Lesions of the orbital prefrontal cortex impair the formation of attentional set in rats

Adolescent treadmill exercise enhances hippocampal brain-derived neurotrophic factor (BDNF) expression and improves cognition in autism-modeled rats

Autism spectrum disorder (ASD) is a prevalent neurodevelopmental disorder characterized by repetitive behaviors and altered communication abilities. Exercise is a low-cost intervention that could improve cognitive function and improve brain plasticity mechanisms. Here, the valproic acid (VPA) model was utilized to induce ASD-like phenotypes in rodents. Animals were exercised on a treadmill and performance was evaluated on a cognitive flexibility task. Biomarkers related to exercise and plasticity regulation were quantified from the prefrontal cortex, hippocampus, and skeletal muscle. Exercised VPA animals had higher levels of hippocampal BDNF compared to sedentary VPA animals and upregulated antioxidant enzyme expression in skeletal muscle. Cognitive improvements were demonstrated in both sexes, but in different domains of cognitive flexibility. This research demonstrates the benefits of exercise and provides evidence that molecular responses to exercise occur in both the central nervous system and in the periphery. These results suggest that improving regulation of BDNF via exercise, even at low intensity, could provide better synaptic regulation and cognitive benefits for individuals with ASD.

Orbitofrontal cortex modulates auditory cortical sensitivity and sound perception in Mongolian gerbils

Sensory perception is dynamic, quickly adapting to sudden shifts in environmental or behavioral context. Although decades of work have established that these dynamics are mediated by rapid fluctuations in sensory cortical activity, we have a limited understanding of the brain regions and pathways that orchestrate these changes. Neurons in the orbitofrontal cortex (OFC) encode contextual information, and recent data suggest that some of these signals are transmitted to sensory cortices. Whether and how these signals shape sensory encoding and perceptual sensitivity remain uncertain. Here, we asked whether the OFC mediates context-dependent changes in auditory cortical sensitivity and sound perception by monitoring and manipulating OFC activity in freely moving Mongolian gerbils of both sexes under two behavioral contexts: passive sound exposure and engagement in an amplitude modulation (AM) detection task. We found that the majority of OFC neurons, including the specific subset that innervates the auditory cortex, were strongly modulated by task engagement. Pharmacological inactivation of the OFC prevented rapid context-dependent changes in auditory cortical firing and significantly impaired behavioral AM detection. Our findings suggest that contextual information from the OFC mediates rapid plasticity in the auditory cortex and facilitates the perception of behaviorally relevant sounds.

Altered prefrontal and cerebellar parvalbumin neuron counts are associated with cognitive changes in male rats

Exposure to valproic acid (VPA), a common anti-seizure medication, in utero is a risk factor for autism spectrum disorder (ASD). People with ASD often display changes in the cerebellum, including volume changes, altered circuitry, and changes in Purkinje cell populations. ASD is also characterized by changes in the medial prefrontal cortex (mPFC), where excitatory/inhibitory balance is often altered. This study exposed rats to a high dose of VPA during gestation and assessed cognition and anxiety-like behaviors during young adulthood using a set-shifting task and the elevated plus maze. Inhibitory parvalbumin-expressing (PV +) neuron counts were assessed in the mPFC and cerebellar lobules VI and VII (Purkinje cell layers), which are known to modulate cognition. VPA males had increased PV + counts in crus I and II of lobule VII. VPA males also had decreased parvalbumin-expressing neuron counts in the mPFC. It was also found that VPA-exposed rats, regardless of sex, had increased parvalbumin-expressing Purkinje cell counts in lobule VI. In males, this was associated with impaired intra-dimensional shifting on a set-shifting task. Purkinje cell over proliferation may be contributing to the previously observed increase in volume of Lobule VI. These findings suggest that altered inhibitory signaling in cerebellar-frontal circuits may contribute to the cognitive deficits that occur within ASD.

Chemogenetic inactivation of the nucleus reuniens and its projections to the orbital cortex produce deficits on discrete measures of behavioral flexibility in the attentional set-shifting task

The nucleus reuniens (RE) of the ventral midline thalamus is a critical node in the communication between the orbitomedial prefrontal cortex (OFC) and the hippocampus (HF). While RE has been shown to directly participate in memory-associated functions through its connections with the medial prefrontal cortex and HF, less is known regarding the role of RE in executive functioning. Here, we examined the involvement of RE and its projections to the orbital cortex (ORB) in attention and behavioral flexibility in male rats using the attentional set shifting task (AST). Rats expressing the hM4Di DREADD receptor in RE were implanted with indwelling cannulas in either RE or the ventromedial ORB to pharmacologically inhibit RE or its projections to the ORB with intracranial infusions of clozapine-N-oxide hydrochloride (CNO). Chemogenetic-induced suppression of RE resulted in impairments in reversal learning and set-shifting. This supports a vital role for RE in behavioral flexibility - or the ability to adapt behavior to changing reward or rule contingencies. Interestingly, CNO suppression of RE projections to the ventromedial ORB produced impairments in rule abstraction - or dissociable effects elicited with direct RE suppression. In summary, the present findings indicate that RE, mediated in part by actions on the ORB, serves a critical role in the flexible use of rules to drive goal directed behavior. The cognitive deficits of various neurological disorders with impaired communication between the HF and OFC, may be partly attributed to alterations of RE -- as an established intermediary between these cortical structures.

Prefrontal dynamics and encoding of flexible rule switching

Behavioral flexibility, the ability to adjust behavioral strategies in response to changing environmental contingencies and internal demands, is fundamental to cognitive functions. Despite a large body of pharmacology and lesion studies, the underlying neurophysiological correlates and mechanisms that support flexible rule switching remain elusive. To address this question, we trained mice to distinguish complex sensory cues comprising different perceptual dimensions (set shifting). Endoscopic calcium imaging revealed that medial prefrontal cortex (mPFC) neurons represented multiple task-related events and exhibited pronounced dynamic changes during rule switching. Notably, prominent encoding capacity in the mPFC was associated with switching across, but not within perceptual dimensions. We then showed the involvement of the ascending modulatory input from the locus coeruleus (LC), as inhibiting the LC impaired rule switching behavior and impeded mPFC dynamic processes and encoding. Our results highlight the pivotal role of the mPFC in set shifting processes and demonstrate the profound impact of ascending neuromodulation on shaping prefrontal neural dynamics and behavioral flexibility.

Orbitofrontal cortex control of striatum leads economic decision-making

Animals must continually evaluate stimuli in their environment to decide which opportunities to pursue, and in many cases these decisions can be understood in fundamentally economic terms. Although several brain regions have been individually implicated in these processes, the brain-wide mechanisms relating these regions in decision-making are unclear. Using an economic decision-making task adapted for rats, we find that neural activity in both of two connected brain regions, the ventrolateral orbitofrontal cortex (OFC) and the dorsomedial striatum (DMS), was required for economic decision-making. Relevant neural activity in both brain regions was strikingly similar, dominated by the spatial features of the decision-making process. However, the neural encoding of choice direction in OFC preceded that of DMS, and this temporal relationship was strongly correlated with choice accuracy. Furthermore, activity specifically in the OFC projection to the DMS was required for appropriate economic decision-making. These results demonstrate that choice information in the OFC is relayed to the DMS to lead accurate economic decision-making.

