Précis of O'Keefe & Nadel's The hippocampus as a cognitive map

A review of the verbal and visual memory impairments in children with foetal alcohol spectrum disorders

BACKGROUND

Children with Foetal Alcohol Spectrum Disorders (FASD) have significant impairments in memory, negatively affecting academics and daily functioning.

PRIMARY OBJECTIVE

To review published research on: (1) verbal and visual-spatial memory in children with FASD or prenatal alcohol exposure (PAE); (2) animal research on the impact of PAE on memory; and (3) brain areas involved in memory that are affected by PAE.

MAIN OUTCOMES

Verbal memory is one of the main areas of memory affected by gestational alcohol exposure, specifically in encoding and retrieving information. Spatial memory has emerged as a dominant deficit in individuals with FASD, consistent in children, adolescents and adults. There are regions of the brain more typically affected by PAE, which have ties to memory functioning. Animal research has confirmed the presence of impacts to key brain regions involved in memory functioning for those affected by PAE.

CONCLUSION

Memory deficits are a prevalent finding in individuals with PAE. Research in this area is complicated by small sample sizes, difficulty linking animal research to human application and lack of effective connection between existing memory theory and functional memory testing in FASD. New research has shown that there are implications for memory and learning amelioration in children with FASD.

Working Memory, Cues, and Wayfinding in Older Women

Individuals create cognitive maps based on relationships between cues in the environment. Older individuals are often impaired in wayfinding, especially in environments that lack distinctive features. This study examines how working memory ability in older women is related to wayfinding performance in the presence of salient (distinctive, prominent) or nonsalient cues. The degree of salient cue complexity is also examined, thus leading to the hypothesis that salient, complex cues are important in wayfinding and that working memory capacity is related to wayfinding performance. The virtual computer-generated arena is used to test this hypothesis in 20 healthy older women in three different environmental cue conditions varying in salience and complexity. Data analyses indicate that older women perform best in salient cue conditions. A greater working memory capacity is related to improved performance in the nonsalient cue condition. These findings offer preliminary evidence that cue salience is especially important in wayfinding.

Retinoic acid restores adult hippocampal neurogenesis and reverses spatial memory deficit in vitamin A deprived rats

A dysfunction of retinoid hippocampal signaling pathway has been involved in the appearance of affective and cognitive disorders. However, the underlying neurobiological mechanisms remain unknown. Hippocampal granule neurons are generated throughout life and are involved in emotion and memory. Here, we investigated the effects of vitamin A deficiency (VAD) on neurogenesis and memory and the ability of retinoic acid (RA) treatment to prevent VAD-induced impairments. Adult retinoid-deficient rats were generated by a vitamin A-free diet from weaning in order to allow a normal development. The effects of VAD and/or RA administration were examined on hippocampal neurogenesis, retinoid target genes such as neurotrophin receptors and spatial reference memory measured in the water maze. Long-term VAD decreased neurogenesis and led to memory deficits. More importantly, these effects were reversed by 4 weeks of RA treatment. These beneficial effects may be in part related to an up-regulation of retinoid-mediated molecular events, such as the expression of the neurotrophin receptor TrkA. We have demonstrated for the first time that the effect of vitamin A deficient diet on the level of hippoccampal neurogenesis is reversible and that RA treatment is important for the maintenance of the hippocampal plasticity and function.

Modeling the nonlinear properties of the in vitro hippocampal perforant path-dentate system using multielectrode array technology

A modeling approach to characterize the nonlinear dynamic transformations of the dentate gyrus of the hippocampus is presented and experimentally validated. The dentate gyrus is the first region of the hippocampus which receives and integrates sensory information via the perforant path. The perforant path is composed of two distinct pathways: 1) the lateral path and 2) the medial perforant path. The proposed approach examines and captures the short-term dynamic characteristics of these two pathways using a nonparametric, third-order Poisson-Volterra model. The nonlinear characteristics of the two pathways are represented by Poisson-Volterra kernels, which are quantitative descriptors of the nonlinear dynamic transformations. The kernels were computed with experimental data from in vitro hippocampal slices. The electrophysiological activity was measured with custom-made multielectrode arrays, which allowed selective stimulation with random impulse trains and simultaneous recordings of extracellular field potential activity. The results demonstrate that this mathematically rigorous approach is suitable for the multipathway complexity of the hippocampus and yields interpretable models that have excellent predictive capabilities. The resulting models not only accurately predict previously reported electrophysiological descriptors, such as paired pulses, but more important, can be used to predict the electrophysiological activity of dentate granule cells to arbitrary stimulation patterns at the perforant path.

Modeling the nonlinear dynamic interactions of afferent pathways in the dentate gyrus of the hippocampus

The dentate gyrus is the first region of the hippocampus that receives and integrates sensory information (e.g., visual, auditory, and olfactory) via the perforant path, which is composed of two distinct neuronal pathways: the Lateral Perforant Path (LPP) and the Medial Perforant Path (MPP). This paper examines the nonlinear dynamic interactions among arbitrary stimulation patterns at these two afferent pathways and their combined effect on the resulting response of the granule cells at the dentate gyrus. We employ non-parametric Poisson-Volterra models that serve as canonical quantitative descriptors of the nonlinear dynamic transformations of the neuronal signals propagating through these two neuronal pathways. These Poisson-Volterra models are estimated in the so-called "reduced form" with experimental data from in vitro hippocampal slices and provide excellent predictions of the electrophysiological activity of the granule cells in response to arbitrary stimulation patterns. The data are acquired through a custom-made multi-electrode-array system, which stimulated simultaneously the two pathways with random impulse trains and recorded the neuronal postsynaptic activity at the granule cell layer. The results of this study show that significant nonlinear interactions exist between the LPP and the MPP that may be critical for the integration of sensory information performed by the dentate gyrus of the hippocampus.

