Excitability of the Primary Motor Cortex Increases More Strongly with Slow- than with Normal-Speed Presentation of Actions

Introduction

The aim of the present study was to investigate how the speed of observed action affects the excitability of the primary motor cortex (M1), as assessed by the size of motor evoked potentials (MEPs) induced by transcranial magnetic stimulation (TMS).

Methods

Eighteen healthy subjects watched a video clip of a person catching a ball, played at three different speeds (normal-, half-, and quarter-speed). MEPs were induced by TMS when the model''s hand had opened to the widest extent just before catching the ball (“open”) and when the model had just caught the ball (“catch”). These two events were locked to specific frames of the video clip (“phases”), rather than occurring at specific absolute times, so that they could easily be compared across different speeds. MEPs were recorded from the thenar (TH) and abductor digiti minimi (ADM) muscles of the right hand.

Results

The MEP amplitudes were higher when the subjects watched the video clip at low speed than when they watched the clip at normal speed. A repeated-measures ANOVA, with the factor VIDEO-SPEED, showed significant main effects. Bonferroni''s post hoc test showed that the following MEP amplitude differences were significant: TH, normal vs. quarter; ADM, normal vs. half; and ADM, normal vs. quarter. Paired t-tests showed that the significant MEP amplitude differences between TMS phases under each speed condition were TH, “catch” higher than “open” at quarter speed; ADM, “catch” higher than “open” at half speed.

Conclusions

These results indicate that the excitability of M1 was higher when the observed action was played at low speed. Our findings suggest that the action observation system became more active when the subjects observed the video clip at low speed, because the subjects could then recognize the elements of action and intention in others.     

Effectiveness of using an unskilled model in action observation combined with motor imagery training for early motor learning in elderly people: a preliminary study

Abstract

Aim of the study: To investigate a more available model for the early phase of motor learning after action observation combined with motor imagery training in elderly people. To address the purpose, we focused on a slow, unskilled model demonstrating an occasional error.

Materials and methods: A total of 36 elderly people participated in the current study and were assigned to either the unskilled or skilled model observation groups (n?=?12, respectively), or the control group (n?=?12). The participants in the observation groups observed the assigned a video clip of an unskilled or skilled model demonstrating a ball rotation task. During the observation, the participants were instructed to imagine themselves as the person in the video clip. The participants in the control group read a scientific paper during the equivalent period of action observation and motor imagery. We measured ball rotation performance (the time required for five rotations, the number of ball drops) in pre- and post-intervention (observation combined with motor imagery training for intervention groups or reading for control group).

Results: Ball rotation performance (ball rotation speed) significantly improved in the unskilled model observation group compared to the other two groups.

Conclusions: Intervention for action observation using unskilled model combined with motor imagery was effective for improving motor performance during the early phase of motor learning.     

Motor learning by observing

Learning complex motor behaviors like riding a bicycle or swinging a golf club is based on acquiring neural representations of the mechanical requirements of movement (e.g., coordinating muscle forces to control the club). Here we provide evidence that mechanisms matching observation and action facilitate motor learning. Subjects who observed a video depicting another person learning to reach in a novel mechanical environment (imposed by a robot arm) performed better when later tested in the same environment than subjects who observed similar movements but no learning; moreover, subjects who observed learning of a different environment performed worse. We show that this effect is not based on conscious strategies but instead depends on the implicit engagement of neural systems for movement planning and control.     

