Delayed Alternation Research Articles

The ventral midline thalamus coordinates prefrontal–hippocampal neural synchrony during vicarious trial and error

When faced with difficult choices, the possible outcomes are considered through a process known as deliberation. In rats, deliberation is thought to be reflected by pause-and-reorienting behaviors, better known as vicarious trial and errors (VTEs). While VTEs are thought to require medial prefrontal cortex (mPFC) and dorsal hippocampal (dHPC) interactions, no empirical evidence has yet demonstrated such a dual requirement. The nucleus reuniens (Re) of the ventral midline thalamus is anatomically connected with both the mPFC and dHPC, is required for HPC-dependent spatial memory tasks, and is critical for mPFC-dHPC neural synchronization. Currently, it is unclear if, or how, the Re is involved in deliberation. Therefore, by examining the role of the Re on VTE behaviors, we can better understand the anatomical and physiological mechanisms supporting deliberation. Here, we examined the impact of Re suppression on VTE behaviors and mPFC-dHPC theta synchrony during asymptotic performance of a HPC-dependent delayed alternation (DA) task. Pharmacological suppression of the Re increased VTE behaviors that occurred with repetitive choice errors. These errors were best characterized as perseverative behaviors, in which some rats repeatedly selected a goal arm that previously yielded no reward. We then examined the impact of Re suppression on mPFC-dHPC theta synchrony during VTEs. We found that during VTEs, Re inactivation was associated with a reduction in mPFC-dHPC theta coherence and mPFC-to-dHPC theta directionality. Our findings suggest that the Re contributes to deliberation by coordinating mPFC-dHPC neural interactions.

CNS safety pharmacology: A focus on cognitive functions

IntroductionThe guidelines from different agencies do not include studies on cognitive functions as part of safety pharmacology. This is unfortunate as it seems important to verify that drugs entering into the central nervous system (CNS) are devoid of detrimental effects on cognition. Our aim is to show examples on how an evaluation of unwanted effects of drugs on cognitive functions may be included in preclinical studies. Rather than a review of the scientific context, the present text is an appeal for a wider consideration of cognition as a safety pharmacology endpoint. MethodsThe following procedures provide an index of the ability of substances to induce cognitive deficits in rodents. In the passive avoidance (PA) test, rats receiving an electric shock show on a later occasion an avoidance of the shock-associated environment. In the social recognition (SR) test, rats recognize familiar congeners. In the Morris water maze (MWM) test, rats placed into a tank containing water learn to find an invisible escape platform using extra-maze visual cues. In the delayed alternation (DA) test, rats placed in a Skinner box learn to alternate their pressing behavior between two levers in order to obtain food rewards. In the operant reversal (OR) test, rats adapt their behavior following a change of the reinforcement rule. ResultsStandard reference agents were used to confirm that the different assays were able to detect pharmacologically induced cognitive impairments. Diazepam decreased associative memory performances in the PA test. MK-801-induced memory deficits in SR. Haloperidol increased escape latencies in the MWM test. Scopolamine decreased the number of correct responses in the DA test, and nicotine decreased the number of correct responses in the OR test. The relationship between the doses administered and the effects observed was also evaluated. DiscussionCognitive assays may provide utility in determining potential undesirable effects or discharging perceived risks with novel CNS drugs under development.

In vivo polymerization of poly(3,4-ethylenedioxythiophene) in the living rat hippocampus does not cause a significant loss of performance in a delayed alternation task

