Phonological Alexia during Left Inferior Temporal Cortical Stimulation

Current cognitive models propose that reading can be achieved through phonological or lexical/semantic pathways. However, the anatomical networks subserving these processes remain largely unravelled. The objective of this report is to describe a case of isolated phonological alexia induced by electrical stimulation of the basal temporal cortex. A 19 year-old woman with refractory left temporal epilepsy was submitted to EEG monitoring with subdural electrodes and cortical stimulation as part of the evaluation for epilepsy surgery. The subdural electrodes were located in the basal temporal lobe, around the fusiform gyrus. Electrical stimulation of one of the electrodes induced reproducible alexia mostly involving pseudo words with visual, morphological and normalization errors. This pattern is consistent with phonological alexia. No other language, memory or visuo-spatial deficits were elicited. The epileptogenic area was surgically excised, sparing this functionally important region. The patient remains seizure free and no additional neuropsychological deficit was found after surgery. This represents the first case of isolated phonological alexia induced by a circumscribed lesion in the left inferior occipito-temporal cortex. Functional imaging studies suggested that this region of the brain harbours the visual word form area, an area selectively involved in reading. This case strengthens this possibility. Furthermore, it seems to indicate that the phonological pathway of reading segregates from the whole word lexico-semantic pathway already at this early stages of processing, in the basal occipito-temporal cortex. This case also suggests that neuropsychological testing of the basal occipito-temporal cortex in pre-surgical epilepsy patients should include tests for phonological alexia.