Active inference unifies intentional and conflict-resolution imperatives of motor control

The field of motor control has long focused on the achievement of external goals through action (e.g., reaching and grasping objects). However, recent studies in conditions of multisensory conflict, such as when a subject experiences the rubber hand illusion or embodies an avatar in virtual reality, reveal the presence of unconscious movements that are not goal-directed, but rather aim at resolving multisensory conflicts; for example, by aligning the position of a person’s arm with that of an embodied avatar. This second, conflict-resolution imperative of movement control did not emerge in classical studies of motor adaptation and online corrections, which did not allow movements to reduce the conflicts; and has been largely ignored so far in formal theories. Here, we propose a model of movement control grounded in the theory of active inference that integrates intentional and conflict-resolution imperatives. We present three simulations showing that the active inference model is able to characterize movements guided by the intention to achieve an external goal, by the necessity to resolve multisensory conflict, or both. Furthermore, our simulations reveal a fundamental difference between the (active) inference underlying intentional and conflict-resolution imperatives by showing that it is driven by two different (model and sensory) kinds of prediction errors. Finally, our simulations show that when movement is only guided by conflict resolution, the model incorrectly infers that is velocity is zero, as if it was not moving. This result suggests a novel speculative explanation for the fact that people are unaware of their subtle compensatory movements to avoid multisensory conflict. Furthermore, it can potentially help shed light on deficits of motor awareness that arise in psychopathological conditions.     

Subconscious Visual Cues during Movement Execution Allow Correct Online Choice Reactions

Part of the sensory information is processed by our central nervous system without conscious perception. Subconscious processing has been shown to be capable of triggering motor reactions. In the present study, we asked the question whether visual information, which is not consciously perceived, could influence decision-making in a choice reaction task. Ten healthy subjects (28±5 years) executed two different experimental protocols. In the Motor reaction protocol, a visual target cue was shown on a computer screen. Depending on the displayed cue, subjects had to either complete a reaching movement (go-condition) or had to abort the movement (stop-condition). The cue was presented with different display durations (20–160 ms). In the second Verbalization protocol, subjects verbalized what they experienced on the screen. Again, the cue was presented with different display durations. This second protocol tested for conscious perception of the visual cue. The results of this study show that subjects achieved significantly more correct responses in the Motor reaction protocol than in the Verbalization protocol. This difference was only observed at the very short display durations of the visual cue. Since correct responses in the Verbalization protocol required conscious perception of the visual information, our findings imply that the subjects performed correct motor responses to visual cues, which they were not conscious about. It is therefore concluded that humans may reach decisions based on subconscious visual information in a choice reaction task.     

Sensorimotor Recalibration Depends on Attribution of Sensory Prediction Errors to Internal Causes

Sensorimotor learning critically depends on error signals. Learning usually tries to minimise these error signals to guarantee optimal performance. Errors can, however, have both internal causes, resulting from one’s sensorimotor system, and external causes, resulting from external disturbances. Does learning take into account the perceived cause of error information? Here, we investigated the recalibration of internal predictions about the sensory consequences of one’s actions. Since these predictions underlie the distinction of self- and externally produced sensory events, we assumed them to be recalibrated only by prediction errors attributed to internal causes. When subjects were confronted with experimentally induced visual prediction errors about their pointing movements in virtual reality, they recalibrated the predicted visual consequences of their movements. Recalibration was not proportional to the externally generated prediction error, but correlated with the error component which subjects attributed to internal causes. We also revealed adaptation in subjects’ motor performance which reflected their recalibrated sensory predictions. Thus, causal attribution of error information is essential for sensorimotor learning.     

The Case of Watson vs. James: Effect-Priming Studies Do Not Support Ideomotor Theory

In this paper we show that response facilitation in choice reaction tasks achieved by priming the (previously perceived) effect is based on stimulus-response associations rather than on response-effect associations. The reduced key-press response time is not accounted for by earlier established couplings between the key-press movement and its subsequent effect, but instead results from couplings between this effect and the contingent key-release movement. This key-release movement is an intrinsic part of the entire performed response action in each trial of a reaction-time task, and always spontaneously follows the key-press movement. Eliminating the key-release movement from the task leads to the disappearance of the response facilitation, which raises the question whether response-effect associations actually play a role in studies that use the effect-priming paradigm. Together the three experiments presented in the paper cast serious doubts on the claim that action-effect couplings are acquired and utilized by the cognitive system in the service of action selection, and that the priming paradigm by itself can provide convincing evidence for this claim. As a corollary, we question whether the related two-step model for the ideomotor principle holds a satisfying explanation for how anticipation of future states guides action planning. The results presented here may have profound implications for priming studies in other disciplines of psychology as well.     

