Naming tools and animals: asymmetries observed during direct electrical cortical stimulation

Semantically bounded disorders of verbal processing that result in selective dysnomias for items belonging to specific semantic categories have been well documented in lesion studies. Most commonly dissociations between the categories of living versus non-living things have been reported. Processing of living things such as animals seems to be impaired after bilateral lesions, whereas lesions resulting in impairment of processing of non-living things such as tools seem to be restricted to the left hemisphere. In this study, we tested the naming capabilities of epilepsy patients with subdural electrodes implanted for localization of the epileptogenic zone and preoperative mapping of cognitive functions. Tool and animal items were used, and the results show that during stimulation of the left hemisphere dysnomias for tool items were more pronounced than for animal items. This asymmetry is discussed within a model of more widely bilaterally distributed processing of living category members as compared to more restricted left-sided representation of non-living category members.