An intriguing new hypothesis that seeks to explain all of the diverse psychological symptoms associated with autism. Here's the abstract:
While significant advances have been made in identifying the neuronal structures and cells affected, a unifying theory that could explain the manifold autistic symptoms has still not emerged. Based on recent synaptic, cellular, molecular, microcircuit, and behavioral results obtained with the valproic acid (VPA) rat model of autism, we propose here a unifying hypothesis where the core pathology of the autistic brain is hyper-reactivity and hyper-plasticity of local neuronal circuits. Such excessive neuronal processing in circumscribed circuits is suggested to lead to hyper-perception, hyper-attention, and hyper-memory,which may lie at the heart of most autistic symptoms. In this view, the autistic spectrum are disorders of hyper-functionality, which turns debilitating, as opposed to disorders of hypo-functionality, as is often assumed. We discuss how excessive neuronal processing may render the world painfully intense when the neocortex is affected and even aversive when the amygdala is affected, leading to social and environmental withdrawal. Excessive neuronal learning is also hypothesized to rapidly lock down the individual into a small repertoire of secure behavioral routines that are obsessively repeated.
Of course, all of the usual caveats apply: this is just a hypothesis, the rat model is a crude approximation, etc, etc. And yet, there is something alluring about this paper's complete inversion of the standard autistic model, as hypofunctionality is traded for hyperfunctionality. You can read the whole paper in the new Frontiers of Neuroscience, which is the coolest new journal I've seen in quite some time. I want to talk some more about the unique open access model of Frontiers, but that will have to wait until I'm not paying by the minute for internet access in a foreign country.
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My son is diagnosed PDD-NOS, and the "Intense World Syndrome" hypothesis presented in this paper certainly rings true to me:
Not just sensory stimuli but also the internal stream of mind-chatter are so intense that the autistic person is unable to tune it all out at will, in the manner the rest of us take for granted.
Thank you for posting that, and for indulging the rambling of a layman.
Utterly fascinating, Jonah, thanks.
This is intriguing. My daughter is diagnosed with mild autism, though she seems to be rapidly adapting to interacting with neurotypicals through ABA therapy. For my own part, I have an ASD (Asperger's) and I'm not sure how my internal experience of my brain functioning compares with what would be expected due to this. I know I usually reach (often rapidly) a sort of "saturation" where I feel overwhelmed by social cues and the demands others are making by talking to me, talking at me, demanding adecisionrighthererightnowwhileImstillspeakingtoyouwhatdoyoumeanyouneedtothinkaboutitwithoutbeingbombardedwithmoreverbalnoise, and that I find it very difficult to cope when my attention is involuntarily diverted from something I'm engaged in...
Interesting, but is it really new?
Isn't hyperplasticity already a part of the "standard model"? I thought it was pretty established that certain neurons in an autistic brain are somehow over-connective, causing them to organize themselves in overly rigid, self-reinforcing patterns.
As for hyperreactivity: does it exist separately from hyperplasticity? If cells connect too closely because of their plasticity, they might become hyperreactive even if individual neurons have the exact same signalling properties as in non-autistic persons.
Just some thoughts:
The hypothesised "hyperfunctionality" is a symptom, not the root cause. Sure, the neurons are "overfunctioning" in a sense, but this is in turn caused by the underfunctioning of some regulatory mechanism, which is in turn caused by something else, and so on. The regulation of connectivity and signaling between neurons forms the basis of mind and intelligence and is probably very complicated. That's why autism research is so fascinating: it is so closely related to the general problem of the human mind.
I'm not an expert, just interested, and happy for any answers.
Karl: The sensory-threshold issues are certainly part of the standard picture for autistic disorders; it sounds like these guys are trying to extend that down to the neurological level.
In general: It does ring true, but for that very reason we need to be cautious about taking it for "obvious". That said, hyperplasticity could easily give rise to derivative hypofunctionality; e.g. a "defensive" filter that becomes too general, thus blocking important data. Similarly, hyperfunctionality can be derivative of filtering failure, if someone learns how to handle the extra data (in a later processing phase).
