Piloting and dead reckoning dissociated by fimbria-fornix lesions in a rat food carrying task

Control rats and rats with fimbria-fornix (FF) lesions were tested in a foraging task that required that they emerge from either a visible or hidden home base onto an open field to hunt for food pellets, which they then carry back to the home base to eat. Once they were proficient at returning to a location, they and the home base were moved so that they emerged to forage from a new starting position. When the location of a visible home base was moved, both groups of rats learned to make accurate returns. When the location of a hidden home base was moved, control rats first carried the food to the old location and then accurately returned to the new location as their second choice. Thus, as early as a first 'reversal' trial, they displayed spatial memory for both locations while the FF rats perseverated in returning to the old location. In returning to familiar start points, the rats may use distal visual (allothetic) cues and piloting, while when returning to new start points they may use self-movement (ideothetic) cues and dead reckoning. That FF lesions dissociated the two kinds of navigation suggests a role for the hippocampus in navigation based on ideothetic cues.     

Place cells and place navigation

The assumption that hippocampal place cells (PCs) form the neural substrate of cognitive maps can be experimentally tested by comparing the effect of experimental interventions on PC activity and place navigation. Conditions that interfere with place navigation (darkness, cholinergic blockade) but leave PC activity unaffected obviously disrupt spatial memory at a post-PC level. Situations creating a conflict between egocentric and allocentric orientation (place navigation in the Morris water maze filled with slowly rotating water) slow down spatial learning. PC recording in rats searching food pellets in a rotating arena makes it possible to determine which firing fields are stable relative to the room (allocentrically dependent on sighted extramaze landmarks), to the surface of the arena (dependent on egocentric path integration mechanisms and intra-arena cues), or disappear during rotation. Such comparison is made possible by the computerized tracking system simultaneously displaying a rat's locomotion and the respective firing rate maps both in the room reference and arena reference frames. More severe conflict between allocentric and egocentric inputs is produced in the field clamp situation when the rat searching food in a ring-shaped arena is always returned by rotation of the arena to the same allocentric position. Ten-minute exposure to this condition caused subsequent disintegration or remapping of 70% PCs (n = 100). Simultaneous examination of PC activity and navigation is possible in the place avoidance task. A rat searching food in a stationary or rotating arena learns to avoid an allocentrically or egocentrically defined location where it receives mild electric footshock. In the place preference task the rat releases pellet delivery by entering an unmarked goal area and staying in it for a criterion time. Both tasks allow direct comparison of the spatial reference frames used by the PCs and by the behaving animal.     

Spatial cues more salient than color cues in cotton-top tamarins (Saguinus oedipus) reversal learning.

Animals living in stable home ranges have many potential cues to locate food. Spatial and color cues are important for wild Callitrichids (marmosets and tamarins). Field studies have assigned the highest priority to distal spatial cues for determining the location of food resources with color cues serving as a secondary cue to assess relative ripeness, once a food source is located. We tested two hypotheses with captive cotton-top tamarins: (a) Tamarins will demonstrate higher rates of initial learning when rewarded for attending to spatial cues versus color cues. (b) Tamarins will show higher rates of correct responses when transferred from color cues to spatial cues than from spatial cues to color cues. The results supported both hypotheses. Tamarins rewarded based on spatial location made significantly more correct choices and fewer errors than tamarins rewarded based on color cues during initial learning. Furthermore, tamarins trained on color cues showed significantly increased correct responses and decreased errors when cues were reversed to reward spatial cues. Subsequent reversal to color cues induced a regression in performance. For tamarins spatial cues appear more salient than color cues in a foraging task. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Finding your way in the dark: The retrosplenial cortex contributes to spatial memory and navigation without visual cues.

Path integration is presumed to rely on self-motion cues to identify locations in space and is subject to cumulative error. The authors tested the hypothesis that rats use memory to reduce such errors and that the retrosplenial cortex contributes to this process. Rats were trained for 1 week to hoard food in an arena after beginning a trial from a fixed starting location; probe trials were then conducted in which they began a trial from a novel place in light or darkness. After control injections, rats searched around the training location, showing normal spatial memory. Inactivation of the retrosplenial cortex disrupted this search preference. To assess accuracy during navigation, rats were then trained to perform multiple trials daily, with a fixed or a different starting location in light or darkness. Retrosplenial cortex inactivation impaired accuracy in darkness. The retrosplenial cortex may provide mnemonic information, which decreases errors when navigating in the dark. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Radial-arm maze behavior by rats with dorsal hippocampal lesions: Effects of cuing.

