Difference between Okinawan and Dutch older adults in prefrontal brain activation

Abstract

Background: Older adults in Okinawa (Japan) are known for healthy aging and longevity. This is the first study to explore brain activation during executive functioning in Okinawan older adults in comparison to Western-European (Dutch) older adults.

Methods: A total number of 80 participants were included in the study (41 from the Netherlands and 39 from Okinawa), with ages between 65 and 80 years). The groups did not differ for sex and handedness. Brain activation was measured during a visual working memory task and a verbal fluency task, for bilateral frontal cortex using functional near infrared spectroscopy (fNIRS). We investigated oxygenated hemoglobin (HbO) levels and laterality index.

Results: Both groups performed within the normal range for their population. During verbal fluency, less activation in the left frontal gyrus was observed in Okinawa participants as compared to Dutch participants, and more activation in the anterior superior parts of the frontal gyrus. For the n-back task, the Okinawa group exhibited less activation in the right dorsolateral prefrontal cortex and more activation in the bilateral anterior frontal gyrus. Although laterality indices were similar for both tasks, Okinawa participants showed stronger left lateralization during category fluency.

Conclusion: Our results reveal less activation of the task-relevant areas in participants from Okinawa as compared to Dutch participants. It could be hypothesized, with caution, that Okinawan older adults may need less executive processing resources to perform the task. Other differences in activation may be related to different strategy use, which may be studied in more detail in future investigations.

Keywords: Okinawa; blue zones; executive function; functional near infrared spectroscopy (fNIRS); healthy aging; prefrontal brain activation.

FIGURE 1

(a) The stimuli shapes presented in the n-back task. (b) Schematic illustration of the n-back task. Dashed blue line represents the duration of stimulus presentation (3 s), while the solid blue line represents the duration of one trial (variable with a maximum duration of 8 s). Dashed black line represents the duration of the baseline period (120 or 90 s), while the solid black line represents the duration of one block (120 s). Pictures are based on the Presentation software (Neurobehavioral Systems www.neuorbs.com), adapted from Kaufman (2004).

FIGURE 2

Functional near infrared spectroscopy (fNIRS) sources and detectors locations. Optodes (S, sources; D, detectors) and channel placement. (a) Placement of the sources and detectors on the cap. (b) Distribution of sources (red dots) and detectors (blue dots) projected on the brain surface.

FIGURE 3

(a) Verbal fluency level contrasts for oxygenised hemoglobin (HbO). Only significant channels (that survive FDR corrected threshold p_FDR < 0.05) are shown. The color scale on the right represents the t-value of the channels indicated in the figures under (a,b). For HbO contrasts, positive t-values (red) correspond to relatively larger activity in the Groningen group as compared to Okinawa group, and negative t-values (blue) correspond to larger activity for the Okinawa group. (b) Verbal fluency HbO level contrasts between groups. Same as (a) after correction for educational level. (c) Relative levels of HbO time courses. Level of Oxyhemoglobin in two different channels for two groups. Black vertical line denotes onset (at t = 0 s) and offset of the trial (at t = 60 s). Solid lines represent grand averages of time courses and shaded areas represent standard error of mean (SEM): red, Okinawa group; blue, Groningen group.

FIGURE 4

(a) N-back level contrasts for oxygenised hemoglobin (HbO). Only significant channels (that survive FDR corrected threshold p_FDR < 0.05) are shown. The color scale on the right represents the t-value of the channels indicated in the figures under (a,b). For HbO contrasts, positive t-values (red) correspond to relatively larger activity in Groningen group as compared to Okinawa group, and negative t-values (blue) correspond to larger activity for the s Okinawa group. (b) N-back level contrasts for HbO, after correction for educational level. (c) Relative HbO levels time courses. Level of Oxyhemoglobin in two different channels for two groups. Black vertical line denotes onset (at t = 0 s) and offset of the trial (at t = 60 s). Solid lines represent grand averages of time courses and shaded areas represent standard error of mean (SEM): red, Okinawa group; blue, Groningen group.