Pharmacogenetic activation of parvalbumin interneurons in the prefrontal cortex rescues cognitive deficits induced by adolescent MK801 administration

The cognitive symptoms of schizophrenia (SZ) present a significant clinical burden. They are treatment resistant and are the primary predictor of functional outcomes. Although the neural mechanisms underlying these deficits remain unclear, pathological GABAergic signaling likely plays an essential role. Perturbations with parvalbumin (PV)-expressing fast-spiking (FS) interneurons in the prefrontal cortex (PFC) are consistently found in post-mortem studies of patients with SZ, as well as in animal models. Our studies have shown decreased prefrontal synaptic inhibition and PV immunostaining, along with working memory and cognitive flexibility deficits in the MK801 model. To test the hypothesized association between PV cell perturbations and impaired cognition in SZ, we activated prefrontal PV cells by using an excitatory DREADD viral vector with a PV promoter to rescue the cognitive deficits induced by adolescent MK801 administration in female rats. We found that targeted pharmacogenetic upregulation of prefrontal PV interneuron activity can restore E/I balance and improve cognition in the MK801 model. Our findings support the hypothesis that the reduced PV cell activity levels disrupt GABA transmission, resulting in the disinhibition of excitatory pyramidal cells. This disinhibition leads to an elevated prefrontal excitation/inhibition (E/I) balance that could be causal for cognitive impairments. Our study provides novel insights into the causal role of PV cells in cognitive function and has clinical implications for understanding the pathophysiology and management of SZ.

Adolescent female valproic acid rats have impaired extra-dimensional shifts of attention and enlarged anterior cingulate cortices

In order to develop better treatments for autism spectrum disorder (ASD) it is critical to understand the developmental trajectory of the disorder and the accompanying brain changes. This study used the valproic acid (VPA) model to induce ASD-like symptoms in rodents. Prior studies have demonstrated that VPA animals are impaired on executive function tasks, paralleling results in humans with ASD. Here, VPA adolescent female rats were impaired on a set-shifting task and had enlarged frontal cortices compared to control females. The deficits observed in the VPA female rats mirrors results in females with ASD. In addition, adolescent VPA females with enlarged frontal cortices performed the worst across the entire task. These brain changes in adolescence are also found in adolescent humans with ASD. These novel findings highlight the importance of studying the brain at different developmental stages.

Structural and functional organization of the midline and intralaminar nuclei of the thalamus

The midline and intralaminar nuclei of the thalamus form a major part of the "limbic thalamus;" that is, thalamic structures anatomically and functionally linked with the limbic forebrain. The midline nuclei consist of the paraventricular (PV) and paratenial nuclei, dorsally and the rhomboid and nucleus reuniens (RE), ventrally. The rostral intralaminar nuclei (ILt) consist of the central medial (CM), paracentral (PC) and central lateral (CL) nuclei. We presently concentrate on RE, PV, CM and CL nuclei of the thalamus. The nucleus reuniens receives a diverse array of input from limbic-related sites, and predominantly projects to the hippocampus and to "limbic" cortices. The RE participates in various cognitive functions including spatial working memory, executive functions (attention, behavioral flexibility) and affect/fear behavior. The PV receives significant limbic-related afferents, particularly the hypothalamus, and mainly distributes to "affective" structures of the forebrain including the bed nucleus of stria terminalis, nucleus accumbens and the amygdala. Accordingly, PV serves a critical role in "motivated behaviors" such as arousal, feeding/consummatory behavior and drug addiction. The rostral ILt receives both limbic and sensorimotor-related input and distributes widely over limbic and motor regions of the frontal cortex-and throughout the dorsal striatum. The intralaminar thalamus is critical for maintaining consciousness and directly participates in various sensorimotor functions (visuospatial or reaction time tasks) and cognitive tasks involving striatal-cortical interactions. As discussed herein, while each of the midline and intralaminar nuclei are anatomically and functionally distinct, they collectively serve a vital role in several affective, cognitive and executive behaviors - as major components of a brainstem-diencephalic-thalamocortical circuitry.

Mediodorsal Thalamus Is Critical for Updating during Extradimensional Shifts But Not Reversals in the Attentional Set-Shifting Task

Cognitive flexibility, attributed to frontal cortex, is vital for navigating the complexities of everyday life. The mediodorsal thalamus (MD), interconnected to frontal cortex, may influence cognitive flexibility. Here, male rats performed an attentional set-shifting task measuring intradimensional (ID) and extradimensional (ED) shifts in sensory discriminations. MD lesion rats needed more trials to learn the rewarded sensory dimension. However, once the choice response strategy was established, learning further two-choice discriminations in the same sensory dimension, and reversals of the reward contingencies in the same dimension, were unimpaired. Critically though, MD lesion rats were impaired during the ED shift, when they must rapidly update the optimal choice response strategy. Behavioral analyses showed MD lesion rats had significantly reduced correct within-trial second choice responses. This evidence shows that transfer of information via the MD is critical when rapid within-trial updates in established choice response strategies are required after a rule change.

Heavy Ion Minibeam Therapy: Side Effects in Normal Brain

The purpose of this work was to investigate whether minibeam therapy with heavy ions might offer improvements of the therapeutic ratio for the treatment of human brain cancers. To assess neurotoxicity, we irradiated normal juvenile rats using 120 MeV lithium-7 ions at an absorbed integral dose of 20 Gy. Beams were configured either as a solid parallel circular beam or as an array of planar parallel minibeams having 300-micron width and 1-mm center-to-center spacing within a circular array. We followed animals for 6 months after treatment and utilized behavioral testing and immunohistochemical studies to investigate the resulting cognitive impairment and chronic pathologic changes. We found both solid-beam therapy and minibeam therapy to result in cognitive impairment compared with sham controls, with no apparent reduction in neurotoxicity using heavy ion minibeams instead of solid beams under the conditions of this study.

Prefrontal cortex VAMP1 gene network moderates the effect of the early environment on cognitive flexibility in children

During development, genetic and environmental factors interact to modify specific phenotypes. Both in humans and in animal models, early adversities influence cognitive flexibility, an important brain function related to behavioral adaptation to variations in the environment. Abnormalities in cognitive functions are related to changes in synaptic connectivity in the prefrontal cortex (PFC), and altered levels of synaptic proteins. We investigated if individual variations in the expression of a network of genes co-expressed with the synaptic protein VAMP1 in the prefrontal cortex moderate the effect of early environmental quality on the performance of children in cognitive flexibility tasks. Genes overexpressed in early childhood and co-expressed with the VAMP1 gene in the PFC were selected for study. SNPs from these genes (post-clumping) were compiled in an expression-based polygenic score (PFC-ePRS-VAMP1). We evaluated cognitive performance of the 4 years-old children in two cohorts using similar cognitive flexibility tasks. In the first cohort (MAVAN) we utilized two CANTAB tasks: (a) the Intra-/Extra-dimensional Set Shift (IED) task, and (b) the Spatial Working Memory (SWM) task. In the second cohort, GUSTO, we used the Dimensional Change Card Sort (DCCS) task. The results show that in 4 years-old children, the PFC-ePRS-VAMP1 network moderates responsiveness to the effects of early adversities on the performance in attentional flexibility tests. The same result was observed for a spatial working memory task. Compared to attentional flexibility, reversal learning showed opposite effects of the environment, as moderated by the ePRS. A parallel ICA analysis was performed to identify relationships between whole-brain voxel based gray matter density and SNPs that comprise the PFC-ePRS-VAMP1. The early environment predicts differences in gray matter content in regions such as prefrontal and temporal cortices, significantly associated with a genetic component related to Wnt signaling pathways. Our data suggest that a network of genes co-expressed with VAMP1 in the PFC moderates the influence of early environment on cognitive function in children.

