Stefan Vogt

Neural Circuits Underlying Imitation Learning of Hand Actions: An Event-Related fMRI Study

The neural bases of imitation learning are virtually unknown. In the present study, we addressed this issue using an event-related fMRI paradigm. Musically naive participants were scanned during four events: (1) observation of guitar chords played by a guitarist, (2) a pause following model observation, (3) execution of the observed chords, and (4) rest. The results showed that the basic circuit underlying imitation learning consists of the inferior parietal lobule and the posterior part of the inferior frontal gyrus plus the adjacent premotor cortex (mirror neuron circuit). This circuit, known to be involved in action understanding, starts to be active during the observation of the guitar chords. During pause, the middle frontal gyrus (area 46) plus structures involved in motor preparation (dorsal premotor cortex, superior parietal lobule, rostral mesial areas) also become active. Given the functional properties of area 46, a model of imitation learning is proposed based on interactions between this area and the mirror neuron system.

Prefrontal involvement in imitation learning of hand actions: Effects of practice and expertise

In this event-related fMRI study, we demonstrate the effects of a single session of practising configural hand actions (guitar chords) on cortical activations during observation, motor preparation and imitative execution. During the observation of non-practised actions, the mirror neuron system (MNS), consisting of inferior parietal and ventral premotor areas, was more strongly activated than for the practised actions. This finding indicates a strong role of the MNS in the early stages of imitation learning. In addition, the left dorsolateral prefrontal cortex (DLPFC) was selectively involved during observation and motor preparation of the non-practised chords. This finding confirms Buccino et al.s [Buccino, G., Vogt, S., Ritzl, A., Fink, G.R., Zilles, K., Freund, H.-J., Rizzolatti, G., 2004a. Neural circuits underlying imitation learning of hand actions: an event-related fMRI study. Neuron 42, 323-334] model of imitation learning: for actions that are not yet part of the observers motor repertoire, DLPFC engages in operations of selection and combination of existing, elementary representations in the MNS. The pattern of prefrontal activations further supports Shallices [Shallice, T., 2004. The fractionation of supervisory control. In: Gazzaniga, M.S. (Ed.), The Cognitive Neurosciences, Third edition. MIT Press, Cambridge, MA, pp. 943-956] proposal of a dominant role of the left DLPFC in modulating lower level systems and of a dominant role of the right DLPFC in monitoring operations.

From visuo-motor interactions to imitation learning: Behavioural and brain imaging studies

Abstract We review three areas of research and theory relating to the involvement of motor processing in action observation: behavioural studies on imitation learning, behavioural work on short-term visuomotor interactions, and related neurophysiological and neuroimaging work. A large number of behavioural studies now indicate bi-directional links between perception and action: visual processing can automatically induce related motor processes, and motor actions can direct future visual processing. The related concept of direct matching (Rizzolatti et al., 2001) does not, however, imply that observed actions are transduced into a corresponding motor representation that would guarantee an instant and accurate imitation. Rather, studies on the mirror neuron system indicate that action observation engages the observers own motor prototype of the observed action. This allows for enhanced action recognition, imitation recognition, and, predominantly in humans, imitation and observational learning. Despite the clear impact of action observation on motor representations, recent neuroimaging work also indicates the overlap of imitation learning with processes of non-imitative skill acquisition.

Vision of the hand and environmental context in human prehension

Abstract.Previous findings on the role of visual contact with the hand in the control of reaching and grasping have been contradictory. Some studies have shown that such contact is largely irrelevant, while more recent ones have emphasised its importance. In contrast, information arising from the surrounding environment has received relatively little attention in the study of prehensile actions. In order to identify the roles of both sources of information, we made kinematic comparisons between three conditions. In the first, reaching was performed in a dimly lit room and compared with a second condition in which reaches in the dark, but with the thumb and first finger illuminated, were made to a luminous object. This contrast allows the effects of environmental context to be identified. A comparison between the second and a third condition, in which both vision of the hand and the environment was removed, but the object was still visually available, enabled the assessment of how and when vision of the hand plays a role. Removing environmental cues had effects both early and late in the reach, while vision of the hand was only crucial in the period after peak deceleration. In addition, removal of both sources of information resulted in larger grip apertures. Differences and similarities between our findings and those of other studies are discussed, as is the ongoing debate about the relative importance of visual feedback of the hand in the control and co-ordination of prehensile actions. We conclude with suggestions for further research based on the set-up used in the present study.