After extended implantation times, traditional intracortical neural probes exhibit a foreign-body reaction characterized by a reactive glial sheath that has been associated with increased system impedance and signal deterioration. Previously, we have proposed that the local in vivo polymerization of an electronically and ionically conducting polymer, poly(3,4-ethylenedioxythiophene) (PEDOT), might help to rebuild charge transport pathways across the glial scar between the device and surrounding parenchyma (Richardson-Burns et al 2007 J. Neural Eng. 4 L6–13). The EDOT monomer can be delivered via a microcannula/electrode system into the brain tissue of living animals followed by direct electrochemical polymerization, using the electrode itself as a source of oxidative current. In this study, we investigated the long-term effect of local in vivo PEDOT deposition on hippocampal neural function and histology. Rodent subjects were trained on a hippocampus-dependent task, delayed alternation (DA), and implanted with the microcannula/electrode system in the hippocampus. The animals were divided into four groups with different delay times between the initial surgery and the electrochemical polymerization: (1) control (no polymerization), (2) immediate (polymerization within 5 min of device implantation), (3) early (polymerization within 3–4 weeks after implantation) and (4) late (polymerization 7–8 weeks after polymerization). System impedance at 1 kHz was recorded and the tissue reactions were evaluated by immunohistochemistry. We found that under our deposition conditions, PEDOT typically grew at the tip of the electrode, forming an ∼500 µm cloud in the tissue. This is much larger than the typical width of the glial scar (∼150 µm). After polymerization, the impedance amplitude near the neurologically important frequency of 1 kHz dropped for all the groups; however, there was a time window of 3–4 weeks for an optimal decrease in impedance. For all surgery–polymerization time intervals, the polymerization did not cause significant deficits in performance of the DA task, suggesting that hippocampal function was not impaired by PEDOT deposition. However, GFAP+ and ED-1+ cells were also found at the deposition two weeks after the polymerization, suggesting potential secondary scarring. Therefore, less extensive deposition or milder deposition conditions may be desirable to minimize this scarring while maintaining decreased system impedance.

Object Alternation

We studied behavioral variant frontotemporal dementia (bvFTD) using object alternation (OA) as a novel probe of cognition. This task was adopted from animal models and is sensitive to ventrolateral-orbitofrontal and medial frontal function in humans. OA was administered to bvFTD patients, normal controls, and a dementia control group with Alzheimer disease (AD). Two other frontal lobe measures adopted from animal models were administered: delayed response (DR) and delayed alternation (DA). Brain volumes were measured using the semiautomatic brain region extraction method. Compared with the normal controls, bvFTD patients were significantly impaired on OA and DR. For OA and DR, sensitivities and specificities were 100% and 51.5% (cutoff=22.5 errors) and 9.5% and 98% (cutoff=1.5 errors), respectively. Negative predictive value (NPV) for OA was 100% at all prevalence rates. Comparing AD with bvFTD, there were no significant differences on OA, DR, or DA. Nevertheless, positive predictive value (PPV) and NPV were good at all prevalence rates for OA (cutoff=36.5 errors) and DA (cutoff=6 errors); PPV was good for DR (cutoff=9 errors). Error scores above cutoffs favored diagnosis of AD. Performance on OA was significantly related to medial frontal gray matter atrophy. OA, together with DR and DA, may facilitate assessment of bvFTD as a novel probe of medial frontal function.

Motor stereotypies and cognitive perseveration in non-human primates exposed to early gestational irradiation

A number of psychiatric illnesses have been associated with prenatal disturbance of brain development, including autism, attention deficit hyperactivity disorder, and schizophrenia. Individuals afflicted with these disorders exhibit both repetitive motor and cognitive behavior. The potential role that environmental insult to the developing brain may play in generating these aberrant behaviors is unclear. Here we examine the behavioral consequences of an early gestational insult in the non-human primate. Rhesus macaques were exposed to x-irradiation during the first trimester of development to disrupt neurogenesis. The behavior of five fetally irradiated monkeys (FIMs) and five control monkeys (CONs) was observed as they matured from juvenile (1.5years) to adult ages (4–5years). Home-cage behavior was indistinguishable in the two groups. In the testing cage, circling was prevalent in both groups at juvenile ages, persisting to adulthood in three of the five FIMs. One FIM executed a ritualized motor sequence marked by semi-circling and undulating head movements. Seven macaques (4 FIMs, 3 CONs) were tested on a spatial Delayed Alternation (DA) task as adults. Perseverative errors and non-perseverative errors were recorded in early stages of the testing, at the 0 delay interval. While performing DA, FIMs made more errors of perseveration than CONs yet the number of total errors committed did not differ between groups. The presence of motor stereotypies and cognitive perseveration in fetally irradiated non-human primates suggests that environmental insult to the embryonic brain may contribute to repetitive motor and cognitive behaviors in neuropsychiatric diseases.

