The presence of neither a spindle nor its refractory period impedes propagation of fine auditory information through the lemniscal system from thalamus to cortex. A) Timeseries of the auditory stimulus (speech syllable /da/), and its neural phase-locked evoked response extracted from the right auditory cortex in NREM2 and 3 sleep (combined). B) Location of the right auditory cortex region of interest from which data are extracted. C) Frequency domain plot of FFR amplitude across conditions. D) FFR fundamental frequency (98 Hz) amplitude during Spindle, Clear, and Refractory periods. FFR, frequency-following response; Spindle, responses during a spindle; Refract, responses measured during the refractory period; Clear, responses measured during neither a spindle nor refractory period.