Language comprehension in the balance: the robustness of the action-compatibility effect (ACE)

How does language comprehension interact with motor activity? We investigated the conditions under which comprehending an action sentence affects people''s balance. We performed two experiments to assess whether sentences describing forward or backward movement modulate the lateral movements made by subjects who made sensibility judgments about the sentences. In one experiment subjects were standing on a balance board and in the other they were seated on a balance board that was mounted on a chair. This allowed us to investigate whether the action compatibility effect (ACE) is robust and persists in the face of salient incompatibilities between sentence content and subject movement. Growth-curve analysis of the movement trajectories produced by the subjects in response to the sentences suggests that the ACE is indeed robust. Sentence content influenced movement trajectory despite salient inconsistencies between implied and actual movement. These results are interpreted in the context of the current discussion of embodied, or grounded, language comprehension and meaning representation.     

Voluntary finger movement in man: Cerebral potentials and theory

Three different brain potentials preceeding voluntary rapid finger flexion can be recorded from the skull surface by time reversed averaging. The early cortical activity preceding unilateral movement is bilateral and widespread (Bereitschaftspotential, BP). The same applies for the second potential (pre-motion positivity, PMP). Only the third potential (motor potential, MP) is unilateral and restricted to the contralateral motor cortex. In a total of 87 experiments with 39 subjects, the BP started on the average 750 ms (SD 360, SE 38.5) prior to rapid finger flexion. Its largest amplitude was found mid-parietally and averaged-5.3 V (SD 2.32, SE 0.4). Such amplitudes were found with averages of 800 and more movements per experiment. However, at the beginning of an experiment the BP is larger. Preceding finger movement, the BP was found bilaterally over the parietal and precentral cortex and over the midline. Over the frontal cortex, either no potential or positivity was recorded. In normal subjects, the BP always begins bilaterally and symmetrically. At parietal leads, it remains bilaterally-symmetrical. A slight contralateral preponderance begins about 400 ms prior to movement only over motor cortex, which becomes statistically significant at 150 ms. When comparing the parietal BP amplitude with the precentral amplitude on the ipsilateral side, where no superposition of the MP occurs, there is more negativity parietally than precentrally, although the parietal skull is about 11% thicker than the precentral. The BP is a negative shift of the cortical DC potential probably representing a preparatory process in the dendritic network of those cortical areas that are involved in the intended movement.The PMP is the next potential occurring 90–80 ms ( , SD 34.2, SE 2.95) prior to the first action potential in the contracting muscle (EMG). It was found in 85% of our subjects. The PMP has at its maximum, mid-parietally, a mean amplitude of +1.7 V (SD 1.6, SE 0.28). Like the BP, the PMP is bilateral and widespread in parietal and precentral leads of both sides and in the midline with a maximum at the anterior parietal region, despite the parietal skull being thicker than precentral. The short and the relatively constant onset time suggests that the PMP might reflect cortical activity (motor command) related to initiation of the tactually guided rapid finger movement under study.The MP starting 60–50 ms ( , SD 19.4, SE 3.1) prior to first activity in the agonist EMG is the last potential to occur and is the only unilateral potential: its localisation is limited to the hand area of the motor cortex contralateral to the moving finger. In bipolar recordings, contralateral versus ipsilateral precentral or contralateral precentral versus vertex, it appears as a sharp additional negativity. This additional negativity averaged-1.3 V (SD 0.64, SE 0.08). The MP reflects the motor cortical activity immediately preceding the movement.After movement onset, a complex potential is recorded, that is also seen with passive finger movement, largely representing a somatosensory (proprioceptive) evoked response. The possible meaning of the movement-related potentials is discussed in relation to a theory of central motor function.Supported by the Deutsche ForschungsgemeinschaftHabilitationsschrift of L.D. submitted to the Faculty of Clinical Medicine, University of Ulm (1974)     

