Perceptual attentional set-shifting is impaired in rats with neurotoxic lesions of posterior parietal cortex

A frontoparietal network for volitional control of gaze following

Gaze following is a major element of non-verbal communication and important for successful social interactions. Human gaze following is a fast and almost reflex-like behaviour, yet it can be volitionally controlled and suppressed to some extent if inappropriate or unnecessary, given the social context. In order to identify the neural basis of the cognitive control of gaze following, we carried out an event-related fMRI experiment, in which human subjects' eye movements were tracked while they were exposed to gaze cues in two distinct contexts: A baseline gaze following condition in which subjects were instructed to use gaze cues to shift their attention to a gazed-at spatial target and a control condition in which the subjects were required to ignore the gaze cue and instead to shift their attention to a distinct spatial target to be selected based on a colour mapping rule, requiring the suppression of gaze following. We could identify a suppression-related blood-oxygen-level-dependent (BOLD) response in a frontoparietal network comprising dorsolateral prefrontal cortex (dlPFC), orbitofrontal cortex (OFC), the anterior insula, precuneus, and posterior parietal cortex (PPC). These findings suggest that overexcitation of frontoparietal circuits in turn suppressing the gaze following patch might be a potential cause of gaze following deficits in clinical populations.

Mitragynine improves cognitive performance in morphine-withdrawn rats

RATIONALE

The treatment of opiate addiction is an unmet medical need. Repeated exposure to opiates disrupts cognitive performance. Opioid substitution therapy, with, e.g., methadone, may further exacerbate the cognitive deficits. Growing evidence suggests that mitragynine, the primary alkaloid from the Kratom (Mitragyna speciosa) leaves, may serve as a promising alternative therapy for opiate addiction. However, the knowledge of its health consequences is still limited.

OBJECTIVES

We aimed to examine the cognitive effects of mitragynine substitution in morphine-withdrawn rats. Furthermore, we asked whether neuronal addiction markers like the brain-derived neurotrophic factor (BDNF) and Ca²⁺/calmodulin-dependent kinase II alpha (αCaMKII) might mediate the observed effects.

METHODS

Male Sprague-Dawley rats were given morphine at escalating doses before treatment was discontinued to induce a spontaneous morphine withdrawal. Then, vehicle or mitragynine (5 mg/kg, 15 mg/kg, or 30 mg/kg) substitution was given for 3 days. A vehicle-treated group was used as a control. Withdrawal signs were scored after 24 h, 48 h, and 72 h, while novel object recognition (NOR) and attentional set-shifting (ASST) were tested during the substitution period.

RESULTS

Discontinuation of morphine significantly induced morphine withdrawal signs and cognitive deficit in the ASST. The substitution with mitragynine was able to alleviate the withdrawal signs. Mitragynine did not affect the recognition memory in the NOR but significantly improved the reversal learning deficit in the morphine-withdrawn rats.

CONCLUSIONS

These data support the idea that mitragynine could be used as safe medication therapy to treat opiate addiction with beneficial effects on cognitive deficits.

Prefrontal deep projection neurons enable cognitive flexibility via persistent feedback monitoring

Cognitive flexibility, the ability to alter strategy according to changing stimulus-response-reward relationships, is critical for updating learned behavior. Attentional set-shifting, a test of cognitive flexibility, depends on the activity of prefrontal cortex (PFC). It remains unclear, however, what role PFC neurons play to support set-shifting. Using optogenetics and two-photon calcium imaging, we demonstrate that medial PFC activity does not bias sensorimotor responses during set-shifting, but rather enables set-shifting by encoding trial feedback information, a role it has been known to play in other contexts. Unexpectedly, the functional properties of PFC cells did not vary with their efferent projection targets. Instead, representations of trial feedback formed a topological gradient, with cells more strongly selective for feedback information located further from the pial surface, where afferent input from the anterior cingulate cortex was denser. These findings identify a critical role for deep PFC projection neurons in enabling set-shifting through behavioral feedback monitoring.

Task Switching and the Role of Motor Reprogramming in Parietal Structures

Human behaviour amazes with extraordinary flexibility and the underlying neural mechanisms have often been studied using task switching. Despite extensive research, the relative importance of "cognitive" and "motor" aspects during switching is unclear. In the current study we examine this question combining EEG analysis techniques and source localization to examine whether the selection of the response, or processes during the execution of the response, contribute most to switching effects. A clear dissociation was observed in the signal decomposition, since codes relating to motor aspects play a significant role in task switching and the scope of the switching costs. This was not the case for signals that denote reaction selection or decision processes that respond to selection or basic stimulus processing codes. On a functional neuroanatomical level, these modulations in motor processes showed a clear temporal sequence in that motor codes are processed primarily in superior parietal regions (Brodman area 7) and only then in premotor regions (Brodman area 6). The observed modulations may reflect motor reprogramming processes. The study shows how EEG signal analysis in combination with brain mapping methods can inform debates on theories of human cognitive flexibility.

Behavioral Tasks Evaluating Schizophrenia-like Symptoms in Animal Models: A Recent Update

BACKGROUND

Schizophrenia is a serious mental illness that affects more than 21 million people worldwide. Both genetics and the environment play a role in its etiology and pathogenesis. Symptoms of schizophrenia are mainly categorized into positive, negative, and cognitive. One major approach to identify and understand these diverse symptoms in humans has been to study behavioral phenotypes in a range of animal models of schizophrenia.

OBJECTIVE

We aimed to provide a comprehensive review of the behavioral tasks commonly used for measuring schizophrenia-like behaviors in rodents together with an update of the recent study findings.

METHODS

Articles describing phenotypes of schizophrenia-like behaviors in various animal models were collected through a literature search in Google Scholar, PubMed, Web of Science, and Scopus, with a focus on advances over the last 10 years.

RESULTS

Numerous studies have used a range of animal models and behavioral paradigms of schizophrenia to develop antipsychotic drugs for improved therapeutics. In establishing animal models of schizophrenia, the candidate models were evaluated for schizophrenia-like behaviors using several behavioral tasks for positive, negative, and cognitive symptoms designed to verify human symptoms of schizophrenia. Such validated animal models were provided as rapid preclinical avenues for drug testing and mechanistic studies.

CONCLUSION

Based on the most recent advances in the field, it is apparent that a myriad of behavior tests are needed to confirm and evaluate the congruency of animal models with the numerous behaviors and clinical signs exhibited by patients with schizophrenia.

