Table 1 Results from various functional neuroimaging analyses in subjective cognitive decline

Alexander et al.

[25]

EEG

Eyes open and closed resting. Visual working memory task

Average power spectra over 4 s periods during resting state. Measure of phase synchrony during task.

Participants with SCD recruited from general population with complaint of memory problems increasing over time and informant confirmation. Controls age and gender matched.

79 SCD, 79 control

Greater α band power, increased frontal θ power, and increased spatiotemporal wave activity during working memory in SCD. Greater α power and wave activity related to lower verbal memory performance and reaction time, and greater reverse digit span performance.

Increase

Rodda et al.

[26]

fMRI

Verbal episodic memory task

Voxelwise task contrasts. Group comparison with ANOVA. Cluster correction.

Participants with SCD had persistent memory concerns and were recruited from a memory clinic. Controls were recruited from a prior study and were similar to SCD in age and education.

10 SCD, 10 control

Greater left prefrontal cortex activation in SCD during encoding. No differences in recognition rate.

Increase

Maestu et al.

[27]

MEG

Sternberg’s letter-probe task

MEG source reconstruction. Nonparametric permutation testing to identify spatio-temporal clusters that distinguish the groups.

Participants with SCD recruited from memory clinic with memory deterioration confirmed by informant. Participants scored below 9 on the Geriatric Depression Scale and greater than 13 on the Memory Failures of Everyday test. Healthy elderly control participants recruited from university educational courses.

12 SCD, 18 control

Greater task-related activation within 200–900 ms after stimulus onset in SCD in parietal, temporal, occipital, motor/premotor, and dorsal prefrontal regions.

Increase

Rodda et al.

[28]

fMRI

Divided attention task with visual letters and auditory numbers

Voxelwise task contrasts. Group comparison with ANOVA. Cluster correction.

Participants with SCD had persistent perceived decline from prior memory performance and were recruited from a memory clinic. Controls were recruited as part of a prior study.

11 SCD, 10 control

Greater thalamus, caudate, posterior cingulate, hippocampus, and parahippocampus task-related activation in SCD. No differences on performance.

Increase

Dumas et al.

[29]

fMRI

N-back working memory task

Voxelwise analysis. Group comparisons with random effects ANOVA (group by working memory load). Cluster-level correction.

Healthy, older, post-menopausal women recruited from general population. Participants identified as SCD if they endorsed > 20% of the items of the Cognitive Complaint Index and as control otherwise.

12 SCD, 11 control

Greater working memory task-related activity in precuneus, midfrontal, and cingulate gyri in SCD.

Increase

Hafkemeijer et al.

[30]

fMRI

Eyes closed resting state

Independent components analysis and dual regression.

Participants with SCD recruited from memory outpatient clinic.

25 SCD, 29 control

Greater DMN and medial temporal connectivity in SCD.

Increase

Dillen et al.

[31]

fMRI

Eyes open resting state

Functional seed-based correlation analysis.

Participants with SCD recruited from outpatient memory clinic. Healthy controls recruited from general population through advertisements. Participants with SCD had memory complaint scores > 24 and normal cognitive test results.

27 SCD, 25 control

Greater functional connectivity between retrosplenial cortex and ventromedial prefrontal cortex in SCD.

Increase

Sun et al.

[32]

fMRI

Eyes closed resting state

Voxelwise amplitude of low-frequency fluctuation analysis. Group differences evaluated with voxelwise general linear model analysis.

Participants with SCD recruited from a memory clinic. Participants with SCD reported persistent decline in memory corroborated by an informant. Healthy controls recruited from the general population and did not harbor cognitive concerns.

25 SCD, 61 control

Greater low-frequency signal amplitude in superior temporal, cerebellar, occipital, and inferior parietal cortex in SCD. Greater low-frequency amplitude associated with poor verbal learning within the SCD group.

Increase

Cespon et al.

[33]

EEG

Simon task

Evaluation of P300 latency and amplitude during executive control processes.

Participants recruited from general population and split into low-SCD and high-SCD groups based on scores of a memory complaints questionnaire.

18 low-SCD, 16 high-SCD

Greater medial prefrontal negativity during task associated with greater degree of subjective cognitive decline.

Increase

Lazarou et al.

[34]

EEG

Administration of pictures of facial affect during EEG

N170 event-related potential evaluation.

Participants recruited from a memory clinic. SCD status based on SCD international working group suggestions.

14 SCD, 12 control

Greater N170 (negative) amplitude in response to faces expressing fear.

Increase

Verfaillie et al.

[35]

fMRI

Resting state

Parcellation-based functional connectivity analysis. Linear regression evaluated strength of association between SCD and connectivity strength.

