Associative encoding in anterior piriform cortex versus orbitofrontal cortex during odor discrimination and reversal learning

Recent proposals have conceptualized piriform cortex as an association cortex, capable of integrating incoming olfactory information with descending input from higher order associative regions such as orbitofrontal cortex (OFC). If true, encoding in piriform cortex should reflect associative features prominent in these areas during associative learning involving olfactory cues. To test this hypothesis, we recorded from neurons in OFC and anatomically related parts of the anterior piriform cortex (APC) in rats, learning and reversing novel odor discriminations. Findings in OFC were similar to what we have reported previously, with nearly all the cue-selective neurons exhibiting substantial plasticity during learning and reversal. Also, many of the cue-selective neurons were originally responsive in anticipation of the outcomes early in learning, thereby providing a single-unit representation of the cue-outcome associations. Some of these features were also evident in firing activity in APC, including some plasticity across learning and reversal. However, APC neurons failed to reverse cue selectivity when the associated outcome was changed, and the cue-selective population did not include neurons that were active prior to outcome delivery. Thus, although representations in APC are substantially more associative than expected in a purely sensory region, they do appear to be somewhat more constrained by the sensory features of the odor cues than representations in downstream areas of OFC.

Inhibitory Control in Children with Frontal Infarcts Related to Sickle Cell Disease

Evidence from past studies indicates that children with traumatic brain injury experience difficulties with inhibitory control. Less is known about inhibitory control in children with frontal brain injury related to cerebral infarction. We compared the inhibitory performance of children with frontal infarcts related to sickle cell disease with that of a control group of children with sickle cell disease but no history of cerebral infarction. On a stimulus-response reversal task, children with frontal infarcts made significantly more accuracy errors in the inhibitory condition than controls. Findings from this study and from previous research suggest that impairments in inhibitory control are common following frontal injury in a range of pediatric populations.

Effects of levodopa and subthalamic nucleus stimulation on cognitive and affective functioning in Parkinson's disease

In Parkinson's disease (PD), levodopa and subthalamic nucleus (STN) stimulation lead to major improvement in motor symptoms. Effects of both treatments on cognition and affective status are less well understood. Motor, cognitive, and affective symptoms may relate to the dysfunctioning of parallel cortico-striatal loops. The aim of this study was to assess cognition, behavior, and mood, with and without both treatments in the same group of PD patients. A group of 22 nondemented PD patients was included in this study. Patients were tested twice before surgery (off and on levodopa) and twice 3 months after surgery (OFF and ON STN stimulation, off levodopa). Cognitive and affective effects of STN stimulation and levodopa had some common, but also different, effects. STN stimulation improved performance on the planning test, associated with the dorsolateral prefrontal cortex. However, the treatments had opposite effects on tests associated with the orbitofrontal cortex; specifically, levodopa impaired while STN stimulation improved performance on the extinction phase of a reversal/extinction task. Acutely, both treatments improved motivation and decreased fatigue and anxiety. On chronic treatment (3 months after surgery), depression improved, whereas apathy worsened 3 months after surgery. To conclude, there were significant but contrasting effects of levodopa and STN stimulation on cognition and affective functions.

Selective bilateral amygdala lesions in rhesus monkeys fail to disrupt object reversal learning

Neuropsychological studies in nonhuman primates have led to the view that the amygdala plays an essential role in stimulus-reward association. The main evidence in support of this idea is that bilateral aspirative or radiofrequency lesions of the amygdala yield severe impairments on object reversal learning, a task that assesses the ability to shift choices of objects based on the presence or absence of food reward (i.e., reward contingency). The behavioral effects of different lesion techniques, however, can vary. The present study therefore evaluated the effects of selective, excitotoxic lesions of the amygdala in rhesus monkeys on object reversal learning. For comparison, we tested the same monkeys on a task known to be sensitive to amygdala damage, the reinforcer devaluation task. Contrary to previous results based on less selective lesion techniques, monkeys with complete excitotoxic amygdala lesions performed object reversal learning as quickly as controls. As predicted, however, the same operated monkeys were impaired in making object choices after devaluation of the associated food reinforcer. The results suggest two conclusions. First, the results demonstrate that the amygdala makes a selective contribution to stimulus-reward association; the amygdala is critical for guiding object choices after changes in reward value but not after changes in reward contingency. Second, the results implicate a critical contribution to object reversal learning of structures nearby the amygdala, perhaps the subjacent rhinal cortex.

Age differences in task switching and response monitoring: evidence from ERPs

This study investigates age differences in the flexible adaptation to changing demands on task switching and conflict processing. We applied a cued task-switching version of the Stroop task and manipulated the ratio of conflict trials. During task preparation, the P300 varied as a function of conflict ratio and a later positive component was larger for switch than non-switch trials. Stimulus-related conflict processing as indicated by a negativity for incompatible trials (Ni) was delayed for older adults. Moreover, the Ni varied as a function of conflict ratio and was larger for switch than for non-switch trials. Age differences were also obtained in the correct response negativity (CRN). CRN was larger on incompatible trials and this CRN-compatibility effect was enhanced when incompatible trials were infrequent in younger, but not in older adults. Our findings suggest impairments of older adults primarily in response-related conflict processing and in the flexible adaptation to changing task contexts.

Changes in Brain Functioning From Infancy to Early Childhood: Evidence From EEG Power and Coherence Working Memory Tasks

Using measures of EEG power and coherence with a longitudinal sample, the goal of this study was to examine developmental changes in brain electrical activity during higher order cognitive processing at infancy and early childhood. Infants were recruited at 8 months of age and performed an infant working-memory task based on a looking version of the A-not-B task. At age 4.5 years, one half of the original sample returned for a follow-up visit and were assessed with age-appropriate working-memory tasks. At infancy, working memory was associated with changes in EEG power from baseline to task across the entire scalp, whereas in early childhood, working memory was associated with changes in EEG power from baseline to task at medial frontal only. Similar results were found for the EEG coherence data. At infancy, working memory was associated with changes in EEG coherence from baseline to task across all electrode pairs and by 4.5 years of age, EEG coherence changed from baseline to working-memory task at the medial frontal/posterior temporal pairs and the medial frontal/occipital pairs. These EEG power and coherence longitudinal data suggest that brain electrical activity is widespread during infant cognitive processing and that it becomes more localized during early childhood. These findings may yield insight into qualitative changes in cortical functioning from the infant to the early childhood time periods, adjustments that may be indicative of developmental changes in brain specialization for higher order processes.

Exercise improves memory acquisition and retrieval in the Y-maze task: Relationship with hippocampal neurogenesis

Enhanced physical activity is associated with improvements in cognitive function in rodents as well as in humans. The authors examined in detail which aspects of learning and memory are influenced by exercise, using a spatial Y-maze test combined with a 14-day exercise paradigm at different stages of learning. The authors show that 14 days of wheel running promotes memory acquisition, memory retention, and reversal learning. The exercise paradigm that was employed also significantly increased the number of maturing neurons, suggesting that an increase in neurogenesis underlies the positive effects of exercise on Y-maze performance. Finally, the authors show that memory acquisition in itself does not have a major impact on the number of immature neurons. However, memory retention testing and reversal learning both cause a significant reduction in the number of doublecortin and Ser133- phosphorylated pCREB-positive cells, indicating that a decrease in neurogenesis might be a prerequisite for optimal memory retrieval.

