Let’s Make Sense of It: The Relationship Between ADHD and Altered Sensory Processing

December 13, 2023January 19, 2024, by Melanie Auger-Zivic

Attention Deficit Hyperactivity Disorder (ADHD) is a complex neurological disorder¹ that is characterized by symptoms of inattention, hyperactivity and impulsivity. While the stereotypical image often conjured by the term “ADHD” involves a hyperactive young child who cannot sit still and struggles to focus, there are multiple lesser-known symptoms associated with the condition. These less recognized symptoms can have a significant impact on both quality of life and academic performance of individuals with ADHD. To elaborate, the way the brain works with ADHD not only manifests as difficulty paying attention and hyperactivity but can also give rise to issues with sensory processing.

In fact, a significant portion of people with ADHD struggle with how they process sensory information. This means they might have either increased or decreased sensitivity to things like touch, sound, or sight. Interestingly, one study found that women with ADHD are almost twice as likely than men with ADHD to have these sensory challenges², with rates of 43% for women versus 22% for men.

So, what exactly does this mean?

First, let’s understand sensory processing

Our brain absorbs information from the environment through seven senses³: sight, smell, touch, hearing, taste, balance (vestibular) and movement (proprioception). Sensory processing is what happens when the brain receives information from the environment, interprets it and responds to it. Let’s consider tactile processing, which relates to our sense of touch. When our skin touches an object, it sends a signal to our brain that conveys details about the texture, pressure and temperature of the object.

Say you encounter a soft blanket when you sit down on a friend’s couch, as soon as your fingers make contact, sensory signals are transmitted to your brain, carrying details about the temperature, texture, and pressure of the fabric. Your brain then processes this information and recognizes the softness and warmth of the blanket. If the sensation is perceived as pleasant, your brain might signal you to keep touching the blanket and drape it over yourself. If it is perceived as unpleasant, your brain will signal for you to stop touching the blanket and not wrap it around yourself.

The perception of pleasantness vs unpleasantness is a key factor that distinguishes neurotypical brains from those with sensory processing issues.

Neurotypical people typically have a larger range of tolerance for sensory stimulation. Within this range, they find a variety of stimuli pleasant and enjoyable meaning that the amount of stimulation needed for them to experience satisfaction and contentment is varied and flexible. On the other hand, those with a smaller range of tolerance for sensory stimulation might get uncomfortable more easily. They require a more specific and less adaptable level of stimulation in order to feel content. This manifests as issues in sensory processing, where the individual is either less sensitive (hyposensitivity) or more sensitive (hypersensitivity) to sensory stimulation.

Low Responders (Hyposensitivity) vs. High Responders (Hypersensitivity)

Those who are hyposensitive can be called low responders because they don’t respond much to regular sensory input, while those who are hypersensitive can be called high responders because they respond very strongly to sensory input. In other words, low responders need more intense or prolonged stimulation than those with typical sensory processing. On the other hand, those who are hypersensitive will be disproportionately responsive to stimulation, making them uncomfortable with even a small amount of stimulation.

Hyposensitivity and ADHD

Because of their higher threshold for adequate stimulation, low responders/hyposensitive people will display a variety of behaviors to increase the level of stimulation. They will perform “sensory-seeking behaviors”⁴ also known as “stimming” which can involve any of the seven senses. For example, tactile stimming can look like hand flapping, twirling hair around fingers and touching objects. Vestibular stimming can look like rocking back and forth, spinning and jumping. Auditory stimming can look like repetitive noises and listening to the same song over and over again. These self-stimulating behaviors help the hyposensitive person to manage sensory input and regulate their responses to the environment. As previously mentioned, this hyposensitivity occurs in a subset of the ADHD population.

To expand, low responders may need constant movement, which can be seen as fidgeting and an inability to sit still. This is why we keep fidget toys at our tutoring center to lend to our students with ADHD while they’re studying with us to help keep them focused and engaged through adequate stimulation.

Hyposensitive people will also often have higher pain thresholds, leading them to be more likely to injure themselves. In fact, those with ADHD are twice as likely to injure themselves⁵ than their neurotypical counterparts. Although this propensity for injury is not only due to hyposensitivity, it does play a role. Another factor that contributes to injuries in people with ADHD is poor coordination that leads to clumsiness, which is discussed in this blog post.

