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Prestimulation effects on blink and cardiac reflexes of 15-month human infants
M T Balaban1, B J Anthony, F K Graham
1University of Wisconsin.
Insights
Infant startle reflex modulation shows developmental differences. At 15 months, brief prestimulation shortened blink latency and attenuated heart rate, but did not significantly alter blink magnitude, indicating complex reflex development.
Area of Science:
- Developmental psychology
- Neuroscience
- Human infant studies
Background:
- Reflex startle modulation by prestimulation is established in adult species.
- This phenomenon follows a complex developmental trajectory in humans.
- Previous research indicated a lack of typical inhibitory modulation in 15-month-old infants.
Purpose of the Study:
- To investigate prestimulus effects on the startle reflex in 15-month-old human infants.
- To assess developmental changes in startle blink magnitude and latency.
- To examine concurrent heart rate responses to auditory stimuli in infants.
Main Methods:
- Measured startle blink magnitude and onset latency in infants.
- Recorded concurrent heart rate changes.
- Utilized single-stimulus (tone, white noise) and paired-stimulus conditions (tone followed by noise at 125ms and 225ms intervals).
Main Results:
- Paired conditions showed insignificant increases in blink magnitude compared to noise alone.
- Significant shortening of blink onset latency was observed in paired conditions.
- Significant attenuation of heart rate responses occurred under paired-stimulus conditions.
Conclusions:
- Findings suggest a dissociation between blink magnitude and latency modulation in infant startle reflexes.
- Evidence points to a dissociation between somatic (blink) and autonomic (heart rate) reflex modulation.
- The study highlights the complex and ongoing development of reflex modulation in human infants.
Abstract:
Reduction of reflex startle by brief changes in prestimulation is a robust phenomenon in adults of several species. Although the phenomenon does not require structures above midbrain, it has a long and uneven developmental course. This study of human infants assessed prestimulus effects at 15 months, within a period which has failed, in past work, to show the usual inhibitory modulation. Magnitude and onset latency of the startle blink and concurrent changes in heart rate were measured under four conditions: 2 single-stimulus conditions, 25-msec, 84-dB, 1000-Hz tone or 50-msec, 109-dB white noise; 2 paired-stimulus conditions, noise bursts preceded by tone at lead times of 125 msec or 225 msec. Compared to noise-alone, paired conditions elicited insignificant increases in blink size, significant shortening of blink onset latency, and significant attenuation of heart rate responses. The findings add to growing evidence of a dissociation between modulating effects on blink magnitude and latency and of a dissociation between modulating effects on somatic and autonomic reflexes.