Acquisition learning is stronger for aversive than appetitive events

Abstract

Appetitive and aversive learning are both key building blocks of adaptive behavior, yet knowledge regarding their differences is sparse. Using a capsaicin heat pain model in 36 healthy participants, this study directly compared the acquisition and extinction of conditioned stimuli (CS) predicting pain exacerbation and relief. Valence ratings show stronger acquisition during aversive compared to appetitive learning, but no differences in extinction. Skin conductance responses and contingency ratings confirmed these results. Findings were unrelated to individual differences in pain sensitivity or psychological factors. Our results support the notion of an evolutionarily hardwired preponderance to acquire aversive rather than appetitive cues as is protective for acute aversive states such as pain but may contribute to the development and maintenance of clinical conditions such as chronic pain, depression or anxiety disorders.

Fig. 1. Differential conditioning paradigm.

A pain intensity of about VAS 40 was induced by applying thermal heat stimuli to capsaicin-pretreated skin (tonic pain). An increase and decrease in temperature level led to pain exacerbation (VAS 80) and pain relief (VAS 0), respectively. The design consisted of habituation, acquisition, and extinction training. Assignment of geometric figures to experimental conditions was pseudo-randomized (example shown here).

Fig. 2. Individual pain intensity and (un)pleasantness ratings.

Pain intensity (a) and pain (un)pleasantness (b) ratings during all experimental phases for all US types on 0–100 VAS (A) and −50–50 VAS (B) in mean ± standard error of the mean of raw values. Displayed are ratings for the US_increase and US_decrease during training (train) and acquisition (acq) and ratings for the US_medium during training, acquisition, and extinction (ext). Single data points are displayed in gray. Data are provided for N = 36 subjects.

Fig. 3. Valence ratings.

a Valence ratings (raw value) during the habituation (Hab), acquisition (Acq 1–Acq 4), and extinction phases (Ext 1–Ext3).b Differential valence ratings (raw value) of CS_increase/CS_decrease relative to CS_medium (i.e., |(CS_medium−CS_decrease|) during the habituation (Hab), acquisition (Acq 1−Acq 4), and extinction phases (Ext 1−Ext3). An absolute difference of 0 (solid line) indicates equal valence ratings for CS_increase/CS_decrease and CS_medium. Ratings are given as means ± standard error of the mean. Single data points in transparent colors. Dashed lines separate the phases. Data are provided for N = 36 subjects.

Fig. 4. Contingency ratings.

Contingency ratings (raw value) were obtained after acquisition (Acq) and extinction (Ext) training. Single data points in transparent colors. Ratings are given in means ± standard error of the mean. The dashed line separates the phases. Data are provided for N = 36 subjects.

Fig. 5. SCR amplitudes.

a SCR amplitudes for the CS during acquisition and extinction training. b SCR amplitudes to the US for the entire acquisition phase. SCR is given in log-transformed means ± standard error of the mean using the natural logarithm. Single data points in transparent colors. Data provided for n = 31 subjects.

Fig. 6. Differential SCR amplitudes.

Differential SCR amplitudes for the CS during acquisition and extinction training between CS_increase/CS_decrease and CS_medium (e.g., (CS_medium−CS_decrease). Ratings are given in log-transformed means ± standard error of the mean using the natural logarithm. Single data points in transparent colors. Data are provided for n = 30 subjects.