I’ve already described how the bottom-up nature of Autistic sensory processing leads to us being overstimulated and easily distracted by things like ambient noise and visual clutter. There is an additional neurological feature of Autism that contributes to our sensory issues and meltdowns in a significant way—our difficulty adjusting to a stimulus over time.

Neurotypical brains engage in sensory adaptation and habituation: the longer they are in the presence of a sound, smell, texture, or visual cue, the more their brain learns to ignore it, and allow it to fade into the background. Their neurons become less likely to be activated by a cue the longer they are around it. The exact opposite is true for Autistic people: the longer we are around a stimulus, the more it bothers us.

When we’re overloaded, we become irritable, or filled with despair; we might even start self-harming to get an endorphin rush or ground ourselves. Our bodies are visibly tense with anxiety, and we’re difficult to engage with during these times. What non-Autistic folks often don’t realize is that Autistic people experience intense sensory input as if it were physical pain.

— Unmasking Autism by Devon Price (Page 105)