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At least 811 records · Page 45Linked to original sources
PubMed1999

Head direction cells in rats with hippocampal or overlying neocortical lesions: evidence for impaired angular path integration.

Rodents use two distinct navigation strategies that are based on environmental cues (landmark navigation) or internal cues (path integration). Head direction (HD) cells are neurons that discharge when the animal points its head in a particular direction and are responsive to the same cues that support path integration and landmark navigation. Experiment 1 examined whether HD cells in rats with lesions to the hippocampus plus the overlying neocortex or to just the overlying neocortex could maintain a stable preferred firing direction when the rats locomoted from a familiar to a novel environment, a process thought to require path integration. HD cells from both lesion groups were unable to maintain a similar preferred direction between environments, with cells from hippocampal rats showing larger shifts than cells from rats sustaining only cortical damage. When the rats first explored the novel environment, the preferred directions of the cells drifted for up to 4 min before establishing a consistent firing orientation. The preferred direction was usually maintained during subsequent visits to the novel environment but not across longer time periods (days to weeks). Experiment 2 demonstrated that a novel landmark cue was able to establish control over HD cell preferred directions in rats from both lesion groups, showing that the impairment observed in experiment 1 cannot be attributed to an impairment in establishing cue control. Experiment 3 showed that the preferred direction drifted when HD cells in lesioned animals were recorded in the dark. It was also shown that the anticipatory property of anterodorsal thalamic nucleus HD cells was still present in lesioned animals; thus, this property cannot be attributed to an intact hippocampus. These findings suggest that the hippocampus and the overlying neocortex are involved in path integration mechanisms, which enable an animal to maintain an accurate representation of its directional heading when exploring a novel environment.

Action Potentials↗
PubMed2002

Competition between memory systems: acetylcholine release in the hippocampus correlates negatively with good performance on an amygdala-dependent task.

Lesions of the amygdala impair acquisition of a food conditioned place preference (CPP) task. In contrast, lesions of the fornix facilitate acquisition on this task, showing that an intact hippocampal system can interfere with learning an amygdala-dependent task. Our recent findings indicate that acetylcholine (ACh) release in the hippocampus increases while rats perform a hippocampus-dependent spontaneous alternation task. To the extent that ACh output in the hippocampus reflects activation of that brain area in learning and memory, the results obtained with fornix lesions suggest that ACh release in the hippocampus might be negatively correlated with learning on a CPP task. Using in vivo microdialysis, release of ACh was measured in the hippocampus while rats learned and were tested on an amygdala-dependent CPP task and a hippocampus-dependent spontaneous alternation task. Release of ACh in the hippocampus increased when rats were tested on either task. The magnitude of the increase in release of hippocampal ACh was negatively correlated with good performance on the amygdala-dependent CPP task. These findings suggest that ACh release may reflect activation and participation of the hippocampus in learning and memory, but in a manner that can be detrimental to performance on a task dependent on another brain area.

Acetylcholine↗
PubMed1993

Visual and spatial trials paired in a new behavioral procedure: effects of benactyzine.

A paired discrimination (PD) task in which visual and spatial discrimination trials were combined is offered as a method for the evaluation of drug effects on various behavioral parameters. Acquisition of the PD task is characterized by six different parameters simultaneously recorded each session. Analysis of memory requirements suggest that intact reference memory is involved in the performance of both types of trials while working memory is involved only in the performance of the spatial trial. Benactyzine (1-4 mg/kg), an anticholinergic drug, was tested for its effects on visual and spatial tasks presented either separately or in the PD combination. Benactyzine-induced mydriasis was also determined for its possible role in photophobic-induced errors. Benactyzine was found to differentially increase the number of errors performed during the spatial but not during the visual trials. The data are in accord with earlier finding of specific cholinergic involvement in working memory processes. Thus, low doses of benactyzine, and the PD task, can prove useful in the cognitive analysis of cholinergic hypofunction and its reversal by memory-enhancing drugs.

Animals↗
PubMed2005

The effect of intrahippocampal injections of ritanserin (5HT2A/2C antagonist) and granisetron (5HT3 antagonist) on learning as assessed in the spatial version of the water maze.

5HT(2A/2C) and 5HT(3) receptors have an important role in cognitive behavior specially in spatial learning and memory but the literature concerning the role of these receptors in hippocampus in cognition remains controversial. In the present study a 5HT(2A/2C) antagonist ritanserin (0, 2, 4, 8 microg/0.5 microl) and a 5HT(3) antagonist granisetron (0.0, 0.05, 0.25, 0.5 microg/0.5 microl) were injected bilaterally into the CA1 region of rat hippocampus, 20 min before each training session in Morris Water Maze (MWM) task. Compare with control group, ritanserin (4 microg/0.5 microl) significantly reduced the escape latency and traveled distance of swimming to platform, but granisetron (0.25 microg/0.5 microl) significantly increased those parameters. Both drugs had no effect on escape latency and traveled distance of a non-spatial visual discrimination task. These results suggest a differential role of 5HT(2A/2C) and 5HT(3) receptors during spatial learning that ritanserin improves rat performance in spatial discrimination task whereas granisetron impairs it.

