How does movement affect decision-making?

How does the brain decide about movements?

Where does the striker shoot on the penalty kick - at the goalkeeper or in the corner? Researchers have now found out how our brain decides between two types of movement using rhesus monkeys. Their study, published in the specialist journal “Neuron”, shows that the brain does not rely on abstract, rule-based decisions, but instead takes into account the costs and benefits of possible movements.

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The striker runs free, gets the ball, shoots - and goal, goal, goal! What has happened there? The approaching striker had to decide: does he aim at the goalkeeper assuming that he will jump into one of the corners, or does he aim at the empty space to his left or right? The two alternatives require different planning of the movement. While the goalkeeper represents a direct, i.e. physically visible goal, the corner is an indirect goal, an empty space that only results from the position of the objects and people around him.

Scientists from the German Primate Center (DPZ) and the Bernstein Center for Computational Neuroscience in Göttingen have deciphered how the nerve cells in the brain of rhesus monkeys enable the decision to make one movement or the other. “In an uncertain choice situation - he doesn't know what the goalkeeper will do - the striker has to decide on one of two goals with different characters. We wanted to find out how this decision-making process is controlled in the brain, ”says Christian Klaes, first author of the study.

One plan or two in the brain?

It has long been known that the planning of targeted movements is controlled by two cerebral regions: the parietal arm movement region and the dorsal premotor cortex. The Göttingen neuroscientists wanted to find out what happens in the brain regions responsible for movement planning when it has to be considered which of the movements should be carried out. The decision could be made at the level of coding the selection rules for the target. If this is the case, only those nerve cells should be active in the planning areas of the brain that plan the movement towards the target that corresponds to the selected rule.

Alternatively, the decision could be made at the level at which the competing motor goals associated with the two rules (direct and indirect) are stored. In this case, the movement plan for the straight shot would be weighed against the movement plan for the corner shot. Accordingly, the two alternative movement plans should coexist in the brain and compete with each other.

The experiment: squares and points on the screen

For their experiment, the scientists working with Alexander Gail trained rhesus monkeys to either touch a direct target in the form of a point on a monitor or an indirect target. The experimental setup was such that the rhesus monkey was briefly shown a visual stimulus in the form of a point that was either on the left or right side of the monitor. After a short period of memory, a green or a blue square sometimes appeared. If the green square appeared, the point had to be touched directly; if the blue square appeared, the side opposite the point should be touched. If the monkey did not receive a green or blue cue, it could decide for itself which side of the monitor to touch. At the same time, the activity of the nerve cells in the sensorimotor area of ​​the brain was measured with microelectrodes.

Remarkably, it was found that both the neurons for the direct and the indirect spatial targets were active. "Our results show that the brain plans the alternative movements, i.e. both the shot in the middle and the shot in the corner, in parallel before the final decision is made," says Klaes. Gail sees a clear parallel to decisions for different physical goals, such as the teammates.

More comprehensive cost-benefit analysis

"In rule-based decisions, the sensorimotor system initially appears to map all possible movement goals in order to then use the same processing mechanisms that are also used when choosing between different physical goals," says Gail. Primates therefore not only make their decisions about certain behaviors by weighing abstract rules, but also include the movement goals associated with the various rules.

Distributing the decision-making process to different processing steps in the brain has the advantage that a more comprehensive cost-benefit calculation is possible. “For our goal scorer it is not enough to know that the goalkeeper mostly jumps to the left, he also has to consider that the shots on the opposite side often do not succeed well. So he has to weigh both factors in order to be successful, ”says Gail. "Our women's national team seems to understand these relationships intuitively - at least that's what their success suggests," said Gail, referring to the upcoming soccer World Cup. (Neuron, 2011; doi: 10.1016 / j.neuron.2011.02.053)

(German Primate Center, May 12, 2011 - NPO)

May 12, 2011