One of our favourite nerdy things to talk about at The Neurodiversity Practice are theories that underlie neurodivergent nervous systems.
There are lots of theories about how neurodivergent brains work. Here, we explore two in particular that are enormously useful in every day life: Bottom-Up Processing, and Predictive Processing Theory.
Bottom-up and top-down processing
Firstly, let’s think about “bottom-up” and “top-down” processing theory.
This theory describes two complementary ways the brain makes sense of the world. Bottom-up processing begins with raw sensory information: sights, sounds, smells, textures, and other bodily signals are taken in and then assembled into a meaningful perception. This approach is driven by what is actually present in the environment, and emphasises detail, accuracy, and sensory evidence.
Bottom-up processing is driven by what is actually present in the environment, and emphasises detail, accuracy, and sensory evidence.
Top-down processing works in the opposite direction, using prior knowledge, expectations, memories, and context to interpret incoming information quickly and efficiently. Instead of building perception from scratch, the top-down process runs a simulation of what a person is likely to perceive. It’s about seeing the bigger picture.
Predictive processing theory
Next up: Predictive processing theory adds an extra layer to the bottom-up processing idea. It suggests that the brain is fundamentally a prediction-making system.
According to this theory, the brain constantly generates top-down predictions about what it expects to perceive and then compares those predictions with bottom-up sensory input. When the incoming information matches expectations, perception feels smooth and effortless. When it doesn’t, a “prediction error” occurs and the brain must either update its predictions, or pay closer attention to the sensory data.
Predictive processing therefore explains perception as a dynamic balance between sensory evidence and prior beliefs, with learning and adaptation happening through the continuous adjustment of that balance. The relative contribution of bottom-up, sensory information, and top-down predictions, as well as sensitivity to “prediction errors” is weighted differently in different brains and nervous systems.
The relative contribution of bottom-up information and top-down predictions is weighted differently in different brains and nervous systems.
How this relates to the autistic experience
Research* suggests that many autistic nervous systems tend to lean more heavily on current bottom-up information, and rely less on top-down predictions, expectations and filters.
This can help us understand some of the key differences we see in autistic people’s experience of the world. If we follow these theories, it becomes very understandable that autistic people often feel sensory input more intensely, and become more easily overwhelmed by the sensory environment. The lights, the sounds, the smells, the physical touch… it can all get too much, very fast.
Autistic people are often quite particular about what sensations they can tolerate, and stick to foods, clothes, and experiences that feel manageable. In children, this can show up as fussy eating, difficulties in loud places (or afterwards), and being sensitive to labels or sock seams.
If we follow these theories, it becomes very understandable that autistic people often feel sensory input more intensely
It also clears up why autistic people often experience increased anxiety: if your brain is constantly creating new understandings of the world around you, rather than relying on prior expectations, life is likely to feel inherently less predictable and less certain. This could feel stressful and chaotic, like anything could happen: ‘akin to ‘opening your sock drawer and finding a pineapple’, as Lawson and colleagues put it.
You may feel on edge, and easily emotionally triggered by things that might seem small. It may be harder to generalise what is understood in one situation to another, as even small differences may feel bigger. In an unpredictable world, it would make sense to have a preference for sameness, routine, and control, in order to feel safe.
Autistic people can feel distressed when things change at the last minute, don’t go to plan, deviate from expectations, or seem unclear. In children, this can show up as seeming rigid, needing things to be their own way, being nervous about new things, and having meltdowns over things that seem to be small.
In an unpredictable world, it would make sense to have a preference for sameness, routine, and control, in order to feel safe.
It shines a light on why social interactions and communication – which are often inherently unpredictable – may feel uncomfortable, confusing, or exhausting for autistic people. Social rules are often unsaid, which is a problem for a brain that operates on concrete information. Many autistic people dislike “small talk” and often feel on the edge of social groups. In children, this can show up as differences in play, struggling to follow others’ leads when playing, or taking jokes more literally.
A bottom-up processing approach that focuses on detail, rather than the bigger picture, can contribute to the “double empathy problem”, where communication between autistic and non-autistic people can sometimes be mismatched. This isn’t the “fault” of the autistic person - it’s about different styles.