Healthy older adults recruited from general population if they had a family history of Alzheimer’s disease. Participants subsequently classified as SCD if they responded “Yes” to the question “Do you think your memory is becoming worse?”

68 SCD, 56 control

Greater connectivity between posterior DMN and medial temporal regions, in SCD.

Increase

Kawagoe et al.

[36]

fMRI

Eyes closed resting state

Principle component multivariate pattern analysis for functional connectivity.

Participants recruited from the general population. Subjective memory score measured as a continuous variable.

155 participants with SCD as a continuous variable

Greater connectivity between lingual gyrus and cuneus, lingual gyrus and precuneus, superior parietal lobe and postcentral gyrus, and between cuneus and many occipital and association areas in SCD.

Increase

Bajo et al.

[37]

MEG

Sternberg’s letter-probe task.

Functional connectivity patterns, via synchronization likelihood, evaluated for task hits.

Participants with SCD recruited from memory clinic with memory deterioration confirmed by informant. Participants scored below 9 on the Geriatric Depression Scale and greater than 13 on the Memory Failures of Everyday test. Healthy elderly control participants recruited from university educational courses.

12 SCD, 25 control

Diffuse lower synchronization between electrode pairs in α and β bands in SCD.

Decrease

Wang et al.

[38]

fMRI

Eyes closed resting state

Independent components analysis and dual regression.

Participants recruited through advertisements and through referrals from medical centers. Group classification then based on results of neuropsychological assessment, self-, and informant-report. All participants classified by clinical consensus panel.

23 SCD, 16 control

Lower connectivity between right hippocampus and the DMN in SCD.

Decrease

Yasuno et al.

[18]

fMRI

Eyes closed resting state

Region-of-interest based Pearson’s correlation functional connectivity analysis.

Participants with and without SCD recruited from hospital psychiatry unit. SCD classification based on Reisberg criteria.

23 SCD, 30 control

Lower functional connectivity between retrosplenial cortex and dorsomedial prefrontal cortex, and between retrosplenial and anterior cingulate cortex in SCD. No differences between groups in amyloidopathy.

Decrease

Lopez-Sanz et al.

[39]

MEG

Eyes closed resting state

MEG source reconstruction and spectral analysis. Groups differences assessed with ANCOVA.

Participants recruited from a hospital neurology department, a center for the prevention of cognitive impairment, and a senior center. Cognitive concerns self-reported and SCD status determined by multidisciplinary panel.

39 SCD, 41 control

Diffuse lower relative α power in SCD. No differences in α peak frequency slowing.

Decrease

Contreras et al.

[40]

fMRI

Eyes closed resting state

Independent components analysis resting-state network analysis.

Participants with SCD had cognitive concerns but tested normally on cognitive tests. Controls had no significant cognitive concerns.

16 SCD, 13 control

Greater functional connectivity within all resting-state networks negatively associated with the cognitive complaint index.

Decrease

Dillen et al.

[41]

fMRI

Resting state

Region-of-interest based temporal network modeling.

Participants with SCD recruited from outpatient memory clinic. Healthy controls recruited from general population through advertisements. Participants with SCD had memory complaint scores > 24 and normal cognitive test results.

28 SCD, 25 control

Decreased functional connectivity between hippocampus and posterior DMN in SCD. Retrosplenial cortex mediated connectivity between hippocampus and DMN in controls but not SCD.

Decrease

Hayes et al.

[42]

fMRI

Event-related visual memory encoding task

Voxelwise contrasts based on subsequently remembered items. Higher level analysis carried out with FMRIB’s Local Analysis of Mixed Effects.

Participants with and without SCD recruited from general population. However, participants with SCD saw a medical professional regarding their complaints prior to participation.

23 SCD, 41 control

Weaker task-related activity related to successful encoding in occipital, superior parietal, and cingulate cortex in SCD. No differences in retrieval performance.

Decrease

Hu et al.

[43]

fMRI

Intertemporal decision task with an episodic imagination task embedded within

Voxelwise task contrasts for choice process and subjective valuation components of task. Group level factorial designs.

Participants with SCD recruited from memory clinic and reported decline in memory with onset in the past 5 years. Control participants recruited from the general population and reported no cognitive concerns.

20 SCD, 24 control

Poor temporal reward decision-making related to reduced hippocampal engagement in SCD. Lower insulae activation during task-switching in SCD.

Decrease

Mazzon et al.

[44]

EEG

Eyes closed resting state and Rey’s Auditory Verbal Learning task

Kruskal-Wallis and Wilcoxon rank sum tests compared groups on regional relative band power.

