A slow touch activates the brain differently than a fast touch.
It is clear that touch is important to humans. When you see someone who is sad, your first impulse is to want to comfort them. The natural way to do that is with a light touch to the arm or a hug.
A fascinating paper by India Morrison, Malin Bjornsdotter, and Hakan Olausson in The Journal of Neuroscience published in June, 2011 explores how the brain reacts to touch.
In their studies participants were stroked on the arm with a paintbrush while lying in a magnetic resonance imaging (MRI) scanner. The strokes were either slow or fast. Unsurprisingly, the soft strokes were rated as more pleasant than the fast ones. After all, a caress is a slow movement, not a fast one.
MRI allows researchers to measure the blood flowing to different regions of the brain. The brain is a very energy hungry organ, and so areas that are particularly active when doing a particular kind of thinking tend to draw more blood to them. As a result, it is possible to get a window into what the brain is doing.
The insula is a structure deep in the brain.
In these studies, an area of the brain called the
insula was more active when people were stroked on the arm slowly than when they were stroked quickly. The insula is region deep in the brain.
That's not all.
The participants in these studies also saw videos. When people saw someone being stroked slowly on the arm, the insula was also active (though the region that was active was just next to the one active when people were actually being touched). This suggests that the insula is helping people to interpret the movements they see in the world in addition to helping them experience the comfort of someone else's touch.
Just from these data, you might think that this has mostly to do with the speed of the movements themselves.
In one last condition, participants saw a hand stroking an inanimate object (like a bowl). In this case, the insula was not strongly active. That is, the insula seems to respond specifically to caressing movements directed at people.
Obviously, anything we feel must happen somewhere in the brain. The fact that we find slow touch to be more pleasant and comforting than fast touch means that the brain is involved in some way. What is interesting is that the brain is organized so that areas that help us understand what we see in the world are near to areas that help us to feel what is happening to ourselves. The brain seems to capitalize on our ability to understand ourselves to understand other things happening in the world.
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