Michiel van Elk

Compromised motor planning and Motor Imagery in right Hemiparetic Cerebral Palsy

We investigated whether motor planning problems in people with Hemiparetic Cerebral Palsy (HCP) are paralleled by impaired ability to use Motor Imagery (MI). While some studies have shown that individuals with HCP can solve a mental rotation task, it was not clear if they used MI or Visual Imagery (VI). In the present study, motor planning and MI were examined in individuals with right HCP (n=10) and controls. Motor planning was measured using an object manipulation task, where participants had to anticipate the end of the motor action. MI was measured using a mental rotation paradigm, where participants judged laterality of hands presented from a back view and a palm view. To test if participants used MI or VI we compared reaction times of lateral versus medial rotations, under the assumption that MI is subject to biomechanical constraints of rotated hands, but VI is not. Individuals with HCP had a higher proportion of task failures due to inappropriate grip choice, exemplifying impaired planning. Second, individuals with HCP did not show a reaction time difference between lateral and medial rotations, indicating an impaired ability to use MI. These findings show that compromised motor planning in HCP is paralleled by an impairment in the ability to use MI. Training of MI may be a useful entry-point for rehabilitation of motor planning problems.

Joint action modulates motor system involvement during action observation in 3-year-olds

When we are engaged in a joint action, we need to integrate our partner’s actions with our own actions. Previous research has shown that in adults the involvement of one’s own motor system is enhanced during observation of an action partner as compared to during observation of an individual actor. The aim of this study was to investigate whether similar motor system involvement is present at early stages of joint action development and whether it is related to joint action performance. In an EEG experiment with 3-year-old children, we assessed the children’s brain activity and performance during a joint game with an adult experimenter. We used a simple button-pressing game in which the two players acted in turns. Power in the mu- and beta-frequency bands was compared when children were not actively moving but observing the experimenter’s actions when (1) they were engaged in the joint action game and (2) when they were not engaged. Enhanced motor involvement during action observation as indicated by attenuated sensorimotor mu- and beta-power was found when the 3-year-olds were engaged in the joint action. This enhanced motor activation during action observation was associated with better joint action performance. The findings suggest that already in early childhood the motor system is differentially activated during action observation depending on the involvement in a joint action. This motor system involvement might play an important role for children’s joint action performance.

Action Semantic Knowledge About Objects Is Supported by Functional Motor Activation

The present study assessed the functional organization of action semantics by asking subjects to categorize pictures of an actor holding objects with a correct or incorrect grip at either a correct or incorrect goal location. Overall, reaction times were slower if the object was presented with an inappropriate posture, and this effect was stronger for goal violations compared with grip violations (Experiment 1). In addition, the retrieval of action semantics was found accompanied by the implicit activation of motor representations. Body-related objects (e.g., cup) were classified faster when a movement toward the subjects body was required, whereas world-related objects (e.g., pincers) were responded to faster with a movement in the opposite direction (Experiments 2 and 3). In contrast, when subjects were required to retrieve only visual semantics (Experiment 4), no interference effects of postural information were observed, and motor representations were only partially activated. These findings suggest that action semantics can be accessed independently from visual semantics and that the retrieval of action semantics is supported by functional motor activation reflecting the prototypical use of an object.

Extending the Body to Virtual Tools Using a Robotic Surgical Interface: Evidence from the Crossmodal Congruency Task

The effects of real-world tool use on body or space representations are relatively well established in cognitive neuroscience. Several studies have shown, for example, that active tool use results in a facilitated integration of multisensory information in peripersonal space, i.e. the space directly surrounding the body. However, it remains unknown to what extent similar mechanisms apply to the use of virtual-robotic tools, such as those used in the field of surgical robotics, in which a surgeon may use bimanual haptic interfaces to control a surgery robot at a remote location. This paper presents two experiments in which participants used a haptic handle, originally designed for a commercial surgery robot, to control a virtual tool. The integration of multisensory information related to the virtual-robotic tool was assessed by means of the crossmodal congruency task, in which subjects responded to tactile vibrations applied to their fingers while ignoring visual distractors superimposed on the tip of the virtual-robotic tool. Our results show that active virtual-robotic tool use changes the spatial modulation of the crossmodal congruency effects, comparable to changes in the representation of peripersonal space observed during real-world tool use. Moreover, when the virtual-robotic tools were held in a crossed position, the visual distractors interfered strongly with tactile stimuli that was connected with the hand via the tool, reflecting a remapping of peripersonal space. Such remapping was not only observed when the virtual-robotic tools were actively used (Experiment 1), but also when passively held the tools (Experiment 2). The present study extends earlier findings on the extension of peripersonal space from physical and pointing tools to virtual-robotic tools using techniques from haptics and virtual reality. We discuss our data with respect to learning and human factors in the field of surgical robotics and discuss the use of new technologies in the field of cognitive neuroscience.

Using goal- and grip-related information for understanding the correctness of other's actions: an ERP study.

