Neurophysiological Correlates of Affiliative Behaviour between Humans and Dogs

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Abstract

Few physiological parameters for positive human–companion animal contact have been identified and those that are established have all been in humans. The implication is that if the physiological reactions are mutual, dogs would experience the same psychological benefits from these neurophysiological changes as humans. Therefore, we have determined the role of certain neurochemicals during affiliation behaviour on an interspecies basis. Our results indicate that concentrations of β-endorphin, oxytocin, prolactin, β-phenylethylamine, and dopamine increased in both species after positive interspecies interaction, while that of cortisol decreased in the humans only. Indicators of mutual physiological changes during positive interaction between dog lovers and dogs may contribute to a better understanding of the human–animal bond in veterinary practice.

Introduction

In 1929 it was shown that when a human strokes a dog the mean arterial blood pressure (MAP) of the dog declines (cited by Cusack and Smith, 1984). More than 50 years later it was shown that blood pressure in humans also decreases during such positive interaction with dogs (Katcher et al., 1983). As an increase in sympathetic nervous system activity is associated with stress and an increase in MAP, the decline in blood pressures brought about through positive human–animal contact is suggestive of a decrease in sympathetic activity and a de-stressing experience (Ganong, 1995).

An experiment was designed to investigate the neurochemical and hormonal correlates for human–dog affiliation behaviour based on available knowledge of neurochemical changes during affiliation behaviour. The hypothesis was that a specific plasma profile of neurochemicals and hormones underlies the physiological responses associated with overt positive human–dog interaction. The decision to choose plasma concentrations of β-endorphin, oxytocin, prolactin, β-phenylethylamine, dopamine, and cortisol for monitoring was based on previous research in this area (Carter et al., 1997; Liebowitz, 1983).

On the assumption that the decline in blood pressure in both humans and animals is also, by extension, an indicator of positive human–dog interaction, we used it as an indicator of the timing to take blood samples for analysis of the selected plasma variables.

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Subjects and methods

Eighteen adult, human Caucasian subjects (eight males and 10 females, aged 19–55 years [average 30 years]) participated on a voluntary self-selected basis. It was required that they all possessed feelings of affection towards dogs. Individuals were healthy and not on prescription medication. Eighteen adult canine subjects (seven males, three castrated males; 11 females, five spayed) were selected on the basis that they were known to have placid temperaments and were used to human contact as

Results

Mean arterial blood pressure tended to decrease in both species during positive interaction (Table I). The time taken for such decrease following the commencement of the session of interaction was between 5 and 24 min in all the humans and between 5 and 23 min in all the dogs. The average time for a decrease in blood pressure was 15 min.

With positive interaction, both species showed significant increases in plasma β-endorphin, oxytocin, prolactin, phenyl acetic acid, and dopamine. In the human

Discussion

The results indicated that a significant decrease in blood pressure can be achieved between 5 and 24 min of positive interspecific interaction in both humans and dogs. Changes in plasma concentrations of the measured neurochemicals are similar in both humans and dogs. The assumption that a decrease in blood pressure could be an indicator of concurrent biochemical changes is supported. However, the decrease of blood pressure is is unlikely to be the cause of the chemical changes, but probably

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