NMDA receptor antagonism impairs reversal learning in developing rats

Four experiments examined the effect of dizocilpine maleate (MK-801), a noncompetitive N-methyl-Daspartate (NMDA) receptor antagonist, on reversal learning during development. On postnatal days (PND) 21, 26, or 30, rats were trained on spatial discrimination and reversal in a T-maze. When MK-801 was administered (intraperitoneally) before both acquisition and reversal, 0.18 mg/kg generally impaired performance, whereas doses of 0.06 mg/kg and 0.10 mg/kg, but not 0.03 mg/kg, selectively impaired reversal learning (Experiments 1 and 3). The selective effect on reversal was not a result of sensitization to the second dose of MK-801 (Experiment 2) and was observed when the drug was administered only during reversal in an experiment addressing state-dependent learning (Experiment 4). Spatial reversal learning is more sensitive to NMDA-receptor antagonism than is acquisition. No age differences in sensitivity to MK-801 were found between PND 21 and 30.

Reduced orbitofrontal-striatal activity on a reversal learning task in obsessive-compulsive disorder

CONTEXT

The orbitofrontal cortex (OFC)-striatal circuit, which is important for motivational behavior, is assumed to be involved in the pathophysiology of obsessive-compulsive disorder (OCD) according to current neurobiological models of this disorder. However, the engagement of this neural loop in OCD has not been tested directly in a cognitive activation imaging paradigm so far.

OBJECTIVE

To determine whether the OFC and the ventral striatum show abnormal neural activity in OCD during cognitive challenge.

DESIGN

A reversal learning task was employed in 20 patients with OCD who were not receiving medication and 27 healthy controls during an event-related functional magnetic resonance imaging experiment using a scanning sequence sensitive to OFC signal. This design allowed investigation of the neural correlates of reward and punishment receipt as well as of "affective switching," ie, altering behavior on reversing reinforcement contingencies.

RESULTS

Patients with OCD exhibited an impaired task end result reflected by a reduced number of correct responses relative to control subjects but showed adequate behavior on receipt of punishment and with regard to affective switching. On reward outcome, patients showed decreased responsiveness in right medial and lateral OFC as well as in the right caudate nucleus (border zone ventral striatum) when compared with controls. During affective switching, patients recruited the left posterior OFC, bilateral insular cortex, bilateral dorsolateral, and bilateral anterior prefrontal cortex to a lesser extent than control subjects. No areas were found for which patients exhibited increased activity relative to controls, and no differential activations were observed for punishment in a direct group comparison.

CONCLUSIONS

These data show behavioral impairments accompanied by aberrant OFC-striatal and dorsal prefrontal activity in OCD on a reversal learning task that addresses this circuit's function. These findings not only confirm previous reports of dorsal prefrontal dysfunction in OCD but also provide evidence for the involvement of the OFC-striatal loop in the pathophysiology of OCD.

Relationship between limbic and cortical 5-HT neurotransmission and acquisition and reversal learning in a go/no-go task in rats

RATIONALE

Specific brain structures have been suggested to be involved in impulsive responding assessed by a variety of operant tasks. Central serotonin (5-HT) function has also been widely implicated in impulsivity; however, little research has addressed the regional aspect of 5-HT roles in different impulsive indices of task performance.

OBJECTIVE

We analyzed the relationships between acquisition and reversal learning in a go/no-go task as different behavioral measures of impulsivity and focal concentrations of 5-HT and its metabolites in the brain.

MATERIALS AND METHODS

Rats administered with parachloroamphetamine (PCA) and vehicle were tested in both acquisition and reversal phases in a go/no-go visual discrimination task. Neurochemical analysis was performed to determine 5-HT concentrations in micropunched brain tissues.

RESULTS

PCA administration induced regionally 5-HT depletion in the brain and impaired learning performance in both tests. For both tests, significant negative correlations between learning performance and 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) concentrations were observed in the medial prefrontal cortex (mPFC) and amygdala (Amyg). In contrast, significant negative correlations between learning performance and 5-HT and 5-HIAA concentrations were observed for the orbitofrontal cortex (OFC) exclusively in the reversal learning phase.

CONCLUSIONS

The present data indicate that 5-HT neurotransmission to the mPFC and Amyg is involved in inhibitory control over responses to discriminated stimuli associated with the go/no-go paradigm common to both tests. In contrast, 5-HT neurotransmission to the OFC is especially involved in additional processes associated with reversal learning.

Discrimination learning and reversal of the conditioned eyeblink reflex in a rodent model of autism

Offspring of rats exposed to valproic acid (VPA) on gestational day (GD) 12 have been advocated as a rodent model of autism because they show neuron loss in brainstem nuclei and the cerebellum resembling that seen in human autistic cases . Studies of autistic children have reported alterations in acquisition of classical eyeblink conditioning and in reversal of instrumental discrimination learning . Acquisition of discriminative eyeblink conditioning depends on known brainstem-cerebellar circuitry whereas reversal depends on interactions of this circuitry with the hippocampus and prefrontal cortex. In order to explore behavioral parallels of the VPA rodent model with human autism, the present study exposed pregnant Long-Evans rats to 600 mg/kg VPA on GD12 and tested their offspring from Postnatal Day (PND26-31) on discriminative eyeblink conditioning and reversal. VPA rats showed faster eyeblink conditioning, consistent with studies in autistic children . This suggests that previously reported parallels between human autism and the VPA rodent model with respect to injury to brainstem-cerebellar circuitry are accompanied by behavioral parallels when a conditioning task engaging this circuitry is used. VPA rats also showed impaired reversal learning, but this likely reflected "carry-over" of enhanced conditioning during acquisition rather than a reversal learning deficit like that seen in human autism. Further studies of eyeblink conditioning in human autism and in various animal models may help to identify the etiology of this developmental disorder.

Differential involvement of hippocampal calcineurin during learning and reversal learning in a Y-maze task

The regulation and function of the calcium-dependent phosphatase calcineurin (CaN, protein phosphatase 2B) in learning and memory remain unclear, although recent work indicates that CaN may play a differential role in training and reversal training. To gain more insight into the involvement of CaN in these two types of learning, hippocampal CaN activity, protein levels, and expression patterns were studied in mice subjected to a reference memory version of the Y-maze task. We show that (1) training but not habituation induces a decrease in cytosolic CaN activity, (2) the recovery of cytosolic CaN activity is reversal training specific and does not reflect normal restoration of basal levels unrelated to subsequent learning, (3) cytosolic protein levels for the catalytic subunit of CaN (CaNA) are decreased at the early phase of training, but not at the early phase of reversal training, (4) CaNA immunoreactivity in the dorsal hippocampus is enhanced in the CA1 and CA3 area (but not in the dentate gyrus [DG] or subiculum [SUB]) only during reversal training. These findings indicate that memory formation is accompanied by reduced CaN activity, whereas adapting to changes in a familiar environment is accompanied by restored CaN activity. Moreover, reversal training selectively affects hippocampal CA3 and CA1 regions, suggesting a specific function of these hippocampal subregions in reversal learning.