Increased volumes of lobule VI in a valproic acid model of autism are associated with worse set-shifting performance in male Long-Evan rats

Autism spectrum disorder (ASD) is a neurodevelopmental disorder with a skewed sex-based diagnostic ratio. While males are at a higher risk for ASD, it is critical to understand the neurobiology of the disorder to develop better treatments for both males and females. Our prior work has demonstrated that VPA (valproic acid) treated offspring had impaired performance on an attentional set-shifting task. The current study used MRI and regions of interest analyses to measure the volumes of cerebellar subregions in VPA and controls rats that had participated in the attentional set-shifting task. VPA males had significantly more volume in lobule VI compared to male controls. VPA female rats had significantly less volume in lobules I, IV and X compared to female controls. In addition, it was revealed that decreases in volume for VPA females was associated with worse performance. Males with increases in lobule VI were also impaired on the set-shifting task. Similar volumetric differences within the cerebellum have been observed in humans with ASD, which suggests that the VPA model is capturing some of the same brain changes observed in humans with ASD, and that these changes in volume may be impacting cognition.

The orbitofrontal cortex is necessary for learning to ignore

Animals learn not only what is potentially useful but also what is meaningless and should be disregarded. How this is accomplished is a key but seldom explored question in psychology and neuroscience. Learning to ignore irrelevant cues is evident in latent inhibition-the ubiquitous phenomenon where presenting a cue several times without consequences leads to retardation of subsequent conditioning to that cue.1,2 Does learning to ignore these cues, because they predict nothing, involve the same neural circuits that are critical to learning to make predictions about other "real world" impending events? If so, the orbitofrontal cortex (OFC), as a key node in such networks, should be important.3 Specifically, the OFC has been hypothesized to participate in the recognition of hidden task states, which are not directly signaled by explicit outcomes.4 Evaluating its involvement in pre-exposure learning during latent inhibition would be an acid test for this hypothesis. Here, we report that selective chemogenetic inactivation of rat orbitofrontal cortex principal neurons during stimulus pre-exposure markedly reduces latent inhibition in subsequent conditioning. Inactivation only during pre-exposure ensured that the observed effects were due to an impact on the acquisition of information prior to its use in any sort of behavior, i.e., during latent learning. Further behavioral tests confirmed this, showing that the impact of OFC inactivation during pre-exposure was limited to the latent inhibition effect. These results demonstrate that the OFC is important for latent learning and the formation of associations even in the absence of explicit outcomes.

The anterior thalamic nuclei and cognition: A role beyond space?

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Anterior thalamic nuclei important for specific classes of temporal discriminations.

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Anterior thalamic nuclei required for hippocampal-dependent contextual processes.

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Critical role for anterior thalamic nuclei in selective attention.

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Significance of anterior thalamic – anterior cingulate interactions.

The anterior thalamic nuclei are a vital node within hippocampal-diencephalic-cingulate circuits that support spatial learning and memory. Reflecting this interconnectivity, the overwhelming focus of research into the cognitive functions of the anterior thalamic nuclei has been spatial processing. However, there is increasing evidence that the functions of the anterior thalamic nuclei extend beyond the spatial realm. This work has highlighted how these nuclei are required for certain classes of temporal discrimination as well as their importance for processing other contextual information; revealing parallels with the non-spatial functions of the hippocampal formation. Yet further work has shown how the anterior thalamic nuclei may be important for other forms of non-spatial learning, including a critical role for these nuclei in attentional mechanisms. This evidence signals the need to reconsider the functions of the anterior thalamic within the framework of their wider connections with sites including the anterior cingulate cortex that subserve non-spatial functions.

Chemogenetics Reveal an Anterior Cingulate-Thalamic Pathway for Attending to Task-Relevant Information

In a changing environment, organisms need to decide when to select items that resemble previously rewarded stimuli and when it is best to switch to other stimulus types. Here, we used chemogenetic techniques to provide causal evidence that activity in the rodent anterior cingulate cortex and its efferents to the anterior thalamic nuclei modulate the ability to attend to reliable predictors of important outcomes. Rats completed an attentional set-shifting paradigm that first measures the ability to master serial discriminations involving a constant stimulus dimension that reliably predicts reinforcement (intradimensional-shift), followed by the ability to shift attention to a previously irrelevant class of stimuli when reinforcement contingencies change (extradimensional-shift). Chemogenetic disruption of the anterior cingulate cortex (Experiment 1) as well as selective disruption of anterior cingulate efferents to the anterior thalamic nuclei (Experiment 2) impaired intradimensional learning but facilitated 2 sets of extradimensional-shifts. This pattern of results signals the loss of a corticothalamic system for cognitive control that preferentially processes stimuli resembling those previously associated with reward. Previous studies highlight a separate medial prefrontal system that promotes the converse pattern, that is, switching to hitherto inconsistent predictors of reward when contingencies change. Competition between these 2 systems regulates cognitive flexibility and choice.

Measuring executive function in sheep (Ovis aries) using visual stimuli in a semi-automated operant system

BACKGROUND

Cognitive impairment is a distinguishing feature of many neurodegenerative diseases. The intra-dimensional (ID) extra-dimensional (ED) attentional set shift task is part of a clinical battery of tests used to evaluate executive function in Huntington's and Alzheimer's disease patients. The IDED task, however, has not translated well to pre-clinical rodent models of neurological disease.

NEW METHOD

The ability to perform executive tasks coupled with a long lifespan makes sheep (Ovis aries) an ideal species for modelling cognitive decline in progressive neurodegenerative conditions. We describe the methodology for testing the performance of sheep in the IDED task using a semi-automated system in which visual stimuli are presented as coloured letters on computer screens.

RESULTS

During each stage of IDED testing, all sheep (n = 12) learned successfully to discriminate between different colours and letters. Sheep were quick to learn the rules of acquisition at each stage. They required significantly more trials to reach criterion (p < 0.05) and made more errors (p < 0.05) following stimulus reversal, with the exception of the ED shift (p > 0.05).

COMPARISON WITH EXISTING METHOD(S)

Previous research shows that sheep can perform IDED set shifting in a walk-through maze using solid objects with two changeable dimensions (colour and shape) as the stimuli. Presenting the stimuli on computer screens provides better validity, greater task flexibility and higher throughput than the walk-through maze.

CONCLUSION

All sheep completed each stage of the task, with a range of abilities expected in an outbred population. The IDED task described is ideally suited as a quantifiable and clinically translatable measure of executive function in sheep.

Choline Plus Working Memory Training Improves Prenatal Alcohol-Induced Deficits in Cognitive Flexibility and Functional Connectivity in Adulthood in Rats

Fetal alcohol spectrum disorder (FASD) is the leading known cause of intellectual disability, and may manifest as deficits in cognitive function, including working memory. Working memory capacity and accuracy increases during adolescence when neurons in the prefrontal cortex undergo refinement. Rats exposed to low doses of ethanol prenatally show deficits in working memory during adolescence, and in cognitive flexibility in young adulthood. The cholinergic system plays a crucial role in learning and memory processes. Here we report that the combination of choline and training on a working memory task during adolescence significantly improved cognitive flexibility (performance on an attentional set shifting task) in young adulthood: 92% of all females and 81% of control males formed an attentional set, but only 36% of ethanol-exposed males did. Resting state functional magnetic resonance imaging showed that functional connectivity among brain regions was different between the sexes, and was altered by prenatal ethanol exposure and by choline + training. Connectivity, particularly between prefrontal cortex and striatum, was also different in males that formed a set compared with those that did not. Together, these findings indicate that prenatal exposure to low doses of ethanol has persistent effects on brain functional connectivity and behavior, that these effects are sex-dependent, and that an adolescent intervention could mitigate some of the effects of prenatal ethanol exposure.

