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Reaction time is among the most replicated behavioral proxies for cognitive aging. It reflects central nervous system efficiency — how quickly the brain processes a stimulus and generates a response. Slowing reaction time tracks closely with broader cognitive decline, particularly in memory and executive function, making it a measurable early signal long before clinical symptoms appear. A landmark study across 233,000 participants confirmed that processing speed is the primary mediator of age-related memory decline.

The N-back task directly measures the capacity to hold and manipulate information in working memory — a core cognitive reserve biomarker. Age-related decline in working memory is driven by prefrontal cortex dysfunction, specifically reduced persistent neuronal firing during memory maintenance. The 2-back variant used in Neurograph captures the most clinically relevant threshold of cognitive load. A 2025 cognitive aging clock study in npj Aging found N-back performance among the five most predictive features of biological brain age.

The Stroop Color-Word test is one of the most validated instruments in all of cognitive neuroscience, with over 700 published studies. It measures the brain's ability to inhibit a dominant response and direct attention under conflict — a faculty controlled by the prefrontal cortex and anterior cingulate cortex, both among the first regions to degenerate in cognitive decline. The interference effect is a sensitive, progressive biomarker for early executive dysfunction. A 2025 npj Aging study identified Stroop as the single strongest contributor to cognitive age prediction.

Speech is a cognitively complex behavior engaging memory, executive function, motor control, and language processing simultaneously. Changes in acoustic features — pitch variability, speech rate, pause duration, and rhythm — precede clinical symptoms of cognitive impairment by years. AI models trained on voice biomarkers have now achieved AUC scores above 0.94 in detecting mild cognitive impairment, comparable to cerebrospinal fluid biomarkers but non-invasive and collectable on any device.

Individual alpha frequency — the dominant oscillatory rhythm of the resting brain — slows measurably and predictably with age and cognitive decline. Measured from frontal EEG electrodes, it is one of the most replicated biomarkers in clinical neurophysiology. Combined with frontal asymmetry and HRV coherence from the Muse 2 PPG sensor, the Neurograph Scan builds a physiological layer on top of behavioral scores — detecting patterns invisible to any browser-based test.