The effect of N-methyl-D-aspartate receptor blockade on acetylcholine efflux in the dorsomedial striatum during response reversal learning

Separate experiments found that activation of N-methyl-d-aspartate (NMDA) receptors or increased acetylcholine (ACh) efflux in the rat dorsomedial striatum is critical for learning when conditions require a shift in strategies. Increasing evidence indicates that NMDA receptor activity affects cholinergic efflux in the basal ganglia. The present studies determined whether NMDA receptor blockade in the dorsomedial striatum with dl-2-amino-5-phosphonopentanoic acid (AP-5) affects dorsomedial striatal ACh output in a resting condition, as well as during response reversal learning. Experiment 1 investigated the effects of AP-5 (12.5, 25 or 50 muM) infused into the dorsomedial striatum on ACh output in a resting condition. AP-5 infusion at 25 and 50 muM led to a 20% and 40% decrease in dorsomedial striatal ACh output, respectively. AP-5 (12.5 muM) infusion did not change dorsomedial striatal ACh output from basal levels. Experiment 2 determined whether dorsomedial striatal ACh efflux increases during response reversal learning and whether AP-5, at a dose that does not affect basal levels, modifies response reversal learning and ACh efflux. Following acquisition of a response discrimination, rats had microdialysis probes bilaterally inserted into the dorsomedial striatum prior to the reversal learning test. After baseline samples, rats received a response reversal learning test for 30 min. Control rats rapidly improved in the reversal learning session while simultaneously exhibiting an approximately 40% increase in ACh output compared with baseline levels. AP-5 (12.5 muM) treatment during testing significantly impaired response reversal learning while concomitantly blocking an increase in ACh output. These findings suggest that NMDA receptor activation in the dorsomedial striatum may facilitate a shift in response patterns, in part, by increasing ACh efflux.

The role of the ventromedial prefrontal cortex in abstract state-based inference during decision making in humans

Many real-life decision-making problems incorporate higher-order structure, involving interdependencies between different stimuli, actions, and subsequent rewards. It is not known whether brain regions implicated in decision making, such as the ventromedial prefrontal cortex (vmPFC), use a stored model of the task structure to guide choice (model-based decision making) or merely learn action or state values without assuming higher-order structure as in standard reinforcement learning. To discriminate between these possibilities, we scanned human subjects with functional magnetic resonance imaging while they performed a simple decision-making task with higher-order structure, probabilistic reversal learning. We found that neural activity in a key decision-making region, the vmPFC, was more consistent with a computational model that exploits higher-order structure than with simple reinforcement learning. These results suggest that brain regions, such as the vmPFC, use an abstract model of task structure to guide behavioral choice, computations that may underlie the human capacity for complex social interactions and abstract strategizing.

A double dissociation of dorsal and ventral hippocampal function on a learning and memory task mediated by the dorso-lateral striatum

The objectives of this research were to further delineate the neural circuits subserving proposed memory-based behavioural subsystems in the hippocampal formation. These studies were guided by anatomical evidence showing a topographical organization of the hippocampal formation. Briefly, perpendicular to the medial/lateral entorhinal cortex division there is a second system of parallel circuits that separates the dorsal and ventral hippocampus. Recent work from this laboratory has provided evidence that the hippocampus incidentally encodes a context-specific inhibitory association during acquisition of a visual discrimination task. One question that emerges from this dataset is whether the dorsal or ventral hippocampus makes a unique contribution to this newly described function. Rats with neurotoxic lesions of the dorsal or ventral hippocampus were assessed on the acquisition of the visual discrimination task. Following asymptotic performance they were given reversal training in either the same or a different context from the original training. The results showed that the context-specific inhibition effect is mediated by a circuit that includes the ventral but not the dorsal hippocampus. Results from a control procedure showed that rats with either dorso-lateral striatum damage or dorsal hippocampal lesions were impaired on a tactile/spatial discrimination. Taken together, the results represent a double dissociation of learning and memory function between the ventral and dorsal hippocampus. The formation of an incidental inhibitory association was dependent on ventral but not dorsal hippocampal circuitry, and the opposite dependence was found for the spatial component of a tactile/spatial discrimination.

Dopamine and noradrenaline efflux in the medial prefrontal cortex during serial reversals and extinction of instrumental goal-directed behavior

The prefrontal cortex (PFC) of the rat supports cognitive flexibility, the ability to spontaneously adapt goal-directed behavior in response to radically changing situational demands. We have shown previously that transient inactivation of the rat medial PFC (mPFC) impairs initial reversal learning in a spatial 2-lever discrimination task. Given the importance of dopamine (DA) for PFC function, we studied DA (and noradrenaline [NA]) efflux in the mPFC during reversal learning. We observed a higher and more extended increase in DA efflux in rats performing the first reversal compared with controls performing the previously acquired discrimination. The results of an additional experiment suggest that such a difference between the reversal- and control-induced DA increases was absent during a third reversal. During the extinction session, DA efflux did not increase from basal levels. Increases in NA efflux were less than in DA and did not differ between control and any condition. We conclude that prefrontal DA activity is increased during execution of instrumental discrimination tasks and that this increase is amplified during the acquisition of a first, but not of later reversals. These data corroborate our previous findings and indicate that DA is critically involved in this form of cognitive flexibility.

Genetic and dopaminergic modulation of reversal learning in a touchscreen-based operant procedure for mice

Mice are uniquely suited as experimental subjects for various approaches to the study of the molecular and genetic basis of behavior, and there has been a corresponding explosion in the use of mice in behavioral neuroscience. Rats and monkeys, however, remain the preferred species for high-order cognitive models largely due to the unavailability of valid, reliable and translatable endpoint measures of behavior in the mouse. Here we present further development and validation of a touchscreen-based operant method for measuring cognition that is comparable to methods used in other species and human patients. C57BL/6J mice were found to show good performance on visual discrimination and reversal learning using this method. Demonstrating the sensitivity of the paradigm to genetic factors, C57BL/6J and DBA/2J mice exhibited marked differences in discrimination and reversal learning. Systemic treatment with the selective D1-like agonist, SKF81297, produced an impairment in the early phase of reversal learning, but did not alter visual discrimination, in C57BL/6J mice. The same treatment impaired spatial working memory on the T-maze delayed alternation task, but did not alter control measures of behavior including motivation and locomotor activity. These data demonstrate the sensitivity of visual discrimination and reversal learning measured by this method to genetic factors and pharmacological challenge, and thereby provide an extension and further validation of the method for measuring cognition in mice. When combined with emerging molecular techniques uniquely suited to this species such as genetic engineering and RNA modification this paradigm could provide a powerful new tool for behavioral neuroscience.

Anatomy of a decision: striato-orbitofrontal interactions in reinforcement learning, decision making, and reversal

The authors explore the division of labor between the basal ganglia-dopamine (BG-DA) system and the orbitofrontal cortex (OFC) in decision making. They show that a primitive neural network model of the BG-DA system slowly learns to make decisions on the basis of the relative probability of rewards but is not as sensitive to (a) recency or (b) the value of specific rewards. An augmented model that explores BG-OFC interactions is more successful at estimating the true expected value of decisions and is faster at switching behavior when reinforcement contingencies change. In the augmented model, OFC areas exert top-down control on the BG and premotor areas by representing reinforcement magnitudes in working memory. The model successfully captures patterns of behavior resulting from OFC damage in decision making, reversal learning, and devaluation paradigms and makes additional predictions for the underlying source of these deficits.

