|Author:||Chen, Pang Wai William|
|Title:||Kinesthetic motor imagery among tai-chi practitioners : an event-related potential study|
Hong Kong Polytechnic University -- Dissertations
|Department:||Department of Rehabilitation Sciences|
|Pages:||x, 172 leaves : ill. (some col.) ; 30 cm.|
|Abstract:||Tai-chi is a mind-and-body activity involving top-down intention (yi,意) for guiding and monitoring sequence of body movements called "forms". This study aimed to explain the preparatory processes associated with tai-chi using the motor imagery theory. It was hypothesized that mental preparation of tai-chi is composed of visualization and transformation processes. The visualization process was represented by the N250 component whilst the transformation process was represented by the N400 followed by the late positive component (LPC) elicited from the motor-related regions. Using a motor imagery paradigm, tai-chi masters who had experiences in practicing the forms would show differences in the task behaviors as well as in the amplitudes and latency of N250 and N400 with normal counterpart. Sixteen tai-chi practitioners (8 males, 8 females) were recruited in this study. Their mean year of practicing tai-chi was 13.9 (SD=8.80). Their experience in tai-chi was further quantified with two custom-made questionnaires: Tai Chi Questionnaire (TCQ) and Tai Chi Motor imagery Questionnaire (TCMIQ). The TCQ collects evidence on subjects' experience in practicing tai-chi whilst the TCMIQ measures the tendency of the tai-chi subject employing kinesthetic or visual motor imagery style when receiving training in the study. Twenty health subjects (8 males, 12 females) who were age (p=0.645) and education level (p=0.562) matched were recruited as the control group. The two experimental tasks used for eliciting subjects' event-related potentials were the kinesthetic motor image generation and transformation tasks. All subjects were trained to memorize the position and movements of each body part involved in each tai-chi form and associate a Chinese character with each of the six forms. The training ended when the subject achieved 80% accuracy on the naming and memorization of all the forms. An image generation trial was always followed by a corresponding image transformation trial. In a generation trial, the subject was required to recall the first-person image representing the 1st movement sequence of a form prompted by viewing a character on the computer screen. The subject was to maintain the recalled image till the end of the trial. In a transformation trial, the subject viewed a number (2nd, 3rd or 4th) displayed on the screen which showed the movement sequence step which the visualization ended. The subject was to begin visualizing the images associated with the changes in positions of body parts from the 1st to the designated movement sequence (e.g. 3rd movement sequence). By the end of 3,000ms, the subject was asked to verify the direction of the movement of a specific body part (e.g. left hand shifting to the left) displayed on the screen at the moment when the movement had ended by pressing the "Y" (for yes) and "N" (for no) key. The response time and accuracy rate in making the responses were recorded. The trials were organized in six blocks with 60 trials in one block giving a total of 180 generation and 180 transformation trials. The total administration time was 54 minutes included 6 minutes for one block with a two-minute break in between the blocks. The behavioral results on the motor imagery tasks indicates that the tai-chi group was more accurate than the control group in both the generation (p=0.020) and transformation (p=0.004) tasks. In contrast, the tai-chi group performed significantly slower than the control group on both tasks (generation: p<0.001; transformation: p=0.006). The electrical activities of subjects in the two groups captured in the generation task were significantly different in their amplitudes (P200 (p≤0.003) and N250 (p≤0.003)). The differences in the amplitude of P200 were found in the anterior (centro-parietal) regions which was associated with retrieval of motor-related information from long term memory. The years of experience in practicing tai-chi was significantly correlated with the P200 amplitude (r=-0.43 to 0.66, p<0.01). The N250 was found significantly more negative-going in the tai-chi than control group over the frontal, central and parietal regions (p≤ 0.003), which was associated with perceiving meaningful motor actions. The years of tai-chi experience was found to moderately correlated with the amplitude of N250 elicited at the frontal-central region (r=-0.33 to -0.54, p<0.05) These findings suggest that the tai-chi subjects tended to engage more intensively than those without tai-chi experience when generating familiar stationary motor image displayed in the 1st motor sequence.|
For the transformation task, tai-chi group were revealed to have shorter latency than non tai-chi group in most of the ERP components, except the N100. The P200 elicited by the tai-chi group during the transformation of images were less-positive than the non tai-chi group and its topography covered extensive anterior to posterior regions. The N250 elicited was also more negative-going over extensive anterior to posterior regions. Different from P200, the N400 elicited by the tai-chi group was more positive-going than the non tai-chi group over fronto-central areas. The differences in LPC between the two groups were less obvious. Topography indicated that tai-chi group displayed more negative-going N400. Instead, the former group had significantly shorter N400 latency than the latter group over fronto-centro-parietal sites, and higher accuracy rate in manipulation of images of tai-chi forms. Whilst, between-group differences in LPC amplitudes and latency were statistically non-significant. The years of tai-chi experience was found to moderately correlated with the amplitude of P200 elicited at the frontal-central region (r=-0.53 to -0.89, p<0.01) and the amplitude of N250 elicited at the frontal-centralparietal region (r=-0.52 to -0.79, p<0.01). Whilst, the year of tai-chi experience was found moderately correlated with the amplitude of N400 elicited at the frontal-central-parietal region (r=-0.44 to -0.64, p<0.05) in the transformation task. These findings suggest tai-chi forms is likely to first involve generation of these images. More importantly, the retrieval of motor-related images and had them maintained for manipulation in the motor-related working memory (Chow et al., 2007; Fallgatter, Muelle & Strik, 1997; Kekoni et al., 1996; Romero et al., 2000) would be more intensive. Despite the stimuli used in the tasks might have biased against the control subjects, tai-chi subjects appear to generate and transform the motor images more effectively. The differences in the between-group ERPs suggest that tai-chi subjects tended to rely more on retrieval of motor information, visuo-spatial, sequencing and integrating motor plan functions to generate and transform tai-chi related body movements. This suggests that practice of tai-chi apart from modifying body movements may modulate subjects' mental processing in particular on motor-related images. This perhaps can explain findings from previous studies that individuals who practiced tai-chi had higher cognitive functions than those who did not. Our findings shed light on the cognitive and mental components of tai-chi and the potential gains in practicing tai-chi. They are useful for designing tai-chi interventions for rehabilitation of patients.
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