Learning and Memory, Part II: Molecular Mechanisms of Synaptic Plasticity

Abstract

Learning and Memory, Part I, described how shortterm memories are consolidated into long-term memories and the brain regions involved in this process. 1 Lombroso PJ Ogren MP Learning and memory: I. Brain regions involved in two types of learning and memory. J Am Acad Child Adolesc Psychiatry. 2008; 47: 1219-1223 Google Scholar As previously discussed, the hippocampus is required for the formation of declarative memories (conscious memories of events and facts). This type of memory was destroyed in the famous clinical case of H.M. after he sustained a bilateral hippocampal resection to treat his disabling seizures. Despite the severity of his memory deficits, H.M. retained his ability to form nondeclarative memories (unconscious habit learning), which requires brain structures outside the hippocampus. In fact, his performance on motor learning tasks, which require nondeclarative memory, was perfectly normal. One example of this sort of task is mirror writing; H.M. was asked to keep his pen within a narrow border along the edge of a star while observing the pen and his hand through a mirror, which reverses right and left. H.M.'s motor learning in this task improved for several days, although he recalled neither the individual administering the test nor the instructions from one day to the next.