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.

Imagery and perception-action mediation in imitative actions

This paper describes two lines of research exploring a hypothetical function of imagery in the context of imitative actions: the mediation between perceptual and motor processes. Both experimental approaches, a sequence learning task and a timing imitation task, demonstrate that engagement into imagery as a temporally distinct activity between observation and performance is not required for accurate imitation. Moreover, evidence is provided that generative processes can take place during event observation itself, thus making a separate recoding stage redundant. Nevertheless, in the absence of a visual display, imagery of a movement sequence exerted similar learning effects as physical and observational practice, and visual and motor imagery were found to be equally effective rehearsal strategies for maintenance of temporal information in short-term memory.

Chapter 3 Human Skill and Motor Control: Some Aspects of the Motor Control - Motor Learning Relation

Publisher Summary This chapter describes some aspects of the motor control and motor learning relation. The chapter recapitulates some of the changes in perspective that have taken place in the field and discusses their value for an integrative perspective on motor control and psychomotor skill acquisition. In the chapter, the theoretical part of the steps from research on motor control to problems of skill acquisition and training are explored. The presentation is organized around two polarities—motor control or motor learning and prescriptive/emergent theories. Within the two frameworks the changing conceptualization and contrasts of motor control or motor learning are traced and compared. In addition, the chapter presents the short historical perspective of recent motor control or motor learning approaches. It explores the motor control tenets of a selection of theories under the two categories outlined in the chapter. The chapter concludes with an experimentation discussion in which original experiments on motor control and learning, from both a computational and an ecological perspective, are presented and explained.

The neural correlates of velocity processing during the observation of a biological effector in the parietal and premotor cortex

While there have been several studies investigating the neural correlates of action observation associated with hand grasping movements, comparatively little is known about the neural bases of observation of reaching movements. In two experiments, using functional magnetic resonance imaging (fMRI), we defined the cortical areas encoding reaching movements and assessed their sensitivity to biological motion and to movement velocity. In the first experiment, participants observed video-clips showing either a biological effector (an arm) or a non-biological object (rolling cylinder) reaching toward a target with a biological and a non-biological motion, respectively. In the second experiment, participants observed video-clips showing either a biological effector (an arm) or a non-biological object (an arrow) reaching toward a target with the same biological motion profiles. The results of the two experiments revealed activation of superior parietal and dorsal premotor sites during observation of the biological motion only, independent of whether it was performed by a biological effector (reaching arm) or a non-biological object (reaching arrow). These areas were not activated when participants observed the non-biological movement (rolling cylinder). To assess the responsiveness of parietal and frontal sites to movement velocity, the fMRI repetition-suppression (RS) technique was used, in which movement was shown with same or different velocities between consecutive videos, and observation of identical stimuli was contrasted with observation of different stimuli. Regions of interest were defined in the parietal and frontal cortices, and their response to stimulus repetition was analyzed (same vs. different velocities). The results showed an RS effect for velocity only during the observation of movements performed by the biological effector and not by the non-biological object. These data indicate that dorsal premotor and superior parietal areas represent a neural substrate involved in the encoding of reaching movements and that their responsiveness to movement velocity of a biological effector could be instrumental to the discrimination of movements performed by others.

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.

Braking reaching movements:a test of the constant tau-dot strategy under different viewing conditions

Following F. Zaal and R. J. Bootsma (1995), the authors studied whether the decelerative phase of a reaching movement could be modeled as a constant tau-dot strategy resulting in a soft collision with the object. Specifically, they investigated whether that strategy is sustained over different viewing conditions. Participants (N = 11) were required to reach for 15- and 50-mm objects at 2 different distances under 3 conditions in which visual availability of the immediate environment and of the reaching hand were varied. Tau-dot estimates and goodness-of-fit were highly similar across the 3 conditions. Only within-participant variability of tau-dot estimates was increased when environmental cues were removed. That finding suggests that the motor system uses a tau-dot strategy involving the intermodal (i.e., visual, proprioceptive, or both) specification of information to regulate the decelerative phase of reaching under restricted viewing conditions. The authors provide recommendations for improving the derivation of