Sen. Dianne Feinstein, D-Calif., who has been in frail health after a shingles diagnosis this year, appeared to get confused during a committee vote Thursday, adding to concerns about whether the 90-year-old lawmaker can perform her duties despite her physical decline.

After Sen. Patty Murray, D-Wash., the chairwoman of the Senate Appropriations Committee, asked members to vote on the Defense Appropriations Act, the clerk called on Feinstein to cast her vote. The senator then began reading aloud a statement, instead of saying how she wanted to vote, with either an "aye" or "nay" response.

As Feinstein continued to read her statement, an aide nudged her to vote, while Murray, who was sitting immediately left of Feinstein, told the senior senator to "just say, 'Aye,'" according to footage.

Feinstein then smiled before saying, "Aye."

This year, Feinstein was absent for more than two months because of a bout with the shingles. In a Senate where the Democratic Party holds a slim 51-49 majority (when counting the three independents that caucus with the Democrats), her temporary departure stalled confirmations of President Joe Biden's judicial nominees, among other business. Some congressional Democrats asked that she resign.

She returned in May, in a wheelchair, after recovering from encephalitis, an inflammation of the brain that can be a dangerous complication of shingles. She has since occasionally sounded confused, The Washington Post has reported, and once told a reporter who had asked about her return to the Senate that "I haven't been gone," appearing irritated. "No, I've been here. I've been voting."

A representative for Feinstein could not immediately be reached Thursday night, but a spokesperson told CBS News that the senator was "trying to complete all of the appropriations bills before recess, the committee markup this morning was a little chaotic, constantly switching back and forth between statements, votes, and debate and the order of bills."

"The senator was preoccupied, didn't realize debate had just ended and a vote was called. She started to give a statement, was informed it was a vote and then cast her vote," the spokesperson said.

Feinstein is not running for reelection but has said she plans to serve out the rest of her term, which ends in early 2025, The Post has reported.

Her condition has fueled debate over whether she is fit enough to continue to serve and whether there should be term limits to lawmakers in an increasingly aging Congress. Feinstein, the longest-serving female senator, was elected to the Senate in 1992.

This week, Senate Majority Leader Mitch McConnell, R-Ky., 81, abruptly froze mid-sentence as he was trying to explain how lawmakers were almost done pushing through a major defense budget bill. "We've had good bipartisan cooperation and a string of - " McConnell said, before freezing and staying silent for 20 seconds, while staring straight ahead. The episode occurred four months after McConnell had fallen at a private dinner and suffered a concussion and a broken rib.

Feinstein is the oldest lawmaker in Congress. The incumbent class is also the oldest in Congress's history, with an overall median age of 59, The Post reported. For senators, the median age is 65, the highest ever. One House member, Rep. Maxwell Frost, D-Fla., 26, belongs to Generation Z, generally defined as those born from 1997 to 2012.