Chong, T. T., R. Cunnington, et al. (2008). "FMRI adaptation reveals mirror neurons in human inferior parietal cortex." Curr Biol 18(20): 1576-80..
Mirror neurons, as originally described in the macaque, have two defining properties [1, 2]: They respond specifically to a particular action (e.g., bringing an object to the mouth), and they produce their action-specific responses independent of whether the monkey executes the action or passively observes a conspecific performing the same action. In humans, action observation and action execution engage a network of frontal, parietal, and temporal areas. However, it is unclear whether
these responses reflect the activity of a single population that represents both observed and executed actions in a common neural code or the activity of distinct but overlapping populations of exclusively perceptual and motor neurons . Here, we used fMRI adaptation to show that the right inferior parietal lobe (IPL) responds independently to specific actions regardless of whether they are observed or executed. Specifically, responses in the right IPL were attenuated when participants observed a recently executed action relative to one that had not previously been performed. This adaptation across action and perception demonstrates that the right IPL responds selectively to the motoric and perceptual representations of actions and is the first evidence for a neural response in humans that shows both defining properties of mirror neurons
This is a very cool and cleverly designed study. Basically, they were looking for areas that showed adaptation (decreased BOLD amplitude) for observed actions that followed the same executed actions relative to observed actions that were not previously executed. Here is the result:
They observed adaption in one of their ROIs in the right parietal lobe (ROIs included IFG, IPL, and STS). If you buy the adaptation logic -- it seems reasonable to me -- this means that mirror neurons live in the right parietal lobe of humans. So we finally have some direct evidence for the existence of mirror neurons in humans. Cool. I knew someday we'd have decent evidence. It is surprising, though, that no mirror neurons were found in the frontal lobe or the left hemisphere (where damage can lead to disorders of action production and recognition), but let's not get bogged down in details.
A couple of points are relevant. One is that if this result holds, it means that human mirror neurons and monkey mirror neurons are different. Chong et al. used pantomimed gestures. Classic F5 mirror neurons don't respond to pantomime. In effect, we have a new animal that needs to be studied in its own right. Who knows, maybe the function of these human mirror neurons are completely different! Another relevant point is that just because some form of mirror neuron exists in humans doesn't mean that this system supports action understanding. The Chong et al. study has nothing to say about this question. So all previous critiques of the action understanding portion of the mirror neuron doctrine still hold.
T CHONG, R CUNNINGTON, M WILLIAMS, N KANWISHER, J MATTINGLEY (2008). fMRI Adaptation Reveals Mirror Neurons in Human Inferior Parietal Cortex Current Biology, 18 (20), 1576-1580 DOI: 10.1016/j.cub.2008.08.068