Analysis of Variance↗
PubMed1984

Proposed neural circuitry for spatial memory in the primate brain.

The possible cerebral cortical circuitry for spatial memory in primates is discussed in light of a conceptual model and clinical as well as animal behavioral data. It is proposed that spatial memory formation begins with the arrival of sensory information in primary sensory areas and involves progressive elaboration through parasensory and higher-order association cortices. The connectivity between the association areas and the paralimbic and limbic regions is viewed as critical to the consolidation process. Finally, the execution of spatial behavior is presumed to involve the post-Rolandic and paralimbic projections to the frontal lobe. It is hoped that this conceptualization may provide a framework for further studies dealing with spatial memory.

Animals↗
PubMed1976

A theory of behavioral generality and specificity during mild stress.

A definitional system is given for the concepts of generality and specificity for behavioral variables, relating to signs and sizes of their intercorrelations. In particular, a mapping sentence is provided for defining the universe of observations for emotional behavior of mice under mild stress. Its three content facets are: (a) the temporal features of frequency, latency, and duration, (b) type of control, autonomic or voluntary, and (c) the experimental situation, the apparatus. Data from three studies published previously by other authors are analyzed by Smallest Space Analysis (SSA-I). In each case, the smallest space is found to be partitioned into contiguous regions corresponding to the elements of the three facets.

Animals↗
PubMed2000

Effects of repetitive motor training on movement representations in adult squirrel monkeys: role of use versus learning.

Current evidence indicates that repetitive motor behavior during motor learning paradigms can produce changes in representational organization in motor cortex. In a previous study, we trained adult squirrel monkeys on a repetitive motor task that required the retrieval of food pellets from a small-diameter well. It was found that training produced consistent task-related changes in movement representations in primary motor cortex (M1) in conjunction with the acquisition of a new motor skill. In the present study, we trained adult squirrel monkeys on a similar motor task that required pellet retrievals from a much larger diameter well. This large-well retrieval task was designed to produce repetitive use of a limited set of distal forelimb movements in the absence of motor skill acquisition. Motor activity levels, estimated by the total number of finger flexions performed during training, were matched between the two training groups. This experiment was intended to evaluate whether simple, repetitive motor activity alone is sufficient to produce representational plasticity in cortical motor maps. Detailed analysis of the motor behavior of the monkeys indicates that their retrieval behavior was highly successful and stereotypical throughout the training period, suggesting that no new motor skills were learned during the performance of the large-well retrieval task. Comparisons between pretraining and posttraining maps of M1 movement representations revealed no task-related changes in the cortical area devoted to individual distal forelimb movement representations. We conclude that repetitive motor activity alone does not produce functional reorganization of cortical maps. Instead, we propose that motor skill acquisition, or motor learning, is a prerequisite factor in driving representational plasticity in M1.

Animals↗
PubMed2006

A model of antennal wall-following and escape in the cockroach.

Cockroaches exploit tactile cues from their antennae to avoid predators. During escape running the same sensors are used to follow walls. We hypothesise that selection of these mutually exclusive behaviours can be explained without representation of the stimulus or an explicit switching mechanism. A neural model is presented that embodies this hypothesis. The model incorporates behavioural and neurophysiological data and is embedded in a mobile robot in order to test the response to stimuli in the real world. The system is shown to account for data on escape direction and high-speed wall-following in the cockroach, including the counter-intuitive observation that faster running cockroaches maintain a closer distance to the wall. The wall-following behaviour is extended to include discrimination of tactile escape cues according to behavioural context. We conclude by highlighting questions arising from the robot experiments that suggest interesting hypotheses to test in the cockroach.

Animals↗
PubMed2006

Movement characteristics support a role for dead reckoning in organizing exploratory behavior.

Rat exploration is an organized series of trips. Each exploratory trip involves an outward tour from the refuge followed by a return to the refuge. A tour consists of a sequence of progressions with variable direction and speed concatenated by stops, whereas the return consists of a single direct progression. We have argued that processing self-movement information generated on the tour allows a rat to plot the return to the refuge. This claim has been supported by observing consistent differences between tour and return segments independent of ambient cue availability; however, this distinction was based on differences in movement characteristics derived from multiple progressions and stops on the tour and the single progression on the return. The present study examines movement characteristics of the tour and return progressions under novel-dark and light conditions. Three novel characteristics of progressions were identified: (1) linear speeds and path curvature of exploratory trips are negatively correlated, (2) tour progression maximum linear speed and temporal pacing varies as a function of travel distance, and (3) return progression movement characteristics are qualitatively different from tour progressions of comparable length. These observations support a role for dead reckoning in organizing exploratory behavior.

Animals↗
PubMed2005

Memory-dependent novelty-related location preferences: sex-related attenuation of forgetting by D-glucose and tacrine.

