Hand Imitation Research Articles

Bayesian evidence for the neural dissociation between finger and hand imitation skills

Abstract For limb apraxia ‒ a heterogeneous disorder of higher motor cognition following stroke ‒ an enduring debate has arisen regarding the existence of dissociating neural correlates for finger and hand gestures in the left hemisphere. We re-assessed this question asking whether previous attempts analysing pooled samples of patients with deficits in only one and patients with deficits in both imitation types might have led to systematically biased results. We conducted frequentist and Bayesian, voxelwise, and regionwise lesion symptom mappings on (i) the full sample (N=96) in which all patients with hand and/or finger imitation apraxia as well as without apraxia were included and (ii) three sub-samples, which excluded those patients from the full sample showing isolated hand imitation deficits, isolated finger imitation deficits or shared (finger and hand) imitation deficits. Anatomical analyses revealed a cortical dissociation of finger imitation deficits (located more anteriorly) and of hand imitation deficits (located more posteriorly). The presence of patients with shared deficits did indeed dilute associations that appeared stronger in the respective isolated samples. Also, brain regions truly associated with hand imitation deficits showed a positive bias for finger imitation deficits, when the sample contained patients with shared deficits. In addition, our frequentist parameters uncovered that some of our Bayesian evidence supported reverse associations (damage protecting from rather than increasing the deficit). Anatomo-behavioral analyses that analyse patients with shared (hand and finger) and isolated (hand or finger) imitation deficits together in one sample do indeed lead to undesirable biases. This explains why some earlier studies failed to detect the apparent neural dissociation between hand and finger imitation deficits.

Visuo-spatial complexity potentiates the body-part effect in intransitive imitation of meaningless gestures.

Recent studies on the imitation of intransitive gestures suggest that the body part effect relies mainly upon the direct route of the dual-route model through a visuo-transformation mechanism. Here, we test the visuo-constructive hypothesis which posits that the visual complexity may directly potentiate the body part effect for meaningless gestures. We predicted that the difference between imitation of hand and finger gestures would increase with the visuo-spatial complexity of gestures. Second, we aimed to identify some of the visuo-spatial predictors of meaningless finger imitation skills. Thirty-eight participants underwent an imitation task containing three distinct set of gestures, that is, meaningful gestures, meaningless gestures with low visual complexity, and meaningless gestures with higher visual complexity than the first set of meaningless gestures. Our results were in general agreement with the visuo-constructive hypothesis, showing an increase in the difference between hand and finger gestures, but only for meaningless gestures with higher visuo-spatial complexity. Regression analyses confirm that imitation accuracy decreases with resource-demanding visuo-spatial factors. Taken together, our results suggest that the body part effect is highly dependent on the visuo-spatial characteristics of the gestures.

Localizing apraxia in corticobasal syndrome: a morphometric MRI study.

Apraxia localization has relied on voxel-based, lesion-symptom mapping studies in left hemisphere stroke patients. Studies on the neural substrates of different manifestations of apraxia in neurodegenerative disorders are scarce. The primary aim of this study was to look into the neural substrates of different manifestations of apraxia in a cohort of corticobasal syndrome patients (CBS) by use of cortical thickness. Twenty-six CBS patients were included in this cross-sectional study. The Goldenberg apraxia test (GAT) was applied. 3D-T1-weighted images were analyzed via the automated recon-all Freesurfer version 6.0 pipeline. Vertex-based multivariate General Linear Model analysis was applied to correlate GAT scores with cortical thickness. Deficits in imitation of meaningless gestures correlated with bilateral superior parietal atrophy, extending to the angular and supramarginal gyri, particularly on the left. Finger imitation relied predominantly on superior parietal lobes, whereas the left angular and supramarginal gyri, in addition to superior parietal lobes, were critical for hand imitation. The widespread bilateral clusters of atrophy in CBS related to apraxia indicate different pathophysiological mechanisms mediating praxis in neurodegenerative disorders compared to vascular lesions, with implications both for our understanding of praxis and for the rehabilitation approaches of patients with apraxia.