Abnormal reinforcement learning in a mice model of autism induced by prenatal exposure to valproic acid

Individuals with autism spectrum disorder (ASD) display dysfunction in learning from environmental stimulus that have positive or negative emotional values, posing obstacles to their everyday life. Unfortunately, mechanisms of the dysfunction are still unclear. Although early intervention for ASD victims based on reinforcement learning are commonly used, the mechanisms and characteristics of the improvement are also unknown. By using a mice model of ASD produced by prenatal exposure to valproic acid (VPA), the present work discovered a delayed response-reinforcer forming, and an impaired habit forming in a negative reinforcement learning paradigm in VPA exposure male offspring. But the extinction of the learned skills was found to become faster than normal male animals. Since escape action of nosepoking and the motility remain unchanged in the VPA male offspring, the impaired learning and the accelerated extinction are caused by deficits in higher brain functions underlying association between the animals' behavioral responses and the outcomes of such responses. The results further suggest that the rodent ASD model produced by prenatal exposure to VPA reproduces the deficits in reasoning or building the contingency between one's own behaviors and the consequent outcomes of the behavior seen in ASD patients.

Early Life Stress Drives Sex-Selective Impairment in Reversal Learning by Affecting Parvalbumin Interneurons in Orbitofrontal Cortex of Mice

Poverty, displacement, and parental stress represent potent sources of early life stress (ELS). Stress disproportionately affects females, who are at increased risk for stress-related pathologies associated with cognitive impairment. Mechanisms underlying stress-associated cognitive impairment and enhanced risk of females remain unknown. Here, ELS is associated with impaired rule-reversal (RR) learning in females, but not males. Impaired performance was associated with decreased expression and density of interneurons expressing parvalbumin (PV+) in orbitofrontal cortex (OFC), but not other inter-neuron subtypes. Optogenetic silencing of PV+ inter-neuron activity in OFC of control mice phenocopied RR learning deficits observed in ELS females. Localization of reversal learning deficits to PV+ interneurons in OFC was confirmed by optogenetic studies in which neurons in medial prefrontal cortex (mPFC) were silenced and associated with select deficits in rule-shift learning. Sex-, cell-, and region-specific effects show altered PV+ interneuron development can be a driver of sex differences in cognitive dysfunction.

Goodwill et al. investigate the effect of early life stress (ELS) on cognitive development in a mouse model. Using a combination of genetic, histological, optogenetic, and behavioral techniques, they find that ELS leads to female-selective impairments in the ability to engage in rule reversal, but not other forms of attentional learning. Impairments are associated with diminished parvalbumin (PV) expression and a decreased density of PV+ interneurons in the orbitofrontal cortex (OFC).

The attention set-shifting test is sensitive for revealing sex-based impairments in executive functions following developmental lead exposure in rats

The literature on lead (Pb) exposure has focused in large part on hippocampal-based learning and memory deficits, although frontoexecutive dysfunctions are known to exist in Pb-exposed humans. This study examined the effects of perinatal (PERI) and early postnatal (EPN) developmental low-level Pb-exposures in rats on frontoexecutive functions, using the Attention Set-Shift Test (ASST). Control males and females performed the ASST similarly. Male EPN rats had difficulty with simple discrimination (SD) of odors and failed to complete the compound discrimination (CD) stage of the ASST. All other Pb-exposed rats completed the training and testing. Male PERI rats performed worse on the SD, intradimensional (ID), and intradimensional-reversal (ID-Rev) ASST stages when compared to male Control rats. Female EPN rats performed similar to Controls on the ID-Rev rats, whereas PERI rats performed better the trials-to-criterion on the ID-Rev than EPN and Control rats. Pb-exposed female rats had significant difficulty performing the ED/ED-Rev stages, with the number of trials-to-criterion double that required by Pb-exposed and Control male rats and Control female rats. Together, the ASST results showed that developmental Pb-exposure induces frontoexecutive dysfunction that persists into adulthood, with different sex-based vulnerabilities dependent upon the time-period of neurotoxicant exposure.

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.

Neural mechanisms of navigation involving interactions of cortical and subcortical structures

Animals must perform spatial navigation for a range of different behaviors, including selection of trajectories toward goal locations and foraging for food sources. To serve this function, a number of different brain regions play a role in coding different dimensions of sensory input important for spatial behavior, including the entorhinal cortex, the retrosplenial cortex, the hippocampus, and the medial septum. This article will review data concerning the coding of the spatial aspects of animal behavior, including location of the animal within an environment, the speed of movement, the trajectory of movement, the direction of the head in the environment, and the position of barriers and objects both relative to the animal's head direction (egocentric) and relative to the layout of the environment (allocentric). The mechanisms for coding these important spatial representations are not yet fully understood but could involve mechanisms including integration of self-motion information or coding of location based on the angle of sensory features in the environment. We will review available data and theories about the mechanisms for coding of spatial representations. The computation of different aspects of spatial representation from available sensory input requires complex cortical processing mechanisms for transformation from egocentric to allocentric coordinates that will only be understood through a combination of neurophysiological studies and computational modeling.

Attentional deficits and altered neuronal activation in medial prefrontal and posterior parietal cortices in mice with reduced dopamine transporter levels

The executive control function of attention is regulated by the dopaminergic (DA) system. Dopamine transporter (DAT) likely plays a role in controlling the influence of DA on cognitive processes. We examined the effects of DAT depletion on cognitive processes related to attention. Mice with the DAT gene genetically deleted (DAT+/- heterozygotes) were compared to wild type (WT) mice on the Attentional Set-Shifting Task (ASST). Changes in neuronal activity during the ASST were shown with early growth response genes 1 and 2 (egr-1 and egr-2) immunohistochemistry in the medial prefrontal cortex (mPFC) and in the posterior parietal cortex (PPC). Heterozygotes were impaired in tasks that tax reversal learning, attentional-set formation and set-shifting. Densities of egr-2 labeled cells in the mPFC were lower in mutant mice when compared with wild-types in intradimensional shift of attention (IDS), extradimensional shift of attention and extradimensional shift of attention-reversal phases of the ASST task, and in PPC in the IDS phase of the task. The results demonstrate impairments of the areas associated with attentional functions in DAT+/- mice and show that an imbalance of the dopaminergic system has an impact on the complex attention-related executive functions.

