Motor imagery has a priming effect on motor execution in people with multiple sclerosis.

Priming is a learning process that refers to behavioral changes caused by previous exposure to a similar stimulus. Motor imagery (MI), which involves the mental rehearsal of action representations in working memory without engaging in actual execution, could be a strategy for priming the motor system. This study investigates whether MI primes action execution in Multiple Sclerosis (MS). Here, 17 people with MS (PwMS) and 19 healthy subjects (HS), all right-handed and good imaginers, performed as accurately and quickly as possible, with a pencil, actual or mental pointing movements between targets of small (1.0 × 1.0 cm) or large (1.5 × 1.5 cm) size. In actual trials, they completed five pointing cycles between the left and right targets, whereas in mental trials, the first 4 cycles were imagined while the fifth was actually executed. The fifth cycle was introduced to assess the MI priming effect on actual execution. All conditions, presented randomly, were performed with both dominant (i.e., right) and non-dominant arms. Analysis of the duration of the first 4 cycles in both actual and mental trials confirmed previous findings, showing isochrony in HS with both arms and significantly faster mental than actual movements (anisochrony) in PwMS (p < 0.01) [time (s); HS right: actual: 4.23 ± 0.15, mental: 4.36 ± 0.16; left: actual: 4.32 ± 0.15, mental: 4.43 ± 0.18; PwMS right: actual: 5.85 ± 0.16, mental: 5.99 ± 0.21; left: actual: 6.68 ± 0.20, mental: 5.94 ± 0.23]; anisochrony in PwMS was present when the task was performed with the non-dominant arm. Of note, temporal analysis of the fifth actual cycle showed no differences between actual and mental trials for HS with both arms, whereas in PwMS the fifth actual cycle was significantly faster after the four actual cycles for the non-dominant arm (p < 0.05) [time (s); HS right: actual: 1.03 ± 0.04, mental: 1.03 ± 0.03; left: actual: 1.08 ± 0.04, mental: 1.05 ± 0.03; PwMS right: actual: 1.48 ± 0.04, mental: 1.48 ± 0.06; left: actual: 1.66 ± 0.05, mental: 1.48 ± 0.06]. These results seem to suggest that a few mental repetitions of an action might be sufficient to exert a priming effect on the actual execution of the same action in PwMS. This would indicate further investigation of the potential use of MI as a new motor-cognitive tool for MS neurorehabilitation.

Time-of-day influences resting-state functional cortical connectivity.

Time-of-day is rarely considered during experimental protocols investigating motor behavior and neural activity. The goal of this work was to investigate differences in functional cortical connectivity at rest linked to the time of the day using functional Near-Infrared Spectroscopy (fNIRS). Since resting-state brain is shown to be a succession of cognitive, emotional, perceptual, and motor processes that can be both conscious and nonconscious, we studied self-generated thought with the goal to help in understanding brain dynamics. We used the New-York Cognition Questionnaire (NYC-Q) for retrospective introspection to explore a possible relationship between the ongoing experience and the brain at resting-state to gather information about the overall ongoing experience of subjects. We found differences in resting-state functional connectivity in the inter-hemispheric parietal cortices, which was significantly greater in the morning than in the afternoon, whilst the intra-hemispheric fronto-parietal functional connectivity was significantly greater in the afternoon than in the morning. When we administered the NYC-Q we found that the score of the question 27 ("during RS acquisition my thoughts were like a television program or film") was significantly greater in the afternoon with respect to the morning. High scores in question 27 point to a form of thought based on imagery. It is conceivable to think that the unique relationship found between NYC-Q question 27 and the fronto-parietal functional connectivity might be related to a mental imagery process during resting-state in the afternoon.

Spatial constraints and cognitive fatigue affect motor imagery of walking in people with multiple sclerosis.

Motor imagery (MI) is the mental simulation of an action without any overt motor execution. Interestingly, a temporal coupling between durations of real and imagined movements, i.e., the so-called isochrony principle, has been demonstrated in healthy adults. On the contrary, anisochrony has frequently been reported in elderly subjects or those with neurological disease such as Parkinson disease or multiple sclerosis (MS). Here, we tested whether people with MS (PwMS) may have impaired MI when they imagined themselves walking on paths with different widths. When required to mentally simulate a walking movement along a constrained pathway, PwMS tended to overestimate mental movement duration with respect to actual movement duration. Interestingly, in line with previous evidence, cognitive fatigue was found to play a role in the MI of PwMS. These results suggest that investigating the relationship between cognitive fatigue and MI performances could be key to shedding new light on the motor representation of PwMS and providing critical insights into effective and tailored rehabilitative treatments.