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Machines of chainstitches 104 create imitation of hand stitches 209 from one material side. Every hand stitch is formed from two threads, therefore the seams are more accented and very short length pick stitches are larger than created seams from real hand stitches 209. The length of the hand stitches is determined by the distance between a sewing needle and a hook needle of the machine. To create different length hand stitches a gauge set of the machine has to be changed. Because of different appearance of the stitches on top and bottom fabric surfaces the machines are used for top stitching of seams which are seen on a ready garment from one side only. In men suit manufacturing there are: top stitching of a jacket's lining, top stitching on pockets, fronts, etc. of jackets, vests, trousers. There are also available chainstitch 104 machines which create different variations of the hand stitches: double row hand stitches, parallel hand stitches, angular hand stitches. Comparing with the machines of real hand stitches 209, the machines of chainstitches 104 are much lower priced and have much higher productivity .

Praxis deficits in patients with Parkinson’s disease

AbstractBackgroundLimb apraxia has been described in several neurological disorders including Parkinson’s disease (Leiguarda and Marsden, 2000) and may predict progression to Alzheimer’s dementia in patients with mild cognitive impairment. Our aim was to study presence of apraxia and subtypes of deficits in patients with idiopathic Parkinson’s Disease.Method20 patients with idiopathic Parkinson’s disease, recruited from the Oxford Parkinson’s Disease Centre, were tested for presence of limb apraxia, measured on a battery of tasks, comparing their performance to deficits measured using the UPDRS, and independent measures of cognition (MOCA), and dexterity. Results were analysed using Pearson’s correlations, with correction for multiple comparisonsResultDetailed neuropsychological testing revealed significant deficits in praxis with 9 out of 20 patients displaying significant ideomotor deficits on finger and hand imitation, 2 patients showing ideational deficits on pantomime of tool use. Most patients made errors in the praxis tasks even though they did not qualify as apraxic per se, with only one patient performing faultlessly at all the screening tasks.Both ideational and ideomotor deficits correlated with Part 3 of the UPDRS score. Similarly, Part 3 of the UPDRS correlated with cognitive performance on the MOCA. Ideomotor deficits also correlated with deficits in dexterity and response inhibition. Whereas deficits in dexterity correlated with PD severity; praxis and cognitive deficits did not.ConclusionThe study shows different deficits in limb praxis assessed using batteries of tasks in patients with Parkinson’s disease. We identified relationships between praxis deficits and cognitive as well as motor performance in PD patients. Testing for apraxia in PD patients might provide a useful way for stratifying patients’ impairments, progression to PD dementia and response to treatment.

Using multi-level Bayesian lesion-symptom mapping to probe the body-part-specificity of gesture imitation skills

Past attempts to identify the neural substrates of hand and finger imitation skills in the left hemisphere of the brain have yielded inconsistent results. Here, we analyse those associations in a large sample of 257 left hemisphere stroke patients. By introducing novel Bayesian methods, we characterise lesion symptom associations at three levels: the voxel-level, the single-region level (using anatomically defined regions), and the region-pair level. The results are inconsistent across those three levels and we argue that each level of analysis makes assumptions which constrain the results it can produce. Regardless of the inconsistencies across levels, and contrary to past studies which implicated differential neural substrates for hand and finger imitation, we find no consistent voxels or regions, where damage affects one imitation skill and not the other, at any of the three analysis levels. Our novel Bayesian approach indicates that any apparent differences appear to be driven by an increased sensitivity of hand imitation skills to lesions that also impair finger imitation. In our analyses, the results of the highest level of analysis (region-pairs) emphasise a role of the primary somatosensory and motor cortices, and the occipital lobe in imitation. We argue that this emphasis supports an account of both imitation tasks based on direct sensor-motor connections, which throws doubt on past accounts which imply the need for an intermediate (e.g. body-part-coding) system of representation.

The Effects of Language Intervention Using Manual Signing on Utterances of Young Children with Language Developmental Delay

