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.
Since the question is most powerful PERSON, rather than most powerful Senator. According to the Constitution the President of the Senate, ex officio, also serving as Vice President, is the highest ranking officer of the Senate. Joe Biden. 2nd most powerful person, most powerful Senator, is President pro tempore, Robert Byrd. Also 3rd in line, behind VP and Speaker of the House, for the Presidency.