Participants recruited from a memory center. Inclusion criteria for SCD included persistent memory complaints within the past 5 years, normal cognitive performance, and no psychiatric disease.

8 SCD, 7 control

Lower parietal β and γ band power in SCD during a memorization task.

Decrease

Yang et al.

[45]

fMRI

Eyes closed resting state

Amplitude of low-frequency fluctuation evaluation. Support vector machine evaluation of ALFF for group discrimination.

Participants with SCD recruited from a memory clinic. Healthy controls recruited from general population. SCD determination based on the SCD international working group definition and made by experienced neurologists.

44 SCD, 57 control

Lower amplitude and fraction amplitude of low-frequency fluctuations in precuneus, anterior cingulum, and cerebellum in SCD.

Decrease

Lopez-Sanz et al.

[46]

MEG

Eyes closed resting state

Source power spectra estimation and group classification based on source power analysis with regularized logistic regression with the Least Absolute Shrinkage and Selection Operator.

Participants recruited from a hospital neurology department, a center for the prevention of cognitive impairment, and a senior center. Cognitive concerns self-reported and SCD status determined by multidisciplinary panel.

91 SCD, 70 control

Lower relative α band power, predominantly in frontal regions, associated with SCD.

Decrease

Viviano et al.

[47]

fMRI

Eyes closed resting state

Region-of-interest based functional connectivity analysis.

Participants with and without SCD recruited from general population. However, participants with SCD saw a medical professional regarding their complaints prior to participation.

35 SCD, 48 control

Lower functional connectivity between retrosplenial cortex and precuneus in SCD.

Decrease

Wang et al.

[48]

fMRI

Eyes closed resting state

Vertex-based functional connectivity analysis and graph-theoretic approaches to the functional connectome.

Participants with SCD recruited from memory clinic and status determined by two psychiatrists according to the international working group standard proposed by Jessen et al. Participants without SCD recruited from general population.

32 SCD, 40 control

Lower subgraph centrality in occipital and paracentral regions in SCD.

Decrease

Babiloni et al.

[49]

EEG

Eyes closed resting.

Spectral and cortical source analysis of EEG data.

Participants with SCD recruited from outpatient clinics with memory centers. Participants with SCD had z-scores > − 1.5 on cognitive battery. Controls also recruited from the clinics, but without and neurologic or psychiatric disease, and without social limitations.

53 SCD, 79 control

Greater frontal δ band amplitude, lower parietal and occipital θ and α1 (8–10.5 Hz) amplitude, and greater occipital α2 (10.5–13 Hz) amplitude in SCD.

Complex

Erk et al.

[50]

fMRI

Visual memory encoding, recall, and recognition tasks. N-Back working memory task

Voxelwise task contrasts. Group comparison with ANOVA (full-factorial design). Family-wise error correction across whole brain at p < .05, or across a-prior hippocampal and dorsolateral prefrontal regions of interest.

Participants with SCD recruited from memory clinic and had informant corroboration. Healthy controls without complain recruited from the general population. All participants scored within 1.5 standard deviations on all subtests of the Consortium to Establish a Registry for Alzheimer’s Disease.

19 SCD, 20 control

Lower posterior hippocampal activation and greater right dorsolateral prefrontal cortex activation during recall in SCD. No differences in task performance or task-related activity during memory encoding. No group differences in N-back task.

Complex

Vega et al.

[51]

fMRI

Resting state

Voxelwise seed-based functional connectivity. Second-level regression analysis associated cognitive complaint index with voxelwise connectivity.

Healthy, older, post-menopausal women recruited from general population. Participants identified as SCD if they endorsed > 20% of the items of the Cognitive Complaint Index and as control otherwise. Cognitive complaints evaluated as a continuous variable.

31 SCD (continuous)

Greater within executive control network and within middle temporal gyrus connectivity, and lower frontal cortex functional connectivity in SCD.

Complex

Lopez-Sanz et al.

[52]

MEG

Eyes closed resting state

Source reconstruction and phase synchronization functional connectivity analysis.

Participants recruited from a hospital neurology department, a center for the prevention of cognitive impairment, and a senior center. Cognitive concerns self-reported and SCD status determined by multidisciplinary panel.

41 SCD, 39 control

Increased α-band connectivity between anterior regions and decreased α-band connectivity between posterior regions in SCD.

Complex

Jiang et al.

[53]

fMRI

Eyes closed resting state

Vertex-based functional connectivity analysis.

Participants with SCD recruited from memory clinic and status determined by two psychiatrists according to the international working group standard proposed by Jessen et al., [1]. Participants without SCD recruited from general population.

