Facilitation of spatial working memory performance following intra-prefrontal cortical administration of the adrenergic alpha1 agonist phenylephrine

α7 nicotinic acetylcholine receptors in the hippocampal circuit: taming complexity

Cholinergic innervation of the hippocampus uses the neurotransmitter acetylcholine (ACh) to coordinate neuronal circuit activity while simultaneously influencing the function of non-neuronal cell types. The α7 nicotinic ACh receptor (nAChR) subtype is highly expressed throughout the hippocampus, has the highest calcium permeability compared with other subtypes of nAChRs, and is of high therapeutic interest due to its association with a variety of neurological disorders and neurodegenerative diseases. In this review, we synthesize research describing α7 nAChR properties, function, and relationship to cognitive dysfunction within the hippocampal circuit and highlight approaches to help improve therapeutic development.

Chronic, Multi-Site Recordings Supported by Two Low-Cost, Stationary Probe Designs Optimized to Capture Either Single Unit or Local Field Potential Activity in Behaving Rats

Rodent models of cognitive behavior have greatly contributed to our understanding of human neuropsychiatric disorders. However, to elucidate the neurobiological underpinnings of such disorders or impairments, animal models are more useful when paired with methods for measuring brain function in awake, behaving animals. Standard tools used for systems-neuroscience level investigations are not optimized for large-scale and high-throughput behavioral battery testing due to various factors including cost, time, poor longevity, and selective targeting limited to measuring only a few brain regions at a time. Here we describe two different "user-friendly" methods for building extracellular electrophysiological probes that can be used to measure either single units or local field potentials in rats performing cognitive tasks. Both probe designs leverage several readily available, yet affordable, commercial products to facilitate ease of production and offer maximum flexibility in terms of brain-target locations that can be scalable (32-64 channels) based on experimental needs. Our approach allows neural activity to be recorded simultaneously with behavior and compared between micro (single unit) and more macro (local field potentials) levels of brain activity in order to gain a better understanding of how local brain regions and their connected networks support cognitive functions in rats. We believe our novel probe designs make collecting electrophysiology data easier and will begin to fill the gap in knowledge between basic and clinical research.

Acute vagus nerve stimulation enhances reversal learning in rats

Cognitive flexibility is a prefrontal cortex-dependent neurocognitive process that enables behavioral adaptation in response to changes in environmental contingencies. Electrical vagus nerve stimulation (VNS) enhances several forms of learning and neuroplasticity, but its effects on cognitive flexibility have not been evaluated. In the current study, a within-subjects design was used to assess the effects of VNS on performance in a novel visual discrimination reversal learning task conducted in touchscreen operant chambers. The task design enabled simultaneous assessment of acute VNS both on reversal learning and on recall of a well-learned discrimination problem. Acute VNS delivered in conjunction with stimuli presentation during reversal learning reliably enhanced learning of new reward contingencies. Enhancement was not observed, however, if VNS was delivered during the session but was not coincident with presentation of to-be-learned stimuli. In addition, whereas VNS delivered at 30 HZ enhanced performance, the same enhancement was not observed using 10 or 50 Hz. Together, these data show that acute VNS facilitates reversal learning and indicate that the timing and frequency of the VNS are critical for these enhancing effects. In separate rats, administration of the norepinephrine reuptake inhibitor atomoxetine also enhanced reversal learning in the same task, consistent with a noradrenergic mechanism through which VNS enhances cognitive flexibility.

Axo-axonic synapses: Diversity in neural circuit function

The chemical synapse is the principal form of contact between neurons of the central nervous system. These synapses are typically configured as presynaptic axon terminations onto postsynaptic dendrites or somata, giving rise to axo-dendritic and axo-somatic synapses, respectively. Beyond these common synapse configurations are less-studied, non-canonical synapse types that are prevalent throughout the brain and significantly contribute to neural circuit function. Among these are the axo-axonic synapses, which consist of an axon terminating on another axon or axon terminal. Here, we review evidence for axo-axonic synapse contributions to neural signaling in the mammalian nervous system and survey functional neural circuit motifs enabled by these synapses. We also detail how recent advances in microscopy, transgenics, and biological sensors may be used to identify and functionally assay axo-axonic synapses.