Rapid tryptophan depletion improves decision-making cognition in healthy humans without affecting reversal learning or set shifting

Rapid tryptophan (Trp) depletion (RTD) has been reported to cause deterioration in the quality of decision making and impaired reversal learning, while leaving attentional set shifting relatively unimpaired. These findings have been attributed to a more powerful neuromodulatory effect of reduced 5-HT on ventral prefrontal cortex (PFC) than on dorsolateral PFC. In view of the limited number of reports, the aim of this study was to independently replicate these findings using the same test paradigms. Healthy human subjects without a personal or family history of affective disorder were assessed using a computerized decision making/gambling task and the CANTAB ID/ED attentional set-shifting task under Trp-depleted (n=17; nine males and eight females) or control (n=15; seven males and eight females) conditions, in a double-blind, randomized, parallel-group design. There was no significant effect of RTD on set shifting, reversal learning, risk taking, impulsivity, or subjective mood. However, RTD significantly altered decision making such that depleted subjects chose the more likely of two possible outcomes significantly more often than controls. This is in direct contrast to the previous report that subjects chose the more likely outcome significantly less often following RTD. In the terminology of that report, our result may be interpreted as improvement in the quality of decision making following RTD. This contrast between studies highlights the variability in the cognitive effects of RTD between apparently similar groups of healthy subjects, and suggests the need for future RTD studies to control for a range of personality, family history, and genetic factors that may be associated with 5-HT function.

Simultaneous specification of amplitudes and directions of bimanual reversal movements

Intermanual interactions are modulated by task requirements in the course of motor preparation. In particular, amplitude coupling is strong when identical amplitudes are specified concurrently for the 2 hands but relaxed when different amplitudes are specified. Similarly, directional coupling is symmetric when symmetric directions are specified concurrently but turns to parallel when parallel directions are specified. Here, the author investigated whether the modulations of amplitude coupling and directional coupling in the course of motor preparation are independent or interact. Application of the timed-response procedure, which enables one to manipulate the time available for motor preparation, in 9 participants revealed a weakly interactive pattern. Directional coupling tended to be reduced when different rather than same amplitudes were specified concurrently, and amplitude coupling tended to be reduced when parallel rather than symmetric directions were specified concurrently. In general, interactive effects were also apparent in the rates at which directions and amplitudes were specified. Those observations are consistent with the notion that intermanual amplitude and direction interference are mediated by different but partially overlapping neural structures.

fMRI investigation of cortical and subcortical networks in the learning of abstract and effector-specific representations of motor sequences

A visuo-motor sequence can be learned as a series of visuo-spatial cues or as a sequence of effector movements. Earlier imaging studies have revealed that a network of brain areas is activated in the course of motor sequence learning. However, these studies do not address the question of the type of representation being established at various stages of visuo-motor sequence learning. In an earlier behavioral study, we demonstrated that acquisition of visuo-spatial sequence representation enables rapid learning in the early stage and progressive establishment of somato-motor representation helps speedier execution by the late stage. We conducted functional magnetic resonance imaging (fMRI) experiments wherein subjects learned and practiced the same sequence alternately in normal and rotated settings. In one rotated setting (visual), subjects learned a new motor sequence in response to an identical sequence of visual cues as in normal. In another rotated setting (motor), the display sequence was altered as compared to normal, but the same sequence of effector movements was used to perform the sequence. Comparison of different rotated settings revealed analogous transitions both in the cortical and subcortical sites during visuo-motor sequence learning-a transition of activity from parietal to parietal-premotor and then to premotor cortex and a concomitant shift was observed from anterior putamen to a combined activity in both anterior and posterior putamen and finally to posterior putamen. These results suggest a putative role for engagement of different cortical and subcortical networks at various stages of learning in supporting distinct sequence representations.

Thalamic and hippocampal mechanisms in spatial navigation: A dissociation between brain mechanisms for learning how versus learning where to navigate

Various studies of hippocampus and medial thalamus (MT) suggest that these brain areas play a crucial, marginal, or no essential role in spatial navigation. These divergent views were examined in experiments using electrolytic Lesions of fimbria-fornix (FF) or radiofrequency or neurotoxic Lesions of MT of rats subsequently trained to find a stable visible (experiment 1) or hidden platform (experiments 2 and 3) in a water maze (WM) pool. Rats with electrolytic Lesions of FF or radiofrequency Lesions of MT were impaired in swimming to a stable visible platform, particularly the MT Lesion Group, suggesting impairment of WM strategies acquisition. Additional Lesioned rats were then tested in a hidden platform version of the WM task. Some rats were given Morris's nonspatial pretraining prior to Lesioning to provide them with training in the required WM behavioral strategies. Nonspatially Pretrained rats with FF Lesions eventually were able to navigate to the hidden platform, but the accuracy of place responding was impaired. This impairment occurred without problems in the motoric control of swimming or the use of WM behavioral strategies, suggesting that these rats had a spatial mapping impairment. Radiofrequency MT Lesions blocked acquisition of WM behavioral strategies by Naive rats throughout 3 days of training, severely impairing performance on all aspects of the hidden platform task. Nonspatially Pretrained rats given the same MT Lesions readily learned the hidden platform location and were indistinguishable from controls throughout spatial training. Rats given neurotoxic Lesions of MT for removal of cells were only mildly impaired and improved considerably during training, suggesting an important role for fibers of passage in WM strategies learning. The results provide a clear dissociation between a role for MT in learning WM behavioral strategies and the hippocampal formation in spatial mapping and memory. This is the first identification of a brain area, MT, that is essential for learning behavioral strategies that by themselves do not constitute the solution to the task but are necessary for the successful use of an innate learning ability: place response learning using spatial mapping.

Holeboard discrimination learning in mice

We have adapted to mice a holeboard-learning task, which allows simultaneous assessment of spatial working and reference-memory performance. The holeboard apparatus consists of an open-field chamber with a 16-hole floor insert. Across trials, animals have to learn that the same four holes of 16 are always baited. Here, we show that C57BL/6 mice readily acquire this task within 4 days when submitted to six trials per day or within 8 days when submitted to only four trials per day. We also show that C57BL/6, Swiss-Webster, CD-1 and DBA/2 mice acquire this task similarly, despite the fact that some differences could be observed in measures of exploratory activity during habituation and training. Moreover, the muscarinic antagonist scopolamine disrupts learning at doses of 0.1 and 1.0 mg/kg, although the highest dose appeared to have side-effects. Lastly, we found that amyloid precursor protein transgenic mice have a selective disruption in their working-memory performance only during reversal training (i.e. after a change in the configuration of the baited holes). Overall, our data indicate that this spatial learning task is well adapted to mice and will be useful to characterize spatial memory in various genetic or pharmacological mouse models.

The time of prenatal immune challenge determines the specificity of inflammation-mediated brain and behavioral pathology

Disturbance to early brain development is implicated in several neuropsychiatric disorders including autism, schizophrenia, and mental retardation. Epidemiological studies have indicated that the risk of developing these disorders is enhanced by prenatal maternal infection, presumably as a result of neurodevelopmental defects triggered by cytokine-related inflammatory events. Here, we demonstrate that the effects of maternal immune challenge between middle and late gestation periods in mice are dissociable in terms of fetal brain cytokine responses to maternal inflammation and the pathological consequences in brain and behavior. Specifically, the relative expression of pro- and anti-inflammatory cytokines in the fetal brains in response to maternal immune challenge may be an important determinant among other developmental factors for the precise pathological profile emerging in later life. Thus, the middle and late gestation periods correspond to two windows with differing vulnerability to adult behavioral dysfunction, brain neuropathology in early adolescence, and of the acute cytokine responses in the fetal brain.

