Effects of inter-food interval on the variety effect in an instrumental food-seeking task. Clarifying the role of habituation

Abstract

Food variety increases consumption and the rate of instrumental behavior that is reinforced by food in humans and animals. The present experiment investigated the relationship between the variety effect and habituation to food by testing the role of the interval between successive food presentations on responding in an operant food-seeking task. Habituation to food was expected at short, but not long, interfood intervals. The effects of variety on food’s long-term reinforcing value were also tested. Four groups of rats were trained to lever-press on different random-interval (RI) schedules of reinforcement to earn 45-mg food pellets. Half the rats in each group received an unpredictable mix of grain and sucrose pellets, while the other half consistently received sucrose pellets. Response rate began at a high rate and then decreased within each 30-min session for groups that received short inter-pellet intervals (i.e., RI-3 s and RI-6 s reinforcement schedules) but not in groups that received longer inter-pellet intervals (i.e., RI-12 s and RI-24 s). A variety effect in the form of higher responding in the mix group than the sucrose-only group was also only evident at the shorter intervals. Habituation and variety effects were also most evident with the short intervals when we controlled for the number of reinforcers earned, suggesting that they were not merely due to rapid satiation. The variety effect also appeared quickly when groups trained with longer inter-pellet intervals (RI-12 s and RI-24 s) were transitioned to shorter intervals (RI-3 s and RI-6 s). There was no effect of variety on resistance to extinction or on resistance to the response-suppressing effects of pre-session feeding. The results more clearly link this version of the variety effect to the short-term effect of variety on food habituation.

Acute regulation of habituation learning via posttranslational palmitoylation

“…Habituation learning was initially described in the context of reflex responses 1,8 , however there has since been broad recognition that habituation learning is a widespread mechanism associated with and to some degree prerequisite for more complex cognitive processes and behaviors [3][4][5][6]11 . While our understanding of habituation learning both at the molecular and cellular level has been informed predominantly by molecular-genetic studies in invertebrates [18][19][20][21][22][23][24][25][26][27][28] , whether and how additional genetic and circuit mechanisms regulate vertebrate habituation learning has remained largely unclear.…”

“…Habituation is an evolutionarily conserved non-associative form of learning characterized by a response decrement to repeated stimuli. One of the simplest forms of learning, habituation is defined by ten behavioral characteristics 1,2 , and has been associated with a wide range of behaviors and physiological responses including feeding and drug seeking [3][4][5] , neuroendocrine responses to stress 6 , and mechanosensory 7,8 , olfactory 9 and acoustic startle responses 10 . Moreover, because habituation enables animals to focus selectively on relevant stimuli, it is thought to be a prerequisite for more complex forms of learning 2 .…”

Striatal Activity and Reward Relativity: Neural Signals Encoding Dynamic Outcome Valuation

“…These sensory-specific satiety signals have been primarily linked to specific food outcomes. The process is akin to a dishabituation effect in that a new food substance removes the habituation toward a pre-exposed food item and reignites the motivation for consumption (Bouton et al, 2013; Thraikill et al, 2015). Our signals could be working in this manner, and it would support the result that these activations that dishabituate are robust solely in the mixed session with exposure to the alternatives is necessary for the neural effect to take place.…”

“…An example of general context effects would be variety influences, with possible incentive value shifts depending upon more or less variety within a situation (Webber et al, 2015). Variety effects are defined as enhanced responding when animals are exposed to diverse sets of alternatives compared with exposure to repetitive identical items (Thrailkill et al, 2015). This form of relative encoding mainly disregards single outcomes and primarily focuses on general properties, such as the size of the outcome set or the rate of outcome shifts.…”

“…This form of relative encoding mainly disregards single outcomes and primarily focuses on general properties, such as the size of the outcome set or the rate of outcome shifts. Variety effects can involve dishabituation and contrast to reduce sensory-specific satiety, and invigorate food consumption and operant responding for food (Bouton et al, 2013; Thrailkill et al, 2015). Another generalization effect on behavior was obtained that appeared as a transfer of value from one outcome to another (Webber et al, 2015).…”