Imitation and observational learning of hand actions: Prefrontal involvement and connectivity

Action processing and mirror neuron function in patients with amyotrophic lateral sclerosis: an fMRI study

Amyotrophic lateral sclerosis (ALS) is a highly debilitating and rapidly fatal neurodegenerative disease. It has been suggested that social cognition may be affected, such as impairment in theory of mind (ToM) ability. Despite these findings, research in this area is scarce and the investigation of neural mechanisms behind such impairment is absent. Nineteen patients with ALS and eighteen healthy controls participated in this study. Because the mirror neuron system (MNS) is thought to be involved in theory of mind, we first implemented a straightforward action-execution and observation task to assess basic MNS function. Second, we examined the social-cognitive ability to understand actions of others, which is a component of ToM. We used fMRI to assess BOLD activity differences between groups during both experiments. Theory of mind was also measured behaviorally using the Reading the Mind in the Eyes test (RME). ALS patients displayed greater BOLD activity during the action-execution and observation task, especially throughout right anterior cortical regions. These areas included the right inferior operculum, premotor and primary motor regions, and left inferior parietal lobe. A conjunction analysis showed significantly more co-activated voxels during both the observation and action-execution conditions in the patient group throughout MNS regions. These results support a compensatory response in the MNS during action processing. In the action understanding experiment, healthy controls performed better behaviorally and subsequently recruited greater regions of activity throughout the prefrontal cortex and middle temporal gyrus. Lastly, action understanding performance was able to cluster patients with ALS into high and lower performing groups, which then differentiated RME performance. Collectively, these data suggest that social cognition, particularly theory of mind, may be affected in a subset of patients with ALS. This impairment may be related to functioning of the MNS and other regions related to action processing and understanding. Implications for future research are discussed.

Non-physical practice improves task performance in an unstable, perturbed environment: motor imagery and observational balance training

For consciously performed motor tasks executed in a defined and constant way, both motor imagery (MI) and action observation (AO) have been shown to promote motor learning. It is not known whether these forms of non-physical training also improve motor actions when these actions have to be variably applied in an unstable and unpredictable environment. The present study therefore investigated the influence of MI balance training (MI_BT) and a balance training combining AO and MI (AO+MI_BT) on postural control of undisturbed and disturbed upright stance on unstable ground. As spinal reflex excitability after classical (i.e., physical) balance training (BT) is generally decreased, we tested whether non-physical BT also has an impact on spinal reflex circuits. Thirty-six participants were randomly allocated into an MI_BT group, in which participants imagined postural exercises, an AO+MI_BT group, in which participants observed videos of other people performing balance exercises and imagined being the person in the video, and a non-active control group (CON). Before and after 4 weeks of non-physical training, balance performance was assessed on a free-moving platform during stance without perturbation and during perturbed stance. Soleus H-reflexes were recorded during stable and unstable stance. The post-measurement revealed significantly decreased postural sway during undisturbed and disturbed stance after both MI_BT and AO+MI_BT. Spinal reflex excitability remained unchanged. This is the first study showing that non-physical training (MI_BT and AO+MI_BT) not only promotes motor learning of “rigid” postural tasks but also improves performance of highly variable and unpredictable balance actions. These findings may be relevant to improve postural control and thus reduce the risk of falls in temporarily immobilized patients.

Where there is a goal, there is a way: what, why and how the parieto-frontal mirror network can mediate imitative behaviours

The relationships between mirror neurons (MNs) and motor imitation, and its clinical implications in autism spectrum disorder (ASD) have been widely investigated; however, the literature remains—at least partially—controversial. In this review we support a multi-level action understanding model focusing on the mirror-based understanding. We review the functional role of the parieto-frontal MNs (PFMN) network claiming that PFMNs function cannot be limited to imitation nor can imitation be explained solely by the activity of PFMNs. The distinction between movement, motor act and motor action is useful to characterize deeply both act(ion) understanding and imitation of act(ion). A more abstract representation of act(ion) may be crucial for clarifying what, why and how an imitator is imitating. What counts in social interactions is achieving goals: it does not matter which effector or string of motor acts you eventually use for achieving (proximal and distal) goals. Similarly, what counts is the ability to recognize/imitate the style of act(ion) regardless of the way in which it is expressed. We address this crucial point referring to its potential implications in ASD.

