Data and analysis scripts for the research project "The meaning of social touch for client reef fish"
Rewards are both “liked” and “wanted”. Indeed, according to the incentive salience hypothesis the brain mechanisms involved in how much of a reward is determined by both its incentive salience (“wanting”) or by the actual hedonic impact of reward (“liking”) are dissociable, with the first being mediated by the (mostly dopaminergic) mesolimbic decision making network, and the latter being amplified by several functionally interactive but anatomically distributed locations referred to as "hedonic hotspots”. The processing of these hedonic mechanisms is suggested to be mediated by opioid neurotransmission, however most of evidence comes from humans and other mammals regarding drug addictive behaviour. Here we argue that, in mutualistic associations, client fish seek to interact with cleanerfish not only due to the immediate benefits of being cleaned, but due to its hedonic impact, modulated by the opioid system. For that we asked two questions: do fish ‘like’ to be cleaned?; and if so, how much do they ‘want’ to be cleaned? To tackle the first, we used a conditioned place preference paradigm and found that fish showed a preference for the compartment paired with a cleaner, an effect that was proportional to the time spent interacting with the cleaner during conditioning. Treatment with the μ-opioid receptor agonist DAMGO dose-dependently increased preference, while treatment with the antagonist naloxone decreased it. To test for fish “want”, we used an detour task and found that client fish are able to circumvent barriers to reach a cleanerfish-adjacent compartment, with the strongest response in the second trial, and response strength decreasing to baseline levels in the third trial. Response strength was not affected by treatment with either naloxone nor DAMGO. Our results show that cleaner-client interactions are hedonically positive for clients, an effect that is mediated by the opiodergic system, suggesting the presence of an hedonic opiodergic function. Visual contact with cleanerfish is sufficient to activate incentive salience programs, but the opioid system was not found to participate. Overall, we provide first evidence confirming the incentive sensitisation theory in a teleost fish and the pharmacological dissociation between liking and wanting.
The following represent data packages:
- client_CPP.csv: Data on the validation of conditioned place preference (CPP) using cleanerfish as stimuli, with client fish C. auriga as subjects
- naloxone_CPP.csv: Data on the effects of acute naloxone (mu-opioid receptor antagonist) on client fish preference and locomotor patterns in the CPP
- DAMGO_CPP.csv: Data on the effects of acute DAMGO (mu-opioid receptor agonist) on client fish preference and locomotor patterns in the CPP
- detour_drugs.csv: Data on the effects of acute naloxone or DAMGO on client fish performance in the detour task
The script file (CPP.R) can be opened directly on R to reproduce the analysis used in the project.
This project was financed by a small grant from The Fisheries Society of the British Isles to Marta Soares