Hypersensitivity and ADHD

On the other hand, a person with hypersensitivity will have a lower threshold for stimulation than average. They can easily feel overwhelmed and irritated when their senses get too much input. For example, bright lights, certain textures or even moderate background noise can create discomfort. Everyday stimuli that might not bother others can become intense and distressing for high responders, impacting their ability to function throughout the day.

A certain portion of individuals with ADHD consists of high responders. In fact, one study⁶ investigating the factors contributing to elevated stress levels in children with ADHD discovered that hypersensitivity is a significant influence for some of these children. In this experiment, children with and without ADHD took part in a test called the Sensory Challenge Protocol. This test is designed to see how the autonomic nervous system⁷, which regulates the body’s stress response, reacts when presented with various stimuli relating to touch, sight, sound and smell. They found that children with ADHD were significantly more stressed with an average level stimulation compared to their neurotypical counterparts. In other words, a subgroup of children with ADHD seems to be hypersensitive/high responders.

The authors of this study even contemplate the possibility of including heightened sensitivity to stimuli as a possible criterion for diagnosing ADHD subgroups. In fact, a more recent study⁸ has provided further evidence to support the inclusion of altered sensory sensitivity in diagnosing ADHD, including both hypo- and hypersensitivity to stimuli. However, for now this factor isn’t considered when diagnosing ADHD.

The Takeaway

Oftentimes, ADHD is presented as a simple attention/behavioural disorder, but it comes with a variety of other symptoms. Children and adults with ADHD may get irritated by hearing too many noises or feel overwhelmed in a brightly lit room due to sensory over stimulation. On the other end, they may fidget or look for more stimulation if they’re not stimulated enough.

These factors are important to consider as they can be used to help accommodate those with ADHD and help them find coping mechanisms to lessen the effects of hypersensitivity or use tools that provide adequate stimulation. These sensory profiles typically follow children into adulthood as well, so coping mechanisms are essential at any stage of life.

If you are an adult student with ADHD, it is important to know whether you have sensory processing issues that might be contributing to a sense of overwhelm or making it more difficult to focus on tasks. This way, you can make small changes to alter your study and life habits that can greatly benefit you in the long run. The same goes for parents whose children have ADHD: considering their sensitivity to sensory stimulation can have a significant impact on their well-being as well as help you understand their needs. More research is still being done that will help us further understand ADHD and its multifaceted nature.

Footnotes

Additional References and Sources

Antrop, I., Roeyers, H., Van Oost, P., & Buysse, A. (2000). Stimulation seeking and hyperactivity in children with ADHD. Journal of Child Psychology and Psychiatry, 41(2), 225–231. https://doi.org/10.1017/s0021963099005302

Bijlenga, D., Tjon-Ka-Jie, J. Y. M., Schuijers, F., & Kooij, J. J. S. (2017). Atypical sensory profiles as core features of adult ADHD, irrespective of autistic symptoms. European Psychiatry, 43, 51–57. https://doi.org/10.1016/j.eurpsy.2017.02.481

Curatolo, P., D’Agati, E., & Moavero, R. (2010). The neurobiological basis of ADHD. Italian Journal of Pediatrics, 36(1), 79. https://doi.org/10.1186/1824-7288-36-79

Hove, M. J., Zeffiro, T. A., Biederman, J., Li, Z., Schmahmann, J., & Valera, E. M. (2015). Postural sway and regional cerebellar volume in adults with attention-deficit/hyperactivity disorder. NeuroImage: Clinical, 8, 422–428. https://doi.org/10.1016/j.nicl.2015.05.005

Low, P. (2022, March 30). Overview of the Autonomic Nervous System. Merck Manuals Consumer Version. Retrieved April 14, 2022, from https://www.merckmanuals.com/en-ca/home/brain,-spinal-cord,-and-nerve-disorders/autonomic-nervous-system-disorders/overview-of-the-autonomic-nervous-system

Reynolds, S., Lane, S. J., & Gennings, C. (2009). The moderating role of sensory overresponsivity in HPA activity. Journal of Attention Disorders, 13(5), 468–478. https://doi.org/10.1177/1087054708329906