People who more frequently check their Facebook app have smaller grey matter volume in the reward centre of the brain
Previous studies have already examined the role of social reinforcement in Facebook use, with number of “Likes” correlating with basic social reinforcement by peer groups.
Researchers have also found the nucleus accumbens region – which is often regarded as the brain’s reward centre – shows increased neural reactivity in people reporting high intensity of Facebook use, with Facebook ‘Likes’ perceived as rewarding stimuli that reinforce continuous Facebook use.
In a study newly published in Behavioural Brain Research, researchers from Ulm University in Germany used a smartphone tracking app to accurately record 62 participants’ Facebook usage (as opposed to self-reported usage) over five weeks.
They then analysed the data alongside structural MRI brain scans, to see whether there was any correlation.
Left and right nucleus accumbens volume was negatively correlated with Facebook usage – participants who opened the Facebook app more frequently and those who stayed on the app longer had smaller nuclei in both hemispheres.
Frequency of daily Facebook usage was also associated with higher online social network addictive tendencies (self-reported via questionnaire).
The association between frequency of Facebook checking and grey matter volume of left/right nucleus accumbens remained significant after adjustment.
In contrast, no such association could be established with either the amygdala or hippocampus region which were used as controls.
“In our opinion the present findings are intriguing, because the nucleus accumbens represent a core region of the reward circuitry,” say the authors, led by Professor Dr Christian Montag from the university’s Institute of Psychology and Education.
“The users of the smartphones are checking their Facebook account in expectation of ‘Likes’, nice comments etc. In general the striatum [of which the nucleus accumbens is a main component] has been often implicated in human traits such as impulsivity and sensitivity to rewards.”
Evidence also seems to show a more direct involvement of the nucleus accumbens in impulsivity.
“This sheds some light on the present data, because persons who check Facebook more often might also be characterised by being more impulsive with regard to incoming signals from the smartphone,” say the authors.
However, it remains to be elucidated whether lower volumes of the accumbens constitute a factor for increased social media use, or whether it results as a consequence of higher usage.
Altogether the shared variance between nucleus accumbens volumes and Facebook variables was about 11%.
The results are “an important step towards unravelling the neural basis of problematic Internet use,” say the authors, who suggest that an interesting additional research avenue might be the inclusion of hormonal markers such as oxytocin, due to its relevance in social interactions.
A limitation of the study is its focus on structural MRI as the nucleus accumbens of the ventral striatum represents only one of the many important candidates in the human brain, they add.