Show me your best side: Lateralization of social and resting behaviors in feral horses.

The study explores the phenomenon of lateralization, or side bias in brain processing, by examining social and resting behaviours in feral horses. The researchers noted a preference for right-sided positioning during affiliative social interactions, while left-sided positioning was favoured during significant periods of rest.

Understanding lateralization

• The phenomenon of lateralization refers to the unequal distribution of mental functions across the two hemispheres of the brain. For instance, certain tasks or behaviours may be processed primarily in the right or left hemisphere.
• This phenomenon is observed across various species and can manifest in sensorial, motor, and behavioural asymmetries. The study analysed this lateralization in the context of social and resting behaviours of feral horses, particularly keeping an eye on affiliative (friendly, bonding) and agonistic (competitive or conflicting) behaviours.

Method of investigation

• Data collection was done using digital video cameras mounted on tripods and drones. This allowed researchers to closely monitor and analyse the behaviours of 37 feral horses, belonging to eight different harems in Northern Portugal.
• The primary focus of observation was the frequency and duration of specific social interactions, including affiliative actions such as grooming and aggressive behaviours, along with resting periods.

Key findings of the study

• The analysis observed that during affiliative interactions, horses showed a preference for the right side of recipients. These interactions were not only more frequently performed, but also lasted longer when the other horse was positioned to the right.
• In the case of resting behaviours, specifically during recumbent resting when the horses were lying down, episodes on the left side appeared to last longer.
• The right-side bias seen in affiliative behaviour aligns somewhat with the valence-specific hypothesis, which suggests left-hemisphere dominance for positive affect behaviours. However, the apparent left-side resting bias might relate more to synchronization or perhaps other factors.

Context-dependent lateralization

• Although patterns of lateralization were observed, the findings also discuss how such biases may be context dependent. In other words, different situations might bring out different lateral preferences.
• Understanding these behavioural asymmetries in feral horses could provide valuable insights into the complexities of lateralization, and its role from an ecological and evolutionary standpoint. This could help enhance our understanding of brain function and behaviour in other species as well.