A comparison of Lewis and Fischer rat strains on autoshaping (sign-tracking), discrimination reversal learning and negative automaintenance

Lewis (LEW) and Fischer (F344) rat strains differ on a number of physiological characteristics, such as hypothalamic-pituitary-adrenal (HPA) axis activity, as well as on behavioral tasks, including those that measure impulsivity and drug reward. Since autoshaping, the phenomenon where animals approach and contact reward-paired conditioned stimuli, has been linked to HPA axis functioning, impulsivity and drug taking, the present study compared LEW and F344 rats on the rate of acquisition and performance of the autoshaping response. Rats were trained on an autoshaping procedure where insertions of one retractable lever (CS(+)) were paired response-independently with food, while insertions of another lever (CS(-)) were not paired with food. LEW rats acquired the autoshaping response more rapidly and also performed the autoshaping response at a higher rate than F344 rats. No differences between the strains were observed when rats were trained on a discrimination reversal where the CS(+) and CS(-) levers were reversed or during a negative auto-maintenance phase where CS(+) lever contacts cancelled food delivery. Potential physiological mechanisms that might mediate the present results, including strain differences in HPA axis and monoamine neurotransmitter activity, are discussed. The finding that LEW (as compared to F344 rats) more readily acquire autoshaping and perform more responses is consistent with research indicating that LEW rats behave more impulsively and more readily self-administer drugs of abuse.

Beyond spatial memory: the anterior thalamus and memory for the temporal order of a sequence of odor cues

Influential recent proposals state that the anterior thalamic (AT) nuclei constitute key components of an "extended hippocampal system." This idea is, however, based on lesion studies that used spatial memory tasks and there has been no evidence that AT lesions cause deficits in any hippocampal-dependent nonspatial tasks. The present study investigated the role of the AT nuclei in nonspatial memory for a sequence of events based on the temporal order of a list of odors, because this task has recently been shown to depend on the integrity of the hippocampal formation. After preoperative training, rats with excitotoxic lesions of the AT nuclei showed a severe and selective postoperative impairment when required to remember the order of pseudorandom sequences of six odors. The rats with AT lesions were able instead to learn two new tasks that required recognition memory and the identification of the prior occurrence of events independent of their order. These results strongly matched those described after hippocampal lesions and provide the first unequivocal evidence of a detrimental effect of an AT lesion on a nonspatial hippocampal-dependent memory task.

Involvement of the medial prefrontal cortex in central cardiovascular modulation in the rat

The medial prefrontal cortex (MPFC) and specifically its ventral portion (vMPFC) have been reported to modulate autonomic responses. On the cardiovascular system, this modulation is characterized by an influence on arterial blood pressure, regional blood flow as well as cardiac sympathetic and parasympathetic responses. The vMPFC also modulates baroreflex activity. Several neurotransmitters are present in the vMPFC. Among them L-glutamate, acetylcholine and noradrenaline are involved with cardiovascular modulation. In the present review, we describe evidences on the mechanisms involved in the vMPFC-related cardiovascular modulation.

Use of salient and non-salient visuospatial cues by rats in the Morris Water Maze

In the Morris Water Maze (MWM), an animal learns the location of a hidden platform relative to distal visual cues in a process known as spatial learning. The visual cues used in MWM experiments are invariably salient in nature, and non-salient cues, such as subtle environmental variations, have not traditionally been considered to play a significant role. However, the role of non-salient cues in spatial navigation has not been adequately investigated experimentally. The objective of this experiment was therefore to determine the relative contribution of salient and non-salient visual cues to spatial navigation in the MWM. Animals were presented with an environment containing both types of visual cues, and were tested in three successive phases of water maze testing, each with a new platform location. Probe tests were used to assess spatial accuracy, and several cue variation trials were run in which both salient and non-salient visual cues were manipulated. It was observed that removal of the salient visual cues did not cause a significant deterioration in performance unless accompanied by disruption of the non-salient visual cues, and that spatial navigation was unimpaired when only the salient visual cues were removed from view. This suggests that during place learning in Long-Evans rats, non-salient visual cues may play a dominant role, at least when salient cue presentation is limited to four cues.

Dopamine D2 receptors mediate reversal learning in male C57BL/6J mice

Dopamine is critical for directing goal-oriented behavior. We investigated dopamine D2 receptor involvement in reversal learning and reinforcement efficacy in mice lacking functional dopamine D2 receptors and their heterozygous and wild-type littermates. Mice discriminated between two odors to receive a food reinforcer. One odor signaled a reinforcer (S+); the other odor signaled no reinforcer (S-). After mice learned the S+/S- relationship, we inverted the reinforcement contingencies. The necessary number of trials to relearn the new reinforcement contingencies served as our index of reversal learning. Mice lacking functional dopamine D2 receptors repeatedly failed to inhibit previously reinforced responses during reversal trials. In a separate experiment, mice responded for reinforcers on a progressive ratio schedule of reinforcement. Mice lacking functional dopamine D2 receptors earned significantly fewer reinforcers than did heterozygous mice. Our results suggest that dopamine D2 receptors regulate reversal learning and influence the reinforcing efficacy of natural rewards.

Cognitive Inflexibility after Prefrontal Serotonin Depletion Is Behaviorally and Neurochemically Specific

We have previously demonstrated that prefrontal serotonin depletion impairs orbitofrontal cortex (OFC)-mediated serial discrimination reversal (SDR) learning but not lateral prefrontal cortex (PFC)-mediated attentional set shifting. To address the neurochemical specificity of this reversal deficit, Experiment 1 compared the effects of selective serotonin and selective dopamine depletions of the OFC on performance of the SDR task. Whereas serotonin depletions markedly impaired performance, OFC dopamine depletions were without effect. The behavioral specificity of this reversal impairment was investigated in Experiment 2 by examining the effect of OFC serotonin depletion on performance of a modified SDR task designed to distinguish between 3 possible causes of the impairment. The results showed that the reversal deficit induced by prefrontal serotonin depletion was not due to a failure to approach a previously unrewarded stimulus (enhanced learned avoidance) or reduced proactive interference. Instead, it was due specifically to a failure to inhibit responding to the previously rewarded stimulus. The neurochemical and behavioral specificity of this particular form of cognitive inflexibility is of particular relevance to our understanding of the aetiology and treatment of inflexible behavior apparent in many neuropsychiatric and neurodegenerative disorders involving the PFC.

The contribution of NMDA receptors in the dorsolateral striatum to egocentric response learning

The present study examined the effects of the N-methyl-D-aspartate (NMDA) competitive antagonist, 2-amino-5-phosphonopentanoic acid (AP-5), injected into the dorsolateral striatum on the acquisition and reversal learning of a response discrimination. Male Long-Evans rats were tested across 2 consecutive days in a modified cross-maze. An infusion of either saline or AP-5 (5 or 25 nM) occurred 5 min prior to testing. In acquisition rats learned to turn left or right. In reversal learning rats learned to turn in the opposite direction. An AP-5 infusion at 25 nmol, but not 5 nmol, impaired response acquisition. Neither AP-5 dose impaired response reversal learning. The results suggest that NMDA receptors in the dorsolateral striatum are critical for the initial learning of an egocentric response discrimination.