Delayed alternation performance in rats following recovery from early iron deficiency

Early iron deficiency (ID) is one of the most common nutrient deficiencies in both developed and developing countries. This condition has been linked to perturbations in myelin formation, alterations of monoamine neurotransmitter systems particularly in the striatum, and deficits in energy metabolism particularly in the hippocampus (HP) and prefrontal cortex (PFC) in rats. Early ID has also been traced to long-term behavioral consequences in children in domains linked to these neuropathologies. The current experiment assesses formerly iron deficient (FID) adult rats on a delayed alternation (DA) task — a procedure thought to be sensitive to PFC dysfunction. Rat dams were started on an iron deficient chow at gestational day (G) 2 and maintained on this diet until postnatal day (P) 7; behavioral training began at P 65 when animals were iron replete. FID animals exhibited accelerated acquisition (p = 0.002) and fewer errors (p = 0.003) on the DA task compared to controls. These findings may reflect an imbalance between hippocampal and prefrontal modulation of this behavior most likely emanating from long-term hippocampal disinhibition by early ID that persists in spite of early iron treatment from P 7.

Rule knowledge aids performance on spatial and object alternation tasks by alcoholic patients with and without Korsakoff's amnesia.

Delayed alternation (DA) and object alternation (OA) tasks traditionally have been used to measure defective response inhibition associated with dysfunction of frontal brain systems. However, these tasks are also sensitive to nonfrontal lesions, and cognitive processes such as the induction of rule-learning strategies also are needed in order to perform well on these tasks. Performance on DA and OA tasks was explored in 10 patients with alcohol-induced persisting amnestic disorder (Korsakoff's syndrome), 11 abstinent long-term alcoholics, and 13 healthy non-alcoholic controls under each of two rule provision conditions: Alternation Rule and Correction Rule. Results confirmed that rule knowledge is a crucial cognitive component for solving problems such as DA and OA, and therefore, that errors on these tasks are not due to defective response inhibition alone. Further, rule-induction strategies were helpful to Korsakoff patients, despite their poorer performance on the tasks. These results stress the role of multiple cognitive abilities in successful performance on rule induction tasks. Evidence that these cognitive abilities are served by diffusely distributed neural networks should be considered when interpreting behavioral impairments on these tasks.

The effect of cingulate cortex lesions on task switching and working memory.

Anatomic interconnections between the prefrontal and anterior cingulate cortices suggest that these areas may have similar functions. Here we report the effect of anterior cingulate removal on task switching, error monitoring, and working memory. Neuroimaging studies have implicated the cingulate cortex in all these processes. Six macaques were taught task switching (TS) and delayed alternation (DA) paradigms. TS required switching between two conditional response tasks with mutually incompatible response selection rules. DA required alternation between two identically covered food-well positions. In the first set of experiments, anterior cingulate lesions did not consistently impair TS or DA performance. One animal performed worst on both TS and DA and in this animal the cingulate sulcus lesion was most complete. In the second set of experiments, we confirmed that larger anterior cingulate lesions, which included the sulcus, consistently impaired TS but only led to a mild and equivocal impairment of DA. The TS error pattern, however, did not suggest an impairment of TS per se. The consequence of a cingulate lesion is, therefore, distinct to that of a prefrontal lesion. TS error distribution analyses provided some support for a cingulate role in monitoring responses for errors and subsequent correction but the pattern of reaction time change in TS was also indicative of a failure to sustain attention to the task and the responses being made.

Primate rhinal cortex participates in both visual recognition and working memory tasks: functional mapping with 2-DG.

The rhinal cortex in the medial temporal lobe has been implicated in object recognition memory tasks and indeed is considered to be the critical node in a visual memory network. Previous studies using the 2-deoxyglucose method have shown that thalamic and hippocampal structures thought to be involved in visual recognition memory are also engaged by spatial and object working memory tasks in the nonhuman primate. Networks engaged in memory processing can be recognized by analysis of patterns of activation accompanying performance of specifically designed tasks. In the present study, we compared metabolic activation of the entorhinal and perirhinal cortex during the performance of three working memory tasks [delayed response (DR), delayed alternation (DA), and delayed object alternation (DOA)] to that induced by a standard recognition memory task [delayed match-to-sample (DMS)] and a sensorimotor control task in rhesus monkeys. A region-of-interest analysis revealed elevated local cerebral glucose utilization in the perirhinal cortex in animals performing the DA, DOA, and DMS tasks, and animals performing the DMS task were distinct in showing a strong focus of activation in the lateral perirhinal cortex. No significant differences were evident between groups performing memory and control tasks in the entorhinal cortex. These findings suggest that the perirhinal cortex may play a much broader role in memory processing than has been previously thought, encompassing explicit working memory as well as recognition memory.

