According to new study preprint, meaning that it hasn't been peer reviewed yet in bioRxiv, this study claim that the COVID-19 lockdown has affected peoples' brain structure.

Researchers Tom Salomon and colleagues scanned 50 healthy volunteers in Israel. All of them were given an MRI scan between May and July of 2020, which was after the end of the original lockdown period in Israel. Crucially, all of the same volunteers had also been scanned before COVID started, mostly in 2019. 

Changes in the amygdalae diminished as time elapsed from lockdown relief, suggesting that the intense experience associated with the pandemic outbreak induced volumetric changes in brain regions commonly associated with stress and anxiety

They suggested that stress and anxiety could be the source of the observed phenomenon, due to its well-recorded functional and structural associations. Nevertheless, it is hard to draw clear conclusions as many aspects of life have changed in this time period, and could have potentially affected different regions in the brain – from limiting social interactions, increased financial stress, changes in physical activity, work routine, and many more.