Age-related alterations in default mode network: impact on working memory performance - PubMed (original) (raw)

Fabio Sambataro et al. Neurobiol Aging. 2010 May.

Abstract

The default mode network (DMN) is a set of functionally connected brain regions which shows deactivation (task-induced deactivation, TID) during a cognitive task. Evidence shows an age-related decline in task-load-related modulation of the activity within the DMN during cognitive tasks. However, the effect of age on the functional coupling within the DMN and their relation to cognitive performance has hitherto been unexplored. Using functional magnetic resonance imaging, we investigated functional connectivity within the DMN in older and younger subjects during a working memory task with increasing task load. Older adults showed decreased connectivity and ability to suppress low frequency oscillations of the DMN. Additionally, the strength of the functional coupling of posterior cingulate (pCC) with medial prefrontal cortex (PFC) correlated positively with performance and was lower in older adults. pCC was also negatively coupled with task-related regions, namely the dorsolateral PFC and cingulate regions. Our results show that in addition to changes in canonical task-related brain regions, normal aging is also associated with alterations in the activity and connectivity of brain regions within the DMN. These changes may be a reflection of a deficit in cognitive control associated with advancing age that results in deficient resource allocation to the task at hand.

(c) 2008 Elsevier Inc. All rights reserved.

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Conflict of interest statement

Disclosure statement: None of the authors have any actual or potential conflicts of interest.

Figures

Figure 1

Figure 1. Behavioral results. Older adults performed worse than younger subjects at higher task load (2-Back) (A), and were slower than younger subjects at both 1-back and 2-back (B)

Accuracy is indicated as mean % correct responses. Error bars indicate standard error of the mean. *, p<0.05; §, p<0.01.

Figure 2

Figure 2. Default mode network ICs at 1-back across groups. Two components were identified: 1-back-ANT (A, Old; B, Young) and 1-back-POST (C, Old; D, Young). The anterior component included mPFC, and right superior parietal regions, whereas the posterior component encompassed pCC, precunes and bilateral posterior parietal regions

Coronal, sagittal and axial sections illllustrating the spatial pattern of DMN activity across groups. Sagittal and axial slices are overlaid on a T1 template. The color bar indicates T-values. Time courses represent the temporal profile of each component across groups (black) overlaid on the paradigm “box-car” design (red).

Figure 3

Figure 3. Default mode network ICs at 2-back across groups. Two components were identified: 2-back-ANT (A, Old; B, Young) and 2-back-POST (C, Old; D, Young). Anterior components included mPFC and aCC. Posterior components included pCC, precunes and bilateral posterior parietal regions

Coronal, sagittal and axial sections display the spatial pattern of DMN activity across groups. Sagittal and axial slices are overlaid on a T1 template. The color bar indicates T-values. Time courses represent the temporal profile of each component across group (black) overlaid on the paradigm “box-car” design (red).

Figure 4

Figure 4. Percent power spectral density (PSD) mean change in the low frequency bin (0.03–0.08 Hz) at 1-back and 2-back in the Posterior COIs within the DMN. Older adults showed significantly decreased power attenuation in the low frequency domain relative to younger subjects when switching from the task condition (On) to the control task condition (Off)

Error bars indicate standard error of the mean. *, p<0.05; §, p<0.01.

Figure 5

Figure 5. Age and task load effects on spatial extent within the DMN regions. Older adults showed decreased recruitment of pCC in the DMN, and a decreased task load–related engagement of this area relative to younger subjects, who instead showed increased recruitment. Younger subjects showed greater recruitment of mPFC at both task loads

The differences shown are calculated as (2-back – 1-back) percent voxel extent differences for all the DMN ICs for each age group. +, effect of age p= 0.007; *, effect of interaction p=0.05; ‡, effect of age, p= 0.03.

Figure 6

Figure 6. General linear model analysis of task-induced-deactivations (TIDs) in young and older adults across different task loads. Older adults showed smaller extent of TIDs relative to young subjects in both mPFC and posterior midline regions (A). Subjects showed greater deactivations at 2-back in middle dorsal cingulate and BA10 (B). There was a significant age-by-task-load interaction in the retrosplenial pCC (C) and posterior parahippocampus (D), with older adults showing relatively decreased deactivation with increasing task load (see also Figure 7) when compared to younger subjects (see Supplementary materials for details)

Middlesagittal (x=0, A, B, C, F, G) and axial sections (z=−9, D) of the T1 template with overlaid deactivation t-maps. The color bar indicates T-values.

Figure 7

Figure 7. Timecourse of deactivations in older and young subjects across different task loads in pCC. Older adults showed significantly decreased deactivations in these regions relative to younger subjects [F(1,55)=8.841, p=0.004]. TIDs increased with task load [F(1,55)= 5.590, p=0.021], and this change was greater in younger subjects than in older adults [F(1,55)= 5.026, p=0.029]. (A) shows the mean signal across all the task in the pCC; the bars represent the standard error of the mean. (B) shows the mean timecourse in the first two blocks of the task (the baseline and the activation condition, 1-back and 2-back) in the pCC scaled to the mean (see Supplementary materials for details)

The vertical dashed line represents the beginning [a 6-sec delay was added to account for the HRF lag time (Glover 1999)] during the activation condition of the task. Time is measured in units of TR, MR signal in arbitrary units; the bars represent the standard error of the mean.

Figure 8

Figure 8. Correlation of TIDs with behavioral performance at 2-back. Accuracy correlated positively (A) with deactivation in the mPFC and PCC during 2-back, and negatively (B) with deactivation in aCC and posterior parietal cortex

Correlation t-maps are overlaid T1 template, and are showed on the middlesagittal plane. The color bar indicates T-values.

Figure 9

Figure 9. Functional connectivity with pCC: negative (A, B) and positive (C) coupling. DLPFC, VLPFC and posterior parietal cortices showed a decreased negative coupling with pCC in older as compared to younger subjects (A). All subjects showed a greater negative coupling in DLPFC with increasing task load (B).Older adults showed decreased positive functional coupling relative to younger subjects between pCC and mPFC (C)

Maps of voxel-wise connectivity of the pCC during the n-back task overlaid on an T1 template, and shown in the mid-sagittal plane (C), or rendered on the surface of the cortex (A, B). The color bar indicates T-values.

Figure 10

Figure 10. Accuracy correlated (r=0.44) with positive coupling between mPFC (BA10) and pCC both (A, B) at 2-back task. Though not statistically significant, older adults showed higher correlation (r=0.41) between performance and positive coupling between mPFC and pCC when compared to younger subjects (r=0.29)

Midsagittal slice of the correlation t-maps overlaid on a T1 template. The scatterplot (B) reflects accuracy (measured as percent correct) and functional coupling represented as correlation [z′(r)] values for old (circles, continuous line) and young (triangles, dashed line) subjects. The color bar indicates T-values.

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