Lesions Responsible for Phonological Paraphasia and Auditory–verbal Short-term Memory Disturbances in Aphasia

Fluent speech with phonological paraphasia is characteristic of conduction aphasia and Wernicke’s aphasia. Phonological paraphasia is characterized by speech sound errors that still convey the intended meaning. Some patients with phonological paraphasia show auditory–verbal short-term memory (STM) disturbances. However, it is not certain that phonological paraphasia results from such memory disturbances. We compared the overlapping lesions of 30 patients with phonological paraphasia, with the most relevant lesions of 38 patients with auditory–verbal STM disturbances (digit span and letter span). The results showed that the overlapping lesions of patients with phonological paraphasia were located in the subcortical white matter in the left supramarginal gyrus, regardless of the type of aphasia. The lesions most relevant to digit span disturbances were located in the subcortical white matter in the left angular gyrus, and those most relevant to letter span disturbances were located in the left superior temporal cortex. Although the lesions most relevant to phonological paraphasia and those most relevant to auditory–verbal STM disturbances were closely located, they did not correspond. These findings suggest that the cause of phonological paraphasia is not auditory–verbal STM disturbances but non-conduction of a large amount of information through underlying white matter lesions, and that two auditory–verbal STM storage sites exist in the human brain.