The chronicity effect.

The chronicity effect is derived from two other general principles that underlie clinical neuropsychological test interpretation. These are (1) localization principle: elementary functions are related to specific cortical areas; (2) Diaschisis: functions located at a distance from an acute lesion may be affected by that lesion. The chronicity effect states that as a nonprogressive lesion becomes chronic, diaschisis tends to recede. In an illustrative detailed case study, a man with encephalitis concentrated in the left temporoparietal area was tested five times over a 6-year period. In the first testing at 5 weeks many of his abilities were impaired. In subsequent months, all abilities except reading returned to the normal range. His dyslexia became permanent, while other abilities not related to the area of tissue damage returned to normal functioning.