Music depends on the perception and production of complex temporal patterns, or rhythms, as a vital part of its power to communicate. These experiments investigated the neuroanatomical substrate of rhythm perception and production in patients with focal cerebral lesions, and in neuroimaging studies with normals. The hypotheses focused on the role of the primary and secondary auditory cortex, as well as the cerebellum and other motor-related areas. / Experiment I. To estimate the extent of removals in the region of auditory cortex in neurosurgical patients, a 3D probabilistic map of Heschl's gyrus (HG) was developed from magnetic resonance imaging (NW scans of normals. The map was coregistered with patent MRIs, revealing that most removals involved only anterior secondary auditory cortical regions, with relatively little encroachment onto primary auditory cortex. Additionally, this experiment compared the volumes of HG between hemispheres and found a consistent L > R asymmetry in the volume of cortical white matter, which could contribute directly to the preferential left-hemisphere processing of speech. / Experiment II. Using a paradigm contrasting reproduction of auditory and visual rhythms, four groups of patients were tested: those with right or left anterior temporal-lobe removals (RT-a, LT-a) and those with similar removals which also included HG (RT-A, LT-A). RT-A patients were impaired on auditory but not visual rhythms, particularly when accurate reproduction of stimulus durations was required. In contrast, LT-a, RT-a and LT-a patients were not impaired. These results demonstrated a role for the right anterior secondary auditory cortical regions in the retention of auditory temporal information. / Experiment III. The rhythm reproduction paradigm was adapted for a positron emission tomography (PET) activation study in normals. These data confirmed the participation of secondary auditory regions in the retention of auditory temporal information. They also demonstrated a supra-modal contribution of the lateral cerebellar cortices, vermis and basal ganglia to the task, pointing to a distributed system of neural structures involved in the production of a timed motor response from external stimuli. / The results are discussed in relation to possible interhemispheric differences in auditory temporal processing as well as the role of the cerebellum in motor and perceptual timing.

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