Changes in brain activation in stroke patients after mental practice and physical exercise: a functional MRI study

Abstract

Mental practice is a new rehabilitation method that refers to the mental rehearsal of motor imagery content with the goal of improving motor performance. However, the relationship between activated regions and motor recovery after mental practice training is not well understood. In this study, 15 patients who suffered a first-ever subcortical stroke with neurological deficits affecting the right hand, but no significant cognitive impairment were recruited. 10 patients underwent mental practice combined with physical practice training, and 5 patients only underwent physical practice training. We observed brain activation regions after 4 weeks of training, and explored the correlation of activation changes with functional recovery of the affected hands. The results showed that, after 4 weeks of mental practice combined with physical training, the Fugl-Meyer assessment score for the affected right hand was significantly increased than that after 4 weeks of practice training alone. Functional MRI showed enhanced activation in the left primary somatosensory cortex, attenuated activation intensity in the right primary motor cortex, and enhanced right cerebellar activation observed during the motor imagery task using the affected right hand after mental practice training. The changes in brain cortical activity were related to functional recovery of the hand. Experimental findings indicate that cortical and cerebellar functional reorganization following mental practice contributed to the improvement of hand function.

Keywords: brain activation; cortical activation; cortical reorganization; functional recovery; mental practice; motor imagery; nerve regeneration; neural regeneration; somatosensory cortex; stroke.

Conflict of interest statement

Conflicts of interest: None declared.

Figures

Figure 1

Functional MRI paradigm of motor execution (ME) and motor imagery (MI) tasks. The total experiment included two runs, one run for the MI task and one run for the ME task. Each run was 6 minutes 24 seconds, and divided into a 24-second preparatory stage and a 6-minute task stage. During each run, subjects received auditory prompts every 30 seconds, asking them to either rest or to perform the MI/ME task of thumb-to-palm opposition with the affected hand, and always starting from rest. Min: Minute; s (sec): second.

Figure 2

Comparison of pre-training and post-training Fugl-Meyer assessment scores for hand function between the treatment group receiving MP combined with PP training (MP + PP) and the control group receiving PP training alone (PP). Data are expressed as mean ± SD. A paired t-test showed post-training Fugl-Meyer assessment scores were higher than pre-training Fugl-Meyer assessment scores in the two groups (**P < 0.01). A two-sample t-test showed post-training Fugl-Meyer assessment scores in the MP + PP group were higher than post-training Fugl-Meyer assessment scores in the PP group (*P < 0.05). MP: Mental practice; PP: physical practice; pre-FMA: pre-training Fugl-Meyer assessment score; post-FMA: post-training Fugl-Meyer assessment score.

Figure 3

Average brain activation maps contrasted from motor execution (ME) and motor imagery (MI) minus rest in the two groups before and after training. The eight images (A–H) are cross-sectional images at the MNI coordinate of z from the 32 to 44 mm level. The color in the images represents the activation intensity. Color changes from red to yellow represent increasing activity intensity. (A) Before training, the treatment group (MP + PP) receiving mental practice (MP) combined with physical practice (PP) training during the ME task showed increased activation intensity in the left primary somatosensory cortex (S1), the cingulate gyrus, and right anterior cingulate area. (B) After training, the treatment group during the ME task showed increased left S1 activation intensity. (C) Before training, the treatment group during the MI task showed increased activation intensity in the right primary motor cortex (M1) and inferior frontal operculum. (D) After training, the treatment group showed decreased activation intensity in the right M1, but increased activation intensity in the left S1 during the MI task. (E) Before training, the control group (PP) receiving PP training during the ME task showed increased activation intensity in the left S1 and inferior parietal cortex. (F) After training, the control group showed increased activation intensity in the right inferior parietal cortex, right M1, and left S1 during the ME task. (G) Before training, the control group showed increased activation intensity in the right inferior frontal cortex and right M1 during the MI task. (H) After training, the control group showed increased activation intensity in the left and right superior temporal gyrus, left inferior frontal gyrus, and right M1 during the MI task.

Figure 4

Average brain activation maps derived from the comparison of motor execution (ME) and motor imagery (MI) between groups (post-training) and within groups (post-training minus pre-training). Clusters with significant differences were overlapped on render views (posterior, on the left; anterior, on the right (row 1), right, on the left; left, on the right (row 2), inferior, on the left; superior, on the right (row 3). The color in the image represents activated intensity. Red to yellow represents higher activation intensity. (A) After training, activation intensity in the right cerebellum, right temporal gyrus, left inferior frontal gyrus, and left primary somatosensory cortex (S1) was higher in the treatment group (MP + PP) receiving mental practice (MP) combined with physical practice (PP) training, compared with the control group receiving PP training during the ME task. (B) After training, the activation intensity of the right angular gyrus, right inferior frontal gyrus, right middle frontal gyrus, left superior frontal gyrus, and left supplementary motor area in the treatment group was higher compared with the control group during the MI task. (C) In the treatment group, the activation intensity of the left S1, right supramarginal gyrus, and right angular gyrus was higher after training compared with before training during the ME task. (D) In the treatment group, the activation intensity of the cerebellum bilaterally, left inferior temporal gyrus, left sub-gyral gyrus, right angular gyrus, corpus callosum, and S1 bilaterally during the MI task was higher after training compared with before training. (E) In the control group, the activation intensity of the left supramarginal gyrus and right occipital lobe during the ME task was higher after training compared with before training. (F) In the control group, the activation intensity of the left pons during the MI task was higher after training compared with before training.

Figure 5

Correlation between increased Fugl-Meyer assessment score and increased ipsilesional S1 and decreased contralesional M1 activation intensity in the two groups before and after training. (A) Pearson rank correlation analysis showed that increased ipsilesional S1 activation intensity was positively correlated with FMA score for post-and pre-training in the treatment group performing the MI task (r = 0.695, P = 0.026). (B) Pearson rank correlation analysis showed that decreased right M1 activation intensity was negatively correlated with FMA score for post- and pre-training in the treatment group (r = –0.644, P = 0.044). (C) Pearson rank correlation analysis showed that decreased right M1 activation intensity was negatively correlated with FMA score for post- and pre-training in the treatment group (r = –0.644, P = 0.044). (D) Pearson rank correlation analysis showed that decreased right M1 activation intensity was not correlated with FMA score for post- and pre-training in the control group (r = –0.289, P = 0.638). MI: Motor imagery; d: the difference score of post-training minus pre-training; T: activated intensity; S1: primary somatosensory cortex; M1: primary motor cortex; MP: mental practice; PP: physical practice; FMA: Fugl-Meyer assessment; dFMA: the value in the ordinate axis name.