Mirror Neurons in ASD: influence of the high-pass filter
How the High-Pass Filter Hypothesis explains Mirror Neuron deficits in Autism Spectrum Disorders
In my previous article “The High-Pass Filter Hypothesis for Autism Spectrum Disorders” I described how people with ASD perceive reality through a high-pass filter, and how that lead to them storing concepts into narrower categories with sharper boundaries. I will now explain how such narrower categories might explain the Mirror Neuron disfunctions documented into the Autism Spectrum.
Let’s see an exaggerated example. In Image 1, you can see the receptive fields for a behavior, like showing sympathy. There are a number of ways one human can show sympathy to another using body language: he can smile with his mouth, make smiley eyes, adopt an open posture with his arms standing wide on his sides and the hands open, and so on. Accordingly to the High-Pass Filter Hypothesis, an ASD person tends to have separate narrow categories for each behavior. In this case (left side of Image 1), an autistic person has three separate sub-behaviors (eyes, mouth, body language) associated to the behavior “show sympathy”. Only one of those sub-behaviors observed in others is associated to the motor behavior the person does when she actually wants to communicate sympathy. If the ASD person sees someone else doing one of the non-associated behaviors, like the body language one, she will not associate to her behavior to show the same emotion and thus won’t mirror it (no mirror neuron will fire).
A neurotypical person instead somehow merges all the single sub-behaviors into a single behavior “showing sympathy” and thus their mirror neuron for that behavior will fire when any of the sub-behaviors will be observed in others.
The previous example is of course exaggerated to give the reader a better understanding of the phenomenon. What is more likely to happen in reality, is that people with ASD will tend to have more “hows” to demonstrate a same “intent”. Only one of the “hows” is the one they actually perform when fulfilling that intent; the other “hows” are behaviors observed with others and recognized as fulfillers for the same intent. I postulate then that normal mirror neuron firing happens only when the same “how” usually used by the person is observed; other “hows” produce a lessened, if any, response.
A more formal formulation would be the following:
Given the space of movements corresponding to a behaviour, a higher number of movement categories will lead to a smaller receptive field for each category. The chances of the observed behavior falling into the single category which is preferered by the person to execute the behavior are lower, so less times the signal will be mirrored.