Arcuate fasciculus, mirror neurons, and memes

I have wanted to get to this post all week but the farm has taken all my time and energy.  I hope tomorrow’s rainy forecast verifies for many reasons.  Onward.

The arcuate fasciculus (AF) is a horizontal bundle of nerve fibers running between the posterior Wernicke’s area in the auditory cortex and the motor cortex associated with Broca’s area in the front.  Mirror neurons are motor neurons which fire/respond when an animal sees another animal perform some action; these neurons would be involved in performing the observed action but in their mirror functioning, they just respond to perceptual input and are not part of a behavioral enaction.  Memes, as conceived by Richard Dawkins, are units or forms of cultural meaning transmitted through social communication.  Going from my post on 4/7/14 about the MEMBRAIN, i.e., our brain functions as a membrain around our mind and some communication is privileged so its reception and expression is facilitated by specialized channels through the MEMBRAIN.


We have known about the AF for a long time because damage to it results in conduction aphasia, i.e., the person cannot repeat the words they just heard though they may be able to comprehend and respond conversationally.  Evidently the AF enables a person to repeat verbatim.  Long years ago I worked with a young autistic boy who understood almost no language and uttered no meaningful speech but who could and did repeat (echolalia) what was said quite accurately in a sort of inverse of conduction aphasia.  So this part of the MEMBRAIN filters phonological information and passes it straight through to areas concerned with motoric output.  Maybe it helps us repeat things we do not initially understand as an aid to comprehension or to repeat things we do understand for better memorization.  The AF also seems to help with the phonological analysis needed for fluent reading (another specialized channel).  I finally got around to reading an article about this by Yeatman et. all. in the Journal of Cognitive Neuroscience 23:11 about the AF and phonological abilities.  Their findings were interesting but what really caught my attention was the basic work they did imaging the AF  in both the right and left hemispheres. While some neuroanatomists have thought the AF was strictly a left sided structure, being involved with language as it is, it turns out that careful imaging also reveals an AF structure in the right hemisphere.  Is it concerned with language?  Or does it participate in the usual right hemisphere functions of emotional communication, prosody, and pragmatics?  Does it carry information about emotional expression, so that we can mimic the expression of another?  The AF is variable on both sides and in both sexes; could gifted mimics like Rich Little or Jim Carrey, have a more prominent right AF? Does someone who is exceptionally empathic or tuned into the expression of microemotions have a more developed right AF?

Thinking about the AF I considered how similar its function is to mirror neurons, which were only discovered maybe 20 years ago.  When a monkey sees another monkey pick up a nut, the neurons involved in picking up a nut fire in response to the percept.  Different neurons fire if the other monkey picks up the nut to give away or to crack.   The AF is a special exemplar of long fiber bundles connecting front and back areas but other larger tracts such as the superior longitudinal fasciculus connect many such areas.  Again, specialized channels in the MEMBRAIN.

Now consider memes, cultural bits which pass into and out of our minds with noticeable facility.  We hear a snippet of music and play a longer passage back in our minds sometimes all day long.  Or we talk about time being up, going faster, crawling, etc and understand easily the conventional metaphor of our culture.  Memes are probably supported by more dynamic functional organizations involving non-specialized neurons, unlike the AF or mirror neurons but they still provide flexible specialized channels into the mind.  There’s a lot more to consider here but dinner calls.

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