Biomedical subjects

R C Honey

Publications and source records attributed to R C Honey.

At least 19 recordsLinked to original sources

PubMed2003

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

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 first 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.

Animals↗

PubMed2003

Representational blending in human conditional learning: Implications for associative theory.

In two experiments, participants were presented with pictures of different foods (A, B, C, D, X,) and learned which combinations resulted in an allergic reaction in a fictitious patient, Mr X. In Problem 1, when A or B (but not C or D) was combined with food X an allergic reaction occurred, and when C or D (but not A or B) was combined with Y an allergic reaction occurred. In Experiment 1, participants also received Problem 2 in which A, B, C, and D interacted with foods V and W either in the same way as X and Y, respectively, or in a different way. Participants performed more proficiently in the former than in the latter condition. In Experiment 2, after training on Problem 1, participants judged whether or not novel combinations of foods (e.g., AB, CD, AD, CB) would cause an allergic reaction in Mr X. They were no more likely to indicate that AB or CD would cause an allergic reaction than AD or CB, but made their judgements more rapidly and with greater confidence on AB and CD trials than on AD and CB trials. These results (1) indicate that shared representations come to be addressed by the components of similar compounds (e.g., AX and BX) that have predicted the same outcome (an allergic reaction), and (2) are inconsistent with standard, associative theories of learning, but (3) are consistent with findings from nonhuman animals and with a connectionist interpretation of these findings.

Association↗

PubMed2002

Sensory preconditioning in rats with lesions of the anterior thalamic nuclei: evidence for intact nonspatial 'relational' processing.

Rats with neurotoxic lesions centered in the anterior thalamic nuclei were trained in two versions of a nonspatial, sensory preconditioning procedure. In both versions, two stimulus compounds (AX and BY) were first presented and then X, but not Y, was paired with an aversive unconditioned stimulus. This procedure resulted in greater conditioned responding to A than B. Anterior thalamic lesions had no apparent effect on these two examples of sensory preconditioning, nor did they affect fear conditioning or conditioned taste aversion. In contrast, the same lesions led to a severe deficit on a test of spatial memory. These results help to refine our understanding of the contribution of the anterior thalamic nuclei to spatial memory.

Acoustic Stimulation↗

PubMed2002

Involvement of the rat medial prefrontal cortex in novelty detection.

The prefrontal cortex in humans has been implicated in processes that underlie novelty detection and attention. This study examined the contribution of the rat medial prefrontal cortex to novelty detection using the targeting, or orienting, response (OR) as a behavioral index. Lesions to the medial prefrontal cortex (specifically the prelimbic and infralimbic cortices) influenced neither the OR to a novel visual stimulus from a localized light source (V1), nor the change in this OR over the course of a series of exposures to V1. However, after exposure to V1, the OR to a 2nd visual stimulus from the same source, V2, was more pronounced in control rats than in lesioned rats. These results suggest that the medial prefrontal cortex in the rat contributes to the process of novelty detection.

Animals↗

PubMed2002

The influence of selective lesions to components of the hippocampal system on the orienting [correction of orientating] response, habituation and latent inhibition.

The contribution that components of the hippocampal system in the rat make to the modulation of attention or stimulus processing was assessed using several simple behavioural assays: the orienting response (OR) to a novel stimulus, the subsequent habituation and dishabituation of this OR, and the latent inhibition effect that typically results from repeated exposure to a stimulus. Excitotoxic lesions of components of the hippocampal system produce dissociable effects on the OR, habituation and latent inhibition: lesions of the entorhinal cortex have no effect on the OR or changes in the OR during exposure to a stimulus, but disrupt latent inhibition; lesions of the subiculum disrupt the OR but not latent inhibition; and lesions of the hippocampus disrupt the OR and latent inhibition. These effects have important implications for our understanding of habituation and latent inhibition, and the neural mechanisms involved in attentional modulation.

Animals↗

PubMed2002

Acquired equivalence and distinctiveness of cues: I. Exploring a neural network approach.

Rats were placed in 4 contexts (A, B, C, D) where they received 2 auditory stimuli (X, Y); in A and B, presentations of X were paired with food and those of Y were not, and in C and D, Y was paired with food and X was not. Rats then received combinations of contexts that had provided congruent (AB, CD) or incongruent (AD, CB) information about X and Y's relationship to food. Responding was more variable during congruent than incongruent trials (Experiment 1) and was systematically increased and decreased during congruent (relative to incongruent) trials by the presentation of food or no food, respectively (Experiment 2). These results support a connectionist approach to acquired changes in stimulus distinctiveness.

