Abstract

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.

Highlights

  • Even within the first few weeks after birth, infants appear to be able to imitate certain facial and manual gestures (Meltzoff and Moore, 1977)

  • Deficits of imitation skills are a common symptom of apraxia, a disorder of motor cognition which most often occurs after left hemisphere (LH) stroke (Donkervoort et al, 2000), and which cannot be explained by primary deficits of the sensor-motor system or disturbed communication (Dovern et al, 2012)

  • The data were drawn from a database providing lesion and behavioural information of stroke patients enrolled in previous studies of motor cognition of the University Hospital of Cologne and the Research Centre Jülich

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Summary

Introduction

Even within the first few weeks after birth, infants appear to be able to imitate certain facial and manual gestures (Meltzoff and Moore, 1977). These apparently hard-wired skills (Meltzoff and Moore, 1977, 1997) may provide the foundation for much of our subsequent learning, including language acquisition, socialisation and enculturation (Brass and Heyes, 2005). LH damage can impair all of these skills, whereas right hemisphere (RH) damage appears only to impair a subset (upper face, feet and fingers: (Goldenberg and Karnath, 2006))

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