Table 3.
Summary of significant findings from studies using graph theory methods to assess connectivity.
| 1. Mild cognitive impairment (MCI) v. Healthy control (HC) | |||||||
|---|---|---|---|---|---|---|---|
| Authors (Year) | Connectivity approach |
Analysis basis† |
Recording context† |
Significant metric |
Significant bands† |
Group effects |
Ref. |
| Choi et al. (2021) | PLV | Source - WNME | Rest - EC | Clustering coefficient | Alpha1 | MCI < HC | 21 |
| Beta2 | MCI > HC | ||||||
| Das and Puthankattil (2020) | WPLI | Sensors - avg. regions | Rest - EC, EO; Task - Mental arithmetic |
Eccentricity | Gamma (task) | MCI < HC | 23 |
| Leaf Fraction | Alpha1 (rest) | MCI < HC | |||||
| Eccentricity, diameter |
Delta, theta, alpha1, alpha2, beta (task, rest) | MCI > HC | |||||
| Betweenness centrality | Alpha1, alpha2 (task) | MCI > HC | |||||
| Dattola et al. (2021) | LLC | Source - eLORETA | Rest - EC | Network robustness | Broadband (1–40 Hz) | MCI < HC | 24 |
| Duan et al. (2020) | Coherence, PCOR |
Sensors -NA | Rest - EC | Clustering coefficient, node strength |
Theta, alpha1 | MCI < HC | 26 |
| Resilience | Theta | MCI < HC | |||||
| Versatility | Alpha2 | MCI < HC | |||||
| Path length | Theta, alpha1 | MCI > HC§ | |||||
| Betweenness centrality | Theta | MCI > HC | |||||
| Franciotti et al. (2019) | Granger causality | Sensors - pairs | Rest - EC | Degree, in-degree, out-degree, local efficiency, global efficiency | NA | MCI < HC | 32 |
| Frantzidis et al. (2014) | Relative wavelet entropy | Sensors - pairs | Rest - EC | Small worldness, clustering coefficient, nodal strength & significance ratio (betweenness centrality) |
Broadband (>1 Hz) | MCI < HC | 35 |
| Ioulietta et al. (2020) | PCOR | Sensors-NA | Rest - EC, EO | Clustering coefficient, strength | Broadband (0.3-75 Hz) | MCI < HC | 48 |
| Josefsson et al. (2019) | JDE | Sensors-NA | Task - memory | Clustering coefficient, small worldness |
Beta | MCI < HC | 56 |
| Eccentricity | Beta | MCI > HC | |||||
| La Foresta et al. (2019) | LLC | Source - eLORETA | Rest - EC | Path length | 1–40 Hz (Broadband) | MCI > HC§ | 62 |
| Lazarou et al. (2022) | PCOR | Sensors-NA | Task - visual attention, memory |
Clustering coefficient, strength | Broadband (0.3-70 Hz) | MCI < HC | 63 |
| Li et al. (2021) | PSI, DTF | Sensors-NA | Rest - EC | Clustering coefficient, node degree, global efficiency |
Theta | MCI < HC | 67 |
| Mammone et al. (2018) | PDI | Sensors - pairs | Rest - EC | Path length | Broadband (1–40 Hz) | MCI > HC§ | 70 |
| Clustering coefficient, global efficiency | Broadband (1–40 Hz) | MCI < HC | |||||
| Miraglia et al. (2016) | LLC | Source - eLORETA | Rest - EC, EO | Small worldness | Delta, theta | MCI < HC | 73 |
| Miraglia et al. (2023) | LLC | Source - eLORETA | Hypervent | Global efficiency | Alpha1, alpha2 | MCI < HC | 74 |
| Požar et al. (2020) | PLI | Sensors - avg. regions | Rest - EC | Vertex degree, degree divergence, leaf fraction | Delta | MCI < HC | 83 |
| Vertex eccentricity, diameter | Delta | MCI > HC | |||||
| Vecchio et al. (2014) | LLC | Source - sLORETA, eLORETA | Rest - EC | Clustering coefficient | Alpha1 | MCI > HC | 105 |
| Vecchio et al. (2016) | LLC | Source - sLORETA, eLORETA | Rest - EC | Small worldness | Delta | MCI < HC | 106 |
| Vecchio et al. (2021) | LLC | Source - eLORETA | Rest - EC | Small worldness | Delta, Theta | MCI < HC | 109 |
| Wei et al. (2015) | PSI | Sensors - pairs | Task - visual attention | Clustering coefficient | Alpha, beta | MCI < HC | 115 |
| PSI | Sensors - pairs | Task - visual attention | Path length | Alpha, beta | MCI < HC§ | ||
| PSI | Sensors - pairs | Task - visual attention | Small worldness | Alpha | MCI < HC | ||
| Xu et al. (2014) | MSC | Sensors-NA | Rest - EC | Clustering coefficient | Theta, alpha1, alpha2 | MCI < HC | 117 |
| Shortest path length | Theta, alpha1, alpha2 | MCI > HC§ | |||||
| Youssef et al. (2021) | Debiased WPLI |
Sensors-NA | Rest - EC (pre-, post-task) |
Clustering coefficient, global efficiency |
