Experimental research examining the neural bases of nondeclarative memory has offered intriguing insight into how functional and dysfunctional implicit learning affects the brain. Long-term modifications of synaptic transmission, in particular, are currently considered the most plausible mechanism underlying memory trace encoding and compulsions, addiction, anxiety, and phobias. Therefore, an effective psychotherapy must be directed to erase maladaptive implicit memories and aberrant synaptic plasticity. This article describes the neurobiological bases of pathogenic memory disruption to provide some insight into how psychotherapy works. At least two mechanisms of unwanted memory erasing appear to be implicated in the effects of psychotherapy: inhibition of memory consolidation/reconsolidation and extinction. Behavioral evidence demonstrated that these two ways to forget are profoundly distinct in nature, and it is increasingly clear that their cellular, synaptic, and molecular underpinnings are different. Accordingly, the blockade of consolidation/reconsolidation erases memories by reversing the plasticity associated with memory maintenance, whereas extinction is a totally new form of plasticity that, similar to the plasticity underlying the old memory, requires protein synthesis-dependent synaptic remodeling.