An fMRI Study of Impairments to Speech Perception in Patients with Vascular Sensory Aphasia

The aim of the present work was to use the noninvasive fMRI method to identify neurophysiological correlates of impairments at the sensory stage of the perception of verbal information, i.e., phonematic hearing, in patients with sensory aphasia after acute impairments to cerebral circulation in the left hemisphere of the brain. This was addressed by recording the fMRI equivalent of mismatch negativity in response to verbal phonemes – the syllables “ba” and “pa” – using the oddball paradigm in 20 healthy subjects and 23 patients with post-stroke sensory aphasia. Calculation of mismatch negativity contrast in healthy subjects identified activation of the superior temporal and inferior frontal gyri in the right and left hemispheres. Patients showed significant activation of the auditory zone of the cortex only in the right hemisphere, activation at this site was less marked in terms of volume and intensity than in healthy subjects, and correlated with the extent of speech preservation. Thus, recording of the fMRI equivalent of mismatch negativity provides a sensitive method for studies of impaired perception of speech sounds.