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Why elder adults have a higher fall risk in dual-task daily life: A Preliminary fMRI Study
Yijia Zheng1, Ye Wang1,2, Yi Zhu1, Xiaoying Wang1,3, Jue Zhang1,4, and Jing Fang1,4

1Academy for Advanced Interdisciplinary Studies, Peking University, Beijing, China, 2Neuroscience and Intelligent Media Institute, Communication University of China, Beijing, China, 3Department of Radiology, Peking University First Hospital, Beijing, China, 4College of Engineering, Peking University, Beijing, China

Synopsis

Reduced plantar sensation can lead to weakened balance ability in elder adults and an addition of cognitive tasks will further weaken it. Thereby, we attempted to explore the brain activity pattern of the elder and of young adults under foot stimuli and in dual-task condition. The results revealed that elder adults have significantly stronger cortical excitability than young do, and that foot stimuli induced stronger cortical excitability compared with dual-task condition. In conclusion, these phenomena may be due to the elder adults’ inadequate central reserve. Besides, added cognitive task can further reduce the brain’s response through diminished sensory input.

Introduction

It is generally accepted that loss of balance has become a common problem in elder adults and the risk of death or serious injury caused by a fall increases with age[1]. Human balance control is a complex physiological process and the central nervous system(CNS) plays an important role in balance control[2]. In addition, as a dynamic equilibrium process, balance control not only requires maintaining balance but also often necessitates simultaneous cognitive tasks[3, 4]. And the probability of occurrence of falls in elder adults with cognitive impairment is twice than that of normal elder adults[5]. However, central nervous regulatory mechanisms of weakened balance control under dual-task or multi-task in daily life are not clear now.

Purpose

To better understand the mechanism of weakened balance ability in elder adults, we attempted to explore the brain activity pattern of the elder and of young adults under foot stimuli and dual-task (cognitive task and foot stimuli) condition by using a self-designed magnetic resonance imaging-compatible tactile stimulation system.

Materials and Methods

Subjects:

16 healthy young adults (22.2 ± 2.1 years; 11 males) and sixteen healthy elder adults (61.8 ± 6.5 years; 9 males) were recruited for this study. All subjects provided informed consent as approved by the Institutional Review Board of Peking University First Hospital, Beijing.

Protocol:

In the fMRI protocol, each block was 30s in duration and repeated three times(Fig.1). The first part of the fMRI protocol was used to compare the brain response patterns of elder and young adults under the foot stimuli and the second was used to further understand the response of dual-task in elder adults.

MRI images acquisition

MRI scans were performed on a GE 3T scanner (Signa Excite HD). BOLD data were acquired using a standard echo-planar imaging sequence (repetition time/echo time, 2000/30 ms; flip angle, 90°; image matrix, 64×64; thickness/spacing, 4 mm/1 mm; field of view, 230×230 mm2; 28 interleaved axial slices; and 30 repetition times.) A high-resolution structural image was acquired using a three-dimensional fast spoiled gradient echo sequence for anatomical localization (repetition time/echo time, 7.8/3.0 ms; flip angles, 20°; inversion time, 450 ms; field of view, 240×240 mm2; slice thickness, 2.0 mm with 1.0 mm overlap; in-plane resolution, 1×1 mm2.)

Data and statistical analysis

BOLD data were preprocessed with Statistical Parametric Mapping software (SPM8). Next, one sample t-test was used to obtain group analysis results. In addition, two sample t-tests were used to explore difference of brain activity patterns between conditions. Brain regions related to sensory processing of the foot and lower limbs are defined as regions of interest (ROIs), which include the bilateral dorsomedial somatosensory cortex (dmS1) (Fig.2). And the average percent signal change (PSC) value of each ROI was calculated. Then, the differences of PSC values within each ROI were analyzed through two-tailed paired t-tests.

Results

Two sample t-test results showed that compared to young adults, foot stimuli to elder adults elicits increased excitability of bilateral postcentral gyrus, precentral gyrus, supplementary motor area, middle frontal gyrus, inferior parietal lobule, superior parietal lobule, middle cingulate gyrus, angular gyrus, supramarginal gyrus, superior temporal gyrus, middle temporal gyrus, left precuneus, right superior frontal gyrus, and insula (uncorrected, p < 0.001, cluster size ≥ 10).

Whole-brain group-level comparison revealed that, in comparison dual-task condition foot stimuli only was associated with greater activation within the bilateral supplementary motor area, superior frontal gyrus, left side of central lobule, angular gyrus, middle frontal gyrus, right postcentral gyrus, superior parietal gyrus, and supramarginal gyrus in elder adults (uncorrected, p < 0.001, cluster size ≥ 10).

ROI analysis further showed that there was no significant difference in the excitability of the left dmS1 and the right dmS1 between young and elder adults (Fig.4). ROI analysis also revealed that, as compared to foot stimuli only condition, the left dmS1 (p < 0.05) as well as the right dmS1 (p < 0.05) were significantly inhibited under the dual-task condition in elder adults (Fig.4.).

Discussion

This study found that elder adults showed a stronger cortical response to foot stimuli, and this is probably due to their inadequate central reserve and lower brain network efficiency. However, there was significant reduced PSC value in the bilateral dmS1 under dual-task, which suggested a decrease of sensory input of foot in elder adults. Thus, we believe that diminished sensory input is likely to be related to weakened balance control under dual-task or multi-task in the elder adults’ daily lives.

Acknowledgements

This work was supported by grants from the National Natural Science Foundation of China (grant no. 11372013 and 11572003).

References

1.Manchester, D., et al.,Journals of Gerontology, 1989. 44(4): p. M118-M127.

2.Gribble, P.A., et al., Archives of Physical Medicine and Rehabilitation, 2004. 85(4): p. 589-592.

3.Yogev-Seligmann, G., et al., Movement Disorders, 2008. 23(3): p. 329-342.

4.Logsdon, R.G., et al., Alzheimers care today, 2007. 8(4): p. 309-318.

5.Tinetti, M.E., , et al.,New England Journal of Medicine, 1988. 319(26): p. 1701-1707.

Figures

Fig.1. Experimental design. A block-designed BOLD fMRI protocol, including two parts, was completed to quantify the cortical response. The elder adults completed the first and second part, the young adults completed the first part. (a). The first part of the fMRI protocol including rest block and foot stimuli block. (b). The second part of the fMRI protocol including cognitive block and dual-task (cognitive task and foot stimuli task) block. During the cognitive task, the researchers randomly reported a three-digit number, and the subjects did continuous subtraction by three. (c). MRI-compatible tactile stimulation system used to simulate the plantar sensation.

Fig.2. The ROIs associated with foot and lower limb somatosensory processing: left and right dmS1

Fig.3. The brain activity pattern of the young and the elder adults under the foot stimuli and the dual-task. statistical parametric maps representing the group average of both stimulation conditions were false discovery rate corrected (p < 0.05) and overlaid on the pial surface.

Fig.4. Percent Signal Change (PSC) in brain ROIs. No significant difference between young adults and elder adults was found in the left dmS1 (p = 0.234, a) and right dmS1 (p = 0.127, b) under the foot stimuli. The PSC of both left dmS1 (p = 0.018, c) and right dmS1 (p = 0.027, d) were significantly higher under foot stimuli condition compared with dual-task condition in elder adults (*, p < 0.05, error bars indicate mean standard error).

Proc. Intl. Soc. Mag. Reson. Med. 26 (2018)
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