Simultaneous measurements of cerebral oxygenation changes during brain activation by near-infrared spectroscopy and functional magnetic resonance imaging in healthy young and elderly subjects

Abstract

Near infrared spectroscopy (NIRS) and functional magnetic resonance imaging (fMRI) both allow non-invasive monitoring of cerebral cortical oxygenation responses to various stimuli. To compare these methods in elderly subjects and to determine the effect of age on cortical oxygenation responses, we determined motor-task-related changes in deoxyhemoglobin concentration ([HHb]) over the left motor cortex in six healthy young subjects (age 35 +/- 9 years, mean +/- SD) and five healthy elderly subjects (age 73 +/- 3 years) by NIRS and blood-oxygen-level-dependent (BOLD) fMRI simultaneously. The motor-task consisted of seven cycles of 20-sec periods of contralateral finger-tapping at a rate as fast as possible alternated with 40-sec periods of rest. Time-locked averages over the seven cycles were used for further analysis. Task-related decreases in [HHb] over the motor cortex were measured by NIRS, with maximum changes of -0.83 +/- 0.38 mumol/L (P < 0.01) for the young and -0.32 +/- 0.17 mumol/L (P < 0.05) for the elderly subjects. The BOLD-fMRI signal increased over the cortex volume under investigation with NIRS, with maximum changes of 2.11 +/- 0.72% (P < 0.01) for the young and 1.75 +/- 0.71% (P < 0.01) for the elderly subjects. NIRS and BOLD-fMRI measurements showed good correlation in the young (r = -0.70, r(2) = 0.48, P < 0.001) and elderly subjects (r = -0.82, r(2) = 0.67, P < 0.001). Additionally, NIRS measurements demonstrated age-dependent decreases in task-related cerebral oxygenation responses (P < 0.05), whereas fMRI measurements demonstrated smaller areas of cortical activation in the elderly subjects (P < 0.05). These findings demonstrate that NIRS and fMRI similarly assess cortical oxygenation changes in young subjects and also in elderly subjects. In addition, cortical oxygenation responses to brain activation alter with aging.

Figure 1

MRI activation maps showing the area of activation (yellow arrows) over the left motor cortex for a young subject (Panel 1–6, from medial to lateral) and for an elderly subject (Panel 7–12, from medial to lateral) during a 20‐sec contralateral finger‐tapping task. The NIRS optode positioning was marked with vitamin E capsules, as shown in Panel 2 and 6, and Panel 8 and 12 (white arrows).

Figure 2

Time course of finger‐tapping activity represented by vertical peaks and periods of rest represented by horizontal lines (upper panel), time course of changes in deoxyhemoglobin ([HHb]), oxyhemoglobin ([O₂Hb]), and total hemoglobin ([tHb]) concentrations as measured by NIRS (middle panel), and time course of changes in the maximum BOLD‐fMRI signal (lower panel) over the left motor cortex in a young subject during seven cycles of contralateral finger‐tapping for 20 sec and rest for 40 sec.

Figure 3

Grand‐average changes in deoxyhemoglobin ([HHb]), oxyhemoglobin ([O₂Hb]), and total hemoglobin ([tHb]) concentrations as measured by NIRS over the left motor cortex in healthy young (n = 6, —•—) and elderly subjects (n = 5, —○—) during a 20‐sec contralateral finger‐tapping task. The individual changes were time‐locked averages over seven cycles of finger‐tapping. Data are presented as mean ± SD. P‐values representing the effect of time for both groups and P‐values representing the time‐by‐group interaction are shown (repeated‐measures ANOVA).

Figure 4

Grand‐average changes in BOLD‐fMRI signal due to deoxyhemoglobin concentration changes over the left motor cortex in healthy young (n = 6, —•—) and elderly subjects (n = 5, —○—) during a 20‐sec contralateral finger‐tapping task. The two graphs represent consecutively the BOLD‐fMRI signal changes in the cortex area with maximum activation (maximum fMRI) and in the banana‐shaped interoptode cortex volume underneath the NIRS optodes (interoptode fMRI). The individual changes were time‐locked averages over seven cycles of finger‐tapping. Data are presented as mean ± SD. P‐values representing the effect of time for both groups and P‐values representing the time‐by‐group interaction are shown (repeated‐measures ANOVA).

Figure 5

Correlation between changes in deoxyhemoglobin concentration ([HHb]) as measured by NIRS and changes in BOLD‐fMRI signal over the left motor cortex in healthy young (n = 6, —•—) and elderly subjects (n = 5, —○—) during a 60‐sec period involving 20 sec of contralateral finger‐tapping and 40 sec of rest. For each subject, the time‐locked average changes over 7 cycles of finger‐tapping are shown, including 15 points of 4‐sec periods.