Functional Mapping of the Human Auditory Cortex: fMRI Investigation of a Patient with Auditory Agnosia from Trauma to the Inferior Colliculus.

OBJECTIVE To use functional magnetic resonance imaging to map the auditory cortical fields that are activated, or nonreactive, to sounds in patient M.L., who has auditory agnosia caused by trauma to the inferior colliculi. BACKGROUND The patient cannot recognize speech or environmental sounds. Her discrimination is greatly facilitated by context and visibility of the speaker's facial movements, and under forced-choice testing. Her auditory temporal resolution is severely compromised. Her discrimination is more impaired for words differing in voice onset time than place of articulation. Words presented to her right ear are extinguished with dichotic presentation; auditory stimuli in the right hemifield are mislocalized to the left. METHODS We used functional magnetic resonance imaging to examine cortical activations to different categories of meaningful sounds embedded in a block design. RESULTS Sounds activated the caudal sub-area of M.L.'s primary auditory cortex (hA1) bilaterally and her right posterior superior temporal gyrus (auditory dorsal stream), but not the rostral sub-area (hR) of her primary auditory cortex or the anterior superior temporal gyrus in either hemisphere (auditory ventral stream). CONCLUSIONS Auditory agnosia reflects dysfunction of the auditory ventral stream. The ventral and dorsal auditory streams are already segregated as early as the primary auditory cortex, with the ventral stream projecting from hR and the dorsal stream from hA1. M.L.'s leftward localization bias, preserved audiovisual integration, and phoneme perception are explained by preserved processing in her right auditory dorsal stream.