Aphasia : clinical and anatomical profiles

Abstract

Aphasia is one of the most common cognitive symptoms in brain–damaged patients. Examination of language and related functions is an important part of the neurological examination. To understand symptoms of aphasia, basic knowledge of neuroanatomy is necessary. I propose a four axes theory of functional neuroanatomy of the brain ; anterior–posterior axis (output vs. input), left–right axis (temporal/analytic vs. spatial/synthetic), dorsal–ventral axis (sensory to motor vs. sensory to semantic), and inner–outer axis (basic/innate vs. complex/acquired). This simple theory allows us to estimate the clinical features of each aphasia type. For instance, the Broca's area is located in the left inferior frontal gyrus that corresponds to the anterior, left, dorsal and outer area. The location of the Broca's area suggests the clinical features of Broca's aphasia. For the screening of language functions we observe spontaneous speech, listening comprehension, repetition, naming, reading and writing abilities. The types of aphasia can be determined mainly by the performance on speech fluency, listening comprehension and repetition. The classic aphasia types were based on the clinical syndromes that result from cerebral infarction in the territory of the left middle cerebral artery. In contrast, three variants of primary progressive aphasia are associated with the underlying neurodegenerative diseases. Thus, these two types of aphasia classification are different with each other, which may confuse clinicians. Linguistic features of each type of aphasia, however, could be understood by the functional neuroanatomy of language.