the brains of organisms and serve to create feelings of relaxation, happiness and pain relief. In primates, laughter and social grooming trigger opioid release in the brain, which is thought to form and maintain social bonds. In a study performed on rhesus monkeys, lactating females with 4- to 10-week-old infants were given low doses of naloxone, an opioid antagonist that blocks the opioid receptor and inhibits the effects of endogenous opioids. In comparison to the control females, who were given saline solutions, the naloxone females groomed their infants and other members of their group less. The naloxone females were also observed to be less protective of their young, which is uncharacteristic of new mothers. This decline in social interactions upon naloxone injection suggests that opioid antagonists interfere with maternal involvement in social actions – here, social grooming. We could hypothesize therefore that higher levels of opioids in new rhesus mothers cause increased levels of social involvement and 'maternal' characteristics, aiding the development and learning of the newborn. Criticism for studies quoted Above all, the main criticism regarding studies concerning social grooming is that almost all of them focus on primates and a narrow range of species within primates themselves. This, therefore, does not give us a well-rounded idea of what the cognitive or behavioural basis for social grooming is, nor does it completely outline all the effects (benefits or costs) of it. Moreover, we may not have all the relevant data concerning social grooming even in a well-studied species. Secondly, data for most species is derived based on the members of a single group. In primates, whose behaviour is highly flexible depending on the socio-environmental conditions, this poses as a particular challenge. Thirdly, most studies are observational and short-termed. Hence the direct link between social grooming and fitness or mate choice outcomes cannot be studied directly as in long-term direct or captive studies. See also Cleaner fish Cleaning symbiosis Community cohesion Licking Personal grooming Social cohesion References Further reading External links Articles containing video clips Cleaning Ethology Hygiene Mutualism (biology) fr:Toilettage