Study object and group:
AD patients who came to Changsha First Hospital from January 2022 to December 2022 were selected, and the inclusion criteria were: (1) : Patients >60 years of age, (2) probable diagnosis of AD (International Classification of Diseases 10th Edition of the World Health Organization (ICD-10)), (3) MMSE score of 11-26, with more than 6 years of education, and (5) CDR score of 1-2, volunteered to participate in this study. Exclusion criteria: (1) no self-care ability. (2) other diseases affecting cognitive function (vascular dementia, Parkinson's disease, frontotemporal dementia, epilepsy, severe anemia, severe liver and kidney insufficiency, etc.), (3) refused to participate in this experiment, (4) could not complete the fNIRS examination, (5) suffered from depression, (6) Head MRI showed Fazekas scale≥ 2. Recruit a matching control group based on the basic situation of the enrolled. Before fNIRS monitoring, all subjects were evaluated by Mini-Mental State Examination (MMSE), which was divided into two groups: control group (subjects with MMSE>26 points were considered to have normal cognition) and AD group (with MMSE<26 points, in line with the sodium standard).
The qualified personnel are investigated, and the unified questionnaire is adopted by the professionally trained investigators, and the face-to-face questionnaire survey is conducted after the informed consent of the surveyed subjects. The content includes general demographic information (gender, age, education, retirement years, pre-retirement employment, marital status, way of living, handedness, medical history) and lifestyle habits (smoking, alcohol consumption).
General data collection:
The general data include age, sex, education, handedness, marital status, past illness, and life after retirement. Previous medical history: Chronic medical history, including hypertension, diabetes, hyperlipidemia, cardiovascular and cerebrovascular diseases, was 0 for those without chronic medical history, 1 for those with one chronic medical history, and 2 for those with two chronic medical histories or more.
fNIRS tool:
A 53-channel fNIRS device ((BS-7000, Wuhan Znion Technology Co, Ltd, China) was used to measure the three types of relative concentration changes of Oxy-Hb, Deoxy-Hb, and Total-Hb by near-infrared light of a specific wavelength. The instrument has 16 pairs of emission and detector probes. The wavelengths of light emitted are 690 nm and 830 nm, and the frequency is 15.625 Hz. The distance between each emitter and detector is 2.9–3.1 cm. The area between the emitter and detector probes consists of a channel. Each probe was positioned on the scalp of the forehead. The optode arrangement is shown in Fig. 1 and is
based on the 10/20 System of Electrode Placement method, which is also commonly used in EEGs (Okamoto et al., 2004). A total of 16 pairs of optodes and 53 channels. The numbers represent remitter probes, with the letters representing detector probes[5].
A total of 16 pairs of optodes and 53 channels. The numbers represent remitter probes, with the letters representing detector probes. Channels 01 (ch01), ch04.ch10, ch40, ch47 and ch52 belong to the Pre-Motor and Supplementary Motor Cortex (PreM and SMC). Ch02, ch03, ch05, ch07, ch08, ch13, ch44, ch46, ch49, ch50, ch51 and ch53 belong to the Broca's area. Ch06, ch11, ch14, ch17, ch18, ch20, ch25, ch31, ch32, ch34, ch39, ch42 and ch45belong to the dorsolateral prefrontal cortex (DLPFC). Ch12, ch24, ch26, ch38belong to the frontal eye fields (FEF). Ch09, ch15, ch16, ch19, ch21, ch22, ch23, ch27, ch28, ch29, ch30, ch33, ch35, ch36, ch37, ch41, ch43 and ch48 belong to the frontal pole area (FPA). All tasks are completed in the morning (8am - 12pm), first completing the resting state task and then completing the VFT task.
MMSE:
An initial assessment of cognitive function, currently the most widely used scale, includes orientation (10 points), immediate memory (3 points), attention and numeracy (5 points), recall (3 points), and verbal ability (9 points), out of a possible 30 points.
Resting data acquisition:
The patient was seated and rested for 5 minutes while wearing the fNIRS device. The patient was asked to relax, look at the black cross 50cm in front, and keep the head as stable as possible. The original fNIRS data of the patient was collected for 150 seconds[3].
Verbal fluency test (VFT) data acquisition:
The patient was seated and rested for 5 minutes while wearing the fNRS device. Before the task began, the patient followed the voice prompt to count for 30 seconds. Then complete 3 groups of tasks (please name a variety of vegetables, please name a variety of fruits, please name a variety of animals), each group of tasks lasts 20 seconds。Then continue to followed the voice prompt to count for 60seconds[4]
fNIRS data preprocessing:
fNIRS signal is processed by MATLAB2014b. The original fNIRS data were converted to the concentration changes of Oxy-Hb and Deoxy-Hb using the modified Beer-Lambert Law[28]. Physiological noise (heart noise ~1Hz, respiratory noise ~ 0.25Hz, Mayer signal ~0.1Hz) and mechanical noise were filtered by band-pass filter with cut-off frequency range of 0.005Hz ~0.1Hz, and motion artifacts were identified and removed. The data is then split into task time and resting time. Baseline correction was performed for each subject by subtracting average resting state data (30 seconds before task start and 60 seconds after task completion) from the task data[29]. For VFT tasks, the signal of each channel is collected for further analysis of the characteristics. The characteristics selected were activation value(T value), slope, and average oxygenated hemoglobin concentration[30-31]. Because Oxy-Hb has a better signal-to-noise ratio, it can reflect task-related cortical activation more directly than Deoxy-Hb. Therefore, this study focused on the changes of Oxy-Hb. The standard Hemodynamic response function (HRF) in this study was generated by convolution of the stimulation mode (i.e., the 60-second task cycle and the 90-second rest cycle) with the typical hemodynamic response function composed of two gamma functions[32]. The activation value (T value) is defined as the ratio of the weight factor (when the measurement data is linearly fitted to the HRF) to the standard error[33]. The meaning of the T-value in this study is conceptually the same as in the fMRI field, where a high T-value indicates a strong correlation between the signal and HRF.
By measuring the difference in mean oxygen and hemoglobin values between the task and the pre-task phase, the mean changes in oxygenated hemoglobin concentrations across 53 channels were calculated. The mean oxygenated hemoglobin value is the average over the entire test time window. The slope indicates the speed of activation.
For the resting state data, the correlation of hemoglobin changes among different channels was calculated using NIRS-KIT[34] software, and the R-value was calculated by Spearman correlation analysis. r≥0.5 was defined as a connection between channels, and the number of connecting edges between each functional zone was analyzed, and the strength of functional connections of each functional zone in the resting state was represented by the size of the edge number. Use BrainNets[35] to make correlation matrix plots. On the basis of correlation matrix, channels are taken as network nodes and the connections between channels are taken as network edges. By calculating the number of network edges of correlation coefficient r≥0.5, the strength of each functional connection area is further analyzed. The number of edges of networks with intra-hemispheric connections and inter-hemispheric connections, as well as short connections (connections between each functional area in the hemisphere and its own connections and connections between other functional areas) and long connections (connections between each functional area and functional areas in the other hemisphere) were counted respectively.
statistical method
SPSS27.0 statistical software was used for data processing. Normal test was performed on the measurement data. The measurement data conforming to normal distribution were expressed as (X±s), and the two independent samples T-test was used for comparison between groups. The measurement data that did not conform to the normal distribution were represented by M (Q1, Q3), and the measurement data of the Mann-Whitney U test line were represented by (x±s) for inter-group comparison. Counting data were expressed as relative numbers, and Chi-square test was used for comparison between groups. Spearman correlation analysis was used, and p<0.05 indicated statistically significant difference between the two groups.