UC Irvine

Plethysmographic signals were recorded in four body regions (fingertip, forearm, cerebral cortex, and ophthalmic artery) of normal, healthy subjects during the presentation of brief auditory tones. Tones were presented during either systolic or diastolic phases of the cardiac cycle. Using data processing techniques similar to those employed in cortical evoked potential studies, averaged waveforms were derived which revealed the presence of a polyphasic volumetric response beginning as early as 150 ms (after onset of tones) in some subjects. Grand average waveforms suggested a similar morphology in all four body regions. The rapid onset argued for neural mediation of this response which may represent a sudden, transient flexure of vascular smooth muscle. The presence of this evoked vascular response in the brain suggests a previously unreported responsiveness of the cerebral vasculature in man to simple auditory stimulation.