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Age of first appearance of simultaneous and successive negative contrast in infant rats
Insights
Young rats can distinguish between different reward sizes early on. However, paradoxical effects like simultaneous and successive negative contrast emerge later, with successive negative contrast appearing by 17 days of age.
Area of Science:
- Behavioral Neuroscience
- Developmental Psychology
- Animal Behavior
Background:
- Simultaneous negative contrast (SimNC) and successive negative contrast (SNC) are paradoxical effects related to changes in reward magnitude.
- Understanding the developmental emergence of these effects is crucial for cognitive and behavioral research.
Purpose of the Study:
- To investigate the emergence of SimNC and SNC in developing rats from 11 to 17 days of age.
- To determine the age at which rats exhibit these paradoxical reward effects.
Main Methods:
- Rats aged 11, 14, and 17 days were exposed to different reward magnitudes (milk vs. dry suckling).
- Behavioral measures included attachment latencies and runway speeds to assess discrimination and contrast effects.
- Experiments specifically tested SimNC and SNC under controlled conditions.
Main Results:
- Rats at all tested ages (11, 14, 17 days) could discriminate between cues for large and small rewards.
- SimNC emerged at 14 and 17 days, but not at 11 days, indicating a developmental delay.
- SNC was observed at 17 days but not 14 days in attachment measures, and not at either age in runway measures.
Conclusions:
- The ability to discriminate reward magnitude develops earlier than the emergence of paradoxical contrast effects (SimNC and SNC).
- Successive negative contrast appears to emerge later than simultaneous negative contrast in developing rats.
- These findings contribute to understanding the developmental trajectory of reward processing and decision-making.
Abstract:
Simultaneous (SimNC) and successive negative contrast (SNC), two paradoxical effects that are related to shifts in reward magnitude, were studied in rats from 11 to 17 days of age. Experiments 1 and 2 looked at the emergence of SimNC at 11, 14, and 17 days. At all of these ages, rats were able to discriminate between the large (milk suckling) and small (dry suckling) reward odor cues as measured by attachment latencies, but only the 14- and 17-day-olds showed SimNC. At none of the three ages was a discrimination formed to the differential odor cues in the alley in terms of runway speeds. Experiment 3 was designed as a further test of the absence of SimNC at 11 days. In this experiment, the pups were placed directly on the dam's ventrum to facilitate attachment. As in the earlier experiment, the 11-day-old pups discriminated between the odors signaling the two reward conditions but did not show the SimNC effect. In Experiment 4, SNC was measured in pups 14 and 17 days of age. SNC was shown at 17 days but not at 14 days in the attachment latency measure and at neither age in the run measure. These four experiments extend our earlier findings that the paradoxical effects that emerge out of intermittent schedules of reward magnitude occur earlier than those associated with single abrupt shifts in reward magnitude.