Michael Noonan

Preference of laboratory rats for potentially enriching stimulus objects

In an effort to identify suitable stimulus objects which could be placed into standard laboratory cages in order to provide rats with a degree of environmental enrichment, the preference of rats to spend time near 15 diverse objects was measured in a free-choice paradigm. Rats showed no preference for objects such as pipes and partitions which we had reasoned might satisfy a wall-hugging tendency. They also showed no preference for objects which we had reasoned to be potentially interesting as manipulanda. The rats did show reliable preferences for spending time with some, but not all, chewable objects. A block of wood predrilled with holes was the most attractive, and we cautiously recommend that researchers consider providing laboratory rats with such an object to allow them the opportunity to exercise a fundamental, species-typical behaviour-chewing.

On the laterality of psychogenic somatic symptoms.

Tabulation of cases reported in the literature of unilateral psychogenic somatic symptoms revealed that more symptoms were on the left side of the body than on the right; this result, although falling short of statistical significance, is consistent with recent reviews of hospital records by Stern and by Galin et al. A review of organic diseases and traumata for which lateral preferences have been reported, and a retrospective study of hospital emergency room records, provided no evidence for the hypothesis that the left-sided predominance of psychogenic symptoms is underlain by a generalized greater vulnerability of the left side to organic pathologies. The status of three other explanations for the asymmetrical incidence of psychogenic symptoms is discussed

Comparative organization of the claustrum: what does structure tell us about function?

The claustrum is a subcortical nucleus present in all placental mammals. Many anatomical studies have shown that its inputs are predominantly from the cerebral cortex and its outputs are back to the cortex. This connectivity thus suggests that the claustrum serves to amplify or facilitate information processing in the cerebral cortex. The size and the complexity of the cerebral cortex varies dramatically across species. Some species have lissencephalic brains, with few cortical areas, while others have a greatly expanded cortex and many cortical areas. This evolutionary diversity in the cerebral cortex raises several questions about the claustrum. Does its volume expand in coordination with the expansion of cortex and does it acquire new functions related to the new cortical functions? Here we survey the organization of the claustrum in animals with large brains, including great apes and cetaceans. Our data suggest that the claustrum is not always a continuous structure. In monkeys and gorillas there are a few isolated islands of cells near the main body of the nucleus. In cetaceans, however, there are many isolated cell islands. These data suggest constraints on the possible function of the claustrum. Some authors propose that the claustrum has a more global role in perception or consciousness that requires intraclaustral integration of information. These theories postulate mechanisms like gap junctions between claustral cells or a “syncytium” to mediate intraclaustral processing. The presence of discontinuities in the structure of the claustrum, present but minimal in some primates, but dramatically clear in cetaceans, argues against the proposed mechanisms of intraclaustral processing of information. The best interpretation of function, then, is that each functional subdivision of the claustrum simply contributes to the function of its cortical partner.

The stability and intertest consonance of lateral postural—motor biases in rats: results and implications

Each of six different tests of lateral postural—motor asymmetries was repeatedly administered to 126 rats. Directional reliability was found for rotatory swimming, open-field exploration, and stepping down from a beam. Neonatal posture, turn in an unbaited T maze, and orientation to tail pinch proved not to be reliable across days. The behavioral asymmetries in the open-field and step-down tests were directionally consonant with each other, but neither was related to the asymmetry exhibited in rotatory swimming, implying the existence of at least two independent asymmetrical neural substrates underlying the behaviors. Neither sample-wide directional biases nor major sex differences in bias were found. The sexes were, however, differentially influenced in direction on some tests by the number of males in their natal litters, implying a role for intrauterine exposure to androgens in predisposing rats toward some left- or right-biased behaviors.

Sex Differences in Anterior Commissure Size in the Rat

Earlier studies have shown that the corpus callosum of rats tends to be larger in males than in females. We report here that the anterior commissure of rats is also larger in males than in females. The sizes of the two commissures were positively correlated in both sexes, but significantly more so in females than in males. The anterior commissure size difference in rats reported here is opposite in direction from that reported elsewhere for humans, and we speculate that this may derive from differences in the relative proportions of the constituent fibers that make up the anterior commissure in the two species.

Septal lesions impair rats' Morris test performance but facilitate left-right response differentiation

Lesions in the septum impaired performance on the Morris test, a task in which the rat locates a hidden escape platform by use of fixed landmarks, but facilitated a water maze-based left-right response differentiation, a task in which the rat finds a hidden escape ramp by means of its internal sense of direction. These results are interpreted as supporting an allocentric/egocentric dichotomy with respect to navigation, and support the notion that rats approach spatial problems with a hierarchy of potential solutions in which allocentric solutions take precedence over egocentric ones. The septal lesions are inferred to disrupt the allocentric mapping system.

Behavioral bias and left–right response differentiation in the rat

To examine the proposition that lateral asymmetry facilitates left-right response differentiation in rats, we examined the relationships between the strengths of several behavioral biases and the scores on a learning task requiring left-right response differentiation. No support was found for a simple model positing a monotonic relationship between any behavioral bias and the learning scores. However, performance showed a U-shaped relationship to one behavioral bias. This finding conforms to a curvilinear model in which rats at either extreme of asymmetry are disadvantaged, at low degrees of asymmetry by a lack of navigational reference, and at high degrees by resultant strong position habits; moderately asymmetrical rats have neither disadvantage and are best able to use the asymmetry as a reference in processing left-right information.

Direction and Reliability of Head Tilt in Humans

It has been proposed that asymmetry in the inner ear underlies various manifestations of brain-behaviour asymmetry in the human. Specifically, Previc (1991) argued that an otolith imbalance manifests itself in an asymmetrical head posture, and later (1994) suggested that head tilt may be consonant with other measures of human laterality. The present study tested the reliability of head tilt across days and assessed its relationship with handedness, footedness, and eyedness. As in Prevics earlier studies, a majority of our subjects tilted rightward. Head tilt proved to be highly stable across days but was not correlated with the other laterality measures. These findings suggest that head tilt may reflect an underlying asymmetric substrate that appears not to be directly related to other measures of cerebral hemispheric dominance.

Social–sexual behavior seasonality in captive beluga whales ( Delphinapterus leucas )

Observation of wild beluga whales (Delphinapterus leucas) indicates that this species breeds seasonally, and hormonal assays of captive animals show corresponding fluctuations in reproductive hormones. The question remains, however, whether copulatory behavior itself occurs seasonally. As an index of copulatory behavior, data are reported here on the frequency with which pelvic thrusting occurs over the calendar year. Male-on-female thrusting did vary significantly across months, with a clear peak in activity in March. On the other hand, male-on-male pelvic thrusting did not differ significantly across months. Possible functional roles are suggested for this latter enigmatic behavior.

Improved acquisition of left-right response differentiation in the rat following section of the corpus callosum

Split-brained rats learned a left-right response differentiation in a water maze significantly faster than rats with sham surgery. It is unlikely that this superiority resulted from improvement in performance variables since callosotomized rats did not differ significantly from sham operates in speed of acquisition of a brightness discrimination in the same apparatus. Additionally, callosotomy likewise had no effect on the acquisition of a water-maze task requiring consistent unilateral responses. The superiority of the callosotomized animals in forming the left-right response differentiation supports a hypothesis implicating the forebrain commissures in left-right confusion.