The Neurocognitive Bases of Meaningful Intransitive Gestures: A Systematic Review and Meta-analysis of Neuropsychological Studies.

Researchers and clinicians have long used meaningful intransitive (i.e., not tool-related; MFI) gestures to assess apraxia-a complex and frequent motor-cognitive disorder. Nevertheless, the neurocognitive bases of these gestures remain incompletely understood. Models of apraxia have assumed that meaningful intransitive gestures depend on either long-term memory (i.e., semantic memory and action lexicons) stored in the left hemisphere, or social cognition and the right hemisphere. This meta-analysis of 42 studies reports the performance of 2659 patients with either left or right hemisphere damage in tests of meaningful intransitive gestures, as compared to other gestures (i.e., MFT or meaningful transitive and MLI or meaningless intransitive) and cognitive tests. The key findings are as follows: (1) deficits of meaningful intransitive gestures are more frequent and severe after left than right hemisphere lesions, but they have been reported in both groups; (2) we found a transitivity effect in patients with lesions of the left hemisphere (i.e., meaningful transitive gestures more difficult than meaningful intransitive gestures) but a "reverse" transitivity effect in patients with lesions of the right hemisphere (i.e., meaningful transitive gestures easier than meaningful intransitive gestures); (3) there is a strong association between meaningful intransitive and transitive (but not meaningless) gestures; (4) isolated deficits of meaningful intransitive gestures are more frequent in cases with right than left hemisphere lesions; (5) these deficits may occur in the absence of language and semantic memory impairments; (6) meaningful intransitive gesture performance seems to vary according to the emotional content of gestures (i.e., body-centered gestures and emotional valence-intensity). These findings are partially consistent with the social cognition hypothesis. Methodological recommendations are given for future studies.

Imitation strategies in subjects with schizophrenia: a behavioural approach.

Imitation is a basic human ability, present early in life. Previous studies on control subjects and callosotomized patients showed that imitation occurred mainly in mirror-mode in both groups (60% controls, 66% patients) when they imitate without instructions (free sessions). In contrast, when asked to use the same or opposite limb as the model (driven sessions), controls used anatomical mode (93%), callosotomized patients mainly mirror strategy (61%). It has been suggested that callosotomized subjects prefer the mirror mode because of an impaired capacity for mental rotation, likely due to the lack of the corpus callosum (CC). The present research investigated the imitation strategies used by schizophrenic patients, who also could present anomaly in the interhemispheric connections. Fifteen hospitalized patients with diagnosis of schizophrenia participated in the study. They were asked to imitate upper limb intransitive meaningful and meaningless gestures performed by a model in a video. The results were compared with those from 20 healthy individuals. In driven imitation, controls answered in anatomical mode (95% of the responses), versus 63% of patients' responses. In free imitation sessions the answers in anatomical mode decreased to 39% in control subjects and to 46% in schizophrenic patients. In both driven and free imitation, the differences between the two proportions, conditioned to Diagnosis, resulted significantly different. The present data, in line with previous studies on psychotic and neurological patients showing impairments on imitation, suggest that the neural circuitry leading patients to perform differently from controls likely relates with the functional efficiency of the CC.

A Cognitive Overview of Limb Apraxia.

Since the first studies on limb apraxia carried out by Hugo Liepmann more than a century ago, research interests focused on the way humans process manual gestures by assessing gesture production after patients suffered neurologic deficits. Recent reviews centered their attention on deficits in gesture imitation or processing object-related gestures, namely pantomimes and transitive gestures, thereby neglecting communicative/intransitive gestures. This review will attempt to reconcile limb apraxia in its entirety. To this end, the existing cognitive models of praxis processing that have been designed to account for the complexity of this disorder will be taken into account, with an attempt to integrate in these models the latest findings in the studies of limb apraxia, in particular on meaningful gestures. Finally, this overview questions the very nature of limb apraxia when other cognitive deficits are observed.

Is the Imitative Competence an Asymmetrically Distributed Function?

This study reconsiders behavioral and functional data from studies investigating the anatomical imitation (AI) and the related mental rotation (MR) competence, carried out by our group in healthy subjects, with intact interhemispheric connections, and in split-brain patients, completely or partially lacking callosal connections. The results strongly point to the conclusion that AI and MR competence requires interhemispheric communication, mainly occurring through the corpus callosum, which is the largest white matter structure in the human brain. The results are discussed in light of previous studies and of future implications.

Who is a better teacher for children with autism? Comparison of learning outcomes between robot-based and human-based interventions in gestural production and recognition.

BACKGROUND: Individuals with autism spectrum disorder (ASD) tend to show deficits in engaging with humans. Previous findings have shown that robot-based training improves the gestural recognition and production of children with ASD. It is not known whether social robots perform better than human therapists in teaching children with ASD. AIMS: The present study aims to compare the learning outcomes in children with ASD and intellectual disabilities from robot-based intervention on gestural use to those from human-based intervention. METHODS AND PROCEDURES: Children aged six to 12 with low-functioning autism were randomly assigned to the robot group (N = 12) and human group (N = 11). In both groups, human experimenters or social robots engaged in daily life conversations and demonstrated to children 14 intransitive gestures in a highly-structured and standardized intervention protocol. OUTCOMES AND RESULTS: Children with ASD in the human group were as likely to recognize gestures and produce them accurately as those in the robot group in both training and new conversations. Their learning outcomes maintained for at least two weeks. CONCLUSIONS AND IMPLICATIONS: The social cues found in the human-based intervention might not influence gestural learning. It does not matter who serves as teaching agents when the lessons are highly structured.

