The cerebral anatomy of word reading: From Dejerine to brain imaging

Abstract

The cerebral processes which support word reading may be analyzed into two stages. The first stage takes place within the visual system, and allows for the invariant identification of letters and their order. This process involves sequentially low-level visual areas and the so-called visual word form area (VWFA), located in the lateral occipitotemporal sulcus (Cohen et al., 2000). During the second word processing stage, orthographic information is transferred to language areas, where it will allow the reader to access sound and meaning representations. Pure alexia, or alexia without agraphia, which was perfectly described by Dejerine (1892, 1895), consists in a selective impairment of reading resulting from the disruption or the deafferentation of the VWFA. However, the pathophysiological account put forward by Dejerine was somewhat different from the currently prevailing explanation ( Figure 1 ). During reading, the left occipital cortex (yellow) receives input from the left lateral geniculate through the optic radiations [1] , from the opposite hemisphere through callosal fibers [2] , and it projects to later stations in the reading network. Dejerine proposed that the target of such projections was the angular gyrus, although the corresponding fiber tract was purely hypothetical [3] . According to the current data, the target of occipital projections is actually the VWFA (red), which is reached through the ILF (3′), which was disrupted in the patient reported in Epelbaum et al. (2008) [4] , as it was in Dejerine's patient.