Poor Cerebral Cortex Functions Leads To Impulsive Behaviour


If the front part of the cerebral cortex is less active then people have less control over their social behaviour and automatically follow their inclinations more. This emerged from a study by Inge Volman that will be published on 25 October in the Journal Current Biology. The research was the first to make use of magnetic stimulation (TMS) to suppress this part at the front of the prefrontal cortex. During TMS a changing magnetic field on the head temporarily influences the activity of the underlying part of the brain.

Study subjects in whom the activity of the prefrontal cortex was temporarily suppressed could control their emotional impulses less well than normal. Their amygdala deep in the brain that is responsible for emotional reactions then becomes extra active. This emerged from the study by Inge Volman and her colleagues from the Behavioural Science Institute and the Donders Institute of Radboud University Nijmegen. This study is important for a good understanding of the role played by various parts of the brain and could in the future contribute to the treatment of aggression and social anxiety disorders.

Social-emotional behaviour

Neuroscientist Inge Volman investigates the regulation of social behaviour and emotions. She is particularly interested in how exactly that works in the brain and the factors affecting this. For example, she has previously published a study which revealed that men with more testosterone have a less active prefrontal cortex if they have to control their behaviour.

Yet what exactly happens if your prefrontal cortex is less active? Are you then less capable of managing your behaviour adequately and does that make you more impulsive? Now TMS can be used investigate what happens if the prefrontal cortex in the same study subjects is made more or less active.

Disrupting brain function

TMS is the acronym for transcranial (through the skull) magnetic stimulation. A brief magnetic pulse can temporarily stimulate or suppress brain activity in a small area. Previous experiments used TMS more on top of the head and could therefore influence the movement centres, for example. Volman is the first to have used the technique on the front of the head. She placed the equipment just above the eyelashes as the area she is interested in is located directly underneath these: the foremost part of the cerebral cortex. By doing this she could control and temporarily suppress the activity of the anterior prefrontal cortex (aPFC). At the Donders Institute the TMS equipment is situated next to the brain scanner. This allows the direct measurement of changes in the brain activity as a result of TMS. Many other TMS studies only examine changes in behaviour.

Approach versus avoidance

Volman allowed the study subjects to perform a so-called approach-avoidance task in which they were shown emotional faces. Normally we withdraw when we see an angry face and try to come closer if we see a happy person. The study subjects were asked to respond in exactly the opposite manner. Using a joystick study subjects had to approach angry faces and push away happy faces. They were significantly worse at doing this after disruption of the aPFC. The emotion area – the amygdala – of the study subjects became extra active.

‘This ties in with what we already knew from animal and patient studies. Instead of just measuring and observing behaviour we can also directly influence brain activity with the help of TMS. Furthermore, combining TMS with fMRI makes the design of this study extra special, as then we can observe the effects in both the behaviour and the brain,’ says Volman.

Therapeutic application

Even though we do not know exactly how it works, TMS is already used commercially for the treatment of depression. Based on this study are there possible therapeutic applications of TMS in people who have a disrupted control system?

‘The effect of TMS is temporary and that makes it difficult to apply therapeutically. A possible application could be helping people to overcome a certain behaviour. For example, people suffering from a social anxiety disorder have a strong urge to avoid social situations, such as a party. They are often stuck in a vicious circle: as a result of this avoidance they never learn that they can cope with the situation and so the anxiety increases. This avoidance tendency could possibly be reduced with the help of TMS. Then after a treatment the patient might dare go to a party and discover that it was quite an enjoyable experience. He or she might then dare to go to another party without the need for TMS first.’

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