These theories may also help us to understand why interpreting interoceptive (body) signals and emotional recognition may be harder for autistic folk, because again, these may feel both unpredictable and overwhelming without a dominant top-down filtering process.
In children, this can show up as not knowing when they need the toilet, not noticing if they are too hot or cold, and struggling to regulate their emotions more so than their peers.
How this relates to the ADHD experience
So what about ADHD brains? Here the research is younger and messier, but the emerging picture suggests that while ADHD brains do make and use top-down predictions, they place less confidence in them, and can become easily distracted by current bottom-up sensory input.
The upshot can be a brain that lights up for anything new and interesting, and switches off as soon as something becomes predictable.
This helps explain why boredom can feel genuinely painful for ADHDers (not just a bit dull), and why attention runs on interest rather than importance.
Boredom can feel genuinely painful for ADHDers (not just a bit dull), and attention runs on interest rather than importance
It also helps explain why ADHDers struggle with "time blindness" - where time tends to come in two flavours: "now" and "not now". In children, "five more minutes" can be meaningless, getting out of the door can be a daily battle, and "later" can feel like never.
ADHD brains can also find it harder to filter out the "irrelevant" stuff - the ticking clock, the conversation across the room, the scratchy jumper - so attention gets pulled in lots of directions at once.
And lastly, hyperactivity and impulsivity can be seen as ways for the brain to gather more bottom-up data, to help it decide which bits are important.
When autism and ADHD meet
And if you're both autistic and ADHD (sometimes called AuDHD), you may recognise yourself in both of these descriptions - often at the same time.
Part of you craves sameness and certainty; another part is bored to tears by it.
Part of you craves sameness and certainty; another part is bored to tears by it. The routine that keeps you feeling safe can start to feel like a cage, and the new thing that sparks your interest can also feel overwhelming. It's a real tug-of-war, and it can be exhausting.
Understanding neurodivergent strengths
Autistic strengths such as attention to detail, deep knowledge, original thinking, hyper-empathy and deep emotion, and straightforward, honest communication all fit with a bottom-up processing style.
The popular “monotropism” theory of autism aligns too: it suggests autistic people tend to focus their attention and interests very deeply on a small number of things at a time. This means they can thrive when able to be in an “attention tunnel”, to develop deep expertise for example. However, it can make switching tasks, dividing attention, or coping with interruptions more challenging.
For a “bottom-up” processing system that can be easily distracted or overwhelmed by external input, this type of focused attention makes complete sense. (Many ADHDers recognise themselves in this too - hello, hyperfocus.)
ADHD strengths fit the picture just as neatly. A brain that's drawn to the new and unexpected is often curious, creative, and brilliant at spotting possibilities that others miss. It can be quick-thinking and full of energy, and when something unexpected does happen, ADHDers are often the ones who come alive and handle it - the crisis that sends everyone else into a spin can be exactly where an ADHD brain shines.
A brain that's drawn to the new and unexpected is often curious, creative, and brilliant at spotting possibilities that others miss.
Although research evidence supporting these theories is still in its infancy, clinically, we find this understanding can be very helpful in making sense of the autistic and ADHD experience in a neuroaffirmative way - and points us towards what might help.
What this means for autistic and ADHD parents
As autistic or ADHD parents, these theories highlight a few things our nervous systems might need.
The first is to be aware of our own needs, to allow ourselves to have these needs, and then to adapt our environments accordingly:
For more autistic-leaning brains: predictable routines where possible, clear communication, visual supports, and sensory accommodations to lower uncertainty and overload.
For more ADHD-leaning brains: making time visible (timers and visual countdowns are your friends), building in novelty and interest, small and quick rewards rather than far-off ones, and borrowing other people's focus through body doubling.
And for AuDHD brains: "predictable novelty": the same structure, with something new inside it. For example, the same bedtime routine, but a different story, or the same Saturday morning slot, but each time a different adventure.
Adaptations that fit with the way our nervous systems process information enables our strengths to shine - and helps us to connect with our children.
What this means for autistic and ADHD children
Using this lens of prediction to better understand our child’s behaviour can help us to more clearly see how we can support them, with strategies that can help smooth transitions and prevent meltdowns and shutdowns.
