Improvement and generalization of arm motor performance through motor imagery practice

This study compares the improvement and generalization of arm motor performance after physical or mental training in a motor task requiring a speed-accuracy tradeoff. During the pre- and post-training sessions, 40 subjects pointed with their right arm as accurately and as fast as possible toward targets placed in the frontal plane. Arm movements were performed in two different workspaces called right and left paths. During the training sessions, which included only the right path, subjects were divided into four training groups (n = 10): (i) the physical group, subjects overtly performed the task; (ii) the mental group, subjects imagined themselves performing the task; (iii) the active control group, subjects performed eye movements through the targets, (iv) the passive control group, subjects did not receive any specific training. We recorded movement duration, peak acceleration and electromyographic signals from arm muscles. Our findings showed that after both physical and mental training on the right path (training path), hand movement duration and peak acceleration respectively decreased and increased for this path. However, motor performance improvement was greater after physical compared with mental practice. Interestingly, we also observed a partial learning generalization, namely an enhancement of motor performance for the left path (non-training path). The amount of this generalization was roughly similar for the physical and mental groups. Furthermore, while arm muscle activity progressively increased during the training period for the physical group, the activity of the same muscles for the mental group was unchanged and comparable with that of the rest condition. Control groups did not exhibit any improvement. These findings put forward the idea that mental training facilitates motor learning and allows its partial transfer to nearby workspaces. They further suggest that motor prediction, a common process during both actual and imagined movements, is a fundamental operation for both sensorimotor control and learning.     

Influence of touching an object on corticospinal excitability during motor imagery

We investigated whether corticospinal excitability during the imagery of an action involving an external object was influenced by actually touching the object. Corticospinal excitability was assessed by monitoring motor evoked potentials (MEPs) in the first dorsal interosseous muscle following transcranial magnetic stimulation over the motor cortex during imagery of squeezing a ball—with or without passively holding the ball. The MEPs amplitude during imagery when the ball was held was larger than that when the ball was not held. The MEPs amplitude was not modulated just by holding the ball. In the same experimental condition, the somatosensory evoked potentials (SEPs) in response to the stimulation of median nerve were not modulated by motor imagery or by holding the ball. These results suggest that the corticospinal excitability during imagery of squeezing a ball is enhanced with the real touch of the ball, and the enhancement would be caused by some changes along the corticospinal pathway itself and not by the change in responsiveness along the afferent pathway to the primary somatosensory cortex.     

The orientation dependence of the Hermann grid illusion

The Hermann grid illusion (HGI), elicited by a grid displayed as either horizontal–vertical (HV) or oblique (45°) configuration, was measured as the luminance necessary to cancel the illusory spots at the grid intersections. Overall, the HGI produced by the oblique grid was about one-third of that produced by the HV grid. The observers exhibited different sensitivities to the HGI orientation, and seemed to perceive the illusion in two manners: with moderate anisotropy (reduction of about 20%, three subjects) or large anisotropy (90% reduction, four subjects). The quantitative reduction of the HGI elicited by the oblique pattern tested and its reduction to almost zero in some subjects, constitute a benchmark for any model aimed at explaining the HGI on psychophysical grounds.     

Effects of ventrolateral-ventromedial thalamic lesions on motor coordination and spatial orientation in rats

The ventrolateral-ventromedial (VL-VM) nuclei are classified as a motor area of the thalamus on the basis of predominant input from the cerebellum and the basal ganglia and output to the motor cortex. The sensitivity to electrolytic lesions of the VL-VM thalamic nuclei in rats was evaluated for tests requiring balance and equilibrium. VL-VM lesions impaired acquisition of the rotorod test but had no effect on stationary beam and hole-board tests. A selective impairment was also observed in the Morris water maze, as VL-VM thalamic lesions slowed down acquisition of the hidden platform but not the visible platform condition. These results support the hypothesis that thalamic motor nuclei participate in the acquisition of sensorimotor and spatial learning.     

