Contributions of striatal subregions to place and response learning

The involvement of different subregions of the striatum in place and response learning was examined using a T-maze. Rats were given NMDA lesions of the dorsolateral striatum (DLS), anterior dorsomedial striatum (ADMS), posterior dorsomedial striatum (PDMS), or sham surgery. They were then trained to retrieve food from the west arm of the maze, starting from the south arm, by turning left at the choice point. After 7 d of training, with four trials a day, a probe test was given in which the starting arm is inserted as the north arm, at the opposite side of the maze. A left turn would indicate a "response" strategy; a right turn, a "place" strategy. The rats were then trained for 7 more days, followed by a second probe test. Unlike rats in the other groups, most of the rats in the PDMS group turned left, using the response strategy on both probe tests. These results suggest that the PDMS plays a role in spatially guided behavior.     

Contributions of the dorsal hippocampus and the dorsal subiculum to processing of idiothetic information and spatial memory

It is well established that the dorsal hippocampal formation is crucial for spatial memory in rats. However, little is known about the distinct functions of the dorsal hippocampus and the dorsal subiculum. To examine the role of the dorsal hippocampus and the dorsal subiculum, Long-Evans rats with excitotoxic lesions (NMDA) of the dorsal hippocampus (DH), the dorsal subiculum (DS), or both (DHDS), and controls were trained on a nonmatching-to-place task. Then, to identify the strategy used by each group, they were tested on the same task in the dark with the T-maze being rotated between the sample and the test runs. In the light, rats with combined lesions were impaired. In the dark, groups DH, DS, and controls performed near chance level except in trials without rotation, suggesting the use of a sense of direction. The same rats were trained on a radial-arm maze task. In the light, where proximal visual cues were accessible, combined lesions affected performance whereas in the dark, it was impaired by all lesions. This experiment demonstrated that the dorsal subiculum and the dorsal hippocampus play a crucial role in processing idiothetic information and/or in maintenance of this information in memory.     

Spontaneous alternation behavior in hamsters

Male and female golden hamsters spontaneously alternated successive entries of T-maze arms (derived from a + − maze) rather than body turns during a series of eight consecutive trials except when not confined to the arm chosen on each trial. Only unconfined males failed to alternate on their first opportunity. Confinement to an entered arm for 30 seconds had no effect on females but increased alternation in males. Increasing the visual discriminability of the arms had no effect on alternation in either sex. It was concluded that spontaneous alternation behavior in hamsters depended upon whether or not they were confined to a chosen arm and their sex. It is possible that the phenomenon was escape-related.     

Contributions of the nucleus accumbens and its subregions to different aspects of risk-based decision making

The nucleus accumbens (NAc) has been implicated in mediating different forms of decision making in humans and animals. In the present study, we observed that inactivation of the rat NAc, via infusion of GABA agonists, reduced preference for a large/risky option and increased response latencies on a probabilistic discounting task. Discrete inactivations of the NAc shell and core revealed further differences between these regions in mediating choice and response latencies, respectively. The effect on choice was attributable to reduced win–stay performance (i.e., choosing risky after a being rewarded for a risky choice on a preceding trial). Moreover, NAc inactivation altered choice only when the large/risky option had greater long-term value, in terms of the amount of food that could be obtained over multiple trials relative to the small/certain option. Inactivation of the NAc or the shell subregion also slightly reduced preference for larger rewards on a reward magnitude discrimination. Thus, the NAc seems to play a small role in biasing choice toward larger rewards, but its contribution to behavior is amplified when delivery of these rewards is uncertain, helping to direct response selection toward more favorable outcomes.     

Pattern alternation: Effects of spatial frequency and orientation

Campbell and Howell (1972) reported an effect called “monocular pattern alternation.” They found that a pattern composed of two orthogonal sinusoidal gratings, one horizontal and the other vertical, underwent rivalry when viewed monocularly for a period of time. In the present study, it has been shown that monocular pattern alternation depends upon the orientation of the pattern and the spatial frequency of its components. Fewer reversals were found for an obliquely oriented pattern than for a pattern with components in the horizontal and vertical meridians. Alternation rate was higher when the gratings were similar in frequency but differed in orientation than when the components of the pattern differed in both dimensions. It was concluded that pattern alternation reflects an antagonistic interaction between interdependent channels in the human visual system that respond to orientation and spatial frequency.     

Spontaneous alternation behavior in animals: A review

Factors affecting spontaneous alternation behavior (SAB) in animals, for example, age, gender and species studied; type of apparatus and cues employed; and neuro-anatomical, neuro-chemical and motivational status of the organism, were reviewed. Despite a myriad of experiments showing interesting main effects of such variables, little research has been performed assessing the interactive affects of these factors on alternation behavior. For example, psychologists test rats in central nervous system (CNS) lesion studies, whereas psychopharmacologists tend to assess SAB in mice. Most importantly, studies have not been reported investigating the possible interactions among species, brain lesions and drugs. This is an unfortunate omission since several important alternation models include propositions relating to cholinergic and/or serotonergic coding in the hippocampus. Examination of behavioral studies revealed the primary cue for alternation among invertebrates to be body turn, whereas vertebrates rely primarily on directional and odor cues. Reference to the seeking of stimulus change remains the most compelling motivational account of why animals manifest this ubiquitious and reliable behavior pattern. This review and the unpublished studies were supported by Research Grants MH16962, MH21288, and MH36491 from the National Institute of Mental Health and the Wake Forest University Research and Publication Fund.     

