide range of threshold check sizes, typically 5-10 min of arc was observed. Technical difficulties that need to be overcome to improve these results are discussed.

Adult↗

PubMed1989

Brain potentials in a memory-scanning task. III. Potentials to the items being memorized.

Cerebral potentials evoked by items presented for memorization in a memory-scanning task were recorded from subjects ranging in age from 18 to 86 years old. Subjects were divided into younger (average age = 29 years) and older groups (average age = 66 years). Both verbal (digits) and non-verbal (musical notes) stimuli were used. Digits were presented in the auditory as well as the visual modality, and notes were presented acoustically. Potentials are described in terms of their scalp distribution, latency, and amplitude and are compared between the young and old subjects. Potentials evoked by the memorized items consisted of a positive (P50-90), negative (N100-150), positive (P185-225) sequence in the first 250 msec following stimulus onset. A sustained potential shift then followed whose amplitude differed with the items being memorized. The shift was positive in the parietal region being largest (5 microV) with verbal items presented visually and slightly smaller (3 microV) with non-verbal auditory stimuli (the notes); in contrast, verbal auditory digits were not associated with a detectable sustained parietal potential shift. In the frontal recordings there was a sustained potential shift accompanying all stimulus types, which was more negative in the young subjects. The amplitude of these sustained potential shifts differed as a function of the position of the item in the memorized set. These results provide electrophysiological evidence of brain activity during memorization that varies with the items being processed as well as differing between young and old subjects.

Acoustic Stimulation↗

PubMed1989

Brain potentials in a memory-scanning task. I. Modality and task effects on potentials to the probes.

Event-related potentials were measured in normal young subjects during a memory-scanning paradigm modified from one proposed by Sternberg. The stimuli used were verbal (digits) and non-verbal (musical notes) with the verbal stimuli and notes presented acoustically and the verbal stimuli also presented visually. In this paradigm each set of stimuli was presented for memorization, and then, after a 2 sec interval, a probe item appeared and was identified by the subject as belonging or not belonging to the memorized set. Memorized set sizes of 1, 3 and 5 items were studied. The potentials are described in terms of scalp distribution, latency and amplitude, and are compared with behavioral descriptors of performance (accuracy and reaction time). These potentials are also compared with those evoked by an auditory target-detection task ('odd-ball' paradigm) in the same subject at the same session. The potentials evoked by the probe stimuli consisted of a positive (P50-90), negative (N100-150), positive (P185-225) sequence in the first 250 msec, followed by a later, long-lasting (approximately 700 msec) positive component (labeled P3). This positivity consisted of an earlier component (latency of approximately 350-400 msec) with a frontal distribution, followed by a larger and later parietal component. The amplitude of the frontal component and the latency of the parietal component varied with the number of items in the memorized set differently from behavioral reaction times. Stimulus modality also affected both the amplitude and latency of the sustained parietal positive potential. Memory processes associated with the P3 complex in the 'odd-ball' task and the long-lasting positivity in the memory-scanning task are discussed.

Adult↗

PubMed1989

Brain potentials in a memory-scanning task. II. Effects of aging on potentials to the probes.

Brain potentials accompanying the classification of probe items as being members of a previously presented list were recorded from subjects ranging in age from 18 to 86 years old. A group of older subjects (average age = 66 years) was compared to a younger group (average age = 29 years). The items tested were verbal (digits) and non-verbal (musical notes). Digits were presented in the auditory and visual modalities, and notes were presented acoustically. Reaction times (RTs) and performance accuracy were computed. Potentials are described in terms of scalp distribution, latency and amplitude as a function of the type of stimulus (verbal/non-verbal, auditory/visual) and age group (younger/older). Evoked potentials to target notes in an auditory target-detection ('odd-ball') task were also recorded for comparison with the memory tasks. Potentials evoked by probes consisted of a sequence of sensory components in the first 250 msec followed by a cognitive component that was positive in polarity and sustained in duration (approximately 700 msec labeled P3), consisting of an earlier frontal component, P3a (mean latency: younger = 385 msec, older = 406 msec), and a large (15 microV) and later parietal constituent, P3b (mean latency: younger = 574 msec, older = 630 msec). The frontal derivation of the younger subjects showed a sustained negative bias of the wave forms in the latency range of 200-500 msec (P2 to P3) compared to the older subjects. Reaction times were longer in older subjects than in younger subjects for all stimulus types and set sizes. For the potentials evoked by the probes the younger group had consistently larger late parietal components (P3b) than the older group, whereas the late frontal potentials (P3a) were larger for the older than younger subjects. Except for visual stimuli, the latencies of the parietal sustained potentials were not influenced by subject age in contrast to the uniform changes in RT for all stimulus types. Significant amplitude and latency effects on the parietal sustained potentials accompanied the different stimulus types and memorized-set sizes which were similar for the two age groups. These results suggest that the effects of aging on short-term memory are primarily on response selection, as evidenced by RT slowing with aging, and not on memory-scanning processes as evidenced by the similarity of the latency measures of the accompanying brain potentials between the two age groups.

Adult↗

PubMed1989

Effects of click polarity on auditory brain-stem potentials: a three-channel Lissajous' trajectory study.

Three-channel Lissajous' trajectories (3CLTs) of the auditory brain-stem evoked potentials (ABEP) were recorded from 16 adult subjects (28 ears) in response to rarefaction (R), condensation (C) and alternating polarity (A) clicks. 3CLTs were analysed and described in terms of their geometrical measures. All 3CLTs included 5 planar segments (named 'a', 'b', 'c', 'd' and 'e') whose latencies, durations, orientations, sizes and shapes were not affected by click polarity. Occasionally, planar segment 'd' was not defined, and its absence was parallelled by the absence of peak IV in the Vertex-Mastoid records. A small (0.03 microV), but significant increase was found in the trajectory amplitude of planar segment 'e' in C clicks. The effects of click polarity on 3CLT observed in this study suggest that some previously described ABEP changes with click polarity were the result of interactions between electrode positions and relative contributions of overlapping generators. The effects on the fourth and fifth ABEP components may be the results of changes in the temporal overlap of the activity of their generators.

Acoustic Stimulation↗

PubMed1989

Brainstem auditory evoked potentials with increased stimulus rate in patients suffering from systemic lupus erythematosus.

Central nervous system involvement in systemic lupus erythematosus is frequently occult, may be the presenting sign, and is a bad prognostic indicator. At present, there is no reliable, sensitive laboratory test for the evaluation and diagnosis of subclinical central nervous system involvement of the disease. Brainstem auditory evoked potentials with and without increased stimulus rate have been used to diagnose ischemic lesions in the central nervous system. Brainstem auditory evoked potentials, with and without increased stimulus rate, was used to investigate 15 systemic lupus erythematosus patients, 20 normal participants, and 5 patients receiving corticosteroids for bronchial asthma. A significant statistical difference was found in the net effect of increased stimulus rate in comparisons of the systemic lupus erythematosus patients with the normal group. Brainstem auditory evoked potentials, with increased stimulus rate, demonstrated subclinical involvement of the central nervous system in systemic lupus erythematosus, reinforcing the notion that increased stimulus rate measures are sensitive to ischemic changes, in this case, even in neurologically asymptomatic patients.

Acoustic Stimulation↗