Working Memory Impairments in Alcohol‐Dependent Participants Without Clinical Amnesia

The delayed alternation (DA) task is highly sensitive to the deficits of nonhuman animals with alcohol-related brain damage. DA is thought to measure working memory which serves as a temporary store for processing of information. However, performance on this type of task has only been investigated in alcohol-dependent humans with severe cognitive deficits. The aim of the current study was to explore the validity of DA as a test sensitive to alcohol-related brain damage by manipulating storage and processing components in three versions of the task. It was hypothesized that alcohol-dependent people would perform worse than control participants and that their deficits would be more pronounced in DA versions with maximal working memory demands. A sample of 12 alcohol-dependent participants without Wernicke-Korsakoff syndrome was compared with a sample of 12 nonalcohol-dependent controls on three versions of DA. These versions, in order of increasing working memory demand, were single alternation (LR), double alternation (LLRR), and asymmetric alternation (LRRR). DA was administered on a personal computer and performance measured by the number of trials taken to reach criterion. Alcohol-dependent participants, compared with the control participants, took more trials to reach learning criterion on DA on all versions when analyzed together (p = 0.002). Performance on DA was also found to deteriorate with increased working memory demands in both groups of participants (p < 0.001). However, the deficits of alcohol-dependent participants were most pronounced on the DA task with moderate (LLRR) as opposed to extreme (LRRR) working memory demands. The results indicate that both storage and processing demands are necessary for task performance and demonstrate sensitivity of DA to alcohol-related brain injury.

Measures of Prefrontal System Dysfunction in Posttraumatic Stress Disorder

Clinical observations have suggested that individuals who have suffered traumatic stressful events exhibit disruption in abilities mediated by frontal brain systems. Therefore, this study employed tasks sensitive to frontal lobe dysfunction, including delayed response (DR), delayed alternation (DA), object alternation (OA), delayed matching-to-sample (DMTS), and delayed nonmatching-to-sample (DNMTS), with participants having posttraumatic stress disorder (PTSD). Compared to controls, the PTSD participants were unimpaired on DA and DMTS, but they showed deficits on DR, OA, and DNMTS tasks. This pattern of results suggests disruption of functioning in selective prefrontal brain systems. Results are discussed in the context of the neuropsychological features of PTSD, as well as possible neuropathological and etiological underpinnings of this disorder.

Orbitofrontal function, object alternation and perseveration.

Object alternation (OA) is a well-established measure of perseveration and orbitofrontal function in non-human primates. Although several studies have used OA to examine orbitofrontal system dysfunction in humans with neurological and psychiatric disease, this task itself has not been validated as a bona fide measure of frontal dysfunction in humans. To address this issue, six patients with bilateral frontal lobe lesions documented by computerized tomography (CT) or magnetic resonance imaging (MRI) and 15 healthy controls were given OA, as well as other measures of frontal system dysfunction, delayed alternation (DA), delayed response (DR), and the Wisconsin Card Sorting Test (WCST). The CT and MRI scans were interpreted blindly. The patients with bilateral frontal lesions were significantly impaired on OA, DA, DR and the WCST. Analyses of the CT/MRI lesions suggest that the neuroanatomical regions involved in the deficits on OA include Brodmann areas 10, 24, 32 and 47, as well as possibly 11, and that OA is a sensitive measure of ventrolateral-orbitofrontal and medial frontal dysfunction in humans. Our findings lend further support for the use of experimental paradigms adopted from animal models to study the functional neuroanatomy and neuropsychological mechanisms underlying cognitive functions in humans with neurological and psychiatric disease.

Dissociation of mnemonic coding and other functional neuronal processing in the monkey prefrontal cortex.