Valproic acid treated female Long-Evans rats are impaired on attentional set-shifting

Autism spectrum disorder (ASD), is a neurodevelopmental disorder characterized by social deficits, communication impairments, restrictive behaviors, and cognitive flexibility deficits. The valproic acid (VPA) model of autism has been widely used to examine changes in rodent behavior and neurobiology to better understand ASD. This study examined social and anxiety behavior as well as cognitive flexibility in VPA and control offspring. Results for social behavior were consistent with prior studies showing reduced sociability in VPA rats and increased self-grooming, which may be viewed as a repetitive behavior. VPA rats also had deficits in performing the set-shifting task, with female VPA rats demonstrating greater impairment compared to female control rats and male VPA rats. These results support the hypothesis that females diagnosed with ASD may suffer from different symptoms and present a unique behavioral profile compared to males with ASD. Female VPA rats were also less likely to form an attentional set; offering evidence that the VPA model of autism is encompassing executive function deficits similar to those observed in humans with ASD.

Chemogenetic Inactivation of Orbitofrontal Cortex Decreases Cue-induced Reinstatement of Ethanol and Sucrose Seeking in Male and Female Wistar Rats

BACKGROUND

The orbitofrontal cortex (OFC) encodes internal representations of outcomes and subjective value to facilitate flexible reward seeking. OFC activation is associated with drug seeking in both human subjects and animal models. OFC plays a role in alcohol use, but studies in animal models have produced conflicting results with some showing decreased seeking after OFC inactivation but others showing increased seeking or no changes. In part, this may be due to the different measures of alcohol seeking used (e.g., homecage drinking vs. operant seeking).

METHODS

We characterized the impact of transient inactivation of OFC (primarily lateral and, to a lesser extent, ventral subregions) using inhibitory hM4Di designer receptors exclusively activated by designer drugs (DREADDs). OFC neurons were transiently inhibited during 10% and 20% alcohol (ethanol, EtOH) and sucrose homecage consumption, fixed ratio (FR1) operant self-administration, and cue-induced reinstatement of either 10% EtOH or sucrose in male and female rats.

RESULTS

OFC inactivation did not affect sucrose or EtOH consumption in the homecage, nor did it influence seeking or consumption under FR1 operant conditions. In contrast, OFC inactivation suppressed cued-induced reinstatement for both EtOH and sucrose in both male and female rats.

CONCLUSIONS

Our results are aligned with previous work indicating a selective suppressive effect of OFC inactivation on reinstatement for alcohol and other drugs of abuse. They extend these findings to demonstrate no effect on homecage consumption or FR1 seeking as well as showing an impact of sucrose reinstatement. These data indicate that OFC plays a uniquely important role when reward seeking is driven by associations between external stimuli and internal representations of reward value, both for natural and drug rewards. They further implicate the OFC as a key structure driving relapse-associated seeking and potentially contributing to alcohol use disorder and other diseases of compulsive reward seeking.

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.

Neural Correlates of Strategy Switching in the Macaque Orbital Prefrontal Cortex

We can adapt flexibly to environment changes and search for the most appropriate rule to a context. The orbital prefrontal cortex (PFo) has been associated with decision making, rule generation and maintenance, and more generally has been considered important for behavioral flexibility. To better understand the neural mechanisms underlying the flexible behavior, we studied the ability to generate a switching signal in monkey PFo when a strategy is changed. In the strategy task, we used a visual cue to instruct two male rhesus monkeys either to repeat their most recent choice (i.e., stay strategy) or to change it (i.e., shift strategy). To identify the strategy switching-related signal, we compared nonswitch and switch trials, which cued the same or a different strategy from the previous trial, respectively. We found that the switching-related signal emerged during the cue presentation and it was combined with the strategy signal in a subpopulation of cells. Moreover, the error analysis showed that the activity of the switch-related cells reflected whether the monkeys erroneously switched or not the strategy, rather than what was required for that trial. The function of the switching signal could be to prompt the use of different strategies when older strategies are no longer appropriate, conferring the ability to adapt flexibly to environmental changes. In our task, the switching signal might contribute to the implementation of the strategy cued, overcoming potential interference effects from the strategy previously cued. Our results support the idea that ascribes to PFo an important role for behavioral flexibility.SIGNIFICANCE STATEMENT We can flexibly adapt our behavior to a changing environment. One of the prefrontal areas traditionally associated with the ability to adapt to new contingencies is the orbital prefrontal cortex (PFo). We analyzed the switching related activity using a strategy task in which two rhesus monkeys were instructed by a visual cue either to repeat or change their most recent choice, respectively using a stay or a shift strategy. We found that PFo neurons were modulated by the strategy switching signal, pointing to the importance of PFo in behavioral flexibility by generating control over the switching of strategies.

Activity in orbitofrontal neuronal ensembles reflects inhibitory control

Stopping, or inhibition, is a form of self-control that is a core element of flexible and adaptive behavior. Its neural origins remain unclear. Some views hold that inhibition decisions reflect the aggregation of widespread and diverse pieces of information, including information arising in ostensible core reward regions (i.e., outside the canonical executive system). We recorded activity of single neurons in the orbitofrontal cortex (OFC) of macaques, a region associated with economic decisions, and whose role in inhibition is debated. Subjects performed a classic inhibition task known as the stop signal task. Ensemble decoding analyses reveal a clear firing rate pattern that distinguishes successful from failed inhibition and that begins after the stop signal and before the stop signal reaction time (SSRT). We also found a different and orthogonal ensemble pattern that distinguishes successful from failed stopping before the beginning of the trial. These signals were distinct from, and orthogonal to, value encoding, which was also observed in these neurons. The timing of the early and late signals was, respectively, consistent with the idea that neuronal activity in OFC encodes inhibition both proactively and reactively.

The effects of histone deacetylase inhibitors on the attentional set-shifting task performance of alcohol-dependent rats

OBJECTIVES

Alcohol dependence causes extensive damage to the central nervous system, resulting in impaired brain structure and behavioral changes. Moreover, histone deacetylase (HDAC) inhibitors restrain the activity of HDAC and cause increased histone acetylation, which may be related to alcohol dependence.

METHODS

Ethanol dependence was modelled in animals by persistent alcohol exposure and tested in the conditioned place preference (CPP) paradigm. To induce CPP, the alcohol-treated rats were given orally gradient concentration (3%, 6%, and 9% v/v) alcohol administration for 20 consecutive days. The sodium butyrate (NaB)-treated rats were injected daily. Cognitive flexibility was evaluated using an attentional set-shifting task (ASST) in which the rats performed a series of seven consecutive discriminations after the final CPP paradigm.

RESULTS

Ethanol administration induced alcohol dependence behaviors, with more time spent in the ethanol-paired compartment. Compared with the CPP scores of the control group, the scores of the ethanol- and NaB-treated groups were significantly higher. In the ASST, alcohol-treated rats had significantly increased number of trials to reach criteria (TTC) in most phases, higher error rate, and lower cognitive levels compared to the control group. Moreover, the present findings demonstrated that NaB combined with ethanol caused cognitive deficits as the result of an increased number of TTC during the ASST.

CONCLUSIONS

The attentional/cognitive flexibility of the prefrontal cortex of alcohol-dependent rats was damaged and the NaB administration procedure itself did not produce cognitive deficits, but instead exacerbated cognitive impairment in alcohol-dependent rats.

