The process of memory formation has been investigated using the model of one-trial passive avoidance training in the one-day old domestic chick. We have unraveled a biochemically coherent cascade of processes which, beginning with transient ion and neurotransmitter flux, and by way of a sequence of interacting pre- and post-synaptic intracellular signalling steps, results in gene activation and the synthesis of cell adhesion molecules which appear to be the effective agents in the structural processes involved in remodelling of synaptic and neuronal circuits. Further, in a related series of experiments we have shown that these biochemical and morphological changes are accompanied by significant changes in the neurophysiological status of the neurons on the IMHV and LPO, in particular in terms of their engagement in bouts of high-frequency firing. However, much remains to be clarified, particularly the meaning of the time-dependent shifts in the location of the trace, and the ways in which these molecular and cellular events translate into changes in behavior in the animal.