Deepinder Goyal’s wearable startup Temple has published its first validation study for a proprietary brain flow metric. The preprint compares the metric against transcranial Doppler ultrasound, an established technique for measuring cerebral blood-flow velocity. The findings provide an early signal that the device can track short-term changes in brain blood flow under controlled conditions, though peer review is still pending.
Study Design and Key Findings
The preprint study enrolled 23 healthy adults, with data from 20 participants analysed under each test protocol. Researchers evaluated Temple’s wearable during stationary cycling and during transitions from standing to lying down. The brain flow metric showed a median within-subject correlation of about 0.8 with middle cerebral artery blood-flow velocity across both activities.
During the postural test, participants’ heart rates declined when they lay down while cerebral blood-flow velocity increased. Temple’s brain flow metric moved in the same direction as the Doppler reading despite the opposing change in heart rate. Goyal stated that any device measuring only heart rate would have gotten this completely wrong.
Limitations and Scientific Context
The study does not establish that Temple can accurately measure absolute cerebral blood flow or diagnose medical conditions. It only suggests that the wearable can follow the direction and pattern of short-term changes under controlled experimental conditions. The authors said further research involving other measurement techniques and cerebrovascular challenges is needed to determine whether the metric specifically reflects cerebral activity and clinical potential.
Goyal acknowledged the limited scope of the research, which involved one study, two interventions, and healthy adults. He added that further validation studies of the Brain Flow metric and Temple’s Entropy metric are already under way. The startup is also offering to loan devices to qualified researchers seeking to test the metrics independently.
Temple Wearable and Market Position
Temple is developing a wearable intended to continuously track signals associated with cerebral blood flow from the side of the head. Unlike conventional consumer wearables that focus on heart rate, blood oxygen, and sleep, Temple is betting on measurements taken near the temple. The device uses a small optical sensor that detects signals and converts them into a Brain Flow reading.
Temple raised around ₹493 crore earlier this year from investors including Peak XV Partners, Steadview Capital, NK Squared, and Goyal. The round reportedly valued the startup at approximately ₹1,700 crore, or about $204 million. Its valuation later nearly doubled to $375 million through an employee stock ownership plan liquidity programme, reflecting strong investor interest.
Goyal recently said Temple had reduced the size of the wearable to less than half that of the earlier version. The startup is preparing to open limited-edition preorders, with shipments expected before the end of 2026. Temple also acquired London-based longevity medicine practice Longevous to strengthen clinical and scientific expertise for the launch.
The validation study offers an early but limited indication that Temple’s Brain Flow metric can follow short-term changes in cerebral blood-flow velocity. More peer-reviewed research and independent testing will be needed before the device can be positioned as a clinical or diagnostic tool. With preorders approaching and further validation underway, Temple is moving closer to proving whether its forehead-worn wearable can deliver meaningful brain health insights.