An Integrated Model of Action Selection: Distinct Modes of Cortical Control of Striatal Decision Making

Making decisions in environments with few choice options is easy. We select the action that results in the most valued outcome. Making decisions in more complex environments, where the same action can produce different outcomes in different conditions, is much harder. In such circumstances, we propose that accurate action selection relies on top-down control from the prelimbic and orbitofrontal cortices over striatal activity through distinct thalamostriatal circuits. We suggest that the prelimbic cortex exerts direct influence over medium spiny neurons in the dorsomedial striatum to represent the state space relevant to the current environment. Conversely, the orbitofrontal cortex is argued to track a subject's position within that state space, likely through modulation of cholinergic interneurons.

Behavior Model for Assessing Decline in Executive Function During Aging and Neurodegenerative Diseases

Executive dysfunction is a characteristic of several psychiatric and neurodegenerative diseases. Interestingly, executive function, which is mediated by the prefrontal cortex (PFC), commonly declines during aging. The attentional set-shifting task (AST) is commonly and extensively used to assess executive function in rodents, primates, and humans. When properly employed, this task can behaviorally assess attention, response inhibition, and cognitive flexibility. The following section uses research on age-related decline in executive function to demonstrate the methods employed and highlight areas that can confound a study if not employed properly.

The role of the orbitofrontal cortex in alcohol use, abuse, and dependence

One of the major functions of the orbitofrontal cortex (OFC) is to promote flexible motivated behavior. It is no surprise, therefore, that recent work has demonstrated a prominent impact of chronic drug use on the OFC and a potential role for OFC disruption in drug abuse and addiction. Among drugs of abuse, the use of alcohol is particularly salient with respect to OFC function. Although a number of studies in humans have implicated OFC dysregulation in alcohol use disorders, animal models investigating the association between OFC and alcohol use are only beginning to be developed, and there is still a great deal to be revealed. The goal of this review is to consider what is currently known regarding the role of the OFC in alcohol use and dependence. I will first provide a brief, general overview of current views of OFC function and its contributions to drug seeking and addiction. I will then discuss research to date related to the OFC and alcohol use, both in human clinical populations and in non-human models. Finally I will consider issues and strategies to guide future study that may identify this brain region as a key player in the transition from moderated to problematic alcohol use and dependence.

Indices of comparative cognition: assessing animal models of human brain function

Understanding the cognitive capacities of animals is important, because (a) several animal models of human neurodegenerative disease are considered poor representatives of the human equivalent and (b) cognitive capacities may provide insight into alternative animal models. We used a three-stage process of cognitive and neuroanatomical comparison (using sheep as an example) to assess the appropriateness of a species to model human brain function. First, a cognitive task was defined via a reinforcement-learning algorithm where values/constants in the algorithm were taken as indirect measures of neurophysiological attributes. Second, cognitive data (values/constants) were generated for the example species (sheep) and compared to other species. Third, cognitive data were compared with neuroanatomical metrics for each species (endocranial volume, gyrification index, encephalisation quotient, and number of cortical neurons). Four breeds of sheep (n = 15/sheep) were tested using the two-choice discrimination-reversal task. The 'reversal index' was used as a measure of constants within the learning algorithm. Reversal index data ranked sheep as third in a table of species that included primates, dogs, and pigs. Across all species, number of cortical neurons correlated strongest against the reversal index (r2 = 0.66, p = 0.0075) followed by encephalization quotient (r2 = 0.42, p = 0.03), endocranial volume (r2 = 0.30, p = 0.08), and gyrification index (r2 = 0.16, p = 0.23). Sheep have a high predicted level of cognitive capacity and are thus a valid alternative model for neurodegenerative research. Using learning algorithms within cognitive tasks increases the resolution of methods of comparative cognition and can help to identify the most relevant species to model human brain function and dysfunction.

Do the rat anterior thalamic nuclei contribute to behavioural flexibility?

The rodent anterior thalamic nuclei (ATN) are vital for spatial memory. A consideration of their extensive frontal connections suggests that these nuclei may also subserve non-spatial functions. The current experiments explored the importance of the ATN for different aspects of behavioural flexibility, including their contribution to tasks typically associated with frontal cortex. In Experiment 1, rats with ATN lesions were tested on a series of response and visual discriminations in an operant box and, subsequently, in a water tank. The tasks included assessments of reversal learning as well switches between each discrimination dimension. Results revealed a mild and transient deficit on the operant task that was not specific to any stage of the procedure. In the water tank, the lesion animals were impaired on the reversal of a spatial discrimination but did not differ from controls on any other measure. Experiment 2 examined the impact of ATN damage on a rodent analogue of the 'Stroop', which assesses response choice during stimulus conflict. The lesion animals successfully acquired this task and were able to use contextual information to disambiguate conflicting cue information. However, responding during the initial presentation of conflicting cue information was affected by the lesion. Taken together, these results suggest that the ATN are not required for aspects of behavioural flexibility (discrimination learning, reversals or high-order switches) typically associated with the rat medial prefrontal cortex. The results from Experiment 2 suggest that the non-spatial functions of the ATN may be more aligned with those of the anterior cingulate cortex.

Prefrontal cortex dysfunction in hypoxic-ischaemic encephalopathy contributes to executive function impairments in rats: Potential contribution for attention-deficit/hyperactivity disorder

OBJECTIVES

The attention-deficit/hyperactivity disorder (ADHD) compromises the quality of life of individuals including adaptation to the social environment. ADHD aetiology includes perinatal conditions such as hypoxic-ischaemic events; preclinical studies have demonstrated attentional deficits and impulsive-hyperactive outcomes after neonatal hypoxic and/or ischaemic intervention, but data are missing to understand this relationship. Thus, the aim of this study was to evaluate executive function (EF) and impulsivity, and tissue integrity and dopaminergic function in the prefrontal cortex (PFC) of rats submitted to hypoxia-ischaemia (HI).

METHODS

At postnatal day (PND) 7, male Wistar rats were divided into control (n = 10) and HI groups (n = 11) and the HI procedure was conducted. At PND60, the animals were tested in the attentional set-shifting (ASS) task to EF and in the tolerance to delay of reward for assessment of impulsivity. After, morphological analysis and the dopaminergic system were evaluated in the PFC.

RESULTS

Animals subjected to HI had impairments in EF evidenced by a behavioural inflexibility that was correlated to PFC atrophy. Moreover, HI animals presented reduced D2 receptors in the ipsilateral side of ischaemia in the PFC.

CONCLUSIONS

Animals submitted to HI presented impaired EF associated with tissue atrophy and dopaminergic disturbance in the PFC.

Animal Learning in a Multidimensional Discrimination Task as Explained by Dimension-Specific Allocation of Attention

Reinforcement learning describes the process by which during a series of trial-and-error attempts, actions that culminate in reward are reinforced, becoming more likely to be chosen in similar circumstances. When decisions are based on sensory stimuli, an association is formed between the stimulus, the action and the reward. Computational, behavioral and neurobiological accounts of this process successfully explain simple learning of stimuli that differ in one aspect, or along a single stimulus dimension. However, when stimuli may vary across several dimensions, identifying which features are relevant for the reward is not trivial, and the underlying cognitive process is poorly understood. To study this we adapted an intra-dimensional/ extra-dimensional set-shifting paradigm to train rats on a multi-sensory discrimination task. In our setup, stimuli of different modalities (spatial, olfactory and visual) are combined into complex cues and manipulated independently. In each set, only a single stimulus dimension is relevant for reward. To distinguish between learning and decision-making we suggest a weighted attention model (WAM). Our model learns by assigning a separate learning rule for the values of features of each dimension (e.g., for each color), reinforced after every experience. Decisions are made by comparing weighted averages of the learnt values, factored by dimension specific weights. Based on the observed behavior of the rats we estimated the parameters of the WAM and demonstrated that it outperforms an alternative model, in which a learnt value is assigned to each combination of features. Estimated decision weights of the WAM reveal an experience-based bias in learning. In the first experimental set the weights associated with all dimensions were similar. The extra-dimensional shift rendered this dimension irrelevant. However, its decision weight remained high for the early learning stage in this last set, providing an explanation for the poor performance of the animals. Thus, estimated weights can be viewed as a possible way to quantify the experience-based bias.