Maturation of the flight motor pattern without movement inManduca sexta

The development of the flight motor pattern was studied by recording acutely with fine wire electrodes inserted in the thoracic muscles of pharate moths of known age and by recording chronically for up to 8 days with implanted electrodes. Externally visible morphological characteristics by which the age of a pharateManduca sexta can be established were identified (Table 1). Bouts of activity lasting approximately 30 min to 2 h and alternating with inactive periods of similar duration were recorded as early as the ninth day after pupation and on all successive days until early on the day of eclosion, typically 19 days after pupation (Figs. 1,5). During the 3 days preceding the day of eclosion a rhythmic flight motor pattern was produced (Fig. 2). The rhythmic activity ceased 5^1/2–10^1/2 h before eclosion and only an occasional, large potential change was recorded from the thoracic muscles during this time (Fig. 3). During the 3 days of rhythmic activity the percent-age of time that the animal was active did not change (Fig. 4). The flight motor pattern matured, in that the cycle-time decreased and became less variable (Fig. 6). The approximate flight phase relationship between an elevator muscle and the dorsal longitudinal depressor muscle did not become less variable as the cycle-time improved. The flight motor pattern produced by pharate moths caused neither movement of the scutum nor an increase in thoracic temperature in marked contrast to the consequences of adult motor activity (Fig. 7). Intracellular recording from the dorsal longitudinal muscle of pharate moths 20–30 h before eclosion showed that, after repeated stimulation of the motor nerve at 2/s, only small junctional potentials were elicited (Fig. 8). A burst of 6 stimuli at 50/s elicited 2–5 active membrane responses and a contraction. These observations explain the absence of thoracic movement in immature animals producing the flight motor pattern and the presence of movement in immature animals stimulated to eclose. They also show that the neuromuscular junction matures rapidly during the day before eclosion.     

Bilateral tDCS on Primary Motor Cortex: Effects on Fast Arm Reaching Tasks

BackgroundThe effects produced by transcranial direct current stimulation (tDCS) applied to the motor system have been widely studied in the past, chiefly focused on primary motor cortex (M1) excitability. However, the effects on functional tasks are less well documented.ObjectiveThis study aims to evaluate the effect of tDCS-M1 on goal-oriented actions (i.e., arm-reaching movements; ARM), in a reaction-time protocol.Methods13 healthy subjects executed dominant ARM as fast as possible to one of two targets in front of them while surface EMG was recorded. Participants performed three different sessions. In each session they first executed ARM (Pre), then received tDCS, and finally executed Post, similar to Pre. Subjects received three different types of tDCS, one per session: In one session the anode was on right-M1 (AR), and the cathode on the left-M1 (CL), thus termed AR-CL; AL-CR reversed the montage; and Sham session was applied likewise. Real stimulation was 1mA-10min while subjects at rest. Three different variables and their coefficients of variation (CV) were analyzed: Premotor times (PMT), reaction-times (RT) and movement-times (MT).Resultstriceps-PMT were significantly increased at Post-Sham, suggesting fatigue. Results obtained with real tDCS were not different depending on the montage used, in both cases PMT were significantly reduced in all recorded muscles. RT and MT did not change for real or sham stimulation. RT-CV and PMT-CV were reduced after all stimulation protocols.ConclusiontDCS reduces premotor time and fatigability during the execution of fast motor tasks. Possible underlying mechanisms are discussed.     