The posterior parietal cortex as integrative hub for whisker sensorimotor information

Our daily life consists of a continuous interplay between incoming sensory information and outgoing motor plans. Particularly during goal-directed behavior and active exploration of the sensory environment, brain circuits are merging sensory and motor signals. This is referred to as sensorimotor integration and is relevant for locomotion, vision or tactile exploration. The somatosensory (tactile) system is an attractive modality to study sensorimotor integration in health and disease, motivated by the need for revolutionary technology that builds upon conceptual understanding of sensorimotor integration, such as brain-machine-interfaces and neuro-prosthetics. In this perspective, we focus on the rat whisker system and put forward the posterior parietal cortex as a potential circuit where sensorimotor integration could occur during active somatosensation.

The influence of offspring, parity, and oxytocin on cognitive flexibility during the postpartum period

Pregnancy and the postpartum period are times of profound behavioral change including alterations in cognitive function. This has been most often studied using hippocampal-dependent tasks assessing spatial learning and memory. However, less is known about the cognitive effects of motherhood for tasks that rely on areas other than the hippocampus. We have previously shown that postpartum females perform better on the extradimensional phase of an attentional set shifting task, a measure of cognitive flexibility which is dependent on the medial prefrontal cortex (mPFC). The present experiments aimed to extend this work by examining the importance of postpartum stage as well as offspring and parity in driving improved mPFC cognitive function during motherhood. We also examined whether the neuropeptide oxytocin, which plays a role in regulating numerous maternal functions, mediates enhanced cognitive flexibility during motherhood. Our results demonstrate that compared to virgin females, cognitive flexibility is enhanced in mothers regardless of postpartum stage and is not affected by parity since both first (primiparous) and second (biparous) time mothers showed the enhancement. Moreover, we found that improved cognitive flexibility in mothers requires the presence of offspring, as removal of the pups abolished the cognitive enhancement in postpartum females. Lastly, using an oxytocin receptor antagonist, we demonstrate that oxytocin signaling in the mPFC is necessary for the beneficial effects of motherhood on cognitive flexibility. Together, these data provide insights into the temporal, experiential and hormonal factors which regulate mPFC-dependent cognitive function during the postpartum period.

Goal-Directed Behavior and Instrumental Devaluation: A Neural System-Level Computational Model

Devaluation is the key experimental paradigm used to demonstrate the presence of instrumental behaviors guided by goals in mammals. We propose a neural system-level computational model to address the question of which brain mechanisms allow the current value of rewards to control instrumental actions. The model pivots on and shows the computational soundness of the hypothesis for which the internal representation of instrumental manipulanda (e.g., levers) activate the representation of rewards (or "action-outcomes", e.g., foods) while attributing to them a value which depends on the current internal state of the animal (e.g., satiation for some but not all foods). The model also proposes an initial hypothesis of the integrated system of key brain components supporting this process and allowing the recalled outcomes to bias action selection: (a) the sub-system formed by the basolateral amygdala and insular cortex acquiring the manipulanda-outcomes associations and attributing the current value to the outcomes; (b) three basal ganglia-cortical loops selecting respectively goals, associative sensory representations, and actions; (c) the cortico-cortical and striato-nigro-striatal neural pathways supporting the selection, and selection learning, of actions based on habits and goals. The model reproduces and explains the results of several devaluation experiments carried out with control rats and rats with pre- and post-training lesions of the basolateral amygdala, the nucleus accumbens core, the prelimbic cortex, and the dorso-medial striatum. The results support the soundness of the hypotheses of the model and show its capacity to integrate, at the system-level, the operations of the key brain structures underlying devaluation. Based on its hypotheses and predictions, the model also represents an operational framework to support the design and analysis of new experiments on the motivational aspects of goal-directed behavior.

Frontal Lobe Contusion in Mice Chronically Impairs Prefrontal-Dependent Behavior

Traumatic brain injury (TBI) is a major cause of chronic disability in the world. Moderate to severe TBI often results in damage to the frontal lobe region and leads to cognitive, emotional, and social behavioral sequelae that negatively affect quality of life. More specifically, TBI patients often develop persistent deficits in social behavior, anxiety, and executive functions such as attention, mental flexibility, and task switching. These deficits are intrinsically associated with prefrontal cortex (PFC) functionality. Currently, there is a lack of analogous, behaviorally characterized TBI models for investigating frontal lobe injuries despite the prevalence of focal contusions to the frontal lobe in TBI patients. We used the controlled cortical impact (CCI) model in mice to generate a frontal lobe contusion and studied behavioral changes associated with PFC function. We found that unilateral frontal lobe contusion in mice produced long-term impairments to social recognition and reversal learning while having only a minor effect on anxiety and completely sparing rule shifting and hippocampal-dependent behavior.

Exposure to activity-based anorexia impairs contextual learning in weight-restored rats without affecting spatial learning, taste, anxiety, or dietary-fat preference

Relapse rates are high amongst cases of anorexia nervosa (AN) suggesting that some alterations induced by AN may remain after weight restoration.

OBJECTIVE

To study the consequences of AN without confounds of environmental variability, a rodent model of activity-based anorexia (ABA) can be employed. We hypothesized that exposure to ABA during adolescence may have long-term consequences in taste function, cognition, and anxiety-like behavior after weight restoration.

METHODS

To test this hypothesis, we exposed adolescent female rats to ABA (1.5 h food access, combined with voluntary running wheel access) and compared their behavior to that of control rats after weight restoration was achieved. The rats were tested for learning/memory, anxiety, food preference, and taste in a set of behavioral tests performed during the light period.

RESULTS

Our data show that ABA exposure leads to reduced performance during the novel object recognition task, a test for contextual learning, without altering performance in the novel place recognition task or the Barnes maze, both tasks that test spatial learning. Furthermore, we do not observe alterations in unconditioned lick responses to sucrose nor quinine (described by humans as "sweet" and "bitter," respectively). Nor Do we find alterations in anxiety-like behavior during an elevated plus maze or an open field test. Finally, preference for a diet high in fat is not altered.

DISCUSSION

Overall, our data suggest that ABA exposure during adolescence impairs contextual learning in adulthood without altering spatial leaning, taste, anxiety, or fat preference.

