Zoology/Biology session

Differentiating between emotional states can be essential in social relationships, as it allows animals to evaluate the internal state and motivations of others, and enables appropriate behavioural responses. This ability can be beneficial in intra- and also in interspecific relationships. Previous behavioural research has shown that dogs, who have lived in the social environment of humans for thousands of years and were selected for cooperation, can not only discriminate certain human emotions, but also respond accordingly and integrate emotional cues of different modalities. However, the neural mechanisms that support the decoding of human emotional cues in the dog brain remain unexplored.

We hypothesise that there are specific activity patterns in the dog brain corresponding to different human emotions and their valences, independent of modality and the sex of the person giving the stimuli.

To test this, we presented healthy adult dogs (N=35) with emotional odour and vocal stimuli from males and females differing in their valence (joy and fear), and measured their brain responses using electroencephalography (EEG). The odour stimuli were sweat samples validated in previous experiments (collected in joyful and fearful situations). For vocal stimuli, natural non-verbal vocalisations (laughing and screaming) were used. For data analysis, we performed a power spectrum analysis focusing on six frequency bands (delta: 1-4 Hz, theta: 4-8 Hz, alpha: 8-12 Hz, beta: 12-30 Hz, low gamma: 30-60 Hz and high gamma: 60-100 Hz). The effects of emotion and sex were tested using generalised linear mixed-effects models.

By analysing the responses to odour stimuli, we found distinct emotion-based patterns of activity in all frequency bands. Power was generally lower for fear- than for joy-conveying stimuli. In the delta band, this effect was sex-independent, being present only for male stimuli in the theta and alpha bands, and only for female stimuli in the beta, low and high gamma bands. For joy odours, we detected a sex difference only in the theta band, and for fear odours only in the high gamma band: power was always higher for male odours than for female odours. In the future, we will also analyse the responses to the vocal stimuli.

We are the first to reveal the neural correlates of human emotional odour discrimination in dogs. The finding that emotion discrimination incorporates multiple bands, indicates the involvement of different neural mechanisms in emotional processing. Our results suggest that there is sex-independent encoding of emotional valence in the lowest frequency band, with emotional stimuli being partially encoded in a sex-dependent manner in higher frequency bands.

I was involved in designing the experimental protocol, the collection and preparation of the samples used, data collection and various stages of data analysis.