TABLE 2.
Summary table of systematic review findings for functional connectivity and graph theory measures. Age effects are counts (%) of studies
| Measure | Number of Studies | Total N‐Size | Negative effect of age for all or some networks, together with absence of any positive age effects | No age differences in any networks | Positive effect of age for all or some networks, together with absence of any negative age effects | Varied direction of age effect by network | Level of certainty |
|---|---|---|---|---|---|---|---|
| Within‐network connectivity (static) | 50 | 21,110 | 36 (72%) | 0 (0%) | 1 (2%) | 13 (26%) | High a |
| Between‐network connectivity (static) | 37 | 16,518 | 5 (14%) | 1 (3%) | 20 (54%) | 11 (30%) | High a |
| Segregation, modularity, integration | 32 | 9330 | 30 (94%) | 0 (0%) | 1 (3%) | 1 (3%) | High |
| Local efficiency | 9 | 1145 | 7 (78%) b | 0 (0%) | 0 (0%) | 2 (22%) | High |
| Global efficiency | 13 | 1768 | 7 (54%) c | 3 (23%) | 3 (23%) | 0 (0%) | High |
| Within‐network connectivity (dynamic) | 7 | 993 | 7 (100%) d | 0 (0%) | 0 (0%) | 0 (0%) | Moderate |
| Between‐network connectivity (dynamic) | 8 | 1709 | 0 (0%) | 0 (0%) | 8 (100%) d | 0 (0%) | Moderate |
| Lateralization of functional connectivity at rest | 9 | 2889 | 8 (89%) | 0 (0%) | 1 (11%) | 0 (0%) | High |
| Posterior–anterior shift in functional connectivity at rest | 8 | 2124 | 0 (0%) | 0 (0%) | 7 (88%) | 1 (12%) e | High |
| Within‐subject BOLD variability | 6 | 1321 | 3 (50%) | 0 (0%) | 1 (17%) | 2 (33%) | Low |
| Metabolic connectivity | 9 | 827 | 1 (11%) | 0 | 4 (44%) | 4 (44%) | Low |
Consistency of findings was considered high, with distinct and consistent age effects seen in higher‐order and primary processing networks, see Sections 3.2.1 and 3.2.2.
100% of studies reported reduced local efficiency in higher‐order networks, see Section 3.7.2.
When nodal scale is held constant at 90–114, consistency of findings increased to 83% of studies showing negative effect of age, see section 3.4.2 and Table S8.
For dynamic within‐ and between‐network connectivity, the measures vary across studies although the direction of age effect was consistent, see section 3.6.
For posterior–anterior shift, “varied” direction of age effects indicates partial support for the HAROLD and PASA models, respectively, see section 3.5.