Atropine-induced, state-dependent learning for spatial information, but not for visual cues

This study investigates state-dependent learning employing atropine. The reaction of rats to (1) the presentation of novel stimuli, (2) habituation to intermittent presentations of the same stimulus at the same local, (3) spatial change at the site of stimulus presentation, and (4) a visual stimulus change, was investigated in the straight alleyway test, controlling for the possible development of behavioral and/or pharmacological tolerance. Our findings reveal that rats habituated to stimulus presentation at a specific location, when under an atropine effect, do react to stimulus presentation at another location, or to a different stimulus, when under an atropine effect, indicating that this drug does not interfere with the acquisition of spatial or visual information. Differently, however, rats habituated to stimulus presentation at a specific location in the absence of an atropine effect are unable to react to spatial change when under the atropine effect, but do react to a visual stimulus change. This suggests that atropine interferes either with the retrieval of previously acquired spatial information or with the comparison of previously acquired spatial information with current information, but does not interfere with visual recognition. These findings reveal that atropine interferes with the use of spatial information acquired in the absence of a drug effect.

Human hippocampal-dependent tasks: Is awareness necessary or sufficient?

The hippocampus has been shown to be required for the acquisition of declarative or explicit memory. Whether all hippocampal-dependent forms of learning and memory are explicit is an open question. Controversy has emerged about the existence of implicit hippocampal-dependent tasks. Two implicit tasks that may involve the hippocampusare a relational eye tracking task (Ryan et al. (2000) Psychol Sci 11:454-461) and transitive inference (Greene et al. (2006) J Cognit Neurosci 18:1156-1173; Greene et al. (2001) Mem Cognit 29:893-902). Recently, it was shown that both of these tasks may depend upon task awareness (Smith et al. (2006) J Neurosci 26:11304-11312; Smith and Squire (2005) J Neurosci 25:10138-10146). It is argued that in both cases, distinct, explicit versions of the tasks were created, which do not disprove the implicit nature of the original tasks.

Effects of Post-Training Lesions in the Hippocampus and the Parietal Cortex onldiothetic Information Processing in the Rat

Dead reckoning can be defined as the ability to navigate using idiothetic information based on self-movement cues without using allothetic information such as environmental cues. In the present study, we investigated the effects of hippocampal and parietal cortex lesions on homing behavior using dead reckoning in rats. Experimentally naive Wistar rats were trained with a homing task in which rats were required to take a food pellet from a cup in the arena and to return home with the pellet. After training, rats were divided into a control (CONT) group (n = 16), hippocampal lesioned (HIPP) group (n = 16), and parietal cortex lesioned (PARC) group (n = 16), and rats in the lesioned groups underwent surgery. After surgery, Test 1 (with four cups) and Test 2 (with one cup but the outgoing path was diverted by a barrier) were conducted. The HIPP group showed severe impairment in homing, but the performance of the PARC group did not differ from that of the CONT group. HIPP rats either approached wrong doors or ate the pellet in the arena. Circular statistics showed that homing directions of CONT and PARC rats showed concentration towards home, whereas those of HIPP rats did not. Our results exhibiting HIPP rats' failure in homing agree with many previous studies, but the results obtained from PARC rats were different from previous studies. These results indicate that the intact hippocampus is important for dead reckoning, but the role of the parietal cortex in dead reckoning is still not clear.

Modeling the nonlinear dynamic interactions of the lateral and the medial perforant path of the hippocampal dentate gyrus

We present a new method to characterize the nonlinearities resulting from the co-activity of two pathways that converge on a common postsynaptic element. We investigated the nonlinear dynamic interactions between the lateral perforant pathway (LPP) and the Medial Perforant Pathway (MPP) of the hippocampal dentate gyrus, and the effects of these cross-pathway interactions on granule cell output. A third order Volterra-Poisson modeling approach was implemented to capture the interactions between the two pathways. The kernels presented pathway specific signatures as they capture the nonlinear dynamics of each pathway individually in the form of self-kernels, and the nonlinear interactions between the two pathways in the form of cross-kernels. Data were collected in-vitro from acute slices of adult rats via a multi-electrode array recording system. The stimuli were dual-site random impulse trains with Poisson distributed inter-impulse intervals. The recorded responses from the granule cells were population spikes, simplified as discrete impulses with variable amplitudes. Our results indicated that the third order nonlinear interactions between the LPP and the MPP needs to be included in the model in order to achieve adequate predictive accuracy and indicate that this approach can be generalized to complex interactions between distinct inputs to the same set of neurons.

A simple neural network model of the hippocampus suggesting its pathfinding role in episodic memory retrieval

The goal of this work is to extend the theoretical understanding of the relationship between hippocampal spatial and memory functions to the level of neurophysiological mechanisms underlying spatial navigation and episodic memory retrieval. The proposed unifying theory describes both phenomena within a unique framework, as based on one and the same pathfinding function of the hippocampus. We propose a mechanism of reconstruction of the context of experience involving a search for a nearly shortest path in the space of remembered contexts. To analyze this concept in detail, we define a simple connectionist model consistent with available rodent and human neurophysiological data. Numerical study of the model begins with the spatial domain as a simple analogy for more complex phenomena. It is demonstrated how a nearly shortest path is quickly found in a familiar environment. We prove numerically that associative learning during sharp waves can account for the necessary properties of hippocampal place cells. Computational study of the model is extended to other cognitive paradigms, with the main focus on episodic memory retrieval. We show that the ability to find a correct path may be vital for successful retrieval. The model robustly exhibits the pathfinding capacity within a wide range of several factors, including its memory load (up to 30,000 abstract contexts), the number of episodes that become associated with potential target contexts, and the level of dynamical noise. We offer several testable critical predictions in both spatial and memory domains to validate the theory. Our results suggest that (1) the pathfinding function of the hippocampus, in addition to its associative and memory indexing functions, may be vital for retrieval of certain episodic memories, and (2) the hippocampal spatial navigation function could be a precursor of its memory function.