In 4 experiments with 180 male Wistar and Long-Evans rats, Ss with bilateral dorsal hippocampal lesions were impaired when tested on standard (noncued) versions of the radial-arm maze, but other hippocampal groups performed almost as well as cortical and operated control groups when salient visual cues were added to each arm. Preoperative training on the noncued, but not the cued, maze interfered with the benefits of postoperatively cuing hippocampal groups. Control groups performed equally well under all cuing and training conditions. Procedures that eliminated response sequencing did not affect performance of hippocampal or control groups. Results are interpreted as reflecting hippocampal involvement in mediating spatial cues, but not necessarily along the lines predicted by cognitive map theory. It is suggested that deficits of animals with hippocampal lesions represent 1 manifestation of a general impairment in processing information. (39 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Lateralization of Spatial Learning in the Avian Hippocampal Formation.

The authors investigated lateralization of spatial learning within the avian hippocampal formation (HF). In Experiment 1, homing pigeons (Columba livia) with unilateral lesions of the right or left HF were trained to locate a goal in a square room containing local landmarks and global room cues. All groups learned the task. During probe trials, when landmarks were rotated or removed, intact pigeons and left HF-lesioned pigeons relied exclusively on global room cues to locate the food goal. Pigeons with right HF lesions were the only group to demonstrably use the landmarks. The results suggest that the right HF is preferentially involved in the representation of global environmental space, whereas only the left HF may be sensitive to local landmarks for navigation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Discharge correlates of hippocampal complex spike neurons in behaving rats passively displaced on a mobile robot

This study investigated location-, movement-, and directional-selectivity of action potential discharges of hippocampal neurons in awake rats subjected to passive displacements in order to estimate vestibular contributions to this activity. Water-deprived rats were habituated to being restrained in a sling mounted on a moving robot. The extracellular activity of single complex-spike cells in area CA1 of the hippocampus was recorded with glass micropipettes in the rats during passive translations, rotations, and immobility. The robot made a standardized series of trajectories starting from each of four corners of a square enclosure surrounded by black curtains. A drop of water was delivered to the rat each time the robot arrived at one designated corner of the arena. The activities of 29 neurons were investigated in 45 recording sessions (16 of which were in total darkness) in four rats. Hippocampal neurons recorded in 31 sessions (9 sessions in the dark) had significant location-selective increases or decreases in firing rate as the rat was passively displaced or immobile within the experimental arena. In 20 sessions (6 in the dark) direction-selective discharges were found when the rat was in the corners. In six sessions, cells discharged selectively during movement initiation or termination. These data suggest that information essential for path integration is present in the hippocampus and that inertial cues could play a vital role in hippocampal spatial functions. These results resemble those of O'Mara et al. ([1994] J Neurosci 14:6511) using the same protocol in macaques, suggesting similarities in hippocampal processing and function.     

Hierarchical structures: Chunking by food type facilitates spatial memory.

Three experiments assessed the ability of male Sprague-Dawley rats to organize the spatial locations of different food types in a hierarchical manner to maximize the efficiency of working memory. Independent groups were exposed, on a 12-arm radial maze, to baiting arrangements varying in the stability of the pattern and type of food used as bait. Training rats with stable, differentiable baiting arrangements produced increased accuracy in choice performance, hierarchically ordered patterns of choice selection, slower growth of proactive interference when trials were massed, and the learning of the geometrical relations among food types independent of other extramaze cues. Such findings are strong evidence of the rat's ability to encode and use local cues for navigation, based on properties of the reinforcer. The applicaton of a chunking strategy may provide for more efficient use of working memory by facilitating information storage, recall, or resetting mechanisms. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mutation analysis using the restriction site mutation (RSM) assay

Although two decades of research suggests that the hippocampus plays a special role in place learning, the present paper describes a series of studies using swimming pool spatial tasks that show that hippocampal rats have considerable place learning ability, which includes the abilities of finding, remembering, and searching for places. The same studies also show that when environmental cues are uninformative, as is the case early in original learning and again in reversal learning, hippocampal rats are impaired. Since control rats quickly resolve spatial ambiguity in these situations, it is argued that they must have a system with which they can calibrate spatial cues. The discussion considers the possibility that they use dead reckoning with path integration, a spatial strategy that provides guidance based on cues generated by a point of reference and subsequent self-movement and not the cues in the environment through which they are moving. With path integration an animal can monitor its location and at the same time attach spatial meaning to cues that it encounters. An ability to recalibrate external cues may provide the tuning that allows control rats to quickly acquire place responses while hippocampal rats are constrained by the processes of associative learning.     

Haptic perception of the distance walked when blindfolded.

