Using internal memory representations in associative learning to study hallucination-like phenomenon

Variables influencing conditioning-evoked hallucinations: overview and future applications

Hallucinations occur in the absence of sensory stimulation and result in vivid perceptual experiences of nonexistent events that manifest across a range of sensory modalities. Approaches from the field of experimental and cognitive psychology have leveraged the idea that associative learning experiences can evoke conditioning-induced hallucinations in both animals and humans. In this review, we describe classical and contemporary findings and highlight the variables eliciting these experiences. We also provide an overview of the neurobiological mechanisms, along with the associative and computational factors that may explain hallucinations that are generated by representation-mediated conditioning phenomena. Through the integration of animal and human research, significant advances into the psychobiology of hallucinations are possible, which may ultimately translate to more effective clinical applications.

Targeted effects of ketamine on perceptual expectation during mediated learning in rats

RATIONALE

While neural correlates of hallucinations are known, the mechanisms have remained elusive. Mechanistic insight is more practicable in animal models, in which causal relationships can be established. Recent work developing animal models of hallucination susceptibility has focused on the genesis of perceptual expectations and perceptual decision-making. Both processes are encompassed within mediated learning, which involves inducing a strong perceptual expectation via associative learning, retrieving that memory representation, and deciding whether this internally generated percept is predictive of an external outcome. Mediated learning in rodents is sensitive to many psychotomimetic manipulations. However, we do not know if these manipulations selectively alter learning of perceptual expectations versus their retrieval because of their presence throughout all task phases.

OBJECTIVES

Here, we used mediated learning to study the targeted effect of a psychotomimetic agent on the retrieval of perceptual expectation.

METHODS

We administered (R,S)-ketamine to rats selectively during the devaluation phase of a mediated learning task, when the representation of the expected cue is retrieved, to test the hypothesis that internally generated perceptual experiences underlie this altered mediated learning.

RESULTS

We found that ketamine increased only mediated learning at a moderate dose in rats, but impaired direct learning at the high dose.

CONCLUSIONS

These results suggest that ketamine can augment retrieval of perceptual expectations and thus this may be how it induces hallucination-like experiences in humans. More broadly, mediated learning may unite the conditioning, perceptual decision-making, and even reality monitoring accounts of psychosis in a manner that translates across species.

Cognitive behavioral therapy (CBT), acceptance and commitment therapy (ACT), and Morita therapy (MT); comparison of three established psychotherapies and possible common neural mechanisms of psychotherapies

Psychotherapies aim to relieve patients from mental distress by guiding them toward healthier attitudes and behaviors. Psychotherapies can differ substantially in concepts and approaches. In this review article, we compare the methods and science of three established psychotherapies: Morita Therapy (MT), which is a 100-year-old method established in Japan; Cognitive Behavioral Therapy (CBT), which-worldwide-has become the major psychotherapy; and Acceptance and Commitment Therapy (ACT), which is a relatively young psychotherapy that shares some characteristics with MT. The neuroscience of psychotherapy as a system is only beginning to be understood, but relatively solid scientific information is available about some of its important aspects such as learning, physical health, and social interactions. On average, psychotherapies work best if combined with pharmacotherapies. This synergy may rely on the drugs helping to "kickstart" the use of neural pathways (behaviors) to which a patient otherwise has poor access. Improved behavior, guided by psychotherapy, can then consolidate these pathways by their continued usage throughout a patient's life.

Neural Substrates of Incidental Associations and Mediated Learning: The Role of Cannabinoid Receptors

The ability to form associations between different stimuli in the environment to guide adaptive behavior is a central element of learning processes, from perceptual learning in humans to Pavlovian conditioning in animals. Like so, classical conditioning paradigms that test direct associations between low salience sensory stimuli and high salience motivational reinforcers are extremely informative. However, a large part of everyday learning cannot be solely explained by direct conditioning mechanisms - this includes to a great extent associations between individual sensory stimuli, carrying low or null immediate motivational value. This type of associative learning is often described as incidental learning and can be captured in animal models through sensory preconditioning procedures. Here we summarize the evolution of research on incidental and mediated learning, overview the brain systems involved and describe evidence for the role of cannabinoid receptors in such higher-order learning tasks. This evidence favors a number of contemporary hypotheses concerning the participation of the endocannabinoid system in psychosis and psychotic experiences and provides a conceptual framework for understanding how the use of cannabinoid drugs can lead to altered perceptive states.