Evidence for a basal temporal visual language center: cortical stimulation producing pure alexia.

Area of Science:

• Neuroscience
• Cognitive Neuroscience
• Neurolinguistics

Background:

• Theories of pure alexia have historically focused on white matter tract disruptions in the temporooccipital region.
• Recent functional imaging suggests basal temporal and occipital cortices are involved in reading, but their precise roles are debated.

Purpose of the Study:

• To confirm the involvement of the basal temporal region in the cognitive process of reading.
• To elucidate the specific functions of this area in visual language processing.

Main Methods:

• Extraoperative electrical stimulation of the dominant hemisphere using subdural electrodes in three epilepsy patients.
• Mapping of stimulation-induced deficits during presurgical evaluation.

Main Results:

• Cortical stimulation of the dominant posterior fusiform and inferior temporal gyri reproduced pure alexia in all subjects.
• Stimulation caused selective reading difficulties, sparing auditory comprehension and writing.
• Difficulties in picture naming were also observed, indicating broader visual processing roles.
• The identified region is contiguous with the basal temporal language area (BTLA) and corresponds to the visual word form area (VWFA).

Conclusions:

• Evidence supports a distinct visual language area in the dominant fusiform and occipitotemporal gyri, adjacent to the BTLA.
• This visual language area plays a role in both lexical processing and the processing of nonlexical symbols.