Transcutaneous trigeminal nerve stimulation modulates the hand blink reflex.

The hand-blink reflex (HBR) is a subcortical response, elicited by the electrical stimulation of the median nerve, whose magnitude is specifically modulated according to the spatial properties of the defensive peripersonal space (DPPS) of the face. For these reasons, the HBR is commonly used as a model to assess the DPPS of the face. Little is known on the effects induced by the activation of cutaneous afferents from the face on the DPPS of the face. Therefore, we tested the effect of non-painful transcutaneous trigeminal nerve stimulation (TNS) on the amplitude of the HBR. Fifteen healthy participants underwent HBR recording before and after 20 min of sham- and real-TNS delivered bilaterally to the infraorbital nerve in two separate sessions. The HBR was recorded bilaterally from the orbicularis oculi muscles, following non-painful median nerve stimulation at the wrist. The HBR amplitude was assessed in the "hand-far" and "hand-near" conditions, relative to the hand position in respect to the face. The amplitudes of the hand-far and hand-near HBR were measured bilaterally before and after sham- and real-TNS. Real-TNS significantly reduced the magnitude of the HBR, while sham-TNS had no significant effect. The inhibitory effect of TNS was of similar extent on both the hand-far and hand-near components of the HBR, which suggests an action exerted mainly at brainstem level.

Thinking Before Doing: A Pilot Study on the Application of Motor Imagery as a Learning Method During Physical Education Lesson in High School.

Motor imagery (MI), i. e., the mental simulation of an action without its actual execution, is a promising technique to boost motor learning via physical practice in rehabilitation, sport, and educational fields. The purpose of the present pilot study was to test the feasibility and the effectiveness of the application of MI as learning methodology place alongside conventional teaching technique as employed for physical education lessons. Thirty-three high school students from two classes were enrolled for instruction in the underhand serve in volleyball. One group, the motor imagery group (MIG) carried out the physical exercise along with the kinesthetic MI of the action, while the other group (the control group) was limited to the merely physical exercise. The training period lasted 8 weeks. MI duration and the duration of real movement (ME), the isochrony index (differences between real and imagined movements duration), and the number of balls which passed over the net (NBN) were evaluated before and after training. Results showed a significant improvement in the isochrony index for the MIG group exclusively; namely, MI duration became more similar to ME duration. Moreover, in MIG a significantly negative relationship appeared between the percentage change in the isochrony index and the difference between NBN before and after training. These findings suggest improvement in sensorimotor representation of the action, which lies at the basis of enhanced motor performance. The present study constitutes initial proof of concept on the application of MI as learning technique applicable to physical education lesson at high school.

Consolidation and retention of motor skill after motor imagery training.

Complex motor tasks are learned through training which results in lasting improvement in sensorimotor performance and accuracy. Learning a motor skill is commonly attained via physical execution. However, research has shown that cognitive training, such as motor imagery (MI), effectively facilitates skill learning. Neurophysiological findings suggest that learning-induced plasticity in the human motor cortex, subserving consolidation and retention of motor skills, is stronger after movement execution (ME) than after MI training. Here, we designed an experimental task able to test for the fast and slow learning phases and for retention of motor skills for both MI and ME. We hypothesize that differences between MI and ME training would emerge in terms of reduced consolidation and retention of motor skills. Twenty-four young healthy subjects were divided into two groups, performing MI or ME training. Participants wore sensor-engineered gloves and their sensorimotor performance was assessed over a period of 15 days with 4-days training. We analysed the touch duration (TD), the inter-tapping interval (ITI), movement rate and accuracy. Results showed that (i) during the first phase of acquisition of motor skills, sensorimotor performance improved similarly in MI and ME groups; (ii) during the second learning phase movement rate increased more in ME than MI group and this difference was mainly driven by differences in the duration of TD; (iii) consolidation deficits with MI training reflected in impaired retention of the acquired skills, as TD and ITI were larger and movement rate was lower in the MI group with respect to the ME, till to 10 days after the last training session. Explicit component of motor learning, accuracy, was maintained in retention phase in both groups. Following our hypothesis, our findings show that MI training is as effective as ME within the first learning phase, but consolidation and retention of motor skills are less effective following MI training. This study highlights MI limitations and suggests option to enhance MI, as by providing an external sensory feedback.

