Seventy patients with Alzheimer’s disease participated in the study. The subjects were recruited from outpatient clinic and diagnosed with probable Alzheimer’s disease according to the National Institute of Neurological and Communicative Disorders and Stroke and Alzheimer’s Disease and Related Disorders Association [19]. Interviews for diagnosis and evaluation were conducted by neurologists or neuropsychologists. Exclusion criteria were 1) patients with degenerative brain diseases such as Lewy body dementia, Parkinson’s disease, Huntington’s chorea, Down’s syndrome, Creutzfeldt-Jakob disease, 2) history of head trauma with loss of consciousness or mental retardation, 3) previous history of cerebrovascular disease or stroke on brain magnetic resonance imaging, and 4) current or past psychiatric illness. This study has been approved by the Institutional Review Board, and all participants have given written consent after fully understanding the study (2016-03-041).

Global cognitive status was assessed by Korean Mini-Mental State Examination (K-MMSE) [20] and clinical dementia rating (CDR) [21]. In order to evaluate NPS, the Korean version of the Neuropsychiatric Inventory (NPI) [22] was used to interview caregivers of patients with dementia. The NPI consists of the following 12 neuropsychiatric domains: hallucinations, delusions, agitation/aggression, depression, anxiety, irritability, disinhibition, euphoria, apathy, aberrant motor behavior, change in night-time sleep behavior, and changes in appetite and eating. The NPI assesses the frequency and severity of 12 behavioral symptoms, and at the same time, the degree of distress of the caregiver. The scores were calculated by multiplying the frequency of the symptoms (from 1 to 4) by the intensity (from 1 to 3). The total score ranges from 0 to 144, with higher scores indicating more severe NPS. According to a previous study [23], NPS were divided into four subsyndromes: apathy, hyperactivity (the sum of agitation, disinhibition, irritability, euphoria, and aberrant motor behavior scores), psychosis (delusions, hallucinations, and night-time behavior disturbances) and affective syndrome (depression and anxiety).

Structural and functional images were acquired on a 3 T MR scanner (Philips Achieva, Best, The Netherlands). Functional images were acquired while subjects were asked to keep their eyes closed and to not think of anything in particular. Thirty-five contiguous 3.5-mm-thick axial slices covering the entire brain were collected using a T2*-weighted echo-planar imaging sequence depicting the blood-oxygenation-level-dependent (BOLD) signal (TE=30 ms; TR=3,500 ms; flip angle=90°; field of view=240 mm; slice gap: 2 mm). High-resolution T1-weighted MR images (axial slices with 1-mm slice thickness; TE=1.89ms; TR=1,670 ms; flip angle=9°; field of view=250 mm) were collected prior to functional data acquisition.

The mean and standard deviation of demographic and clinical data excluding gender were calculated. Preprocessing and data analysis were performed using a combination of the statistical parametric mapping (SPM12) software (Wellcome Department of Cognitive Neurology, University College London, London, UK) and the intuitive resting-state functional connectivity (iRSFC) toolbox (https://github.com/skyeong/iRSFC). Preprocessing steps included discarding of the first 4 volumes, slice time correction, realignment, normalization to SPM13 echo-planar imaging template, smoothing with 6-mm full-width at half-maximum Gaussian kernel, linear detrending, and 0.009-0.08 Hz bandpass filtering. In addition, regression correction for spurious variables included rigid body transformation motion effects, global mean signal, white matter signal, and CSF signal. To identify the DMN, seed-based functional connectivity was calculated by placing seeds in the medial prefrontal cortex (12, 51, 36; Montreal Neurological Institute (MNI); seed radius=3 mm) and the precuneus (-6, -63, 27; MNI; seed radius=3 mm). The coordinate for seeds was determined according to a previous study [24]. The medial prefrontal cortex seed was selected for the anterior DMN and the precuneus was chosen for the posterior DMN. The network measure averages the fisher-Z transformed correction between all seed pairs in a network using iRSFC toolbox. The correlation between NPS subsyndromes and network values is then calculated using SPM13. Significant clusters were determined based on family-wise error (FWE) corrected p<0.05 with a cluster-determining threshold at uncorrected p<0.001. One sample t-tests were used to evaluate which brain regions showed significant functional connectivity with two seed regions. The details of one sample t-tests can be found in Supplementary Materials.

As shown in Table 1, patients with Alzheimer’s disease group consisted of 17 males and 53 females with an average age of 79.06±6.44 years. Mean K-MMSE and CDR score were 18.96±5.13 and 0.91±0.46.

The NPS subsyndrome scores were as follows. Apathy 2.44±3.27, hyperactivity 3.56±5.76, psychosis 1.81±3.32 and affective syndrome 2.14±3.69.

Hyperactivity subsyndrome score was negatively correlated with network measure of the left medical prefrontal cortex (MNI -4, 36, 46; 397 voxels; z=5.00) (Figure 1). Other NPS subsyndromes score did not show any significant correlation with network measure.

Patients exhibited significant functional connectivity with the medial prefrontal cortex seed in the widespread frontal regions including the medial prefrontal cortex, the dorsolateral prefrontal cortex, the inferior frontal gyrus, the primary motor cortex, and the middle temporal gyrus, the angular gyrus, the precuneus, the cuneus, the caudate, the cerebellum, and the pons. On the other hand, patients showed significant functional connectivity with the precuneus seed in the widespread posterior regions including the precuneus, the angular gyrus, and the frontopolar cortex, the middle frontal gyrus, the premotor cortex, the inferior frontal gyrus, the middle temporal gyrus, and the cerebellum. The detailed results were summarized in the Supplementary Table 1 and 2 (in the online-only Data Supplement).