Lateralization of the human mirror neuron system.

Area of Science:

• Neuroscience
• Cognitive Neuroscience
• Comparative Psychology

Background:

• A specific cortical network (inferior frontal, inferior parietal, posterior superior temporal cortices) is linked to action representation and imitation in primates and humans.
• This network is considered a potential evolutionary precursor to language systems.
• The lateralization of imitation circuitry in humans remains unclear, contrasting with language's left-hemisphere dominance.

Purpose of the Study:

• To investigate the lateralization of the human mirror system involved in imitation.
• To compare the neural activity patterns during imitation with those of primary sensory and motor areas.
• To explore the implications for the evolutionary origins of language.

Main Methods:

• Functional magnetic resonance imaging (fMRI) study.
• Participants imitated finger movements.
• Lateralized visual stimuli and motor responses were employed.

Main Results:

• Imitation showed bilateral activity in the inferior frontal and inferior parietal cortex, with stronger activation ipsilateral to the stimulus and response hand.
• This ipsilateral pattern contrasts with the contralateral activation typical of primary visual and motor cortices.
• The right superior temporal sulcus (STS) exhibited reliable signal increases for both left and right-sided imitation tasks.

Conclusions:

• The visual and motor components of the human mirror system are not predominantly left-lateralized.
• The left hemisphere's specialization for language likely evolved from different precursors, such as auditory or multimodal action representations.