Effects of motor imagery training after chronic,complete spinal cord injury

Abnormalities in brain motor system function are present following spinal cord injury (SCI) and could reduce effectiveness of restorative interventions. Motor imagery training, which can improve motor behavior and modulate brain function, might address this concern but has not been examined in subjects with SCI. Ten subjects with SCI and complete tetra-/paraplegia plus ten healthy controls underwent assessment before and after 7 days of motor imagery training to tongue and to foot. Motor imagery training significantly improved the behavioral outcome measure, speed of movement, in non-paralyzed muscles. Training was also associated with increased fMRI activation in left putamen, an area associated with motor learning, during attempted right foot movement in both groups, despite foot movements being present in controls and absent in subjects with SCI. This fMRI change was absent in a second healthy control group serially imaged without training. In subjects with SCI, training exaggerated, rather than normalized, baseline derangement of left globus pallidus activation. The current study found that motor imagery training improves motor performance and alters brain function in subjects with complete SCI despite lack of voluntary motor control and peripheral feedback. These effects of motor imagery training on brain function have not been previously described in a neurologically impaired population, and were similar to those found in healthy controls. Motor imagery might be of value as one component of a restorative intervention.     

Combined effect of motor imagery and peripheral nerve electrical stimulation on the motor cortex

Although motor imagery enhances the excitability of the corticospinal tract, there are no peripheral afferent inputs during motor imagery. In contrast, peripheral nerve electrical stimulation (ES) can induce peripheral afferent inputs; thus, a combination of motor imagery and ES may enhance the excitability of the corticospinal tract compared with motor imagery alone. Moreover, the level of stimulation intensity may also be related to the modulation of the excitability of the corticospinal tract during motor imagery. Here, we evaluated whether a combination of motor imagery and peripheral nerve ES influences the excitability of the corticospinal tract and measured the effect of ES intensity on the excitability induced during motor imagery. The imagined task was a movement that involved touching the thumb to the little finger, whereas ES involved simultaneous stimulation of the ulnar and median nerves at the wrist. Two different ES intensities were used, one above the motor threshold and another above the sensory threshold. Further, we evaluated whether actual movement with afferent input induced by ES modulates the excitability of the corticospinal tract as well as motor imagery. We found that a combination of motor imagery and ES enhanced the excitability of the motor cortex in the thenar muscle compared with the other condition. Furthermore, we established that the modulation of the corticospinal tract was related to ES intensity. However, we found that the excitability of the corticospinal tract induced by actual movement was enhanced by peripheral nerve ES above the sensory threshold.     

Effects of caffeine withdrawal on motor performance and heart rate changes

Heavy caffeine Users and Non-users were tested twice using a signalled reaction time paradigm, while heart rate was recorded. During the 7-day interval between the two sessions, the User group maintained normal caffeine intake for the first 5 days and abstained from caffeine during the last 2 days, which constituted a withdrawal period. The Non-users abstained from caffeine (as they usually do) during the entire 7-day period. The analyses of the reaction time (RT) data indicated no differences during Session 1 and a significant group difference during Session 2, with the Non-users exhibiting faster RT's. The Users exhibited no change between Sessions 1 and 2, while the Non-users showed a decrease in RT's (increased speed) across Sessions, which may be indicative of a practice effect. The analysis of the heart rate data from the 5-s period prior to the imperative stimulus yielded no differences during Session 1, and a significant group difference in Session 2, with the Non-users exhibiting larger decelerations. Across the two Sessions, the Non-users showed an increase in the magnitude of the heart rate deceleration, while the Users exhibited a decline in the size of the deceleration. Since the magnitude of heart rate deceleration has been interpreted as an index of attention, it appears that the Users were exhibiting less efficient attention during withdrawal from caffeine (Session 2) than were the Non-users. This conclusion is supported by the RT data, showing slower response times for the Users during Session 2, as compared to Non-users.     

Effects of centrolateral or medial thalamic lesions on motor coordination and spatial orientation in rats

The effects of central lateral (CL) or medial thalamic lesions were evaluated on tests requiring balance and equilibrium (rotorod, stationary beam, and hole-board), and spatial orientation (Morris water maze). Lesions of the medial nuclei impaired rotorod and spatial orientation, while CL lesions impaired only rotorod performance. Neither lesion affected stationary beam and hole-board tests or visuomotor guidance while swimming toward a visible platform. These spatial and sensorimotor deficits cannot be explained by reduced cerebral activation, but instead are attributable to specific projections from the anterior intralaminar nuclei to the basal ganglia and neocortex.     

基于Adaboost技术的大脑运动意识任务分类

本文提出了应用机器学习技术Adaboost算法与Fisher判别式分析作为基本分类器相结合的方法,实现大脑想象左右手运动意识任务的分类.利用Morlet小波滤波方法提取优化的运动相关脑电特征,对两组实验数据4个受试者运动相关脑电模式进行分类,平均最大分类正确率达到88.11%.通过最大分类正确率,最大互信息等评价指标比较,验证了Adaboost技术在改善大脑运动意识任务分类性能的有效性,从而为脑机接口系统应用中大脑运动意识任务分类提供了新的思路.     