Current Developments on the Role of α1-Adrenergic Receptors in Cognition, Cardioprotection, and Metabolism

The α₁-adrenergic receptors (ARs) are G-protein coupled receptors that bind the endogenous catecholamines, norepinephrine, and epinephrine. They play a key role in the regulation of the sympathetic nervous system along with β and α₂-AR family members. While all of the adrenergic receptors bind with similar affinity to the catecholamines, they can regulate different physiologies and pathophysiologies in the body because they couple to different G-proteins and signal transduction pathways, commonly in opposition to one another. While α₁-AR subtypes (α_1A, α_1B, α_1C) have long been known to be primary regulators of vascular smooth muscle contraction, blood pressure, and cardiac hypertrophy, their role in neurotransmission, improving cognition, protecting the heart during ischemia and failure, and regulating whole body and organ metabolism are not well known and are more recent developments. These advancements have been made possible through the development of transgenic and knockout mouse models and more selective ligands to advance their research. Here, we will review the recent literature to provide new insights into these physiological functions and possible use as a therapeutic target.

New frontiers in translational research: Touchscreens, open science, and the mouse translational research accelerator platform

Many neurodegenerative and neuropsychiatric diseases and other brain disorders are accompanied by impairments in high-level cognitive functions including memory, attention, motivation, and decision-making. Despite several decades of extensive research, neuroscience is little closer to discovering new treatments. Key impediments include the absence of validated and robust cognitive assessment tools for facilitating translation from animal models to humans. In this review, we describe a state-of-the-art platform poised to overcome these impediments and improve the success of translational research, the Mouse Translational Research Accelerator Platform (MouseTRAP), which is centered on the touchscreen cognitive testing system for rodents. It integrates touchscreen-based tests of high-level cognitive assessment with state-of-the art neurotechnology to record and manipulate molecular and circuit level activity in vivo in animal models during human-relevant cognitive performance. The platform also is integrated with two Open Science platforms designed to facilitate knowledge and data-sharing practices within the rodent touchscreen community, touchscreencognition.org and mousebytes.ca. Touchscreencognition.org includes the Wall, showcasing touchscreen news and publications, the Forum, for community discussion, and Training, which includes courses, videos, SOPs, and symposia. To get started, interested researchers simply create user accounts. We describe the origins of the touchscreen testing system, the novel lines of research it has facilitated, and its increasingly widespread use in translational research, which is attributable in part to knowledge-sharing efforts over the past decade. We then identify the unique features of MouseTRAP that stand to potentially revolutionize translational research, and describe new initiatives to partner with similar platforms such as McGill's M3 platform (m3platform.org).

α1-Adrenergic Receptors in Neurotransmission, Synaptic Plasticity, and Cognition

α₁-adrenergic receptors are G-Protein Coupled Receptors that are involved in neurotransmission and regulate the sympathetic nervous system through binding and activating the neurotransmitter, norepinephrine, and the neurohormone, epinephrine. There are three α₁-adrenergic receptor subtypes (α_1A, α_1B, α_1D) that are known to play various roles in neurotransmission and cognition. They are related to two other adrenergic receptor families that also bind norepinephrine and epinephrine, the β- and α₂-, each with three subtypes (β₁, β₂, β₃, α_2A, α_2B, α_2C). Previous studies assessing the roles of α₁-adrenergic receptors in neurotransmission and cognition have been inconsistent. This was due to the use of poorly-selective ligands and many of these studies were published before the characterization of the cloned receptor subtypes and the subsequent development of animal models. With the availability of more-selective ligands and the development of animal models, a clearer picture of their role in cognition and neurotransmission can be assessed. In this review, we highlight the significant role that the α₁-adrenergic receptor plays in regulating synaptic efficacy, both short and long-term synaptic plasticity, and its regulation of different types of memory. We will also present evidence that the α₁-adrenergic receptors, and particularly the α_1A-adrenergic receptor subtype, are a potentially good target to treat a wide variety of neurological conditions with diminished cognition.

