Development and habituation of the heart rate orienting response to auditory and visual stimuli in the rat

Studied development and habituation of responsivity to sound and visual stimuli in 120 8-19 day old Sprague-Dawley pups by using a change in heart rate (HR) as the indicant response (Exp I). A change in HR to sound (white noise) first occurred around 14-25 days of age and was acceleratory in nature. Within 3 days, the direction of the HR response shifted to bradycardia. The HR response to light was also characterized by tachycardia in young pups (14 days), which shifted to bradycardia as the pups matured (16 days and older). In Exp II, the HR response of 15- and 19-day-old Ss was studied at 3 auditory stimulus intensities (60, 70, and 90 db, B scale). Stimulus intensity influenced the magnitude of the cardiac response in the 19-day-old pups. Data suggest that even weak sensory stimuli elicited a defensive reaction (HR acceleration) during the 1st few days that followed onset of function in each sensory system; later in development, the same stimulus elicited an orienting response (cardiac deceleration). (25 ref) (PsycINFO Database Record (c) 2006 APA, all rights reserved).