Effect of a fatiguing protocol on motor imagery accuracy

This study was devised to evaluate the influence of muscle fatigue on athletes ability to perform motor imagery. Performance impairment is a consequence of fatigue, but alterations on perception and mental activity may also occur. To test whether peripheral fatigue affects mental processes, ten sports students imagined three consecutive countermovement jumps before and after a fatiguing protocol, through repetition of upright movements, at 70% of maximal voluntary contraction, until exhaustion. Autonomic nervous system responses and imagined movement durations were considered the dependent variables. Actual duration was systematically overestimated during both visual and kinesthetic imagery, but motor imagery duration and autonomic responses were similar without and under fatigue. Results suggest that muscle fatigue, unlike fatigue induced by prolonged exercise, does not elicit mental fatigue and therefore does not alter motor imagery accuracy.     

Disturbance of motor imagery after cerebellar stroke

The authors studied the possible involvement of the cerebellum in nonexecutive motor functions needed for a normal performance of complex motor patterns by analyzing (using chronometric evaluation) finger movement sequences and their respective motor imagery (a mental simulation of motor patterns). Patients suffering from a cerebellar stroke (n=11) were compared with aged-matched control volunteers (n=11). Patients that had apparently recovered from a unilateral cerebellar stroke showed a marked slowing of motor performance in both hands (ipsi- and contralateral to lesion). This effect was accompanied by a similar slowing of motor imagery, suggesting that the cerebellum, traditionally implicated in the control of motor execution, is also involved in nonexecutive motor functions such as the planning and internal simulation of movements.     

Effects of sleep deprivation and exercise on cognitive, motor performance and mood

This study examined the effect of 30 h of sleep deprivation and intermittent physical exercise, on both cognitive and psychomotor function as well subjective ratings of mood. Six subjects with the following physical characteristics participated in the study (Mean +/- S.D.): age 22 +/- 0.3 years, height 180 +/- 5 cm, body mass: 77 +/- 5 kg, VO2peak 44 +/- 5 ml kg(-1) min(-1). Three subjects engaged in normal sedentary activities while three others cycled on a cycle ergometer at 50% VO2peak for 20 min out of every 2 h during 30 h of sleep deprivation. One week later sleep deprivation was repeated with a cross over of subjects. Every 4 h, subjects completed simple and two-choice reaction time tasks at both rest and during exercise, a computerized tracking task, a number cancellation task, and an assessment of subjective mood state as measured by the POMS questionnaire. A 3 x 4 repeated measures ANOVA revealed that resting but not exercising reaction times were significantly slower with sleep deprivation. Sleep deprivation was also associated with significantly greater negative disturbances to subjective vigour, fatigue and depression assessed by the Profile of Mood States questionnaire. Compared to those who have been deprived of sleep alone, individuals that performed 5 h of intermittent moderate exercise during 30 h of sleep deprivation appeared to be more vulnerable to negative mood disturbances and impairment in reaction times. This could result in greater risk of accident due to a reduced capacity to respond quickly.     

基于脑卒中后运动康复领域的运动想象的研究

脑卒中后造成的神经性损伤是目前导致患者运动功能性障碍的主要原因之一,为社会和患者家庭造成巨大的精神和经济负担。运动想象易学习、成本低,是辅助脑卒中后患者康复的重要手段之一,对改善患者运动功能障碍、提高生活质量具有重要意义。本文主要总结运动想象对脑卒中后康复的积极作用,概述运动想象的生理表现和理论模式、运动想象能力的影响因素、运动想象能力的评分标准,并分析目前运动想象在辅助脑卒中后患者运动功能的康复治疗过程中存在的实验对象单一、评估方法主观化、实验设备分辨率低等缺陷,希望帮助脑卒中后患者更加科学、有效地使用运动想象疗法。     

Passive reading and motor imagery about hand actions and tool-use actions: an fMRI study

