Reduced grey matter volume in parts of the medial temporal lobe, which is (theorized to be) vital for storing memories.

[Regular Caffeine Consumption Affects Brain Structure - Neuroscience News](https://neurosciencenews.com/caffeine-gray-matter-17781/)
_Frequent caffeine consumption reduces gray matter volume in areas of the right medial temporal lobe, including the hippocampus. Ten days of “caffeine abstinence” helps regenerate gray matter._
the researchers observed changes in the gray matter
The difference was particularly striking in the right medial temporal lobe, including the hippocampus, a region of the brain that is essential to memory consolidation.
“Our results do not necessarily mean that caffeine consumption has a negative impact on the brain,” emphasizes Reichert.
after just 10 days of coffee abstinence it had significantly regenerated in the test subjects
“The changes in brain morphology seem to be temporary, but systematic comparisons between coffee drinkers and those who usually consume little or no caffeine have so far been lacking,” says Reichert.

Sleep - Caffeine did not affect it

[[Sleep quality is not influenced by caffeine]]
surprising: the caffeine consumed as part of the study did not result in poor sleep
the participants’ depth of sleep was equal, regardless of whether they had taken the caffeine or the placebo capsules