Theta (pre-task) |
MCI > HC | 119 |
| 2. Alzheimer’s disease (AD) v. Healthy control (HC) | |||||||
|---|---|---|---|---|---|---|---|
| Authors (Year) | Connectivity approach |
Analysis basis† |
Recording context† |
Significant metric |
Significant bands† |
Group effects |
Ref. |
| Afshari and Jalili (2016) | DTF | Sensors-NA | Rest - EC | Global efficiency, attack tolerance |
Alpha, beta | AD < HC | 1 |
| Local efficiency | Alpha, beta | AD > HC | |||||
| Bagattini et al. (2022) | PDC | Sensors - avg. regions | Task - enumeration | Divisibility | Theta | AD > HC | 9 |
| Cai et al. (2018) | PSI | Sensors – pairs, global | Rest - EC | Cross-frequency, regional synchronization strength, local efficiency, small worldness | Delta-theta, delta-alpha, delta-beta | AD < HC | 14 |
| Global efficiency | Delta-alpha, delta-beta | AD > HC | |||||
| Local efficiency | Theta-alpha | AD < HC | |||||
| Cai et al. (2020) | NIPLV | Sensors-NA | Rest - EC | Clustering coefficient | Cross-frequency, beta | AD < HC | 15 |
| Participation coefficient | Cross-frequency, delta (parietal) | AD < HC | |||||
| Participation coefficient | Cross-frequency (frontal), delta (frontal-central), alpha |
AD > HC | |||||
| Node degree proportion | Delta (posterior) |
AD < HC | |||||
| Node degree proportion | Delta (frontal) | AD > HC | |||||
| Cecchetti et al. (2021) | LLC | Source - eLORETA | Rest - EC | Path length | Theta | AD < HC§ | 19 |
| Nodal strength, clustering coefficient | Alpha2 | AD < HC | |||||
| Nodal strength, local efficiency, clustering coefficient | Theta | AD > HC | |||||
| Choi et al. (2021) | PLV | Source - WNME | Rest - EC | Clustering coefficient | Alpha1 | AD < HC | 21 |
| Theta | AD > HC | ||||||
| Dattola et al. (2021) | LLC | Source - eLORETA | Rest - EC | Network robustness | Broadband (1–40 Hz) | AD < HC | 24 |
| Duan et al. (2020) | Coherence, PCOR |
Sensors-NA | Rest - EC | Clustering coefficient, node strength |
Alpha1 | AD < HC | 26 |
| Resilience | Alpha1, alpha2 | AD < HC | |||||
| Betweenness centrality, versatility |
Alpha1, alpha2 | AD > HC | |||||
| Path length | Alpha1, alpha2 | AD > HC§ | |||||
| Engels et al. (2015) | PLI | Sensors - avg. regions | Betweenness centrality | Beta (posterior) |
AD < HC | 28 | |
| Betweenness centrality | Alpha1, alpha2, beta (anterior)^ |
AD > HC | |||||
| Escudero et al. (2016) | IPC | Sensors-NA | Rest - EC | Degree centrality, efficiency |
Broadband (0.5-40 Hz) | AD < HC | 29 |
| Franciotti et al. (2019) | Granger causality | Sensors - pairs | Rest - EC | Degree, in-degree, out-degree, local efficiency, global efficiency, out-degree assortativity | NA | AD < HC | 32 |
| Franciotti et al. (2022) | MI | Sensors-NA | Rest - EC | Network assortativity | Broadband (1-100 Hz) | AD < HC | |
| Frantzidis et al. (2014) | Relative wavelet entropy | Sensors - pairs | Rest - EC | Small worldness, clustering coefficient, nodal strength (betweenness centrality) |
Broadband (>1 Hz) | AD < HC | 35 |
| Ioulietta et al. (2020) | PCOR | Sensors-NA | Rest - EC, EO | Clustering coefficient, strength | Broadband (0.3-75 Hz) | AD < HC | 48 |
| Jalili (2016) | Coherence, PCOR, PO, SL |
Sensors-NA | Rest - EC, EO | Global & local efficiency, betweenness centrality | Alpha | AD < HC | 49 |
| Assortativity | Alpha | AD > HC | |||||
| Jalili (2017) | PCOR | Sensors - pairs | Rest - EC, EO | Local efficiency, modularity (EC) | Delta, theta, alpha, beta, gamma | AD < HC | 50 |
| Kabbara et al. (2018) | PLV | Source - WNME | Rest - EC | Global efficiency | Theta | AD < HC | 57 |
| Integration | Theta, alpha1, alpha2 | AD < HC | |||||
| Connector hubs & node vulnerability | Broadband (0.1–45 Hz) | AD < HC | |||||
| Clustering coefficient | Theta | AD > HC | |||||
| Segregation | Theta, alpha1, alpha2 | AD > HC | |||||
| Provincial hubs |
0.1–45 Hz (Broadband) | AD > HC | |||||
| La Foresta et al. (2019) | LLC | Source - eLORETA | Rest - EC | Path length | Broadband (1–40 Hz) | AD > HC§ | 62 |
| Clustering coefficient | AD < HC | ||||||
