Previous investigations reveal altered brain function in horses performing oral stereotypic behaviour, though to date no studies have sought to elucidate the brain mechanisms underlying locomotor stereotypy of the horse. The aim of this study was to utilise behavioural probes previously successfully utilised to expose basal ganglia dysfunction in rodent and human models, including spontaneous blink rate (SBR), behavioural initiation (BI) and an extinction learning paradigm featuring reward devaluation, to initialise the neurologic studies of locomotor stereotypy, and compare neural aspects of the locomotor and oral stereotypy phenotype.

Crib-biting horses demonstrated significantly lower SBR than control (p<0.05) and weaving (p<0.01) animals, though behaviour initiation was significantly increased for crib-biters (p<0.01) and weavers (p<0.05) compared to controls. Both crib-biting and weaving horses acquired the initial operant response significantly faster than controls (p<0.001) and thus displayed accelerated learning. Additionally, crib-biting horses performed significantly more operant responses during extinction phase 1 and 2 compared to weaving (p<0.001 and p<0.01 respectively) and control animals (p<0.001 and p<0.001 respectively). Finally, crib-biting horses required significantly more trials to reach total extinction criterion compared to control (p<0.001) and weaving (p<0.01) cohorts.

These findings are in agreement with previous research, with crib-biting horses establishing a bias to habitual responding, even in the context of minimal training. This tendency combined with the SBR and BI data, corroborates previous post-mortem evidence of up-regulated ventral and down-regulated dorsomedial activity in the striatum group of brain structures. In contrast, weaving animals were resistant to over-training and failed to display habitual responding, at any phase of the investigation. This, when taken alongside increased BI and faster rate of learning, is suggestive of heightened ventral striatal activity, but a normal functioning dorsal striatum. This is first known report of differences in striatal functioning between two different stereotypies within a single species.