Investigation of memory-trace replay in medial prefrontal cortex by template matching.
ARL NSMA, Univ. Arizona, Tucson, AZ
The hippocampus is considered to play an important role in the initial acquisition of memory, possible by indirectly linking together new neocortical cell assemblies. The process of consolidation is thought to involve the gradual formation of direct links through a process of hippocampally orchestrated, spontaneous reactivation of recent neuronal activity patterns. In medial prefrontal cortex, the detailed structure of pairwise cross-correlograms obtained from neural ensemble recordings during behavior can reappear during slow wave sleep on a time-scale that is compressed by a factor of about 6 (Euston and McNaughton, SfN Abstract, 2004) suggesting that the memory-trace is replayed much faster than the speed observed during behavior.
In this study, we analyzed the reactivation of multi-neuronal spike patterns in the medial prefrontal cortex using an independent method known as template matching. Several rats were trained to run a sequential task on a circular arena. The recording data typically consists of 30 min of pre-sleep, 1 hour of behavior, and 30 min of post-sleep. The templates were constructed by averaging the firing patterns during each leg of sequential behavior (mean template duration 2.4 sec, divided into 24 bins). The correlation between behaviorally-derived templates and firing patterns during slow-wave sleep showed significant increases in the sleep session after the behavior. Reversing the temporal order of the template columns, however, failed to show significant correlations with either sleep epoch. In addition, the best replay of forward templates occurred at compression factors of 4X to 8X, which is consistent with the estimation obtained by pairwise cross-correlation methods. The further analysis of firing patterns during UP states in post-sleep is now in progress, aiming to elucidate if the replay tends to occur within a single UP state or over consecutive UP states.
These results support the conjecture that reactivation of memory traces in medial prefrontal cortex may play an important role in memory consolidation.
Grant/Other Support: MH046823
Keyword (Complete): memory; replay; consolidation; prefrontal cortex; template matching