Functional magnetic resonance imaging (FMRI) detects focal MRI
signal changes in brain tissue that are believed to result from
changes in neuronal activity. We describe the dependence of this
response in auditory cortex on the rate of presentation of simple
speech stimuli. Speech syllables were presented to five normal
subjects at rates ranging from 0.17 to 2.5 Hz, while the subjects
performed a phoneme discrimination task. Regions studied with FMRI
during this task included the lateral aspect of both temporal
lobes. All subjects showed bilateral superior temporal lobe MRI signal
increases that were coincident with stimulus presentation and
performance of the task. The magnitude of this response increased in a
monotonic, non-linear manner with increasing stimulus rate. This
rate-response relationship was nearly identical in right and left
hemispheres. The relationship may reflect metabolic activity
integrated over time and subject to non-linear characteristics of
neuronal recovery or blood flow regulation. The dependence of response
magnitude on stimulation rate supports the hypothesis that the FMRI
phenomenon indirectly reflects neuronal metabolic activity. The
measures provided here should assist in the design of optimal
activation strategies for the human auditory cortex. ISSN