Abstract: Abstract Pyramidal neurons of the rat medial prefrontal cortex have been shown to react to chronic stress by retracting their apical dendrites and by spine loss. We extended these findings by focusing on the basilar dendritic tree of layer III pyramidal neurons in both hemispheres of the rat prelimbic cortex. Animals were subjected to daily restraint stress for 1 week (6 h/day), during either the resting or the activity period. The morphology of basilar dendrites and spines of Golgi–Cox-stained neurons in the left and right hemispheres was digitally reconstructed and analyzed. We observed the following: (i) there was an inherent hemispheric asymmetry in control rats during the resting period: the number of spines on proximal dendrites was higher in the left than in the right hemisphere; (ii) basal dendrites in controls displayed a diurnal variation: there was more dendritic material during the resting period than in the activity period; (iii) chronic stress reduced the length of basal dendrites in only the right prelimbic cortex; (iv) chronic stress reduced spine density on proximal basal dendrites; (v) restraint stress during the activity period had more pronounced effects on the physiological stress parameters than restraint stress during the resting period. Our results show dynamic hemisphere-dependent structural changes in pyramidal neurons of the rat prelimbic cortex that are tightly linked to periods of resting and activity. These morphological alterations reflect the capacity of the neurons to react to external stimuli and mirror presumptive changes in neuronal communication.

Abstract: Abstract  Many animal species that rely mainly on calls to communicate produce individual acoustic structures, but we wondered whether individuals of species better known as visual communicants, with small vocal repertoires, would also exhibit individual distinctiveness in calls. Moreover, theoretical advances concerning the evolution of social intelligence are usually based on primate species data, but relatively little is known about the social cognitive capacities of non-primate mammals. However, some non-primate species demonstrate auditory recognition of social categories and possess mental representation of their social network. Horses (Equus caballus) form stable social networks and although they display a large range of visual signals, they also use long-distance whinny calls to maintain contact. Here, we investigated the potential existence of individual acoustic signatures in whinny calls and the ability of horses to discriminate by ear individuals varying in their degree of familiarity. Our analysis of the acoustic structure of whinnies of 30 adult domestic horses (ten stallions, ten geldings, ten mares) revealed that some of the frequency and temporal parameters carried reliable information about the caller’s sex, body size and identity. However, no correlations with age were found. Playback experiments evaluated the behavioural significance of this variability. Twelve horses heard either control white noise or whinnies emitted by group members, familiar neighbours or unfamiliar horses. While control sounds did not induce any particular response, horses discriminated the social category of the callers and reacted with a sound-specific behaviour (vigilance and attraction varied with familiarity). Our results support the existence of social knowledge in horses and suggest a process of vocal coding/decoding of information.

Abstract: Abstract  The ability to select the greater numerosity over another in small sets seems to stem from the calculation of which set contains more, and has been taken as evidence of a primordial representation at the roots of the primate numerical system. We tested 56 horses (Equus caballus) in a paradigm previously used with human infants and nonhuman primates. Horses saw two quantities paired in contrasts—2 versus 1, 3 versus 2, 6 versus 4 and a control for volume, 2 versus 1 big—and had to make a choice by snout touching the container holding the numerosity selected. The horses spontaneously selected the greater of the two quantities when the numerosities were small. These results add to evidence showing spontaneous quantity assessment in a variety of species.

Abstract: The long-held belief that human dominance and equine submission are key to successful training and that the horse must be taught to [`]respect' the trainer infers that force is often used during training. Many horses respond by trialling unwelcome evasions, resistances and flight responses, which readily become established. When unable to cope with problem behaviours, some handlers in the past might have been encouraged to use harsh methods or devices while others may have called in a so-called [`]good horseman' or [`]horse whisperer' to remediate the horse. Frequently, the approaches such practitioners offer could not be applied by the horse's owner or trainer because of their lack of understanding or inability to apply the techniques. Often it seemed that these [`]horse-people' had magical ways with horses (e.g., they only had to whisper to them) that achieved impressive results although they had little motivation to divulge their techniques. As we begin to appreciate how to communicate with horses sensitively and consistently, misunderstandings and misinterpretations by horse and trainer should become less common. Recent studies have begun to reveal what comprises the simplest, most humane and most effective mechanisms in horse training and these advances are being matched by greater sharing of knowledge among practitioners. Indeed, various practitioners of what is referred to here as [`]natural horsemanship' now use techniques similar to the [`]whisperers' of old, but they are more open about their methods. Reputable horse trainers using natural horsemanship approaches are talented observers of horse behaviour and respond consistently and swiftly to the horse's subtle cues during training. For example, in the roundpen these trainers apply an aversive stimulus to prompt a flight response and then, when the horse slows down, moves toward them, or offers space-reducing affiliative signals, the trainer immediately modifies his/her agonistic signals, thus negatively reinforcing the desired response. Learning theory and equine ethology, the fundamentals of the emerging discipline of equitation science, can be used to explain almost all the behaviour modification that goes on in these contexts and in conventional horsemanship. By measuring and evaluating what works and what does not, equitation science has the potential to have a unifying effect on traditional practices and developing branches of equitation.