Dose-dependent reductions in spatial learning and synaptic function in the dentate gyrus of adult rats following developmental thyroid hormone insufficiency

Thyroid hormones are critical for the development and maturation of the central nervous system. Although somatic and neurological effects are well documented following severe thyroid hormone deprivation, much less is known of the functional consequences of moderate levels of hormone insufficiency. We have previously demonstrated that severe thyroid hormone reductions in the postnatal period are associated with impairments in synaptic transmission in the dentate gyrus. The present study was performed to examine the dose-response relationships of moderate levels of hormone disruption on synaptic function in the dentate gyrus in an in vivo preparation and to determine the effects on spatial learning. Pre- and postnatal thyroid hormone insufficiency was induced by administration of 3 or 10 ppm propylthiouracil (PTU) to pregnant and lactating dams via the drinking water from gestation day (GD) 6 until postnatal day (PN) 30. This regimen produced a 47% and 65% reduction in serum T4, in the dams of the low and high-dose groups, respectively. At the time of testing of adult offspring, hormone status had returned to control levels. In littermates, field potentials evoked in the dentate gyrus in response to stimulation of the perforant path were assessed under urethane anesthesia. The data reveal dose-dependent reductions in synaptic transmission and impairments in long-term potentiation (LTP) of the EPSP component of the compound field potential. In contrast, LTP of the population spike measure was paradoxically enhanced. Spatial learning in the Morris water maze was profoundly impaired in high-dose animals. Although the majority of subjects in the low-dose group eventually acquired the task, their acquisition rate lagged behind control values. Reversal learning was assessed in all animals reaching criterion performance and found to be impaired in PTU-exposed animals relative to controls. These data support previous findings in area CA1 in vitro, extend observations associated with dentate gyrus synaptic function to a lower dose range, and provide correlative evidence of behavioral disruption in a hippocampal-dependent learning task following developmental thyroid hormone insufficiency.

Dissociating prefrontal contributions during a recency memory task

Neuroimaging studies of normal young adults have consistently found right prefrontal cortex (RPFC) activity during the performance of recency memory tasks. However, it is unclear whether the involvement of RPFC during these tasks reflects retrieval processes or executive processes such as: strategic ordering or monitoring. In the current study, we distinguish between those PFC regions that are more related to retrieval processes, versus strategic ordering processes. An event-related fMRI study was conducted in which eight young subjects were scanned while performing verbal episodic retrieval tasks (recognition and recency memory tasks), and verbal non-memory strategic organizing control tasks (reverse alphabetizing of words). The fMRI results show that young subjects engaged right dorsolateral PFC during recency and reverse alphabetizing control tasks. Left ventral PFC was engaged across all tasks; however, a subset of voxels within this region was more active during retrieval tasks. Left dorsolateral and right ventral PFC activity was more related to the performance of reverse alphabetizing tasks, respectively. We conclude that right dorsolateral PFC activity during recency memory reflects more general strategic organizational or monitoring processes, and is not EM-specific.

Event-related potentials elicited by distractors in an auditory oddball paradigm in schizophrenia

Patients with schizophrenia are affected more adversely than healthy controls by distracting conditions, due to their inability to adequately apportion attentional resources to targets or distractors. We attempted to re-evaluate the effects of distractors in 25 patients with chronic schizophrenia and in 12 controls. They performed an auditory target-detection task with 1500 Hz tone distractors and an additional control condition where a 1500-Hz tone was used as the target. The rate of target misses for patients with schizophrenia was 3.79% in non-distractor conditions and 14.79% in distractor conditions. Significantly reduced N100 responses to distractors and distractor condition targets were found. P300 responses to all target stimulus categories were reduced, but P300 responses to distractors were equal to those in the control group. There was a reduction of P300 amplitudes to distractors in both groups; however, only the control group showed significant enlargement of P300 amplitude when the distractors became the target stimuli. There is evidence that patients with schizophrenia tend to be less able to allocate their attentional resources adequately to target vs. distractor stimuli. When the distractors became the target stimuli, their responses remained unchanged, which suggests their inability to appropriately integrate stimulus information with contextual information.

Neurologic examination abnormalities in children with bipolar disorder or attention-deficit/hyperactivity disorder

BACKGROUND

Attention-deficit/hyperactivity disorder (ADHD) and bipolar disorder (BPD) are frequently comorbid and overlapping diagnoses. To move beyond diagnosis toward unique pathophysiology, we evaluated both ADHD and BPD children for neurologic examination abnormalities (NEAs) in comparison with normal control (NC) children.

METHODS

We performed the Revised Physical and Neurological Examination for Soft Signs in three groups (ADHD, BPD, NC). Then, a rater blind to diagnosis evaluated their motor performance. Results were analyzed with a multiple analysis of covariance.

RESULTS

Subjects with ADHD were impaired on repetitive task reaction time. In contrast, pediatric BPD subjects, both with and without comorbid ADHD, were impaired on sequential task reaction time.

CONCLUSIONS

This differential pattern of NEAs by diagnosis suggests pathophysiologic differences between ADHD and BPD in children. Repetitive motor performance requires inhibition of nonrelevant movements; ADHD subjects' impairment in this domain supports the hypothesis that ADHD involves a core deficit of fronto-striato-basal ganglia neurocircuitry. In contrast, BPD subjects' impaired sequential motor performance is consistent with behavioral data showing impaired attentional set-shifting and reversal learning in BPD subjects. Further study, going beyond symptom description to determine pathophysiologic differences, is required to refine neuronal models of these often comorbid diagnoses.

Deficits on a probabilistic response-reversal task in patients with pediatric bipolar disorder

OBJECTIVE

Patients with bipolar disorder become hyperhedonic when manic and anhedonic when depressed; therefore, it is important to test whether patients with bipolar disorder show deficits on behavioral paradigms exploring reward/punishment mechanisms.

METHOD

A probabilistic response-reversal task was administered to 24 bipolar children and 25 comparison subjects.

RESULTS

Patients made more errors during probabilistic reversal, took longer to learn the new reward object, and were less likely to meet the learning criterion.

CONCLUSIONS

Children with bipolar disorder may have a reversal learning deficit.

Human neural learning depends on reward prediction errors in the blocking paradigm

Learning occurs when an outcome deviates from expectation (prediction error). According to formal learning theory, the defining paradigm demonstrating the role of prediction errors in learning is the blocking test. Here, a novel stimulus is blocked from learning when it is associated with a fully predicted outcome, presumably because the occurrence of the outcome fails to produce a prediction error. We investigated the role of prediction errors in human reward-directed learning using a blocking paradigm and measured brain activation with functional magnetic resonance imaging. Participants showed blocking of behavioral learning with juice rewards as predicted by learning theory. The medial orbitofrontal cortex and the ventral putamen showed significantly lower responses to blocked, compared with nonblocked, reward-predicting stimuli. In reward-predicting control situations, deactivation in orbitofrontal cortex and ventral putamen occurred at the time of unpredicted reward omissions. Responses in discrete parts of orbitofrontal cortex correlated with the degree of behavioral learning during, and after, the learning phase. These data suggest that learning in primary reward structures in the human brain correlates with prediction errors in a manner that complies with principles of formal learning theory.

