Dopamine Signaling Is Critical for Supporting Cue-Driven Behavioral Control

Mesolimbic dopamine has been implicated in reward learning. Fischbach-Weiss and Janak (this issue) use optogenetics to attenuate dopamine signaling and study its role in cue-driven motivated behaviour

The serial blocking effect: a testbed for the neural mechanisms of temporal-difference learning

Temporal-difference (TD) learning models afford the neuroscientist a theory-driven roadmap in the quest for the neural mechanisms of reinforcement learning. The application of these models to understanding the role of phasic midbrain dopaminergic responses in reward prediction learning constitutes one of the greatest success stories in behavioural and cognitive neuroscience. Critically, the classic learning paradigms associated with TD are poorly suited to cast light on its neural implementation, thus hampering progress. Here, we present a serial blocking paradigm in rodents that overcomes these limitations and allows for the simultaneous investigation of two cardinal TD tenets; namely, that learning depends on the computation of a prediction error, and that reinforcing value, whether intrinsic or acquired, propagates back to the onset of the earliest reliable predictor. The implications of this paradigm for the neural exploration of TD mechanisms are highlighted

Retrieval-mediated learning involving episodes requires synaptic plasticity in the hippocampus

A novel association can form between two memories even when the events to which they correspond are not physically present. For example, once an integrated memory has formed that binds the (when, where, and what) components of an event together, this memory can be triggered by one of its components, and updated with coincident information in the environment. The neural basis of this form of retrieval-mediated learning is unknown. Here, we show, for the first time, that NMDA receptors in the rat hippocampus are required for retrieval-mediated learning involving episodes, but not for the expression of such learning or for retrieval-mediated learning involving simple associations between the components of episodes. These findings provide a novel insight into learning processes that serve the desirable function of integrating stored information with new information, but whose operation might also provide a substrate for some of the cognitive symptoms of schizophrenia and Alzheimer's disease

Different methods of fear reduction are supported by distinct cortical substrates

Understanding how learned fear can be reduced is at the heart of treatments for anxiety disorders. Tremendous progress has been made in this regard through extinction training in which the aversive outcome is omitted. However, current progress almost entirely rests on this single paradigm, resulting in a very specialized knowledgebase at the behavioural and neural level of analysis. Here, we used a dual-paradigm approach to show that different methods that lead to reduction in learned fear in rats are dissociated in the cortex. We report that the infralimbic cortex has a very specific role in fear reduction that depends on the omission of aversive events but not on overexpectation. The orbitofrontal cortex, a structure generally overlooked in fear, is critical for downregulating fear when novel predictions about upcoming aversive events are generated, such as when fear is inflated or overexpected, but less so when an expected aversive event is omitted

Agency Rescues Competition for Credit Assignment Among Predictive Cues from Adverse Learning Conditions

A fundamental assumption of learning theories is that the credit assigned to predictive cues is not simply determined by their probability of reinforcement, but by their ability to compete with other cues present during learning. This assumption has guided behavioral and neural science research for decades, and tremendous empirical and theoretical advances have been made identifying the mechanisms of cue competition. However, when learning conditions are not optimal (e.g., when training is massed), cue competition is attenuated. This failure of the learning system exposes the individual’s vulnerability to form spurious associations in the real world. Here, we uncover that cue competition in rats can be rescued when conditions are suboptimal provided that the individual has agency over the learning experience. Our findings reveal a new effect of agency over learning on credit assignment among predictive cues, and open new avenues of investigation into the underlying mechanisms

Peer review without gatekeeping

eLife is changing its editorial process to emphasize public reviews and assessments of preprints by eliminating accept/reject decisions after peer review

The amygdala and flavour preference conditioning: Crossed lesions and inactivation

Current studies examined whether temporary inactivation of the amygdala influenced the learning and/or expression of conditioned flavour preferences and whether interactions between the amygdala and the nucleus accumbens contribute to this learning. Experiments 1A and 1B examined temporary inactivation of the amygdala in rats, by the administration of muscimol through chronically implanted cannulae, given during acquisition and/or expression of flavour preferences based on a sucrose reinforcer. Despite differences in the number of training trials and control procedures, in both of Experiments 1A and 1B inactivation during training attenuated, but did not totally prevent, the acquisition of a preference for the CS+ (conditioned stimulus) flavour over the CS−. Inactivation during testing had no effect on the preference for the CS+. In Experiment 2A rats were given access to a CS+ flavour paired with fructose and a CS− flavour without fructose prior to testing the preference for the CS+ over the CS− in the absence of the reinforcer. In Experiment 2B the same rats were tested for their preference with another set of CS+ and CS− flavours and maltodextrin as the reinforcing solution. Contralateral unilateral lesions of the amygdala and nucleus accumbens attenuated, but did not totally prevent, flavour preference learning based on either fructose or maltodextrin compared to either ipsilateral or sham lesioned animals. These results suggest that the amygdala plays a role in the learning, but not expression, of flavour preferences and that this role is partially dependent on interactions with the nucleus accumbens

Associative structures in animal learning: Dissociating elemental and configural processes

The central concern of associative learning theory is to provide an account of behavioral adaptation that is parsimonious in addressing three key questions: (1) under what conditions does learning occur, (2) what are the associative structures involved, and (3) how do these affect behavior? The principle focus here is on the second question, concerning associative structures, but we will have cause to touch on the others in passing. This question is one that has exercised theorists since Pavlov’s descriptions of the conditioning process, where he identifies the shared significance of the study of conditioned reflexes for psychologists and neuroscientists alike