본 연구는 손짓기호를 활용한 언어중재가 언어발달지체 유아의 시작발화, 반응발화, 명료한 발화에 미치는 효과를 알아보고자 하였다. 연구는 대상자간 중다기초선 설계를 통해 기초선, 중재, 유지 단계로 진행되었다. 손짓기호를 활용한 언어중재는 교사와 유아 간 놀이 상황에서 목표어휘에 해당하는 손짓기호와 말을 모방 훈련하는 과정과 모방훈련 없이 시간지연, 손짓기호 단서 제공, 우발교수 환경구성 등 자연적인 언어 중재 전략을 통해 자발적인 발화를 유도하는 과정으로 구성되었다. 교사와 유아 간의 자연스러운 놀이 맥락에서 이루어지는 의사소통 중 유아의 자발적인 시작발화, 반응발화, 조음이 명료한 발화를 수집하여 각각의 어절 수를 측정하였다. 연구 결과 손짓기호를 활용한 언어중재는 언어발달지체 유아의 시작발화, 반응발화, 명료한 발화를 향상시키는데 효과가 있었다. 연구 결과에 근거하여 언어발달지체 유아의 발화 촉진에 긍정적인 영향을 줄 수 있는 손짓기호를 활용한 언어중재의 효율성에 대해 논의하였다.The purpose of this study was to investigate the effects of language intervention using manual signing on utterances of 2 young children with language developmental delay. Utterance was operationally defined as initiating utterance, responding utterance, and intelligible utterance. The study used multiple baseline across subjects design: initial baseline, intervention, and maintenance condition. Intervention was implemented twice per week, each session was proceeded for 30 minute. Language intervention using manual signing was composed of the two phase: manual signing and utterance imitation training and the naturalistic language intervention. The utterances of each child was collected using the event recording system. Then the number of words of initiating utterances, correct responding utterances, and intelligible utterances two observer had agreed were calculated. The results of this study were as follows. The language intervention using manual signing increased the number of words of initiating, responding, and intelligible utterances of the 2 young children with language developmental delay. The effects were maintained after the termination of intervention. This indicates that language intervention using manual signing would be used as an effective intervention for utterance improvement of young children with language developmental delay having hand imitation skills.

Dementia Apraxia Test (DATE): A Brief Tool to Differentiate Behavioral Variant Frontotemporal Dementia from Alzheimer's Dementia Based on Apraxia Profiles.

Standardized praxis assessments with modern, empirically validated screening tests have substantially improved clinical evaluation of apraxia in patients with stroke. Although apraxia may contribute to early differential diagnosis of Alzheimer's dementia (AD) and behavioral variant frontotemporal dementia (bvFTD), no comparable test is readily available to clinicians for this purpose to date. To design a clinically useful apraxia test for the differentiation of AD and bvFTD. 84 test items pertaining to twelve praxis subdomains were evaluated for their efficacy to discriminate between patients with bvFTD (n = 24), AD (n = 28), and elderly healthy controls (HC; n = 35). Items were then selected based on discriminative value and psychometric properties. Items indicative of mild AD comprised spatially complex imitation of hand and finger postures and to a lesser degree, pantomime of common object-use. Buccofacial apraxia including imitation of face postures, emblematic face postures, and repetition of multisyllabic pseudowords differentiated bvFTD from HC and AD. The final test version consisting of 20 items proved highly efficient for the discrimination of biologically confirmed dementia patients from HC (sensitivity 91% , specificity 71%) but also for differential diagnosis of bvFTD and AD (sensitivity 74% , specificity 93%). Assessment of praxis profiles effectively contributes to diagnosis and differential diagnosis of AD and bvFTD. The Dementia Apraxia Test (DATE) is a brief and easy to administer cognitive tool for dementia assessment, has a high inter-rater reliability (Cohen's κ= 0.885) and demonstrates content validity.

Shared neural substrates of apraxia and aphasia

Apraxia is regularly associated with aphasia, but there is controversy whether their co-occurrence is the expression of a common basic deficit or results from anatomical proximity of their neural substrates. However, neither aphasia nor apraxia is an indivisible entity. Both diagnoses embrace diverse manifestations that may occur more or less independently from each other. Thus, the question whether apraxia is always accompanied by aphasia may lead to conflicting answers depending on which of their manifestations are considered. We used voxel based lesion symptom mapping (VLSM) for exploring communalities between lesion sites associated with aphasia and with apraxia. Linguistic impairment was assessed by the Aachen Aphasia Test (AAT) subtests naming, comprehension, repetition, written language, and Token Test. Apraxia was examined for imitation of meaningless hand and finger postures and for pantomime of tool use.There were two areas of overlap between aphasia and apraxia. Lesions in the anterior temporal lobe interfered with pantomime of tool use and with all linguistic tests. In the left inferior parietal lobe there was a large area where lesions were associated with defective imitation of hand postures and with poor scores on written language and the Token Test. Within this large area there were also two spots in supramarginal and angular gyrus where lesions were also associated with defective pantomime.We speculate that the coincidence of language impairment and defective pantomime after anterior temporal lesions is due to impaired access to semantic memory. The combination of defective imitation of hand postures with poor scores on Token Test and written language is not easily compatible with a crucial role of parietal regions for the conversion of concepts of intended actions into motor commands. It accords better with a role of left inferior parietal lobe regions for the categorical perception of spatial relationships.

