Iacoboni et al. (2004)

Grasping the intentions of others with one’s own mirror neuron system.

Background information: The discovery of a special class of neurons in the premotor cortex of monkeys has provided some clues with respect to the mechanisms that underlie our understanding of the intentions of others. These “mirror neurons” are premotor neurons that fire when the monkey performs object-directed actions such as grasping, tearing, manipulating, holding, but also when the animal observes somebody else, either another monkey or a human experimenter, performing the same class of actions. In fact, even the sound of an action in the dark activates these neurons. This research extends the investigation of these neurons to humans.

Aim: To investigate the neural and functional mechanisms underlying understanding the intentions of others.

Method: 23 right-handed participants with a mean age of 26 years (15 female and 8 male) watched film clips of three types of stimuli: context only (scenes containing objects), grasping hand actions without a context, and grasping hand actions performed in two different contexts. In the last condition the context suggested the intention associated with the grasping action (either drinking or cleaning). Their brains were scanned using fMRI as they watched the films.

The same action done in two different contexts acquires different meanings and may reflect two different intentions. The researchers investigated whether the observation of the same grasping action, either embedded in contexts that cued the intention or in the absence of a context, elicited the same or different activity in mirror neuron areas for grasping in the human brain. If the mirror neuron system simply codes the type of observed action and its immediate goal, then the activity in mirror neuron areas should not be influenced by the presence or the absence of context. However, if the mirror neuron system codes the intention associated with the action, then the presence of a context that cues the observer should modulate activity in mirror neuron areas

Results: Observing grasping actions embedded in contexts yielded greater activity in mirror neuron areas in the inferior frontal cortex, associated with grasping, than observing grasping actions in the absence of contexts or while observing contexts only.

Conclusion: Premotor mirror neuron areas—areas active during the execution and the observation of an action—previously thought to be involved only in action recognition are actually also involved in understanding the intentions of others, which is the basis of empathy.

Evaluation:

Strengths of the study: The experimental design controlled for handedness and had a mix of genders. The film-watching was conducted under identical conditions for each participant.

Limitations of the study: Activity in the front parietal lobe when watching intention could have more to do with the complexity of the pictured action, which had a person’s hand and a cup and two different contexts. Therefore, there was more going on than in the other pictures, and this relates to the internal validity of the findings. This was also quite a limited sample, with a narrow and quite young age-range. To establish reliability, it would need to be repeated with a wider age-range.

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