Molecular and cellular mechanisms of memory allocation in neuronetworks

Determining how neuronal networks encode memories is a key goal of neuroscience. Although neuronal circuit processes involved in encoding, storing and retrieving memory have attracted a great deal of attention, the processes that allocate individual memories to specific neurons within a network have remained elusive. Recent findings unraveled the first insights into the processes that modulate memory allocation in neuronetworks. They showed that neurons in the lateral amygdala compete to take part in auditory fear conditioned memory traces and that the levels of the transcription factor CREB (CAMP-response element binding protein) can affect the probability of a neuron to be recruited into a given memory representation. CREB-mediated transcriptional regulation involves several signaling pathways, known to mediate nuclear responses to diverse behavioral stimuli, along with coordinated interactions with multiple other transcription activators, coactivators and repressors. Moreover, activation of CREB triggers an autoinhibitory feedback loop, a metaplastic process that could be used to allocate memories away from cells that have been recently involved in memory. Beyond CREB, there may be a host of other processes that dynamically modulate memory allocation in neuronetworks by shaping cooperation and competition among neurons. (C) 2007 Elsevier Inc. All rights reserved.