The ability to detect the distance walked when blindfolded using only haptic information generated by the walking activity was investigated. Participants walked a straight path until told to stop, turned, and attempted to return to their starting point. The path was completely featureless. Counting was prevented. Blindfolded, sighted participants traveled with a long cane or a trained sighted guide. Gait was varied or distorted In all experiments the return distance was a linear function of the set distance, with some participants giving and some conditions resulting in remarkably sensitive performances. The magnitude of errors was a linear function of step length. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Verbal and spatial interference effects in congenitally blind and sighted subjects.

Compared 8 congenitally blind, 8 sighted, and 8 blindfolded sighted female school students (mean age 16 yrs) using a selective interference technique. Ss categorized the words of sentences and the corners of figures while responding either spatially (by typing), verbally, or while tapping. Spatial responding slowed RTs more than tapping or verbal responding in the figure condition, and verbal and spatial responding were slower than tapping in the sentence categorization. No major differences were found between the response patterns of the 3 groups. It is argued that many imagery tasks involve a heavy dependence on spatial information processing, and to the extent that the blind and the sighted perform similarly in such situations, it follows that they are using similar spatial representations. Implications for studies of imagery and the representational skills of the blind are discussed. (French abstract) (16 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The hippocampus, objects, and their contexts.

Rats with hippocampal aspiration lesions and controls were trained on delayed nonmatching to sample with small complex goal boxes, presented trial uniquely. A series of experiments then used pairs of large or small boxes, presented repeatedly. The lesions impaired choice accuracy when the rats were tested with large empty boxes but not when small boxes containing 3-dimensional objects were used. There was a comparable impairment when the rats were tested with pairs of large complex boxes, which contained arrays of objects, identical to those used in the smaller boxes but necessarily spaced further apart. Subsequent experiments revealed that the lesion deficit with large boxes was reduced by insertion of a continuous line of distinctive objects and eliminated by trial-unique presentation of large boxes. The results are discussed in terms of (non) spatial accounts of hippocampal function and the compensatory effects of novel object cues. We conclude that, for hippocampal rats, spatial cues, although useless, can nonetheless be profoundly disruptive. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Brain aging: changes in the nature of information coding by the hippocampus

Advanced age in rats is associated with a decline in spatial memory capacities dependent on hippocampal processing. As yet, however, little is known about the nature of age-related alterations in the information encoded by the hippocampus. Young rats and aged rats identified as intact or impaired in spatial learning capacity were trained on a radial arm maze task, and then multiple parameters of the environmental cues were manipulated to characterize the changes in firing patterns of hippocampal neurons corresponding to the presence of particular cues or the spatial relationships among them. The scope of information encoded by the hippocampus was reduced in memory-impaired aged subjects, even though the number of neurons responsive to salient environmental cues was not different from that in young rats. Furthermore, after repeated manipulations of the cues, memory-intact aged rats, like young rats, altered their spatial representations, whereas memory-impaired aged rats showed reduced plasticity of their representation throughout testing. Thus changes in hippocampal memory representation associated with aging and memory loss can be characterized as a rigid encoding of only part of the available information.     

Systematic comparison of the effects of hippocampal and fornix-fimbria lesions on acquisition of three configural discriminations

The effects of lesions to the hippocampal system on acquisition of three different configural tasks by rats were tested. Lesions of either the hippocampus (kainic acid/colchicine) or fornix-fimbria (radiofrequency current) were made before training. After recovery from surgery, rats were trained to discriminate between simple and compound-configural cues that signaled the availability or nonavailability of food when a bar was pressed. When positive cues were present, one food pellet could be earned by pressing a lever after a variable time had elapsed. The trial terminated on food delivery (variable interval 15 s). This procedure eliminates some possible alternative explanations of the results of previous experiments on configural learning. Hippocampal lesions increased rates of responding and retarded acquisition of a negative patterning task (A+, B+, AB-); using a ratio measure of discrimination performance these lesions had a milder retarding effect on a biconditional discrimination (AX+, AY-, BY+, BX-), and they had no effect on a conditional context discrimination (X: A+, B-; Y: A-, B+). Fornix-fimbria lesions did not affect acquisition of any of these tasks but increased rates of responding. The results suggest that several task parameters determine the involvement of the hippocampus in configural learning; however, all tasks tested can also be learned to some extent in the absence of an intact hippocampal system, presumably by other learning/memory systems that remain intact following surgery. The lack of effect of fornix-fimbria lesions on any of these tasks suggests that retrohippocampal connections with other brain areas may mediate hippocampal contributions to the learning of some configural tasks. An analysis of these results and of experiments on spatial learning situations suggests that involvement of the hippocampus is a function of the degree to which correct performance depends on a knowledge of relationships among cues in a situation.     

What's communication got to do with it? Gesture in children blind from birth.

