Abstract
Multiple cortical areas of the human brain motor system interact coherently in the low frequency range (<0.1 Hz), even in the absence of explicit tasks. Following stroke, cortical interactions are functionally disturbed. How these interactions are affected and how the functional organization is regained from rehabilitative treatments as people begin to recover motor behaviors has not been systematically studied. We recorded the intrinsic functional magnetic resonance imaging (fMRI) signals from 30 participants: 17 young healthy controls and 13 aged stroke survivors. Stroke participants underwent mental practice (MP) or both mental practice and physical therapy (MP+PT) within 14–51 days following stroke. We investigated the network activity of five core areas in the motor-execution network, consisting of the left primary motor area (LM1), the right primary motor area (RM1), the left pre-motor cortex (LPMC), the right pre-motor cortex (RPMC) and the supplementary motor area (SMA). We discovered that (i) the network activity dominated in the frequency range 0.06–0.08 Hz for all the regions, and for both able-bodied and stroke participants (ii) the causal information flow between the regions: LM1 and SMA, RPMC and SMA, RPMC and LM1, SMA and RM1, SMA and LPMC, was reduced significantly for stroke survivors (iii) the flow did not increase significantly after MP alone and (iv) the flow among the regions during MP+PT increased significantly. We also found that sensation and motor scores were significantly higher and correlated with directed functional connectivity measures when the stroke-survivors underwent MP+PT but not MP alone. The findings provide evidence that a combination of mental practice and physical therapy can be an effective means of treatment for stroke survivors to recover or regain the strength of motor behaviors, and that the spectra of causal information flow can be used as a reliable biomarker for evaluating rehabilitation in stroke survivors.
Highlights
Hemiparesis is one of the most common deficits observed following stroke (Dromerick and Reding, 1995)
We used a spectral Granger causality (GC) approach on resting-state functional magnetic resonance imaging (fMRI) data of 30 participants to investigate the organization of motor-execution network for young able-bodied and aged stroke survivors along with substantial changes after the stroke survivors underwent mental practice alone or combined mental and physical therapy
As expected we found that node activity for each Regions of interest (ROIs) was significantly higher in AB condition than SS condition but unexpectedly there was no significant difference between node activities for SS, mental practice (MP), and MP+physical therapy (PT) conditions
Summary
Hemiparesis is one of the most common deficits observed following stroke (Dromerick and Reding, 1995). The functional imbalance within the motor system following stroke (James et al, 2009; Wang et al, 2010; Grefkes and Fink, 2011; Inman et al, 2012) can be due to damage of the white axonal tracts connecting brain motor areas (Turken et al, 2008; Granziera et al, 2012). Mental practice (MP) and physical therapy (PT) are two evidence-based interventions currently used to improve motor movement, coordination and balance following stroke (Page et al, 2002; Jackson et al, 2004; Butler and Page, 2006). Likewise various forms of PT have been shown to be effective in ameliorating motor weakness following stroke (Wolf et al, 2006; Langhorne et al, 2011). We studied the brain network mechanism for motor function recovery as a result of: MP only, and MP and PT in combination
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