Assessment of intradimensional/extradimensional attentional set-shifting in rats

The rat intradimensional/extradimensional (ID/ED) task, first described by Birrell and Brown 18 years ago, has become the predominant means by which attentional set-shifting is investigated in rodents: the use of rats in the task has been described in over 135 publications by researchers from nearly 90 universities and pharmaceutical companies. There is variation in the protocols used by different groups, including differences in apparatus, stimuli (both stimulus dimensions and exemplars within), and also the methodology. Nevertheless, most of these variations seem to be of little consequence: there is remarkable similarity in the profile of published data, with consistency of learning rates and in the size and reliability of the set-shifting and reversal 'costs'. However, we suspect that there may be inconsistent data that is unpublished or perhaps 'failed experiments' that may have been caused by unintended deviations from effective protocols. The purpose of this review is to describe our approach and the rationale behind certain aspects of the protocol, including common pitfalls that are encountered when establishing an effective local protocol.

Functional Heterogeneity within Rat Orbitofrontal Cortex in Reward Learning and Decision Making

Rat orbitofrontal cortex (OFC) is located in the dorsal bank of the rhinal sulcus, and is divided into the medial orbital area, ventral orbital area, ventrolateral orbital area, lateral orbital area, dorsolateral orbital area, and agranular insular areas. Over the past 20 years, there has been a marked increase in the number of publications focused on the functions of rat OFC. While collectively this extensive body of work has provided great insight into the functions of OFC, leading to theoretical and computational models of its functions, one issue that has emerged relates to what is defined as OFC because targeting of this region can be quite variable between studies of appetitive behavior, even within the same species. Also apparent is that there is an oversampling and undersampling of certain subregions of rat OFC for study, and this will be demonstrated here. The intent of the Viewpoint is to summarize studies in rat OFC, given the diversity of what groups refer to as "OFC," and to integrate these with the findings of recent anatomical studies. The primary aim is to help discern functions in reward learning and decision-making, clearing the course for future empirical work.

Control without Controllers: Toward a Distributed Neuroscience of Executive Control

Executive control refers to the regulation of cognition and behavior by mental processes and is a hallmark of higher cognition. Most approaches to understanding its mechanisms begin with the assumption that our brains have anatomically segregated and functionally specialized control modules. The modular approach is intuitive: Control is conceptually distinct from basic mental processing, so an organization that reifies that distinction makes sense. An alternative approach sees executive control as self-organizing principles of a distributed organization. In distributed systems, control and controlled processes are colocalized within large numbers of dispersed computational agents. Control then is often an emergent consequence of simple rules governing the interaction between agents. Because these systems are unfamiliar and unintuitive, here we review several well-understood examples of distributed control systems, group living insects and social animals, and emphasize their parallels with neural systems. We then reexamine the cognitive neuroscience literature on executive control for evidence that its neural control systems may be distributed.

Choline and Working Memory Training Improve Cognitive Deficits Caused by Prenatal Exposure to Ethanol

Prenatal ethanol exposure is associated with deficits in executive function such as working memory, reversal learning and attentional set shifting in humans and animals. These behaviors are dependent on normal structure and function in cholinergic brain regions. Supplementation with choline can improve many behaviors in rodent models of fetal alcohol spectrum disorders and also improves working memory function in normal rats. We tested the hypothesis that supplementation with choline in the postnatal period will improve working memory during adolescence in normal and ethanol-exposed animals, and that working memory engagement during adolescence will transfer to other cognitive domains and have lasting effects on executive function in adulthood. Male and female offspring of rats fed an ethanol-containing liquid diet (ET; 3% v/v) or control dams given a non-ethanol liquid diet (CT) were injected with choline (Cho; 100 mg/kg) or saline (Sal) once per day from postnatal day (P) 16–P30. Animals were trained/tested on a working memory test in adolescence and then underwent attentional set shifting and reversal learning in young adulthood. In adolescence, ET rats required more training to reach criterion than CT-Sal. Choline improved working memory performance for both CT and ET animals. In young adulthood, ET animals also performed poorly on the set shifting and reversal tasks. Deficits were more robust in ET male rats than female ET rats, but Cho improved performance in both sexes. ET male rats given a combination of Cho and working memory training in adolescence required significantly fewer trials to achieve criterion than any other ET group, suggesting that early interventions can cause a persistent improvement.

The rat retrosplenial cortex as a link for frontal functions: A lesion analysis

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Retrosplenial cortex lesions do not reproduce the pattern of effects of medial frontal damage.

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Retrosplenial cortex lesions spare tests of behavioural flexibility.

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Effort-based decision making does not require the retrosplenial cortex.

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Reveals specific conditions when nonspatial tasks engage retrosplenial cortex.

Cohorts of rats with excitotoxic retrosplenial cortex lesions were tested on four behavioural tasks sensitive to dysfunctions in prelimbic cortex, anterior cingulate cortex, or both. In this way the study tested whether retrosplenial cortex has nonspatial functions that reflect its anatomical interactions with these frontal cortical areas. In Experiment 1, retrosplenial cortex lesions had no apparent effect on a set-shifting digging task that taxed intradimensional and extradimensional attention, as well as reversal learning. Likewise, retrosplenial cortex lesions did not impair a strategy shift task in an automated chamber, which involved switching from visual-based to response-based discriminations and, again, included a reversal (Experiment 2). Indeed, there was evidence that the retrosplenial lesions aided the initial switch to response-based selection. No lesion deficit was found on an automated cost-benefit task that pitted size of reward against effort to achieve that reward (Experiment 3). Finally, while retrosplenial cortex lesions affected matching-to-place task in a T-maze, the profile of deficits differed from that associated with prelimbic cortex damage (Experiment 4). When the task was switched to a nonmatching design, retrosplenial cortex lesions had no apparent effect on performance. The results from the four experiments show that many frontal tasks do not require the retrosplenial cortex, highlighting the specificity of their functional interactions. The results show how retrosplenial cortex lesions spare those learning tasks in which there is no mismatch between the internal and external representations used to guide behavioural choice. In addition, these experiments further highlight the importance of the retrosplenial cortex in solving tasks with a spatial component.

Effects of lesions of the subthalamic nucleus/zona incerta area and dorsomedial striatum on attentional set-shifting in the rat

Patients with Parkinson's disease (PD) show cognitive impairments, including difficulty in shifting attention between perceptual dimensions of complex stimuli. Inactivation of the subthalamic nucleus (STN) has been shown to be effective in ameliorating the motor abnormalities associated with striatal dopamine (DA) depletion, but it is possible that STN inactivation might result in additional, perhaps attentional, deficits. This study examined the effects of: DA depletion from the dorsomedial striatum (DMS); lesions of the STN area; and the effects of the two lesions together, on the ability to shift attentional set in the rat. In a single session, rats performed the intradimensional/extradimensional (ID/ED) test of attentional set-shifting. This comprises a series of seven, two-choice discriminations, including acquisitions of novel discriminations in which the relevant stimulus is either in the currently attended dimension (ID) or the currently unattended dimension (ED shift) and reversals (REVs) following each acquisition stage. Bilateral lesions were made by injection of 6-hydroxydopamine (6-OHDA) into the DMS, resulting in a selective impairment in reversal learning. Large bilateral ibotenic acid lesions centered on the STN resulted in an increase in trials to criterion in the initial stages, but learning rate improved within the session. There was no evidence of a 'cost' of set-shifting - the ED stage was completed in fewer trials than the ID stage - and neither was there a cost of reversal learning. Strikingly, combined lesions of both regions did not resemble the effects of either lesion alone and resulted in no apparent deficits.

