Memory could be conceptualized as the capability to encode, store and retrieve information to guide behavior. Memory may be stored in different manners depending on synaptic characteristics for information processing, which may modulate synchronization of firing of neuronal assemblies. This book focuses on some of the mechanisms that modulate the synaptic activity underlying both the organization and expression of memory. Thus, memory is viewed from the point of view of its synaptic determinants. This book is the integrated compilation of a large body of experimental evidence related to some cellular and subcellular events underlying plastic changes of neural circuits forming the memory traces related to some memory systems. Moreover, this view of memory is considered from both a normal viewpoint and from that of some atypical situations.