The structure of individual differences in heterogeneous stock mice across problem types and motivational systems.

Sixty Heterogeneous Stock (HS) mice received a battery of six problem-solving tasks and three control procedures. The problem-solving tasks included Hebb-Williams, a place learning task conducted in a plus maze, radial maze, a working memory test following the radial maze, a set of detour problems and a visual non-matching to sample task. The control procedures consisted of land and water activity measures and a light-dark test. The correlation matrix derived from these tasks did not exhibit positive manifold, that is, positive correlations across all problem-solving tasks. Principal components analysis reduced the correlation matrix to four components with eigenvalues exceeding 1.0. Instead of the general factor solution common in the study of human problem-solving, this component structure appeared more congenial to a modular interpretation, with the four components each explaining approximately the same magnitude of matrix variance.

Memory-enhancing effects of DHEAS in aged mice on a win-shift water escape task.

The steroid hormone, dehydroepiandrosterone (DHEA) and its sulfate (DHEAS) have been implicated in age-associated deficits in memory. Numerous studies have demonstrated the effectiveness of these neurosteroids to enhance retention and ameliorate the effects of various memory-blocking agents, but few studies have directly assayed their effects on memory in aged animals. The present study investigated the memory-enhancing effects of DHEAS in a win-shift (nonmatching-to-sample) task in aged mice using water escape motivation. Sixteen CD-1 mice, 18-20 months old, were trained to a moderate criterion of 7/10 correct trials and were then divided into two equal groups based on acquisition performance. One group received oral administration of DHEAS (1.5 mg/mouse/day) in a vehicle solution (0.0015% methyl salicylate) while the other group received the vehicle alone. DHEAS effects were assessed using a procedure in which delay intervals (0, 120, and 240 s) were interposed between sample and comparison trials over the course of three test sessions. The group receiving DHEAS recorded significantly higher retention scores across 3 days of testing, particularly at the 120-s delay interval, indicating that DHEAS enhanced working memory in these aged animals.

Physical restraint produces rapid acquisition of the pigeon's key peck.

The acquisition and maintenance of autoshaped key pecking in pigeons was studied as a function of intertrial interval. At each of six intervals, which ranged from 12 seconds to 384 seconds, four pigeons were physically restrained during training while four other pigeons were not restrained. Restrained subjects acquired key pecking faster and with less intragroup variability at each interval. The effects of restraint were specific to acquisition and were not evident in maintained responding after five postacquisition sessions.

Autoshaping, random control, and omission training in the rat.

The role of the stimulus-reinforcer contingency in the development and maintenance of lever contact responding was studied in hooded rats. In Experiment I, three groups of experimentally naive rats were trained either on autoshaping, omission training, or a random-control procedure. Subjects trained by the autoshaping procedure responded more consistently than did either random-control or omission-trained subjects. The probability of at least one lever contact per trial was slightly higher in subjects trained by the omission procedure than by the random-control procedure. However, these differences were not maintained during extended training, nor were they evident in total lever-contact frequencies. When omission and random-control subjects were switched to the autoshaping condition, lever contacts increased in all animals, but a pronounced retardation was observed in omission subjects relative to the random-control subjects. In addition, subjects originally exposed to the random-control procedure, and later switched to autoshaping, acquired more rapidly than naive subjects that were exposed only on the autoshaping procedure. In Experiment II, subjects originally trained by an autoshaping procedure were exposed either to an omission, a random-control, or an extinction procedure. No differences were observed among the groups either in the rate at which lever contacts decreased or in the frequency of lever contacts at the end of training. These data implicate prior experience in the interpretation of omission-training effects and suggest limitations in the influence of stimulus-reinforcer relations in autoshaping.