Monday, September 19, 2011

Mirror Neuron Forum - Some additional discussion - Part IV

Here is some commentary on Iacoboni’s response to my answers to question 1.

Iacoboni writes,

“The ventral/dorsal dichotomous interpretational framework (as invoked in GH’s answer to Question 1) is too simplistic to account for extant data on the MN system (and probably other systems too). We now know that MNs exist in areas well outside the classical dorsal stream (Mukamel et al., 2010).”

In Mukamel et al. it was reported that cells in the human medial temporal lobe respond both during action execution and action observation. We could argue about whether or not these are “real” mirror neurons in sense of functioning to support action understanding given that they are outside of the motor system and as such not likely to be involved in motor simulation. But that is beside the point. The question is whether the existence of mirror neurons in the human hippocampus calls into question my claim that the dorsal stream mirror system supports sensory motor integration while the ventral stream supports action understanding. As a single data point, the existence of hippocampal mirror neurons is irrelevant to my claim. We can see this clearly if we consider the same argument in a different context: suppose I claimed that neurons with an ON-center Off-surround receptive field were critically involved in pitch perception in auditory cortex and someone countered that ‘it is more complicated than that because ON-center Off-surround cells have been found well outside the auditory system including the retina’. The argument misses the point completely.

Iacoboni continues,

“Furthermore, it is unclear why hypotheses about the functions of MNs must be mutually exclusive …. It is likely … that association learning plays some role in shaping the responses of MNs. However, there is no reason to assume, as GH does, that because association learning plays a role in shaping MN responses that MNs cannot implement any form of action understanding.”

I agree completely. MNs could in principle be involved in multiple processes. But again, it’s an empirical question. My point is simply that the empirical record as a whole does not support the action understanding interpretation.

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