Chronic Restraint Stress Affects Network Oscillations in the Anterior Cingulate Cortex in Mice

The anterior cingulate cortex (ACC) is vulnerable to stress. Its dysfunction is observed in psychiatric disorders manifested as alterations in network oscillations. Mechanisms linking stress load to disturbed emotional-cognitive behaviors are of essential importance to further elucidate therapeutic strategies for psychiatric diseases. Here, we analyzed the effects of chronic restraint stress (CRS) load in juvenile mice on kainic acid (KA)-induced network oscillations in ACC slice preparations and on the forced swim test (FST). The immobility time (IT) was shortened at the beginning of the FST in CRS mice. Power spectral density (PSD) obtained from KA-induced oscillations in field potentials in the superficial layers of the ACC were altered in slices from the CRS mice. The PSD was decreased in CRS mice at the alpha (8-12 Hz), beta (13-30 Hz), low gamma (30-50 Hz), and high gamma (50-80 Hz) components. Noradrenaline increased the PSD of the theta (3-8 Hz) components in both the control and CRS groups, and also in alpha components only in the CRS group. Dopamine did not modulate the PSD of any frequency components in the control mice, whereas it enhanced the PSD of theta and alpha components in CRS mice. It was suggested that chronic stress load affects the dynamics of the network oscillations in the ACC with enhanced cathecolaminergic modulation.

Excitation of prefrontal cortical neurons during conditioning enhances fear memory formation

Animals can remember a situation associated with an aversive event. Contextual fear memory is initially encoded and consolidated in the hippocampus and gradually consolidated in multiple brain regions over time, including the medial prefrontal cortex (PFC). However, it is not fully understood how PFC neurons contribute to contextual fear memory formation during learning. In the present study, neuronal activity was increased in PFC neurons utilizing the pharmacogenetic hM3Dq-system in male mice. We show that fear expression and memory formation are enhanced by increasing neuronal activity in PFC during conditioning phase. Previous studies showed that the activation of hM3Dq receptor in a subset of amygdala neurons enhanced fear memory formation and biased which neurons are allocated to a memory trace, in which immediate early gene c-fos was preferentially expressed following memory retrieval in these pre-activated neurons. In this study, hM3Dq activation in PFC could not change the probability of c-fos expression in pre-activated neurons flowing memory retrieval. Instead, the number c-fos positive neurons following memory retrieval was significantly increased in the basolateral amygdala. Our results suggest that neuronal activity in PFC at the time of learning modulates fear memory formation and downstream cellular activity at an early phase.

Effects of Noradrenergic Stimulation Upon Context-Related Extinction Learning Performance and BOLD Activation in Hippocampus and Prefrontal Cortex Differ Between Participants Showing and Not Showing Renewal

While the neural structures mediating context-related renewal of extinction are well established, the neurotransmitter systems processing renewal remain elusive. Noradrenergic stimulation before extinction improved learning, but did not alter renewal. Since context processing already during initial conditioning can influence renewal, in this fMRI study we investigated how noradrenergic stimulation by a single dose of atomoxetine (ATO) before initial acquisition of a context-related predictive-learning task affects subsequent learning and renewal in humans. ATO participants showing contextual renewal (REN) exhibited a selective extinction learning deficit compared to placebo (PLAC) and ATO participants lacking renewal (ATO NoREN), probably owing to formation of more stable associations during acquisition. New learning and retrieval during the extinction phase as well as initial acquisition were unimpaired. In ATO REN, higher activation in right inferior frontal gyrus (iFG) during acquisition may have supported the formation of more stable associations, while reduced activation in hippocampus and left iFG during extinction was associated with impaired context encoding and response inhibition. During recall, ATO REN showed reduced overall context-dependent renewal associated with higher activation in medial PFC and right hippocampus. The results demonstrate the importance of noradrenergic processing in inferior frontal cortex and hippocampus for human extinction learning, but not necessarily initial conditioning. Since an identical atomoxetine treatment evoked diverging blood-oxygen level dependent (BOLD) activation patterns in REN and NoREN participants, the effect is presumably related to the participants’ preferred processing strategies that may have recruited differentially interconnected networks in which noradrenergic stimulation produced diverging consequences. In the ATO REN group, probably an additive effect of their preferred processing strategy, which pre-activated the noradrenergic system, and the experimental treatment caused a shift beyond the optimal working range of the noradrenergic system, thus modulating BOLD activation in a way that impaired extinction learning and recall.

