Introduction: The mirror neuron system (MNS) has been suggested to subserve action understanding and learning [1]. Whether it is triggered by action goals or means remains to be elucidated: The MNS is activated by static images of action goals [2] as well as actions with invisible outcome [3]. Here we tested whether attention directed to the means or the end of an intentional movement has differential effects on the MNS.
Methods:
20 right-handed volunteers (10 m, 18–37 y) watched video sequences of 24s each, in which hands were shown from two different perspectives placing a cube from left to right and vice versa. In half of the trials subjects indicated whether the hand was turned during the movement, in the other half whether the cube was placed on or next to the target locations. Thus subjects either paid attention to the action means or the end position thereof. Gaze fixation to avoid differential eye movements was monitored using ASL. GE-EPIs were acquired on a 1.5T Scanner (Siemens Sonata). A random effects analysis was performed using SPM2, at a corrected cluster threshold of p<0.05.
Results: Error rates indicated that means judgements were slightly more difficult than end position judgments (4.2±0.6% vs. 3.0±0.4%). fMRI data analysis revealed bilateral involvement of the intraparietal sulcus and premotor cortex in addition to widespread activation of occipital cortex in all conditions (compared to baseline). Judging the means of an action compared to its end position showed activation of the left supramarginal gyrus, right motor and ventral premotor cortex (BA6, BA44) apart from the bilateral inferior occipito-temporal junction (incl. V5). Inversely, judging the end differentially activated the superior frontal and angular gyrus bilaterally, as well as the left precuneus and middle temporal gyrus.
Conclusion: Although identical video stimuli were used in all conditions, attentional focus on either the means of an action or its end triggered differential activation of the inferior parietal and premotor cortex. The results suggest that the MNS is sensitive to attentional modulation and top down control and that attention to the means of an action rather than its end enhances MNS activation.
References: [1] Rizzolatti & Craighero, Annu Rev Neurosci 2004
[2] Umilta et al., Neuron 2001
[3] Johnson-Frey et al., Neuron 2003