The role of rat posterior parietal cortex in coordinating spatial representations during place avoidance in dissociated reference frames on a continuously rotating arena (Carousel)

On the Carousel maze, rats are trained to avoid a sector of a circular rotating arena, punishable by a mild electric foot-shock. In the room frame (RF) variant, the punishable sector remains stable relative to the room, while in the arena frame (AF) version, the sector rotates with the arena. The rats therefore need to disregard local olfactory, tactile and self-motion cues in RF condition and distal extra-maze landmarks in the AF task. In both primates and rodents, the coordination of various spatial reference frames is thought to depend on the posterior parietal cortex (PPC). We have previously shown that PPC-lesioned rats can solve both variants of the Carousel avoidance task. Here we aimed to determine the effects of bilateral thermocoagulation lesion of the PPC in Long-Evans rats on the ability to transition between multiple spatial strategies. The rats were first trained in five sessions in one condition and then another five sessions in the other. The following training schemes were used: RF to AF, RF to RF reversal (sector on the opposite side), and AF to RF. We found a PPC lesion-associated impairment in the transition from the AF to RF task, but not vice versa. Furthermore, PPC lesion impaired performance in RF reversal. In accordance to the literature, we also found an impairment in navigation guided by intra-maze visuospatial cues, but not by extra-maze cues in the water maze. Therefore, the PPC lesion-induced impairment is neither specific to distant cues nor to allocentric processing. Our results thus indicate a role of the PPC in the flexibility in spatial behaviors guided by visual orientation cues.

Theta, mental flexibility, and post-traumatic stress disorder: connecting in the parietal cortex

Post-traumatic stress disorder (PTSD) is a mental health injury characterised by re-experiencing, avoidance, numbing and hyperarousal. Whilst the aetiology of the disorder is relatively well understood, there is debate about the prevalence of cognitive sequelae that manifest in PTSD. In particular, there are conflicting reports about deficits in executive function and mental flexibility. Even less is known about the neural changes that underlie such deficits. Here, we used magnetoencephalography to study differences in functional connectivity during a mental flexibility task in combat-related PTSD (all males, mean age = 37.4, n = 18) versus a military control (all males, mean age = 33.05, n = 19) group. We observed large-scale increases in theta connectivity in the PTSD group compared to controls. The PTSD group performance was compromised in the more attentionally-demanding task and this was characterised by 'late-stage' theta hyperconnectivity, concentrated in network connections involving right parietal cortex. Furthermore, we observed significant correlations with the connectivity strength in this region with a number of cognitive-behavioural outcomes, including measures of attention, depression and anxiety. These findings suggest atypical coordination of neural synchronisation in large scale networks contributes to deficits in mental flexibility for PTSD populations in timed, attentionally-demanding tasks, and this propensity toward network hyperconnectivity may play a more general role in the cognitive sequelae evident in this disorder.

Attentional Set-Shifting Across Species

Attentional set-shifting, as a measure of executive flexibility, has been a staple of investigations into human cognition for over six decades. Mediated by the frontal cortex in mammals, the cognitive processes involved in forming, maintaining and shifting an attentional set are vulnerable to dysfunction arising from a number of human neurodegenerative diseases (such as Alzheimer's, Parkinson's and Huntington's diseases) and other neurological disorders (such as schizophrenia, depression, and attention deficit/hyperactivity disorder). Our understanding of these diseases and disorders, and the cognitive impairments induced by them, continues to advance, in tandem with an increasing number of tools at our disposal. In this chapter, we review and compare commonly used attentional set-shifting tasks (the Wisconsin Card Sorting Task and Intradimensional/Extradimensional tasks) and their applicability across species. In addition to humans, attentional set-shifting has been observed in a number of other animals, with a substantial body of literature describing performance in monkeys and rodents. We consider the task designs used to investigate attentional set-shifting in these species and the methods used to model human diseases and disorders, and ultimately the comparisons and differences between species-specific tasks, and between performance across species.

Executive function

Components of human executive function, like rule generation and selection in response to stimuli (attention set-shifting) or overcoming a habit (reversal learning), can be reliably modelled in rodents. The rodent paradigms are based upon tasks that assess cognitive flexibility in clinical populations and have been effective in distinguishing the neurobiological substrates and the underlying neurotransmitter systems relevant to executive function. A review of the literature on the attentional set-shifting task highlights a prominent role for the medial region of the prefrontal cortex in the ability to adapt to a new rule (extradimensional shift) while the orbitofrontal cortex has been associated with the reversal learning component of the task. In other paradigms specifically developed to examine reversal learning in rodents, the orbitofrontal cortex also plays a prominent role. Modulation of dopamine, serotonin, and glutamatergic receptors can disrupt executive function, a feature commonly exploited to develop concepts underlying psychiatric disorders. While these paradigms do have excellent translational construct validity, they have been less effective as predictive preclinical models for cognitive enhancers, especially for cognition in health subjects. Accordingly, a more diverse battery of tasks may be necessary to model normal human executive function in the rodent for drug development.

Systemic inflammation impairs attention and cognitive flexibility but not associative learning in aged rats: possible implications for delirium

Delirium is a common and morbid condition in elderly hospitalized patients. Its pathophysiology is poorly understood but inflammation has been implicated based on a clinical association with systemic infection and surgery and preclinical data showing that systemic inflammation adversely affects hippocampus-dependent memory. However, clinical manifestations and imaging studies point to abnormalities not in the hippocampus but in cortical circuits. We therefore tested the hypothesis that systemic inflammation impairs prefrontal cortex function by assessing attention and executive function in aged animals. Aged (24-month-old) Fischer-344 rats received a single intraperitoneal injection of lipopolysaccharide (LPS; 50 μg/kg) or saline and were tested on the attentional set-shifting task (AST), an index of integrity of the prefrontal cortex, on days 1-3 post-injection. Plasma and frontal cortex concentrations of the cytokine TNFα and the chemokine CCL2 were measured by ELISA in separate groups of identically treated, age-matched rats. LPS selectively impaired reversal learning and attentional shifts without affecting discrimination learning in the AST, indicating a deficit in attention and cognitive flexibility but not learning globally. LPS increased plasma TNFα and CCL2 acutely but this resolved within 24-48 h. TNFα in the frontal cortex did not change whereas CCL2 increased nearly threefold 2 h after LPS but normalized by the time behavioral testing started 24 h later. Together, our data indicate that systemic inflammation selectively impairs attention and executive function in aged rodents and that the cognitive deficit is independent of concurrent changes in frontal cortical TNFα and CCL2. Because inattention is a prominent feature of clinical delirium, our data support a role for inflammation in the pathogenesis of this clinical syndrome and suggest this animal model could be useful for studying that relationship further.