Motor Preparatory Activity in Posterior Parietal Cortex is Modulated by Subjective Absolute Value

For optimal response selection, the consequences associated with behavioral success or failure must be appraised. To determine how monetary consequences influence the neural representations of motor preparation, human brain activity was scanned with fMRI while subjects performed a complex spatial visuomotor task. At the beginning of each trial, reward context cues indicated the potential gain and loss imposed for correct or incorrect trial completion. FMRI-activity in canonical reward structures reflected the expected value related to the context. In contrast, motor preparatory activity in posterior parietal and premotor cortex peaked in high “absolute value” (high gain or loss) conditions: being highest for large gains in subjects who believed they performed well while being highest for large losses in those who believed they performed poorly. These results suggest that the neural activity preceding goal-directed actions incorporates the absolute value of that action, predicated upon subjective, rather than objective, estimates of one''s performance.     

Biomechanical causes of trapeziometacarpal arthroplasty failure

Trapeziometacarpal joint prosthesis revision has been widely reported, mainly due to loosening of the trapezium cup. Our hypothesis is that current prostheses do not sufficiently respect the kinematics of this joint. CT scan acquisitions enabled us to determine the position of the first metacarpal relative to the trapezium in three different characteristic postures, in subjects in different stages of arthrosis. A CAD model of a current prosthesis was inserted into the numerical 3D model of the joint under the different postures. In the numerical model, we observe penetration of the cup by the head of the prosthesis. This virtual penetration could, in vivo, amount to overstressing the prosthetic elements, which would lead to loosening of the cup or of the metacarpal stem and luxation of the prosthesis.     

Mirroring Pain in the Brain: Emotional Expression versus Motor Imitation

Perception of pain in others via facial expressions has been shown to involve brain areas responsive to self-pain, biological motion, as well as both performed and observed motor actions. Here, we investigated the involvement of these different regions during emotional and motor mirroring of pain expressions using a two-task paradigm, and including both observation and execution of the expressions. BOLD responses were measured as subjects watched video clips showing different intensities of pain expression and, after a variable delay, either expressed the amount of pain they perceived in the clips (pain task), or imitated the facial movements (movement task). In the pain task condition, pain coding involved overlapping activation across observation and execution in the anterior cingulate cortex, supplementary motor area, inferior frontal gyrus/anterior insula, and the inferior parietal lobule, and a pain-related increase (pain vs. neutral) in the anterior cingulate cortex/supplementary motor area, the right inferior frontal gyrus, and the postcentral gyrus. The ‘mirroring’ response was stronger in the inferior frontal gyrus and middle temporal gyrus/superior temporal sulcus during the pain task, and stronger in the inferior parietal lobule in the movement task. These results strongly suggest that while motor mirroring may contribute to the perception of pain expressions in others, interpreting these expressions in terms of pain content draws more heavily on networks involved in the perception of affective meaning.     

Writing in the Air: Contributions of Finger Movement to Cognitive Processing

The present study investigated the interactions between motor action and cognitive processing with particular reference to kanji-culture individuals. Kanji-culture individuals often move their finger as if they are writing when they are solving cognitive tasks, for example, when they try to recall the spelling of English words. This behavior is called kusho, meaning air-writing in Japanese. However, its functional role is still unknown. To reveal the role of kusho behavior in cognitive processing, we conducted a series of experiments, employing two different cognitive tasks, a construction task and a stroke count task. To distinguish the effects of the kinetic aspects of kusho behavior, we set three hand conditions in the tasks; participants were instructed to use either kusho, unrelated finger movements or do nothing during the response time. To isolate possible visual effects, two visual conditions in which participants saw their hand and the other in which they did not, were introduced. We used the number of correct responses and response time as measures of the task performance. The results showed that kusho behavior has different functional roles in the two types of cognitive tasks. In the construction task, the visual feedback from finger movement facilitated identifying a character, whereas the kinetic feedback or motor commands for the behavior did not help to solve the task. In the stroke count task, by contrast, the kinetic aspects of the finger movements influenced counting performance depending on the type of the finger movement. Regardless of the visual condition, kusho behavior improved task performance and unrelated finger movements degraded it. These results indicated that motor behavior contributes to cognitive processes. We discussed possible mechanisms of the modality dependent contribution. These findings might lead to better understanding of the complex interaction between action and cognition in daily life.     

