PhD Transfer Exam
Thursday July 20th, 2017 at 1:10 pm – Ramsay Wright Building, RW 432
Xiao Yu (Takehara-Nishiuchi Lab)
” Prefrontal long-range projection facilitating the formation of temporal association”
The ability to form associations between related events separated in time is important as it allows us to adapt to similar events in the future based on past experiences. I recently found that chemogenetic enhancement of neuron activity in the medial prefrontal cortex (mPFC) enables rats to form stimulus associations over a temporal gap that was prohibitively long for untreated rats to learn. Accompanying this improved learning were ramping increases of theta and beta oscillations in the mPFC during the temporal gap. These findings suggest that mPFC network activity during the gap determines whether two stimuli are associated across the gap. My recent and future work extend this finding in two directions. First, I show that enhancing mPFC activity after learning had no effect on memory formation, suggesting that elevated mPFC activity during learning is critical for memory enhancement. Second, to determine long-range projections through which mPFC activity enhances memory formation, I traced mPFC efferent projections and identified sub regions and cortical layers at which mPFC projections terminate. This, along with past behavioral literature, led me to hypothesize that mPFC projections to the lateral entorhinal cortex (LEC), nucleus reuniens (RE), and mediodorsal thalamus (MD) may be involved in memory enhancement. To test this idea, I will examine the impact of selective chemogenetic activation of the mPFC projections to one of these efferent regions on the formation of temporal associative memories. I will also monitor the activity of mPFC axon terminals in these efferent regions while rats form temporal stimulus associations while learning to ignore irrelevant stimuli. Through these two complementary experiments, I will be able to uncover how the mPFC routes the information on the behavioral relevance of stimuli to specific downstream targets, thereby uncovering a circuit basis on memory regulation by the mPFC.