Retrograde amnesia in rats with lesions to the hippocampus on a test of spatial memory

The present study examined remote spatial memory in a test that spans several months to determine whether remote memories are spared relative to more recent ones, as predicted by models of memory consolidation. At 3, 6 or 12 months of age, groups of rats received forced-choice training as to the location of food reward in a cross maze. At 12.5 months, rats received bilateral neurotoxic lesions to the hippocampus or a control surgical procedure and 2 weeks later their memory for the spatial location was tested. Their performance was compared to that of rats with hippocampal or control lesions with no prior training on several measures of savings. The hippocampal group with no pre-training, as expected, was severely impaired in learning the location of the food reward. Compared to this group, rats with hippocampal lesions that were pre-trained consistently performed better at the shortest training-surgery interval but not at the longer ones. That is, rats with hippocampal lesions exhibited retrograde amnesia at all training-surgery intervals and a forgetting curve that paralleled that of the control groups. The results were interpreted within a framework that distinguishes between relational and associative context, and as providing evidence that the hippocampus is necessary for the retention and retrieval of memories that are bound to relational context, regardless of the age of the memory.

Transgenic mouse in vivo library of human Down syndrome critical region 1: association between DYRK1A overexpression, brain development abnormalities, and cell cycle protein alteration

Down syndrome is the most frequent genetic cause of mental retardation, having an incidence of 1 in 700 live births. In the present study we used a transgenic mouse in vivo library consisting of 4 yeast artificial chromosome (YAC) transgenic mouse lines, each bearing a different fragment of the Down syndrome critical region 1 (DCR-1), implicated in brain abnormalities characterizing this pathology. The 152F7 fragment, in addition to genes also located on the other DCR-1 fragments, bears the DYRK1A gene, encoding for a serine-threonine kinase. The neurobehavioral analysis of these mouse lines showed that DYRK1A overexpressing 152F7 mice but not the other lines display learning impairment and hyperactivity during development. Additionally, 152F7 mice display increased brain weight and neuronal size. At a biochemical level we found DYRK1A overexpression associated with a development-dependent increase in phosphorylation of the transcription factor FKHR and with high levels of cyclin B1, suggesting for the first time in vivo a correlation between DYRK1A overexpression and cell cycle protein alteration. In addition, we found an altered phosphorylation of transcription factors of CREB family. Our findings support a role of DYRK1A overexpression in the neuronal abnormalities seen in Down syndrome and suggest that this pathology is linked to altered levels of proteins involved in the regulation of cell cycle.

Hippocampal modulation of sensorimotor processes

While the hippocampus makes unique contributions to memory, it has also long been associated with sensorimotor processes, i.e. innate processes involving control of motor responses to sensory stimuli. Moreover, hippocampal dysfunction has been implicated in neuropsychiatric diseases, such as schizophrenia and anxiety disorders, primarily characterized by non-mnemonic deficits in the processing of and responding to sensory information. This review is concerned with the hippocampal modulation of three sensorimotor processes in rats-locomotor activity, prepulse inhibition (PPI) of the startle reflex, and the startle reflex itself-whose alterations are related to human psychosis or anxiety disorders. Its main purpose is to present and discuss the picture emerging from studies examining the effects of pharmacological manipulations of the dorsal and ventral hippocampus by local drug microinfusions. While a role of the hippocampus in regulating locomotor activity, PPI, and startle reactivity has also been suggested based on the effects of hippocampal lesions, the microinfusion studies have revealed additional important details of this role and suggest modifications of notions based on lesion studies. In summary, the microinfusion studies corroborate that hippocampal mechanisms can directly influence locomotor activity, PPI, and startle reactivity, and that aberrant hippocampal function may contribute to neuropsychiatric diseases, in particular psychosis. The relation between different sensorimotor processes and hippocampal neurotransmission, the role of ventral and dorsal hippocampus, and the extrahippocampal mechanisms mediating the hippocampal modulation of different sensorimotor processes can partly be dissociated. Thus, the hippocampal modulation of these sensorimotor processes appears to reflect multiple operations, rather than one unitary operation.

Reward value invariant place responses and reward site associated activity in hippocampal neurons of behaving rats

To investigate the involvement of the hippocampal-accumbens system in goal-oriented displacement behaviors, hippocampal neuronal activity was recorded in rats learning and recalling new distributions of different volumes of liquid reward among the arms of a plus maze. Each arm had a reward box containing a water trough and identical visual cues that could be illuminated independently. As the water-restricted rat successively visited the respective boxes, it received 7, 5, and 3 drops of water, and then 1 drop, provided at 1-s intervals. (Reward distributions were reassigned daily and mid-session.) In the training phase, reward boxes were lit individually. In the recall phase, the lamps on all arms were lit and then turned off as the rat visited the boxes in order of descending value. Neuronal firing rates were analyzed for changes related to reward value or to shifts between learning and recall phases. The principal finding is that place responses remained unchanged after these manipulations and that these neurons showed no evidence of explicit coding of reward value. In addition, two other types of responses appeared while the rat was stationary at the reward boxes awaiting multiple rewards. These were observed primarily in neurons within the dentate gyrus, but also in CA1. Position-selective reward site responses were regular at 20-60 impulses per second, while position-independent discharges bursted irregularly at about 5 impulses per second. Such responses could explain controversial reports of reward dependence in hippocampal neurons. The higher incidence of the latter responses in the temporal ("ventral") hippocampus is consistent with the distinctive anatomical and functional properties of this subregion.

Impaired Performance of Fornix-Transected Rats on a Distal, but Not on a Proximal, Version of the Radial-Arm Maze Cue Task

Fornix-transected and sham-operated rats were trained on radial maze cue tasks in which the relative positions of the cues were either fixed (F condition) or varied (V condition) across trials. Proximal and distal visual stimuli were used in 2 different experiments. With proximal stimuli, fornix-transected rats were transiently impaired in the V condition and performed as well as controls in the F condition. However, using extramaze stimuli, fornix-transected rats were severely impaired in the V condition but performed normally in the F condition. According to histological analyses, performance on these cue tasks varied along with the extent of cholinergic depletion in the hippocampus. At the behavioral level, the location and stability of stimuli's relative positions seemed to have influenced rats' performance.

