[Editorial] Molecular mechanisms of memory consolidation, reconsolidation, and persistence

In the last decades there have been significant advances in our understanding of the cellular and subcellular mechanisms underlying changes in synaptic connectivity that subserve memory formation. The so called Theory of Synaptic Plasticity and Memory has gathered a wealth of experimental support from different areas of neuroscience to become the main phenomenological description of memory at the behavioural level. This special issue of neural plasticity compiles some of the most recent advances in our understanding of the mechanisms underlying formation and persistence of different types of memories from invertebrates to humans. Contributions from different laboratories around the world pinpoint hot topics in this area of memory research, highlighting growing avenues for future research.Fil: Merlo, Emiliano. University of Cambridge; Reino Unido. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Bekinschtein, Pedro Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Biología Celular y Neurociencia "Prof. Eduardo de Robertis". Universidad de Buenos Aires. Facultad de Medicina. Instituto de Biología Celular y Neurociencia; ArgentinaFil: Sietse, Jonkman. Icahn School of Medicine at Mount Sinai; Estados UnidosFil: Medina, Jorge Horacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Biología Celular y Neurociencia "Prof. Eduardo de Robertis". Universidad de Buenos Aires. Facultad de Medicina. Instituto de Biología Celular y Neurociencia; Argentina. Universidad de Buenos Aires. Facultad de Medicina. Departamento de Ciencias Fisiológicas; Argentin

Opposing roles for striatonigral and striatopallidal neurons in dorsolateral striatum in consolidating new instrumental actions.

Comparatively little is known about how new instrumental actions are encoded in the brain. Using whole-brain c-Fos mapping, we show that neural activity is increased in the anterior dorsolateral striatum (aDLS) of mice that successfully learn a new lever-press response to earn food rewards. Post-learning chemogenetic inhibition of aDLS disrupts consolidation of the new instrumental response. Similarly, post-learning infusion of the protein synthesis inhibitor anisomycin into the aDLS disrupts consolidation of the new response. Activity of D1 receptor-expressing medium spiny neurons (D1-MSNs) increases and D2-MSNs activity decreases in the aDLS during consolidation. Chemogenetic inhibition of D1-MSNs in aDLS disrupts the consolidation process whereas D2-MSN inhibition strengthens consolidation but blocks the expression of previously learned habit-like responses. These findings suggest that D1-MSNs in the aDLS encode new instrumental actions whereas D2-MSNs oppose this new learning and instead promote expression of habitual actions

Post-learning infusion of anisomycin into the anterior cingulate cortex impairs instrumental acquisition through an effect on reinforcer valuation

The integrity of the rodent anterior cingulate cortex (ACC) is essential for various aspects of instrumental behavior, but it is not clear if the ACC is important for the acquisition of a simple instrumental response. Here, it was demonstrated that post-session infusions of anisomycin into the rat ACC completely prevented the acquisition of instrumental responding. The experimental use of post-session intracranial infusions of plasticity inhibitors is assumed to affect local consolidation of plasticity, but not behavioral task performance. However, in associative appetitive conditioning, post-session intracranial infusion of pharmaco-active compounds could actually interfere with subsequent task performance indirectly through retrospective effects on the valuation of ingested rewards. Thus, it was subsequently demonstrated that the intracranial infusion of anisomycin into the ACC after sucrose pellet consumption significantly reduced subsequent pellet consumption, suggesting that the infusion of anisomycin into the ACC produced conditioned taste avoidance. In the third experiment, an innovative procedure was introduced that dissociated the effects of intracranial infusions after conditioning sessions on task-learning and unconditioned stimulus valuation. With this procedure, the infusion of anisomycin into the ACC after instrumental sessions did not affect instrumental reinforcer valuation or the acquisition of instrumental responding, suggesting that plasticity in the ACC is not necessary for the acquisition of instrumental behavior

Delayed rewards facilitate habit formation

The transition from goal-directed to habitual forms of instrumental behaviour is determined by variables such as the amount of training, schedules of reinforcement, the availability of choices, and exposure to drugs of abuse. Less is known about the control of goal-directed behaviour when reinforcement is delayed rather than immediate. In these experiments, we investigated in rats the role of response-outcome contiguity on the control of goal-directed action, assessed through satiety-specific outcome devaluation tests. In Experiment 1 using a within-subjects design we observed goal-directed behaviour after six days of FR1 training when the outcome was presented immediately following the lever press, but not when it was delayed for 20 s, revealing habit formation with delayed outcomes. Experiment 2 revealed that the habitual control observed with 20 s delays of reinforcement can be prevented if, immediately before each instrumental training session, the rats were exposed to the experimental context in the absence of both the lever and reinforcement. In summary, these experiments suggest that response-outcome contiguity plays an important role in the control of goal-directed actions and habits

The role of contextual conditioning in the effect of reinforcer devaluation on instrumental performance by rats

Different groups of rats received different amounts of training to lever press for a food reinforcer before an aversion was conditioned to the food. This devaluation of the reinforcer reduced responding in both subsequent extinction and reinforced tests of responding to a degree that was independent of the amount of instrumental training. Moreover, interpolating context extinction between aversion conditioning and the extinction test reduced the magnitude of the devaluation effect, thereby indicating that Pavlovian contextual conditioning may play a role in the instrumental devaluation effect