Interocular transfer in the split-brain rat.

After the 1991 development of a method to transect the optic chiasm in the rat, the authors investigated interocular transfer in split-chiasm rats with corpus callosum section and callosum intact. Rats were monocularly trained on an orientation discrimination, reversed with the other eye, and retrained with the 1st eye on the 2nd-eye problem or reversal. In split-chiasm rats, the 2nd-eye S+ (correct stimulus) showed strong transfer (55% savings) to the 1st eye. S- (incorrect stimulus) did not; reversal and transfer groups differed significantly. Split-brain rats retrained with the 1st eye on the 2nd eye S+ required no more trials than original learning, as if they had not experienced this problem. Split-brain rats retested with the original S+ showed modest (19%) savings. The findings establish interhemispheric communication via the callosum and suggest, as in findings of cat and monkey studies, the disruption of transfer by callosal section.

Early experience modifies the lateralization of emotionality in parietal lesioned rats.

Male rats that were handled or not handled in infancy were given either unilateral parietal cortex lesions or unilateral parietal cortex lesions plus corpus callosum section as adults and tested on two independent measures of rodent emotionality, the Rodent Emotionality Rating scale and the open field. Lateralization of emotionality measured by open field ambulation and rearing only appeared in handled animals with right parietal cortex lesions plus transection of the corpus callosum. Notwithstanding, both the left and right parietal cortex were found to be involved in both aspects of emotionality when the corpus callosum was intact. It was the transection of the corpus callosum that brought out the interactive effects of the early experience manipulation and unilateral parietal lesion. Thus we have identified yet another role for the corpus callosum; one of mediating the effects of early experience in the lesioned brain.

Relation of rotation to egocentric and allocentric spatial learning in the rat.

In this experiment, we asked whether the relation between amphetamine-induced rotation and the learning and retention of left-right discrimination extends to allocentric spatial learning or is limited to egocentric spatial tasks. Rotation was established following injections of d-amphetamine sulfate, and rats were classified as nonrotators, midrotators, or strong rotators. Animals were successively trained on navigation in the Morris water maze (allocentric) and delayed spatial alternation in a water T-maze (egocentric). There were no rotation effects in water maze learning but rotators and nonrotators differed significantly in delayed spatial alternation learning but not relearning. Strong rotators learned more slowly than midrotators, clearly implying that rotational bias and directional learning are not linearly related. We show that it is egocentric spatial learning that is facilitated by a nigrostriatal dopamine asymmetry and extend the generality of the left-right discrimination findings.

Strain and sex differences in amphetamine-induced rotation.

Studies of rotational behavior in female rats have investigated Fischer, Sprague-Dawley, Madison, WI, and Holtzman strains. The present study of amphetamine-induced rotational preference looked at the most widely used of the pigmented strains, Long-Evans hooded rats, examining rotation in females and comparing rotational magnitude and direction to males of the same strain. We corroborate in Long-Evans animals the greater rotation of females, but our findings oppose the right-sided female and left-sided male rotational preferences reported in earlier studies. Only female rats in this experiment had a significant directional bias, and it was to the left. This result strongly points to the importance of strain in the lateralization expressed by rotation.

Effects of unilateral parietal lesions on spatial localization in the rat.

In the first of two experiments, rats with left or right parietal lesions and controls were tested in place and landmark navigation in the water maize. Right parietal lesions resulted in deficits in both tasks, but especially landmark navigation. Lateralized effects appeared mainly in latency to find the platform. Experiment 2 investigated the role of the corpus callosum. Split-brain rats with unilateral parietal lesions were tested on the same two tasks. Place and landmark deficits were particularly severe, but lateralization was weaker. Callosum section had its own effect, impairing the learning of both tasks. There appear to be additive effects of unilateral cortical lesions and bisection of the hemispheres. The impairment from left lesions equaled the right-lesion deficit because of the interruption of compensatory information from the intact right hemisphere and the effect of callosum section itself.

Visuospatial asymmetries and interocular transfer in the split-brain rat.

Interocular transfer (IOT), hemispheric superiority, and cerebral dominance were examined in split-brain female albino rats. Callosum-sectioned and intact animals were monocularly trained in the Morris water maze and tested in IOT and reversal phases. In the IOT phase, split-brain rats entered more nontarget quadrants and headed less accurately toward the platform than did controls. For both split-brain animals and controls, right-eye training resulted in shorter latencies and fewer nontarget entries than did left-eye training. Analyses of cerebral dominance showed shorter latencies and smaller heading errors over all 3 phases in rats that were trained with the nondominant eye. Right-eye dominant controls were less affected by platform reversal. Split-brain rats were inferior to controls in latency to find the platform and in target quadrant entries. This finding establishes a spatial cognitive deficit from callosum section.