Single-neuron activity was recorded in the prefrontal cortex of three monkeys during the performance of a spatial delayed alternation (DA) task and during the presentation of a variety of visual, auditory, and somatosensory stimuli. The aim was to study the relationship between mnemonic neuronal processing and other functional neuronal responsiveness at the single-neuron level in the prefrontal cortex. Recordings were performed in both experimental situations from 152 neurons. The majority of the neurons (92%) was recorded in the prefrontal cortex. Nine of the neurons were recorded in the dorsal bank of the anterior cingulate sulcus and two in the premotor cortex. Of the total number of neurons recorded in the prefrontal area, 32% fired in relation to the DA task performance and 39% were responsive to sensory stimulation or to the movements of the monkey outside of the memory task context. Altogether 42% of the recorded neurons were neither activated by the various stimuli nor by the DA task performance. Three types of task-related neuronal activity were recorded: delay related, delay and movement related, and movement related. The majority of the task-related neurons (n = 33, 73%) fired in relation to the delay period. Of the delay-related neurons, 26 (79%) were spatially selective. The number of spatially selective delay-related neurons of the whole population of recorded neurons was 18%. Twelve task-related neurons (27%) fired in relation to the response period of the DA task. Five of these neurons changed their firing rate during the delay period and were classified as delay/movement-related neurons. Contrary to the delay-related neurons, less than half (42%) of the response-related neurons were spatially selective. The majority (70%) of the delay-related neurons could not be activated by any of the sensory stimuli used and did not fire in relation to the movements of the monkey. The remaining portion of the delay-related neurons was activated by stationary and moving visual stimuli or by visual fixation of an object. In contrast to the delay-related neurons, the majority (66%) of the task-related neurons firing in relation to the movement period were also responsive to sensory stimulation outside of the task context. The majority of these neurons responded to visual stimulation, visual fixation of an object, or tracking eye movements. One neuron gave a somatomotor and another a polysensory response. The majority (n = 37, 67%) of all neurons responding to stimulation outside of the task context did not fire in relation to the DA task performance. The majority of their responses was elicited by visual stimuli or was related to visual fixation of an object or to eye movements. Only six neurons fired in relation to auditory, somatosensory, or somatomotor stimulation. This study provides further evidence about the significance of the dorsolateral prefrontal cortex in spatial working memory processing. Although a considerable number of all DA task-related neurons responded to visual, somatosensory, and auditory stimulation or to the movements of the monkey, most delay-related neurons engaged in the spatial DA task did not respond to extrinsic sensory stimulation. These results indicate that most prefrontal neurons firing selectively during the delay phase of the DA task are highly specialized and process only task-related information.

Behavioral Characterization of Quinolinate-Induced Lesions of the Medial Striatum: Relevance for Huntington's Disease

Huntington’s disease (HD) is an inherited neurodegenerative disorder in which the striatum undergoes marked atrophic changes. Patients with HD typically have impaired cognitive function, including deficient visuospatial skills, lack of cognitive flexibility and poor recall of memories. The relationship between these cognitive abnormalities and the striatal degeneration of HD is incompletely understood. In order to explore this issue, we studied the behavior of rats with histologically confirmed bilateral quinolinate (QUIN)-induced lesions of the medial striatum. In a series of Morris Water Maze (MWM) experiments and Delayed Alternation (DA) tests, QUIN-lesioned animals exhibited: (i) impaired acquisition of visuospatial skills; (ii) impaired “transfer of learning”; (iii) perseverative behavior; (iv) deficient retrieval or retention of stored memories. The lesioned rats were unimpaired when swimming to a visible platform, while moving spontaneously in behavior boxes, and when performing various specialized tests of motor function. These results indicate that QUIN-induced lesions of the medial striatum can produce impairments of visuospatial skills, cognitive flexibility, and recall. These are the categories of cognitive function that are disturbed in HD. This suggests that the striatal degeneration of HD could be a sufficient explanation for the cognitive abnormalities associated with the illness.

The effects of prefrontal intracortical microinjections of an alpha-2 agonist, alpha-2 antagonist and lidocaine on the delayed alternation performance of aged rats

A selective alpha-2 agonist medetomidine, a selective alpha-2 antagonist atipamezole and lidocaine were injected into the prefrontal cortex of aged rats that had been trained to perform a delayed alternation (DA) task in a T maze. Medetomidine at the dose of 0.01 μg/μl improved the memory task performance in four of five rats. The fifth rat improved its performance at the dose of 1.0 μg/μl. Atipamezole did not have any effect on the task performance. The effect of a systemic dose of medetomidine (3 μg/kg), which was previously shown to improve the task performance in old rats, was reversed by an intracortical injection of atipamezole. Lidocaine impaired the DA performance significantly. The results suggest that the beneficial effects of medetomidine on the working memory of old rats are mediated at least partly through the prefrontal cortex.

