Objective of the study: This study aimed at characterizing output features of the higher-order motor control centers (hoMCCs), including secondary (premotor cortex [Pre] and supplementary motor area [SMA]) and associa...Objective of the study: This study aimed at characterizing output features of the higher-order motor control centers (hoMCCs), including secondary (premotor cortex [Pre] and supplementary motor area [SMA]) and association (prefrontal cortex [PFC]) motor regions to the primary motor cortex (M1) during graded force tasks. It is well known that one of the major roles of the primary motor cortex (M1) is controlling motor output such as muscle force. However, it is unclear how the hoMCCs interact with M1 in regulating voluntary muscle contractions. Methods: fMRI data was acquired during graded force tasks and fMRI-based effective connectivity (EC) and muscle force analyses were performed to study the relationship between hoMCCs-M1 effective connectivity and voluntarily exerted handgrip force. Results: The results show that there is a consistent information flow from the hoMCCs to M1 under all force conditions, suggesting a hierarchical control mechanism in the brain in regulating voluntary muscle force. Only the premotor cortex exhibited a significant role in mediating the level of force production through its EC with M1 but that role diminished when the exerted force was high, suggesting perhaps a ceiling and/or fatigue effect on the EC. A flip in the direction of EC from the primary sensory cortex (S1) to the hoMCCs (PFC, SMA, and Pre) at lower force levels while at higher forces EC was observed from the hoMCCs to S1. Conclusion: The hoMCCs regulate M1 output to produce desired voluntary muscle force. Only the Pre-to-M1 connectivity strength directly correlates with the force level especially from low to moderate levels. The hoMCCs are involved in modulating higher force production likely by strengthening M1 output and downgrad<span style="font-size:12px;line-height:102%;font-family:Verdana;">ing</span><span style="font-size:12px;line-height:102%;font-family:Verdana;"> inhibition from S1 to M1.</span>展开更多
Objectives:To examine the effects of 16-week Tai Chi(TC) training on postural stability and associated physiological factors in older subjects,forty elderly individuals(aged ≥ 60 years) living in the community were r...Objectives:To examine the effects of 16-week Tai Chi(TC) training on postural stability and associated physiological factors in older subjects,forty elderly individuals(aged ≥ 60 years) living in the community were randomly placed into either the TC intervention group(n=22) or the control group(n=18).The former underwent a supervised TC exercise program for 16 weeks,while the latter received general education for a comparable time period.Measurements:Postural stability was assessed by timed stance tests in single-leg stance with the eyes open(SLO) or closed(SLC),and tandem stance with the eyes closed(TSC).Proprioceptive function was evaluated by measuring ankle and knee kinesthesia.The maximum concentric strength of the knee flexors and extensors,ankle plantarflexors and dorsiflexors was measured by isokinetic dynamometer.Moreover,the reaction time of different muscles in the lower extremity was also examined by measuring the onset latency of the muscles to perturbations on the ankle joint using an electromyography system.Results:After the 16-week TC intervention,significant TC training effects were gained on knee kinesthesia,knee flexor strength,latency of semitendinous muscle,and postural stability in SLO.For the other measures,no significant training effects were found.Conclusions:The 16-week TC intervention was found to be beneficial for the improvement of postural stability and associated physiological factors.However,there are discrepancies in TC training effects on different factors in the sensorimotor system.展开更多
文摘Objective of the study: This study aimed at characterizing output features of the higher-order motor control centers (hoMCCs), including secondary (premotor cortex [Pre] and supplementary motor area [SMA]) and association (prefrontal cortex [PFC]) motor regions to the primary motor cortex (M1) during graded force tasks. It is well known that one of the major roles of the primary motor cortex (M1) is controlling motor output such as muscle force. However, it is unclear how the hoMCCs interact with M1 in regulating voluntary muscle contractions. Methods: fMRI data was acquired during graded force tasks and fMRI-based effective connectivity (EC) and muscle force analyses were performed to study the relationship between hoMCCs-M1 effective connectivity and voluntarily exerted handgrip force. Results: The results show that there is a consistent information flow from the hoMCCs to M1 under all force conditions, suggesting a hierarchical control mechanism in the brain in regulating voluntary muscle force. Only the premotor cortex exhibited a significant role in mediating the level of force production through its EC with M1 but that role diminished when the exerted force was high, suggesting perhaps a ceiling and/or fatigue effect on the EC. A flip in the direction of EC from the primary sensory cortex (S1) to the hoMCCs (PFC, SMA, and Pre) at lower force levels while at higher forces EC was observed from the hoMCCs to S1. Conclusion: The hoMCCs regulate M1 output to produce desired voluntary muscle force. Only the Pre-to-M1 connectivity strength directly correlates with the force level especially from low to moderate levels. The hoMCCs are involved in modulating higher force production likely by strengthening M1 output and downgrad<span style="font-size:12px;line-height:102%;font-family:Verdana;">ing</span><span style="font-size:12px;line-height:102%;font-family:Verdana;"> inhibition from S1 to M1.</span>
文摘Objectives:To examine the effects of 16-week Tai Chi(TC) training on postural stability and associated physiological factors in older subjects,forty elderly individuals(aged ≥ 60 years) living in the community were randomly placed into either the TC intervention group(n=22) or the control group(n=18).The former underwent a supervised TC exercise program for 16 weeks,while the latter received general education for a comparable time period.Measurements:Postural stability was assessed by timed stance tests in single-leg stance with the eyes open(SLO) or closed(SLC),and tandem stance with the eyes closed(TSC).Proprioceptive function was evaluated by measuring ankle and knee kinesthesia.The maximum concentric strength of the knee flexors and extensors,ankle plantarflexors and dorsiflexors was measured by isokinetic dynamometer.Moreover,the reaction time of different muscles in the lower extremity was also examined by measuring the onset latency of the muscles to perturbations on the ankle joint using an electromyography system.Results:After the 16-week TC intervention,significant TC training effects were gained on knee kinesthesia,knee flexor strength,latency of semitendinous muscle,and postural stability in SLO.For the other measures,no significant training effects were found.Conclusions:The 16-week TC intervention was found to be beneficial for the improvement of postural stability and associated physiological factors.However,there are discrepancies in TC training effects on different factors in the sensorimotor system.
