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Patterned (single) alternation in infant rats after combined or separate lesions of hippocampus and amygdala
N J Lobaugh1, P L Greene, M Grant
1Department of Psychology, University of Texas, Austin 78712.
Insights
The developing hippocampus and amygdala play crucial roles in patterned alternation (PA) learning in infant rats, especially with longer intertrial intervals. Combined lesions impair PA more than individual lesions.
Area of Science:
- Neuroscience
- Developmental Psychology
- Behavioral Neuroscience
Background:
- The developing brain exhibits distinct neuroplasticity and memory functions.
- The hippocampus and amygdala are critical for learning and memory consolidation.
- Patterned alternation (PA) is a measure of learning and memory in infant animals.
Purpose of the Study:
- To investigate the roles of the developing hippocampus and amygdala in patterned alternation (PA) learning in infant rats.
- To determine how hippocampal and amygdaloid lesions affect PA performance across different intertrial intervals (ITIs).
- To examine the combined effects of hippocampal and amygdaloid lesions on PA.
Main Methods:
- Infant rats (10-11 days old) received bilateral electrolytic hippocampal or amygdaloid lesions, or sham surgeries.
- Animals were trained on a straight runway task for patterned alternation (PA) with varying intertrial intervals (30-60 seconds).
- Performance was assessed based on the emergence and size of PA.
Main Results:
- Hippocampal lesions impaired PA learning at longer intertrial intervals (30-60s) but not at shorter intervals (8-15s).
- Amygdaloid lesions alone did not affect PA learning at an 8s ITI.
- Combined hippocampal and amygdaloid lesions significantly delayed PA emergence and reduced its size, even at a short 8s ITI.
Conclusions:
- The hippocampus is essential for PA learning, particularly with longer intertrial intervals.
- The amygdala contributes to PA learning, especially when combined with hippocampal involvement.
- These findings suggest distinct and interacting roles for the hippocampus and amygdala in the development of memory functions.
Abstract:
The role of the developing hippocampus and the amygdala on patterned (single) alternation (PA) in the infant rat was investigated in 4 experiments. In Experiments 1 and 2, pups were given 2 bilateral electrolytic hippocampal lesions or sham surgeries at 10 or 11 days of age and were trained 6 days later in a straight runway. In Experiment 1, there were 120 trials in 1 day, with an 8-, a 15-, or a 30-s intertrial interval (ITI). PA learning occurred in lesion and sham pups at the 8- and 15-s ITIs, but it was reduced in both groups at the 30-s ITI. In Experiment 2, training was extended to 240 trials over 2 days, with a 30- or 60-s ITI. Sham and lesion pups showed PA at the 30-s ITI, but the emergence of PA was delayed in the lesion pups at the 60-s ITI. In Experiment 3, amygdaloid lesions had no effect on PA learning at the 8-s ITI. However, when pups with hippocampal and amygdaloid lesions were trained at the 8-s ITI, the emergence of PA was delayed, and its size was reduced (Experiment 4). The results of these experiments argue for a role of the hippocampus in PA learning at long ITIs and suggest that, even in 16-day-old pups exposed to an 8-s ITI, the combined hippocampal and amygdaloid lesion produces a deficit greater than either the hippocampal or the amygdaloid lesion. The results are discussed in relation to current theories that distinguish between 2 levels of memory function.