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Biomedical subjects

H S Hoffman

Publications and source records attributed to H S Hoffman.

At least 19 recordsLinked to original sources
PubMed1991

Comparison of reflex modification procedures and auditory brainstem response in high-risk neonates.

This study compared the results of reflex modification (RM)--an objective technique for assessing brainstem sensorineural processing--with those of auditory brainstem response (ABR) for a group of high-risk infants at comparable postconceptional ages. For the RM procedure, an eyeblink-eliciting tap to the glabella was presented either alone or accompanied by a brief 90dB SPL tone. 37 high-risk infants were tested with both RM and ABR at a mean postconceptional age of 37.3 weeks. Seven had an increased brainstem conduction time ('failed ABR') and eight did not exhibit significant reflex augmentation ('failed RM'), seven of whom also failed the ABR. These data provide evidence that sensory stimuli which affect the neural mechanisms responsible for the organization of the startle response and auditory processing share essential neural components.

Auditory Pathways↗
PubMed1991

Cardiac reactions to two psychological stressors, acting in combination.

56 student volunteers (mean age 21 yr.) participated in a study designed to assess how the Stroop procedure and delayed auditory feedback affect cardiac activity when they are used individually as well as when they are combined in the same task. In a preliminary study, listening to tape-recorded instructions on how to relax produced a significant decrease in cardiac activity. In the major study, when used individually, both the Stroop procedure and delayed auditory feedback produced significant increases in cardiac activity. The largest increase, however, occurred with systolic blood pressure and was induced by delayed auditory feedback. When the Stroop procedure was used in combination with delayed auditory feedback, systolic blood pressure again increased, but this effect was no greater than when delayed auditory feedback was used alone. This pattern of results implies that, when combined, the Stroop procedure and delayed auditory feedback have largely independent effects on cardiac activity and that, when tested under similar conditions, delayed auditory feedback has the larger effect.

Adult↗
PubMed1990

The blink reflex: maturation and modification in the neonate.

The onset and development of the delayed blink response, elicited by a tap to the glabella, and its modification by an acoustic stimulus (tone), were studied longitudinally in 36 healthy preterm and 43 term infants. Blink amplitude increased with gestational age. By term postconceptional age, the responses of the preterm infants to tap alone, and to both tap and tone, were not significantly different from those of the term infants. These results suggest that neurological development, as reflected by the blink reflex and its modification, proceeds in an orderly, sequential fashion and that the mechanisms affecting these brainstem processes are not altered by environmental influences.

Blinking↗
PubMed1989

Sensory processing in the term and preterm infant: use of reflex modification procedures.

The present study uses the glabellar reflex and reflex modification procedures to assess acoustic and tactile sensory processing capabilities in the human neonate. Fourteen term infants and 28 clinically stable preterm infants were given identical test paradigms. Augmentation testing consisted of a 16 V dc tap presented simultaneously with a 90 dB SPL tone; inhibition testing consisted of a 16 V tap preceded 900 msec. by an identical tap. All 14 term infants showed augmentation with 8 of 14 at p less than 0.05 level and eleven of 14 showed significant inhibition at the 900 msec intertap interval. However, only 12 of 28 preterm infants demonstrated significant augmentation and none showed reliable inhibition. These data indicate that areas of the central nervous system that process sensory stimuli are not fully developed at the time of birth even in the term infant. Further, the neural system for augmentation and inhibition may be independent of each other.

Acoustic Stimulation↗
PubMed1989

Altered brainstem sensory processing as assessed by reflex modification procedures in infants at risk for apnea.