Spatial memory and choice behavior in the radial arm maze after fornix transection

In the radial arm maze task, it is well established that performance of rats with hippocampal damage is severely impaired on the place version, which relies heavily, if not exclusively, on spatial information. However, very little is known about the effects of hippocampal damage on actual choice behavior. To address this issue, sham-operated (SH) and fornix-transected (FX) rats were trained and tested on the place task in the eight-arm radial maze. The following measures were recorded: the frequency of re-entry errors, the number of choices separating repeated visits to the same arm, the latency to arm re-entry, the distribution and targets of microchoices defined as orientations toward an arm or entries in the proximal portion of an arm [Brown, M.F., 1992. Does a cognitive map guide choices in the radial arm maze? J. Exp. Psychol., Anim. Behav. Processes 18, 56-66]. These measures were used as indexes of performance, within-trial retroactive intrusion, memory trace decay and choice behavior, respectively. As generally observed in the literature, the frequency of errors was higher in rats of the FX group than in rats of the SH group; the impairment persisted even after the training criterion was reached. The analysis of latency to arm re-entry and of the number of choices separating re-entries suggested that this impairment was the result of faster memory decay rather than retroactive interference. Both FX and SH groups exhibited a systematic pattern of microchoices, but the frequency of microchoices was higher in FX lesioned rats than in SH controls. Moreover, in lesioned animals, relatively fewer of the initial microchoices were directed toward the baited arms during training-to-criterion. Some of the results provide support to the working memory theory [Olton, D.S., Becker, J.T., Handelmann, G.E., 1979. Hippocampus, space, and memory. Behav. Brain Sci. 2, 313-365], whereas others look more consistent with the cognitive map view [O'Keefe, J., Nadel, L., 1978. The Hippocampus as a Cognitive Map. Clarendon Press, Oxford]. The discussion suggests that both theories and a distinction between prospective and retrospective memory may be required to account for the function of the hippocampal formation in memory.

The human hippocampus and spatial and episodic memory

Finding one's way around an environment and remembering the events that occur within it are crucial cognitive abilities that have been linked to the hippocampus and medial temporal lobes. Our review of neuropsychological, behavioral, and neuroimaging studies of human hippocampal involvement in spatial memory concentrates on three important concepts in this field: spatial frameworks, dimensionality, and orientation and self-motion. We also compare variation in hippocampal structure and function across and within species. We discuss how its spatial role relates to its accepted role in episodic memory. Five related studies use virtual reality to examine these two types of memory in ecologically valid situations. While processing of spatial scenes involves the parahippocampus, the right hippocampus appears particularly involved in memory for locations within an environment, with the left hippocampus more involved in context-dependent episodic or autobiographical memory.

Multisensory processing in the elaboration of place and head direction responses by limbic system neurons

This review explores the roles of several sensory modalities in the establishment and maintenance of discharges correlated with head position and orientation in neurons of the hippocampus and associated structures in the Papez circuit. Focus is placed on the integration of signals related to environmental cues and to displacement movements, both of external and internal origin. While the visual, vestibular and motor systems each exert influences, position and head direction signals are nevertheless maintained in the absence of any one of these respective inputs. Context-related changes in hippocampal discharge correlates are also highlighted. These characteristics provide these signals with robustness and flexibility, properties particularly suited for cognitive processes such as contextual processing, memory and planning.

Position sensitivity in phasically discharging nucleus accumbens neurons of rats alternating between tasks requiring complementary types of spatial cues

To determine how hippocampal location-selective discharges might influence downstream structures for navigation, nucleus accumbens neurons were recorded in rats alternating between two tasks guided respectively by lit cues in the maze or by extramaze room cues. Of 144 phasically active neurons, 80 showed significant behavioral correlates including displacements, immobility prior to, or after reward delivery, as well as turning, similar to previous reports. Nine neurons were position-selective, 22 were sensitive to task and platform changes and 40 others were both. Although the accumbens neurons showed the same behavioral correlate in two or four functionally equivalent locations, these responses were stronger at some of these places, evidence for position sensitivity. To test whether position responses were selective for room versus platform cues, the experimental platform was rotated while the rat performed each of the two tasks. This revealed responses to changes in position relative to both platform and room cues, despite the fact that previous studies had shown that place responses of hippocampal neurons recorded in the same task are anchored to room cues only. After these manipulations and shifts between the two tasks, the responses varied among simultaneously recorded neurons, and even in single neurons in alternating visits to reward sites. Again this contrasts with the uniformity of place responses of hippocampal neurons recorded in this same task. Thus accumbens position responses may derive from hippocampal inputs, while responses to context changes are more likely to derive from other signals or intrinsic processing. Considering the accumbens as a limbic-motor interface, we conclude that position-modulated behavioral responses in the accumbens may be intermediate between the allocentric reference frame of position-selective discharges in the hippocampus and the egocentric coding required to organize movement control. The conflicting responses among simultaneously recorded neurons could reflect competition processes serving as substrates for action selection and learning.

Melanin concentrating hormone increase hippocampal synaptic transmission in the rat

A retrograde facilitation has been demonstrated in the one trial step-down inhibitory avoidance of melanin-concentrating hormone (MCH), when it was infused into rat hippocampal formation. Considering the high density of specific binding sites for the MCH peptide on the hippocampus and the participation of this structure on learning and memory processes we have studied the effects of MCH on the hippocampal synaptic transmission. For this purpose, slices of rat hippocampus were perfused with different concentration of MCH. The main result of the present study was a long-lasting potentiation on the hippocampal evoked response on dentate gyrus induced by MCH (4-11 microM) at 30, 60 and 120 min with a maximum effect at 120 min. Previous perfusion of DL - 2- amino - 5 phosphonovaleric acid (APV, 20 microM) was unable to impair the increased hippocampal evoked response induced by MCH 4 microM. On the other hand, the channel blocker Dizocilpine (MK-801, 10 microM) completely impaired the increased hippocampal synaptic plasticity induced by MCH perfusion. We postulate the increased hippocampal synaptic efficacy induced by MCH as one of the mechanisms underlying the retrograde facilitation on the inhibitory avoidance paradigm, observed after MCH hippocampal microinjection. We cannot rule out other MCH neurochemical mechanism and other areas of the brain involved in the MCH effects.

