Functional near infrared spectroscopy detects cortical activation changes concurrent with memory loss in postmenopausal women with Type II Diabetes

Abstract

Older adults with Type II Diabetes Mellitus (DM) experience mild cognitive impairment, specifically in the domain of recall/working memory. No consistent causative structural cortical deficits have been identified in persons with DM (PwDM). Memory deficits may be exacerbated in older adult females, who are at the highest risk of cardiovascular decline due to DM. The focus of the current study was to evaluate functional cortical hemodynamic activity during memory tasks in postmenopausal PwDM. Functional Near Infrared Spectroscopy (fNIRS) was used to monitor oxyhemoglobin (HbO) and deoxyhemoglobin (HbR) during memory-based tasks in a cross-sectional sample of postmenopausal women with DM. Twenty-one community-dwelling DM females (age = 65 ± 6 years) and twenty-one age- and sex-matched healthy controls (age = 66 ± 6 years) were evaluated. Working memory performance (via N-back) was evaluated while study participants donned cortical fNIRS. Health state, metabolic data, and menopausal status data were also collected. Deficits in working memory accuracy were found in the DM group as compared to controls. Differences in HbO responses emerged in the DM group. The DM group exhibited altered PFC activity magnitudes and increased functional cortical activity across ROIs compared to controls. HbO and HbR responses were not associated with worsened health state measures. These data indicate a shift in cortical activity patterns with memory deficits in postmenopausal PwDM. This DM-specific shift of HbO is a novel finding that is unlikely to be detected by fMRI. This underscores the value of using non-MRI-based neuroimaging techniques to evaluate cortical hemodynamic function to detect early mild cognitive impairment.

Keywords: Brain; Cognition; Cortical oxygenation; Dementia; Neuroimaging; fNIRS.

Fig. 1

Illustration of experimental stimuli during the N-back single task and N-back + motor performance (dual-task) during fNIRS testing. Subjects viewed a fixation cross during N-back single task blocks; they viewed real-time feedback on their force production during N-back + motor performance (dual-task) blocks. The order of N-back presentation was block randomized within each testing type. N-back single task tasks always occurred prior to N-back + motor performance dual-tasks

Fig. 2

Cortical fNIRS layout and sensitivity map. A Geometrical layout of sources (red) and detectors (blue) with respect to the international 10–10 EEG system (Oostenveld and Praamstra 2001). Bold black ovals denote the regions of interest (ROIs), which are subsequently labeled nearby in purple boldface. ROIs included: prefrontal cortex (PFC), supplementary motor area (SMA), primary motor cortex (M1), primary sensory cortex (S1), and Broadmann Area 40 (B40). Hemisphere side as well as anterior and posterior of the cranium are noted. B Correspondent sensitivity map overlaid onto the Colin27 brain model. Sensitivity computed and displayed with AtlasViewer (Aasted et al. 2015)

Fig. 3

Group mean and standard error (SE) for MoCA and working memory data. White bars indicate data from the control group, gray bars indicate data from the DM group. Significant differences between Groups at p < 0.05 (*) and p < 0.001 (****) are shown. A Total MoCA scores. B Domain specific MoCA scores. C Correct response rates (accuracy) in N-back evaluations. D Response times in N-back evaluations

Fig. 4

fNIRS t-scores for HbO during single-task and dual-task evaluations for each Group, depicted by ROI and Hemisphere. Mean and standard error (SE) values are shown. Significant at p < 0.01 (**), p < 0.005 (***), p < 0.001 (****) are shown. White bars indicate right hemisphere, gray bars indicated left hemisphere

Fig. 5

fNIRS t-scores for HbO during N-back single-task evaluations (0-, 1-, and 2-back Conditions), depicted by ROI and Hemisphere. Data are averaged across Group. Mean and standard error (SE) values are shown. Significant differences between N-back Conditions at p < 0.001 (****) are shown. White bars indicate right hemisphere, black bars indicate left hemisphere

Fig. 6

fNIRS t-scores for HbR collapsed across all Tasks and Conditions, depicted by ROI and Hemisphere. Mean and standard error (SE) values are shown. Significant differences at p < 0.005 (***) and p < 0.001 (****) are shown. White bars indicate right hemisphere, black bars indicated left hemisphere