Deepinder Goyal’s Temple wearable has released its first brain flow study, revealing promising results in tracking cerebral blood flow changes. The preprint, published on medRxiv on September 4, 2026, tested 23 healthy adults in Meerut and compared Temple’s Brain Flow index with Transcranial Doppler (TCD) during exercise and posture changes.
Researchers found that Temple closely followed middle cerebral artery blood velocity in both tests. Median within-person correlations reached 0.795 during cycling and 0.799 during postural changes, indicating a strong relationship between the wearable’s readings and actual cerebral blood dynamics.
The Temple device uses an optical sensor placed near the temple to generate its proprietary Brain Flow index, analyzing optical signals from tissue near the skin surface. In contrast, TCD measures blood velocity inside the middle cerebral artery using ultrasound.
An important finding suggests the signal is not simply a reflection of heart rate. During the posture test, heart rate decreased while middle cerebral artery blood velocity increased, yet Temple’s Brain Flow index followed the cerebral blood velocity pattern during the same transition.
Despite these promising results, several limitations prevent the Temple wearable from being considered a proven brain monitoring device. The study used normalized relative signals rather than absolute blood flow measurements. Optical readings near the temple can also capture signals from the scalp and other superficial blood vessels. The study involved a small group of young, healthy adults and remains a preprint without peer review. Temple Pvt Ltd funded the research, though authors reported no competing interests.
Goyal called the study ‘the first step’ while sharing the findings on X. The next stage will require independent studies that separate scalp circulation from brain circulation. Larger and more diverse trials could determine whether Temple’s Brain Flow index reflects genuine cerebral activity.