Reflex modification procedures were used to test sensory processing in premature infants to examine the relationship between respiratory abnormalities and brainstem neuronal function. A total of 73 premature infants at risk for apnea and/or infants receiving methylxanthine therapy was given a 12-h pneumocardiogram and reflex modification test at a comparable postconceptional age, before discharge. Reflex modification was tested using a controlled eyeblink-eliciting tap to the glabella presented either alone or with a 1 kHz 90-dB SPL tone. The amplitude of the glabellar tap eyeblink and acoustically modified blink were lower in infants discharged on cardiac/apnea monitors (n = 36) than in the unmonitored group (1.44 and 1.59 volts versus 2.15 and 2.39 V, p less than 0.005, respectively). At follow-up, 12 monitored infants had clinically significant apnea after discharge. The records of this subgroup of infants revealed a significantly lower augmentation of the glabellar eyeblink response when compared to all infants screened for respiratory abnormalities and to the other monitored babies (p less than 0.01). The data suggest that abnormalities of the ventilatory pattern and occurrence of clinical apnea in preterm infants may in some measure be related to acoustic sensory processing, implying an alteration of brainstem neuronal function and organization.

Acoustic Stimulation↗
PubMed1988

Reflex modification audiometry: assessment of acoustic sensory processing in the term neonate.

Behavioral and physiological work in animals and adult humans have established the sensitivity of various procedures and allowed delineation of the neuroanatomical pathways involved in sensory processing. Herein we used the glabellar reflex and reflex modification procedures to assess acoustic sensory processing capabilities in the term newborn infant. The eyeblink-eliciting device consisted of a miniature solenoid which could deliver a controlled tap. A photoreflective densitometer attached to a TDH-39 earphone assessed the eyeblinks. A total of 98 term infants was studied to determine how a response to a reflex-eliciting event (tap) was modified (either augmented or inhibited) by a mild exteroceptive stimulus (tone) which was presented at an appropriate lead interval. Ninety adult subjects were given identical testing procedures and their data were compared to that of the infants. The results of this study showed that newborn infants reliably exhibited an eyeblink response after a tap to the glabella. With fixed intensity tones, frequencies from 1 to 4 kHz produced equivalent amounts of reflex augmentation in infants and adult subjects. Blink amplitude increased as a function of increased tap and tone intensity in both infants and adults. State change was shown to affect the amplitude of the reflexive eyeblink, but not the augmentation effect. However, neonates failed to show inhibition to either acoustic lactile stimuli at an interstimulus interval that produced significant inhibition in the adult. These data indicate that reflex modification procedures provide an objective assessment of acoustic sensory processing in the term neonate.(ABSTRACT TRUNCATED AT 250 WORDS)

Acoustic Stimulation↗
PubMed1987

Inhibition of the eyeblink reflex in the human infant.

In human adults the eyeblink elicited by a given stimulus can be inhibited if that stimulus is preceded by another stimulus at an appropriate lead interval. In the present work, pairs of eyeblink-eliciting stimuli separated by 300-1200 msec were presented to sleeping preterm and full-term infants as well as to adults. Preterm infants did not exhibit reliable inhibition at any interval. Full-term infants did so, but they required longer interstimulus intervals than were needed for inhibition in the adult subjects. Results imply that the neural systems that mediate reflex inhibition are functional at birth, but that they are relatively slow to act.

Adolescent↗
PubMed1986

Reflex augmentation of a tap-elicited eyeblink: the effects of tone frequency and tap intensity.

The amplitude of the human eyeblink elicited by a mild tap between the eyebrows can be increased if a brief tone is presented simultaneously with the tap. In two experiments we examined how this reflex augmentation effect varies with changes in the frequency characteristics of the tone and with changes in the intensity of the tap. We also examined how these effects change in the course of development. For newborn infants and for adults, fixed intensity tones with frequencies of either 1, 2, or 4 kHz produced equivalent amounts of reflex augmentation. Furthermore, while blink amplitude was an increasing function of tap intensity in both populations, the amount of reflex augmentation engendered by a simultaneously presented tone was independent of the intensity of the tap.

Acoustic Stimulation↗
PubMed1985

Reflex modification by acoustic signals in newborn infants and in adults.

This research asked whether the reflexive eyeblink elicited by a tap to the glabella (the flat region of skin between the eyebrows) is modified by acoustic signals which either precede or accompany the tap. Five experiments employing identical reflex modification procedures on neonates and adults suggest developmental differences in processing auditory stimuli. Neonates failed to exhibit reflex inhibition by either prior acoustic or tactile stimuli. Adults exhibited robust reflex inhibition to these same stimuli. Neonates, however, exhibited reliable reflex augmentation when mild (70 dB re: 0.0002 dyne/cm2) tones were presented simultaneously with the tap. For adults, tone intensities of at least 90 dB were necessary to obtain reliable reflex augmentation. The developmental processes implied by these findings are discussed.

