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Effort Changes How We Experience Movement

Wednesday, 29 June 2016

It has been shown time and again that people will think they’ve walked further if the walk is difficult. Give them a heavy backpack, or make them walk up a hill, and they will consistently overestimate how far they had to travel. But why is this?

Our brains keep track of our position in space using ‘place cells’. These ‘place cells’ make it possible for us to navigate through space, using information about where we are and where we’ve been to get us to where we want to go. So why is it that if we introduce a little difficulty to a person’s movement these place cells become less accurate in judging how far we’ve moved?

Experiments conducted by Blake Porter, a psychology PhD student, suggest that it may have something to do with how this ‘place’ information is encoded. The cells in your brain fire at different rate speeds, and tend to fire in relation to other cells around them. Blake was hoping to determine whether an increase in walking difficulty would change which cells were firing, or if it would just change how the cells were firing.

Blake recorded the activity of rat ‘place cells’ as the rats moved from one end of a box to the other for a reward. He then increased the angle of the box to 15 degrees and then 25 degrees in order to make the task progressively more difficult for the rats.

So, is it a change in cell firing, or a change in the cells which is making us less able to measure steep walking distances? Strangely, Blake found that it may be both. Some ‘place cells’ would only become active when the box was flat, while others would only be active at 15 degrees or 25 degrees. However, some cells were active at two or three different levels of difficulty. The cells which were active in more than one setting (for example, when the box was flat and when it was at 25 degrees) changed their firing patterns for each setting. If, for example, the cell was firing four times per second when the rat was flat it might end up firing seven times per second when the rat was running up the 15 degree hill.

We now have evidence of how the brain treats a difficult walk compared to an easier walk. The next step for Blake is to find out how this translates to the actual experience of walking. Now that we know the brain treats each level of difficulty differently we need to know what it is about those differences which make a hard walk seem so long.


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