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Biomedical subjects

J Colombo

Publications and source records attributed to J Colombo.

32 records · Page 2Linked to original sources
PubMed1988

Neonatal behavioral organization and visual processing at three months.

In 2 studies, the Range of State cluster derived from infants' scores on the Neonatal Behavioral Assessment Scale with Kansas Supplements (NBAS-K) was found to correlate significantly with visual discrimination performance at 3 months of age. Contrary to the expectation that NBAS-K orientation scores would predict visual discrimination at 3 months, it was neonatal behavioral state organization that related to later cognitive functioning in infancy.

Child Behavior↗
PubMed1987

Auditory-nerve single-neuron thresholds to electrical stimulation from scala tympani electrodes.

Single auditory-nerve neuron thresholds were studied in sensory-deafened squirrel monkeys to determine the effects of electrical stimulus shape and frequency on single-neuron thresholds. Frequency was separated into its components, pulse width and pulse rate, which were analyzed separately. Square and sinusoidal pulse shapes were compared. There were no or questionably significant threshold differences in charge per phase between sinusoidal and square pulses of the same pulse width. There was a small (less than 0.5 dB) but significant threshold advantage for 200 microseconds/phase pulses delivered at low pulse rates (156 pps) compared to higher pulse rates (625 pps and 2500 pps). Pulse width was demonstrated to be the prime determinant of single-neuron threshold, resulting in strength-duration curves similar to other mammalian myelinated neurons, but with longer chronaxies. The most efficient electrical stimulus pulse width to use for cochlear implant stimulation was determined to be 100 microseconds/phase. This pulse width delivers the lowest charge/phase at threshold. The single-neuron strength-duration curves were compared to strength-duration curves of a computer model based on the specific anatomy of auditory-nerve neurons. The membrane capacitance and resulting chronaxie of the model can be varied by altering the length of the unmyelinated termination of the neuron, representing the unmyelinated portion of the neuron between the habenula perforata and the hair cell. This unmyelinated segment of the auditory-nerve neuron may be subject to aminoglycoside damage. Simulating a 10 micron unmyelinated termination for this model neuron produces a strength-duration curve that closely fits the single-neuron data obtained from aminoglycoside deafened animals. Both the model and the single-neuron strength-duration curves differ significantly from behavioral threshold data obtained from monkeys and humans with cochlear implants. This discrepancy can best be explained by the involvement of higher level neurologic processes in the behavioral responses. These findings suggest that the basic principles of neural membrane function must be considered in developing or analyzing electrical stimulation strategies for cochlear prostheses if the appropriate stimulation of frequency specific populations of auditory-nerve neurons is the objective.

Animals↗
PubMed1987

A model of electrical excitation of the mammalian auditory-nerve neuron.

A model of the mammalian auditory-nerve neuron has been developed based on the classical work of Frankenhauser and Huxley [(1964) J. Physiol. 171, 302-315], modified by McNeal [(1976) IEEE Trans. Biomed. Eng. BME-23, 329-336], and Reilly et al. [(1985) IEEE Trans. Biomed. Eng. BME-32, 1001-1011], and fine tuned to represent physiological data obtained from single auditory-nerve fiber experiments in squirrel monkeys. The model is capable of reproducing neural action potential waveforms due to electrical stimulation, and can reliably predict action potential thresholds and strength-duration curves. This paper explains the derivation of the mathematical model and the effects of varying certain independent parameters including fiber diameter, length of the nodes of Ranvier, internodal length, and myelin thickness. The model parameters were selected according to the anatomical findings of Liberman and Oliver [(1984) J. Comp. Neurol. 223, 163-176], and Liberman (Pers. Commun.). The length of the unmyelinated termination of the auditory-nerve that survives after aminoglycoside damage to the inner ear has not been experimentally determined. Therefore, it was investigated as an independent variable in the model. An unmyelinated terminal length of 10.0 micron was found to most accurately describe the experimental neural strength-duration curves obtained from aminoglycoside-deafened squirrel monkeys. The parameter that had the next most significant effect on the model was fiber diameter which affects all conduction pathways, across the membrane and through the fiber. Finally the results of the model are compared with behavioral data obtained from patients and monkeys implanted with cochlear prostheses. In the companion paper [(1987) Hear. Res. 31, 267-286] predictions of the model are quantitatively compared with single-neuron data from squirrel monkeys.

Animals↗
PubMed1987

The stability of visual habituation during the first year of life.

The short-term reliability and long-term stability of visual habituation and dishabituation in infancy were assessed in a sample of 186 infants from 4 age groups (3-, 4-, 7-, and 9-month-olds) seen for 2 within-age sessions and in a sample of 69 infants seen longitudinally at 3, 4, 7, and 9 months of age. Moderate week-to-week reliability (r's = .30-.50) was observed for duration-based and magnitude of habituation variables at all ages, although better reliability was evident at 4 and 9 months than at 3 and 7 months. In most cases, the reliability of habituation magnitude measures was attributable to the reliability of the peak fixation alone. Data from the longitudinal sample suggested that only the duration of peak fixation was consistently stable across the ages tested, although stability for several measures emerged across the 7-9-month testing. No consistent reliability or stability emerged for the presence or magnitude of dishabituation in either sample.

Age Factors↗
PubMed1986

Infants' attentional responses to frequency modulated sweeps.

In 3 experiments, the attentional responses of 4-month-old infants to frequency-modulated (FM) sweeps corresponding to the frequency range of adult-to-infant and adult-to-adult intonation patterns were assessed. In Experiment 1, infants were observed to discriminate "exaggerated" (i.e., adult-to-infant) FM sweeps from "normal" (i.e., adult-to-adult) FM sweeps in a habituation-dishabituation paradigm but did not selectively attend to one over the other. In Experiment 2, where the same stimuli were used in a paired-comparison paradigm, again no differential attention was observed. In Experiment 3, the most exaggerated sweep was paired against a continuous, monotonic pure tone, but again no difference in salience was observed. These data suggest that the extent of modulation or intonation of an auditory stimulus per se does not constitute a salient cue for infants' attention to sound.