Phytochrome-controlled Nyctinasty in Albizzia julibrissin: III. Interactions between an Endogenous Rhythm and Phytochrome in Control of Potassium Flux and Leaflet Movement

Prolonged irradiation during appropriate parts of the diurnal cycle promotes the opening of Albizzia julibrissin leaflets. Leaflets also open without illumination, but such opening starts later and is slower and less complete. Opening in the dark is accompanied by lower potassium efflux from dorsal pulvinule motor cells but equal or greater potassium movement into ventral motor cells than occurs during opening in the light. Far red-absorbing phytochrome inhibits opening in the dark, indicating that its action is similar during endogenously controlled opening and nyctinastic closure; i.e., a high far redabsorbing phytochrome level is associated with low potassium content in ventral motor cells, high potassium content in dorsal motor cells, and a small angle between leaflets.     

Differential Contributions of Vision,Touch and Muscle Proprioception to the Coding of Hand Movements

To further elucidate the mechanisms underlying multisensory integration, this study examines the controversial issue of whether congruent inputs from three different sensory sources can enhance the perception of hand movement. Illusory sensations of clockwise rotations of the right hand were induced by either separately or simultaneously stimulating visual, tactile and muscle proprioceptive channels at various intensity levels. For this purpose, mechanical vibrations were applied to the pollicis longus muscle group in the subjects’ wrists, and a textured disk was rotated under the palmar skin of the subjects’ right hands while a background visual scene was projected onto the rotating disk. The elicited kinaesthetic illusions were copied by the subjects in real time and the EMG activity in the adductor and abductor wrist muscles was recorded. The results show that the velocity of the perceived movements and the amplitude of the corresponding motor responses were modulated by the nature and intensity of the stimulation. Combining two sensory modalities resulted in faster movement illusions, except for the case of visuo-tactile co-stimulation. When a third sensory input was added to the bimodal combinations, the perceptual responses increased only when a muscle proprioceptive stimulation was added to a visuo-tactile combination. Otherwise, trisensory stimulation did not override bimodal conditions that already included a muscle proprioceptive stimulation. We confirmed that vision or touch alone can encode the kinematic parameters of hand movement, as is known for muscle proprioception. When these three sensory modalities are available, they contribute unequally to kinaesthesia. In addition to muscle proprioception, the complementary kinaesthetic content of visual or tactile inputs may optimize the velocity estimation of an on-going movement, whereas the redundant kinaesthetic content of the visual and tactile inputs may rather enhance the latency of the perception.     

Speech Misperception: Speaking and Seeing Interfere Differently with Hearing

Speech perception is thought to be linked to speech motor production. This linkage is considered to mediate multimodal aspects of speech perception, such as audio-visual and audio-tactile integration. However, direct coupling between articulatory movement and auditory perception has been little studied. The present study reveals a clear dissociation between the effects of a listener’s own speech action and the effects of viewing another’s speech movements on the perception of auditory phonemes. We assessed the intelligibility of the syllables [pa], [ta], and [ka] when listeners silently and simultaneously articulated syllables that were congruent/incongruent with the syllables they heard. The intelligibility was compared with a condition where the listeners simultaneously watched another’s mouth producing congruent/incongruent syllables, but did not articulate. The intelligibility of [ta] and [ka] were degraded by articulating [ka] and [ta] respectively, which are associated with the same primary articulator (tongue) as the heard syllables. But they were not affected by articulating [pa], which is associated with a different primary articulator (lips) from the heard syllables. In contrast, the intelligibility of [ta] and [ka] was degraded by watching the production of [pa]. These results indicate that the articulatory-induced distortion of speech perception occurs in an articulator-specific manner while visually induced distortion does not. The articulator-specific nature of the auditory-motor interaction in speech perception suggests that speech motor processing directly contributes to our ability to hear speech.