Overall, they found rats tended to do better in the predictable enriched environment than the standard or unpredictable enriched ones on various tests of sociability, behaviour and emotional response.
This study lends support to what is already generally understood about autism and autism spectrum disorder (ASD) – many people on the spectrum prefer stability and consistency in their environment and activities, and can often find changes to previously set routines upsetting.
However, it is too early to draw further conclusions from the results of this study. The causes of these developmental conditions are not clearly understood, and this rat model is unlikely to be entirely representative of humans with autism. This means we don't know how applicable the findings are or whether they could lead to new treatments.
The Intense World Theory
Two of the researchers who worked on the study have previously published a related paper arguing that ASD could be explained by what they dubbed the "Intense World Theory".
This is the idea that people with ASD have brains that are in "overdrive". This means their experience of environments and emotions could be much more intense, leading them to become withdrawn.
Where did the story come from?
The study was carried out by researchers from Yale University, the University of Michigan and the University of Louisiana at Lafayette in the US. It was supported by the Swiss National Science Foundation.
The study was published in the peer-reviewed scientific journal, Frontiers in Neuroscience. This is an open access journal, so the study is free to read online or download as a PDF.
The Mail Online reporting on this study is reasonable, and indicates at the start of the article that this research involved research in rats, not humans.
What kind of research was this?
This was an animal study using a rat model of autism. It aimed to investigate environmental effects on behaviour and protein expression in the brain.
Autism spectrum disorder (ASD) is a lifelong developmental condition where those affected typically have difficulties with social interaction and communication, and often have quite rigid routines and activities.
People with autism often have some degree of intellectual impairment, while people with Asperger's syndrome usually have normal intelligence or heightened intelligence in some areas. There is no current agreement about whether there are particular underlying disease changes in the brains of people with ASD.
Because people with ASD usually have a preference for a consistent environment and activities, behavioural therapies often focus on these areas. This research aimed to focus on the environment that the child – or, in this case, the rat – grows up in.
The researchers investigated the theory that predictable environments would prevent distressed reactions, while unpredictable enriched environments would lead to abnormal behaviours.
What did the research involve?
The study used a rat model of autism. When unborn rats are exposed to an antiepileptic drug called valproic acid (VPA), it has been shown to create behaviour similar to that seen in people with autism.
In this study, one group of unborn rats were exposed to VPA (given to the mother), while another group of control rats were exposed to inactive saline (salt water) injections.
When the rats were born, the researchers then tested the effect of housing the two groups of rats in one of three different environments:
- standard laboratory conditions – standard bedding, housed in groups of three rats per cage, with the cages kept in a shared room
- predictably enriching conditions – a constant setting of extra toys, treats, smells, running wheel, with six rats per cage (larger than the standard cage); the cages were also kept in an isolated room
- unpredictably enriching conditions – same as for the predictably enriching conditions, but the stimuli were regularly changed during the week
What were the basic results?
The researchers found pre-birth exposure and the subsequent environment had an effect on the rats' social behaviour.
In the standard environment, the VPA rats showed a reduced preference for being social (assessed by how much they sniffed another rat) compared with the control rats, but the two rat groups did not differ in the unpredictable enriched environment.
In the predictable enriched environment, the sociability and exploration of the VPA rats was increased relative to the control rats, in whom it was reduced.
Pre-birth exposure and the subsequent environment had no effect on the rats' pain perception.
When looking at fear response (as indicated by the rats "freezing" in response to the expectation of a shock), VPA rats showed more fear than controls in the standard environment, but did not differ in the predictable enriched environment.
In the unpredictable enriched environment, the VPA rats showed a similar or heightened fear response compared with VPA rats in the standard environment.
Looking at general anxiety (measured by exploring new environments), VPA rats generally explored less than control rats in the standard environments, though they tended towards higher exploration in the predictable enriched environments.
In both rat groups, overall "emotionality" was increased by enrichment, but it increased to a greater extent in the VPA compared with control rats. In the VPA rats, "emotionality" scores were reduced in the predictable enriched environments.
How did the researchers interpret the results?
The researchers concluded that, "Rearing in a predictable environment prevents the development of hyper-emotional features in an autism risk factor, and demonstrates that unpredictable environments can lead to negative outcomes, even in the presence of environmental enrichment."
Overall, this study in a rat model of autism seems to support what is generally already understood about ASD: affected individuals often feel more comfortable with set patterns, routines and environments, and may find unpredictability more challenging.
However, it is hard to draw many solid conclusions from this study, particularly because it is difficult to know exactly how representative this rat model of autism is of humans with autism.
Animal research can often give a good insight into biological and disease processes and how they may work in humans, but we are not identical. With a complex condition such as autism, which does not have a clearly established cause or causes, it is difficult to fully replicate the condition in animals.
The researchers report the VPA model is a well-validated model of autism in rats and has some of the characteristics seen in people with autism. But it is likely differences still exist, so we can't be certain how applicable the findings are.
The study generally supports what is already understood about ASD, and may lend support to environmental and behavioural therapeutic approaches. However, we certainly can't say at this stage whether environmental manipulation in humans would have the ability to prevent or cure ASD.