The maternal brain: an organ with peripartal plasticity

The time of pregnancy, birth, and lactation, is characterized by numerous specific alterations in several systems of the maternal body. Peripartum-associated changes in physiology and behavior, as well as their underlying molecular mechanisms, have been the focus of research since decades, but are still far from being entirely understood. Also, there is growing evidence that pregnancy and lactation are associated with a variety of alterations in neural plasticity, including adult neurogenesis, functional and structural synaptic plasticity, and dendritic remodeling in different brain regions. All of the mentioned changes are not only believed to be a prerequisite for the proper fetal and neonatal development, but moreover to be crucial for the physiological and mental health of the mother. The underlying mechanisms apparently need to be under tight control, since in cases of dysregulation, a certain percentage of women develop disorders like preeclampsia or postpartum mood and anxiety disorders during the course of pregnancy and lactation. This review describes common peripartum adaptations in physiology and behavior. Moreover, it concentrates on different forms of peripartum-associated plasticity including changes in neurogenesis and their possible underlying molecular mechanisms. Finally, consequences of malfunction in those systems are discussed.

Default network connectivity as a vulnerability marker for obsessive compulsive disorder

BACKGROUND

Aberrant functional connectivity within the default network is generally assumed to be involved in the pathophysiology of obsessive compulsive disorder (OCD); however, the genetic risk of default network connectivity in OCD remains largely unknown.

METHOD

Here, we systematically investigated default network connectivity in 15 OCD patients, 15 paired unaffected siblings and 28 healthy controls. We sought to examine the profiles of default network connectivity in OCD patients and their siblings, exploring the correlation between abnormal default network connectivity and genetic risk for this population.

RESULTS

Compared with healthy controls, OCD patients exhibited reduced strength of default network functional connectivity with the posterior cingulate cortex (PCC), and increased functional connectivity in the right inferior frontal lobe, insula, superior parietal cortex and superior temporal cortex, while their unaffected first-degree siblings only showed reduced local connectivity in the PCC.

CONCLUSIONS

These findings suggest that the disruptions of default network functional connectivity might be associated with family history of OCD. The decreased default network connectivity in both OCD patients and their unaffected siblings may serve as a potential marker of OCD.

COMT Genetic Reduction Produces Sexually Divergent Effects on Cortical Anatomy and Working Memory in Mice and Humans

Genetic variations in catechol-O-methyltransferase (COMT) that modulate cortical dopamine have been associated with pleiotropic behavioral effects in humans and mice. Recent data suggest that some of these effects may vary among sexes. However, the specific brain substrates underlying COMT sexual dimorphisms remain unknown. Here, we report that genetically driven reduction in COMT enzyme activity increased cortical thickness in the prefrontal cortex (PFC) and postero-parieto-temporal cortex of male, but not female adult mice and humans. Dichotomous changes in PFC cytoarchitecture were also observed: reduced COMT increased a measure of neuronal density in males, while reducing it in female mice. Consistent with the neuroanatomical findings, COMT-dependent sex-specific morphological brain changes were paralleled by divergent effects on PFC-dependent working memory in both mice and humans. These findings emphasize a specific sex-gene interaction that can modulate brain morphological substrates with influence on behavioral outcomes in healthy subjects and, potentially, in neuropsychiatric populations.

Modafinil reverses phencyclidine-induced deficits in cognitive flexibility, cerebral metabolism, and functional brain connectivity

OBJECTIVE

In the present study, we employ mathematical modeling (partial least squares regression, PLSR) to elucidate the functional connectivity signatures of discrete brain regions in order to identify the functional networks subserving PCP-induced disruption of distinct cognitive functions and their restoration by the procognitive drug modafinil.

METHODS

We examine the functional connectivity signatures of discrete brain regions that show overt alterations in metabolism, as measured by semiquantitative 2-deoxyglucose autoradiography, in an animal model (subchronic phencyclidine [PCP] treatment), which shows cognitive inflexibility with relevance to the cognitive deficits seen in schizophrenia.

RESULTS

We identify the specific components of functional connectivity that contribute to the rescue of this cognitive inflexibility and to the restoration of overt cerebral metabolism by modafinil. We demonstrate that modafinil reversed both the PCP-induced deficit in the ability to switch attentional set and the PCP-induced hypometabolism in the prefrontal (anterior prelimbic) and retrosplenial cortices. Furthermore, modafinil selectively enhanced metabolism in the medial prelimbic cortex. The functional connectivity signatures of these regions identified a unifying functional subsystem underlying the influence of modafinil on cerebral metabolism and cognitive flexibility that included the nucleus accumbens core and locus coeruleus. In addition, these functional connectivity signatures identified coupling events specific to each brain region, which relate to known anatomical connectivity.

CONCLUSIONS

These data support clinical evidence that modafinil may alleviate cognitive deficits in schizophrenia and also demonstrate the benefit of applying PLSR modeling to characterize functional brain networks in translational models relevant to central nervous system dysfunction.

Modulation of fronto-cortical activity by modafinil: a functional imaging and fos study in the rat

Modafinil (MOD) is a wake-promoting drug with pro-cognitive properties. Despite its increasing use, the neuronal substrates of MOD action remain elusive. In particular, animal studies have highlighted a putative role of diencephalic areas as primary neuronal substrate of MOD action, with inconsistent evidence of recruitment of fronto-cortical areas despite the established pro-cognitive effects of the drug. Moreover, most animal studies have employed doses of MOD of limited clinical relevance. We used pharmacological magnetic resonance imaging (phMRI) in the anesthetized rat to map the circuitry activated by a MOD dose producing clinically relevant plasma exposure, as here ascertained by pharmacokinetic measurements. We observed prominent and sustained activation of the prefrontal and cingulate cortex, together with weaker but significant activation of the somatosensory cortex, medial thalamic domains, hippocampus, ventral striatum and dorsal raphe. Correlation analysis of phMRI data highlighted enhanced connectivity within a neural network including dopamine projections from the ventral tegmental area to the nucleus accumbens. The pro-arousing effect of MOD was assessed using electroencephalographic recording under anesthetic conditions comparable to those used for phMRI, together with the corresponding Fos immunoreactivity distribution. MOD produced electroencephalogram desynchronization, resulting in reduced delta and increased theta frequency bands, and a pattern of Fos induction largely consistent with the phMRI study. Altogether, these findings show that clinically relevant MOD doses can robustly activate fronto-cortical areas involved in higher cognitive functions and a network of pro-arousing areas, which provide a plausible substrate for the wake-promoting and pro-cognitive effects of the drug.