The neural effect of stimulus-response modality compatibility on dual-task performance: an fMRI study

Recent fMRI studies suggest that the inferior frontal sulcus (IFS) is involved in the coordination of interfering processes in dual-task situations. The present study aims to further specify this assumption by investigating whether the compatibility between stimulus and response modalities modulates dual-task-related activity along the IFS. It has been shown behaviorally that the degree of interference, as measured by dual-task costs, increases in modality-incompatible conditions (e.g. visual-vocal tasks combined with auditory-manual tasks) as compared to modality-compatible conditions (e.g. visual-manual tasks combined with auditory-vocal tasks). Using fMRI, we measured IFS activity when participants performed modality-compatible and modality-incompatible single and dual tasks. Behaviorally, we replicated the finding of higher dual-task costs for modality-incompatible tasks compared to modality-compatible tasks. The fMRI data revealed higher activity along the IFS in modality-incompatible dual tasks compared with modality-compatible dual tasks when inter-individual variability in functional brain organization is taken into account. We argue that in addition to temporal order coordination (Szameitat et al., 2002), the IFS is involved in the coordination of cognitive processes associated with the concurrent mapping of sensory information onto corresponding motor responses in dual-task situations.

Response reversal and children with psychopathic tendencies: success is a function of salience of contingency change

BACKGROUND

Previous work has inconsistently reported difficulties with response reversal/extinction in children with psychopathic tendencies.

METHOD

We tested the hypothesis that the degree of impairment seen in children with psychopathic tendencies is a function of the salience of contingency change. We investigated the performance of children with psychopathic tendencies on a novel probabilistic response reversal task involving four conditions with gradated reward-punishment contingencies (100-0, 90-10, 80-20 and 70-30; i.e., for the 100-0 contingency, responding to one object is always rewarded while responding to the other is always punished).

RESULTS

In line with predictions, the impairment seen in the children with psychopathic tendencies was an inverse function of the salience of the contingency change.

CONCLUSIONS

We suggest that this data is consistent with suggestions of subtle orbital frontal cortex impairment in children with psychopathic tendencies.

Prefrontal serotonin depletion affects reversal learning but not attentional set shifting

Recently, we have shown that serotonin (5-HT) depletion from the prefrontal cortex (PFC) of the marmoset monkey impairs performance on a serial discrimination reversal (SDR) task, resulting in perseverative responding to the previously correct stimulus (Clarke et al., 2004). This pattern of impairment is just one example of inflexible responding seen after damage to the PFC, with performance on the SDR task being dependent on the integrity of the orbitofrontal cortex. However, the contribution of 5-HT to other forms of flexible responding, such as attentional set shifting, an ability dependent on lateral PFC (Dias et al., 1996a), is unknown. The present study addresses this issue by examining the effects of 5,7-dihydroxytryptamine-induced PFC 5-HT depletions on the ability to shift attention between two perceptual dimensions of a compound visual stimulus (extradimensional shift). Monkeys with selective PFC 5-HT lesions, despite being impaired in their ability to reverse a stimulus-reward association, were unimpaired in their ability to make an extradimensional shift when compared with sham-operated controls. These findings suggest that 5-HT is critical for flexible responding at the level of changing stimulus-reward contingencies but is not essential for the higher-order shifting of attentional set. Thus, psychological functions dependent on different loci within the PFC are differentially sensitive to serotonergic modulation, a finding of relevance to our understanding of cognitive inflexibility apparent in disorders such as obsessive-compulsive disorder and schizophrenia.

A comparison of wild-caught wood mice and bank voles in the Intellicage: assessing exploration, daily activity patterns and place learning paradigms

Our previous work has revealed very high baseline neurogenesis in the dentate gyrus of wood mice as compared particularly to bank voles; a difference which may be related to learning capacity. This study explored whether the newly-developed Intellicage system could be used to compare these species in simple spatial learning paradigms. The Intellicage is essentially a group-housing cage that also allows continuous automatic recording of each individual's behaviour. Seven wild-caught bank voles (Clethrionomys glareolus) were compared with seven wild-caught long-tailed wood mice (Apodemus sylvaticus) in the Intellicage system over 9 days. During the first 90 min after entering the cage, the wood mice were substantially more exploratory than the bank voles (P = 0.003). Over subsequent days, both species showed nocturnal activity increases with voles being 3.7 times more active overall. In the spatial learning paradigms, there were significant species-by-time interactions with wood mice outperforming bank voles on both place learning (P = 0.027) and subsequent reversal (P = 0.006). Conclusions are firstly that the wood mice show superior learning abilities in this paradigm, and secondly that the Intellicage serves as a valuable cognitive testing arena for small wild rodents, or for circumstances where cognition must be compared independent of different responses to handling or novel environments.

Impaired memory and olfactory performance in NaSi-1 sulphate transporter deficient mice

In the present study, NaSi-1 sulphate transporter knock-out (Nas1-/-) mice, an animal model of hyposulphataemia, were examined for spatial memory and learning in a Morris water maze, and for olfactory function in a cookie test. The Nas1-/- mice displayed significantly (P<0.05) increased latencies to find an escape platform in the reversal learning trials at 2 days but not 1 day after the last acquisition trial in a Morris water maze test, suggesting that Nas1-/- mice may have proactive memory interference. While the wild-type (Nas1+/+) mice showed a significant (P<0.02) decrease in time to locate a hidden food reward over four trials after overnight fasting, Nas1-/- mice did not change their performance, resulting in significantly (P<0.05) higher latencies when compared to their Nas1+/+ littermates. There were no significant differences between Nas1-/- and Nas1+/+ mice in the cookie test after moderate food deprivation. In addition, both Nas1-/- and Nas1+/+ mice displayed similar escape latencies in the acquisition phase of the Morris water maze test, suggesting that learning, motivation, vision and motor skills required for the task may not be affected in Nas1-/- mice. This is the first study to demonstrate an impairment in memory and olfactory performance in the hyposulphataemic Nas1-/- mouse.

Serotonergic modulation of prefrontal cortex during negative feedback in probabilistic reversal learning

This study used functional magnetic resonance imaging to examine the effects of acute tryptophan (TRP) depletion (ATD), a well-recognized method for inducing transient cerebral serotonin depletion, on brain activity during probabilistic reversal learning. Twelve healthy male volunteers received a TRP-depleting drink or a balanced amino-acid drink (placebo) in a double-blind crossover design. At 5 h after drink ingestion, subjects were scanned while performing a probabilistic reversal learning task and while viewing a flashing checkerboard. The probabilistic reversal learning task enabled the separate examination of the effects of ATD on behavioral reversal following negative feedback and negative feedback per se that was not followed by behavioral adaptation. Consistent with previous findings, behavioral reversal was accompanied by significant signal change in the right ventrolateral prefrontal cortex (PFC) and the dorsomedial prefrontal cortex. ATD enhanced reversal-related signal change in the dorsomedial PFC, but did not modulate the ventrolateral PFC response. The ATD-induced signal change in the dorsomedial PFC during behavioral reversal learning extended to trials where subjects received negative feedback but did not change their behavior. These data suggest that ATD affects reversal learning and the processing of aversive signals by modulation of the dorsomedial PFC.