Subjectively, the experience of us autistic types is that of poor control over our sensory filtering -- the details vary from individual to individual, but for any given person and sensory mode, you'll often hear that they're either "poorly sensitive", "overly sensitive", or "all-or-nothing". In the last case, they can switch between high or low sensitivity, but not split the difference -- and they can't always control the switch!
Curious as to the references to a "toxic insult" as a trigger - ISTM that the only reason they mention it is because their rat studies of VPA-induced autism are the empirical support they are relying upon for the paper?
They seem to have done quite a lot of work on this.
Too bad they didnt even hit on depression symptomology, a search through the pdf for depress yeilded only one reference.
So I am left wondering how they could have a unifying theory and ignore depression, hmmm?
Its easily noted by more than one set of other providers:
http://aut.sagepub.com/cgi/content/abstract/10/1/103
http://www.ingentaconnect.com/content/klu/jadd/1998/00000028/00000002/0…
Isn't the sensory gating deficit implicated in schizophrenia? And the negative symptoms of schizophrenia somewhat remind me of the autism, specially if the social withdrawing is understood as a defence mechanism against the sensory overwhelming.
"Frontiers of Neuroscience": thanks for the tip!
They seem to have done quite a lot of work on this. Too bad they didn't even hit on depression symptomology, a search through the pdf for 'depress" yeilded only one reference. So I am left wondering how they could have a unifying theory and ignore depression, hmmm?
This isn't necessarily a shortcoming. There is no reason to assume that depression is a primary condition arising directly from patterns of neural organization and development that give rise to the perceptual, cognitive and social patterns associated with autism.
A chronically stressed brain (as a function of living with an autistic mind in a world of highly social creatures) might account entirely for the higher incidence of depression. In that case it would be an incidental rather than primary condition. In fact, depression is incidental to many stress-causing primary conditions. There is nothing about it that is specific to autism.
I just finished reading Proust and the Neurosci. and am still in amazement...to many conincidents.So I investigated the blog and found this. I have a 29 year old daughter with moderate autism...verbal, reads at 5th grade level, great sense of humor, loves words. This hypothesis is one I came to (have a MS in physiology and Phd in philosophy..just a little strange myself) when i found out that people with autism amygdalae are often enlarged. This is a chicken egg problem...since like my daugher they are being constantly startled by the high stim environment, they have fight or flight responses all the time and so the feedback between adrenals and brain must be intense from the time they are born. So are they born with enlarged amygdala or does it hypertrophy from so much activity.And what could this mean in terms of ways to help them lead better lives. Can on be taught to defend against these assaults...auditory retraining seems very helpful for some but not all. But that is repair after the fact. Our daughter would scream as in pain when even seeing a balloon or a not-yet-barking dog. The anticipation of pain was as bad as the thing itself. She is much better a coping now but occasionally it gets to her and she becomes compative..self defense. This whole line of research has given me more hope as a parent than anything so far. I am not hopeful about drugs with all their awful side effects and genetic research is beside the point for my daughter. We need something practical, something we can do with tangible environmental factors that can help now and maybe isn't as dramatic as a cure but helps these wonderful people have a good life.NOW. Katie's Mom
thanks
I'm an aspie girl and one of my special interests is researching autism to the point of obsession, always comparing my situation to what's been written on the subject. And this intense world syndrome is the first thing I've read that makes total sense to me. It feels like a much better fit than anything else I've come across. It seems to describe what life has actually been like for me. So just from experience alone, I would be prone to agree with these conclusions. How else do I explain my inconsistencies I show? For instance,I still can't get used to the idea that people are different from me, with their own thoughts and feelings. It always comes as a shock, as something disturbing that I have to get used to once I find out about it. And yet people tell me all the time that I'm one of the most perceptive people they know when it comes to figuring people out. How can these two opposites coexist in my brain? It's like on one level I'm hyperaware and on another level, I'm just not clicking. I'm not sure this is what the authors of the study were trying to get at but it's still interesting, don't you think?