Arousal↗
PubMed1985

Spectral complexity and infant attention.

In two experiments, infants selectively attended to auditory stimuli that presented an increasingly complex spectral structure. Using 2- and 4-month-olds as subjects, the first study demonstrated this selectivity in comparison to the rate of acoustic change. The second study demonstrated the increased attention of 4-month-olds in response to an increasingly complex structure. Results are discussed with respect to the neural activity produced by these stimuli along the auditory pathway, and an analogy to the literature on visual attention is drawn.

Acoustic Stimulation↗
PubMed1984

Stimulus context and infant orientation discrimination.

In three experiments, the effect of additional "contextual" elements on the discrimination of the orientation of linear and curvilinear segments was investigated with 4-month-old infants. In Experiment 1, paired visual matrices (one which contained some irregularity in orientation of internal elements, vs one which contained no irregularities) were presented. Infants detected irregular matrices significantly better than chance, but such detection was not aided by contextual elements. Discrimination of orientation in Experiment 2 was assessed with a paired-comparison familiarization-novelty paradigm. It was found that the addition of elements here significantly aided discrimination of linear segment orientation, but not curvilinear segment orientation. Experiment 3 investigated why this effect was not found for curvilinear segments; after equating the curvilinear stimuli to linear ones used in Experiment 2 with respect to the closedness of figure, discrimination of curvilinear orientation was observed.

Female↗
PubMed1979

Plasma gamma-glutamyl transpeptidase in heroin addicts.

Plasma gamma-glutamyl transpeptidase was measured in 25 heroin addicts. The purpose was to find out if the long term administration of heroin would lead to a stimulation of GGTP due to the detoxication of this drug in the endoplasmatic reticulum of the liver. In 10 patients the elevation of GGTP could be attributed to liver damage, since other liver enzymes were also increased. 15 patients had normal GGTP activities, in 4 of them accompanied by minor elevations of single other hepatic enzymes. In 11 patients the GGTP activity as weel as that of the other enzymes was normal despite heavy chronic herioin abuse. It is therefore improbable that GGTP can be used to diagnose abuse of this drug and to evaluate the progress of drug detoxication treatments and drug abstention as has been proposed in chronic alcoholism.

Adolescent↗
PubMedDate not supplied

Establishing pharmaceutical care services in an HIV clinic.

OBJECTIVE: To present a brief overview of human immunodeficiency virus (HIV) infection and to describe the implementation of pharmaceutical care services for adult patients with HIV infection. SETTING: University hospital clinic. PRACTICE DESCRIPTION: A pharmacist joined a multidisciplinary team serving HIV-infected patients in January 1994. PRACTICE INNOVATION: Current pharmacy services include taking medication histories, educating patients, counseling patients on compliance, monitoring response to therapy, identifying drug-related problems, documenting all interventions, and making therapeutic decisions and formulary choices. The pharmacist also participates in research. INTERVENTIONS: The pharmacist sees patients immediately after their physician appointments. Patients with one or more of the following characteristics are targeted to receive pharmaceutical care: multiple drugs, history of noncompliance, initiation of new drug therapy, recently discharged from hospital or emergency department, identification of potential adverse effects, identification of potential drug-drug interactions, and presence of drug toxicities. CONCLUSION: Pharmacists are uniquely qualified to provide a wide range of pharmaceutical care services to HIV-positive patients. Pharmacy interventions should lead to improved outcomes and decreased costs for a chronic and very expensive disease.

Adult↗
PubMedDate not supplied

Individual and developmental differences in disengagement of fixation in early infancy.

The current study investigated whether individual and developmental differences in look duration are correlated with the latency for infants to disengage fixation from a visual stimulus. Ninety-four infants (52 3-month-olds, 42 4-month-olds) were tested in a procedure that measured ocular reaction time to shift fixation from a central target to a peripheral target under conditions in which the central-target either remained present ("competition" condition) or was removed from the display ("noncompetition" condition). Look duration was correlated with disengagement latency; longer-looking infants were slower than shorter-looking infants to shift fixation to the peripheral target on competition trials, but not noncompetition trials. Results were similar for 3- and 4-month-olds, although 3-month-olds showed slower latencies on all trials. Furthermore, long-looking infants were not consistently slower, but rather showed greater variability in their response latencies under conditions that required disengagement of fixation. The results support the position that developmental and individual differences in look duration are linked to the development of the neural attentional systems that control the ability to disengage, or inhibit, visual fixation.

Analysis of Variance↗
PubMedDate not supplied

Heart rate-defined phases of attention, look duration, and infant performance in the paired-comparison paradigm.

Four-month-old infants (N = 68) were tested in a paired-comparison familiarization-novelty recognition task in which the length of choice trials was systematically manipulated. Peak look duration during pretest and familiarization periods significantly predicted a dichotomous measure of recognition performance, but recognition was unaffected by choice-trial length. Heart rate (HR) was simultaneously assessed during the task, and the amount of time infants spent in various HR-defined phases of attention was assessed. Longer durations of looking during pretest and familiarization were significantly associated with more time spent in both sustained attention (SA) and attention termination (AT). Of these two variables, only individual differences in AT accounted for significant variance in recognition memory performance. A final analysis addressed the possibility that individual differences in AT mediated the relation between look duration and recognition performance. These findings provide support for the hypothesis that individual differences in the disengagement of attention underlie the relation between look duration and cognitive performance in early to midinfancy.

Attention↗