Noradrenergic α1-Adrenoceptor Actions in the Primate Dorsolateral Prefrontal Cortex

Noradrenergic (NE) α1-adrenoceptors (α1-ARs) contribute to arousal mechanisms and play an important role in therapeutic medications such as those for the treatment of posttraumatic stress disorder (PTSD). However, little is known about how α1-AR stimulation influences neuronal firing in the dorsolateral prefrontal cortex (dlPFC), a newly evolved region that is dysfunctional in PTSD and other mental illnesses. The current study examined the effects of α1-AR manipulation on neuronal firing in dlPFC of rhesus monkeys performing a visuospatial working memory task, focusing on the "delay cells" that maintain spatially tuned information across the delay period. Iontophoresis of the α1-AR antagonist HEAT (2-{[β-(4-hydroxyphenyl)ethyl]aminomethyl}-1-tetralone) had mixed effects, reducing firing in a majority of neurons but having nonsignificant excitatory effects or no effect in remaining delay cells. These data suggest that endogenous NE has excitatory effects in some delay cells under basal conditions. In contrast, the α1-AR agonists phenylephrine and cirazoline suppressed delay cell firing and this was blocked by coadministration of HEAT. These results indicate an inverted-U dose response for α1-AR actions, with mixed excitatory actions under basal conditions and suppressed firing with high levels of α1-AR stimulation such as with stress exposure. Immunoelectron microscopy revealed α1-AR expression presynaptically in axons and axon terminals and postsynaptically in spines, dendrites, and astrocytes. It is possible that α1-AR excitatory effects arise from presynaptic excitation of glutamate release, whereas postsynaptic actions suppress firing through calcium-protein kinase C opening of potassium channels on spines. The latter may predominate under stressful conditions, leading to loss of dlPFC regulation during uncontrollable stress.SIGNIFICANCE STATEMENT Noradrenergic stimulation of α1-adrenoceptors (α1-ARs) is implicated in posttraumatic stress disorder (PTSD) and other mental disorders that involve dysfunction of the prefrontal cortex, a brain region that provides top-down control. However, the location and contribution of α1-ARs to prefrontal cortical physiology in primates has received little attention. This study found that α1-ARs are located near prefrontal synapses and that α1-AR stimulation has mixed effects under basal conditions. However, high levels of α1-AR stimulation, as occur with stress, suppress neuronal firing. These findings help to explain why we lose top-down control under conditions of uncontrollable stress when there are high levels of noradrenergic release in brain and why blocking α1-AR, such as with prazosin, may be helpful in the treatment of PTSD.

Do TRPC channels support working memory? Comparing modulations of TRPC channels and working memory through G-protein coupled receptors and neuromodulators

Working memory is a crucial ability we use in daily life. However, the cellular mechanisms supporting working memory still remain largely unclear. A key component of working memory is persistent neural firing which is believed to serve short-term (hundreds of milliseconds up to tens of seconds) maintenance of necessary information. In this review, we will focus on the role of transient receptor potential canonical (TRPC) channels as a mechanism underlying persistent firing. Many years of in vitro work have been suggesting a crucial role of TRPC channels in working memory and temporal association tasks. If TRPC channels are indeed a central mechanism for working memory, manipulations which impair or facilitate working memory should have a similar effect on TRPC channel modulation. However, modulations of working memory and TRPC channels were never systematically compared, and it remains unanswered whether TRPC channels indeed contribute to working memory in vivo or not. In this article, we review the effects of G-protein coupled receptors (GPCR) and neuromodulators, including acetylcholine, noradrenalin, serotonin and dopamine, on working memory and TRPC channels. Based on comparisons, we argue that GPCR and downstream signaling pathways that activate TRPC, generally support working memory, while those that suppress TRPC channels impair it. However, depending on the channel types, areas, and systems tested, this is not the case in all studies. Further work to clarify involvement of specific TRPC channels in working memory tasks and how they are affected by neuromodulators is still necessary in the future.

Spatial working memory in the touchscreen operant platform is disrupted in female rats by ovariectomy but not estrous cycle