Selective sensorimotor modulation operates during cognitive representation of movement.

Before movement onset, during the reaction time, excitability of M1 is selectively modulated by somatosensory inputs, only in the movement-related muscle. If a similar mechanism operates before the onset of mental movements, then somatosensory afferent inputs are exploited during cognitive representation of movement. We assessed sensorimotor modulation through short latency afferent inhibition (SAI) paradigm before the onset of executed and imagined movements. Participants performed or imagined an abduction of index or little finger, in response to an acoustic signal. SAI was evaluated between a Warning and a Go signal and 100 ms after the Go signal, before the real or expected EMG activity. Results showed a reduction of SAI after the Go signal, in the movement-related muscle, during motor imagery as well as movement execution. There was a positive correlation between the individual degree of sensorimotor modulation during executed and mental movements and between the sensorimotor modulation during mental movements and motor imagery ability. Sensorimotor modulation operates during the cognitive representation of movement with selective disinhibition of the cortical representation of the muscle involved in the task. Sensorimotor modulation mechanisms prior to mental and executed movements likely share overlapping circuits.

Motor sequence learning and intermanual transfer with a phantom limb.

Amputees with phantom limb sometimes report vivid experiences of moving their phantom. Is phantom movement only "imaginary", or, instead, it has physiological properties comparable to those pertaining to real movements? To answer this question, we took advantage of the intermanual transfer of sequence learning, occurring when one hand motor skills improve after training with the other hand. Ten healthy controls and two upper-limb amputees (with and without phantom-movement) were recruited. They were asked to perform with the right (intact) hand a fingers-thumb opposition sequence either in Naïve condition or after an active (Real condition) or a mental (Imagery condition) training with the left (phantom) hand. In healthy controls, the results showed different effects after active training (i.e., faster movement duration (MD) with stable accuracy) and after mental training (i.e., increased accuracy with stable MD). Opposite results between moving-phantom case and static-phantom case were found. In the Real condition, after an "active" training with her phantom hand, the moving-phantom case showed a faster performance of the intact hand. This transfer effect was not different from that found in healthy controls, actually performing the active training with an existing hand (Real condition), but, crucially, it was significantly different from both Imagery and Naïve conditions of controls. Contrariwise, in the static phantom case, the performance during the Real condition was significantly different from the Real condition of healthy controls and it was not significantly different from their Imagery and Naïve conditions. Importantly, a significant difference was found when the transfer effect in Real condition was compared between the two phantom cases. Taken together, these findings provide the first evidence that a phantom limb can learn motor skills and transfer them to the intact limb.

Provision of somatosensory inputs during motor imagery enhances learning-induced plasticity in human motor cortex.

Motor learning via physical practice leads to long-term potentiation (LTP)-like plasticity in motor cortex (M1) and temporary occlusion of additional LTP-like plasticity. Motor learning can be achieved through simulation of movement, namely motor imagery (MI). When combined with electrical stimulation, MI influenced M1 excitability to a larger extent than MI itself. We explored whether a training based on the combination of MI and peripheral nerve stimulation (ESMI) modulates M1 LTP-like plasticity inducing retention of a new acquired skill. Twelve subjects mentally performed thumb-index movements, with synchronous electrical nerve stimulation, following an acoustic cue, in order to increase movement speed. Two control groups physically performed or imagined the same number of finger movements following the acoustic cue. After each training session, M1 LTP-like plasticity was assessed by using PAS25 (paired associative stimulation) technique. Performance was tested before and after training and 24 hours after training. Results showed that physical practice and ESMI training similarly increased movement speed, prevented the subsequent PAS25-induced LTP-like plasticity, and induced retention of motor skill the following day. Training with MI had significant, but minor effects. These findings suggest that a training combining MI with somatosensory input influences motor performance through M1 plasticity similarly to motor execution.

