The pulse at the temple is like a main highway: one look and you can see how the vessels are aging. The pulse at the wrist is more like a quiet side street, where the important details get lost in the noise. Researchers checked both spots and found that age leaves a far sharper mark at the temple.
When the heart contracts, it sends a wave through the vessels. By the time that wave reaches the temple, it has barely changed, but on its way to the wrist it has already bounced off small vessels and lost some of its information. That is why the temple shows more detail about how the arteries are aging. The strongest sign is a change in the curvature of the pulse wave. The stiffer the vessel, the more sharply the curve of the wave shifts.
The practical payoff is straightforward: if a watch or a pair of headphones picks up the pulse at the temple, it can assess vascular health more accurately. But first, measurements need to be taken in the same people with the same sensors, to make sure the difference is not just chance. For now, the pulse at the temple remains the most reliable map for reading age.
The short-wave fNIRS channels that are usually discarded as noise unexpectedly yielded age correlations up to r = −0.852 at a wavelength of 830 nm.
Not published on arXiv. Here are its page, the PDF and the formalization: you can check it yourself, not only read our account.