Abstract
To address the issue of how hippocampal neurons are involved into learning progress, we studied c-Fos expression in rat hippocampal subfields at different stages of appetitive instrumental learning. To model the first stage of learning, we pre-trained animals to approach the lever to obtain the food, and then made this behavior ineffective by not reinforcing it during the last session (“mismatch” group). Another group just acquired lever-pressing behavior at that day (“acquisition” group). Animals of the third group performed this well-trained behavior (“performance” group). The number of Fos-positive neurons in all hippocampal regions of the “mismatch” group animals was higher than in the ones of the home cage control group animals. The number of Fos-positive neurons was increased in CA1 and CA3 areas, but not in the dentate gyrus of both the “acquisition” and “performance” group animals as compared with the control group. We also found segmented c-Fos expression, which was more evident in “acquisition” group animals. Thus, our results suggest that during the first (mismatch) stage of learning hippocampal neurons are activated in an equally distributed manner. The following clustered pattern of activated CA1 neurons during the acquisition stage may reflect specialization of these neurons in respect to the specific lever-pressing behavior.
Highlights
Most behaviors are not learned at once
We found that the overall pattern of hippocampal subfield activations was similar in all groups, but the pattern of neuronal activations inside the CA1 area depended on the learning stage
The results described above demonstrated that distribution of Fos-activated neurons in the hippocampus depended on the learning stage of the appetitive instrumental behavior
Summary
Most behaviors are not learned at once. Instrumental learning progress is often characterized by learning curves based on the success rate [1]. Behavioral characteristics of each stage of instrumental learning should be related to patterns of neuronal activity that underlie this stage. One process that takes place during learning is the development of neuronal activity selectively related to the learned behavior Such experience-dependent “behavioral specialization” of neurons [4] is a stable characteristic [5] [6], which have many examples [7]-[11]. Appearance of such specific activations might be already evident during the earliest newly learned behavioral acts [12] [13]. Experience-dependent changes in activity of single neurons might result in the described phenomenon of correlated or synchronized activities between neurons [15] [16] and establishment of specific neuronal ensembles, groups or systems of coactive neurons where activities are related to the learned task
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