Effect of parietal transcranial magnetic stimulation on spatial working memory in healthy elderly persons--comparison of near infrared spectroscopy for young and elderly.

Kaori Yamanaka,Masaru Mimura,Hiroi Tomioka,Bun Yamagata,Shingo Kawasaki,Akira Iwanami,Yumiko Noda,Willem Jan Riedel

doi:10.1371/journal.pone.0102306

Kaori Yamanaka, Masaru Mimura + Show 6 more

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https://doi.org/10.1371/journal.pone.0102306

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Journal: PloS one	Publication Date: Jul 14, 2014
Citations: 14	License type: CC BY 4.0

Affiliation: Keio University, Showa University, Hitachi (Japan)

Abstract

In a previous study, we succeeded in improving the spatial working memory (WM) performance in healthy young persons by applying transcranial magnetic stimulation (TMS) to the parietal cortex and simultaneously measuring the oxygenated hemoglobin (oxy-Hb) level using near-infrared spectroscopy (NIRS). Since an improvement in WM was observed when TMS was applied to the right parietal cortex, the oxy-Hb distribution seemed to support a model of hemispheric asymmetry (HA). In the present study, we used the same study design to evaluate healthy elderly persons and investigated the effect of TMS on WM performance in the elderly, comparing the results with those previously obtained from young persons. The application of TMS did not affect WM performance (both reaction time and accuracy) of 38 elderly participants (mean age = 72.5 years old). To investigate the reason for this result, we conducted a three-way ANOVA examining oxy-Hb in both young and elderly participants. For the right parietal TMS site in the elderly, TMS significantly decreased the oxy-Hb level during WM performance; this result was the opposite of that observed in young participants. An additional three-way ANOVA was conducted for each of the 52 channels, and a P value distribution map was created. The P value maps for the young participants showed a clearly localized TMS effect for both the WM and control task, whereas the P map for the elderly participants showed less significant channels and localization. Further analysis following the time course revealed that right-side parietal TMS had almost no effect on the frontal cortex in the elderly participants. This result can most likely be explained by age-related differences in HA arising from the over-recruitment of oxy-Hb, differentiation in the parietal cortex, and age-related alterations of the frontal-parietal networks.

Highlights

Cerebral hemispheres are apparently structurally symmetric, but there are laterality in their function, a so called functional hemispheric asymmetry (HA)
We suggested that the functional asymmetry of parietal cortex, remotely connected to the frontal cortex, indirectly influenced the working memory performance
No significant correlations were observed across all the conditions for both young and elderly participants

Summary

Introduction

Cerebral hemispheres are apparently structurally symmetric, but there are laterality in their function, a so called functional hemispheric asymmetry (HA). Among numerous studies in cognitive areas, Tulving et al [1,2] studied neuroanatomical correlates of encoding and retrieval processes of episodic memory as revealed by positron emission tomography (PET). They emerged the functional asymmetry in frontal cortex, and proposed the model of hemispheric encoding/retrieval asymmetry (HERA). Rossi et al [3] used colored magazine pictures to investigate the model of HERA. They used TMS to transiently interfere with either left or right prefrontal brain activity during the task. The result showed that, during encoding, TMS over the left prefrontal cortex (PFC) disturbed the performance than TMS over the right PFC, whereas during retrieval, TMS over the right PFC disturbed the performance than TMS over the left PFC

Results

Discussion

Conclusion