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

Prefrontal regulation of behavioural control: Evidence from learning theory and translational approaches in rodents

Everyday activities require adaptive decision-making and control over our actions to achieve our goals. Sub-regions within the cortex are widely reported to regulate these choices. Here we review rodent studies from two disparate fields of instrumental action control - goal-directed and habitual responding, and impulsive and compulsive behaviour. Our aim was to compare findings across the spectrum, from precision associative learning to translational studies of action control. The evidence suggests that each cortical sub-region performs different roles depending on task requirements and, within tasks, clear dissociations exist between regions. Rather than synthesizing a single role or function for a given region, we should consider regions to be capable of many different functions. Further investigation of cortico-cortical connections and the pattern of input and output circuitry within each region may be needed to identify unique process-specific pathways. Despite differences in the scope and purpose of these two fields, integrating evidence across tasks provides a broader context for testing hypotheses about the role of cortical regions in adaptive actions and decision-making.

Role of Anterior Cingulate Cortex in Instrumental Learning: Blockade of Dopamine D1 Receptors Suppresses Overt but Not Covert Learning

HIGHLIGHTS

Blockade of dopamine D1 receptors in ACC suppressed instrumental learning when overt responding was required.

Covert learning through observation was not impaired.

After treatment with a dopamine antagonist, instrumental learning recovered but not the rat's pretreatment level of effort tolerance.

ACC dopamine is not necessary for acquisition of task-relevant cues during learning, but regulates energy expenditure and effort based decision.

Dopamine activity in anterior cingulate cortex (ACC) is essential for various aspects of instrumental behavior, including learning and effort based decision making. To dissociate learning from physical effort, we studied both observational (covert) learning, and trial-and-error (overt) learning. If ACC dopamine activity is required for task acquisition, its blockade should impair both overt and covert learning. If dopamine is not required for task acquisition, but solely for regulating the willingness to expend effort for reward, i.e., effort tolerance, blockade should impair overt learning but spare covert learning. Rats learned to push a lever for food rewards either with or without prior observation of an expert conspecific performing the same task. Before daily testing sessions, the rats received bilateral ACC microinfusions of SCH23390, a dopamine D1 receptor antagonist, or saline-control infusions. We found that dopamine blockade suppressed overt responding selectively, leaving covert task acquisition through observational learning intact. In subsequent testing sessions without dopamine blockade, rats recovered their overt-learning capacity but not their pre-treatment level of effort tolerance. These results suggest that ACC dopamine is not required for the acquisition of conditioned behaviors and that apparent learning impairments could instead reflect a reduced level of willingness to expend effort due to cortical dopamine blockade.

Differential effects of clozapine, metoclopramide, haloperidol and risperidone on acquisition and performance of operant responding in rats

RATIONALE

Prior research has not systematically investigated the effects of systemic antipsychotic drugs on operant response acquisition, specifically their behavioural microstructure, reinforcement blunting and relative potency in acquisition compared to performance once operant responding has stabilized.

OBJECTIVES

This study aims to systematically investigate the effects of systemically administered clozapine, metoclopramide, haloperidol and risperidone during free operant response acquisition and performance.

METHODS

Following magazine training, food-restricted male Wistar rats lever pressed for food reward in 15 min daily operant conditioning sessions.

RESULTS

All drugs suppressed operant response acquisition and performance. Risperidone and metoclopramide, but not clozapine or haloperidol, suppressed operant responding more potently during acquisition than performance. The dopamine D2-like receptor antagonists haloperidol and metoclopramide that affect the ventral and dorsal striatum blunted reinforcement and decreased inactive lever presses in acquisition. In contrast, the atypical antipsychotics clozapine and risperidone that affect the ventral striatum and prefrontal cortex failed to decrease inactive lever presses during acquisition, suggesting a possible decision-making deficit. Haloperidol decreased active lever pressing over performance days. The drugs did not appear to affect rats' sensitivity to active lever press outcome, even though they suppressed active lever pressing.

CONCLUSIONS

Results suggest that reinforcement impact during operant acquisition is dependent on dopamine D2 receptors while drugs affecting, among other areas, the prefrontal cortex produce a deficit in ability to suppress inactive lever press responses.

Reconsolidation of a well-learned instrumental memory

Once consolidated, memories are dynamic entities that go through phases of instability in order to be updated with new information, via a process of reconsolidation. The phenomenon of reconsolidation has been demonstrated in a wide variety of experimental paradigms. However, the memories underpinning instrumental behaviors are currently not believed to reconsolidate. We show that well-learned lever pressing in rats does undergo reconsolidation, which can be disrupted by systemic administration of the noncompetitive N-methyl-D-aspartate receptor (NMDAR) antagonist (+)-5-methyl-10,11-dihydro-SH-dibenzo[a,d]cyclohepten-5,10-imine maleate (MK-801) when administered prior to a switch to a variable, but not fixed, ratio schedule. Disruption of reconsolidation resulted in a reduction in long-term lever pressing performance and diminished the sensitivity of behavior to contingency change. Further investigation demonstrated that expression of the reconsolidation impairment was not affected by outcome value, implying a deficit in a stimulus–response (S–R) process. The ability to disrupt the performance of well-learned instrumental behaviors is potentially of great importance in the development of reconsolidation-based clinical treatments for conditions that involve compulsive seeking behaviors.

Acquisition of "Start" and "Stop" response thresholds in peak-interval timing is differentially sensitive to protein synthesis inhibition in the dorsal and ventral striatum

Time-based decision-making in peak-interval timing procedures involves the setting of response thresholds for the initiation (“Start”) and termination (“Stop”) of a response sequence that is centered on a target duration. Using intracerebral infusions of the protein synthesis inhibitor anisomycin, we report that the acquisition of the “Start” response depends on normal functioning (including protein synthesis) in the dorsal striatum (DS), but not the ventral striatum (VS). Conversely, disruption of the VS, but not the DS, impairs the acquisition of the “Stop” response. We hypothesize that the dorsal and ventral regions of the striatum function as a competitive neural network that encodes the temporal boundaries marking the beginning and end of a timed response sequence.

Dorsal and ventral striatal protein synthesis inhibition affect reinforcer valuation but not the consolidation of instrumental learning

The evidence for a role of the striatum in the acquisition of uncued instrumental responding is ambiguous. It has been shown that post-session infusions of anisomycin into the core of the nucleus accumbens (NAcc) impaired instrumental acquisition, but pre-training lesions of the NAcc suggest that it is not necessary. Recently, we demonstrated that the infusion of anisomycin into the anterior cingulate cortex impaired instrumental acquisition indirectly through a taste aversion. Thus, we hypothesized that post-session anisomycin infusions into the NAcc affected instrumental acquisition through an effect on reinforcer valuation. For the dorsal striatum, both post-session infusions of anisomycin and pre-training lesion studies suggest that neither the dorsolateral nor the dorsomedial striatum is necessary for the acquisition of instrumental responding. However, it has not been attempted to block plasticity in both regions concurrently, and we hypothesized that both regions independently contribute to acquisition through goal-directed and habitual learning. In the current experiments, we first replicated the effect of unprotected post-session anisomycin infusions into the NAcc on instrumental acquisition. Subsequently, we investigated the effect of protein synthesis inhibition in the NAcc and dorsomedial and dorsolateral striatum concurrently on instrumental acquisition, critically controlling for effects on reinforcer valuation. The anisomycin infusions induced an aversive state, but did not affect instrumental acquisition.