The ontogeny of hippocampal theta power onset during associative learning

초록

The development of hippocampus is accompanied by the emergence of many types of learning and memory. In a previous study (Kim et al., 2016), the ontogeny of hippocampal function was examined by analyzing neural signals from the dorsal hippocampal CA1 area while rat pups performed an associative learning task. During delay eyeblink conditioning, where a tone conditioned stimulus and a periorbital stimulation unconditioned stimulus were presented, three different postnatal (P) age groups showed varying learning rates and neural activity. Specifically, the P24-26 group exhibited higher theta (4-10 Hz) power and conditioned responses; however, the underlying mechanisms were not fully understood. The current study reanalyzed the theta activity reported in Kim et al., 2016 to investigate whether the higher theta power found in the older age group was due to more frequent occurrences of theta power or longer theta durations. The results indicated that the temporal aspects of theta oscillations are affected by associative learning, while the onset of theta power is affected by ontogenetic change. As hippocampal development progresses, theta power becomes more available, which, in turn, increases the chances of the components in associative learning being processed more often in the older age group. These findings suggest that the ontogenetic development of the hippocampus contributes to various mnemonic behaviors through frequent occurrences of hippocampal theta power.

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