Frontal and parietal lobe dysfunction in depression: Delayed alternation and tactile learning deficits

To evaluate frontal and parietal lobe involvement in depression, behavioral tests sensitive to damage in these regions were administered to depressed patients over age 50. Delayed alternation (DA), delayed response and object alternation were used to assess dorsolateral frontal and orbitofrontal function. Tactile learning problems (TOL and TRL) assessed parietal lobe integrity. Depressed patients were significantly impaired on DA, TOL and TRL, suggesting spatial memory (DA) and tactile learning deficits. The functional neuroanatomy underlying these deficits may share features with Parkinson's and Alzheimer's diseases.

Selective delayed alternation deficits in dominantly inherited olivopontocerebellar atrophy

In order to characterize more completely the nature of the frontal lobe-type cognitive changes in patients with dominantly inherited olivopontocerebellar atrophy (OPCA) we administered two tasks sensitive to frontal system dysfunction, delayed alternation (DA) and delayed response (DR), to 12 patients from one OPCA family. Affected members from this family have previously been shown to have a marked and widespread cerebral (including frontal) cortical cholinergic reduction as severe as that observed in Alzheimer's disease. Performance on DA, but not on DR, was significantly impaired in the OPCA patients compared to that in the controls. We suggest that the DA deficits in OPCA could be a consequence of a loss of cholinergic innervation to orbitofrontal or possibly temporal cortical areas and/or damage to the integrity of the cerebellofrontal neuronal connections.

Medial septal lesions impair performance on a preoperatively acquired delayed alternation task

Male hooded rats were preoperatively trained to perform an operant delayed alternation (DA) task. The rats were tested, for 10 days each, on DA at 5-, 10-, 20-, and 30-s delays. The rats were then randomly assigned to serve as control subjects or receive a medial septal lesion. Following surgical recovery the rats were retested on DA in the exact manner as they were tested preoperatively. Prior to surgery the groups did not differ, but all rats improved over days of testing, and performed better at short delays than at long delays. In contrast, group differences were obvious following surgery, with the septal-lesioned subjects showing a clear impairment. The control subjects ranged between 85% correct (end of 5-s delay) to 65% correct (end of 30-s delay), while the septal-lesioned rats ranged between 72% correct (end of 5-s delay) to 50% correct (end of 30-s delay). The results are discussed in terms of a working memory impairment produced by the septal lesions.

Vertical and horizontal coding of space in the monkey dorsolateral prefrontal cortex

Single cell activity in the dorsolateral prefrontal cortex was recorded in a monkey performing a delayed alternation (DA) task in 3 directions, to the left, to the right, and upwards. Among the 127 units studied in all three directions, 18 neurons were spatially selective in one direction (to the left, to the right or upwards), 37 neurons in two directions and 8 neurons in each 3 directions during the performance of the DA task. Of the 9 neurons that were spatially selective upwards, 8 had a specific pattern of activity during the delay period and one during the response period. When several spatial directions are studied in a DA task, as in this work, it becomes evident that the prefrontal cortex contains a large number of spatially selective neurons. The results of this study suggest that there is a spatial memory map in the prefrontal cortex which is needed not only when a DA task is performed to the left and to the right but also in the upward direction.

Effect of combined or separate administration of piracetam and choline on learning and memory in the rat.

Different groups of rats received combined or separate administration of different doses of piracetam (P1:100, P2:200, and P4:400 mg/kg) and choline (C1:100 and C2:200 mg/kg). Compared to control treatment, C1 significantly improved performance in a delayed alternation (DA) task, while P1, P2, P4 or P1C1 had no effect. Moreover, rats receiving P2C1 and P4C1 were significantly inferior in acquiring DA to rats receiving the vehicle or separate administration of P1, P2 or C1. The different treatments with combined or separate administration of P and C had no effect on spontaneous locomotor activity and two-way avoidance conditioning. In a recognition-task only groups C1 and P4 were able to discriminate between familiar and new objects. The combined or separate administration of P1 and C1 on NA, DA, DOPAC, 5-HT, 5-HIAA levels, CAT activity and choline uptake were measured in frontal cortex and hippocampus: the only significant effect was a 5-HT increase in the hippocampus of rats treated with C1.