Motor imagery during action observation modulates automatic imitation effects in rhythmical actions

We have previously shown that passively observing a task-irrelevant rhythmical action can bias the cycle time of a subsequently executed rhythmical action. Here we use the same paradigm to investigate the impact of different forms of motor imagery (MI) during action observation (AO) on this automatic imitation (AI) effect. Participants saw a picture of the instructed action followed by a rhythmical distractor movie, wherein cycle time was subtly manipulated across trials. They then executed the instructed rhythmical action. When participants imagined performing the instructed action in synchrony with the distractor action (AO + MI), a strong imitation bias was found that was significantly greater than in our previous study. The bias was pronounced equally for compatible and incompatible trials, wherein observed and imagined actions were different in type (e.g., face washing vs. painting) or plane of movement, or both. In contrast, no imitation bias was observed when MI conflicted with AO. In Experiment 2, motor execution synchronized with AO produced a stronger imitation bias compared to AO + MI, showing an advantage in synchronization for overt execution over MI. Furthermore, the bias was stronger when participants synchronized the instructed action with the distractor movie, compared to when they synchronized the distractor action with the distractor movie. Although we still observed a significant bias in the latter condition, this finding indicates a degree of specificity in AI effects for the identity of the synchronized action. Overall, our data show that MI can substantially modulate the effects of AO on subsequent execution, wherein: (1) combined AO + MI can enhance AI effects relative to passive AO; (2) observed and imagined actions can be flexibly coordinated across different action types and planes; and (3) conflicting AO + MI can abolish AI effects. Therefore, combined AO + MI instructions should be considered in motor training and rehabilitation.

Multiple roles of motor imagery during action observation

Over the last 20 years, the topics of action observation (AO) and motor imagery (MI) have been largely studied in isolation from each other, despite the early integrative account by Jeannerod (1994, 2001). Recent neuroimaging studies demonstrate enhanced cortical activity when AO and MI are performed concurrently ("AO+MI"), compared to either AO or MI performed in isolation. These results indicate the potentially beneficial effects of AO+MI, and they also demonstrate that the underlying neurocognitive processes are partly shared. We separately review the evidence for MI and AO as forms of motor simulation, and present two quantitative literature analyses that indeed indicate rather little overlap between the two bodies of research. We then propose a spectrum of concurrent AO+MI states, from congruent AO+MI where the contents of AO and MI widely overlap, over coordinative AO+MI, where observed and imagined action are different but can be coordinated with each other, to cases of conflicting AO+MI. We believe that an integrative account of AO and MI is theoretically attractive, that it should generate novel experimental approaches, and that it can also stimulate a wide range of applications in sport, occupational therapy, and neurorehabilitation.

Visual online control processes are acquired during observational practice

This experiment examined whether visual online control processes are coded during observational practice. Participants physically practised an aiming sequence while yoked participants either observed (observational practice) or did nothing (control). Two target sizes were used to vary the importance of visual online control processes. Constant error and variable error indicated that participants acquired the timing constraints through physical practice and observational practice. Kinematic data confirmed that the physical practice and observational practice groups executed similar movement control. Physical practice did result in a performance advantage, but only under large target conditions. These findings indicate that visual online control processes can be effectively acquired through observational practice.

Between-brain connectivity during imitation measured by fNIRS

The present study aimed to step into two-person neuroscience by investigating the hemodynamic correlates of between-brain connectivity involved in imitation and its dependency on pacing stimuli. To test this approach, we used wireless functional near-infrared spectroscopy (fNIRS) to record simultaneously during imitation performance of a paced finger-tapping task (PFT) in two subjects over premotor cortices (PMC). During the imitation (IM) condition, a model and an imitator were recorded while tapping in synchrony with auditory stimuli separated by a constant interval (stimulus-paced mode, St-P), followed by tapping without the pacing stimulus (self-paced mode, Se-P). During the control (CO) condition, each subject (single 1 and 2) performed the PFT task with the same pacing mode pattern, but alone without reference to each other. Using wavelet transform coherence (WTC) analysis evaluating functional connectivity between brains, we found (1) that IM revealed a larger coherence increase between the model and the imitator as compared to the CO condition. (2) Within the IM condition, a larger coherence increase was found during Se-P as compared to St-P mode. Using Granger-causality (G-causality) analysis evaluating effective connectivity between brains, we found (3) that IM revealed larger G-causality as compared to the CO condition and (4) that within the IM condition, the signal of the model G-caused that of the imitator to a greater extent as compared to vice versa. Our findings designate fNIRS as suitable tool for monitoring between-brain connectivity during dynamic interactions between two subjects and that those measurements might thereby provide insight into activation patterns not detectable using typical single-person experiments. Overall, the results of the present study demonstrate the potential of simultaneously assessing brain hemodynamics in interacting subjects in several research areas where social interactions are involved.