Using Viral Vectors to Study the Memory Trace in Mice

The ability to identify neurons that are involved in the acquisition and encoding of a specific memory can facilitate efforts to understand the neuronal and circuit mechanisms that underlie memory formation. In this chapter, we outline a method whereby a population of neurons in the lateral amygdala (LA) that is involved in encoding of a conditioned fear memory can be identified. Using viral-mediated gene delivery, expression levels of the transcription factor CREB (cAMP/Ca²⁺ responsive element binding protein) can be transiently increased in a subpopulation of neurons in the LA in vivo, thereby biasing those neurons towards becoming part of a memory trace. The preferential involvement of those neurons can be assessed using a technique, known as catFISH, in which the localized expression of mRNA for the immediate early gene arc after memory formation can be detected and compared to those neurons expressing virally delivered CREB.