Muscarinic receptor/G-protein coupling is reduced in the dorsomedial striatum of cognitively impaired aged rats

Behavioral flexibility, the ability to modify responses due to changing task demands, is detrimentally affected by aging with a shift towards increased cognitive rigidity. The neurobiological basis of this cognitive deficit is not clear although striatal cholinergic neurotransmission has been implicated. To investigate the possible association between striatal acetylcholine signaling with age-related changes in behavioral flexibility, young, middle-aged, and aged F344 X Brown Norway F1 rats were assessed using an attentional set-shifting task that includes two tests of behavioral flexibility: reversal learning and an extra-dimensional shift. Rats were also assessed in the Morris water maze to compare potential fronto-striatal-dependent deficits with hippocampal-dependent deficits. Behaviorally characterized rats were then assessed for acetylcholine muscarinic signaling within the striatum using oxotremorine-M-stimulated [(35)S]GTPγS binding and [(3)H]AFDX-384 receptor binding autoradiography. The results showed that by old age, cognitive deficits were pronounced across cognitive domains, suggesting deterioration of both hippocampal and fronto-striatal regions. A significant decline in oxotremorine-M-stimulated [(35)S]GTPγS binding was limited to the dorsomedial striatum of aged rats when compared to young and middle-aged rats. There was no effect of age on striatal [(3)H]AFDX-384 receptor binding. These results suggest that a decrease in M2/M4 muscarinic receptor coupling is involved in the age-associated decline in behavioral flexibility.

The cognitive cost of sleep lost

A substantial body of literature supports the intuitive notion that a good night's sleep can facilitate human cognitive performance the next day. Deficits in attention, learning & memory, emotional reactivity, and higher-order cognitive processes, such as executive function and decision making, have all been documented following sleep disruption in humans. Thus, whilst numerous clinical and experimental studies link human sleep disturbance to cognitive deficits, attempts to develop valid and reliable rodent models of these phenomena are fewer, and relatively more recent. This review focuses primarily on the cognitive impairments produced by sleep disruption in rodent models of several human patterns of sleep loss/sleep disturbance. Though not an exclusive list, this review will focus on four specific types of sleep disturbance: total sleep deprivation, experimental sleep fragmentation, selective REM sleep deprivation, and chronic sleep restriction. The use of rodent models can provide greater opportunities to understand the neurobiological changes underlying sleep loss induced cognitive impairments. Thus, this review concludes with a description of recent neurobiological findings concerning the neuroplastic changes and putative brain mechanisms that may underlie the cognitive deficits produced by sleep disturbances.

Levodopa and the feedback process on set-shifting in Parkinson's disease

OBJECTIVE

To study the interaction between levodopa and the feedback process on set-shifting in Parkinson's disease (PD).

METHODS

Functional magnetic resonance imaging (fMRI) studies were performed on 13 PD subjects and 17 age-matched healthy controls while they performed a modified card-sorting task. Experimental time periods were defined based on the types of feedback provided. PD subjects underwent the fMRI experiment twice, once during "off" medication (PDoff) and again after levodopa replacement (PDon).

RESULTS

Compared with normal subjects, the cognitive processing times were prolonged in PDoff but not in PDon subjects during learning through positive outcomes. The ability to set-shift through negative outcomes was not affected in PD subjects, even when "off" medication. Intergroup comparisons showed the lateral prefrontal cortex was deactivated in PDoff subjects during positive feedback learning, especially following internal feedback cues. The cortical activations were increased in the posterior brain regions in PDoff subjects following external feedback learning, especially when negative feedback cues were provided. Levodopa replacement did not completely restore the activation patterns in PD subjects to normal although activations in the corticostriatal loops were restored.

CONCLUSION

PD subjects showed differential ability to set-shift, depending on the dopamine status as well as the types of feedback cues provided. PD subjects had difficulty performing set-shift tasks through positive outcomes when "off" medication, and showed improvement after levodopa replacement. The ability to set-shift through negative feedback was not affected in PD subjects even when "off" medication, possibly due to compensatory changes outside the nigrostriatal dopaminergic pathway.

Neuronal signal dynamics during preparation and execution for behavioral shifting in macaque posterior parietal cortex

Cognitive flexibility arises from our ability to shift behaviors depending on demand changes. Behavioral shifting recruits both a preparatory process for an upcoming behavior and an execution process for the actual behavior. Although neuroimaging studies have shown that several brain regions, including posterior parietal cortex (PPC) participated in each component process, it remains unresolved how such processes are implemented at the single-cell level or even whether these processes are distinctively carried out across microstructures in such regions. By recording single-unit activity from PPC of two monkeys performing an analog of the Wisconsin Card Sorting Test, we found that, in the execution process, two types of neurons exhibited activity modulation depending on whether shift was (shift trial) or was not required (nonshift trial): one type showing larger activity and the other showing smaller activity in the shift trial than in the nonshift trial. In the preparatory process, in contrast, the population activity of both types became larger in the shift trial than in the nonshift trial. The majority of both types exhibited shift-related activity modulation in both processes, whereas the remaining was specialized in the execution process. The former and the latter neurons were spatially intermingled within PPC. Significantly, when the animals performed set shifting spontaneously in prospect of a demand change, the shift-related activity modulation still emerged in both processes. We suggest that both execution and preparation signals are represented within PPC, and that these signals reflect behavioral shifting mechanisms that can be driven by either internal or external triggers.

Fos expression in the brains of rats performing an attentional set-shifting task

Impairments in executive function and cognitive control are a common feature of neuropsychiatric and neurodegenerative disorders. A promising behavioral paradigm for elucidating the neural mechanisms of executive function is extradimensional/intradimensional (ED/ID) shifting, which places demands on executive function by requiring the adjustment of behavioral responses based on affective or attentional information. To augment the understanding of the brain systems required for these aspects of executive function, we examined the induction of Fos protein in rats tested in the ED/ID paradigm. We found increased Fos-like immunoreactivity (Fos-LI) in several cortical areas, including medial and orbital frontal cortex (OFC), in rats performing affective or attentional shifts relative to rats performing control discriminations. However, increased Fos-LI was also present in rats that performed a yoked number of additional control discrimination trials, without affective or attentional shifting. These observations suggest that cortical networks required for affective and attentional shifting are also activated during comparable discrimination tasks that do not require shifting, consistent with a role for these networks in monitoring ongoing behavior even in situations in which adaptation to changing behavioral demands is not required.

