Age-Related Differences in Functional Nodes of the Brain Cortex - A High Model Order Group ICA Study

Abstract

Functional MRI measured with blood oxygen dependent (BOLD) contrast in the absence of intermittent tasks reflects spontaneous activity of so-called resting state networks (RSN) of the brain. Group level independent component analysis (ICA) of BOLD data can separate the human brain cortex into 42 independent RSNs. In this study we evaluated age-related effects from primary motor and sensory, and, higher level control RSNs. One hundred sixty-eight healthy subjects were scanned and divided into three groups: 55 adolescents (ADO, 13.2 ± 2.4 years), 59 young adults (YA, 22.2 ± 0.6 years), and 54 older adults (OA, 42.7 ± 0.5 years), all with normal IQ. High model order group probabilistic ICA components (70) were calculated and dual-regression analysis was used to compare 21 RSN's spatial differences between groups. The power spectra were derived from individual ICA mixing matrix time series of the group analyses for frequency domain analysis. We show that primary sensory and motor networks tend to alter more in younger age groups, whereas associative and higher level cognitive networks consolidate and re-arrange until older adulthood. The change has a common trend: both spatial extent and the low frequency power of the RSN's reduce with increasing age. We interpret these result as a sign of normal pruning via focusing of activity to less distributed local hubs.

Keywords: age; blood oxygen dependent; functional magnetic resonance imaging; hub; independent component analysis; networks; resting state.

Figure 1

The maps in 3D with MNI (coordinates on the right) background present the group mean RSN sources of ADO and YA and YA and OA of combined groupICA analyses with 5 < z < 10 thresholding in red-yellow colour. The overlaid green colour indicates statistically significant differences between the groups (left ADO vs. YA, on right YA vs. OA) after dual regression. Significant difference areas are named and pointed with white arrows. PCC = posterior cingulate gyrus, PreCun = precuneous, ACG = anterior cingulate gyrus.

Figure 2

The salience and executive control networks are show with identical thresholding as in Figure 1. It is notable that adolescents and younger adults have a salience-executive signal source which is separated into two components in the older adults. SMA, supplementary motor area; ACG, anterior cingulate gyrus.

Figure 3

Mean power spectra of the DMN, salience and executive signal sources in each group. Older adults (OA, blue triangles) have less power in all their signal sources compared to younger adults (YA, red circle) and to adolescents (ADO, black box). Significant differences between the groups are marked with symbols ★ ■ ▲ above the spectra.

Figure 4

The image parameters and thresholding are the same as in Figure 1. Notably, the changes occur at a young age. The quadrate PM–PS RSN looses integrity in older adulthood altogether, c.f. Figure S2 in supplementary material. CG, central gyrus, premot, pre-motor cortex, post sens, dorsal to somatosensory cortex.

Figure 5

Auditory and somatosensory results shown in the manner as Figure 1. S1 alters through life but the rest of the sources do not alter significantly through time. CG, central gyrus.

Figure 6

Mean power spectra of in peri-rolandic signal sources presented in a similar way as the power spectral results in Figure 3. The signal sources are visualized in Figures 4 and 5.

Figure 7

Age-related alterations in visual networks shown with identical thresholding as in the previous images. The younger age groups have more power in their signal sources in general. The difference is smaller between the two older age groups. V5 and Vcran fuse in the older age group into a single large source. IPL, inferior parietal lobule; MTG, medial temporal gyrus; Ling g, lingual gyrus; V1, primary; V2, secondary; V3, tertiary, and, V4, quadrature visual cortex, respectively.

Figure 8

Mean power spectra of Visual signal sources with identical illustration of groups and significant changes as in Figures 3 and 6. The signal sources are shown in Figure 7.