Apraxia profile differentiates behavioural variant frontotemporal from Alzheimer's dementia in mild disease stages

ObjectiveDespite refined criteria for behavioural variant frontotemporal dementia (bvFTD), its differentiation from Alzheimer's dementia (AD) remains difficult at early clinical presentation. Apraxia is not considered as a supportive feature for...

Characteristics of canonical intrinsic connectivity networks across tasks and monozygotic twin pairs.

Intrinsic connectivity networks (ICNs) are becoming more prominent in the analyses of in vivo brain activity as the field of neurometrics has revealed their importance for augmenting traditional cognitive neuroscience approaches. Consequently, tools that assess the coherence, or connectivity, and morphology of ICNs are being developed to support inferences and assumptions about the dynamics of the brain. Recently, we reported trait-like profiles of ICNs showing reliability over time and reproducibility across different contexts. This study further examined the trait-like and familial nature of ICNs by utilizing two divergent task paradigms in twins. The study aimed to identify stable network phenotypes that exhibited sensitivity to individual differences and external perturbations in task demands. Analogous ICNs were detected in each task and these ICNs showed consistency in morphology and intranetwork coherence across tasks, whereas the ICN timecourse dynamics showed sensitivity to task demands. Specifically, the timecourse of an arm/hand sensorimotor network showed the strongest correlation with the timeline of a hand imitation task, and the timecourse of a language-processing network showed the strongest temporal association with a verb generation task. The area V1/simple visual stimuli network exhibited the most consistency in morphology, coherence, and timecourse dynamics within and across tasks. Similarly, this network exhibited familiality in all three domains as well. Hence, this experiment is a proof of principle that the morphology and coherence of ICNs can be consistent both within and across tasks, that ICN timecourses can be differentially and meaningfully modulated by a task, and that these domains can exhibit familiality.

Apraxia in left-handers

In typical right-handed patients both apraxia and aphasia are caused by damage to the left hemisphere, which also controls the dominant right hand. In left-handed subjects the lateralities of language and of control of the dominant hand can dissociate. This permits disentangling the association of apraxia with aphasia from that with handedness. Pantomime of tool use, actual tool use and imitation of meaningless hand and finger postures were examined in 50 consecutive left-handed subjects with unilateral hemisphere lesions. There were three aphasic patients with pervasive apraxia caused by left-sided lesions. As the dominant hand is controlled by the right hemisphere, they constitute dissociations of apraxia from handedness. Conversely there were also three patients with pervasive apraxia caused by right brain lesions without aphasia. They constitute dissociations of apraxia from aphasia. Across the whole group of patients dissociations from handedness and from aphasia were observed for all manifestations of apraxia, but their frequency depended on the type of apraxia. Defective pantomime and defective tool use occurred rarely without aphasia, whereas defective imitation of hand, but not finger, postures was more frequent after right than left brain damage. The higher incidence of defective imitation of hand postures in right brain damage was mainly due to patients who had also hemi-neglect. This interaction alerts to the possibility that the association of right hemisphere damage with apraxia has to do with spatial aptitudes of the right hemisphere rather than with its control of the dominant left hand. Comparison with data from right-handed patients showed no differences between the severity of apraxia for imitation of hand or finger postures, but impairment on pantomime of tool use was milder in apraxic left-handers than in apraxic right-handers. This alleviation of the severity of apraxia corresponded with a similar alleviation of the severity of aphasia as manifested by a lower proportion of left-handed patients with global aphasia.

