The purpose of this study is to reveal the stress dependent changes in the interrelationship among cerebral hemodynamics and other physiological signals. We focused on changes in low-frequency background oscillations because their properties may reflect the normality of brain function.
Six healthy subjects participated in the experiment after giving written informed consent. The experiment consisted of two sessions for auditory 3-back tasks with different levels of stress intensity. Under high stress condition, 50-second task block and 10-second rest block were repeated 10 times, while 30-second task and rest blocks were repeated 10 times under low stress condition. Seven pure tones of C major scale were used in the auditory stimuli presentation.
The time-series data of blood pressure (BP), electrocardiogram (ECG), electroencephalogram (EEG) and regional cerebral oxy hemoglobin concentration change (HbCC) were simultaneously recorded with a multi-distance optrode during the experiment. EEG data were measured at C3 and C4 according to international 10-20 system, and HbCC data were obtained from left prefrontal area. To extract intra-cranial component from HbCC data, independent component analysis were used.
We analyzed interrelationships among low-frequency oscillations in BP, amplitude of alpha wave, heart rate and HbCC.
To obtain low-frequency background oscillations, we subtracted the task-related components from the measure time-series data.
Directed coherence function was used to analyze the interrelationship among those variables. It can evaluate not only the correlation but also the direction of contributions to a variable from the other variables.
The results showed that the contribution from BP to HbCC significantly decreased under high stress condition compared to that under low stress condition, which suggests that the distribution of blood flow shifted to systemic circulation due to the increase in stressfulness.