The pulse at the temple beats like a city's main artery: it shows how the roads are aging. At the wrist, the signal looks more like a back street where traffic noise drowns out the important details. Scientists compared these two sites to figure out where age leaves the clearest mark.
Until now it was unclear whether information about vascular aging depends on where you measure. Now it's clear: at the temple, age shows up in 14 stable features of the wave shape, while at the wrist only in 3, and the links at the temple are stronger and more varied. The strongest feature at the temple is a change in the curvature of the pulse wave during systole. Its correlation with age reaches −0.679, comparable to the accuracy of a good medical test.
The secret is that the temple sits closer to the heart than the wrist. The pulse wave reaches it almost without distortion, while at the wrist it has time to reflect off small vessels and lose some information. The analysis confirms this: explaining 85.3% of the variability at the temple takes 5 independent components, while at the wrist just 3 are enough for 100%. In other words, the signal at the temple is richer and less redundant.
The practical payoff is obvious: if wearable devices could pick up the pulse at the temple, they could assess arterial stiffness more accurately without a cuff. That opens the way to glasses, headphones, and patches that continuously monitor vascular aging. But first we need paired measurements in the same people with identical sensors to rule out the influence of different conditions. For now, the pulse at the temple remains the most informative road map you can read age from.
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.