Neuronal responses support a role for orbitofrontal cortex in cognitive set reconfiguration

We are often faced with the need to abandon no-longer beneficial rules and adopt new ones. This process, known as cognitive set reconfiguration, is a hallmark of executive control. Although cognitive functions like reconfiguration are most often associated with dorsal prefrontal structures, recent evidence suggests that the orbitofrontal cortex (OFC) may play an important role as well. We recorded the activity of OFC neurons while rhesus macaques performed an analogue of the Wisconsin Card Sorting Task that involved a trial and error stage. The OFC neurons demonstrated two types of switch-related activity, an early (switch-away) signal and a late (switch-to) signal, when the new task set was established. We also found a pattern of match modulation: a significant change in activity for the stimulus that matched the current perceptual rule (and would therefore be selected). These results extend our understanding of the executive functions of the OFC. They also allow us to directly compare the OFC with the complementary datasets we previously collected in the ventral (VS) and dorsal (DS) striatum. Although both effects are observed in all three areas, the timing of responses aligns the OFC more closely with DS than with VS.

Lesions of the ventral midline thalamus produce deficits in reversal learning and attention on an odor texture set shifting task

The nucleus reuniens (RE) of the ventral midline thalamus is strongly reciprocally connected with the hippocampus (HF) and the medial prefrontal cortex (mPFC) and has been shown to mediate the transfer of information between these structures. It has become increasingly well established that RE serves a critical role in mnemonic tasks requiring the interaction of the HF and mPFC, but essentially not tasks relying solely on the HF. Very few studies have addressed the independent actions of RE on prefrontal executive functioning. The present report examined the effects of lesions of the ventral midline thalamus, including RE and the dorsally adjacent rhomboid nucleus (RH) in rats on attention and behavioral flexibility using the attentional set shifting task (AST). The task uses odor and tactile stimuli to test for attentional set formation, attentional set shifting, behavioral flexibility and reversal learning. By comparison with sham controls, lesioned rats were significantly impaired on reversal learning and intradimensional (ID) set shifting. Specifically, RE/RH lesioned rats were impaired on the first reversal stage of the task which required a change in response strategy to select a previously non-rewarded stimulus for reward. RE/RH lesioned rats also exhibited deficits in the ability to transfer or generalize rules of the task which requires making the same modality-based choices (e.g., odor vs. tactile) to different sets of stimuli in the ID stage of the task. These results demonstrate that in addition to its role in tasks dependent on HF-mPFC interactions, nucleus reuniens is also critically involved cognitive/executive functions associated with the medial prefrontal cortex. As such, the deficits in the AST task produced by RE/RH lesions suggest the ventral midline thalamus directly contributes to flexible goal directed behavior.

Reversal learning and experimenter-administered chronic intermittent ethanol exposure in male rats

RATIONALE

Chronic alcohol exposure is associated with impaired decision making skills, cognitive deficits, and poor performance on tasks requiring behavioral flexibility. Although oral routes of alcohol administration are commonly used to examine effects of alcohol on various behaviors in rodents, only a few investigations have used intragastric exposures to evaluate ethanol's effects on behavioral flexibility in the adult rat.

OBJECTIVES

The aim of the current series of experiments was to determine if behavioral flexibility impairments would be demonstrated across a variety of procedural factors, including route of administration [intraperitoneal injection (i.p.), intragastric gavage (i.g.)], ethanol dose (3-5 g/kg), number of daily exposures (once/day, twice/day), duration of exposure (2-6 weeks), or length of abstinence (5-7 days).

METHODS

Adult male Sprague-Dawley rats were exposed to chronic intermittent ethanol (CIE) or vehicle and evaluated for behavioral intoxication, blood ethanol concentrations (BEC), and performance on a reversal learning odor discrimination task.

RESULTS

While all rats displayed behavioral intoxication and elevated BECs, CIE i.p. rats had prolonged elevation in BECs and made the most errors during the reversal learning task. Unexpectedly, CIE i.g. exposures failed to produce deficits during reversal learning tasks regardless of ethanol dose, frequency/duration of exposure, or length of abstinence.

CONCLUSIONS

Behavioral flexibility deficits resulting from CIE i.p. exposures may be due to the severity and chronicity of alcohol intoxication. Elucidating the impact of ethanol on behavioral flexibility is critical for developing a better understanding of the behavioral consequences of chronic alcohol exposure.

Optogenetic silencing of locus coeruleus activity in mice impairs cognitive flexibility in an attentional set-shifting task

The locus coeruleus (LC) is the sole source of noradrenergic projections to the cortex and essential for attention-dependent cognitive processes. In this study we used unilateral optogenetic silencing of the LC in an attentional set-shifting task (ASST) to evaluate the influence of the LC on prefrontal cortex-dependent functions in mice. We expressed the halorhodopsin eNpHR 3.0 to reversibly silence LC activity during task performance, and found that silencing selectively impaired learning of those parts of the ASST that most strongly rely on cognitive flexibility. In particular, extra-dimensional set-shifting (EDS) and reversal learning was impaired, suggesting an involvement of the medial prefrontal cortex (mPFC) and the orbitofrontal cortex. In contrast, those parts of the task that are less dependent on cognitive flexibility, i.e., compound discrimination (CD) and the intra-dimensional shifts (IDS) were not affected. Furthermore, attentional set formation was unaffected by LC silencing. Our results therefore suggest a modulatory influence of the LC on cognitive flexibility, mediated by different frontal networks.

Interactions between chronic ethanol consumption and thiamine deficiency on neural plasticity, spatial memory, and cognitive flexibility

BACKGROUND

Many alcoholics display moderate to severe cognitive dysfunction accompanied by brain pathology. A factor confounded with prolonged heavy alcohol consumption is poor nutrition, and many alcoholics are thiamine deficient. Thus, thiamine deficiency (TD) has emerged as a key factor underlying alcohol-related brain damage (ARBD). TD in humans can lead to Wernicke Encephalitis that can progress into Wernicke-Korsakoff syndrome and these disorders have a high prevalence among alcoholics. Animal models are critical for determining the exact contributions of ethanol (EtOH)- and TD-induced neurotoxicity, as well as the interactions of those factors to brain and cognitive dysfunction.

METHODS

Adult rats were randomly assigned to 1 of 6 treatment conditions: chronic EtOH treatment (CET) where rats consumed a 20% v/v solution of EtOH over 6 months; severe pyrithiamine-induced TD (PTD-moderate acute stage); moderate PTD (PTD-early acute stage); moderate PTD followed by CET (PTD-CET); moderate PTD during CET (CET-PTD); and pair-fed (PF) control. After recovery from treatment, all rats were tested on spontaneous alternation and attentional set-shifting. After behavioral testing, brains were harvested for determination of mature brain-derived neurotrophic factor (BDNF) and thalamic pathology.

