Insomnia, depression, and anxiety are the most common mental disorders. Treatments are often only moderately effective, with many people experiencing returning symptoms. This is why it is crucial to find new leads for treatments. Notably, these disorders overlap a lot, often occurring together. Could there be a shared brain mechanism behind this phenomenon?
Siemon de Lange, Elleke Tissink, and Eus van Someren, together with their colleagues from the Vrije Universiteit Amsterdam, investigated brain scans of more than 40.000 participants from the UK Biobank. Their study was published in Nature Mental Health. Tissink: ‘In our lab, we explore the similarities and differences between insomnia, anxiety, and depression. Everyone looks at this from a different perspective: some mainly look at genetics and in this study, we look at brain scans. What aspects are shared between the disorders, and what is unique to each one?
Overlap and differences
‘We investigated many different aspects, like the structure and connectivity of the brain tissue. In all three disorders, we observe a reduced surface area of the cerebral cortex, a smaller thalamic volume, and weaker connectivity between different brain regions.’
‘In addition, some abnormalities are unique to each disorder. For example, the severity of insomnia appears to be more closely related to smaller volumes in the brain areas associated with reward. The severity of depression, on the other hand, seems to be more strongly related to a thinner cerebral cortex in brain areas associated with language and emotion. Instead, anxiety is more severe with weaker amygdala reactivity and functional connectivity between regions where dopamine, glutamate, and histamine play a crucial role in communication.
Similar brain circuit
What can we ultimately do with this information? Tissink continues: ‘The regions seem separate from each other, but when you map them out together, they all turn out to be part of the same circuit (amygdala–hippocampus–medial prefrontal cortex circuit). So, even though they are distinct areas, they all appear to represent different pieces of vulnerability within the same puzzle.’
‘A lot of research has been done on the overlap between anxiety and depression, but insomnia is often forgotten. This is the first time that we have investigated all three disorders at the same time, on such a big scale. De comorbidity is extremely high: people may experience these disorders in different stages of their lives, or experience them all at once. There is a lot of discussion about the underlying mechanisms. Thetreatment of insomnia, for example, sometimes also improves depression – but why? By further investigating this question, we hope to find new leads for follow-up research, as well as better treatments.’