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Sign-trackers deploy perceptual, but not cholinergic-attentional, mechanisms to respond to salient cues

Phillips KB, Avila C, Sarter M (2019) Sign-trackers deploy perceptual, but not cholinergic-attentional, mechanisms to respond to salient cues. Neuroscience 2019 Abstracts 331.10. Society for Neuroscience, Chicago, IL.

Summary: Sign-trackers (STs) attribute incentive value to stimuli that predict food and drug rewards and therefore have emerged as a model for studying vulnerability for addiction-like behaviors. Relative to goal-trackers (GTs), who do not imbue discrete predictive stimuli with motivational value, STs also show a reduced capacity for engaging forebrain cholinergic signaling for the processing of behaviorally significant and attention-demanding cues. The greater power of Pavlovian drug cues in STs has been attributed in part to their relatively poor attentional control of such cues. However, when tested in an operant Sustained Attention Task (SAT), STs exhibit only a minor impairment in hit rates but, more robustly, unstable performance over time. These observations raised the question as to the neuro-behavioral or -cognitive mechanisms via which STs perform the SAT. Male and female STs were trained on SAT. The SAT requires the reporting of cues as well as non-cue events via separate levers, yielding four response categories (hits and misses, and correct rejections and false alarms). After reaching criterion, half of STs received bilateral infusions of the cholino-selective neurotoxin 192-IgG saporin while the remaining STs received sham-lesions. Following recovery, performance was assessed on the SAT and a version of SAT incorporating a flashing house light distractor (dSAT). Goal-directed (or top-down) attention is thought to maintain and recover performance during dSAT and mediated via increases in cortical cholinergic activity. In STs, neither SAT nor dSAT performance depended on the integrity of the cholinergic system. We therefore hypothesized that STs perform the SAT using model-free, non-attentional mechanisms, perhaps relying largely on trial-biased perceptual processes to detect salient cues. To test this hypothesis, separate STs and GTs were trained on SAT. The salience of the cue light relative to the house light was varied across operant chambers. In STs, greater perceptual sensitivity reductions were observed as a function of relatively weaker cue salience. In contrast, GTs’ perceptual sensitivity did not relate to cue salience. Associated with their relatively unresponsive cholinergic system, STs rely on perceptual mechanisms, rather than attentional mechanisms, to perform the SAT. The relative absence of (top-down) attentional control of behaviorally significant cues, combined with a propensity to attribute incentive value to such cues, renders STs less likely to reject such cues from guiding their behavior and engaging in alternative action.

Related Products: 192-IgG-SAP (Cat. #IT-01)