Direct study link: https://alz-journals.onlinelibrary.wiley.com/doi/10.1002/alz...

Observational study with an MRI at the end and user-reported activity histories. The results indicate a correlation, not necessarily causation. The study authors don't pretend to imply causation and are straight with these facts.

You can't randomize humans to either do a lot of TV watching for years or stay away from TV for years. So you can you safely assume any study making these correlations is not randomized. It does not mean it should be discarded.

There are a lot of other studies looking at how cortical volume can be preserved through aging with other interventions, however. There are a lot of before/after studies showing aerobic exercise can reduce the brain volume loss associated with aging - https://pubmed.ncbi.nlm.nih.gov/41491407/

So despite this being a correlation study, the result is not surprising. Sedentary activity is correlated with slightly faster degradation of multiple brain measures.

What is interesting in this study is that sedentary work that was intellectually challenging appeared to be somewhat protective. This is also consistent with past studies with before/after measurements around interventions like really intensive skill learning or even meditation.

>The results indicate a correlation, not necessarily causation

Just to drive that home, "Study participants also did not undergo a baseline MRI", which of course could mean that they already had some of these brain changes, which may have driven more TV watching.

>Sedentary activity is correlated with slightly faster degradation of multiple brain measures.

It seems to matter what you do while you're being sedentary, at least according to this study. From the article: "Strikingly, the sedentary element of TV watching didn’t appear to be the main driver for these changes."