Learning and memory deficits have been described in rats and mice after ovariectomy (OVX) and across the estrous cycle. Preclinical researchers therefore often avoid using female animals and, consequently, a large male bias exists in the preclinical cognitive literature. In the present study we examined the role of sex hormones in the touchscreen operant platform using the spatial working memory trial unique nonmatching-to-location (TUNL) task. Twenty-nine Long Evans rats were trained to acquire the TUNL task including three incremental spatial separations (S0, S1, S2). Following 20 consecutive days of training, subjects in experiment 1 (n=15) remained intact and immediately progressed to TUNL testing, while subjects in experiment 2 were OVX (n=6) or sham-operated (n=8) prior to testing. Subjects were tested on 4 spatial separations (S0-3) with a 1s or 6s delay between the sample and nonmatching stimuli. The estrous cycle of intact rats was monitored during the 4weeks of testing. The estrous cycle phase did not significantly affect performance. In contrast, compared to intact rats, OVX impaired performance at larger spatial separations (S2-3) during the 1s delay condition. Further, during the 6s delay, OVX impaired S2 performance, however not S3. Our results suggest a probable shift in cognitive strategy following OVX, when tested with a large and novel spatial separation. Our findings suggest that ovarian hormone deprivation following OVX, but not estrous cycle, impairs spatial working memory as measured by the TUNL task. This research is relevant for future studies utilising the touchscreen TUNL task and for cognitive testing of female rats.

Medial prefrontal cortex and dorsomedial striatum are necessary for the trial-unique, delayed nonmatching-to-location (TUNL) task in rats: role of NMDA receptors

The trial-unique, delayed nonmatching-to-location (TUNL) task is a recently developed behavioral task that measures spatial working memory and a form of pattern separation in touchscreen-equipped operant conditioning chambers. Limited information exists regarding the neurotransmitters and neural substrates involved in the task. The present experiments tested the effects of systemic and intracranial injections of NMDA receptor antagonists on the TUNL task. After training, male Long Evans rats systemically injected with the competitive NMDA receptor antagonist CPP (10 mg/kg) had impaired accuracy regardless of the degree of stimuli separation or length of delay between the sample and test phases. Injections of Ro 25-6981 (6 or 10 mg/kg), an antagonist selective for GluN2B subunit-containing NMDA receptors, did not affect accuracy on the task. Direct infusion of the competitive NMDA receptor antagonist AP5 into mPFC or dmSTR reduced overall accuracy on the TUNL task. These results demonstrate that TUNL task performance depends on NMDA receptors within the mPFC and dmSTR.

Haploinsufficiency of EHMT1 improves pattern separation and increases hippocampal cell proliferation

Heterozygous mutations or deletions of the human Euchromatin Histone Methyltransferase 1 (EHMT1) gene are the main causes of Kleefstra syndrome, a neurodevelopmental disorder that is characterized by impaired memory, autistic features and mostly severe intellectual disability. Previously, Ehmt1^+/− heterozygous knockout mice were found to exhibit cranial abnormalities and decreased sociability, phenotypes similar to those observed in Kleefstra syndrome patients. In addition, Ehmt1^+/− knockout mice were impaired at fear extinction and novel- and spatial object recognition. In this study, Ehmt1^+/− and wild-type mice were tested on several cognitive tests in a touchscreen-equipped operant chamber to further investigate the nature of learning and memory changes. Performance of Ehmt1^+/− mice in the Visual Discrimination & Reversal learning, object-location Paired-Associates learning- and Extinction learning tasks was found to be unimpaired. Remarkably, Ehmt1^+/− mice showed enhanced performance on the Location Discrimination test of pattern separation. In line with improved Location Discrimination ability, an increase in BrdU-labelled cells in the subgranular zone of the dentate gyrus was observed. In conclusion, reduced levels of EHMT1 protein in Ehmt1^+/− mice does not result in general learning deficits in a touchscreen-based battery, but leads to increased adult cell proliferation in the hippocampus and enhanced pattern separation ability.

Locus Ceruleus Norepinephrine Release: A Central Regulator of CNS Spatio-Temporal Activation?

