Lessons learnt from rats playing tag

Playing with other children is an important learning format for functioning in a complex social environment. Through play, children train their resilience and how to deal with emotions. This does not just apply to children, as many animals play when they are young. Marijke Achterberg is an assistant professor at the Faculty of Veterinary Medicine and is researching social play behaviour in rats.

You examine play and games among rats. What does that look like?

Playing rats look amazingly similar to playing children. I look specifically at social play behaviour, which we also call “rough and tumble play”. For children, you can imagine something like tag. Animals do something reasonably similar: they try to touch the other rat's neck with their snout. If the rat is hit or almost hit by another rat, it quickly rolls over. After a successful defence, it will in turn try to touch the other rat's neck. This results in a kind of play fighting.

What exactly are you researching?

I research the brain regions and signalling substances that underlie social play behaviour. What happens in the brain when a child plays, or when does a child need to process complicated social information in order to play optimally? We study this in rats. By studying rats, it is possible to discover the consequences of not being able to play optimally at an early age in both animals and humans.

For example, through research in rats, we now know that adults who did not have optimal play as children seem to be more sensitive to rewarding substances, such as cocaine and alcohol. They also have difficulty with social interactions later in life and have more difficulty with certain cognitive skills, e.g. suppressing behaviour that is not needed/wanted at that time. Recently, we started research into encouraging risky play and what impact this has on problem-solving skills and social competences.

How do you study that?

We investigate this by closely studying and quantifying rat play behaviour (which rat does what and how often?). We can also administer certain substances and see if this affects certain aspects of play behaviour. For example, we know that increasing endogenous opioids with morphine increases play behaviour and that increasing norepinephrine can decrease play behaviour; dopamine increases motivation to play. Administering the substances can either be done over all of the brain or we insert a tube into a very specific part of the brain. In this way, the effect on behaviour of a specific substance in a specific brain region can be measured. This helps us understand at a very zoomed-in level how certain brain structures influence social play.

Do you have a concrete example of such a study?

One example is the effect of Ritalin on social play behaviour. We gave Ritalin to rats and saw that they started playing less. If you translate that to children, I don't think that's a good effect. Playing is incredibly important for learning all kinds of things: developing social and cognitive skills, testing your body's limits and capabilities. Following this insight, we dove deeper into the details. We wanted to understand exactly how this works in the brain and which signalling substances are responsible for this. We found that Ritalin increased motivation to play via dopamine but suppressed play via norepinephrine. We also introduced Ritalin into specific regions of the brain, so we could see exactly which areas are responsible for playing less when Ritalin is administered.

Are there other factors causing children to play less?

Play interaction is often more difficult in children with various disorders within the neurodiverse spectrum. For social play, you need at least a second person, and you need to understand each other. Children with Autism Spectrum Disorder (ASD) do not always initiate interaction. On the other hand, the motivation to play of some children with ADHD is very high: they can be perceived as (too) intense, so that the game partner no longer wants to continue playing.

Furthermore, in the Western world, children have less and less space to play freely outdoors and take (small) risks due to risk-averse adults, busy schedules, "safely designed" outdoor spaces and/or structured environments such as the schoolyard, childcare or out-of-school care centre. It is well known that taking risks during play stimulates physical and mental development, as children learn to recognise their limits through risky play and can practice dealing with unexpected situations. A PhD student in the lab is now investigating whether stimulating risky play in young rats can remedy certain cognitive and stress-related problems. Should that be the case, it is important to encourage this much more in young children.

Why is it important to research this?

Our research shows how important play is for children's well-being and their social, emotional and cognitive capacities later in life. We see what can go wrong with behaviour as well as in the brain as a result of not being able to play or not being able to play enough at a young age. This research also contributes to more fundamental knowledge of how the brain drives behaviour.