Symptoms of significant brain atrophy include progressive cognitive impairment involving multiple cognitive functions, otherwise known as dementia, seizures and aphasia, which is the disruption in the understanding or production of language or both.
The Senate majority leader has somewhat less official power than the Speaker of the House. This is because the vice president is technically the Senate's presiding officer, a ceremonial position that calls chiefly for casting a vote in the event of a tie.
In the House and the Senate, the Speaker and the Majority Leader, respectively, have the vast majority of the agenda-setting power. For the most part these two people control what gets put up for a vote in their respective houses, so they're clearly the two candidates for most powerful person in Congress.