The role of imitation in the observed heterogeneity in EEG mu rhythm in autism and typical development

Dysfunction in an execution/observation matching system, or mirror neuron system, has been proposed to contribute to the social deficits observed in Autism Spectrum Disorder (ASD). Atypical activity in this system, as reflected in attenuation of the EEG mu rhythm, has been demonstrated in several studies; however, normative patterns of activity have been evident in other ASD samples. The current study sought to investigate this poorly understood heterogeneity in social perceptual brain function in ASD. EEG mu rhythm was recorded in a well-characterized sample of 19 children with ASD (mean age=6.4; 1 female) and 19 age-matched typically developing peers (mean age=6.9; 2 females) during execution and observation of goal-directed hand actions. Children were assessed on variables theoretically related to mirror neuron system function (MNS), such as ASD symptoms and imitation ability. Results indicated that MNS activity was associated with facial imitation ability, but not hand imitation ability, in children with ASD and typically developing individuals. Groups were comparable in terms of average MNS activity during both action observation and execution, but, in both groups, a subset of children showed absent or significantly reduced MNS activity during observation of action in conjunction with greater difficulty in imitation. These results emphasize the relationship between EEG indices of MNS function and imitative skill and suggest that dysfunction of the MNS is related to imitation ability in both clinical and typical populations, rather than representing a core deficit or universal impairment in ASD.

Description of interhemispheric disconnection syndrome in a patient with Marchiafava-Bignami disease

Interhemispheric disconnection syndrome (IDS), described by Sperry, Gazzaniga and Bogen, is characterized by the presence of visual and tactile anomia, absence of interhemispheric transference of unilateral somatosensory stimulation of both hands, hemialexia and unilateral left-side apraxia. Subsequently, changes were also observed in the sensory interhemispheric transfer and in tests of crossed motor control. In Marchiafava-Bignami disease (MBD) there have been descriptions of partial IDS. The aim is to describe the dissociations in IDS that are presented in a patient with MBD, using a specialized assessment methodology. Patient and Method: A 54-year-old patient, righthanded, with 11 years of schooling, presented with antecedent chronic alcoholism. Neuropsychological tests were administered for general assessment along with specific tests of interhemispheric transference. Results: Borderline changes were found in visual memory, visual-constructive abilities and attention and executive functioning. In tasks of interhemispheric transference the patient showed changes in: the imitation of hand poses; inter-manual pressure point localization (tactile stimulation); reading aloud of words by visual hemifield; and movement control. Conclusion: Our patient showed a wide lesion of the Corpus Callosum (CC) with relative preservation of the splenium, accompanied by partial disconnection syndrome in the context of a global cognitive deterioration from his chronic alcoholism.

Imitation and speech: commonalities within Broca’s area

The so-called embodiment of communication has attracted considerable interest. Recently a growing number of studies have proposed a link between Broca's area's involvement in action processing and its involvement in speech. The present quantitative meta-analysis set out to test whether neuroimaging studies on imitation and overt speech show overlap within inferior frontal gyrus. By means of activation likelihood estimation (ALE), we investigated concurrence of brain regions activated by object-free hand imitation studies as well as overt speech studies including simple syllable and more complex word production. We found direct overlap between imitation and speech in bilateral pars opercularis (BA 44) within Broca's area. Subtraction analyses revealed no unique localization neither for speech nor for imitation. To verify the potential of ALE subtraction analysis to detect unique involvement within Broca's area, we contrasted the results of a meta-analysis on motor inhibition and imitation and found separable regions involved for imitation. This is the first meta-analysis to compare the neural correlates of imitation and overt speech. The results are in line with the proposed evolutionary roots of speech in imitation.

Imitation of hand and tool actions is effector-independent

Following the theoretical notion that tools often extend one’s body, in the present study, we investigated whether imitation of hand or tool actions is modulated by effector-specific information. Subjects performed grasping actions toward an object with either a handheld tool or their right hand. Actions were initiated in response to pictures representing a grip at an object that could be congruent or incongruent with the required action (grip-type congruency). Importantly, actions could be cued by means of a tool cue, a hand cue, and a symbolic cue (effector-type congruency). For both hand and tool actions, an action congruency effect was observed, reflected in faster reaction times if the observed grip type was congruent with the required movement. However, neither hand actions nor tool actions were differentially affected by the effector represented in the picture (i.e., when performing a tool action, the action congruency effect was similar for tool cues and hand cues). This finding suggests that imitation of hand and tool actions is effector-independent and thereby supports generalist rather than specialist theories of imitation.