Methylphenidate improves cognitive deficits produced by infantile iron deficiency in rats

In humans, iron deficiency early in life produces persistent, impaired cognition. Dietary iron replacement does not ameliorate these problems and to date, no attempt to treat these individuals pharmacologically has been reported. The aim of this work was to test the hypothesis that rats made iron deficient in early infancy exhibit cognitive deficits similar to those seen in humans at adolescence. A second aim was to investigate whether the deficit could be treated pharmacologically. Sprague-Dawley rats were made iron deficient (ID) starting at postnatal day 4 by being placed with iron-deficient dams (vs. control). At weaning, all pups were placed on an iron-sufficient diet for the remainder of the study. At 45 days of age, the animals were tested for attention set shifting. After testing, the animals were assigned to one of three methylphenidate (MePh) dose groups, 1, 5 or 10 mg/kg, p.o., vs. vehicle control and treated daily for 15 days prior to a second round of attention set shift testing and continued throughout testing. The results showed that ID rats performed more poorly than controls overall on attentional set-shift testing. MePh improved ID rats' performance and lower doses were more effective than higher doses. This is the first demonstration that MePh can improve cognitive deficits produced by early ID in animals. These findings may open the possibility of pharmacotherapy to treat the persistent cognitive difficulties in children who were severely iron deficient in early infancy.

Top–Down Attentional Control in Parkinson's Disease: Salient Considerations

Cognitive dysfunction in Parkinson's disease (PD) has been hypothesized to reflect a failure of cortical control. In keeping with this hypothesis, some of the cognitive deficits in PD resemble those seen in patients with lesions in the lateral pFC, which has been associated with top–down attentional control. However, there is no direct evidence for a failure of top–down control mechanisms in PD. Here we fill this gap by demonstrating disproportionate control by bottom–up attention to dimensional salience during attentional set shifting. Patients needed significantly more trials to criterion than did controls when shifting to a low-salient dimension while, remarkably, needing significantly fewer trials to criterion than did controls when shifting to a high-salient dimension. Thus, attention was captured by bottom–up attention to salient information to a greater extent in patients than in controls. The results provide a striking reinterpretation of prior set-shifting data and provide the first direct evidence for a failure of top–down attentional control, resembling that seen after catecholamine depletion in the pFC.

Activation of 5-HT(6) receptors facilitates attentional set shifting

RATIONALE

Prefrontal cortex (PFC)-dependent executive function is disrupted in a range of psychiatric disorders and can be modelled in non-human primates and rodents using attentional set-shifting paradigms. There are few current pharmacological strategies for enhancing attentional set shifting, although the PFC is rich in relevant neurotransmitter targets, including 5-hydroxytryptamine (5-HT). Although 5-HT depletion studies do not support a role for 5-HT in attentional set shifting, the effect of 5-HT activation using specific receptor agonists has not been tested.

OBJECTIVES AND METHODS

This study investigated the effect of a novel, selective 5-HT(6) receptor agonist, WAY181187, in a rat model of PFC-dependent extra-dimensional (ED) attentional set shifting. The effect of this agent on immediate early gene expression in the medial PFC and other regions was also examined.

RESULTS

Compared to vehicle-injected controls, WAY181187 facilitated ED set shifting but did not change other non-ED phases of the task (including intra-dimensional set shifting and reversal). This effect was blocked by the selective 5-HT(6) antagonist SB399885, which alone had no effect. WAY181187 enhanced ED set shifting even when administered after the attentional set had been acquired, thereby ruling out impairments in attentional set formation. In separate experiments, at a dose that increased ED set shifting, WAY181187 increased Fos-like immunoreactivity in the medial PFC in a SB399885-sensitive manner, suggesting a 5-HT(6) receptor-mediated activation of this region.

CONCLUSIONS

Through use of a novel 5-HT agonist, these experiments reveal a previously unrecognised role for 5-HT activation in PFC-dependent executive function, mediated by 5-HT(6) receptor activation.

Characterizing learning by simultaneous analysis of continuous and binary measures of performance

Continuous observations, such as reaction and run times, and binary observations, such as correct/incorrect responses, are recorded routinely in behavioral learning experiments. Although both types of performance measures are often recorded simultaneously, the two have not been used in combination to evaluate learning. We present a state-space model of learning in which the observation process has simultaneously recorded continuous and binary measures of performance. We use these performance measures simultaneously to estimate the model parameters and the unobserved cognitive state process by maximum likelihood using an approximate expectation maximization (EM) algorithm. We introduce the concept of a reaction-time curve and reformulate our previous definitions of the learning curve, the ideal observer curve, the learning trial and between-trial comparisons of performance in terms of the new model. We illustrate the properties of the new model in an analysis of a simulated learning experiment. In the simulated data analysis, simultaneous use of the two measures of performance provided more credible and accurate estimates of the learning than either measure analyzed separately. We also analyze two actual learning experiments in which the performance of rats and of monkeys was tracked across trials by simultaneously recorded reaction and run times and the correct and incorrect responses. In the analysis of the actual experiments, our algorithm gave a straightforward, efficient way to characterize learning by combining continuous and binary measures of performance. This analysis paradigm has implications for characterizing learning and for the more general problem of combining different data types to characterize the properties of a neural system.

Gestational treatment with methylazoxymethanol (MAM) that disrupts hippocampal-dependent memory does not alter behavioural response to cocaine

Schizophrenia is associated with increased rates of substance abuse that are thought to be the result of changes in cortical and mesolimbic dopamine activity. Previous work has shown that gestational methylazoxymethanol acetate (MAM) treatment induces increased mesolimbic dopamine activity when given around the time of embryonic day 17 (ED17), suggesting that MAM treatment may model some aspects of schizophrenia. Given that increased dopaminergic activity facilitates aspects of drug self-administration and reinstatement of drug seeking, the current experiments sought to assess cocaine self-administration in MAM treated animals. Experiment 1 examined the acquisition of cocaine self-administration in ED17 MAM and saline treated rats using a sub-threshold dose of cocaine. In experiment 2 ED17 MAM and saline treated animals were trained to self-administer cocaine and were then assessed under varying doses of cocaine (dose-response), followed by extinction and drug-induced reinstatement of responding. A subset of these animals was trained on a win-shift radial maze task, designed to detect impairments in hippocampal-dependent memory. In experiment 3, MAM and saline treated animals were assessed on a progressive ratio schedule of cocaine delivery. Finally, in experiment 4 MAM and saline treated animals were assessed on cocaine-induced locomotor activity across a range of doses of cocaine. MAM treatment disrupted performance of the win-shift task but did not alter cocaine self-administration or cocaine-induced locomotion. Implications of these results for the MAM model of schizophrenia are discussed.

