Summary Tinnitus is a common disorder characterized by ringing in the ear in the absence of sound. Converging evidence suggests that tinnitus pathophysiology involves damage to peripheral and/or central auditory pathways. However, whether auditory system dysfunction is sufficient to explain chronic tinnitus is unclear, especially in light of evidence implicating other networks, including the limbic system. Using functional magnetic resonance imaging and voxel-based morphometry, we assessed tinnitus-related functional and anatomical anomalies in auditory and limbic networks. Moderate hyperactivity was present in the primary and posterior auditory cortices of tinnitus patients. However, the nucleus accumbens exhibited the greatest degree of hyperactivity, specifically to sounds frequency-matched to patients’ tinnitus. Complementary structural differences were identified in ventromedial prefrontal cortex, another limbic structure heavily connected to the nucleus accumbens. Furthermore, tinnitus-related anomalies were intercorrelated in the two limbic regions and between limbic and primary auditory areas, indicating the importance of auditory-limbic interactions in tinnitus.

Summary The occipital cortex (OC) of early-blind humans is activated during various nonvisual perceptual and cognitive tasks, but little is known about its modular organization. Using functional MRI we tested whether processing of auditory versus tactile and spatial versus nonspatial information was dissociated in the OC of the early blind. No modality-specific OC activation was observed. However, the right middle occipital gyrus (MOG) showed a preference for spatial over nonspatial processing of both auditory and tactile stimuli. Furthermore, MOG activity was correlated with accuracy of individual sound localization performance. In sighted controls, most of extrastriate OC, including the MOG, was de-activated during auditory and tactile conditions, but the right MOG was more activated during spatial than nonspatial visual tasks. Thus, although the sensory modalities driving the neurons in the reorganized OC of blind individuals are altered, the functional specialization of extrastriate cortex is retained regardless of visual experience.

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Early blindness results in both structural and functional changes of the brain. However, these changes have rarely been studied in relation to each other. We measured alterations in cortical thickness (CT) caused by early visual deprivation and their relationship with cortical activity. Structural and functional magnetic resonance imaging was performed in 12 early blind (EB) humans and 12 sighted controls (SC). Experimental conditions included one-back tasks for auditory localization and pitch identification, and a simple sound-detection task. Structural and functional data were analyzed in a whole-brain approach and within anatomically defined regions of interest in sensory areas of the spared (auditory) and deprived (visual) modalities. Functional activation during sound-localization or pitch-identification tasks correlated negatively with CT in occipital areas of EB (calcarine sulcus, lingual gyrus, superior and middle occipital gyri, and cuneus) and in nonprimary auditory areas of SC. These results suggest a link between CT and activation and demonstrate that the relationship between cortical structure and function may depend on early sensory experience, probably via selective pruning of exuberant connections. Activity-dependent effects of early sensory deprivation and long-term practice are superimposed on normal maturation and aging. Together these processes shape the relationship between brain structure and function over the lifespan.

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