Douglas P. Crowne

Some attentional effects of unilateral frontal lesions in the rat

Visual learning, sensory neglect and motor behaviour were studied in rats with unilateral lesions of anteromedial (AM) or dorsolateral (DL) frontal cortex. The purpose was to determine whether the principal features of the syndrome seen after unilateral frontal eye field lesions in primates appear in the rat. In the first two experiments, rats were trained on a visual discrimination using shock avoidance. AM lesions greatly prolonged choice latency but did not increase errors, and this held both for binocular performance and for monocular performance with the contralateral eye. One group of AM-lesion animals was postoperatively maintained in the dark, and their latencies, binocular and monocular, did not differ from the DL controls. Thus, deprivation of visual experience prevented the effects of the AM lesion. The second experiment used simple sensory stimuli to test for visual, auditory and tactile neglect. Ipsiversive circling was also investigated. All rats with AM lesions neglected contralaterally and circled in the first postoperative week. Recovery was underway by the second week and complete in three weeks. The animals were trained preoperatively on a conditioned avoidance problem in which shock was signalled from various points in the visual field. Tested postoperatively, the AM-lesion rats avoided normally. The findings of the two experiments strongly suggest that the functions of AM cortex in the rat are similar to those of the frontal eye field in primates. This cortical region appears to be part of a system which prominently includes the superior colliculus and serves attentional/orienting functions.

The effects of unilateral frontal eye field lesions in the monkey: Visual-motor guidance and avoidance behaviour

Macaque monkeys were tested on a visual-motor guidance task and observations of avoidance behaviour were made following unilateral frontal eye field lesions. Visual-motor guidance was assessed by speed and accuracy of reaching to press recessed, illuminated buttons arrayed in a 90 degree arc in front of the monkey. Unilateral frontal eye field lesions produced a marked neglect of stimulus lights contralateral to the side of the lesions, as shown in greatly increased errors and response latencies. Responses to the most peripheral of the ipsilateral stimulus lights were also affected, although not to the same degree. Partial to complete recovery occurred, usually within a month. A unilateral lesion of the principal sulcus did not cause symptoms of neglect in the visual-motor guidance task. Section of the cerebral commissures partially restored the visual-motor guidance deficit in the frontal eye field-lesioned monkeys, with recovery again occurring. Commissurotomy and the unilateral frontal eye field lesion performed in a single-stage operation produced an initially more severe neglect than the two-stage operation, but recovery was no less rapid. The unilateral frontal eye field lesions resulted in a severe neglect of contralateral threat objects when the monkeys were threatened from both sides (avoidance-avoidance tests). Avoidance was normal when the threat was presented to one side. Commissurotomy fully restored the avoidance-avoidance deficit and made it permanent. These and other recent findings suggest that the contralateral visual field defect and the other symptoms resulting from frontal eye field lesions represent an impairment in directing and sustaining attention in regions of the visual field arising from disruption of a corticothalamotectal sensorimotor integration system.

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.

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.

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.

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.

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.

Some Characteristics and Functional Relations of the Electrical Activity of the Primate Hippocampus and a Hypothesis of Hippocampal Function

The primate hippocampus differs from the hippocampal formation in subprimate species0020 in several important respects.

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.

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.