Herbert L. Petri

Dissociation of hippocampal and striatal contributions to spatial navigation in the water maze.

Two experiments were conducted to compare the effects of fornix/fimbria and caudate-putamen lesions in Long-Evans hooded rats (Rattus norvegicus) trained on two water maze tasks that differed in the type of spatial localization required for optimum solution. In Experiment 1, the lesioned rats and surgical controls were trained on the standard place task in the water maze (Morris, 1981) and given two postacquisition tests (a platform removal probe and platform relocation test). In Experiment 2, rats with similar lesions and control rats were trained on a modified cue navigation task. Fornix/fimbria lesions impaired a late stage of place task acquisition but did not impair acquisition of the cue task. Caudate-putamen lesions resulted in a severe place acquisition impairment and a transient cue acquisition impairment, both of which were characterized by an initial tendency to swim near the wall of the pool. Post-hoc analyses of the direction and angles of departure from the start points suggested that rats with fornix/fimbria lesions used non-allocentric spatial strategies to solve the place task. These rats also demonstrated a significantly weakened spatial bias for the former training quadrant on the platform removal probe and reduced flexibility in navigating to a novel platform location on the platform relocation test. In contrast, rats with caudate-putamen lesions showed a significant spatial bias for the former training quadrant but failed to cross the exact location within the quadrant where the platform was formerly positioned. The results suggest that the hippocampus mediates the allocentric spatial component of the water maze place task while the dorsomedial striatum may play an important role in the acquisition of the procedural aspects of both place and cue versions of the task.

Place navigation in the Morris water task: Effects of reduced platform interval lighting and pseudorandom platform positioning

Two procedural components of place navigation training in the Morris (1981) water task were studied. Specifically, rats were required to escape onto a submerged (hidden) platform located in either a fixed or a pseudorandomly varied position throughout training. Following escape, the animals were either given unrestricted visual access to the extramaze environment for the duration of the platform interval (45 sec) or denied this opportunity through reduced laboratory illumination. The results of the experiment indicate that (1) pseudorandom platform positioning primarily attenuated the rats’ rate of acquisition rather than postasymptotic escape performance, and (2) visibility of distal cues from the goal location during training was not necessary for appropriate place navigation to occur. Further evidence obtained from a transfer test given on the final day of training suggests that rats trained with a pseudorandomly positioned platform may have acquired specific knowledge of multiple goal locations. These findings provide further support for the claim that rats acquire distal cue information primarily while en route to the platform.

Milacemide treatment in mice enhances acquisiton of a Morris-type water maze task

The N-methyl-D-aspartate (NMDA) subtype of the glutamate receptor appears to be involved with processes of learning and memory. A neutral amino acid binding site is known to exist on the NMDA complex. Glycine binds with high affinity to this site and has been found to potentiate NMDA activity. 2-N-Pentylaminoacetamide HCl (milacemide) is a glycine agonist that has been found to enhance performance of rodents in passive and active avoidance tasks and has improved the performance of humans in several word retrieval tasks. We evaluated the effects of milacemide on the performance of male C57BL/6J mice in a complex spatial task, the Morris water maze. Because NMDA receptor activation appears involved in induction of long-term potentiation, it was hypothesized that milacemide administration would be involved in task acquisition. Therefore, mice were treated with either milacemide (10 mg/kg) or vehicle 1 h prior to training on each of 4 consecutive days. Results indicated that mice treated with milacemide learned the task significantly faster than controls over 4 days of training, as measured by mean distance (cm) to reach the goal platform. Therefore, agonism of the glycine site on the NMDA receptor appears to facilitate performance of learning in a spatial memory task.

Partial reinforcement across trials impairs escape performance but spares place learning in the water maze

We studied the effects of partial reinforcement on escape performance and place learning in the water maze. Rats given 50% reinforcement across trials (i.e. the escape platform was present only on odd trials) were compared to controls given 100% reinforcement (platform present on all trials). Control groups either received 8 or 4 trials per day, which was equal to either the total number of trials (100%-8) or reinforced escapes (100%-4) of the 50% group. Analysis of escape performance (latency) revealed that the 50% group was impaired relative to the 100%-8 group, but not the 100%-4 group, during the first 5 days of acquisition. The 50% group was impaired relative to both control groups on days 6-10 of overtraining. However, analyses of within-trial behavior (target annulus preference and thigmotaxis) on nonreinforced trials suggest that the 50% group did learn the location of the hidden platform (place information), in addition to a wall-based thigmotactic response. By dividing the 60s nonreinforced trials into three 20-s time bins, we were able to detect a significant preference for the target annulus early in the trial (bin 1 of trial 40 and bins 1-2 of trial 80). Further, there was a significant increase in time spent in the periphery of the pool, near the wall, in the last time bin of trial 40. Because the platform was in the middle zone, this behavior competed with a place response. We conclude that across-trial partial reinforcement procedures may promote response competition and mask evidence of place learning in addition to weakening escape performance late in training.

Variables Influencing the Shape of Personal Space

Personal space has been defined as the area surrounding a person’s body into which intruders may not come (Sommer, 1969). As conceived by Sommier, personal space has no fixed geographic reference points but is seen as moving with the individual and expanding or contracting as conditons vary (Sommer, 1958). Much contradictory evidence presently exists concerning the variables which control personal space (Evans and Howard, 19T3; Duke and Nowicki, 19T2). Personal space has been studied using both naturalistic and objective techniques; however, as Evans and Howard (19T3) and Duke and Nowicki (19T2) have noted, results obtained with one method are often in conflict with results obtained with others. In addi-

Use of An Auditory Technique in Personal Space Measurement

Summary Personal space was examined in 50 male and female college students by means of a newly developed auditory technique which was validated against simulated and behavioral measures. A multiple regression analysis showed the auditory technique to be a better predictor of behaviorally measured personal space than the Comfortable Interpersonal Distance Scale, a simulated measure. The major advantage of the auditory technique over the simulated measure is its perceived realism.

Effects of imprinting strength on stimulus generalization in chicks (Gallus gallus).

Effects of original imprinting strength on color and shape generalization involving other test objects were investigated in chicks ( Gallus gallus ). Strength of imprinting was manipulated by varying the age at which subjects were initially exposed to the original imprinting stimulus. Results indicated that original imprinting strength affected generalization to color, but not shape cues. The data suggest that original imprinting strength affects the generalization process for those dimensions of the imprinting stimulus exerting strongest stimulus control over following behavior.

Effects of imprinting and isolation on aggressive responses in chicks

The importance of isolation and imprinting as separate factors influencing early aggressive responses in chicks (Gallus gallus) was studied in two separate experiments. In addition the effect of the presence or absence of the imprinting stimulus in the test situation was examined in Experiment 1. Neither imprinting per se, nor the presence of the imprinting stimulus significantly affected aggressiveness. Rearing conditions (isolation vs social rearing) did, however, influence aggressive responses. Isolated chicks were significantly more aggressive than socially reared buds. The adaptedness of selective aggression in socially (naturally) reared chicks, as well as the indiscriminant aggressiveness caused by social deprivation is discussed.