Acoustic Stimulation↗

PubMed2002

Acquired equivalence and distinctiveness of cues: II. Neural manipulations and their implications.

Neural manipulations were used to examine the mechanisms that underlie the acquired equivalence and distinctiveness of cues in rats. Control rats and those with excitotoxic lesions of either the hippocampus (HPC) or entorhinal cortex (EC) acquired the following conditional discrimination: In Contexts A and B, Stimulus X-->food and Stimulus Y-->no food, and in Contexts C and D, Y-->food and X-->no food. Rats then received many food pellets in A but not in C. After this treatment, control rats showed more magazine activity in B than in D--an acquired equivalence-distinctiveness effect. This effect was also evident in HPC rats but not in EC rats. These results indicate that changes in stimulus distinctiveness are dissociable from the process of conditional learning.

Analysis of Variance↗

PubMed2001

Involvement of the entorhinal cortex in a process of attentional modulation: evidence from a novel variant of an IDS/EDS procedure.

Novel behavioral assays were used to assess the role of the entorhinal cortex in modulating attention to components of stimulus compounds. In Stage 1, rats received discrimination training with compounds constructed from 3 dimensions (auditory, visual, and tactile); in each compound the combination of components from 2 dimensions (e.g., auditory and visual) were relevant to the solution of the discrimination, and the remaining dimension (e.g., tactile) was irrelevant. In Stage 2, rats received a different discrimination in which the relevant dimensions were either congruent (auditory and visual) or incongruent (auditory and tactile) with those that were relevant in Stage 1. Sham-operated rats acquired the congruent discrimination more rapidly than the incongruent discrimination--a finding indicative of a process of attentional modulation--whereas rats with excitotoxic lesions of the entorhinal cortex acquired both discriminations equally readily.

Animals↗

PubMed2001

Excitotoxic lesions of the hippocampus leave sensory preconditioning intact: implications for models of hippocampal function.

Learning about contextual cues is markedly disrupted in rats with hippocampal lesions. One analysis of this disruption is that it reflects a general failure to form associations between the elements of complex events. A straightforward prediction of this analysis is that sensory preconditioning will be disrupted by hippocampal lesions. This prediction was assessed by presenting rats with flavored solutions composed of 2 elements (A and X) before X was paired with an injection of the emetic, lithium chloride. A subsequent test revealed that rats were less willing to consume Solution A than they were to consume a control solution, B. This was true of rats with sham lesions and those with excitotoxic lesions of hippocampus. These findings fail to support the proposition that the hippocampus-dependent deficit in contextual conditioning is due to a general disruption to the process of associating the elements of complex events.

Animals↗

PubMed2001

Transfer between contextual conditional discriminations: an examination of how stimulus conjuctions are represented.

In 2 experiments, when rats were placed in 1 pair of contexts, A and B, 2 relationships were in force (X --> food and Y --> no food), and when they were placed in another pair of contexts, C and D, the complementary relationships were operative (Y --> food and X --> no food). In Experiment 1, rats then received a 2nd discrimination that was either contextually congruent (in A and B, Y --> food and X --> no food; in C and D, X --> food and Y --> no food) or contextually incongruent (in A and D, Y --> food and X --> no food; in C and B, X --> food and Y --> no food) with the 1st discrimination. In Experiment 2, the 1st discrimination, involving X and Y, was interleaved with a 2nd discrimination, involving V and W, that was again either congruent (in A and B, V --> food and W --> no food) or incongruent (in A and D, V --> food and W --> no food) with the 1st discrimination. The congruent discriminations were acquired more readily than were the incongruent discriminations.

Animals↗

PubMed2001

Loss of the thalamic nuclei for "head direction" impairs performance on spatial memory tasks in rats.

This study sought to characterize the effects of removing the nuclei of primary importance in relaying the thalamic head direction signal to the hippocampal formation (the anterior dorsal [AD] and lateral dorsal [LD] nuclei) on the performance of a variety of spatial and nonspatial tasks. The results indicate that combined excitotoxic lesions of the AD and LD nuclei produce marked deficits on a variety of spatial tasks. These tasks included T-maze alternation and the ability to locate a hidden platform set at a fixed distance and fixed direction from a beacon in a Morris water maze. Although object recognition appeared unaffected, marked impairments were found in the ability to detect when an object was placed in a novel position (object-in-place memory).

Animals↗

PubMed2000

Associative components of recognition memory.

Recent results indicate that visual recognition memory (as assessed by habituation and dishabituation of the orienting response) is influenced by associative knowledge, and that this influence is mediated by the hippocampus. A standard, associative model of learning has been recently reported to provide a parsimonious explanation for these results.

