DYNAMICS OF BLOOD-FLOW AND OXYGENATION CHANGES DURING BRAIN ACTIVATION - THE BALLOON MODEL

A biomechanical model is presented for the dynamic changes in deoxyhem oglobin content during brain activation, The model incorporates the co nflicting effects of dynamic changes in both blood oxygenation and blo od volume, Calculations based on the model show pronounced transients in the deoxyhemoglobin content and the blood oxygenation level depende nt (BOLD) signal measured with functional MRI, including initial dips and overshoots and a prolonged poststimulus undershoot of the BOLD sig nal. Furthermore, these transient effects can occur in the presence of tight coupling of cerebral blood flow and oxygen metabolism throughou t the activation period. An initial test of the model against experime ntal measurements of flow and BOLD changes during a finger-tapping tas k showed good agreement.