Picture an orchestra where every musician plays at their own tempo. With age, our body resembles such an orchestra: speech, voice and blood flow in the brain do not change at the same time.
Scientists asked people in their forties and in their seventies to name as many words as possible in one minute starting with the syllable "ka". While they spoke, a microphone recorded their voice, and a sensor on the forehead tracked the rush of blood to the frontal part of the brain, the one that picks words. It turned out that the older participants named fewer words (14 versus 17) and made longer pauses (1.6 seconds versus 0.7). Yet their blood flow accelerated more slowly: the peak came at the 33rd second rather than the 16th, and it was higher.
The most surprising part: the difference in speech duration explained only a small fraction of the blood flow lag. This means speech and blood flow change independently, as if the orchestra's conductor aged separately from the musicians. For now this knowledge has no practical application, but it warns us: to understand aging, we need to look at several measures at once, not just one.
Participants over 70 named an average of 3 fewer words than forty-year-olds, but in the last 10 seconds of the task they produced twice as many words: 1.48 versus 0.70. The younger group ran out of steam by the end of the minute, while the older group kept a steady pace.
Not published on arXiv. Here are its page, the PDF and the formalization: you can check it yourself, not only read our account.