Research Article: Altered Effective Connectivity of the Primary Motor Cortex in Stroke: A Resting-State fMRI Study with Granger Causality Analysis

Date Published: November 15, 2016

Publisher: Public Library of Science

Author(s): Zhiyong Zhao, Xiangmin Wang, Mingxia Fan, Dazhi Yin, Limin Sun, Jie Jia, Chaozheng Tang, Xiaohui Zheng, Yuwei Jiang, Jie Wu, Jiayu Gong, Satoru Hayasaka.

http://doi.org/10.1371/journal.pone.0166210

Abstract

The primary motor cortex (M1) is often abnormally recruited in stroke patients with motor disabilities. However, little is known about the alterations in the causal connectivity of M1 following stroke. The purpose of the present study was to investigate whether the effective connectivity of the ipsilesional M1 is disturbed in stroke patients who show different outcomes in hand motor function. 23 patients with left-hemisphere subcortical stroke were selected and divided into two subgroups: partially paralyzed hands (PPH) and completely paralyzed hands (CPH). Further, 24 matched healthy controls (HCs) were recruited. A voxel-wise Granger causality analysis (GCA) on the resting-state fMRI data between the ipsilesional M1 and the whole brain was performed to explore differences between the three groups. Our results showed that the influence from the frontoparietal cortices to ipsilesional M1 was diminished in both stroke subgroups and the influence from ipsilesional M1 to the sensorimotor cortices decreased greater in the CPH group than in the PPH group. Moreover, compared with the PPH group, the decreased influence from ipsilesional M1 to the contralesional cerebellum and from the contralesional superior parietal lobe to ipsilesional M1 were observed in the CPH group, and their GCA values were positively correlated with the FMA scores; Conversely, the increased influence from ipsilesional M1 to the ipsilesional middle frontal gyrus and middle temporal gyrus were observed, whose GCA values were negatively correlated with the FMA scores. This study suggests that the abnormalities of casual flow in the ipsilesional M1 are related to the severity of stroke-hand dysfunction, providing valuable information to understand the deficits in resting-state effective connectivity of motor execution and the frontoparietal motor control network during brain plasticity following stroke.

Partial Text

Stroke is a leading cause of adult disability and has a stable and high death rate [1]. Motor disability is one of the most common deficits observed in stroke patients [2], and impairments in hand function have a particularly serious negative impact on daily activities and the quality of life.

In the current study, we identified the abnormal causal flow of ipsilesional M1 in two subgroups of subcortical stroke. The causal information flow of the ipsilesional M1 was disrupted, mostly involving the motor-execution and fronto-parietal cortices, and this disruption was closely related to the severity of hand dysfunction. Subsequent correlation analyses revealed that the influence from the ipsilesional M1 to the contralesional cerebellum and from the contralesional superior parietal lobe to the ipsilesional M1 correlated positively with the FMA scores, whereas the influence from the ipsilesional M1 to the ipsilesional middle frontal gyrus and temporal gyrus corrected negatively with the FMA scores. These findings may provide new insights into the resting-state functional alterations of brain plasticity following stroke.

In conclusion, we characterized the abnormal directionality of influence both from and to the ipsilesional M1 in subgroups of stroke patients. Our results suggested that the altered effective connectivity of the ipsilesional M1 mainly involved brain areas participating in motor execution and advanced motor control, which were closely related to the severity of hand dysfunction. Future studies should evaluate how rehabilitative therapy changes the specific proportion deficits of the motor execution and frontoparietal motor control networks in interacting with M1, and this evaluation is an essential next step in learning how to improve the therapeutic intervention of stroke patients with hand dysfunction.

 

Source:

http://doi.org/10.1371/journal.pone.0166210