Abstract
In humans, the integrated response to a novel stimulus (orienting reflex, OR) includes behavioral (head turning etc.) and well-characterized physiological components (changes in heart rate, respiration, skin conductance, and EEG patterns). In rodents, the physiological components of the OR include changes in heart rate and cutaneous vasoconstrictor tone, but respiratory changes have so far not been systematically documented. In the present study conducted in adult male Wistar rats, the OR was elicited by 60-dB acoustic tones while animals were in a whole-body plethysmograph for respiratory recordings. In addition to respiration, in different groups of animals we concurrently recorded either EEG, or heart rate (both by biotelemetry), or tail blood flow (using ultrasound Doppler). Acoustic stimuli provoked vigorous tachypneic responses with respiratory rate rising from 80–100 to 450–650 cpm, and with small and variable changes in tidal volume. This respiratory arousal response was often, but not always, accompanied by EEG desynchronization and by variable tail vasoconstriction, and by small and inconsistent changes in the heart rate. We conclude that tachypneic responses are a new highly sensitive index of sensory-induced arousal.
Highlights
The orienting reflex (OR), originally described by Pavlov in 1910 as the “What is that?” reflex, is of continued interest in modern psychophysiology and cognitive neuroscience
Similar to our previous reports (e.g., Garcia et al, 2001; Ootsuka et al, 2008), the tail blood flow signal was highly variable in each animal, with periods of vasodilation (45–60 kHz shift) intermingled with periods of vasoconstriction, when the pulsatile signal was barely detectable
The acoustic stimuli provoked well defined tachypneic responses (Figures 1–3). These responses occurred at relatively short latencies (97 ± 12 ms, range 48–196 ms) and varied in amplitude: respiratory rate increased from 80–110 cpm at rest to a maximum of 350–600 cpm and gradually returned to baseline within several seconds
Summary
The orienting reflex (OR), originally described by Pavlov in 1910 as the “What is that?” reflex (see Pavlov, 1927), is of continued interest in modern psychophysiology and cognitive neuroscience. Initially conceptualized in behavioral terms (turning or orienting toward a novel stimulus), its physiological correlates were emphasized by the late Russian researcher, Evgeni N. Sokolov (1960, 1963a,b) identified the OR as the major unit of perceptual functioning, reflexively directing the organism’s attention to important events in the environment. Sokolov considered the OR as a whole-of-body reflex, involving particular changes in a large range of physiological systems. One of Sokolov’s important generalizations was that this complex phenomenon was considered a unitary system, and always referred to in the singular sense
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