Detecting errors in other’s actions is of pivotal importance for joint action, competitive behavior and observational learning. Although many studies have focused on the neural mechanisms involved in detecting low-level errors, relatively little is known about error-detection in everyday situations. The present study aimed to identify the functional and neural mechanisms whereby we understand the correctness of other’s actions involving well-known objects (e.g. pouring coffee in a cup). Participants observed action sequences in which the correctness of the object grasped and the grip applied to a pair of objects were independently manipulated. Observation of object violations (e.g. grasping the empty cup instead of the coffee pot) resulted in a stronger P3-effect than observation of grip errors (e.g. grasping the coffee pot at the upper part instead of the handle), likely reflecting a reorienting response, directing attention to the relevant location. Following the P3-effect, a parietal slow wave positivity was observed that persisted for grip-errors, likely reflecting the detection of an incorrect hand-object interaction. These findings provide new insight in the functional significance of the neurophysiological markers associated with the observation of incorrect actions and suggest that the P3-effect and the subsequent parietal slow wave positivity may reflect the detection of errors at different levels in the action hierarchy. Thereby this study elucidates the cognitive processes that support the detection of action violations in the selection of objects and grips.

Neural Evidence for Compromised Motor Imagery in Right Hemiparetic Cerebral Palsy

In the present event-related potential (ERP) study we investigated the neural and temporal dynamics of motor imagery in participants with right-sided hemiparetic cerebral palsy (HCP; n = 10) and in left-handed control participants (n = 10). A mental rotation task was used in which participants were required to judge the laterality of hand pictures. At a behavioral level participants with HCP were slower in making hand laterality judgments compared to control subjects, especially when presented with pictures representing the affected hand. At a neural level, individuals with HCP were characterized by a reduced rotation-related negativity (RRN) over parietal areas, that was delayed in onset with respect to control participants. Interestingly, participants that were relatively mildly impaired showed a stronger RRN for the rotation of right-hand stimuli than participants that were more strongly impaired in their motor function, suggesting a direct relation between the motor imagery process and the biomechanical constraints of the participant. Together, the results provide new insights in the relation between motor imagery and motor capabilities and indicate that participants with HCP may be characterized by a compromised ability to use motor imagery.

Suppression of the N1 auditory evoked potential for sounds generated by the upper and lower limbs

Sensory attenuation is typically observed for self-generated compared to externally generated action effects. In the present study we investigated whether auditory sensory suppression is modulated as a function of sounds being generated by the upper or lower limbs. We report sensory attenuation, as reflected in a reduced auditory N1 component, which was comparable for sounds generated by the lower and the upper limbs. Increasing temporal delays between actions and sounds did not modulate suppression of the N1 component, but did have an effect on the latency of the N1 component. In contrast, for the P2 component sensory suppression was only observed for sounds generated by the hands and presented at short latencies. These findings provide new insight into the functional and neural dynamics of sensory suppression and suggest the existence of comparable agency mechanisms for both the upper and the lower limbs.

Semantics in the motor system: motor-cortical beta oscillations reflect semantic knowledge of end-postures for object use

In the present EEG study we investigated whether semantic knowledge for object use is represented in motor-related brain areas. Subjects were required to perform actions with everyday objects and to maintain either a meaningful or a meaningless end posture with the object. Analysis of the EEG data focused on the beta-frequency band, as previous studies have indicated that the maintenance of a posture is reflected in stronger beta-oscillations. Time frequency analysis indicated that the execution of actions resulting in a meaningless compared to a meaningful end posture was accompanied by a stronger beta-desynchronization towards the end of the movement and a stronger subsequent beta-rebound after posture-onset. The effect in the beta-frequency band was localized to premotor, parietal and medial frontal areas and could not be attributed to differences in timing or movement complexity between meaningful and meaningless actions. Together these findings directly show that the motor system is differentially activated during the execution and maintenance of semantically correct or incorrect end postures. This suggests that semantic object knowledge is indeed represented in motor-related brain areas, organized around specific end postures associated with the use of objects.

From left to right: Processing acronyms referring to names of political parties activates spatial associations

In line with previous studies, showing that abstract concepts like “power” or “god” implicitly activate spatial associations, in the present study we hypothesized that spatial associations are coactivated during the processing of acronyms referring to names of political parties as well. In four studies, it was found that the reading of these acronyms was accompanied by the implicit activation of spatial left–right associations. That is, participants responded faster to left-wing parties by means of a left-hand button press and vice versa for right-wing parties (Experiments 1 to 3), and participants responded faster when a political acronym was presented at the side of the screen corresponding to the political orientation of the acronym (Experiment 4). Interestingly, a correlation was observed between the effect size for left-wing parties and participants’ political preferences, suggesting that the reaction time effects reflect the perceived distance of a party to ones own political orientation. Together these findings indicate that spatial representations activated in response to political acronyms do not simply reflect lexical–semantic associations or spatial metaphors, but representations of parties’ political orientation relative to ones own sociopolitical position.

Embodied Language Comprehension Requires an Enactivist Paradigm of Cognition

Two recurrent concerns in discussions on an embodied view of cognition are the “necessity question” (i.e., is activation in modality-specific brain areas necessary for language comprehension?) and the “simulation constraint” (i.e., how do we understand language for which we lack the relevant experiences?). In the present paper we argue that the criticisms encountered by the embodied approach hinge on a cognitivist interpretation of embodiment. We argue that the data relating sensorimotor activation to language comprehension can best be interpreted as supporting a non-representationalist, enactivist model of language comprehension, according to which language comprehension can be described as procedural knowledge – knowledge how, not knowledge that – that enables us to interact with others in a shared physical world. The enactivist view implies that the activation of modality-specific brain areas during language processing reflects the employment of sensorimotor skills and that language comprehension is a context-bound phenomenon. Importantly, an enactivist view provides an embodied approach of language, while avoiding the problems encountered by a cognitivist interpretation of embodiment.