Using the MATRICS to guide development of a preclinical cognitive test battery for research in schizophrenia

Cognitive deficits in schizophrenia are among the core symptoms of the disease, correlate with functional outcome, and are not well treated with current antipsychotic therapies. In order to bring together academic, industrial, and governmental bodies to address this great 'unmet therapeutic need', the NIMH sponsored the Measurement and Treatment Research to Improve Cognition in Schizophrenia (MATRICS) initiative. Through careful factor analysis and consensus of expert opinion, MATRICS identified seven domains of cognition that are deficient in schizophrenia (attention/vigilance, working memory, reasoning and problem solving, processing speed, visual learning and memory, verbal learning and memory, and social cognition) and recommended a specific neuropsychological test battery to probe these domains. In order to move the field forward and outline an approach for translational research, there is a need for a "preclinical MATRICS" to develop a rodent test battery that is appropriate for drug development. In this review, we outline such an approach and review current rodent tasks that target these seven domains of cognition. The rodent tasks are discussed in terms of their validity for probing each cognitive domain as well as a brief overview of the pharmacology and manipulations relevant to schizophrenia for each task.

Comparison of haloperidol, risperidone, sertindole, and modafinil to reverse an attentional set-shifting impairment following subchronic PCP administration in the rat--a back translational study

RATIONALE

Selective cognitive impairments, including those of executive function as assessed using the Wisconsin Card Sort Test or intradimensional-extradimensional (ID-ED) tests, are a key feature of schizophrenia but remain inadequately treated by existing therapies. Recently, however, modafinil has been shown to improve attentional set-shifting performance in patients with schizophrenia.

OBJECTIVE

The present study evaluated the recently described analogous rat ID-ED attentional set-shifting task by investigating the effects of various pharmacological challenges to a phencyclidine (PCP)-induced ED shift impairment, namely, haloperidol, risperidone, sertindole, and modafinil.

MATERIALS AND METHODS

Rats were subjected to a subchronic systemic administration of either saline vehicle or PCP (5 mg/kg i.p. b.i.d. for 7 days) followed by a 7-day washout period. During this period, rats were trained to dig in baited bowls for a food reward and to discriminate based on odor or digging media. In a single test session conducted the day after the washout period (day 8), rats performed a series of discriminations following acute administration of either vehicle, or haloperidol (0.1 mg/kg s.c.), or risperidone (0.2 mg/kg i.p.), or sertindole (1.25 mg/kg p.o.) or modafinil (64 mg/kg p.o.).

RESULTS

The subchronic PCP-induced ED deficit was ameliorated by sertindole and modafinil but not by haloperidol or risperidone.

CONCLUSIONS

Overall, these findings further support that the rat ID-ED test in subchronic PCP-treated rats has utility and validity as a preclinical model of the cognitive symptoms of schizophrenia and demonstrates back-translational potential.

Reversal of subchronic PCP-induced deficits in attentional set shifting in rats by sertindole and a 5-HT6 receptor antagonist: comparison among antipsychotics

Currently accepted treatments for schizophrenia can effectively control positive symptoms but have limited impact on cognitive deficits in schizophrenia. The purpose of these experiments was to address this unmet need by characterizing the effects of classical and second-generation antipsychotics on cognitive impairments associated with schizophrenia. An additional aim was to characterize the part(s) of the pharmacological profile of drugs that were important to reverse deficits. Cognitive deficits were assessed using a frontally mediated attentional set-shifting task in rats that is analogous to tasks used in humans and nonhuman primates that assess executive function. Mirroring findings in patients with schizophrenia, the classical antipsychotic haloperidol was ineffective in treating set-shifting deficits induced by subchronic treatment with phencyclidine (PCP). Similarly, second-generation antipsychotics, risperidone, clozapine, and olanzapine were ineffective. In contrast, selected doses of sertindole and the 5-HT(6) receptor antagonist SB 271046 attenuated PCP-induced set-shifting deficits. Finally, the 5-HT(2A) receptor antagonist M100907 was without effect. Further examination revealed that repeated treatment (21 days) with sertindole, but not olanzapine, also was effective in reversing the executive function deficit. These data suggest that the combination of 5-HT(6) antagonistic activity and the absence of antimuscarinic activity may represent key characteristics of the pharmacological profile for improved antipsychotic drugs for schizophrenia.

Behavioural assays to model cognitive and affective dimensions of depression and anxiety in rats

Animal models have been used extensively to investigate neuropsychiatric disorders, such as depression, and their treatment. However, the aetiology and pathophysiology of many such disorders are largely unknown, which makes validation of animal models particularly challenging. Furthermore, many diagnostic symptoms are difficult to define, operationalize and quantify, especially in experimental animals such as rats. Thus, rather than attempting to model complex human syndromes such as depression in their entirety, it can be more productive to define and model components of the illness that may account for clusters of co-varying symptoms, and that may share common underlying neurobiological mechanisms. In preclinical investigations of the neural regulatory mechanisms linking stress to depression and anxiety disorders, as well as the mechanisms by which chronic treatment with antidepressant drugs may exert their beneficial effects in these conditions, we have employed a number of behavioural tests in rats to model specific cognitive and anxiety-like components of depression and anxiety disorders. In the present study, we review the procedures for conducting four such behavioural assays: the attentional set-shifting test, the elevated-plus maze, the social interaction test and the shock-probe defensive burying test. The purpose is to serve as a guide to the utility and limitations of these tools, and as an aid in optimising their use and productivity.

A mixed filter algorithm for cognitive state estimation from simultaneously recorded continuous and binary measures of performance

Continuous (reaction times) and binary (correct/ incorrect responses) measures of performance are routinely recorded to track the dynamics of a subject's cognitive state during a learning experiment. Current analyses of experimental data from learning studies do not consider the two performance measures together and do not use the concept of the cognitive state formally to design statistical methods. We develop a mixed filter algorithm to estimate the cognitive state modeled as a linear stochastic dynamical system from simultaneously recorded continuous and binary measures of performance. The mixed filter algorithm has the Kalman filter and the more recently developed recursive filtering algorithm for binary processes as special cases. In the analysis of a simulated learning experiment the mixed filter algorithm provided a more accurate and precise estimate of the cognitive state process than either the Kalman or binary filter alone. In the analysis of an actual learning experiment in which a monkey's performance was tracked by its series of reaction times, and correct and incorrect responses, the mixed filter gave a more complete description of the learning process than either the Kalman or binary filter. These results establish the feasibility of estimating cognitive state from simultaneously recorded continuous and binary performance measures and suggest a way to make practical use of concepts from learning theory in the design of statistical methods for the analysis of data from learning experiments.