100,000 brain chemical reactions per second?

I found no reliable scientific count showing exactly “100,000 chemical reactions per second” across the whole brain. The claim does not define what counts as one reaction, and popular repetitions do not give a clear measurement source. The brain’s biochemical activity is enormous: metabolic studies, for example, estimate ATP-molecule turnover, but that is a different measure and cannot be directly equated with a count of “reactions.” The precise figure of 100,000 is therefore unsubstantiated.