One of the first questions a parent asks after hearing that their child may have SPD is “What causes sensory processing disorder?” Unfortunately, science doesn’t have a clear cause identified yet. There are, however, a lot of connections that have been drawn.
Let’s back up for a quick second and talk about what SPD is before we delve into some correlations.
What is sensory processing disorder?
Sensory processing disorder is a neurological disorder that causes difficulties in taking in, interpreting, or responding to sensory information. So, let’s look at what is happening in the nervous system normally. If you reach out and touch something with your eyes closed, sensory information is sent from receptors in your skin through your nerves to your brain. Your brain interprets that sensation and sends a signal back telling your hand to let go of the soggy towel. Someone with sensory processing disorder may have difficulty with any of those steps that happened. For this particular scenario, someone with SPD may not even notice that they tried to dry their hands with a soaked towel or they may even find the feel of any towel obnoxious or even painful. It makes interacting with your environment challenging.
Now, imagine a baby or toddler trying to learn about the world when the information they’re getting, interpreting, or sending to their body isn’t accurate. Even worse, what if that information seemingly changes day to day? What a frustrating experience! It isn’t surprising then that so many children with SPD share many characteristics with those with developmental delay, autism, ADHD, depression and anxiety, and a few other disorders. If you want to learn more about what sensory processing disorder is, you can learn more here.
Again, there is no scientific study proving what causes sensory processing disorder. There are, however, some trends that can show us what may be possible causes.
In the central nervous system
The parts of our bodies that we use frequently get stronger. This is true for the brain and nervous system too. The pathways developing in the nervous system from receptors to the brain and back to various parts of the body are no different. For a developing baby still in the womb, more connections are made than are needed. Towards the end of the pregnancy, a “cell pruning” happens that clears out some of the faulty and lesser connections. One potential cause of SPD is that the cell pruning may have left too many or too few connections.
Another potential cause takes a look at the cerebellum. Some studies have shown that the cerebellum helps to modulate (adjust up or down) sensory input1. Potentially, a faulty cerebellum may be poorly “tuning” up or down one or multiple types of sensory input.
Neurotransmitters like dopamine, serotonin, and norepinephrine also have a significant impact on the nervous system, sleep, arousal, motivation, and attention. Abnormal serotonin levels have been shown to impact fine sensory discrimination2.
The hypothalamus is another part of the nervous system that bears scrutiny. It acts as a relay station, taking sensory information (all but smell) and carrying it to other parts of the brain. The limbic system takes sensory information and gives it emotional connection. Any of these areas of the central nervous system bear scrutiny for their correlations to SPD.
Other potential causes
While we don’t have specific data, there is a clear genetic relation to sensory processing disorder. This doesn’t mean that it always is passed to the offspring. Even the severity of SPD can vary greatly between family members (or may not present at all).
Premature birth and birth traumas also seem to have some association with SPD. Think about the bright lights, beeping equipment, and general busyness of a hospital setting, not to mention the reduced time in utero to develop. It is no wonder parents of premature babies are often told to watch for signs of SPD. Birth traumas may also come with the same hospital time and procedures.
Adoption may also have a link with SPD. I worked with a 6-year-old boy who ate, cramming his mouth full at every meal. His adopted mom said that at his orphanage the food was set out on the tables and then it was every kid for themself. Stuffing food in meant survival. Other children may have experienced sitting in wet diapers or a sheer lack of sensory opportunities.
Heavy metals also have a connection with disorders such as sensory processing disorder3. Lead poisoning is more common than you think. Mercury is another metal that, in excess, can cause SPD like symptoms. If you have any concerns about heavy metals, you can ask your doctor for a blood test.
Thimerosal, phenol, and 2-phenoxyethanol are preservatives sometimes used to keep bacteria and fungi from growing in vaccines after it leaves the manufacturer. Some parents have reported SPD and autistic symptoms arriving after receiving vaccines. Most studies show no connection between vaccines and autism and sensory processing disorder. If you are concerned about vaccines, I recommend that you ask your doctor for the pamphlet with the list of ingredients included with the vaccine and do some research on your own as well as talk to your doctor. Some single dose vaccines can be obtained that contain less preservatives. Always make sure your child is healthy when getting vaccines.
With this many theories and potential causes for sensory processing disorder, confusion is understandable! But guess what, you are on the right track. Reading and learning more about SPD will help your child grow and thrive.
One of the next most important steps you can take is to ask your doctor for a referral to Occupational Therapy (OT). This will give you a great opportunity to continue learning more about SPD and how to help your child.