A method and apparatus for hemodynamically characterizing a neurological or fitness state by dynamic scattering light (DLS) is disclosed herein. In particular, a non-pulsatile blood-shear-rate-descriptive (BSRD) signal(s) is optically generated and analyzed. In some embodiments, the BSRD signal is generated dynamically so as to adaptively maximize (i.e. according to a bandpass or frequency-selection profile) a prominence of a predetermined non-pulsatile physiological signal within the BSRD. In some embodiments, the BSRD is subjected to a stochastic or stationary-status analysis. Alternatively or additionally, the neurological or fitness state may be computed from multiple BSRDs, including two or more of: (i) a [sub-200 Hz, ˜300 Hz] BSRD signal; (ii) a [˜300 Hz, ˜1000 Hz] signal; (iii) a [˜1000 Hz, ˜4000 Hz] signal and (iv) a [˜4000 Hz, z Hz] (z>=7,000) signal.