Severity of neglect predicts accuracy of imitation in patients with right hemisphere lesions

Goldenberg [Goldenberg, G. (1996). Defective imitation of gestures in patients with damage in the left or right hemisphere. Journal of Neurology, Neurosurgery, and Psychiatry, 61, 176-180] proposed that the vulnerability of the imitation of meaningless gestures to right or left brain damage depends on the body parts that are involved in the gestures. Whereas imitation of hand postures was disturbed only in patients with left brain damage, imitation of finger postures was affected to similar degrees in left and right brain damage. Subsequent studies confirmed the selective vulnerability of hand postures to LBD but failed to replicate the severe disturbance of finger postures in RBD. In contrast to Goldenberg's studies, these studies excluded RBD patients with neglect. The present investigation aimed to explore the relationship between spatial neglect and imitation of finger postures in RBD patients. Presence and severity of spatial neglect and accuracy of imitation of hand and finger postures were tested in 50 RBD patients. Disturbance of imitation was much more severe for finger than hand postures and was tightly correlated with severity of neglect. The number of errors was higher for fingers which from the patient's perspective were located on the left side of the examiner's demonstrating hand but this spatial bias was not sufficient to explain all errors. Possible causes for non-lateralized errors could be a general narrowing of the focus of attention and reduced capacity for processing of visual information which have been postulated to be regular companions of the lateral displacement of attention in spatial neglect.

Brief Report: Imitation of Meaningless Gestures in Individuals with Asperger Syndrome and High-functioning Autism

Nineteen people with Asperger syndrome (AS)/High-Functioning Autism (HFA) (ages 7-15) were tested on imitation of two types of meaningless gesture: hand postures and finger positions. The individuals with AS/HFA achieved lower scores in the imitation of both hand and finger positions relative to a matched neurotypical group. The between-group difference was primarily accounted for by performance on a test of visual motor integration, together with a hand imitation deficit which was specifically due to errors in body part orientation. Our findings implicate both visuomotor processes (Damasio and Maurer, 1978) and self-other mapping (Rogers and Pennington, 1991) in ASD imitation deficits. Following Goldenberg (1999), we propose that difficulties with body part orientation may underlie problems in meaningless gesture imitation.

Complex Motor Function in Humans: Validating and Extending the Postulates of Alexandr R. Luria

We used functional brain imaging to reevaluate Luria's postulates and to elaborate the neural circuitry underlying performance of complex motor tasks. The anatomic organization and physiologic functioning of the normal human motor system have great significance for understanding motor dysfunction and remediation in neurology. Working with victims of penetrating head injuries, noted Russian neuropsychologist Aleksandr R. Luria designed several tests of fine motor control to understand their difficulties with complex voluntary movements. This led to his postulates that such function involves the premotor cortices and their interaction with the parietal lobe. Six healthy young adults performed the hand imitation, fist-scissors-gun, and piano key tasks during blood oxygen level-dependent functional magnetic resonance imaging at 3 T. All 3 tasks revealed activation of both premotor and parietal cortices. Furthermore, while hand Imitation relied more on the ventral premotor area and right parietal lobe, fist-scissors-gun and piano key relied more on the supplementary motor cortex. We postulate that differences in task-dependent activations across these tasks relate to degrees of sequential movement, pacing, and imitation. These results uphold Luria's original hypotheses, and extend that work by providing a further characterization of the motor areas involved in complex motor behaviors.

Hemisphere asymmetry for imitation of hand and finger movements, Goldenberg's hypothesis reworked

Goldenberg and co-workers put forward the hypothesis that coding of hand gestures with respect to body parts depends upon the functioning of the left hemisphere while the right hemisphere would be involved in imitation of finger postures. They supported this claim with experimental evidence from lesion studies, however, they failed to back it up with functional neuroimaging data. To verify Goldenberg's hypothesis on hemisphere asymmetries for hand/finger postures imitation, the performance of 35 patients with left hemisphere lesion (L/pts), of 24 patients with right hemisphere lesion (R/pts) and that of 41 matched controls was assessed in two imitation tasks, respectively, taxing hand or finger postures. The data, adjusted for the performance of the controls and for the effect of age were analysed using a multivariate, nonparametric approach. The outcome partly supports Goldenberg and colleagues’ hypothesis: hand minus finger performance did differs between the R/pts and L/pts patients, even considering the pertinent hand–finger performances by control participants, however, in line with neuroimaging evidence, the left hemisphere's contribution is greater than that of the right for both finger and hand posture imitation.