Motor cortical plasticity induced by motor learning through mental practice.

Several investigations suggest that actual and mental actions trigger similar neural substrates. Motor learning via physical practice results in long-term potentiation (LTP)-like plasticity processes, namely potentiation of M1 and a temporary occlusion of additional LTP-like plasticity. However, whether this neuroplasticity process contributes to improve motor performance through mental practice remains to be determined. Here, we tested skill learning-dependent changes in primary motor cortex (M1) excitability and plasticity by means of transcranial magnetic stimulation (TMS) in subjects trained to physically execute or mentally perform a sequence of finger opposition movements. Before and after physical practice and motor-imagery practice, M1 excitability was evaluated by measuring the input-output (IO) curve of motor evoked potentials. M1 LTP and long-term depression (LTD)-like plasticity was assessed with paired-associative stimulation (PAS) of the median nerve and motor cortex using an interstimulus interval of 25 ms (PAS25) or 10 ms (PAS10), respectively. We found that even if after both practice sessions subjects significantly improved their movement speed, M1 excitability and plasticity were differentially influenced by the two practice sessions. First, we observed an increase in the slope of IO curve after physical but not after MI practice. Second, there was a reversal of the PAS25 effect from LTP-like plasticity to LTD-like plasticity following physical and MI practice. Third, LTD-like plasticity (PAS10 protocol) increased after physical practice, whilst it was occluded after MI practice. In conclusion, we demonstrated that MI practice lead to the development of neuroplasticity, as it affected the PAS25- and PAS10- induced plasticity in M1. These results, expanding the current knowledge on how MI training shapes M1 plasticity, might have a potential impact in rehabilitation.

Training the motor cortex by observing the actions of others during immobilization.

Limb immobilization and nonuse are well-known causes of corticomotor depression. While physical training can drive the recovery from nonuse-dependent corticomotor effects, it remains unclear if it is possible to gain access to motor cortex in alternative ways, such as through motor imagery (MI) or action observation (AO). Transcranial magnetic stimulation was used to study the excitability of the hand left motor cortex in normal subjects immediately before and after 10 h of right arm immobilization. During immobilization, subjects were requested either to imagine to act with their constrained limb or to observe hand actions performed by other individuals. A third group of control subjects watched a nature documentary presented on a computer screen. Hand corticomotor maps and recruitment curves reliably showed that AO, but not MI, prevented the corticomotor depression induced by immobilization. Our results demonstrate the existence of a visuomotor mechanism in humans that links AO and execution which is able to effect cortical plasticity in a beneficial way. This facilitation was not related to the action simulation, because it was not induced by explicit MI.

Imagined actions in multiple sclerosis patients: evidence of decline in motor cognitive prediction.

Motor imagery is a mental process during which subjects internally simulate a movement without any motor output. Mental and actual movement durations are similar in healthy adults (isochrony) while temporal discrepancies (anisochrony) could be an expression of neurological deficits on action representation. It is unclear whether patients with multiple sclerosis (PwMS) preserve the capacity to simulate their own movements. This study investigates the ability of PwMS to predict their own actions by comparing temporal features of dominant and non-dominant actual and mental actions. Fourteen PwMS and nineteen healthy subjects (HS) were asked to execute and to imagine pointing arm movements among four pairs of targets of different sizes. Task duration was calculated for both actual and mental movements by an optoelectronic device. Results showed temporal consistency and target-by-target size modulation in actual movements through the four cycles for both groups with significantly longer actual and mental movement durations in PwMS with respect to HS. An index of performance (IP) was used to examine actual/mental isochrony properties in the two groups. Statistical analysis on IP showed in PwMS significantly longer actual movement durations with respect to mental movement durations (anisochrony), more relevant for the non-dominant than dominant arm. Mental prediction of motor actions is not well preserved in MS where motor and cognitive functional changes are present. Differences in performing imagined task with dominant and non-dominant arm could be related to increased cognitive effort required for performing non-dominant movements.

Reduction of bradykinesia of finger movements by a single session of action observation in Parkinson disease.