Parallel associative processing in the dorsal striatum: segregation of stimulus-response and cognitive control subregions

Although evidence suggests that the dorsal striatum contributes to multiple learning and memory functions, there nevertheless remains considerable disagreement on the specific associative roles of different neuroanatomical subregions. We review evidence indicating that the dorsolateral striatum (DLS) is a substrate for stimulus–response habit formation – incremental strengthening of simple S–R bonds – via input from sensorimotor neocortex while the dorsomedial striatum (DMS) contributes to behavioral flexibility – the cognitive control of behavior – via prefrontal and limbic circuits engaged in relational and spatial information processing. The parallel circuits through dorsal striatum interact with incentive/affective motivational processing in the ventral striatum and portions of the prefrontal cortex leading to overt responding under specific testing conditions. Converging evidence obtained through a detailed task analysis and neurobehavioral assessment is beginning to illuminate striatal subregional interactions and relations to the rest of the mammalian brain.     

Bilateral entorhinal cortex lesions impair acquisition of delayed spatial alternation in rats

Entorhinal cortex lesions induce significant reorganization of several homotypic and heterotypic inputs to the hippocampus. This investigation determined whether surviving heterotypic inputs after bilateral entorhinal lesions would support the acquisition of a learned alternation task. Rats with entorhinal lesions or sham operations were trained to acquire a spatial alternation task. Although the sham-operated rats acquired the task within about 3 weeks postsurgery, rats with bilateral entorhinal lesions failed to learn the task after 12 consecutive weeks of training despite heterotypic sprouting of the cholinergic septodentate pathway and the expansion of the commissural/associational fiber plexus within the dentate gyrus. Thus, heterotypic sprouting failed to ameliorate significantly the effects of bilateral entorhinal lesions. Rather, entorhinal lesions produced a persistent impairment of spatial memory, characterized by a mixture of random error production and perseverative responding.     

Contributions of the functional analysis of behavior to the problem of AIDS

Epidemiological patterns in the spread of HIV infection and the potential role of psychologists in encouraging behavioral changes intended to reduce risks of infection are examined. The 1st great wave of AIDS cases in the industrialized countries occurred primarily in specific, fairly self-contained subgroups such as male homosexuals, hemophiliacs, and IV drug users. Large proportions in these groups are either infected or have adapted risk reduction behavior. The risk of infection for the general heterosexual population in industrialized countries is very low but likely to increase progressively unless measures are taken to reduce risks. Psychologists, who expend considerable effort researching and attempting to effect behavioral changes, thus have a potentially significant role in slowing the spread of the AIDS epidemic. The means of avoiding HIV infection in sexually active persons and drug users are known, but the means of motivating individuals to change to less risky behaviors are not as well understood. Several factors have been identified that appear to influence the vulnerability of the organism to HIV infection or to development of AIDS once infected. Several are capable of modification through behavioral changes, such as high-risk sexual practices, use of particular contraceptive methods, inadequate hygiene, poor nutrition, and self-administration of drugs. Several aspects of HIV infection and its spread are capable of producing psychological stress, including anxiety over possible infection and testing, reaction to diagnosis, fear of rejection by others, watching friends and relatives sicken and die of AIDS, encountering suspicious symptoms, and perceiving signs of physical deterioration. Psychological support in these situations can help to prolong life and improve its quality. Examples abound of individuals who continue to display a risk behavior despite being well informed of its risks; physicians who smoke are 1 such group. Information is a necessary but not sufficient condition for adapting preventive behaviors. Functional behavioral analysis suggests that immediate pleasure, ephemeral though it may be, outweighs the mere possibility of an unpleasant consequence at some hypothetical future date.     

A method to analyze the spatial distribution of behavior

This article presents a method comprising an experimental environment, infrared detection system, data collection and processing software, behavior categories, and suggested quantitative analysis methods for studying some spatial properties of behavior. In the chamber, the location of a rat is determined at regular intervals by a 24 × 24 grid of infrared beams; the status of each line used interactively to determine changes in the environment are stored on disk for later analysis. From the status of the receptors, the computer decodes the location of objects in the chamber, and a binary 576-cell matrix is obtained for each sample. The series of matrices allows a number of behavior categories to be defined includingexploration, activity, andtime allocation. Exploration curves and time allocation surfaces are compared using a goodness-of-fit test; activity is assessed with time-series methods. Potential applications to psychological, pharmacological, and ethological research are considered.     

Role of CA3 and CA1 subregions of the dorsal hippocampus on temporal processing of objects

Previous research in the dorsal CA1 and dorsal CA3 subregions of the hippocampus has been shown to play an important role in mediating temporal order memory for spatial location information. What is not known is whether the dorsal CA3 and dorsal CA1 subregions of the hippocampus are also involved in temporal order for visual object information. Rats with dorsal CA1, dorsal CA3 or control lesions were tested in a temporal order task for visual objects using an exploratory paradigm. The results indicated that the controls and the dorsal CA3 lesioned rats preferred the first rather then the last object they had explored previously, indicating good memory for temporal order of object presentation. In contrast, rats with dorsal CA1 lesions displayed a profound deficit in remembering the order of the visual object presentations in that they preferred the last object rather than the first. All three groups of rats preferred a novel object compared to a previously explored object suggesting normal detection of visual object novelty. The results suggest that only the dorsal CA1, but not dorsal CA3, region is critical for processing temporal information for visual objects without affecting the detection of new visual objects.