Using sympathetic skin responses in individuals with spinal cord injury as a quantitative evaluation of motor imagery abilities

Rehabilitation Training after Spinal Cord Injury Affects Brain Structure and Function: From Mechanisms to Methods

Spinal cord injury (SCI) is a serious neurological insult that disrupts the ascending and descending neural pathways between the peripheral nerves and the brain, leading to not only functional deficits in the injured area and below the level of the lesion but also morphological, structural, and functional reorganization of the brain. These changes introduce new challenges and uncertainties into the treatment of SCI. Rehabilitation training, a clinical intervention designed to promote functional recovery after spinal cord and brain injuries, has been reported to promote activation and functional reorganization of the cerebral cortex through multiple physiological mechanisms. In this review, we evaluate the potential mechanisms of exercise that affect the brain structure and function, as well as the rehabilitation training process for the brain after SCI. Additionally, we compare and discuss the principles, effects, and future directions of several rehabilitation training methods that facilitate cerebral cortex activation and recovery after SCI. Understanding the regulatory role of rehabilitation training at the supraspinal center is of great significance for clinicians to develop SCI treatment strategies and optimize rehabilitation plans.

Altered modulation of sensorimotor rhythms with chronic paralysis

After paralysis, the disconnection between the cortex and its peripheral targets leads to neuroplasticity throughout the nervous system. However, it is unclear how chronic paralysis specifically impacts cortical oscillations associated with attempted movement of impaired limbs. We hypothesized that μ- (8-13 Hz) and β- (15-30 Hz) event-related desynchronization (ERD) would be less modulated for individuals with hand paralysis due to cervical spinal cord injury (SCI). To test this, we compared the modulation of ERD from magnetoencephalography (MEG) during attempted and imagined grasping performed by participants with cervical SCI (n = 12) and able-bodied controls (n = 13). Seven participants with tetraplegia were able to generate some electromyography (EMG) activity during attempted grasping, whereas the other five were not. The peak and area of ERD were significantly decreased for individuals without volitional muscle activity when they attempted to grasp compared with able-bodied subjects and participants with SCI,with some residual EMG activity. However, no significant differences were found between subject groups during mentally simulated tasks (i.e., motor imagery) where no muscle activity or somatosensory consequences were expected. These findings suggest that individuals who are unable to produce muscle activity are capable of generating ERD when attempting to move, but the characteristics of this ERD are altered. However, for people who maintain volitional muscle activity after SCI, there are no significant differences in ERD characteristics compared with able-bodied controls. These results provide evidence that ERD is dependent on the level of intact muscle activity after SCI.NEW & NOTEWORTHY Source space MEG was used to investigate sensorimotor cortical oscillations in individuals with SCI. This study provides evidence that individuals with cervical SCI exhibit decreased ERD when they attempt to grasp if they are incapable of generating muscle activity. However, there were no significant differences in ERD between paralyzed and able-bodied participants during motor imagery. These results have important implications for the design and evaluation of new therapies, such as motor imagery and neurofeedback interventions.

Is heart rate variability affected by distinct motor imagery strategies?

Although some studies have reported significant changes in autonomic responses according to the perspective-taking during motor imagery [first person perspective (1P) and third person perspective (3P)], investigations on how the strategies adopted to mentally simulate a given movement affect the heart rate variability (HRV) seem so far unexplored. Twenty healthy subjects mentally simulated the movement of middle-finger extension in 1P and 3P, while electrocardiogram was recorded. After each task, the level of easiness was self-reported. Motor imagery ability was also assessed through the revised version of Movement Imagery Questionnaire (MIQ-R) and a mental chronometry index. The traditional measures of HRV in the time- and frequency-domain were compared between 1P and 3P tasks by using Student's t-test for dependent samples. The MIQ-R results showed that subjects had the same facility to imagine movements in 1P or 3P. The mental chronometry index revealed a similar temporal course only between 1P and execution, while the 3P strategy had a shorter duration. Additionally, the subjective report was similar between the experimental tasks. Regarding the HRV measures, the low frequency component, in log-transformed unit, was significantly higher (p=0.017) in 1P than 3P, suggesting a higher activity of the sympathetic system during 1P. This log-transformed HRV parameter seems to be more sensitive than normalized values for the assessment of the motor imagery ability, together with questionnaires, scales and mental chronometry.