42 SCD, 54 control

Lower vertex-wise index of functional criticality (a measure of signal standard deviation, within cluster correlation, and correlation with components outside a cluster) in the inferior temporal gyri and frontal poles, and greater criticality in precuneus, cingulate, parietal, and ventromedial prefrontal cortices in SCD.

Complex

Li et al.

[54]

fMRI

Eyes open resting state

Whole-brain Pearson’s correlations and graph-theoretic methods to evaluate functional connectivity differences between groups.

Participants with SCD and healthy controls pulled from the Alzheimer’s Disease Neuroimaging Initiative (ADNI) database.

44 SCD, 40 controls

Participants with SCD exhibited greater degree centrality in hippocampus, and fusiform gyrus, and lower inferior parietal degree centrality. No differences between groups in eigen centrality. No differences between groups in amyloidopathy or tauopathy.

Complex

Xie et al.

[55]

fMRI

Eyes closed resting state

Static and dynamic functional connectivity based on connectivity matrices derived from the Automated Anatomical Labeling atlas.

Participants with SCD recruited from a memory clinic. Healthy controls recruited from general population. SCD determination based on the SCD international working group definition and made by experienced neurologists.

40 SCD, 53 control

Centrality frequency (proportion of time a degree centrality hub region appeared in a dynamic functional connectivity analysis) differed between SCD and controls. Lower gyrus rectus and cingulum, and greater hippocampus, calcarine, lingual, and occipital centrality frequency in SCD.

Complex

Yan et al.

[56]

fMRI

Eyes closed resting state

Multimodal (functional connectome and structural connectome via diffusion imaging) classifier training.

Participants with SCD recruited from a memory clinic. Healthy controls recruited from general population. SCD determination based on the SCD international working group definition and made by experienced neurologists.

39 SCD, 45 control

Classification accuracy for distinguishing SCD from controls ranged from 72 to 77% over a set of classifiers trained on connectome data. Important regions for classification included frontal, parietal, temporal, and hippocampal regions.

Complex

Dierks et al.

[57]

EEG

Eyes closed resting.

EEG segmented into microstates based on the locations of centroids of electrical activity during spikes in spatial variance.

Participants with SCD recruited from memory clinic, did not exhibit difficulties in everyday living, and performed less than one standard deviation below age reference average on cognitive tasks. Control subjects did not harbor memory complaints and came from the general population.

31 SCD, 21 control

Duration of microstates, distinct spatial patterns of electrical activity, reduced in dementia. No difference between controls and SCD.

No difference

Lopez-Sanz et al.

[58]

MEG

Eyes closed resting state

Source reconstruction and region-of-interest based functional connectivity analysis. Graph theoretic approaches utilized.

Participants recruited from a hospital neurology department, a center for the prevention of cognitive impairment, and a senior center. Cognitive concerns self-reported and SCD status determined by multidisciplinary panel.

55 SCD, 63 control

Decreased small-world characteristics of mild cognitive impairment brains compared to healthy controls in θ and β bands. Individuals with SCD exhibited a similar pattern, though not significantly different from controls.

No difference

Teipel et al.

[59]

fMRI

Resting state

Pearson’s correlation based functional connectivity. Amplitude of low-frequency fluctuation evaluation. Evaluation of functional connectivity to distinguish SCD via cross-validated discrimination accuracy based on penalized logistic regression.

Participants recruited from the general population and grouped as SCD if they answered “Yes” to the questions “Are you complaining about your memory?” and “Is it a regular complaint that lasts more than 6 months?”

90 SCD, 80 controls

Functional connectivity did not reach significant discrimination accuracy for distinguishing SCD from controls.

No difference

Contreras et al.

[60]

fMRI

Eyes closed resting state

Within- and between-network functional connectivity based on whole-brain parcellation.

Participants drawn from two cohorts. Participants with SCD had cognitive concerns but tested normally on cognitive tests. Controls had no significant cognitive concerns.

27 SCD, 31 control

No significant difference between controls and SCD.

No difference

Scarapicchia et al.

[61]

fMRI

Eyes open resting state

Association between resting-state voxelwise BOLD variability and white matter hyperintensities older adults with and without SCD.

Participants drawn from ADNI database. SCD status determined by ADNI investigators. Participants self-reported cognitive concerns and scored > 15 on the first 12 items of the Cognitive Change Index. Control participants had no significant cognitive concerns.

19 SCD, 19 control

No significant difference between controls and SCD in blood-oxygen-level dependent variability. Higher white matter hyperintensity burden associated with greater variability in temporal regions for controls only.

No difference