Thalamic Aphasia and Irrelevant Verbal Paraphasias : The Potential Mechanisms Underlying Its Characteristic Speech

Abstract

  The hallmarks of thalamic aphasia based on the previous case reports include word-finding difficulties and verbal paraphasias, in particular, irrelevant verbal paraphasias, despite normal articulation, intact repetition, and mild comprehension deficits. However, no group study has been conducted on whether thalamic aphasia frequently involves irrelevant verbal paraphasias compared with the other types of aphasia and potential mechanisms underlying those irrelevant verbal paraphasias has yet to be elucidated. Here we approached the nature of thalamic aphasia by investigating its accompanying irrelevant verbal paraphasias. Compared with aphasic patients with the other types, patients with thalamic aphasia showed the higher ratio of irrelevant verbal paraphasias among the total errors as well as to the relevant verbal paraphasias. In our previous case report on thalamic aphasia, a close relationship between irrelevant verbal paraphasias and selective attentional dysfunction was observed, suggesting selective attentional dysfunction, which is deeply associated with thalamic damage, led to development of irrelevant verbal paraphasias. With the previously proposed mechanisms behind thalamic aphasia, the characteristic speech found in thalamic aphasia might reflect word-finding errors due to inability to activate semantic fields that is related to the target word as well as inability to suppress words that are irrelevant to the target word.