Neuroscientific protocols for exploring the mental lexicon: Evidence from aphasia

Research over the past 30 years has developed several protocols to investigate the anatomo-functional architecture of the mental lexicon. The first is the neuropsychological approach, based on anatomo-clinical correlations in selected groups of brain-damaged patients and on single case studies, in which association and/or dissociation between a damaged brain area and a specific linguistic ability is deeply investigated: this approach has produced relevant insight in the organization of the semantic system. The instrumental approaches studying perfusion and metabolism, such as PET scan and fMRI, have supported these data extending our knowledge on the neural substrates of word comprehension and production. Results from studies using non invasive brain stimulation techniques, have contributed to confirm and refine previous data. Very recently, intraoperative direct electrical stimulation in patients with brain tumours has been proposed in order to make critical surgical decisions on which area can not be removed due to its crucial role in language processing. Right now, the most promising innovative approach suggests to combine different neuroimaging methods in order to overcome the limitations of each technique. In the present chapter, we will present the main achievements obtained through these different approaches.