Acoustic Stimulation↗
PubMed1985

Reflex modification in the rat: the inhibitory effects of intensity and frequency changes in steady tones.

In laboratory rats (as in humans) a low-intensity tone that precedes a high-intensity burst of noise by approximately 100 ms can reduce the amplitude of the startle reaction elicited by the burst of noise. A series of four experiments with rats investigated the relation between the inhibitory effects of tonal frequency change and the length of the silent period (gap) preceding it. The major findings were the following: (a) A gap in an otherwise continuous pure tone inhibited startle when the gap occurred approximately 100 ms prior to the noise burst. (b) Although an increase in gap duration increased the inhibition afforded by the gap, the maximum inhibition was yielded by gaps of 100 ms and greater; this maximum was equivalent to the inhibition yielded by the presentation of a postgap tone alone. (c) A shift in tonal frequency across a 10-ms gap yielded more inhibition than did the same gap with no frequency shift; again the shift yielded equivalent inhibition to the presentation of the postgap tone alone. (d) An increase in the frequency shift increased inhibition when the shift occurred across a 10-ms gap, but not when the shift occurred across a 100-ms gap.

Acoustic Stimulation↗
PubMed1976

Modification of the rat's acoustic startle response by antecedent visual stimulation.

Male hooded and albino rats were exposed to a light flash followed at various temporal intervals by a startle-eliciting 117 db. (re 20 muN/m2) burst of white noise. The visual stimulus engendered startle response inhibition (maximally when the lead time was 64-250 msec) as well as startle response latency reduction (maximally when the lead time was 2-8 msec). The temporal functions for the effects of visual stimuli paralleled those previously reported for startle modification by acoustic events. Further study revealed that, given optimal lead times, inhibition is produced reliably by weaker visual stimuli (3 X 10-6 cd-sec/cm2) than latency reduction (3 X 10-4 cd-sec/cm2). This differential sensitivity to visual stimuli is also analogous to previously reported findings for events in the acoustic environment. It reveals that the neural mechanisms that mediate latency reduction and inhibition can be engaged by either acoustic or visual stimulation.

Acoustic Stimulation↗
PubMed1976

Modification of the pigeon's visual startle reaction by the sensory environment.

A series of seven experiments related amplitude and latency of the pigeon's startle response, elicited by an intense visual stimulus, to antecedent auditory and visual events in the sensory environment. The data indicated that (a) within broad limits the amplitude of the reflex is a positive function of the intensity of the sensory background prevailing at the time of startle elicitation, (b) a change in the sensory environment occurring 15-2,000 msec prior to the startle-eliciting stimulus inhibits the amplitude of the response, and (c) a change in the sensory environment less than 10 msec prior to the startle-eliciting stimulus reduces the latency of the response. These findings are consistent with previous research on acoustic elicited startle in the rat. The overall configuration of the results suggests that a pathway including the reticulospinal tract and the bulbopontine reticular nuclei could be the major mediator of startle. In these terms, latency-reduction effects would occur because of partial activation of this pathway, amplitude inhibition would occur because of cerebellar influence, and amplitude facilitation would reflect cerebral or striatal influences.

Acoustic Stimulation↗
PubMed1975

The role of small changes in the acoustic environment in modifying the startle reflex.

When either the intensity or frequency spectrum of an approximately 70-db. SPL narrow-band noise was abruptly changed by a small amount, the rat's response to a startle stimulus presented 64 msec later was inhibited. When similar small frequency changes preceded the startle stimulus by ony 5 msec, the latency of the startle response was reduced, but even relatively large changes in intensity of the antecedent stimulus had no effect on response latency. These findings provide added support for the generalization that the neural processes associated with startle are engaged by small changes in the auditory environment. They also point to a measure of separation between the processes responsible for inhibition and those responsible for latency shift.

Animals↗