Autism & Synaptic Plasticity

Autism Spectrum Disorder is a disorder that has gripped the households of this generation. Infamously dubbed as the "cancer" of today’s youngsters, the prevalence of the disorder has increased by a whopping 178% from the years 2000 to 2016 alone.

Many explanations have been proposed for autism: initially, the argument that the MMR vaccine — administered during infancy — contains harmful toxins which cause autism in children, caught parents into the midst of the whirlwind that was the anti-vaxxer movement. This was due to a 1998 paper published by Andrew Wakefield, which was later on found to include fraudulent statements and unethical study practices tainted by Wakefield’s own biased opinions.

Then came the proposal that certain foods, such as dairy and gluten, accelerated the onset of autism in children; this lead to parents slashing essential nutrients from their children's diets, hastily replacing cow’s milk with soy and almond replacements and hoarding gluten-free alternatives to cereal. Some even more drastic measures included “cleansing” their child’s diet to include only fruits and water while others involved certain “super” smoothies which self-taught practitioners swore would “cure” every child from autism.

Millions of dollars have gone towards funding medical research on autism. No recent findings have been able to prove that the MMR vaccine is the culprit, neither have they supported the crazy diet ideology; rather, new studies have found that there are certain inheritable genes which may have the ability to cause autism, due to one factor: synaptic plasticity.

Synaptic plasticity, by definition, refers to changes in synaptic strength. It occurs at the synapses, which are the junctions between neurons that allow them to communicate. These changes are thought to affect memory and learning.

Many scientists believe that deletion mutations (deletion of one or more nucleotides in a codon) in ASD-linked genes lead to a reduced number of functional PV-interneurons; PV-interneurons are powerful regulators of pyramidal neuron activity. Pyramidal neurons are a class of neuron found in most mammals.

An action potential, or spike, occurs when a neuron transmits a signal away from itself, down a region of the cell known as an axon. By inhibiting action potentials, PV-interneurons decrease the activity of nearby neurons and signal the production of a protein known as PV in order to regulate their firing rates. The firing rate of a neuron is the number of spikes that occur during a given interval.

An excitatory transmission encourages the generation of an electrical signal, or action potential, while an inhibitory transmission prevents it.

A reduced number of functional PV-interneurons means that excitatory (signal-promoting) cells receive less inhibitory transmission, causing a decrease in inhibition (prevention of the transmission of signals) relative to excitation (promotion of transmission of signals). This is known as the E/I ratio.

This imbalance of the E/I ratio, characterised by the decrease in the inhibition of signals, is believed by researchers to generate an excess of activity in the brain, which delays the normal processing of information in the brain and therefore results in cognitive malfunctions.

Moreover, neurons have regulatory mechanisms that prevent too steep or too lean spikes; synaptic homeostasis (regulation) works to adjust the synaptic strength in order to maintain firing rates, which can retaliate the effects of the deletion mutations that may cause autism. However, it is thought that in individuals with ASD, this regulation is not enough to combat the effects of mutation.

The genetic foundations of ASD are incredibly complex, and modern studies are still unable to provide a solid ground to their findings. However, certain clinical trials have been able to provide a possible explanation which could move the medical world even closer to finding possible medical treatments to a disorder that has affected many families.

Nevertheless, autistic individuals are simply different, not less. All autistic children, quirks and all, should be celebrated for who they are: unique individuals, with unique experiences.