Cortical Timing Age (CTA) A Behavioral Brain-Aging Metric, and the Case That Cortical Timing Declines the Way Muscle Does — by Disuse, Not by Decree

Cortical Timing Age (CTA) is a proposed behavioral brain-aging metric derived from vibrotactile cortical-timing measurement via the Brain Gauge, expressed as a single age-equivalent value. This framework paper synthesizes independently published, peer-reviewed work into a definition, an operational method, and a set of falsifiable predictions. It reports no original data. What this paper establishes: A category error sits at the center of how we think about cognitive aging. Like the loss of muscle once attributed to senescence, much of cortical decline is conditional — driven by disuse and responsive to training — not a fixed verdict. The decline we accept as inevitable is, in substantial part, deconditioning we have lacked the means to see. Brain-aging measurement is a mature field. Structural-MRI methods (BrainAGE, introduced by Franke and Gaser in 2010; the more recent DunedinPACNI) are validated across cohorts and predict dementia conversion, chronic disease, and mortality. CTA enters this established field as a behavioral instrument, not a parallel proposal. The timing variables CTA is built on have documented age trajectories and demonstrated clinical predictive value. Reaction-time variability predicts conversion to mild Alzheimer’s disease in cognitively normal adults (Welhaf et al., 2025) and all-cause mortality in older adults (Lim et al., 2017); Brain Gauge reaction time and its variability show established age-trajectory regressions (Zhang et al., 2011; Hanley et al., 2019). CTA measures function where existing methods measure structure, positioning it upstream of the change MRI detects. It is repeatable weekly or daily, making it suitable for tracking response to intervention or insult on a clinically useful timescale. The metric is trainable: cortical timing responds to load the way muscle does. The framework states falsifiable predictions, written to be tested by working researchers with existing instruments, and complements rather than replaces chronological age, biological age, and structural brain age. This is a framework paper, not a clinical trial. Framework paper. Synthesizes independently published peer-reviewed work; reports no original data. Companion to the forthcoming book An Ageless Mind.