Memory, DISEASES OF.

Memory, DISEASES OF. Memory, or the power of reproducing mental or sensory impressions, is impaired by age, wounds, or injuries to the head or nervous system, fevers, intemperance, and various physical conditions. It is affected in most kinds of mental derangement, but is in a most signal manner obliterated or enfeebled in Dementia. There are, however, examples of memory surviving all other faculties, and preserving a clear and extensive notion of long and complicated series of events amid general darkness and ruin of mind. Incoherence owes some of its features to defective or irregular memory. Cases of so marvellous an exaltation of this faculty as where a whole parliamentary debate could be recalled, or a whole play of Shakespeare's recited by a man at one time, which would be ordinarily impossible for him, are common in the beginning of attacks of mania, and always should suggest disease. There are, however, special affections of the faculty. It may be suspended while the intelligence remains intact. Periods of personal or general history may elude the grasp, and even that continuity of impressions which goes far to constitute the feeling of personal identity is broken up, and a duality or multiplicity of experiences may appear to be conjoined. The converse of this may happen, and impressions that had completely faded away may, under excitement or cerebral disease, return. There are, besides, states in which this power is partially affected, as in the instances where the numbers 5 and 7 were lost, and where a highly-educated man could not retain any conception of the letter F; secondly, where it is perverted, recalling images inappropriately and in an erroneous sequence of order or time, and different from what are desired; and thirdly, where, while the written or printed signs of ideas can be used, the oral or articulate signs are forgotten. Such examples of diseased memory are now classified as amnesia, simple loss of memory; amnesic aphasia, loss of memory of spoken words (see APHASIA); and amnesic agraphia, loss of memory of written words. Most of these special deviations from health depend upon morbid changes in a very limited portion—'Broca's convolution'—of the left side of the brain. The discovery of this fact by Broca was the first of the brilliant discoveries as to the localisation of function in the brain cortex. See Feuchtersleben, Medical Psychology; and Ribot, Les Maladies de la Mémoire (1881).