Lateralization of the human mirror neuron system - PubMed (original) (raw)

Lateralization of the human mirror neuron system

Lisa Aziz-Zadeh et al. J Neurosci. 2006.

Abstract

A cortical network consisting of the inferior frontal, rostral inferior parietal, and posterior superior temporal cortices has been implicated in representing actions in the primate brain and is critical to imitation in humans. This neural circuitry may be an evolutionary precursor of neural systems associated with language. However, language is predominantly lateralized to the left hemisphere, whereas the degree of lateralization of the imitation circuitry in humans is unclear. We conducted a functional magnetic resonance imaging study of imitation of finger movements with lateralized stimuli and responses. During imitation, activity in the inferior frontal and rostral inferior parietal cortex, although fairly bilateral, was stronger in the hemisphere ipsilateral to the visual stimulus and response hand. This ipsilateral pattern is at variance with the typical contralateral activity of primary visual and motor areas. Reliably increased signal in the right superior temporal sulcus (STS) was observed for both left-sided and right-sided imitation tasks, although subthreshold activity was also observed in the left STS. Overall, the data indicate that visual and motor components of the human mirror system are not left-lateralized. The left hemisphere superiority for language, then, must be have been favored by other types of language precursors, perhaps auditory or multimodal action representations.

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Figures

Figure 1.

Figure 1.

Stimuli used in fMRI study of action observation, execution, and imitation. Stimuli consisted of two frames of right or left hands, consecutively flashed for a total of 150 ms to the right or left visual field. Participants participated in four task conditions: observation of a static hand, observation of a moving hand, execution to a static hand, or imitation. The right-hand stimuli shown here all appeared to the right of a fixation cross. Left-hand stimuli appeared to the left of a fixation cross. Both left- and right-hand stimuli were presented in color.

Figure 2.

Figure 2.

All activations are for the comparisons LVF-rest (blue range of voxels) and RVF-rest (red range of voxels). Activations are given as t values, with the left hemisphere on the right side. Here, we show bilateral activations in pars opercularis for both comparisons (A). B, Lateralization of the input: activation of the contralateral visual areas. C, Lateralization of the output: activation of the contralateral motor areas.

Figure 3.

Figure 3.

Views of the activation for areas that are activated in a mirror-like pattern (imitation>execution>observation>observation of static hands) for LVF-RVF trials (top) and RVF-LVF trials (bottom). The pars opercularis of the inferior frontal gyrus (IFG) is activated ipsilaterally. Furthermore, we show activation in areas associated with the human mirror system: the right STS (x = −58; y = −58; z = 6) and bilaterally the posterior parietal (PP) areas (x = −56; y = −26; z = 36; x = 52; y = −30; z = 38).

Figure 4.

Figure 4.

Mean percentage signal change as compared with rest for imitation, execution, action observation, and the control static condition for each ROI (left BA44; right BA44), and each hand (left; right). The BA44 ROI was selected using probabilistic cytoarchitectonic maps. An ANOVA indicates a significant interaction for hemisphere and hand for the imitation condition. No main effect for hemisphere was observed except for the execution condition.

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