Animals↗

PubMed2000

Associative modulation of the orienting response: distinct effects revealed by hippocampal lesions.

The ability of auditory stimuli to modulate rats' tendency to orient to visual targets was assessed. In Experiment 1, trials where an auditory stimulus (A) signaled one visual array (X) were intermixed with unsignaled presentations of a second array (Y). Comparison of the orienting responses (ORs) to X and Y revealed that A produced a transient (unconditioned) and an emerging (conditioned) disruptive influence on the OR to X. In Experiments 2 and 3, trials where A signaled X were intermixed with others where another auditory stimulus (B) signaled Y. Stimulus A's ability to modulate the OR to X was then assessed by presenting A prior to test arrays containing both X and Y. Control rats were more likely to orient to Y than X (Experiments 2 and 3) and rats with excitotoxic lesions of the hippocampus were more likely to orient to X than Y (Experiment 3). These results show that auditory stimuli exert distinct modulatory influences on the OR to visual stimuli with which they are associated.

Animals↗

PubMed2000

A novel contextual dimension for use with an operant chamber: from simple to hierarchical forms of learning.

A novel procedure is described in which the floor temperatures (warm and cool) in an operant chamber are used as contextual cues in 2 experiments with rats. Experiment 1 demonstrated that rats learn the relationship between these thermal contexts and auditory stimuli that have been paired with them. Experiment 2 showed that thermal contexts can serve a conditional function that (a) reflects the operation of a mechanism that is common to conventional, visual contexts and (b) is bound to these contexts' ability to retrieve the nature of the relationship between the auditory stimuli and food.

Analysis of Variance↗

PubMed2000

Associative priming in Pavlovian conditioning.

Any occasion on which an animal is placed in an experimental setting or context and receives pairings of one event with another provides the opportunity for a variety of associative structures to be acquired. These structures range from simple associations, which allow the presentation of one event to activate or prime a memory of the other, to hierarchical associations, which allow a simple association to be primed by some other event (e.g. the context in which the simple association was acquired). Experiments with rats that reveal priming effects consistent with both of these putative associative structures are reviewed.

Animals↗

PubMed1998

Hippocampal lesions disrupt an associative mismatch process.

Novel assays were used to assess inter alia whether the hippocampus is involved in detecting novelty per se or in an associative mismatch process. During training, rats received two audiovisual sequences (tone-left constant light and click-left flashing light). In both sham-operated control rats and those with excitotoxic hippocampal lesions, novel visual targets provoked an orienting response that habituated during training. Moreover, like sham-operated rats, rats with hippocampal lesions acquired associations between the elements of two audiovisual sequences. However, subsequent test trials in which the auditory stimuli preceding the visual targets were switched (click-left constant light and tone-left flashing light) provoked renewed orienting to the visual targets in sham-operated rats but not in hippocampal rats. These results support the view that hippocampal damage results in a failure to detect (or act on) mismatches that are generated when an auditory stimulus associatively evokes the memory of one visual stimulus and a different (familiar) visual stimulus is present in the environment.

Animals↗

PubMed1998

Imprinting, learning and development: from behaviour to brain and back.

Neural and behavioural analyses have shown that the formation of filial preferences in young, precocial birds involves at least two separate processes. One process is an emerging predisposition to approach stimuli with the characteristics of the natural mother. The other (learning) process of filial imprinting results in chicks preferentially-approaching a stimulus to which they have been exposed and involves forming links between the components of the exposed stimulus. The neural substrate for the predisposition is different from that underlying imprinting, and different regions of the chick brain are involved in distinct aspects of learning about imprinting stimuli.

Animals↗

PubMed1998

Acquired relational equivalence: implications for the nature of associative structures.

In 2 experiments, rats received discrimination training in which separate presentations of A and B signaled a common pair of relationships or associations (X-->food and Y-->no food), whereas presentations of C and D signaled a different pair of relationships (X-->no food and Y->food). To assess the nature of the associative structures acquired during this training, rats then received 2 types of reevaluation procedure: In Experiment 1, A was paired with shock and C was not. In Experiment 2, the relationships that A and B had previously signaled (X-->food and Y-->no food) were paired with shock, whereas those that C and D had signaled (Y-->food and X-->no food) were not. After both types of reevaluation treatment, rats showed greater generalized conditioned suppression in the presence of B than D. These results indicate that A, B, C, and D come to evoke memories of the relationship or associations that they have signaled.

Animals↗