It is widely accepted that gesture can serve a communicative function. The purpose of this study was to explore gesture use in congenitally blind individuals who have never seen gesture and have no experience with its communicative function. Four children blind from birth were tested in 3 discourse situations (narrative, reasoning, and spatial directions) and compared with groups of sighted and blindfolded sighted children. Blind children produced gestures, although not in all of the contexts in which sighted children gestured, and the gestures they produced resembled those of sighted children in both form and content. Results suggest that gesture may serve a function for the speaker that is independent of its impact on the listener. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ontogeny of spatial navigation behaviors in the rat: Dissociation of "proximal"- and "distal"-cue-based behaviors.

Rats can use both "proximal" and "distal" cues to locate goal objects in their environments (Morris, 1981). In the proximal-cue situation, local stimuli that spatially co-occur with the goal are available to guide behavior. In the distal-cue situation, there are no cues that co-occur with the goal object; thus to directly locate the goal, the rat must learn about the spatial location of the goal relative to distal cues. Using the Morris water maze, we found that these two navigation behaviors are dissociated during ontogeny. Rats only 17-days-old are capable of using proximal cues to locate a safe platform. It was not until the rats were 20-days-old, however, that they began to display minimal evidence of distal-cue utilization. Control experiments indicated that the 17-day-old subjects' failure on the distal problem was likely due to their inadequate spatial learning skills. These results were interpreted within a Jacksonian perspective of brain–behavior relations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Entorhinal cortex lesions disrupt the transition between the use of intra- and extramaze cues for navigation in the water maze.

[Correction Notice: An erratum for this article was reported in Vol 117(5) of Behavioral Neuroscience (see record 2007-16848-001). The definitions "Present = intramaze landmark present during Stage 2" and "Absent = intramaze landmark absent during Stage 2" appear incorrectly in the caption to Figure 3. These terms and definitions should appear in the caption to Figure 4.] This study with rats examined the effects of excitotoxic lesions to the entorhinal cortex (EC) and hippocampus (HPC) on using extramaze and intramaze cues to navigate to a hidden platform in a water maze. HPC lesions resulted in a disruption to the use of extramaze cues, but not intramaze cues, whereas EC lesions had no effect on the use of these cues when they were encountered for the fast time. However, prior navigation training in which 1 type of cue was relevant disrupted navigation with the other type in rats with EC lesions. Results show that the EC contributes to the processing of spatial information, but that this contribution is most apparent when there is a conflict between 2 sources of navigational cues in the water maze. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hippocampal lesions impair retention of discriminative responding based on energy state cues.

The present research investigated the hypothesis that the hippocampus is involved with the control of appetitive behavior by interoceptive “hunger” and “satiety” signals. Rats were trained to solve a food deprivation intensity discrimination problem in which stimuli produced by 0-hr and 24-hr food deprivation served as discriminative cues for the delivery of sucrose pellets. For Group 0+, sucrose pellets were delivered at the conclusion of each 4-min session that took place under 0-hr food deprivation, whereas no pellets were delivered during sessions that took place when the rats had been food deprived for 24 hr. Group 24+ received the reverse discriminative contingency (i.e., they received sucrose pellets under 24-hr but not under 0-hr food deprivation). When asymptotic discrimination performance was achieved (indexed by greater incidence of food magazine approach behavior on reinforced compared with nonreinforced sessions), half of the rats in each group received hippocampal lesions, and the remaining rats in each group were designated as sham- or nonlesioned controls. Following recovery from surgery, food deprivation discrimination performance was compared for lesioned and control rats in both Groups 0+ and 24+. Discriminative responding was impaired for rats with hippocampal lesions relative to their controls. This impairment was based largely on elevated responding to nonreinforced food deprivation cues. In addition, hippocampal damage was associated with increased body weight under conditions of ad libitum feeding. The results suggest that the inhibition of appetitive behavior by energy state signals may depend, in part, on the hippocampus. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

H-7 stimulates desmosome formation and inhibits growth in KB oral carcinoma cells

Groups of old and young rats were administered three tests of spatial learning and memory that are known to be sensitive to hippocampal dysfunction: the radial arm maze (RAM), spatial non-matching-to-sample (SNMTS), and a spatial vs. local cue-preference task. Old rats performed worse than young rats on the RAM and SNMTS tasks; on the cue-preference task, young rats were biased to use spatial cues, whereas old rats exhibited strong preferences for distinct, local cues. Peripheral injections of glucose (100 mg/kg) improved performance by old rats on the RAM and SNMTS, which correlated with measures of glucose metabolism. Glucose treatment did not affect old rats performance on the cue-preference task. There was evidence that glucose-treatment improved performance of young rats in the RAM test, but not the other tests. The results extend the range of tasks on which glucose-induced cognitive enhancement has been demonstrated in aged rats, and provides further evidence that memory loss resulting from hippocampal dysfunction is especially amenable to glucose treatment.