Assessment of sensorimotor and cognitive deficits induced by a moderate traumatic injury in the right parietal cortex of the rat

The purpose of this study was to set-up a battery of behavioral tests to assess sensorimotor and cognitive deficits following a moderate traumatic brain injury (TBI) in rats. Coordinated walking ability was evaluated in an accelerated rotarod test. Vestibulomotor function and fine motor coordination were assessed by using a beam-walking task. Rotarod and beam-walking performances were both altered in injured rats compared to sham-operated and control rats. A more pronounced and longer-lasting deficit was measured in the beam-walking test. Cognitive function was studied by using the Lashley maze paradigm. A spatial localization deficit was significant for 4 weeks posttrauma in TBI rats. The beam-walking task and the Lashley maze are robust and sensitive methods in detecting sensorimotor and cognitive impairment after TBI in rats, respectively. These tests are proposed for evaluating the ability of new pharmacological agents to improve the functional recovery after a TBI in rats.

Dissociation of place and cue learning by telencephalic ablation in goldfish

This study examined the spatial strategies used by goldfish (Carassius auratus) to find a goal in a 4-arm maze and the involvement of the telencephalon in this spatial learning. Intact and telencephalon-ablated goldfish were trained to find food in an arm placed in a constant room location and signaled by a local visual cue (mixed place-cue procedure). Both groups learned the task, but they used different learning strategies. Telencephalon-ablated goldfish learned the task more quickly and made fewer errors to criterion than controls. Probe trials revealed that intact goldfish could use either a place or a cue strategy, whereas telencephalon-ablated goldfish learned only a cue strategy. The results offer additional evidence that place and cue learning in fish are subserved by different neural substrates and that the telencephalon of the teleost fish, or some unspecified structure within it, is important for spatial learning and memory in a manner similar to the hippocampus of mammals and birds.

Cognitive functions of the temporal lobe in the dog: a review

1 The current paper reviews the role of temporal lobe structures in learning and different kinds of memory, with an emphasis on behavioral tasks that re auditory stimuli. 2 The effects of lesions to structures in the temporal lobe were examined in separate groups of dogs, which were trained on an auditory spatial delayed response, or in a trial-unique auditory delayed match to sample recognition task. 3 Spatial memory was impaired after bilateral hippocampal lesions. On the other hand, neither an anterior temporal lesion or rhinal cortical injury nor combined lesion to the hippocampus and the anterior temporal lobe, affected postoperative retraining and performance of the spatial task. 4 Auditory recognition memory task was not impaired after a hippocampal and/or rhinal cortex lesion. However, postoperative retraining of the task was impaired after a lesion to auditory association areas. 5 These results confirm the role of the hippocampus in spatial memory in the dog. On the other hand, the organization of auditory recognition functions within the temporal lobe appears to be different from those described for visual recognition functions.

Algorithmic behaviour and spatial memory are used by two intertidal fish species to solve the radial maze

We used an eight-arm radial maze to assess the relative contributions of learned patterns of movement (algorithmic behaviour) and spatial memory to the foraging efficiency of two sympatric rocky-shore fish, fifteen-spined stickleback, Spinachia spinachia, and corkwing wrasse, Crenilabrus melops, exploiting nonrenewable food sources. To forage efficiently, subjects had to avoid arms already depleted within a trial. In the absence of spatial cues, sticklebacks and wrasse improved their foraging efficiency by developing the algorithm of visiting every third arm. In the presence of spatial cues (coloured tiles) algorithmic behaviour was largely subsumed by the use of spatial memory. Imposition of a delay within trials reset the behavioural algorithm, so depressing foraging efficiency in the absence of cues, but not in their presence when memory could be used to guide behaviour. Memory retention for previous choices (working memory) lay within the range 0.5-5.0 min, consistent with the characteristic timescale expected for habitats where prey distribution changes rapidly during the tidal cycle. We considered two hypotheses on the type of information memorized: the cue list hypothesis and the spatial configuration hypothesis. The cue list hypothesis predicts that neither random repositioning nor fixed rotation of spatial cues should impair foraging efficiency, whereas the spatial configuration hypothesis predicts that efficiency should be impaired by random repositioning of cues but not by rotation. Data supported the spatial configuration hypothesis. Copyright 1999 The Association for the Study of Animal Behaviour.

A working memory "theory of relativity": elasticity in temporal, spatial, and modality dimensions conserves item capacity in radial maze, verbal tasks, and other cognition

It is remarkable that working memory (WM) capacity for numbers of items remains modest, at approximately 7+/-2 (the so-called "magical number"), across a wide variety of kinds of material. Indeed, consideration of radial maze studies together with more traditional memory research shows that WM capacity remains fairly constant whether the items are verbal or visuospatial, and that this same capacity is true of other species as of humans. In contrast to their limited numerousness, WM items are extremely flexible in ways that are here brought under the heading of "dimensionality." Therefore, the physical items represented in WM, can vary widely in any quantitative characteristic and in the temporal pace at which they are encountered. Combinatorial considerations suggest that WM numerousness results from evolution of a middle ground between a sterile parsimony and an overwhelming excess, for organizing neurocognitive associations. Such natural selection seems likely to have worked opportunistically to yield diverse characteristics of neuronal tissue, from subcellular components to properties of ensembles, which converge on the required cognitive properties of WM. Priming and implicit memory may play supporting roles with WM. These intermediate-term memory phenomena allow certain kinds of background information to be accumulated at higher volume than seems possible from the textbook, "modal model" of memory. By expediting attentional focus on subsets of information already in long-term memory, priming may help WM chunks to emerge in limited number as appropriately scaled "figures" from the primed "ground." The larger neuronal dynamic patterns that embody these cognitive phenomena must regulate their microscopic component systems, automatically selecting those having parameters of temporal persistence, rhythm, and connectivity patterns that are pertinent to the current task. Relevant neural phenomena may include "Hebbian" associativity and persistence of firing patterns in prefrontal or hippocampal neurons. A conceivable basis for scaling and normalizing WM representations, along arbitrarily long or short ranges of any cognitive dimension, involves harmonic multiplier relationships among brain electrical rhythms and/or among topographical spatial periodic representations.

