Global amnesia: organic and functional considerations.

In its most general sense, amnesia is defined as failure of the memory. In clinical usage, the term is used in a more circumspect sense: amnesia is defined as an inability to recollect information in a verbal fashion, although the ability to speak is retained. Such conditions as alexias (memory loss for reading) or apraxias (memory loss for certain motor activities) are not formally considered to be amnesias. Since amnesias are disorders of (verbal) memory, some knowledge of the memory process is necessary before one can study or treat the disorder. The search for a wholly adequate definition for "memory" has bedevilled psychologists for generations. For our purposes, Bartlett's definition will suffice: "memory is an imaginative reconstruction built out of our attitudes towards a whole mass of organized past reactions to experience."l The establishment of a memory for an object is commonly thought to be the result of a three-step process: 1) registration-the object is perceived through the senses and attention is paid to the object; 2) retention (storage)-the physical substrate of the idea is established, and the idea is integrated in some way with older memories; 3) recall (retrieval)-the idea (now a memory) can be elicited anew through association with some new perception. Different amnesias are thought to act at different steps of this process. In addition, memories are said to have two important subjective properties: 1) Time ordering: one perceives some events as having happened before other events. All events are perceived in a time dimension. 2) The sense of personal identity and personal identification: an individual can distinguish past events which are part of his immediate personal experience from past experiences and events conveyed to him from secondary sources. Different amnesias can also interfere with these general properties of memory.