Abstract
Simple SummaryIt is common knowledge that negative emotions in humans are accompanied by both impaired subjective experience as well as maladaptive changes in behavior and physiology. The present paper investigates heart rate—one of the most commonly used emotion-related physiology measures—in the family dog, with the aim of uncovering its potential relationship with emotions. Sleep recordings were conducted following a positive versus a negative social interaction, as sleep alternations are one of the most conspicuous changes in response to negative affect. We observed differences in heart rate following the positive versus negative interactions, however these were only apparent during wakefulness, but not during sleep.The domestic dog (Canis familiaris) has been shown to both excel in recognising human emotions and produce emotion-related vocalisations and postures that humans can easily recognise. However, little is known about the effect of emotional experiences on subsequent sleep physiology, a set of phenomena heavily interrelated with emotions in the case of humans. The present paper examines heart rate (HR) and heart rate variability (HRV) during dogs’ sleep, measures that are influenced by both positive and negative emotions in awake dogs. In Study I, descriptive HR and HRV data is provided on N = 12 dogs about the different sleep stages (wake, drowsiness, non-rapid eye movement (non-REM), REM; scoring based on electroencephalogram (EEG) data). We conclude that wakefulness is characterised by higher HR and lower HRV compared to all sleep stages. Furthermore, drowsiness is characterised by higher HR and lower HRV than non-REM and REM, but only if the electrocardiogram (ECG) samples are taken from the first occurrence of a given sleep stage, not when the longest periods of each sleep stage are analysed. Non-REM and REM sleep were not found to be different from each other in either HR or HRV parameters. In Study II, sleep HR and HRV measures are compared in N = 16 dogs after a positive versus negative social interaction (within-subject design). The positive social interaction consisted of petting and ball play, while the negative social interaction was a mixture of separation, threatening approach and still face test. Results are consistent with the two-dimensional emotion hypothesis in that following the intense positive interaction more elevated HR and decreased HRV is found compared to the mildly negative (lower intensity) interaction. However, although this trend can be observed in all sleep stages except for REM, the results only reach significance in the wake stage. In sum, the present findings suggest that HR and HRV are possible to measure during dogs’ sleep, and can potentially be used to study the effect of emotions not only during but also after such interactions.
Highlights
Despite the existence of some fish and amphibian species that do not show any apparent behavioural signs of sleep [1], it is widely accepted that sleep is an evolutionarily adaptive phenomenon, which has crucial importance for daily normal functioning
Further differences occurred in 1 min versus 20 s (HR, wakefulness: t(11) = 2.279; p = 0.044; heart rate (HR) non-rapid eye movement (REM): t(11) = 2.555; p = 0.027 and pRR50, non-rapid eye movement (non-REM): t(11) = −2.402; p = 0.035)
All of the differences that remained significant after false discovery rate adjustment were in the wake phase (Table 5)
Summary
Despite the existence of some fish and amphibian species that do not show any apparent behavioural signs of sleep [1], it is widely accepted that sleep is an evolutionarily adaptive phenomenon, which has crucial importance for daily normal functioning. Non-REM sleep is often called slow wave sleep, due to the apparent low frequency, high amplitude electroencephalogram (EEG) activity during the “deep sleep” part of this stage. The 5 min recording seems to be the most appropriate interval [57], while dog studies have often used 1 min sampling intervals. Since manual detection of the RR peaks in the ECG recording (due to the sinus arrhythmia that characterizes dog heart rate, automatic measures are hard to apply [58]) is labour-intensive, reducing the sampling interval without compromising data reliability would be highly advantageous. A further important question for sleep ECG measures on short time intervals is the timing of the samples selected for analyses. As no data is available in the literature about changes in canine ECG during successive sleep cycles, we have decided to do our analyses with both of these sampling methods. ECG channel channel of of polysomnography polysomnography recordings recordings conducted conducted after after aa short short positive positive versus versus aa negative negative dog–human social interaction (see later).
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