Prof.dr. Gisella Vetere: "Dissection of a memory engram"

Prof.dr. Gisella Vetere has been invited to visit our department and will give a guest lecture. She is a neuroscientist studying memory in the hippocampus and the cortex, using optogenetic and neural-tagging methods. It is of interest for everyone interested in neural networks and learning mechanisms in biological networks.

Abstract

Engram cells are defined as cells active during memory acquisition, that undergo consequent cellular changes and that integrate in a complex network of cells that, when reactivated by a stimulus linked to the memory acquisition, will result in memory recall. With the advent of optogenetics controlled by immediate early gene promoters (c-fos, arc, etc.), this last characteristic has been extensively studied: tagging and optogenetically stimulating all cells active during the acquisition of a contextual fear memory triggers freezing in a novel neutral context. However, this technique is limited in its tagging temporal specificity. Novel approaches such as FLiCRE use delivered light and intracellular calcium to open and close the tagging window, theoretically reaching temporal specificity only limited by calcium and protein dynamics (sub-second precision). Hence, we can start dissecting the engram: how do different subpopulations of cells, active at specific time points during memory acquisition, integrate into the engram network? Will the optogenetic stimulation of any subpopulation be sufficient to recall the memory in a neutral context, or will some seemingly bear more importance in the network? During contextual fear conditioning, we tagged different hippocampal subpopulations of cells: cells active during the shocks (SHOCKtag), when the animal is in freezing (FREEZtag) or outside of freezing (NOFREEZtag). We found that, while stimulating tagged cells that were active during shock or freezing proved sufficient to trigger freezing and recall fear memory in a different context (as already shown for shock cells), it wasn’t for “no freezing”-active cells. Furthermore, inhibiting shock or freezing cells during memory retrieval reduced freezing behaviors.