The functional anatomy of single-word reading in patients with hemianopic and pure alexia

We investigated single-word reading in normal subjects and patients with al exia following a left occipital infarct, using PET, The most posterior brai n region to show a lateralized response was at the left occipitotemporal ju nction, in the inferior temporal gyrus, This region was activated when norm al subjects, patients with hemianopic alexia and patients with an incomplet e right homonymous hemianopia, but no reading deficit, viewed single words presented at increasing rates. This same area was damaged in a patient with pure alexia ('alexia without agraphia') and no hemianopia, who read words slowly using a letter-by-letter strategy, Although the exact level of the f unctional deficit is controversial, pure alexia is the result of an inabili ty to map a percept of all the letters in a familiar letter string on to th e mental representation of the whole word form. However, the commonest defi cit associated with 'pure' alexia is a right homonymous field defect; an im pairment that may, by itself, interfere with single-word reading because of inability to see the letters towards the end of a word. The relative contr ibutions of pure and hemianopic alexia in individual patients needs to be a ssessed, as the latter has been shown to respond well to specific rehabilit ation programmes.