The Science
Behind Temple
Temple is grounded in established scientific foundations, advanced through original research, and tested by independent validations
Our Scientific Advisory Board
Temple's Brain Flow index tracked the same cerebrovascular changes as the clinical reference standard for cerebral blood flow velocity
Author: Kumar A, et al.
Researchers testing Brain Flow against Transcranial Doppler (TCD) found a significant within-person correlation of approximately 0.8 (p<0.001) between the two. 23 healthy adults were put through two challenges: cycling and a standing-to-supine postural shift. Brain Flow reproduced the direction and time course of MCAv, even when heart rate moved in the opposite direction.
The optical pulse waveform preserves more age-related cardiovascular information at the temple than at the wrist
Study: Temple PPG morphology demonstrates a stronger cardiovascular age signal than wrist sites
Author: Liu D, et al.
Researchers analysed 89 different features of the optical pulse that can change as the heart and blood vessels age. At the temple, 14 of these features showed a strong relationship with age, compared to just 3 at the wrist. The age-related differences at the temple were also found across more aspects of the pulse, and were generally stronger, suggesting that where the pulse is measured can affect how much information it contains about cardiovascular ageing.
Entropy production has actually been measured in exercising humans
Study: Continuous monitoring of entropy production and entropy flow in humans exercising under heat stress
Author: Brodeur N, et al.
Journal: Entropy, 2023
How does the body use and release energy as it works? Researchers studied 11 men resting and cycling in the heat, combining heat and gas-exchange measurements with a thermodynamic model. This let them estimate entropy production, a physical quantity describing irreversible energy transformations, under the conditions of the experiment.
The skin at your head and face has higher capillary density than the skin on lower parts of your body
Study: Regional differences in capillary density of the normal human dermis
Author: Pasyk KA, et al.
Journal: Plastic and Reconstructive Surgery, 1989
Skin is supplied by tiny blood vessels called capillaries. A post-mortem study of 113 tissue samples from 20 body sites found a denser network in the head, face and neck than in lower body regions. These anatomical differences provide background for research into where wearable sensors can pick up signals from blood.
Good health may mean a stable floor and a high ceiling
Author: Seely AJE
Journal: Entropy, 2020
Andrew Seely proposes that health depends on both adequate entropy production at rest and the ability to increase it when demands rise. The idea asks us to consider the body's capacity to respond as well as its baseline.
Even at rest, blood flow to the brain appears to relate to cognitive ability
Study: Cerebral blood flow during rest associates with general intelligence and creativity
Author: Takeuchi H, et al.
Journal: PLOS ONE, 2011
In healthy young adults, MRI measurements of resting blood flow were associated with intelligence test scores. The study identifies a relationship between the two; it does not show that increasing blood flow improves intelligence.
Skin temperature differs between the temple, forehead and wrist
Study: Forehead, temple and wrist temperature assessment of ethnic groups using infrared technology
Author: auf der Strasse W, et al.
Journal: Medical Engineering & Physics, 2022
Where a temperature reading is taken matters. In 289 young men, infrared measurements were higher at the temple than at the forehead or wrist. The researchers compared skin readings across these three sites. They did not measure core temperature alongside them.
Lower total blood flow to the brain is associated with a higher risk of death in older adults
Study: Total cerebral blood flow and mortality in old age: a 12-year follow-up study
Author: Sabayan B, et al.
Journal: Neurology, 2013
Researchers measured brain blood flow in 411 older adults at cardiovascular risk and followed them for an average of 11.8 years. Lower flow at the start was associated with higher mortality during follow-up. The finding connects brain circulation with long-term outcomes in this group, without establishing that raising flow would extend life.
An active lifestyle does not always mean higher daily energy use
Hadza hunter-gatherers lead physically active lives. Yet, after accounting for body size, their total daily energy use was similar to that of adults in Western comparison groups. The result challenges a straightforward link between activity and total calories burned. It does not test what happens when an individual starts exercising.
A temple-worn sensor read heart rate more accurately than a wristwatch during swimming
Study: Validation of the polar OH1 and M600 optical heart rate sensors during front crawl swim training
Author: Olstad BH, Zinner C
Journal: PLOS ONE, 2020
In a study of 26 swimmers, an optical sensor at the temple tracked heart rate more closely against a chest reference than a wristwatch did. This offers a useful example of sensing during movement. Because the two devices were different models, their performance reflects both the hardware and its position.
Cooling and performing compete for the same blood
Author: Périard JD, et al.
Journal: Physiological Reviews, 2021
Blood carries heat to the skin, where it can be released. This review describes how aerobic training can make skin blood vessels widen at a lower core temperature and increase skin blood flow at a given temperature. The response depends on the exercise and heat conditions.
The head is the more accurate optical site for measuring heart rate compared to the wrist
Author: Meier M, Holz C
Journal: Current Issues in Sport Science, 2024
16 people wore matched optical sensors during 13.5-hour outdoor recordings. Median heart-rate error was 7.1% at the forehead and 18.4% at the wrist, with movement affecting accuracy. The study shows why sensor location matters when testing performance outside the laboratory.
The nervous system helps direct blood to the skin for cooling
Study: Skin blood flow in adult human thermoregulation: how it works, when it does not, and why
Author: Charkoudian N
Journal: Mayo Clinic Proceedings, 2003
When the whole body is exposed to substantial heat, skin blood flow can reach 6 to 8 litres per minute. This review explains the nerve signals that widen skin blood vessels and help release heat. Skin circulation is therefore part of the body's active response to its thermal environment.
Higher aerobic fitness is linked to faster blood flow in the brain across adulthood
Study: Elevation in cerebral blood flow velocity with aerobic fitness throughout healthy human ageing
Author: Ainslie PN, et al.
Journal: The Journal of Physiology, 2008
Among 307 men aged 18 to 79, endurance-trained men had higher resting blood speed in the middle cerebral artery than sedentary men. This comparison links fitness with brain circulation across adulthood. It measured velocity rather than the volume of blood flowing per minute, and did not follow changes as individuals trained or aged.
Skin temperature measured at the temple carries information about aerobic fitness
Author: Jastrzębska AD, et al.
Journal: Biology, 2022
Researchers tracked temple skin temperature during recovery from intense exercise in 23 men. Changes in temperature were associated with measures of cardiorespiratory fitness, including aerobic capacity. The finding gives researchers a reason to study the temperature response further; it does not yet provide a reliable fitness test.
Energetic load could become a measurable variable in disease
Picard and Murugan's energy resistance principle explores how living systems resist and transform energy. They propose that excess resistance can contribute to cellular stress and damage. The paper offers a framework for research into health and disease, rather than a validated measurement or treatment.
Body fat and physical activity are linked to brain circulation
Study: Obesity is associated with reduced cerebral blood flow - modified by physical activity
Author: Knight SP, et al.
Journal: Neurobiology of Aging, 2021
MRI scans of 495 older adults showed an association between a higher body mass index, larger waist measures, and lower blood flow through the brain's grey matter. The relationship differed with reported physical activity. These findings bring body composition, activity and brain circulation into the same picture, without showing that changing one will reverse changes in another.
The artery at the temple runs alongside a sensory nerve in the same tissue plane
Author: Janis JE, et al.
Journal: Plastic and Reconstructive Surgery, 2010
The anatomy of the temple varies between people. Researchers examined 25 donated heads to map the superficial temporal artery and the nearby auriculotemporal nerve. Their work describes how these structures relate to each other, adding anatomical detail to the study of this region.
