Comparison of auditory deficits associated with neglect and auditory cortex lesions

Lesions of the visual and somatosensory cortex produce clear contra-lesional deficits. In contrast, unilateral lesions of the auditory cortex produce contra-lesional extinction when two stimuli are simultaneously presented to the left and right ear, but little deficits in the absence of sensory competition. Because auditory extinction is also considered a sign of neglect, the clinical separation of auditory neglect from deficits caused by lesions of the auditory cortex is challenging, as both are expected to frequently co-occur. Here, we directly compared a number of tests previously used for either auditory-cortex lesions or neglect in 29 controls and 27 patients suffering from unilateral auditory-cortex lesions, clinical signs of neglect, or both. The results showed that a dichotic-speech test revealed similar amounts of extinction for both, auditory cortex lesions and neglect. Similar results were obtained for words lateralized by inter-aural time differences. Consistent extinction after auditory cortex lesions was also observed in a dichotic detection task. Neglect produced more general problems with target detection, but no consistent extinction in the dichotic detection task. In contrast, auditory lateralization perception was biased toward the right in neglect, but showed little disruption by auditory cortex lesions. Lateralization of auditory-evoked magnetic fields in auditory cortex was highly correlated with extinction in the dichotic target-detection task. Moreover, activity in the right primary auditory cortex was somewhat reduced by neglect. The results confirm that auditory extinction is similarly observed with lesions of the auditory cortex and auditory neglect. However, dichotic target-detection tasks, auditory-lateralization perception, and magnetoencephalography provide tools to disentangle the two phenomena.