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  • Written by Christopher S. Easthope, Researcher, Spinal Cord Injury Centre, University of Zurich
imageThe hormone oestrogen may play a role in a woman's ability to perform two tasks at the same time.mbeo/Flickr, CC BY

Women are less affected by interference when carrying out certain tasks than men, and hormones may play a part in this discrepancy. Our recent experiment found that the walking pattern of men - who typically have low levels of oestrogen - changed when they had to perform a difficult verbal task at the same time.

By contrast, women who hadn’t yet reached menopause – and likely to have higher levels of oestrogen – showed no sign of such interference.

Published in the Royal Society Open Science journal, our research set out to explore the hypothesis that the ability to swing the right arm, controlled by the brain’s left hemisphere, would be inhibited if using that same part of the brain to perform another task at the same time.

We were surprised to find this inhibition was indeed present in men and women over the age of 60, but not in women under this age.

The Stroop test

Most of us pay little attention to how our limbs move when we walk. Instead, walking serves the simple purpose of getting us from one place to another. In other words walking, and the associated swinging of the arms, are semi-automatic, goal-directed behaviours.

But the coordination of our arm swing changes in a subtle fashion when we are asked to complete certain cognitive (thinking) tasks while walking.

As neuroscientists in the field of spinal cord injuries, our research group is interested in describing and understanding the effects of walking when also performing difficult tasks, and determining whether these additional conditions result in different adaptations to coordination.

This is especially useful when contrasting response patterns to those seen in patients in early stages of neuropathies – conditions resulting from problems in the nervous system.

Classically, a task used to distract research participants from another is the Stroop test, first proposed by John Ridley Stroop in the 1930s. Here, participants are shown a written colour word (such as “green”) written in an incongruent color (such as red).

imageThe Stroop test is often used to see how someone can accomplish one task when another interferes with it.Youtube screenshot

The correct response is the colour of the word (in our example, red) although most people automatically read the word rather than saying the colour it is written in. The task is from the family of “interference” tasks where the brain must successfully integrate multiple and competing stimuli to achieve the correct response.

The brain networks and structures activated during this task have been extensively researched and there is indication they are generally found in the brain’s left hemisphere.

The Stroop test on a treadmill

Our experiment consisted of measuring walking patterns in 83 healthy male and female volunteers of different age groups (20 to 40, 40 to 60 and 60 to 80 years) on a treadmill.

The participants had to walk for a minute while also either completing a Stroop task or just walking normally.

Most participants swung their left and right arm symmetrically when just walking. However, when the men of any age group walked and performed the Stroop test at the same time, the swing in their right arm decreased dramatically. This was also the case in older women (over 60).

Women under 60, though, were able to perform the Stroop task with no significant change in arm-swing symmetry.

The right arm is controlled by the left side of the brain which, as mentioned earlier, is also where the processing areas activated during the Stroop test are.

imageParticipants were asked to walk on a treadmill while performing either a simple reading task or the Stroop test.from

In men and older women, the Stroop test appeared to overwhelm the left brain to the extent that the movement of the arm on the right was reduced.

It may be the hormones

While men and women have a number of important biological differences, the structure and function of our nervous system seems to be quite similar. So we were intrigued to find such a consistent gender difference in how two relatively simple behaviours interact with one another.

While at first glance this would seem to be proof women may be better at multitasking than men, it is important to remember this describes only the coupling of two highly specific behaviours: a verbal interference task and maintaining arm swing during walking.

However, we think the fact premenopausal women seem to be resistant to interference may have something to do with the specific region of the brain we believe is used for both the Stroop task and arm swing - the prefrontal cortex at the front of the brain.

This is a complex and evolutionarily-recent part of the brain that seems to be involved in both cognitive control and the control of some elements of walking.

There is also a lot of evidence oestrogen receptors are present in this region. When oestrogen itself is present, activation of these receptors can lead to the reshaping of neural networks and perhaps improved function in the prefrontal cortex.

This may explain why younger women – who have relatively high levels of oestrogen, at least at certain times of their menstrual cycle, than men and older women – seem to be able to process the Stroop task in their left prefrontal cortex without it interfering with their arm swing.

This is, of course, still speculative but explains the results nicely. As the oestrogen receptors are presumably also present in a man’s prefrontal cortex, the role of oestrogen on the brain in both sexes may be more complicated than we currently appreciate.

There is evidence areas activated during the Stroop task are located in the left hemisphere.

Christopher S. Easthope receives funding from the clinical research priority program of the University of Zurich.

Tim Killeen received funding from the Clinical Research Priority Program for Neuro-Rehab of the University of Zurich.

Authors: Christopher S. Easthope, Researcher, Spinal Cord Injury Centre, University of Zurich

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