Abstract
Inhibitory control, the ability to override a dominant response, is crucial in many aspects of everyday life. In animal studies, striking individual variations are often largely ignored and their causes rarely considered. Hence, our aims were to systematically investigate individual variability in inhibitory control, to replicate the most common causes of individual variation (age, sex and rank) and to determine if these factors had a consistent effect on three main components of inhibitory control (inhibition of a distraction, inhibition of an action, inhibition of a cognitive set). We tested 21 rhesus macaques (Macaca mulatta) in a battery of validated touchscreen tasks. We first found individual variations in all inhibitory control performances. We then demonstrated that males had poorer performances to inhibit a distraction and that middle-aged individuals exhibited poorer performance in the inhibition of a cognitive set. Hence, the factors of age and sex were not consistently associated with the main components of inhibitory control, suggesting a multi-faceted structure. The rank of the subjects did not influence any inhibitory control performances. This study adopts a novel approach for animal behaviour studies and gives new insight into the individual variability of inhibitory control which is crucial to understand its evolutionary underpinnings.
Highlights
While in human psychometric research, individual differences in cognition have been studied since the early twentieth century [21,22,23,24], research on non-human animals’ cognition has, until recently, tended to minimize the importance of variation among individuals [23,24]
This result demonstrates an individual variation in their distraction task performances
When adjusting for the following confounding factors session, trial, order of the blocks and interaction between sex and type of stimulus, the macaques’ performances were still repeatable (Radj = 0.119, CI = [0.04, 0.001], p < 0.0001). This result demonstrates an individual variation in the distraction task performances even when taking into account confounding variables
Summary
While in human psychometric research, individual differences in cognition have been studied since the early twentieth century [21,22,23,24], research on non-human animals’ cognition has, until recently, tended to minimize the importance of variation among individuals [23,24]. In a meta-analysis, Völter et al [27] re-analysed, from an individual difference perspective, two large comparative studies [14,28] These studies measured the inhibition of action (a detour-reaching task) and the inhibition of a cognitive set (the A-not-B task in which the subjects are required to inhibit a previously rewarded behaviour to learn a new reward contingency) in several species. Johnson-Ulrich & Holekamp [36] have demonstrated that lower ranked hyenas (Crocuta Crocuta) living in larger groups have better inhibitory control than higher ranked conspecifics in a common task of inhibition of action, the cylinder task (subject needs to inhibit reaching directly for food through the transparent surface of a cylinder). To summarize, depending on the task, individual’s characteristics (age, sex and rank) can have a strong influence on variations of inhibitory control skills, but this hasn’t been examined systematically
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