Abstract
Mirror neurons are single cells found in macaque premotor and parietal cortices that are active during action execution and observation. In non-human primates, mirror neurons have only been found in relation to object-directed movements or communicative gestures, as non-object directed actions of the upper limb are not well characterized in non-human primates. Mirror neurons provide important evidence for motor simulation theories of cognition, sometimes referred to as the direct matching hypothesis, which propose that observed actions are mapped onto associated motor schemata in a direct and automatic manner. This study, for the first time, directly compares mirror responses, defined as the overlap between action execution and observation, during object directed and meaningless non-object directed actions. We present functional MRI data that demonstrate a clear dissociation between object directed and non-object directed actions within the human mirror system. A premotor and parietal network was preferentially active during object directed actions, whether observed or executed. Moreover, we report spatially correlated activity across multiple voxels for observation and execution of an object directed action. In contrast to predictions made by motor simulation theory, no similar activity was observed for non-object directed actions. These data demonstrate that object directed and meaningless non-object directed actions are subserved by different neuronal networks and that the human mirror response is significantly greater for object directed actions. These data have important implications for understanding the human mirror system and for simulation theories of motor cognition. Subsequent theories of motor simulation must account for these differences, possibly by acknowledging the role of experience in modulating the mirror response.
Highlights
Distinguishing between object and non-object directed actionPraxis, the performance of skilled voluntary action, can be widely divided into actions involving objects, and actions not involving objects
This study investigated common activity across action execution and observation for both object directed and non-object directed actions
We confirmed the existence of a human mirror response for an object directed action in a network of regions comprising bilateral premotor, parietal cortices, precuneus and extrastriate cortex
Summary
Distinguishing between object and non-object directed actionPraxis, the performance of skilled voluntary action, can be widely divided into actions involving objects, and actions not involving objects. Neuroimaging has demonstrated differences in neural activity associated with perception of object directed and non-object directed action. In contrast patients with ideomotor apraxia display selective deficits in the execution of non-object directed actions, such as gestures or sequencing movements in space and time [8]. These deficits to action/gesture production are typically associated with lesions in frontal and parietal regions, more so in the left hemisphere [1] and have been linked to deficits in action/gesture perception in a subset of patients [9,10]
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