Following confinement to one chamber of a two-chamber exploration box (acquisition trial), male and female rats were intraperitoneally injected with saline, glucose (50, 100 mg/kg) or tacrine (1, 3 mg/kg). Twenty-four hours later they were given free access to this chamber and an identical novel one (retention trial). Tendencies to occupy the novel chamber (novelty-related location preferences) were increased by both doses of glucose for females and by the higher dose for males. While neither dose of tacrine affected this response for females, increased preferences occurred for males following the higher dose. However, when the higher doses of both agents were administered 2 h after acquisition, there were no significant effects for either sex. In view of the rats' lack of significant preferences for the novel chamber when treated with saline both immediately and 2 h after acquisition, the results were interpreted as sex-dependent attenuation of forgetting by post-acquisition treatment with both agents.

Animals↗
PubMed2004

Room novelty, sex, scopolamine and their interactions as determinants of general activity and rearing, and light-dark preferences in rats.

Male and female rats were assessed for effects of scopolamine on general activity, rearing and light-dark preferences when tested in either a familiar or a novel room. Males but not females reared more often when tested in the familiar rather than novel room, and the response was increased by scopolamine for all rats combined. Whereas scopolamine increased general activity for females (but not males) in the familiar room, it decreased the response for males (but not females) in the novel room. Females crossed more often between the dark and light sides of a light-dark box and, when treated with saline but not drug, spent more time in the light side than males. Scopolamine reduced the amount of time spent in the light side for females only. While the results were discussed mainly in terms of sex differences in fearfulness, their principal value was in demonstrating the effectiveness of room novelty and sex in determining levels of the behaviors recorded, and drug responsiveness.

Animals↗
PubMed2005

Generalization in place learning across geometrically different environments is impaired by hippocampal lesions in rats.

A recent study (Tommasi & Thinus-Blanc, 2004) found that when rats trained to search for food hidden in the center of a square-shaped enclosure were tested in the absence of food, they searched precisely in the center of the enclosure. Transfer tests carried out in enclosures differing in shape or size (rectangular-, large square-, and equilateral triangle-shaped) showed that rats searched in the geometric center of the novel environments. In the present work, half of those rats were lesioned bilaterally to the hippocampus and were then re-trained and re-tested in the same task, to be compared to sham rats that received the same retraining/re-test protocol. Results show that lesioned rats, although unimpaired in relearning to localize the center of the square-shaped enclosure, performed considerably worse than sham rats in the transfer tests in the enclosures differing in shape, suggesting a relevant role of the hippocampus in geometry-driven place generalization.

Animals↗
PubMed2001

The testosterone metabolite and neurosteroid 3alpha-androstanediol may mediate the effects of testosterone on conditioned place preference.

The abuse of androgens may be related to their ability to produce positive, hedonic interoceptive effects. Conditioned Place Preference (CPP) has been used in many experiments to examine hedonic effects of drugs. This review is focused on studies from our laboratory that utilized CPP to examine potential positive hedonic effects of testosterone (T), and its androgenic metabolite dihydrotestosterone (DHT), and its metabolite 3alpha-androstanediol (3alpha-diol). We hypothesized that administration of a high concentration of 3alpha-diol would produce a CPP, pharmacological concentrations of plasma androgens, and alter androgen receptors (AR) and the function of GABA(A)/benzodiazepine receptor complexes (GBR). In our studies, we observed that systemic 3alpha-diol (1.0 mg/kg) prior to exposure to the non-preferred side of a CPP chamber significantly increased preference for the non-preferred side of the chamber compared to baseline preference and homecage controls. Furthermore, administration of T, DHT, or 3alpha-diol increased levels of these androgens, decreased ARs (decreased seminal vesicle weight and intrahypothalamic AR) and GBR function (decreased GABA-stimulated chloride influx in cortical synaptoneurosomes, and muscimol binding in the hippocampus compared to control groups). With systemic administration of 3alpha-diol that enhanced CPP, concentrations of 3alpha-diol were increased in the nucleus accumbens (NA). Central implants of T, DHT, or 3alpha-diol to the NA also produced a CPP compared to baseline preference and vehicle controls. These data indicate that systemic 3alpha-diol is more effective at enhancing CPP and increasing circulating 3alpha-diol levels than is T or DHT and that central administration of 3alpha-diol to the NA can condition a place preference. These findings indicate that 3alpha-diol produces positive hedonic effects and suggest that T's variable effects on CPP may be due in part to T's metabolism to 3alpha-diol.

Androstane-3,17-diol↗
PubMed2006

The influence of landmark salience in a navigation task: an additive effect between its components.

In 2 experiments, rats were trained in a Morris pool to find a hidden platform in the presence of 1 landmark. After acquisition, the rats were tested without the platform. Experiment 1 tested whether the size of a landmark and its relative distance from the platform are additive effects. On test, the rats' best performance was with a near and big landmark; intermediate performance was with either a near and small landmark or a far and big one; and the worst performance was with a far and small landmark. The results of Experiment 2 suggested that the different distances from the goal of the 2 landmarks might not be sufficient to explain the previous results.

Analysis of Variance↗