Cerebral hemodynamics plays an important role in cognitive performance, and as such, age-related cognitive dysfunction and cerebral hypoperfusion increase the risk of dementia. However, age-related changes in cerebral oxygenation and cognitive function remain unclear. The aim of this study was to investigate age-related declines in cerebral oxygenation and executive function cross-sectionally. Ninety-eight healthy Japanese adults (age range: 23-79 years; 40 males, 58 females) participated in the present study using local advertisements. The participants were divided into 4 age groups: young (20-39 years; M15/F7), 50s (50-59 years; M10/F12), 60s (60-69 years; M9/F31), and 70s (70-79 years; M6/F8). We measured oxygenated hemoglobin (oxy-Hb) signal change in the prefrontal cortex during the Stroop task, and calculated Stroop interference time in cross-sectional design. This test is widely used to measure the ability to properly control attention and behavior in executing tasks, and to evaluate executive functions mainly associated with the prefrontal cortex. Oxy-Hb signal changes in the left prefrontal cortex in the 60s and 70s groups were significantly lower than those in the young group (both P < 0.05). Additionally, Stroop interference time was significantly longer in the 60s and 70s groups than in the young group (both P < 0.05). Furthermore, differences in oxy-Hb signal change between the left and right prefrontal cortex were evident only in the young group. These results suggest that the age-related decrease in executive function is associated with decrease in the cerebral oxygenation hemodynamics in the left prefrontal cortex.
Reduction of Dorsolateral Prefrontal Cortex (DLPFC) blood flow measured by near- infrared spectroscopy (NIRS) is reported to be seen during the wakefulness to the early stage of sleep. DLPFC blood flow can be an index of arousal level, while, NIRS needs to wear an annoying and costly headgear and not suitable for daily use. Using cost-effective and compact Doppler radars attached behind chair back, we conducted multivariate study for 5 healthy subjects (23±1years) to estimate DLPFC blood flow using heart rate and heart rate variability index measured by radars. Estimated DLPFC blood flow correlates with that measured by NIRS (R>0.9) only when DLPFC blood flow decreased with time.
In the measurement techniques of cortical activity by using the functional near-infrared spectroscopy (fNIRS), the differences between resting state and task-performing state is often evaluated. However, the experimental conditions of resting state are not controlled. In this study, we investigated the effects of the low-passed dynamic random-dot patterns (LPDRDs) on the resting-state activities. We measured fNIRS signals from prefrontal cortex (PFC) and right-lateral temporal cortex (rLTC) during a block design paradigms, which is constructed of resting-state block with a LPDRD or a fixation crosshair (FT) after performing a 3-back task. We compared which condition is to be recovered to resting-state earlier after brain activation by the task. The results suggest that the average activity of PFC in the LPDRD condition was significantly lower than in the FT condition, indicating that gazing at the LPDRD in resting-state could be attenuated cortical activity more efficiently.