Article summary with Walk like me, talk like me. The connection between mirror neurons and autism spectrum disorder by Saffin & Tohid - 2020

What is the mirror neuron system?

The mirror neuron system (MNS) is an integrative network that communicates information across multiple regions of the brain. It involves a group of specialized neurons that integrate visual, auditory, and motor stimuli to generate social cognitive processes. They are involved in motor action observation and execution, verbal and non-verbal communication, transitive and intransitive gestures, behavioral, motor, and social communication and interpretation, intention understanding, emotional understanding, and intersubjectivity.

Where are the mirror neurons?

The mirror neurons extend through the dorsal premotor cortex, posterior temporal cortex, somatosensory system, inferior frontal gyrus, ventral premotor cortex, inferior parietal lobe, left medial frontal gyrus, bilateral cerebellum, right temporal lobe, and thalamus. Two kinds of mirror neurons are distinguished:

• Action mirror neurons fire during action observation.
• Inaction mirror neurons demonstrate predictive discharge.

They communicate through a series of network pathways that appear to be damaged in autism and autism spectrum disorder.

What do neuroimaging techniques show when examining the MNS in people with autism?

EEG and fMRI studies show a lack of activity in the mirror neuron system and instances of disrupted connectivity (either under-connectivity and/or over-connectivity in cortical networks) in people with autism. This results in the brain functioning as a less cohesive unit.

How can learning about MNS development help shed light on the development of autism spectrum disorders?

Research shows that MNS activity is present in infants as young as six months old. Even more so, imitative behaviors have been observed in neonates in the first days of their lives. This indicates that they immediately begin responding to their social environment. Knowing when the MNS begins to develop can help in fully understanding how and when disruptions in neural circuitry occur, and how it influences neurodevelopmental disorders.

What are brain mapping and sensory-to-motor mapping?

Brain mapping refers to a set of neuroscience techniques predicated on the mapping of (biological) quantities or properties onto spatial representations of the brain resulting in maps. Sensory-to-motor mapping is a process in which the one observing an action creates a simulation in their mind. These mapping procedures are pairing stimuli with an appropriate response, creating automatic response capability. If an action has not been previously mapped, automatic response and motor resonance are suppressed.

What is the role of brain mapping in autism spectrum disorders?

The mapping system allows people to build a repertoire of social meaning to communicate through motor, verbal, behavioral, and symbolic actions. It also serves to interpret the person´s own internal stimuli and integrate these stimulus-response behaviors with social meaning. If the development of these maps is disrupted, it could lead to impairments in neurotypical function, seen in the stages when children are developmentally expected to begin performing the motor, social, and language skills they had previously observed.

What is the difference between mirror neurons and canonical neurons?

To be able to study the pathophysiology of autism, a distinction needs to be made between mirror neurons and canonical neurons. A mirror neuron refers to a neuron that must be activated when observing an action as well as while executing an action. Canonical neurons are the neurons that respond just by observing a graspable object without performing any action.

Which brain areas are involved in autism and ASD?

• The cerebellum is affected in autism and ASD, showing a reduction in size and differences in cerebellar circuitry. There is a possibility that mirror neurons exist in the cerebellum as some fMRI studies showed separate clusters in brain regions with mirror properties.
• The hippocampus and amygdala have a smaller volume in autistic individuals, and neurons are smaller and showing higher cell density.
• The size of the cerebral lobes is increased in autism. There appear to be mirror neurons located in the parietal and frontal cortex.
• Brain ventricles are increased in size in autism and ASD, but the presence of mirror neurons has not yet been proven.
• The basal ganglia, putamen, and caudate nucleus show a decreased volume in autism. ASD patients may also show gray matter augmentation, mostly in the frontal and temporal lobes, medial frontal gyrus, Broca´s area, posterior temporal cortex, and parietal and occipital subcortical regions.