| Lazarou et al. (2022) | PCOR | Sensors-NA | Task - visual attention, memory | Clustering coefficient, strength, betweenness centrality | Broadband (0.3–70 Hz) | AD < HC | 63 |
| Li et al. (2019) | WPLI | Source - DBTN | Task - WM | Degree, clustering coefficient | Alpha1, alpha2, beta |
AD < HC | 66 |
| Centrality index | Alpha1 | AD < HC | |||||
| Degree, clustering coefficient | Alpha1, alpha2, beta, Superior temporal - all bands | AD > HC | |||||
| Centrality index | Alpha2 | AD > HC | |||||
| Mammone et al. (2018) | PDI | Sensors - pairs | Rest - EC | Path length | Broadband (1–40 Hz) | AD > HC§ | 70 |
| Clustering coefficient, global efficiency | Broadband (1–40 Hz) | AD < HC | |||||
| Mehraram et al. (2020) | WPLI | Sensors - avg. regions | Rest - EC | Clustering coefficient | Alpha | AD < HC | 71 |
| Miraglia et al. (2016) | LLC | Source - eLORETA | Rest - EC, EO | Small worldness | Delta, theta | AD < HC | 73 |
| Peraza et al. (2018) | PLI | Sensors-NA | Rest - EC | Nodal degree, leaf ratio | Alpha | AD < HC | 81 |
| Smith et al. (2016) | WPLI | Sensors-NA | Rest - EC | Clustering coefficient | Beta | AD < HC | 92 |
| Tait et al. (2019) | PLF | Source - eLORETA | Rest - EO | Small worldness, closeness centrality |
Theta | AD < HC | 98 |
| Mean degree, path length | Theta | AD > HC§ | |||||
| Vecchio et al. (2014) | LLC | Source - sLORETA, eLORETA | Rest - EC | Path length | Theta | AD > HC§ | 105 |
| Clustering coefficient | Theta, alpha1 | AD > HC | |||||
| Vecchio et al. (2016) | LLC | Source - sLORETA, eLORETA | Rest - EC | Small worldness | Delta, theta, beta1, beta2 | AD < HC | 106 |
| Alpha | AD > HC | ||||||
| Vecchio et al. (2017) | LLC | Source - sLORETA, eLORETA | Rest - EC | Small worldness | Delta, theta, beta | AD < HC | 107 |
| Alpha | AD > HC | ||||||
| Vecchio et al. (2018) | LLC | Source - sLORETA, eLORETA | Rest - EC (pre-, post-task) |
Small worldness | Alpha2 | AD ↓ HC ↑ |
108 |
| Vecchio et al. (2021) | LLC | Source - eLORETA | Rest - EC | Small worldness | Delta, theta, beta1, beta2 | AD < HC | 109 |
| Alpha1, alpha2 | AD > HC | ||||||
| Vecchio et al. (2022) | LLC | Source - eLORETA | Rest - EC | Small worldness | Delta, theta | AD < HC | 110 |
| Alpha2 | AD > HC | ||||||
| Wang et al. (2014) | MSC | Sensors-NA | Rest - EC | Clustering coefficient | Theta, alpha1, alpha2, beta, gamma | AD < HC | 112 |
| Global, local efficiency, small worldness |
Delta, theta, alpha1, alpha2, beta, gamma | AD < HC | |||||
| Mean network connectivity |
Theta, alpha2, gamma | AD < HC | |||||
| Path length | Delta, theta, alpha1, alpha2, beta, gamma | AD > HC§ | |||||
| Yu et al. (2018) | PDI | Sensors - pairs | Rest - EC | Global efficiency, clustering coefficient, small worldness | Broadband (0.5–30 Hz) | AD < HC | 120 |
| Yu et al. (2021) | Clustering coefficient; Global, local efficiency; nodal, edge between-ness | Sensors - pairs | Rest - EC, EO | Clustering coefficient, global efficiency, local efficiency | Broadband (0.5–30 Hz) | AD < HC | 121 |
| Nodal betweenness, edge betweenness | AD > HC | ||||||
Within-group effects are not shown. †see Supplementary Table S1 for study specifications and technical descriptions; § Greater values on this metric represent lower connectivity; avg = averaged; DTF = directed transfer function; EC = eyes closed; EO = eyes open; Hypervent = hyperventilation; IPC = Imaginary part of coherence; JDE = joint distribution entropy; LLC = lagged linear coherence; LPS = Lagged phase synchronization; MSC = magnitude squared coherence; MI = Mutual information; NA = not available/specified; NIPLV = Normalized imaginary phase locking value; PCOR = Pearson correlations; PDC = partial directed coherence; PDI = Permutation disalignment index; PO = Phase order; PLF = phase locking factor; PLI = phase lag index; PLV = phase locking value; PSLI = phase slope index; PSI = phase synchronization index; Ref = reference number; SL = Synchronization likelihood; WM = working memory; WPLI = weighted phase lag index; WMNE = Weighted minimum norm estimate.