Sensory system development influences the ontogeny of hippocampal associative coding and trace eyeblink conditioning

Abstract

Until recently, it was believed that hippocampal development was the primary rate-limiting factor in the developmental emergence of hippocampal forms of learning, such as trace eyeblink conditioning (EBC). Indeed, hippocampal neuronal activity shows an age-related increase in both complexity and task responsiveness during trace EBC. However, recent work from our laboratory suggests that sensory system development may also play a role. Training with the earlier-developing somatosensory system results in an earlier emergence of trace EBC in rats, suggesting that the development of sensory input to the hippocampus may influence the development of trace EBC. The goal of the current study was to examine the activity of hippocampal CA1 pyramidal cells during acquisition of trace EBC with an early-developing somatosensory CS. Rat pups were trained with a vibration CS on postnatal days (P) 17–19, P21–23, and P24–26 while CA1 pyramidal cell activity was recorded. Results indicated that CA1 neurons show an age-related increase in responsiveness to trial events. Although the magnitude of neuronal responding showed age-related increases in activity, all three age groups demonstrated learning-related increases in firing rate magnitude and peaks in firing rate were evident both at CS onset and offset. These findings suggest that the ontogeny of trace eyeblink conditioning is related to both hippocampal and sensory system development.

Using hippocampal‐dependent eyeblink conditioning to predict individual differences in spatial reorientation strategies in 3‐ to 6‐year‐olds

“…For example, a reduction in the hippocampal neurogenesis of rats has been found to coincide with impaired learning on a hippocampal‐dependent trace EBC task (Shors, Townsend, Zhao, Kozorovitskiy, & Gould, ; Winocur, Wojtowicz, Sekeres, Snyder, & Wang, ). Furthermore, consistent with findings on neuronal activation in the hippocampus of rats during trace EBC (Goldsberry, Kim, & Freeman, ; Plakke, Freeman, & Poremba, ), a functional neuroimaging study with human adults found that the right medial temporal lobe, including the hippocampus, was significantly activated during trace conditioning relative to a non‐hippocampal‐dependent EBC paradigm (Cheng et al, ). Thus, if EBC engages the right rather than left hippocampus, then it may have more underlying neural circuitry in common with spatial reorientation than episodic memory.…”