Norepinephrine (NE) is synthesized in the Locus Coeruleus (LC) of the brainstem, from where it is released by axonal varicosities throughout the brain via volume transmission. A wealth of data from clinics and from animal models indicates that this catecholamine coordinates the activity of the central nervous system (CNS) and of the whole organism by modulating cell function in a vast number of brain areas in a coordinated manner. The ubiquity of NE receptors, the daunting number of cerebral areas regulated by the catecholamine, as well as the variety of cellular effects and of their timescales have contributed so far to defeat the attempts to integrate central adrenergic function into a unitary and coherent framework. Since three main families of NE receptors are represented-in order of decreasing affinity for the catecholamine-by: α2 adrenoceptors (α2Rs, high affinity), α1 adrenoceptors (α1Rs, intermediate affinity), and β adrenoceptors (βRs, low affinity), on a pharmacological basis, and on the ground of recent studies on cellular and systemic central noradrenergic effects, we propose that an increase in LC tonic activity promotes the emergence of four global states covering the whole spectrum of brain activation: (1) sleep: virtual absence of NE, (2) quiet wake: activation of α2Rs, (3) active wake/physiological stress: activation of α2- and α1-Rs, (4) distress: activation of α2-, α1-, and β-Rs. We postulate that excess intensity and/or duration of states (3) and (4) may lead to maladaptive plasticity, causing-in turn-a variety of neuropsychiatric illnesses including depression, schizophrenic psychoses, anxiety disorders, and attention deficit. The interplay between tonic and phasic LC activity identified in the LC in relationship with behavioral response is of critical importance in defining the short- and long-term biological mechanisms associated with the basic states postulated for the CNS. While the model has the potential to explain a large number of experimental and clinical findings, a major challenge will be to adapt this hypothesis to integrate the role of other neurotransmitters released during stress in a centralized fashion, like serotonin, acetylcholine, and histamine, as well as those released in a non-centralized fashion, like purines and cytokines.

The NEWMEDS rodent touchscreen test battery for cognition relevant to schizophrenia

RATIONALE

The NEWMEDS initiative (Novel Methods leading to New Medications in Depression and Schizophrenia, http://www.newmeds-europe.com ) is a large industrial-academic collaborative project aimed at developing new methods for drug discovery for schizophrenia. As part of this project, Work package 2 (WP02) has developed and validated a comprehensive battery of novel touchscreen tasks for rats and mice for assessing cognitive domains relevant to schizophrenia.

OBJECTIVES

This article provides a review of the touchscreen battery of tasks for rats and mice for assessing cognitive domains relevant to schizophrenia and highlights validation data presented in several primary articles in this issue and elsewhere.

METHODS

The battery consists of the five-choice serial reaction time task and a novel rodent continuous performance task for measuring attention, a three-stimulus visual reversal and the serial visual reversal task for measuring cognitive flexibility, novel non-matching to sample-based tasks for measuring spatial working memory and paired-associates learning for measuring long-term memory.

RESULTS

The rodent (i.e. both rats and mice) touchscreen operant chamber and battery has high translational value across species due to its emphasis on construct as well as face validity. In addition, it offers cognitive profiling of models of diseases with cognitive symptoms (not limited to schizophrenia) through a battery approach, whereby multiple cognitive constructs can be measured using the same apparatus, enabling comparisons of performance across tasks.

CONCLUSION

This battery of tests constitutes an extensive tool package for both model characterisation and pre-clinical drug discovery.

A novel 2- and 3-choice touchscreen-based continuous trial-unique nonmatching-to-location task (cTUNL) sensitive to functional differences between dentate gyrus and CA3 subregions of the hippocampus

RATIONALE

The touchscreen continuous trial-unique non-matching-to-location task (cTUNL) has been developed to optimise a battery of tasks under NEWMEDS (Novel Methods leading to New Medication in Depression and Schizophrenia, http://www.newmeds-europe.com ). It offers novel task features of both a practical and a theoretical nature compared to existing touchscreen tasks for spatial working memory.

OBJECTIVES

The objective of this study was to determine whether the cTUNL task is sufficiently sensitive to differentiate between dentate gyrus (DG) and CA3 hippocampal subregion contributions to performance.

METHODS

The effect of DG and CA3 dysfunction on memory for locations in the cTUNL task was tested. Rats were assessed on versions of the task-two-choice and three-choice-that differed in memory load. Performance was challenged using manipulations of delay and the spatial separation between target and sample locations.

RESULTS

Dysfunction of the DG disrupts performance across both delay and spatial separations in two-choice cTUNL when the delay is variable and unpredictable. Increasing the working memory load (three stimuli) increases sensitivity to DG dysfunction, with deficits apparent at fixed, short delays. In contrast, CA3 dysfunction did not disrupt performance.

CONCLUSION

Acquisition of cTUNL was rapid, and the task was sensitive to manipulations of delays and separations. A three-choice version of the task was found to be viable. Finally, both the two- and three-choice versions of the task were able to differentiate between limited dysfunction to different areas within the hippocampus. DG dysfunction affected performance when using unpredictable task parameters. CA3 dysfunction did not result in impairment, even at the longest delays tested.