BACKGROUND: Action observation influences motor performance in healthy subjects and persons with motor impairments. OBJECTIVE: To understand the effects of action observation on the spontaneous rate of finger movements in patients with Parkinson disease (PD). METHODS: Participants, 20 with PD and 14 healthy controls, were randomly divided into 2 groups. Those in the VIDEO group watched video clips showing repetitive finger movements paced at 3 Hz, whereas those in the ACOUSTIC group listened to an acoustic cue paced at 3 Hz. All participants performed a finger sequence at their spontaneous pace at different intervals (before, at the end of, 45 minutes after, and 2 days after training); 8 participants with PD were recruited for a sham intervention, watching a 6-minute video representing a static hand. Finally, 10 patients participated in the same protocol used for the VIDEO group but were tested in the on and off medication states. RESULTS: Both VIDEO and ACOUSTIC training increased the spontaneous rate in all participants. VIDEO intervention showed a greater effect over time, improving the spontaneous rate and reducing the intertapping interval to a larger extent than ACOUSTIC 45 minutes and 2 days after training. Action observation significantly influenced movement rate in on and off conditions, but 45 minutes after training, the effect was still present only in the on condition. No effect was observed after sham intervention. CONCLUSIONS: These findings suggest that the dopaminergic state contributes to the effects of action observation, and this training may be a promising approach in the rehabilitation of bradykinesia in PD.

Temporal expectation in focal hand dystonia.

Patients with writer's cramp present sensory and representational abnormalities relevant to motor control, such as impairment in the temporal discrimination between tactile stimuli and in pure motor imagery tasks, like the mental rotation of corporeal and inanimate objects. However, only limited information is available on the ability of patients with dystonia to process the time-dependent features (e.g. speed) of movement in real time. The processing of time-dependent features of movement has a crucial role in predicting whether the outcome of a complex motor sequence, such as handwriting or playing a musical passage, will be consistent with its ultimate goal, or results instead in an execution error. In this study, we sought to evaluate the implicit ability to perceive the temporal outcome of different movements in a group of patients with writer's cramp. Fourteen patients affected by writer's cramp in the right hand and 17 age- and gender-matched healthy subjects were recruited for the study. Subjects were asked to perform a temporal expectation task by predicting the end of visually perceived human body motion (handwriting, i.e. the action performed by the human body segment specifically affected by writer's cramp) or inanimate object motion (a moving circle reaching a spatial target). Videos representing movements were shown in full before experimental trials; the actual tasks consisted of watching the same videos, but interrupted after a variable interval ('pre-dark') from its onset by a dark interval of variable duration. During the 'dark' interval, subjects were asked to indicate when the movement represented in the video reached its end by clicking on the space bar of the keyboard. We also included a visual working memory task. Performance on the timing task was analysed measuring the absolute value of timing error, the coefficient of variability and the percentage of anticipation responses. Patients with writer's cramp exhibited greater absolute timing error compared with control subjects in the human body motion task (whereas no difference was observed in the inanimate object motion task). No effect of group was documented on the visual working memory tasks. Absolute timing error on the human body motion task did not significantly correlate with symptom severity, disease duration or writing speed. Our findings suggest an alteration of the writing movement representation at a central level and are consistent with the view that dystonia is not a purely motor disorder, but it also involves non-motor (sensory, cognitive) aspects related to movement processing and planning.

Motor imagery influences the execution of repetitive finger opposition movements.

Motor imagery (MI) is the ability to imagine performing a movement without executing it. In literature, there have been numerous reports on the influence of MI on motor practice and the beneficial effects of "mental practice" on the physical performance has been suggested to rely to the close temporal association between motor rehearsal and actual performance. In the present study, we aimed to evaluate whether the addition of a period of motor imagery between two motor practice trials could modify movement execution in a repetitive finger opposition motor task performed at maximal speed and whether the effect of motor imagery on motor practice is dependant on the complexity of movement. We observed that the addition of motor imagery to the sole motor practice was able to influence the performance of repetitive finger opposition movements inducing an increase of the velocity of movement greater than that observed with the motor practice alone. Further the addition of motor imagery was able to induce a modification in the motor strategy in terms of duration of the main phases of movements. This was more evident when subjects executed a finger sequential task with respect to a simple finger tapping task. We assume that mental rehearsal facilitates the brain network involved in sensorimotor control, particularly acting on those neural structures involved in the motor program.