Cerebral correlates of imitation of intransitive gestures: An integrative review of neuroimaging data and brain lesion studies.

The aim of the present review is to investigate the cerebral correlates, more particularly the role of the parietal lobe, when imitating intransitive gestures, a task highly sensitive to apraxic errors. By providing an integrative review of functional imaging and brain lesion studies, we focused our attention on the meaning of gestures (meaningful and meaningless) and the body parts (finger and hand). We found that imitation of intransitive gestures is relying upon a bilateral brain network including fronto-parietal areas irrespective of meaning or body parts. Moreover, we observed that while imitation of meaningful and meaningless gestures is predominantly impacted following left parietal lesions, more brain areas are engaged during meaningless gesture imitation. Concerning body parts, whereas imitation of hand postures is relying upon the left parietal lobe (angular gyrus), imitation of finger postures is more likely to be impaired following lesions in the frontal lobe, insula and basal ganglia. These results question neuropsychological theories on apraxia and open promising avenues for a better understanding of apraxia.

Motor planning and performance in transitive and intransitive gesture execution and imagination: Does EEG (RP) activity predict hemodynamic (fNIRS) response?

The interplay between neural structures and processes underlying motor planning and proper movement initiation and guidance is still a matter of debate. The present study aimed at investigating cortical correlates of motor planning and production when execution and imagery of real-life gestures are performed, with an additional focus on potential specificities of meaningful transitive/intransitive gestures. Electrophysiological (Readiness Potential - RP) and functional near-infrared spectroscopy (fNIRS) measures were analyzed to investigate the relationship between processes supporting action planning, execution and imagination. Participants were instructed to observe videos presenting various gestures and then to execute or to imagine them. We observed comparable RP before gesture execution and imagination, with a "facilitation effect" of transitive gestures in particular for imagination. Further, while the supplementary motor regions showed similar O2Hb profiles during both execution and imagination of transitive/intransitive gestures, premotor and posterior parietal areas showed specificities respectively for execution processes and transitive gesture execution. Finally, regression analyses showed that RP amplitude is a predictive factor of subsequent hemodynamic brain activity during action production. Such predictive role was modulated by both task and gesture type factors.

Neural correlates of transitive and intransitive action imitation: an investigation using voxel-based morphometry.

The ability to reproduce visually presented actions has been studied through neuropsychological observations of patients with ideomotor apraxia. These studies include attempts to understand the neural basis of action reproduction based on lesion-symptom mapping in different patient groups. While there is a convergence of evidence that areas in the parietal and frontal lobes within the left hemisphere are involved in the imitation of a variety of actions, questions remain about whether the results generalize beyond the imitation of tool use and whether the presence of a strong grasp component of the action is critical. Here we used voxel-based lesion-symptom mapping to assess the neural substrates of imitating meaningful (familiar, MF) and meaningless (unfamiliar, ML) tool-related (transitive) and non-tool related (intransitive) actions. The analysis showed that the left parietal cortex was involved in the imitation of transitive gestures, regardless of whether they were meaningful or not. In addition there was poor reproduction of meaningless actions (both transitive and intransitive) following damage of the right frontal cortex. These findings suggest a role of right frontal regions in processing of unfamiliar actions.

The effects of visual half-field priming on the categorization of familiar intransitive gestures, tool use pantomimes, and meaningless hand movements.

Although the control of meaningful gestures is one of the most left-lateralized functions, the relative contribution of the two hemispheres to their processing is still debated. We tested the effects of primes appearing in the left or right visual field in the form of pictures (Experiment 1), and words (Experiment 2) on categorization of movies showing intransitive ("communicative") gestures, tool use (transitive) pantomimes, and meaningless movements. Fifteen participants (eight women) watched 36 movies (12 from each category) primed for 150 ms with either a congruent or incongruent stimulus followed by a 50-ms mask. On congruent trials, a picture or word was directly related to the presented gesture, including nonsense pictures or non-words for meaningless actions. On incongruent trials, a picture or word belonged to a different category. In Experiment 1, intransitive gestures were categorized significantly faster than the other two types of hand movements. Moreover, whereas the categorization of transitive gestures was significantly facilitated by congruent pictures on the right, the effect was weaker for intransitive, and reversed for meaningless movements. In Experiment 2, intransitive gestures were again categorized significantly faster, but transitive significantly slower than the other two gesture categories. Yet, there was now a significant facilitation of intransitive, and inhibition of transitive gesture categorization following congruent prime words in the right visual field, and significantly faster categorization of intransitive gestures following incongruent words in the left visual field. These outcomes lend support to the complexity account of differences in left-hemisphere representations of meaningful gestures reported in the neuropsychological, behavioral, and neuroimaging literature. Nevertheless, they also indicate that the representations of intransitive gestures show some differential, and sometimes counterintuitive sensitivity to right hemisphere processing.