The interaction of cognitive and stimulus-response processes in the control of behaviour

It is argued that both stimulus-response (S-R) and cognitive theories of learning and behaviour capture part of the truth, in that these terms involve two different types of process that are jointly responsible for the control of behaviour. The proposal that both processes coexist is investigated in the context of the production of behaviour. Evidence is presented to show that the weighting attached to S-R and cognitive processes can change as a function of (a) development; (b) experience; and (c) pathology. A model is proposed which is designed to sketch some ideas on how S-R and cognitive processes jointly determine behaviour, and it is related to the notion of behavioural hierarchy. It is argued that the model can help to develop a synthesis between psychology, ethology and neuroscience.

Neuronal cell loss in the CA3 subfield of the hippocampus following cortical contusion utilizing the optical disector method for cell counting

Unilateral cortical contusion in the rat results in cell loss in both the cortex and hippocampus. Pharmacological intervention with growth factors or excitatory neurotransmitter antagonists may reduce cell loss and improve neurological outcome. The window of opportunity for such intervention remains unclear because a detailed temporal analysis of neuronal loss has not been performed in the rodent cortical contusion model. To elucidate the time course of hippocampal CA3 neuronal death ensuing cortical contusion, we employed the optical disector method for assessing the total number of CA3 neurons at 1 and 6 hours, 1, 2, 10, and 30 days following injury. This stereological technique allows reporting of total cell numbers within a given region and is unaffected by change in the volume of the structure or cell size. A rapid and significant reduction in neurons/mm3 in the ipsilateral CA3 field was observed by 1 h following trauma. However, a significant increase in neurons/mm3 was seen at 30 days postinjury. This surprising finding is a result of CA3 volume shrinkage and redistribution of CA3 neurons. Utilization of the optical disector reveals that regardless of an increase in neurons/mm3 at 30 days following injury, CA3 cell loss reaches 41% of control animals by 1 day posttrauma and remains near that level at all subsequent time points examined. It is estimated that there are about 156,000 neurons in the CA3 region in control animals. By 1 h following cortical contusion the cell population decreases to 93,000 neurons indicating a very rapid cell loss. This suggests a window of less than 24 h for pharmacological intervention in order to save CA3 neurons following cortical contusion.

Protein kinase C, learning and memory: a circular determinism between physiology and behaviour

1. In vertebrates as in invertebrates, protein kinase C appears to have a key role in learning and memory, probably given its involvement in synaptic plasticity. 2. Hippocampal PKC in mammalians is activated by learning in a large variety of memory tasks. However, the kind of information processed, the type of task, and the dynamics of learning processes all induce differential changes in the mode of PKC activation and in its anatomy. 3. The behaviourally induced changes in PKC activity are often varying in their magnitude. Inter-individual differences in PKC basal activity are generally correlated to the ability to learn. 4. Pharmacologic activation and inhibition of brain PKC shows that PKC activation plays an important role in cognitive function. 5. Basal PKC stores characterising each individual could be determined by genetic factors and modulated through life by individual experience. 6. The issue of PKC and memory relationships is reformulated through a comprehensive interactionist model which leads to formulating some new testable predictions.

Systemic administration of anti-NGF antibodies to neonatal mice impairs 24-h retention of an inhibitory avoidance task while increasing ChAT immunoreactivity in the medial septum

Neonatal mice received subcutaneous injections of either antibody against murine NGF raised in goat (3 mg, injection volume 50 microliters) or preimmune serum on postnatal days 2, 4, 6, 8, 10, and 12. They were tested on postnatal days 15-16 or 20-21 for learning and 24-h retention of a passive avoidance step-through task. Immunostaining for choline acetyltransferase (ChAT) was measured in two cholinergic forebrain areas (septum and caudate-putamen) on postnatal day 16 or 21. Locomotor activity and exploratory behavior in an open-field test were also assessed on day 17 or 22, following a single administration of either scopolamine (2 mg/kg) or saline solution. While anti-NGF treatment did not affect acquisition on day 15, impairment in retention was evident on day 16. On days 20-21, no effects were found either on acquisition or on retention capabilities. Analysis of ChAT immunostaining revealed a significant increase of ChAT-immunopositive cells in the medial septal area in 16-day-old but not in 21-day-old mice. Behavior in the open-field test and age-typical response to scopolamine were not altered by anti-NGF at either of the two ages considered. These data support the view that immunological neutralization of endogenous NGF specifically affects the maturation of retention capabilities in altricial rodents, and confirm the involvement of forebrain cholinergic mechanisms in early memory processes.

