Reflex modification by the human auditory startle blink by antecedent interruption of a visual stimulus.

The effect of a preceding brief interruption in the illumination of a small numeral eight on the auditory startle blink was investigated in human subjects. In Exp. 1 (n = 9) trials were given in which a 20-msec. interruption of the visual stimulus preceded elicitation of the startle blink by a loud tone at intervals from 80 to 200 msec. Compared to trials on which the digit was continuously lit but the reflex was elicited, the blink was augmented at 80 msec. and depressed at longer intervals. Exp. 2 (n = 24) showed that the depressive effect peaked at about 200 msec. and did not depend upon requiring subjects to make judgements concerning the stimuli. In Exp. 3 (n = 17) dark intervals ranged from 1.25 msec. to 40 msec. and preceded the loud tone by 200 msec. Reflex effects paralleled subjects' reports: dark intervals of 10 msec. or greater reliably inhibited the reflex and subjects reported seeing the dark interval at least 50% of the time at intervals of 8 msec. or greater, suggesting that the reflex method may be useful as an alternative objective technique for measuring visual temporal resolution.

Animal models of declining memory in the aged: short-term and spatial memory in the aged rat.

Short-term and spatial memory were studied in Fischer 344 rats ranging in age from 6 to 26 months of age. Spatial memory, as measured by performance in an 8-armed radial maze, declined gradually with age. In contrast, short-term memory, as measured by retention of previous choices in the spatial maze over short intervals and performance on a modified form of Konorski's discriminated delayed response task, did not decline differentially as a function of age. These findings may be comparable to those obtained in the aged human, who also show marked deficits in spatial memory and little change in primary memory under appropriate test conditions.

Motor and reflexive behavior in the aging rat.

Four age groups of Fischer 344 rats (6-, 12-, 18-, and 24-months of age) were compared on a battery of reflexive and locomotor tasks. The simple reflexive tasks such as placing, hopping, negative geotaxis and surface and mid-air righting showed little or no change as a function of age. In contrast, tasks requiring more coordinated control of motor and reflexive responses such as suspension from a horizontal wire, descent of a wire mesh pole, traversal of an elevated platform and rotorod performance showed significant declines with age, with some declines noticeable early in the lifespan. When these results are compared with the results of tasks conducted with infant rats, it is noted that the reflexive and motor skills that emerge early in development are the least affected by the aging process. This observation suggests a first-in, last-out sequence for reflexive and motor behaviors.

Acoustic startle reflexes in the rat during consummatory behavior.

Auditory startle reflexes were elicited in thirsty rats when they were drinking water or were between drinking boutsmthe reaction was greater during drinking, this enhancement developing over the first few seconds after drinking onset. The startle reaction was lowest immediately after the termination of drinking. Reflex enhancement was reduced when thirsty rats drank milk rather than the more preferred water. The reflex was smaller with increased water deprivation, but enhancement produced by drinking was apparent at all levels of deprivation studied, satiety to 4-days deprivation. The inhibitory effect of a preliminary stimulus was not affected by consummatory behavior. Attention is drawn to suggestive parallels between these behavioral effects and other consequences of consummatory activity, primarily having to do with electrophysiological events and arousal processes