Appetitive vs. Aversive conditioning in humans.

Marta Andreatta,Paul Pauli

doi:10.3389/fnbeh.2015.00128

Marta Andreatta, Paul Pauli

Open Access

https://doi.org/10.3389/fnbeh.2015.00128

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Abstract

In classical conditioning, an initially neutral stimulus (conditioned stimulus, CS) becomes associated with a biologically salient event (unconditioned stimulus, US), which might be pain (aversive conditioning) or food (appetitive conditioning). After a few associations, the CS is able to initiate either defensive or consummatory responses, respectively. Contrary to aversive conditioning, appetitive conditioning is rarely investigated in humans, although its importance for normal and pathological behaviors (e.g., obesity, addiction) is undeniable. The present study intents to translate animal findings on appetitive conditioning to humans using food as an US. Thirty-three participants were investigated between 8 and 10 am without breakfast in order to assure that they felt hungry. During two acquisition phases, one geometrical shape (avCS+) predicted an aversive US (painful electric shock), another shape (appCS+) predicted an appetitive US (chocolate or salty pretzel according to the participants' preference), and a third shape (CS–) predicted neither US. In a extinction phase, these three shapes plus a novel shape (NEW) were presented again without US delivery. Valence and arousal ratings as well as startle and skin conductance (SCR) responses were collected as learning indices. We found successful aversive and appetitive conditioning. On the one hand, the avCS+ was rated as more negative and more arousing than the CS– and induced startle potentiation and enhanced SCR. On the other hand, the appCS+ was rated more positive than the CS– and induced startle attenuation and larger SCR. In summary, we successfully confirmed animal findings in (hungry) humans by demonstrating appetitive learning and normal aversive learning.

Highlights

Predicting threat and food is of crucial importance for any organism’s survival
In order to do so, participants came to the lab early in the morning without breakfast in order to assure that they were hungry, and according to their preference, pieces of chocolate or salty pretzels were used as appetitive Unconditioned Stimuli (US)
The appCS+ compared to the Conditioned Stimuli (CS)– triggered more positive valence ratings, startle attenuation, and greater Skin Conductance Response (SCR)

Summary

Introduction

In classical conditioning (Pavlov, 1927), a cue precedes an aversive event, such as a mild painful electric shock (aversive unconditioned stimulus, US), or an appetitive event, such as a food pellet (appetitive US), several times Afterwards, this stimulus alone ( labeled CS, CS+) is able to elicit either defensive or consummatory responses, respectively. Food as a primary reinforcer must be delivered when the organism is hungry in order to be rewarding (for a recent review see Dickinson and Balleine, 1994; Clark et al, 2012) In human research, this difficulty has been overcome by using money (Austin and Duka, 2010; Delgado et al, 2011; Levy and Glimcher, 2011) or erotic pictures (Klucken et al, 2009, 2013). Neuro-imaging studies have pointed out that primary (i.e., snacks or drinks) and secondary (i.e., money) reinforcers activate some common brain regions (e.g., striatum) and entail distinct patterns of activation (Delgado et al, 2011; Levy and Glimcher, 2011)

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