This 2015 Norwegian rodent study provided:
“New insights into the molecular underpinnings of synaptic plasticity.
We report the first global transcriptome [all RNA found in specific cells] analysis of in vivo synaptic plasticity, using the well-established model of LTP [long-term potentiation, an increase in synaptic strength that underlies memory] in the rat dentate gyrus [a region of the hippocampus where neurogenesis occurs].
We have identified a number of novel lncRNAs [long (more than 200 nucleotides) noncoding (non-protein coding) RNA] that are dynamically regulated in response to LTP. In addition, we also observed an altered expression of multiple classes of repeat elements [mobile DNA sequences often involved in mutations] including retrotransposons [a repeat element type formed by copy-and-paste mechanisms].
The results presented here reveal a vast extension of mRNAs [messenger RNA, a large RNA that carries codes for protein production] previously not associated with neuronal plasticity; the discovery of extensive, dynamic regulation of lncRNAs, repeat elements, and tRNA [transfer RNA that links mRNA and amino acids during protein production] following LTP induction in the adult rat brain.
These findings provide a broader foundation for elucidating the transcriptional and epigenetic regulation of synaptic plasticity.”
“We annotate a total of 10,256 novel lncRNAs in the rat transcriptome.
To infer possible functions of lncRNAs, we correlated  differentially expressed lncRNAs with regulated protein coding genes.
There are no established rules for predicting the function of lncRNAs.”
Regarding repeat elements:
“It is intriguing to consider that expression of repeat elements during LTP is the first step toward retrotransposition and reshaping of the neuronal genome. A hypothetical mechanism for how these repeat elements could be linked to memory, would be that a certain stimuli, whether it is stress or a learning task (here LTP), deregulate the repression of repeat elements which are then rapidly and transiently transcribed. These elements reinsert themselves back into the genome of stimulated neurons where they influence the expression of neighboring genes.
The present work supports the intriguing hypothesis that dynamic retrotransposition may act as a molecular means to reprogram the neuronal genome as part of long-term synaptic plasticity and memory formation.”
See RNA as a proxy signal for context-specific biological activity for more about lncRNA.
http://journal.frontiersin.org/article/10.3389/fnins.2015.00351/full “Dynamic expression of long noncoding RNAs and repeat elements in synaptic plasticity”