The time course of the BOLD response in the human auditory cortex to acoustic stimuli of different duration

The relationship between activity within the human auditory cortices and th e duration of heard tones was investigated by measuring the hemodynamic res ponse with functional magnetic resonance imaging. We demonstrate that there is no significant influence of stimulus duration as used here on the inten sity and spatial extent of the hemodynamic response in the auditory cortice s. We found however, that the time course of the hemodynamic response to th e repeated stimulus presentation exhibited a characteristic decline after t he first stimulus exposure during the activation period. The possible reaso ns for this time course are currently unknown, however, several factors may be involved, including top-down mechanisms and/or the interplay of tissue perfusion and oxygen consumption. (C) 1999 Elsevier Science B.V. All rights reserved.