Age-related alternations in task modulation and rest-task similarity of the functional connectome

Submission No:

2182 

Submission Type:

Abstract Submission 

Authors:

Eric Kwun Kei Ng1, Siwei Liu1, Yijun Wang1, Jia-Hou Poh1, Yng Miin Loke1, Boon Linn Choo1, Beatrice Rui-Yi Loo1, Joseph Lim1, Hee Youn Shim1, Lingjie Zhu1, Joanna Su Xian Chong1, Chenhao Wang1, Juan Zhou1,2

Institutions:

1Centre for Cognitive Neuroscience, Duke-NUS Medical School, Singapore, 2A*STAR-NUS Clinical Imaging Research Centre, Singapore

Introduction:

Brain functional networks show high similarity and subtle differences at rest and task [2]. Accumulating evidence suggests that intrinsic connectivity at rest provides the communication channels of task information [4]; high similarity between the rest and task architectures may indicate less network reconfigurations and better cognitive capacity [9]. Based on this framework, networks during task may become more integrated to handle higher cognitive demands [3]. Previous studies suggested aberrant network organization such as less segregated associative networks at rest in elderly [7]. Whether the ageing brain [6] requires more task-related alternations in connectivity for competent functioning remains to be fully elucidated. Here, we examined such connectivity changes in three age groups during rest and a spatial working memory task.

Methods:

20 adolescents (13-18 years), 20 adults (19-26), and 16 healthy elderly (55-70) performed an 8-10-minute eyes-open task-free fMRI followed by 4 runs of spatial working memory task in a 3T scanner (TR = 2s) [1]. They had to remember the spatial locations of 6 dots (simultaneously presented for 800ms) for 14 seconds. A face (800ms) appeared halfway of the retention period, creating 2 levels of cognitive demands: distraction (D), when they viewed the face passively; and the more demanding interference (I), when they judged and responded if it was a target. After retention, they had to decide if the location of a probe (800ms) matched any of the 6 dots within 4.8 seconds. Task order was counterbalanced (IIDD or DDII; 18 trials per run).
Task accuracy and response time were analyzed with generalized linear mixed models. fMRI data went through standard preprocessing without global signal regression; task activation was removed for task data [4]. Static functional connectivity matrices (FC; Fisher z-transformed Pearson correlation) were obtained for 430 ROIs [8] with additional subcortical ROIs. FC matrices were analyzed with partial least square [5], which identified latent variables (LVs) best capturing the covariance between FC and age group. 1000 permutation and 500 bootstrapping were computed to assess statistical significance of an LV (p < .05) and its most salient FC edges, respectively.
PLS was first conducted on mean task FC to identify general age differences in task architecture. Its task-rest similarity (spatial Pearson correlation) was then compared across groups and correlated with performance. Another PLS was done on task difference FC to probe age-related FC changes due to task demand.

Results:

Groups did not differ in accuracy (mean 72%, SD 22%), but elderly responded slower than the others (p < .001). PLS on task mean FC yielded 2 LVs, featuring age-related increase in the FC between the default mode (DMN) and task-positive networks (Fig. 1 left), and stronger FC within and between task-positive networks in adults than the others (Fig.1 right). Task-rest similarity was the lowest in elderly (mean r = .59, p < .001) while comparable between adolescents and adults. Across all participants, lower similarity was associated with slower response (r = -.31 p = .018) and interestingly better overall accuracy (r = -.3, p = .03).
PLS on task difference FC yielded 1 LV featuring increase in FC within the DMN and control network, and between DMN/control and task-positive networks in elderly compared to adults during interference (Fig. 2). Stronger LV was correlated with slower response (r = .39, p = .003).
Supporting Image: fig1_with_caption.png
   ·Figure 1. Older brain involved higher FC between the default mode and task-positive networks and lower FC among task-positive networks during task
Supporting Image: fig2_with_caption.png
   ·Figure 2. Elderly needed more FC alternations for more difficult condition (interference)
 

Conclusions:

Adult and adolescent task FC was more similar than with the elderly. Compared to adults, elderly FC featured higher coupling between DMN and task-positive networks, more changes to increased task demand, and more task-rest reconfigurations. Ageing brain may be less efficient such that it requires extra reorganization according to various cognitive demands, i.e., more coupling across networks [10]. These extra efforts might have allowed elderly to perform adequately [6], but at the expense of speed.

Imaging Methods:

BOLD fMRI 2

Lifespan Development:

Aging 1

Keywords:

Aging
FUNCTIONAL MRI
Other - functional connectivity, task vs. rest

1|2Indicates the priority used for review