The effects of activating the reticulospinal tract on anticipatory postural adjustments in fine motor movements of the upper extremities / 中华物理医学与康复杂志

ABSTRACT

Objective:To observe any dependence of anticipatory postural adjustment (APA) on the difficulty of fine upper limb tasks and to document any effect of reticulospinal tract (RST) facilitation on APAs during such tasks.Methods:The study′s bivariate mixed design involved 4 different tasks and 3 different priming states. Thirteen healthy, male, right-handed subjects were recruited. They were asked to complete the 4 tasks of reaching, grasping a cup, pinching a card using the thumb or using the little finger, respectively for 10 times 1 in response to two different starting cues delivered through an earphone. Half of the trials with each task were initiated with 114dB white noise to startle and activate the reticulospinal tract (RST), while the others were activated with 80dB beeps as a control. Electromyographic signals were recorded from the bilateral sternocleidomastoid (SCM), lower trapezius (LT), latissimus dorsi (LD), lumbar erector spinae and right anterior deltoid muscles and also from the right flexor and extensor carpi radialis muscles (ECR/FCR). In the subsequent processing the electromyographic time domain and frequency domain indicators were converted into a pre-motor reaction time, a time to muscle peak contraction, an activation latency, and APA or compensatory postural adjustment (CPA) amplitude of the tested muscles. These were compared among the different tasks and stimuli. In addition, the 114dB test tasks were classified as two different priming status as SCM + and SCM - according to whether the sternocleidomastoid muscle (SCM) was activated in advance. Results:After RST activation the pre-motor reaction time and the time to peak contraction of all of the muscles were significantly shortened in all of the tasks. The deltoid muscle reaction times in the SCM + , SCM - and control states were (106.89±43.78)ms, (136.78±48.74)ms and (168.60±73.17)ms, respectively, and those differences are significant. The APA amplitudes of the contralateral LT and ipsilateral LD were significantly greater than normal, but the timing of muscle activation onset and the APA/CPA amplitudes of the ECR/FCR were not affected. The latency in the anticipatory muscle activation of the ECR in the little finger grip task was significantly shorter than that in reaching. Conclusions:The extensor carpi radialis show task-specific early activation in fine tasks of the upper limbs with different difficulties. RST activation can lead to early starting of expected actions, accelerate muscle contraction and increase APA amplitude of some trunk muscles, but it has no significant effect on APA/CPA amplitudes in the forearm muscles.