RESULTS

Moderate TD combined with CET, regardless of treatment order, produced significant impairments in spatial memory, cognitive flexibility, and reductions in brain plasticity as measured by BDNF levels in the frontal cortex and hippocampus. These alterations are greater than those seen in moderate TD alone, and the synergistic effects of moderate TD with CET lead to a unique cognitive profile. However, CET did not exacerbate thalamic pathology seen after moderate TD.

CONCLUSIONS

These data support the emerging theory that subclinical TD during chronic heavy alcohol consumption is critical for the development of significant cognitive impairment associated with ARBD.

Impairment of intradimensional shift in an attentional set-shifting task in rats with chronic bilateral common carotid artery occlusion

Studies of rats with chronic bilateral common carotid artery occlusion (BCCAo), an animal model for vascular dementia (VaD), have reported hippocampus-dependent memory impairment and associated neuropathologies. Patients with VaD also experience attentional shifting dysfunction. However, animal models of VaD have not been used to study attentional function. Therefore, the present study examined attentional function in rats with BCCAo, using attentional set-shifting task (ASST) that required rats to choose a food-baited pot from 2 possible pots. ASST included 6 consecutive sessions including simple discrimination, compound discrimination, intradimensional shifting, extradimensional shifting, and reversals. The BCCAo rats were significantly slower at learning the intradimensional set-shifting task compared to control rats. Previous studies have demonstrated that the cingulate cortex and medial prefrontal cortex are critical to intradimensional and extradimensional set-shifting, respectively. Additionally, inflammatory responses and neuronal dysfunction were observed in rats with chronic BCCAo. In addition, OX-6 positive microglia significantly increased in the forceps minor white matter of BCCAo rats, and glutamate decarboxylase signals co-localized with NeuN were reduced in the anterior cingulate cortex of BCCAo rats, compared to control rats. Impaired neuronal and GABAergic neuronal integrity in the anterior cingulate cortex, damage to white matter, and attentional impairments observed in BCCAo rats suggest dysfunction of brain structures that are associated with attentional impairments observed in patients with VaD.

Housing condition-related changes involved in reversal learning and its c-Fos associated activity in the prefrontal cortex

Our study examined how different housing conditions modulated the acquisition of a spatial reference memory task and also, a reversal task in the 4-radial arm water maze (4-RAWM). The animals were randomly assigned to standard or enriched cages, and, as a type of complementary stimulation along with the environmental enrichment (EE), a group of rats also ran 15 min/day in a Rotarod. Elevated-zero maze results allowed us to discard that our exercise training increased anxiety-related behaviors. 4-RAWM results revealed that the non-enriched group had a worse performance during the acquisition and also, during the first trial of each session with respect to the enriched groups. Regarding the reversal task, this group made more perseverative errors in the previous platform position. Interestingly, we hardly found differences between the two enriched groups (with and without exercise). We also analyzed how the reversal learning, depending on the previous housing condition, modulated the expression of c-Fos-positive nuclei in different subdivisions of the medial prefrontal cortex (cingulate (Cg), prelimbic (PL) and infralimbic (IL) cortices) and in the orbitofrontal (OF) cortex. The enriched groups had higher c-Fos expression in the Cg and OF cortices and lower in the IL cortex respect to the non-enriched animals. In the PL cortex, we did not find significant differences between the groups that performed the reversal task. Therefore, our short EE protocol improved the performance in a spatial memory and a reversal task, whereas the exercise training, combined with the EE, did not produce a greater benefit. This better performance seemed to be related with the specific pattern of c-Fos expression in brain regions involved in cognitive flexibility.

Orbitofrontal cortex mediates the differential impact of signaled-reward probability on discrimination accuracy

Orbitofrontal cortex (OFC) function is critical to decision making and behavior based on the value of expected outcomes. While some of the roles the OFC plays in value computations and behavior have been identified, the role of the OFC in modulating cognitive resources based on reward expectancy has not been explored. Here we assessed the involvement of OFC in the interaction between motivation and attention. We tested mice in a sustained-attention task in which explicitly signaling the probability of reward differentially modulates discrimination accuracy. Using pharmacogenetic methods, we generated mice in which neuronal activity in the OFC could be transiently and reversibly inhibited during performance of our signaled-probability task. We found that inhibiting OFC neuronal activity abolished the ability of reward-associated cues to differentially impact accuracy of sustained-attention performance. This failure to modulate attention occurred despite evidence that mice still processed the differential value of the reward-associated cues. These data indicate that OFC function is critical for the ability of a reward-related signal to impact other cognitive and decision-making processes and begin to delineate the neural circuitry involved in the interaction between motivation and attention.

A critical role for the anterior thalamus in directing attention to task-relevant stimuli

The prefrontal cortex mediates adaption to changing environmental contingencies. The anterior thalamic nuclei, which are closely interconnected with the prefrontal cortex, are important for rodent spatial memory, but their potential role in executive function has received scant attention. The current study examined whether the anterior thalamic nuclei are involved in attentional processes akin to those of prefrontal regions. Remarkably, the results repeatedly revealed attentional properties opposite to those of the prefrontal cortex. Two separate cohorts of rats with anterior thalamic lesions were tested on an attentional set-shifting paradigm that measures not only the ability of stimuli dimensions that reliably predict reinforcement to gain attention ("intradimensional shift"), but also their ability to shift attention to another stimulus dimension when contingencies change ("extradimensional shift"). In stark contrast to the effects of prefrontal damage, anterior thalamic lesions impaired intradimensional shifts but facilitated extradimensional shifts. Anterior thalamic lesion animals were slower to acquire discriminations based on the currently relevant stimulus dimension but acquired discriminations involving previously irrelevant stimulus dimensions more rapidly than controls. Subsequent tests revealed that the critical determinant of whether anterior thalamic lesions facilitate extradimensional shifts is the degree to which the stimulus dimension has been established as an unreliable predictor of reinforcement over preceding trials. This pattern of performance reveals that the anterior thalamic nuclei are vital for attending to those stimuli that are the best predictors of reward. In their absence, unreliable predictors of reward usurp attentional control.

The attentional set shifting task: a measure of cognitive flexibility in mice

Cognitive impairment, particularly involving dysfunction of circuitry within the prefrontal cortex (PFC), represents a core feature of many neuropsychiatric and neurodevelopmental disorders, including depression, post-traumatic stress disorder, schizophrenia and autism spectrum disorder. Deficits in cognitive function also represent the most difficult symptom domain to successfully treat, as serotonin reuptake inhibitors and tricyclic antidepressants have only modest effects. Functional neuroimaging studies and postmortem analysis of human brain tissue implicate the PFC as being a primary region of dysregulation in patients with these disorders. However, preclinical behavioral assays used to assess these deficits in mouse models which can be readily manipulated genetically and could provide the basis for studies of new treatment avenues have been underutilized. Here we describe the adaptation of a behavioral assay, the attentional set shifting task (AST), to be performed in mice to assess prefrontal cortex mediated cognitive deficits. The neural circuits underlying behavior during the AST are highly conserved across humans, nonhuman primates and rodents, providing excellent face, construct and predictive validity.

Mouse Models of Huntington's Disease

In this review, we explore the similarities and differences in the behavioural neurobiology found in the mouse models of Huntington's disease (HD) and the human disease state. The review is organised with a comparative focus on the functional domains of motor control, cognition and behavioural disturbance (akin to psychiatric disturbance in people) and how our knowledge of the underlying physiological changes that are manifest in the HD mouse lines correspond to those seen in the HD clinical population. The review is framed in terms of functional circuitry and neurotransmitter systems and how abnormalities in these systems impact on the behavioural readouts across the mouse lines and how these may correspond to the deficits observed in people. In addition, interpretational issues associated with the data from animal studies are discussed.