Motor imagery reinforces brain compensation of reach-to-grasp movement after cervical spinal cord injury

Individuals with cervical spinal cord injury (SCI) that causes tetraplegia are challenged with dramatic sensorimotor deficits. However, certain rehabilitation techniques may significantly enhance their autonomy by restoring reach-to-grasp movements. Among others, evidence of motor imagery (MI) benefits for neurological rehabilitation of upper limb movements is growing. This literature review addresses MI effectiveness during reach-to-grasp rehabilitation after tetraplegia. Among articles from MEDLINE published between 1966 and 2015, we selected ten studies including 34 participants with C4 to C7 tetraplegia and 22 healthy controls published during the last 15 years. We found that MI of possible non-paralyzed movements improved reach-to-grasp performance by: (i) increasing both tenodesis grasp capabilities and muscle strength; (ii) decreasing movement time (MT), and trajectory variability; and (iii) reducing the abnormally increased brain activity. MI can also strengthen motor commands by potentiating recruitment and synchronization of motoneurons, which leads to improved recovery. These improvements reflect brain adaptations induced by MI. Furthermore, MI can be used to control brain-computer interfaces (BCI) that successfully restore grasp capabilities. These results highlight the growing interest for MI and its potential to recover functional grasping in individuals with tetraplegia, and motivate the need for further studies to substantiate it.

Olfactory ensheathing cell transplantation improves sympathetic skin responses in chronic spinal cord injury

Forty-three patients with chronic spinal cord injury for over 6 months were transplanted with bryonic olfactory ensheathing cells, 2-4 × 10(6), into multiple sites in the injured area under the surgical microscope. The sympathetic skin response in patients was measured with an electromyography/evoked potential instrument 1 day before transplantation and 3-8 weeks after transtion. Spinal nerve function of patients was assessed using the American Spinal Injury Association impairment scale. The sympathetic skin response was elicited in 32 cases before olfactory ensheathing cell transplantation, while it was observed in 34 cases after transplantation. tantly, sympathetic skin response latency decreased significantly and amplitude increased cantly after transplantation. Transplantation of olfactory ensheathing cells also improved American Spinal Injury Association scores for movement, pain and light touch. Our findings indicate that factory ensheathing cell transplantation improves motor, sensory and autonomic nerve functions in patients with chronic spinal cord injury.

Autonomic nervous system correlates in movement observation and motor imagery

The purpose of the current article is to provide a comprehensive overview of the literature offering a better understanding of the autonomic nervous system (ANS) correlates in motor imagery (MI) and movement observation. These are two high brain functions involving sensori-motor coupling, mediated by memory systems. How observing or mentally rehearsing a movement affect ANS activity has not been extensively investigated. The links between cognitive functions and ANS responses are not so obvious. We will first describe the organization of the ANS whose main purposes are controlling vital functions by maintaining the homeostasis of the organism and providing adaptive responses when changes occur either in the external or internal milieu. We will then review how scientific knowledge evolved, thus integrating recent findings related to ANS functioning, and show how these are linked to mental functions. In turn, we will describe how movement observation or MI may elicit physiological responses at the peripheral level of the autonomic effectors, thus eliciting autonomic correlates to cognitive activity. Key features of this paper are to draw a step-by step progression from the understanding of ANS physiology to its relationships with high mental processes such as movement observation or MI. We will further provide evidence that mental processes are co-programmed both at the somatic and autonomic levels of the central nervous system (CNS). We will thus detail how peripheral physiological responses may be analyzed to provide objective evidence that MI is actually performed. The main perspective is thus to consider that, during movement observation and MI, ANS activity is an objective witness of mental processes.