Tuesday, May 23, 2017

The real action understanding network

In The Myth of Mirror Neurons I hypothesized that the action understanding network was much more complicated than the mirror neuron theory supposed.  I pointed to the superior temporal region as a possible hub based on its action observation response properties in both monkeys and humans.  I then went on to speculate about the broad constellation of functional networks that would be needed for true action understanding.  Here's the quote from Chapter 7 in my book:
Other systems that are likely linked up to the posterior temporal (and perhaps STS) action understanding convergence zone include temporal lobe regions that could put the perceived movement in the context of (i) surrounding visually perceived objects (the lateral occipital cortex), (ii) higher-order semantic representations of objects (anterior and/or posterior temporal lobe), (iii) the particular people involved (the fusiform face area), (iv) the broader semantic or autobiographical context (the default network and medial temporal lobe memory areas), and (v) the emotional relevance (amygdala), which together put the meat of understanding on the bones of the perceived action. The network will also have to be interfaced with prefrontal circuits involved (i) in assessing the relevance of the action given the context above, (ii) in directing attention to the action if the context dictates such, and (iii) in selecting an appropriate response, if any.  
A new paper has recently been published in Science describing an fMRI experiment in four monkeys during both agent-object interaction observation and agent-agent, i.e., social interaction observation. Here is a map of activated regions in the two conditions.

Both implicate fairly large networks as we would expect for complex cognitive tasks like figuring what someone is doing. The social interaction map is interesting in that it yields more robust activation and recruits additional, mostly medial and limbic-related structures.  This makes sense for a social species. More specifically, here's a quote from the paper listing the regions activated.
Social interactions, but not physical ones, activated a large set of brain regions beyond the category selective networks and the MNS (Fig. 2, I to N). This social-interaction network (SIN) included parts of the medial prefrontal cortex (mPFC) and anterior cingulate cortex (ACC) (areas 32 and 10mr, and 24b, respectively), dorsomedial prefrontal cortex (dmPFC) (areas F6 or Pre-SMA, 8Bm, and 9m), a temporo-parietal cluster (areas TPOc and 7a), parts of the ventro-lateral prefrontal cortex (vlPFC) (ventral part of F5, ventral part of 44, the posterior part of 47 and 12, and OPro), temporal pole regions (TPOi, STS areas 1 and 2, and TPpro), the perirhinal cortex (36R), dorsal STS areas [social posterior dorsal (sPD) and social anterior dorsal (sAD), located dorsally to posterior lateral (PL) and anterior fundus (AF) face patches, and anterior dorsal (AD), a face patch located dorsally to face patch AF], and cortical and subcortical systems engaged in reward, valence, and emotional processing [caudate; amygdala; and areas 10o, 11l, and 14r of the orbitofrontal cortex (OFC)]
The take home message, to quote again from my book is that action "understanding is a complicated thing with lots of moving parts. You can’t pull out one part and call that the 'basis of action understanding.' It doesn’t work for just the motor bits and it doesn’t work for just the sensory bits." If we are going to make progress in understanding the neurocomputational nature of action understanding, we are going to have map all the parts and their interactions.

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