TEMPLE WEARABLE: CHALLENGES IN MEASURING BRAIN HEALTH

12 Nov 2026

Tags: Internal Security   Cyber & Media   Digital threats

Source: The Indian Express

Context: Zomato founder Deepinder Goyal has launched Temple, a wearable device that claims to monitor cerebral blood flow through a feature called BrainFlow.

• It aims to show how lifestyle factors such as exercise, sleep and meditation influence blood circulation in the brain.
• Medical experts have questioned its scientific validity, particularly its ability to distinguish blood flowing inside the brain from superficial circulation in the scalp.
• The controversy highlights the need for rigorous clinical validation before wearable technologies are used for medical assessment.

Temple Wearable: Technology and Functioning

• Technology used: Photoplethysmography (PPG), an optical technology also used in smartwatches.
• Working mechanism: Shines light into the skin and analyses reflected or absorbed light to detect changes in blood volume associated with each heartbeat.
• BrainFlow: A proprietary feature intended to track cerebral blood flow and assess changes associated with physical activity, sleep and meditation.
• Scientific limitation: Different wavelengths penetrate different tissue depths, but the returning optical signal passes through multiple tissue layers, making it difficult to isolate blood flow originating specifically from the brain.

Why Doctors Question Its Accuracy

• Wrong blood vessel: According to neurologist Dr Vinit Suri, Temple primarily detects circulation associated with the external carotid artery, which supplies structures outside the skull, including the scalp.
• Actual cerebral blood supply: The brain receives blood primarily through the internal carotid arteries and vertebral arteries, not the external carotid artery.
• Signal ambiguity: Changes in blood volume detected beneath the skin cannot automatically be interpreted as changes in cerebral blood flow.
• Lack of clinical validation: Experts have questioned the absence of adequate clinical trials and independent validation.
• Need for RCTs: Robust randomised controlled trials are required to establish the accuracy and clinical usefulness of the device.
• Not a diagnostic instrument: A wearable-derived reading cannot independently establish the adequacy of brain circulation or diagnose neurological conditions.

Evidence and Limitations of BrainFlow

• Transcranial Doppler (TCD): Temple's developers have cited preliminary studies comparing BrainFlow readings with transcranial Doppler ultrasound.
• Study findings: One study involving 23 healthy adults reported a correlation of approximately 0.80 between the two technologies under different conditions, including exercise and postural changes.
• Important limitation: TCD measures the velocity of blood flowing through major intracranial arteries, whereas Temple generates its own proprietary index.
• Interpretation: Correlation between two readings does not establish that both technologies measure the same physiological parameter.

Why Blood Flow Alone Cannot Determine Brain Health

• Multiple dimensions: Brain health depends on neuronal functioning, vascular health, cerebrospinal fluid circulation and the absence of structural abnormalities.
• Neurological damage: Neuronal damage or loss of function cannot be comprehensively assessed through a blood-flow reading.
• Structural abnormalities: Brain tumours, vascular abnormalities and obstruction of cerebrospinal fluid pathways require separate clinical investigations.
• Stroke prediction: No single blood-flow reading can reliably predict a stroke, which may result from blockage or rupture of blood vessels due to multiple risk factors.
• Existing wearables: Validated wearables can monitor parameters such as physical activity, sleep, heart rate and, in certain devices, atrial fibrillation. They cannot comprehensively assess brain health or reliably predict strokes.

Gravity Ageing Hypothesis: Scientific Debate

• Proposition: Deepinder Goyal has associated Temple with the Gravity Ageing Hypothesis, which suggests that gravity continuously pulls blood downwards, making it harder for the brain to maintain adequate circulation and potentially accelerating ageing.
• Scientific criticism: The hypothesis assumes inadequate compensation by the brain for changes in blood circulation and overlooks its natural regulatory mechanisms.
• Cerebral autoregulation: The brain's ability to regulate the diameter of blood vessels to maintain relatively stable cerebral blood flow despite changes in blood pressure and posture.
• Physiological significance: Activities such as standing, lying down, bending and exercising do not automatically cause progressive brain damage due to gravity.
• Evidence gap: Experts point out that no established scientific evidence demonstrates gravity as an independent hidden cause of human brain ageing.

Factors Influencing Brain Ageing

• Inflammation and oxidative stress: Can damage brain cells and contribute to age-related neurological decline.
• Vascular changes: Deterioration of blood vessels can affect oxygen and nutrient supply to brain tissues.
• Neuronal connectivity: Weakening of connections between neurons can affect cognitive functioning.
• Genetic predisposition: Genetic factors influence susceptibility to neurological and age-related disorders.
• Lifestyle factors: Regular physical activity, adequate sleep, balanced nutrition, mental stimulation and social engagement support long-term cognitive health.

Medical Methods for Assessing Brain Health

• Magnetic Resonance Imaging (MRI): Provides detailed images of brain structures and helps identify abnormalities.
• CT Angiography: Uses CT imaging and contrast material to examine blood vessels and detect narrowing, blockages or abnormalities.
• Electroencephalography (EEG): Records electrical activity of the brain, particularly useful in evaluating seizures and certain neurological conditions.
• Transcranial Doppler (TCD): Uses ultrasound to measure blood-flow velocity in major arteries inside the skull.
• Neuropsychological testing: Evaluates cognitive functions such as memory, attention, language and problem-solving ability.
• Clinical relevance: These investigations are selected according to symptoms and medical indications; no single test comprehensively measures overall brain health.

Entropy Score: Another Area of Concern

• Entropy: A scientific concept associated with disorder, uncertainty or energy distribution, also used in biological research.
• Temple's Entropy score: Presented as an indicator of how hard the body is working to sustain itself.
• Limitation: A scientifically established concept does not automatically validate a proprietary health score. Its meaning, reliability and relationship with established physiological parameters require independent validation.

Way Forward

• Clinical validation: Conduct large-scale, independent clinical trials to establish the accuracy and reliability of wearable-derived measurements.
• Scientific transparency: Clearly disclose measurement methodologies, algorithms, limitations and clinical evidence.
• Evidence-based healthcare: Distinguish between actual physiological measurements and algorithm-generated health scores.
• Complementary technology: Use wearables to support preventive healthcare and lifestyle monitoring, not as substitutes for medical diagnosis.
• Avoid self-diagnosis: Encourage professional medical evaluation for neurological symptoms rather than relying on unvalidated wearable readings.

Conclusion: Wearable technologies have significant potential to transform preventive healthcare. However, technological innovation must be supported by scientific validation and clinical evidence. In a complex organ such as the brain, a single physiological indicator or algorithm-generated score cannot provide a comprehensive assessment of health.