Enhancement of verb retrieval ;: neuromodulation, repetition priming, and aphasia rehabilitation

There is an increasing interest in enhancement of cognitive functions. Cognitive enhancement can play a role in improving performance in young individuals, in the maintenance of cognitive functions in aging, and in the rehabilitation of impaired cognitive functions in various neurological conditions, such as stroke. Furthermore, data from studies of cognitive enhancement can be used to increase our understanding of the architecture of the cognitive system, and of the interactions between the building blocks of cognition. This dissertation addresses the enhancement of verb retrieval. Verbs are central to the process of sentence construction, and play therefore a major role in communication. The process of verb retrieval is vulnerable to brain damage, being selectively disrupted in a high proportion of patients who present with aphasia after stroke. Nonetheless, there is relatively little research on the treatment of verb retrieval in aphasia in comparison to other types of impairment. This thesis has a specific focus on understanding the mechanisms of enhancement in verb retrieval, both in healthy individuals, and patients with aphasia. This enhancement is studied with behavioral techniques and transcranial direct current stimulation (tDCS), a non-invasive neuromodulation technique.