Recent studies have shown that motor activations in action verb comprehension can be modulated by task demands (e.g., motor imagery vs. passive reading) and the specificity of action verb meaning. However, how the two factors work together to influence the involvement of the motor system during action verb comprehension is still unclear. To address the issue, the current study investigated the brain activations in motor imagery and passive reading of verbs about hand actions and tool-use actions. Three types of Chinese verbs were used, including hand-action verbs and two types of tool-use verbs emphasizing either the hand or tools information. Results indicated that all three types of verbs elicited common activations in hand motor areas during passive reading and motor imagery. Contrast analyses showed that in the hand verbs and the tool verbs where the hand information was emphasized, motor imagery elicited stronger effects than passive reading in the superior frontal gyrus, supplemental motor area and cingulate cortex that are related to motor control and regulation. For tool-use verbs emphasizing tools information, the motor imagery task elicited stronger activity than passive reading in occipital regions related to visual imagery. These results suggest that motor activations during action verb comprehension can be modulated by task demands and semantic features of action verbs. The sensorimotor simulation during language comprehension is flexible and determined by the interactions between linguistic and extralinguistic contexts.     

Influence of somatosensory input on corticospinal excitability during motor imagery

Our previous studies showed that corticospinal excitability during imagery of squeezing a foam ball was enhanced by somatosensory input generated by passively holding the ball. In the present study, using the same experimental model, we investigated whether corticospinal excitability was influenced by holding the object with the hand opposite to the imagined hand. Corticospinal excitability was assessed by monitoring motor evoked potentials (MEPs) in the first dorsal interosseous muscle following transcranial magnetic stimulation over the motor cortex during motor imagery. Subjects were asked to imagine squeezing a foam ball with the right hand (experiment 1) or the left hand (experiment 2), while either holding nothing (Null condition), a ball in the right hand (Right condition) or a ball in the left hand (Left condition). The MEPs amplitude during motor imagery was increased, only when the holding hand and the imagined hand were on the same side. These results suggest that performance improvement and rehabilitation exercises will be more effective when somatosensory stimulation and motor imagery are done on the same side.     

Effects of prenatal stress on motor performance and anxiety behavior in Swiss mice

Stressor presence during the last weeks of gestation has been associated with behavioral disorders in later life. In this study we support further research on the long term effects of prenatal stress on Swiss mice descendant's behavior. Prenatal stress procedure consisted on restraining the dams under bright light for 45 min, three times per day from the 15th day of pregnancy, until birth. After weaning, offspring's motor performance and spontaneous exploratory behavior were measured by the tight-rope and T-maze tests, respectively. We also evaluated anxiety behavior using elevated plus maze test. We found that maternal stress improves the performance of the animals in the tight rope test and that this effect was sex and age dependent: prenatal stressed males obtained the best scores during the first month of life, while in females the same was achieved at the second month. Spontaneous exploratory behavior analysis revealed that it was elevated in prenatal stressed males and that this effect persisted on time. However, we did not find significant differences on this behavioral response among both females groups. Finally, differences on anxiety behavior were found only in females: prenatally stressed animals showed a higher proportion of entries into the open arms of a plus maze (reduced anxiety) compared to the control group. Our results show that prenatal stress modifies the normal behavior of the progeny: prenatal stressed animals have a better performance in the carried out test. These notably results suggest the existence of an adaptive response to prenatal stress.     

The elevator illusion results from the combination of body orientation and egocentric perception

Perception of body orientation and apparent location of objects are altered when humans are using assisted means of locomotion and the resultant of the imposed acceleration and gravity is no longer aligned with the gravitational vertical. As the otolithic system cannot discriminate the acceleration of gravity from sustained inertial accelerations, individuals would perceive the resultant acceleration vector (GiA) as the vertical. However, when subjects are aligned on the GiA, an increase in the magnitude of GiA induced a lowering of the apparent visual horizon (i.e. “elevator illusion”). The main aim of this study was to quantify the contribution of body and egocentric perception in the elevator illusion. While being exposed to 1 G and 1.3 G and aligned on the GiA acceleration, subjects (N = 20) were asked (1) to set a luminous target to the subjective horizon, (2) to set a luminous target on “straight ahead” position (egocentric task) and (3) to rotate a tilting tube to their subjective perception of body orientation. Results showed that increasing GiA lowered horizon and egocentric settings and induces a backward body tilt perception. Moreover, the elevator illusion can be expressed as the additive combination of two processes: one that is dependent on body tilt perception, and the other that is dependent on egocentric perception. Both misperceptions in hypergravity may be considered to be a consequence of excessive shearing of the otolith organs. However large inter-individual differences in body tilt perception were observed. This last result was discussed in terms of the contribution of extravestibular graviceptors.