Completing the split in the split-brain rat: transection of the optic chiasm.

We describe a stereotaxic technique to transect the optic chiasm in the rat and present illustrative data on the interocular transfer of visual discrimination in chiasm-sectioned and chiasm-plus-forebrain commissure-sectioned animals. Applications of the technique are discussed.

Circling, hemispheric asymmetry, and left-right discrimination.

Three measures of rotational/side preference--amphetamine-induced circling, side of exit from open field start square, and side of turn when suspended by the tail--were assessed, and animals were then tested on a left-right discrimination. In a strong replication of a previous finding, rats showing amphetamine-induced rotation learned and retained the spatial discrimination markedly better than non-rotators. The other directional measures were unrelated to discrimination learning.

Unilateral periarcuate and posterior parietal lesions impair conditional position discrimination learning in the monkey.

Monkeys were trained on a conditional position discrimination in which the conditional cue was a light blinking at two distinct rates and the discriminanda (illuminated buttons) appeared in varying symmetrical positions of eccentricity. Unilateral arcuate, posterior parietal, or principal sulcus lesions were performed at criterion. The monkeys were tested to recovery when a homologous lesion was made contralaterally. The first of two analyses examined a period of 4 weeks following each lesion; the unit of analysis was lesions. The arcuate and parietal lesions produced impairments on both widely eccentric and central discriminanda locations; initially, virtually all responses were deflected to the ipsilateral side. There was significant improvement after the arcuate and parietal lesions from weeks 1 to 4. An analysis of total trials to criterion showed major deficits from the second arcuate and parietal lesions, with the arcuate lesion impairment being particularly severe. These results establish that a spatial concept of left vs right is seriously deranged by unilateral lesions of cortical association areas involved in spatial orientation and discrimination.

Multivariate analysis of putative measures of activity, exploration, emotionality, and spatial behavior in the hooded rat (Rattus norvegicus).

Hooded rats were tested in six situations representing the variables of activity, exploration, emotionality, and spatial preference, detection of change, and learning. The activity, exploration, and emotionality variables and spatial variables were analyzed in separate multivariate analyses, followed by an analysis of the entire set. The first of these resulted in four components: activity, exploration and emotionality, reactivity to handling, and autonomic reactivity (defecation). Four components, defined by the following variables, emerged from the spatial analysis: (a) the tendency to circle, circling direction, and spatial learning; (b) heading error in spatial learning and reversal and open-field directional preference; (c) spatial reversal and direction of turn to escape restraint; and (d) detection of change in spatial arrangement and directional preference in the detection task. The final analysis investigated relations between the activity, exploration, and emotionality variables and the spatial variables, finding only two. The clear dimensionality of these behavioral repertoires emphasizes how important it is to recognize the distinctions among them.

Some effects of commissurotomy on the reinstatement and potentiation of lesion deficits.

Two experiments investigated in rats the effects of cutting the corpus callosum after recovery from unilateral cortical lesions that produce transient symptoms of neglect and circling. Side of lesion was also examined. In Expt. I, 60 rats received left or right lesions of parietal, medial frontal, or motor cortex. After one month of testing for visual, auditory and somatosensory responsiveness and for circling, the callosum was cut, and the sequence of measures was repeated. Callosotomy reinstated neglect after recovery from the lesions in the parietal and medial frontal groups, more severely and consistently in the frontal group. Side of lesion made no difference. Circling was predominantly ipsiversive after the cortical lesions, due entirely to the frontal group. Callosum section markedly potentiated contraversive circling in the left parietal group; right parietal animals showed no preference. This was the only hemisphere difference found. Circling remained ipsiversive in medial frontal animals after callosotomy. These circling biases did not diminish in the postcallosotomy period. Expt. II replicated the circling procedures with 58 animals that were given the same unilateral cortical lesions or were unoperated controls. Callosotomy was performed one month postlesion. Again, left parietal animals circled contraversively, and there was no bias in the right parietal group. A left-right difference was also evident in the motor cortex group, left lesions producing contraversive turning. We confirm the reinstatement of neglect from frontal lesions by callosum section previously found in the monkey and show that it also occurs with parietal lesions. While neglect symptoms do not differ after left or right lesions, circling does: left parietal lesions plus callosotomy produce a marked contraversive tendency that may reflect an elemental spatial lateralization.

Longitudinal development of activity rhythms in Long Evans rats.

A longitudinal examination of activity rhythm development in Long Evans rats aging from 27 to 647 days was conducted. Wheel-running activity was sampled during five test periods: postweanling, periadolescence, young adulthood, presenescence, and senescence. On each test day, data were collected during both light and dark phases of the 12:12 hr light/dark photocycle. Analyses of variance (ANOVAs) on the activity data confirmed a recent cross-sectional study in two respects: First, gradual intensification of mean daily activity to adulthood was followed by a decline in senescence to a level below that found in early youth. Second, in comparison with early adulthood, a decline in activity during the dark phase was combined with an increase during the light phase as aging to senescence occurred.