Making similar adaptations for ourselves and our children can help us create a home that supports our family’s nervous systems, and meets everyone’s needs.
Being aware of our needs, allowing ourselves to have them, and then adapting our environments enables our strengths to shine
Through this lens of bottom-up and top-down processing, autism and ADHD can be better understood as different balances of perception and prediction. We can view them as alternative processing styles rather than deficits, and ones that thrives best in environments designed with that balance in mind.
You don’t need to navigate this on your own.
If the descriptions - and the overwhelm - in this post sound familiar, you might be deep into what we call the “neurodivergent parent triple whammy”. Watch our free webinar on The Triple Whammy to find out more about what we mean - and feel validated and supported, too.
You’re also very welcome to join us in the Neurodivergent Parent Space, a warm community led by three clinical psychologists where you can feel less alone, swap ideas, and learn practical strategies alongside other neurodivergent parents.
Every resource in our ND parent library (including those mentioned in this article) is included, and there’s a free two-week trial, so you can come and see whether it feels like your village. See you there?
Jo
The Neurodiversity Practice is run by clinical psychologists with many years' experience across NHS, private, voluntary & university settings – & we’re parents too, with lived experience of neurodivergence.
Follow us on Instagram @theneurodiversitypractice
Authored by: Dr Jo Mueller, The Neurodiversity Practice
*References
Nb. Some of the language in older articles is not neuroaffirmative, and this does not reflect our views.
Boulter, C., Freeston, M., South, M., & Rodgers, J. (2014). Intolerance of uncertainty as a framework for understanding anxiety in children and adolescents with autism spectrum disorders. Journal of Autism and Developmental Disorders, 44(6), 1391–1402. https://doi.org/10.1007/s1080 3-013-2001-x
Cruys, S., Evers, K., Van der Hallen, R., Van Eylen, L., Boets, B., de-Wit, L., et al. (2014). Precise minds in uncertain worlds: Predic-tive coding in autism. Psychological Review, 121(4), 649–675. https://doi.org/10.1037/a0037665
Hallett, V., Mueller, J., Breese, L., Hollett, M., Beresford, B. A., Irvine, A. L., Pickles, A., Slonims, V., Scott, S., Charman, T., & Simonoff, E. (2020). Introducing ‘Predictive Parenting’: A Feasibility Study of a New Group Parenting Intervention Targeting Emotional and Behavioral Difficulties in Children with Autism Spectrum Disorder. Journal of Autism and Developmental Disorders. https://doi.org/10.1007/s10803-020-04442-2
Lawson, R. P., Mathys, C., & Rees, G. (2017). Adults with autism overestimate the volatility of the sensory environment. Nature neuroscience, 20(9), 1293–1299. https://doi.org/10.1038/nn.4615
Murray, D., Lesser, M., & Lawson, W. (2005). Attention, monotropism and the diagnostic criteria for autism. Autism, 9(2), 139-156. https://doi.org/10.1177/1362361305051398
Palmer, M., Carter Leno, V., Hallett, V., Mueller, J. M., Breese, L., Pickles, A., Slonims, V., Scott, S., Charman, T., & Simonoff, E. (2023). Effects of a Parenting Intervention for Emotional and Behavioral Problems in Young Autistic Children Under Conditions of Enhanced Uncertainty: Two-Year Follow-up of a Pilot Randomized Controlled Trial Cohort (ASTAR) During the United Kingdom COVID-19 Pandemic. Journal of the American Academy of Child and Adolescent Psychiatry, 62(5), 558–567. https://doi.org/10.1016/j.jaac.2022.09.436
Pellicano, E., & Burr, D. (2012). When the world becomes ’tooreal’: A Bayesian explanation of autistic perception. Trends in Cognitive Sciences, 16(10), 504–510. https://doi.org/10.1016/j.tics.2012.08.009.
Sinha, P., Kjelgaard, M. M., Gandhi, T. K., Tsourides, K., Cardin-aux, A. L., Pantazis, D., et al. (2014). Autism as a disorder ofprediction. Proceedings of the National Academy of Sciences of the United States of America, 111(42), 15220–15225. https://doi.org/10.1073/pnas.1416797111