A novel experimental paradigm for studying cognitive functions related to delayed response tasks in mice

Rodents are the animals most commonly employed to model human cognitive functions, but serious problems arise from the non-selective use of behavioral paradigms that measure different processes in rodents than those found in humans. To avoid problems stemming from the use of different paradigms on humans and mice, a new experimental paradigm for mice was developed to study the cognitive functions involved in delayed response tasks. The experiments were conducted in an olfactory tubing maze using three successive delayed response tasks: an alternation task, a non-alternation task, and a reversal task. Mice had to discover the rule by themselves by choosing one of two identical odor cues presented simultaneously at the left and right sides of a testing chamber. The success criterion was set at 10, 8, 6, or 4 consecutive correct responses, with a maximum of 80 trials per task, as used in primates. In the delayed alternation task with the criterion of 10 or 8 consecutive successful trials, the rule was discovered but required many more than 80 trials for most of the mice. With a criterion of 6 or 4, the mice were successful but twice as many trials were necessary to reach the criterion of 6 as opposed to 4. In the delayed non-alternation and reversal tasks, more than 80 trials were needed to figure out the new rule with the criterion of 10 or 8. All mice were successful with the criterion of 6 or 4. The results indicated that no matter what criterion was used, mice were able to discover the two rules on the three consecutive delayed response tasks, but they did so with more or less ease. This novel paradigm for mice should be useful in experiments on pharmacological treatments or for testing transgenic or gene-targeting mice to gain insight into the brain structures involved in this type of task.

Neural correlates of a reversal learning task with an affectively neutral baseline: an event-related fMRI study

Reversal learning may conceptually be dissected into acquiring stimulus-reinforcement associations and subsequently altering behavior by switching to new associations as stimulus-reinforcement contingencies reverse (i.e., affective switching). Previous imaging studies have found regions of the ventrolateral and orbitofrontal cortex (OFC) to be involved in both subprocesses. However, these studies did not contain an affectively neutral baseline, which precluded adequate assessment of main effects of reward, punishment, and affective switching. We aimed to determine the neural substrate of these main effects, and of common and dissociable regions for reward and punishment. Furthermore, we aimed to discriminate between stimulus-punishment association and affective switching, i.e., to assess affective switching proper. To this end, we implemented a reversal learning task with an affectively neutral baseline condition that matched the experimental task in visual complexity and motor demands. Interestingly, we found dorsolateral prefrontal cortex (DLPFC) and anterior PFC to be engaged in affective switching, a finding that has not been reported before to our knowledge. Enhanced responses in these areas may represent their involvement in cognitive set shifting per se unrelated to the affective context in a reversal learning design. In addition, OFC, insular and medial prefrontal cortex regions were involved in affective switching. Left medial and lateral OFC were shown to be common areas for feedback processing, whereas left ventral striatum and left lateral OFC were specifically activated by reward and punishment, respectively. These results extend our understanding of the neural substrate of reversal learning in humans.

Learning ability in aged beagle dogs is preserved by behavioral enrichment and dietary fortification: a two-year longitudinal study

The effectiveness of two interventions, dietary fortification with antioxidants and a program of behavioral enrichment, was assessed in a longitudinal study of cognitive aging in beagle dogs. A baseline protocol of cognitive testing was used to select four cognitively equivalent groups: control food-control experience (C-C), control food-enriched experience (C-E), antioxidant fortified food-control experience (A-C), and antioxidant fortified food-enriched experience(A-E). We also included two groups of young behaviorally enriched dogs, one receiving the control food and the other the fortified food. Discrimination learning and reversal was assessed after one year of treatment with a size discrimination task, and again after two years with a black/white discrimination task. The four aged groups were comparable at baseline. At one and two years, the aged combined treatment group showed more accurate learning than the other aged groups. Discrimination learning was significantly improved by behavioral enrichment. Reversal learning was improved by both behavioral enrichment and dietary fortification. By contrast, the fortified food had no effect on the young dogs. These results suggest that behavioral enrichment or dietary fortification with antioxidants over a long-duration can slow age-dependent cognitive decline, and that the two treatments together are more effective than either alone in older dogs.

BEHAVIORAL DYSCONTROL SCALE-ELECTRONIC VERSION: FIRST EXAMINATION OF RELIABILITY, VALIDITY, AND INCREMENTAL UTILITY

Behavioral Dyscontrol Scale (BDS) is a clinical measure previously shown to be related to frontal lobe integrity, executive abilities, and functional independence. Electronic version of the scale (BDS-EV) was developed and its reliability and validity were examined. The BDS-EV, the original BDS, and a brief battery of traditional clinical tests were administered to 55 community-dwelling adults ages 18 to 68. The results yielded high internal consistency and provided support for convergent, discriminant, and incremental validity. Overall, the results demonstrate the feasibility of converting the BDS into an electronic instrument and support continued research and development of this instrument.

An investigation of the relationship between response latency across several cognitive tasks in the beagle dog

Response latencies (RLs) extracted from simple motor tasks are a commonly used index of human intelligence. To date few human or animal studies have investigated the relationship between an individuals RL scores across a number of diverse cognitive tasks: Does RL remain consistent between individuals across several cognitive domains? Thus, the current study examined how RL measures gathered from beagle dogs (n=13) tested on three different cognitive tasks were related. RL scores were collected following both discrimination and reversal learning and a test of visuospatial memory, the 3 component delayed non-matching to position (3-DNMP) task. RL scores were recorded from the time the choice stimulus was presented until the animal selected a response. Results indicated that strong correlations emerged between 3-DNMP RLs and both the discrimination and reversal RLs, indicating that animals that responded fast on the 3-DNMP task also responded fast on the discrimination and reversal tasks. Interestingly, 3-DNMP RLs were more strongly correlated with reversal learning RLs. Finally, when mean RL performance across the three tasks was examined, strong RL differences emerged indicating that animals displayed significantly slower RLs on the 3-DNMP task than on the discrimination task, while reversal RLs remained indistinguishable from both. In conclusion, RLs show high between task correlations, indicating individual differences, and also vary between tasks, probably because of differences in task difficulty. These results further validate the use of RLs as an index of cognition, and also highlight the importance of further studies using animal models.

The influence of NMDA receptors in the dorsomedial striatum on response reversal learning

In mammals, the dorsomedial striatum is one brain area shown to be critical for the flexible shifting of response patterns. At present, the neurochemical mechanisms that underlie learning during a shift in response patterns are unknown. The present study examined the effects of NMDA competitive antagonist, DL-2-amino-5-phosphonopentanoic acid (AP-5), injected into the dorsomedial striatum on the acquisition and reversal of a response discrimination. Male Long-Evans rats were tested across two consecutive days in a modified cross-maze. Rats received an infusion of either saline or AP-5 (5 or 25 nmol) 5 min prior to each test session. In the acquisition phase rats learned to turn in one direction (right or left) to receive a cereal reinforcement. In the reversal learning phase rats learned to turn in the opposite direction as in the acquisition phase. In both phases, criterion was achieved when a rat made 10 consecutive correct trials. Infusions of AP-5 did not impair acquisition, but impaired reversal learning of a response discrimination in a dose-dependent fashion. The reversal learning deficit induced by AP-5 resulted from reversions back to the originally learned response pattern following the initial shift. These results suggest that activation of NMDA receptors in the dorsomedial striatum are critical for the flexible shifting of response patterns by enhancing the reliable execution of a new response pattern under changing task contingencies.