Spatial, behavioral and sensory correlates of hippocampal CA1 complex spike cell activity: implications for information processing functions

The aim of this review is to better understand hippocampal function drawing almost entirely from single unit recording studies of pyramidal cells in areas CA1 and CA3 of behaving animals. Hippocampal location-selectivity ("place cell activity") as well as place-independent behavioral correlates and sensory-triggered discharges are demonstrated to have common features: (1) abstraction, that is, development within the hippocampal circuit of novel, cue-invariant supramodal representations; (2) varying degrees of generalization or specificity; (3) capacity for abrupt changes in discharge correlates of individual neurons as the animal changes its behavior pattern or its environment changes dramatically; (4) though individual neurons discharge when the subject occupies a certain place, or performs a certain behavior, the ensemble of hippocampal neurons comprehensively represent the whole environment and all behaviors required for the task at hand. A concordance is proposed: hippocampal neuronal discharge correlates represent elements partitioned from information abstracted along one or more systems of categorization or "information domains": the physical structure of the environment, regularities in the behavioral exigencies of the current situation. (Sensory stimuli can be considered as temporally varying features of the environment) Location-selectivity and behavioral correlates are extreme cases, and mixed correlates occur. The hippocampus is proposed to carry out several fundamental processes that transform information: abstraction, partitioning and recombination, that is, formation of conjunctive associations between events. Simultaneously activated neurons could then promote extrahippocampal associations linking together the diverse brain regions at the origin of these signals.

Spatial learning in rats exposed to acute ethanol intoxication on gestational day 8

Pregnant Wistar rats were treated on gestational day 8 (GD 8) with two IP injections of either ethanol (2.9 g/kg in 24% v/v saline solution) or saline. Offspring were tested in the water-maze task at 45 or 90 days of age. The escape latencies of rats trained with a submerged escape platform at a fixed location were similar between control and experimental rats. Analyses of responses on a probe trial carried out 10 days after the training period, revealed that 90-day-old females prenatally exposed to alcohol were less likely to swim in the target region. No differences were observed in this free-swim trial in 45- and 90-day-old male, and 45-day-old female animals. Binding studies of low-affinity GABAA sites in the hippocampus showed an increase in affinity of [3H]GABAA for their binding sites in 90-day-old female offspring prenatally intoxicated with ethanol. Our results demonstrate that acute intoxication with ethanol on GD 8 did not modify acquisition but impaired the retention of spatial learning only in adult female rats. It is possible that the impaired retention will be consequence of higher GABAA receptor affinity.

Differential environmental modulations on locomotor activity, exploration and spatial behaviour in young and old rats

The effects of environmental enrichment on motor activity, exploration and spatial performances were studied in young and old rats. Both young (4 mo old) and old (22 mo old) rats were housed from weaning to testing either in standard or in enriched conditions. All rats were submitted successively to spontaneous alternation test and to object exploration test. Results show that locomotion is decreased by age and enrichment but that the quality of exploration expressed by corrected alternation scores or by the response to spatial change is improved by enrichment sometimes in old, sometimes in young rats. Enrichment tends to accelerate the acquisition of spatial informations in young rats, but it does not succeed to restore the reactivity to spatial change of old rats in the object exploration test. These results, although they do not rule out a persistance of a continued behavioural plasticity during aging, also support the idea that the beneficial effects of environmental stimulations do not succeed to restore high cognitive function, such as the capacity to have a spatial representation, in old animals.

Equivalent performance in the water maze by rats with an inborn high or low learning capacity in a shuttle box paradigm

The learning capacity of rats with an inborn high performance (HP) and low performance (LP) in an avoidance shuttle box paradigm, was evaluated in the Morris water maze. Escape latencies evaluated in HP and LP rats indicate that acquisition and retention of spatial information were not different from control animals. When a free swim trial was carried out, all groups showed a significant preference towards the target quadrant. Our results suggest that the altered hippocampal physiology described in HP and LP rats does not influence the performance of a spatial tasks such as the Morris water maze.

Effects of hippocampal lesions on spatial delayed responses in dog

Thirteen dogs were trained to perform spatial delayed responses to auditory cues in a three-choice Nencki testing apparatus with a delay of 0 s and then 10 s with a criterion of 90% correct responses in 90 consecutive trials. Then six dogs received bilateral surgical removal of the hippocampus via the cortex of the suprasylvian gyrus (without additional injury to the entorhinal and parahippocampal cortex). Three dogs received control surgical ablation of the suprasylvian gyrus, which was damaged in ablation of the hippocampus, and four dogs served as intact controls. After the surgery or rest period, the dogs were tested for their retention (10-s delay), and then they were given additional tests with extended delays (30, 60, and 120 s) and with distractions during the 60-s delay period. In comparison with both control groups, dogs with hippocampal ablations had moderately impaired postoperative retention, as evidenced by the elevated numbers of errors on criterion. In subsequent stages of testing with extended delays, the impairment was greater and was significantly correlated with the extent of injury to the hippocampus. These data, together with an analysis of the animals' responses to the three-choice situation, indicate that in dogs lesions of the hippocampus impair spatial memory.

Soft-diet feeding during development enhances later learning abilities in female rats

We investigated whether a decrease in masticatory work affected not only jaw bone growth but also radial eight-arm maze learning, and whether there was a sexual difference in this effect, if any. Male and female rats, weaned at 3 weeks of age, were fed either pelleted or powdered chow until 16 weeks of age and learning experiments were conducted at 10-13 weeks of age. Almost all of the five dimensions of the jaw bones were greater in rats fed pelleted chow than in rats fed powdered chow in both sexes. The number of correct choices in the last five trials was significantly greater in female, but not in male, rats fed powdered chow, and the number of trials to attain at least seven correct choices in the first eight choices in five consecutive trials was greater in female rats fed pelleted chow than in female rats fed powdered chow and in male rats fed either powdered or pelleted chow. These results suggest that 1) a decrease in masticatory work due to soft-diet feeding during development enhances later learning ability preferentially in female rats, and 2) the reported sexual inferiority of female rats in learning and memory functions is due to hard-diet feeding as the standard laboratory condition.

