Objective: 

Extensively used neuroimaging methods such as PET and fMRI are based on the functional interaction between nerve-cell activity and cerebral blood flow. While changes in brain perfusion are mostly attributed to flow metabolism coupling, it is commonly assumed that they are not affected by modulations in systemic hemodynamics. This assumption was challenged by the present study, which explored the interaction between systemic and cerebral hemodynamics during attentional processing with a specific focus on the temporal dynamics of this linkage.

Methods: 

Using transcranial Doppler sonography, blood flow velocities in the middle cerebral arteries (MCA) of both hemispheres were recorded while 50 subjects performed a cued reaction time task. The task involved motor reactions on a visual stimulus, which was preceded by an acoustic warning signal (interstimulus interval 5 s). Blood pressure and heart rate were also continuously monitored.

Results: 

Doppler sonography revealed a right dominant blood flow response. The extent of the increase measured in second two of the interstimulus interval showed a clear positive association with reaction speed. Task related changes in blood pressure and heart rate proved predictive of changes in MCA flow velocities in limited time windows of the response.

Conclusions: 

Besides an association between cerebral blood flow and attentional performance, the results suggest a marked impact of systemic hemodynamics on the blood flow response. The observed time-dependence of all interactions underlines the importance of the temporal aspect in the investigation of relationships between hemodynamic, neural and psychological processes, and therefore emphasizes the suitability of methods enabling high time resolution analyses.