Lifestyle and exercise

More research on TV and violence

“Violent films, video games and TV shows DO make boys aggressive,” according to the Daily Mail. The newspaper says that the study of teenage boys on which this news story was based also found that “the more violent the scenes and the longer they last, the more normal the behaviour seems”.

The small study looked at brain activity and automatic nervous response (skin sweating) in boys aged 14 to 17 years who were watching short video clips of low-to-moderate levels of aggressive behaviour. The researchers found that sweating and brain response to moderate aggression reduced over time, but response to milder scenes did not change as much. Despite what has been implied by the media, this study did not look at the boys’ behaviour.

Crucially, although this study may suggest some short-term changes in the brain activity of teenage boys watching aggressive material, it cannot tell us if it would actually influence their actions.

Where did the story come from?

The study was carried out by researchers from the US National Institutes of Health and other research centres in the US and Germany. It was funded by the US National Institutes of Health and National Institute of Neurological Disorders and Stroke. The study was published in the peer-reviewed journal Social Cognitive and Affective Neuroscience.

The Daily Mail and BBC News headlines exaggerate the findings of this study, drawing a direct link between TV violence and teenage aggression. However, this research looked at how viewing violent images affected brain activity, not whether this could actually lead to aggressive behaviour. The headline in The Daily Telegraph provides a better reflection of the study, linking on-screen violence to “desensitisation” of teenage brains. Importantly, BBC news noted that “another academic said it was almost impossible to explain violence in these terms”.

What kind of research was this?

This was laboratory research in volunteers looking at teenage boys’ brain activity and nervous system response when watching aggressive behaviour.

This type of study can identify the body’s short-term responses to watching aggressive behaviour. However, it cannot tell us about the effects of long-term viewing of aggressive behaviour, or how the watcher’s behaviour might be altered. The best way to investigate this would be to enrol a group of children, assess their TV viewing and video game use, and follow them up to see if their behaviour differed according to how much on-screen aggression they watched.

What did the research involve?

The researchers enrolled 22 healthy male volunteers aged 14 to 17 years (average age 15.9 years). The boys were shown a set of short videos with differing levels of aggression, and their brain activity and automatic nerve responses were monitored to check for any differences.

The boys visited the test centre twice. During the first visit they were assessed for any psychiatric or nervous system problems. On this first visit their levels of aggression and their exposure to violence in the media and their community were also assessed. At their second visit they underwent the brain scanning part of the study.

At the start of the second visit the boys rated their emotional state on a standard scale. The videos used in the test lasted for four seconds and had no sound. They came from commercially-available DVDs and showed, for example, fist fights, street brawls or stadium violence. After watching each video, the boys were asked to press a button to indicate whether the video was more or less aggressive than the last one they watched. There were 60 videos that had been rated by a different group of similarly aged boys for the level of aggression shown (low, mild or moderate). These were played to the boys in a random order.

The researchers assessed the volunteers’ brain activity while they were watching these videos, and recorded their automatic nervous responses. Brain activity was assessed using a form of magnetic resonance imaging called fMRI. Automatic nerve responses were measured by testing how sweaty the boys’ skin was using electrical sensors (sweaty skin is better at carrying weak electrical currents than dry skin). The boys’ emotional state was assessed immediately after watching all the videos, and then again one day and two weeks after the test.

The researchers compared the boys’ brain activity and skin conductance while the boys watched the different levels of aggression on screen. These analyses also assessed whether the boys’ responses changed over time, i.e. whether responses to clips seen later in the sequence were different to those of equal aggression seen earlier in the sequence.

What were the basic results?

The researchers found that the level of aggression in the video clips did not affect the boys’ automatic nervous response (how sweaty their skin was). However, their skin did get less sweaty as they watched more videos, showing that they had a reduced automatic nervous response to the videos over time. When the researchers assessed the boys’ responses to each level of aggression over time, they found that there was little change in response to low aggression videos, some reduction in response to mild aggression videos, and the largest reduction in response to moderate aggression videos. This suggested that the boys became desensitised to the videos displaying mild or moderate aggression, the two strongest aggression levels shown.

The researchers also found that boys who watched more violence in the media and video games in their home lives showed less change in their response to the videos over time.

The boys’ brain activity also differed when watching videos of different aggression levels. These differences in activity were found in areas of the brain called the ‘lateral orbitofrontal cortex’ (lOFC) and the ‘fronto-parieto-temporo-occipital network’. The lOFC area has been linked with viewing aggressive videos or video games in previous brain imaging studies in adults.

The researchers also found that the boys’ brain responses to the videos changed over time, with changes in the activity seen in the fronto-parieto-temporo-occipital network. They also found that there were some variations in the way that the lOFC and some areas of the fronto-parieto-temporo-occipital network responded to specific levels of viewed aggression over time. Responses to the low and mild aggression videos increased over time, while responses to the moderate aggression videos reduced over time. This suggested that the boys’ brains were becoming sensitised to the low and mild aggression videos, but desensitised to the moderate aggression videos.

How did the researchers interpret the results?

The researchers concluded that, over time, watching aggressive videos is associated with a reduction in automatic nervous system response (as indicated by sweating) and response in certain areas of the brain. They suggest that this may restrict a person’s ability to link the consequences of aggression with an emotional response and, therefore, may “potentially [promote] aggressive attitudes and behaviour”.


This small study, without a control group, has investigated the short-term responses of the brain and automatic nervous system seen in healthy adolescent boys watching aggressive video clips. It cannot tell us what long-term effects (if any) viewing violence may have on the brain or whether any short- or long-term responses might affect adolescent behaviour.

Equally, without a control group we do not know what the effect of watching other types of video might be on these regions of the brain or on sweating. We also don’t know whether being placed within the unusual setting of an MRI scanner might itself have affected the participants’ neurological or physical responses. Also, the results may not apply to different age groups or to girls.

There has long been interest in whether viewing violence, particularly in children and adolescents, could lead to the development of aggressive behaviour. While understanding whether viewing violence desensitises the brain to aggression is important, unfortunately, the current study is not able to prove whether viewing violence leads to aggressive behaviour. It is likely that a person’s behaviour is influenced by a wide range of factors, rather than a single factor such as viewing violence.

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