Covariations between hippocampal mossy fibres and working and reference memory in spatial and non-spatial radial maze tasks in mice

Male mice from nine inbred mouse strains were tested at the age of 3 months in either a spatial or a non-spatial version of the radial maze. Only four out of eight arms contained food rewards, permitting simultaneous assessment of working and reference memory in both situations. Other animals from the same strains were processed histologically to estimate the strain-specific extents of the mossy fibre projections. No significant between-task correlations were obtained for either working or reference memory. However, measures of working and reference memory correlated with each other within tasks. This suggests that these concepts may perhaps not be validly used in the mouse. Large, positive correlations of the size of the intra- and infrapyramidal mossy fibre projection with both working and reference memory were obtained in the spatial radial maze task, but not in the non-spatial one. We conclude that heritable variations of the hippocampal intra- and infrapyramidal mossy fibre projection influence processes related to spatial learning capabilities in radial mazes.

Effects of septal and/or raphe cell suspension grafts on hippocampal choline acetyltransferase activity, high affinity synaptosomal uptake of choline and serotonin, and behavior in rats with extensive septohippocampal lesions

At 31 days of age, Long-Evans female rats sustained aspirative lesions of the septohippocampal pathways and, 14 days later, received intrahippocampal suspension grafts prepared from the region including the medial septum and the diagonal band of Broca (Group S, n = 11), from the region including the mesencephalic raphe (Group R, n = 11) or from both regions together (Group S+R, n = 11). Sham-operated (Group Sham, n = 9) and lesion-only (Group Les, n = 11) rats served as non-grafted controls. Seven Sham, 7 Les and 8 rats from each transplant group were tested for home cage activity (6 months after grafting) and radial maze performance (between 7.5 and 8.5 months post-grafting). One month after completion of behavioral testing, the dorsal hippocampi of these rats were prepared for measuring choline acetyltransferase (ChAT) activity and high affinity synaptosomal uptake of both [3H]choline and [3H]serotonin. The remaining rats were used for histological verifications on brain sections stained for acetylcholinesterase (AChE). The lesions increased locomotor activity, impaired radial maze learning and, in the dorsal hippocampus, reduced AChE positive staining, decreased ChAT activity (-73%) as well as high affinity uptake of both choline (-81%) and serotonin (-82%). Neither type of transplant produced any significant behavioral recovery. However, septal transplants increased hippocampal AChE positivity, restored ChAT activity and enhanced choline uptake to 116% and 70% of the values found in sham-operated rats, respectively; they had no significant effect on uptake of serotonin. Transplants from the raphe region had weak effects on hippocampal AChE positivity, increased both the ChAT activity and the choline uptake to 70% ad 38% of the sham-operated rats, respectively, and produced an (over)compensation of the serotonin uptake which reached 324% of the values found in sham-operated rats. The co-transplantation of both regions resulted in restoration of ChAT activity (113% of sham-operated rats values), choline uptake (83% of sham-operated rats) and serotonin uptake (129% of sham-operated rats). Our neurochemical data show that after extensive denervation of the hippocampus, intrahippocampal grafts of fetal neurons may foster a neurotransmitter-specific recovery which depends upon the anatomical origin of the grafted cells: a graft rich in serotonergic neurons overcompensates the serotonergic deficit, a graft rich in cholinergic neurons attenuates the cholinergic deficit, whereas a mixture of both types of grafts produces recovery from both types of deficits. Thereby, both the feasibility and the interest of the co-grafting technique are confirmed.(ABSTRACT TRUNCATED AT 400 WORDS)

Damage to the hippocampal formation in rats selectively impairs the ability to learn cue relationships

We assessed the contribution of the hippocampal formation to performance in tasks that require rats to respond to a relationship between discriminative stimuli. The first experiment employed a nonmatching-to-sample procedure in a Y-maze. Three pairs of boxes were used which differed in brightness of the walls and in the odors that they contained. The rats were trained prior to receiving kainic acid and colchicine-induced damage to the hippocampal formation or electrolytic damage to the amygdala. After surgery all rats performed the nonmatching-to-sample task accurately if both brightness and odor cues were present in the sample and choice boxes or if the boxes contained either visual cues alone or odor cues alone. If the available cue modality was different in sample and choice boxes, then the amygdala-damaged, but not the hippocampal-damaged, rats performed accurately. In the second experiment control rats or rats with hippocampal formation damage were trained postoperatively in a conditional black/white discrimination task in a Y-maze. Only the control group successfully learned to select the white arm if the start box was illuminated and the black arm if the start box was dark. Subsequently, both groups learned a simple black/white discrimination. The same rats were tested in the hidden platform version of the Morris water task and only the control group learned to swim accurately to the goal. Both groups learned to swim accurately to a visible black platform. The results are consistent with the notion that the hippocampal formation is essential to learning that involves control exerted by a configural relationship among cues, independently of the spatial or conditional requirements of tasks.

Scopolamine treatment and fimbria-fornix lesions: mimetic effects on radial maze performance

Long-Evans female rats were "trained" in an 8-arm radial maze and subsequently tested under systemic treatment with physostigmine (0.05 mg/kg, IP), scopolamine methylbromide (MBr) and scopolamine hydrobromide (HBr; 0.5 mg/kg, IP), whose effects were compared to those of aspirative lesions of the fimbria-fornix pathways. During the predrug trials, rats with lesions showed impaired performances compared to those of intact rats. Whereas physostigmine had no significant effect in either group, scopolamine HBr impaired performances of intact rats in a manner closely parallel to all measured behavioral effects of the lesions (errors, "correct arms" and strategies). The scopolamine HBr-induced deficits were not correlated with the percentage of "spatial" strategies. Under scopolamine HBr treatment the performances of rats showing preferences for "spatial" strategies did not differ significantly from those of rats showing preferences for "orientation" strategies. These results provide further support for the involvement of cholinergic processes in working memory and suggest that scopolamine-induced central cholinergic disruption may mimic the effects of fimbria-fornix lesions in an 8-arm radial maze. They also somewhat qualify previous reports on 1) the poor sensitivity of an uninterrupted radial maze testing procedure to pharmacological treatment and 2) the abilities of rats to resist muscarinic blockade depending on the strategies they use in the maze.