Lateralization of emotionality in right parietal cortex of the rat.

Lesions of right parietal cortex in the rat increase activity in the open field compared with left parietal lesions, especially after section of the corpus callosum. Left or right motor or medial frontal cortex lesions do not have a lateralized effect. This evidence of a localized asymmetry between the cerebral hemispheres strongly implies that right parietal cortex has a role in emotionality in this species. Our findings suggest a functional similarity to right parietal cortex in man.

Effects of age on nocturnal activity rhythms in rats.

Running wheel data were analyzed to examine changes in nocturnal activity rhythms with age in Long Evans rats. Five male animals 30 days of age, the same five rats at 70 days of age, and five older animals at 13 months were given free access to activity wheels in a colony room maintained on an LD12:12 cycle. All subjects demonstrated enhancement of activity during the dark phase of the 24-h cycle. A statistically significant decrease in activity of old rats in comparison with weanling rats was observed only in the dark phase (P less than .0001). The age difference was marginal in the light phase compared to that in the dark phase. However, a marked increase in percentage of time spent active in the light phase was observed in the old animals. This may be a combined result of visual hyposensitivity and insomnia that became apparent with increasing age. Mechanisms that control initiation and maintenance of locomotor behavior may become less responsive with age to periodic alternative of light and dark phases.

Parietal and frontal eye field neglect in the rat.

Rats were given unilateral aspiration lesions of parietal, medial frontal, or dorsolateral frontal (motor) cortex and then tested for visual, auditory and tactile neglect, and for circling. All medial frontal lesion animals showed contralateral neglect in each modality and circled ipsiversively. The parietal lesion rats initially displayed contralateral visual and auditory neglect as severe as that in the medial frontal group. Three weeks after the lesions, the parietal group had a smaller residual deficit on the visual test than the medial frontal group. In the first week, parietal animals responded less than the medial frontals to stroking the vibrissae but were more responsive to mild pinching of a toe contralateral to the lesion side. In striking contrast to the medial frontal animals, the parietal group circled strongly to the contralateral side. No rat with a motor cortex lesion neglected or circled preferentially. Like medial frontal cortex, unilateral parietal lesions also produce neglect and circling, but there are important features distinguishing unilateral lesion effects in these two regions.

Recalled parent-child relations and need for approval of homosexual and heterosexual men.

Young adult male homosexuals were recruited from a homosexual group and were given the Roe-Siegelman Parent-Child Relations questionnaire and the Marlowe-Crowne social desirability scale. Compared to a control group of heterosexuals, the homosexual group rated their mothers significantly more rejecting and their fathers less loving and more rejecting. The Love-Reject factor also showed the between-groups difference for the ratings of fathers; for mothers, the Love-Reject factor difference was marginally significant. The homosexual group also had a significantly higher mean score on the social desirability scale. This study, using direct subject selection and control of test administration, gives a close replication of important parts of Siegelman's (1974) results, especially the ratings of fathers' child-rearing practices and the homosexual-heterosexual difference on the social desirability scale.

Pineal lesion produces bilateral visual and auditory inattention in the rat.

Unilateral lesions in such brain regions as medial frontal cortex and superior colliculus produce polysensory neglect contralateral to the lesion. Since the pineal gland is an unpaired brain structure, both electrophysiologically and hormonally responsive to visual and auditory stimulation, it may modulate bilateral sensory attention mechanisms. Long-Evans male rats were given pineal or sham lesions and were tested behaviourally. Sensory assessment revealed that in comparison to sham animals rats with pineal lesion exhibited unilateral visual and auditory neglect to stimuli presented on either side of the body. Animals with pineal lesions were more likely than sham-lesioned animals to demonstrate visual allesthesis and, compared to sham-lesioned rats, showed extinction on the left side to bilateral simultaneous visual stimulation. This is the first report that midline neuroendocrine damage can produce bilateral sensory inattention.

A method to section the corpus callosum in the rat.

A simply constructed instrument and a surgical procedure are described for transecting the corpus callosum in the rat. The callosum can be cut in its entirety, or the cut can be limited to anterior or posterior halves. The procedure obviates lateralized incidental damage.

Brief deprivation of vision after unilateral lesions of the frontal eye field prevents contralateral inattention.

Brief deprivation of vision after unilateral lesions of the frontal eye field prevents the appearance of contralateral inattention to visual, auditory, and somatosensory stimuli. The forced circling that accompanies inattention, however, is not affected. An equivalent preoperative period in the dark only partly reduces inattention symptoms. Visual deprivation does not reduce or prevent inattention resulting from lesions of the superior colliculus.