Neocortical Ablations Research Articles

Brain and behavioral asymmetries for spatial preference in rats

Rats were handled daily for 3 min between birth and weaning, or were nonhandled controls. When adult, 4 males from each litter received a right neocortical ablation, a left ablation, a sham operation, or no surgery. A month later all animals were tested in the open field for 4 days, and their initial direction of movement from the starting square (whether right or left) was recorded. Non-handled rats with intact brains (sham-operated and no-surgery groups pooled) had a mean directionality score near zero, thus indicating no right-left spatial preference. However, non-handled animals without a left hemisphere were significantly more biased in going to the ipsilateral side than were their siblings with right-brain ablations. Thus, in non-handled animals behavioral symmetry in making spatial choices is due to balanced brain asymmetry, in which the right hemisphere biases the animal to move leftward while the left hemisphere acts to inhibit this response. In contrast, intact handled rats had a significant preference to go to the left, thus suggesting that in handled animals the right hemisphere controls spatial preference.

Effect of prior experience on bar-pressing in rats without neocortex

Rats in which all neocortex had been surgically removed produced similar patterns of performance to those previously established for rabbits with total neocortical ablations in a bar-pressing task for food reward. The animals deprived of neocortex developed inefficient patterns of food-tray related behaviours and a limit to their bar-pressing performance for intermittent rewards in the region of 4–10 presses per reward. The lesioned animals were also unable to form a sequential brightness discrimination on a GO-NOGO schedule using a bar-press response. Neither prior experience of other instrumental learning situations nor experience of working in the same apparatus and using the same instrumental response were sufficient to improve subsequent bar-press performance for intermittent reward in the neocortically lesioned animals. Previous success in improving such performance by pretraining procedures designed to facilitate identification of the part of the apparatus to be manipulated by the animal cannot easily be explained, therefore, on the basis of such incidental factors as increased behavioural sophistication or of increased familiarity with the apparatus and the instrumental response itself. The data are consistent with the view that the neodecorticate's difficulty in the bar-pressing situations for intermittent rewards is due to inadequate identification of cues associated with the object to be manipulated rather than to an associative learning deficit.

Infantile stimulation induces brain lateralization in rats.

The hypothesis tested was that the effects of early experiences are asymmetrically distributed in the two brain hemispheres. Litters were either handled or not handled between birth and weaning, and the weanlings were reared in either laboratory cages or enriched environments between 21 and 50 days. When approximately 135 days old, animals within each of the four treatment groups had a right neocortical ablation, a left neocortical ablation, a sham operation, or no surgery. About 1 month later, all animals were given the open-field test for emotionality and exploratory behavior. Ablating either the right or left neocortex increased the activity scores of nonhandled controls, but there was no evidence of lateralization. However, the groups handled in infancy did show lateralization. Ablating the left brain did not significantly increase activity, but ablating the right brain caused extreme scores: handled rats without enrichment experience were the most active, and handled rats also placed into the enriched environment had near-zero scores in the open field.

Temporal and parietal association cortex lesions and spatial and black-white reversal learning in the rat

In Experiment 1, rats with parietal, temporal, or frontopolar neocortex ablations and nonoperated controls were trained on seven spatial reversals. The animals with parietal association cortex damage were found to be deficient on this task compared to all other groups. In Experiment 2, rats with either temporal or striate neocortical ablations or subcortical lesions of the lateroposterior thalamic nucleus and nonoperated controls were trained on a black-white reversal task. The rats with temporal damage committed significantly more errors than all other groups. These results together with those of previous research suggest that a dissociation exists between the effects of parietal and temporal association cortex ablations on reversal learning in the rat. It was suggested that the visual functions of the temporal association cortex might be mediated by connections with either the striate cortex or the lateroposterior thalamic nucleus.

Recovery of feeding in rats following frontal neocortical ablations

This study examines behavioral recovery from the aphagia-adipsia syndrome following frontal neocortical ablation in relation to the recovery of neurological function in the brain-damaged animal. Regulation of food and water intake in the post recovery period was also investigated. Behavioral recovery occurs in three articulated stages of improving sensori-motor function which reflect the animal's underlying neurological recovery. The first stage is one in which food and water intake can be accomplished only by reflexive sucking. In the second stage, goal directed scraping of the surface of solid foods and ingestion of soft foods are possible. In the final stage, chewing and biting are re-established and normal weight regulation is maintained on a standard laboratory diet. After recovery, sensori-motor deficits remain which do not impair feeding and drinking unless mechanically difficult diets are presented. Except for a response deficit in the insulin-induced overeating test and an increased sensitivity to quinine adulterated food, recovered animals respond normally to a series of regulatory challenges.

Differential and reversal conditioning in partially neodecorticate rabbits

Normal rabbits and rabbits with extensive unilateral or bilateral neocortical lesions were required to differentiate between visual and auditory stimuli in a Pavlovian situation and then to reverse that differentiation. It was found that neocortical ablations had no effect on the initial differentiation and that the lesioned animals were superior to normals in their performance on the reversal task. The lesioned animals in particular did not show the same tendency as normals to continue responding to the negative stimulus under reversal conditions. Possible sources of the apparently greater efficiency shown by the neodecorticates are discussed.

Effects of neocortical ablations on eating elicited by hypothalamic stimulation

Unilateral and two-stage bilateral ablations had marked effects on stimulation-bound feeding. These included temporary or permanent failure to feed, increase in current thresholds, and reduction in the persistence of feeding during stimulation. Analysis of the data by a multiple regression technique indicated that the failure to feed was related to the amount of unilateral and bilateral damage to the frontal, but not other cortical regions. Changes in threshold were not related to frontal damage as such; rather, these changes appeared to be a function of an interaction between the sites of stimulation and amount of cortical damage. Persistence changes were related to the degree of frontal damage. Failure to feed appeared to reflect disorganization of food-seeking rather than consummatory responses.

Deficient brightness discrimination in hooded but not albino rats given neocortical ablations

Hooded and albino rats with lesions of the neucortex overlying hippocampus and normal rats of both strains were trained in an operant discrimination. Though the normal groups did not differ from one another and the neocortically lesioned albinos did not differ from the unlesioned rats, when compared to the other groups the hooded group was found to be deficient in the acquisition of the task. A greater amount of cell loss and gliosis was observed in the thalamus of the hooded rats.

Contour discrimination in the rat following removal of posterior neocortex.

Long-Evans hooded rats were trained on one of three two-choice visual discrimination problems. The stimuli, black equilateral triangles on white Plexiglas, were equated for total luminous flux and total black-white area, but differed in amount of contour, defined as total amount of black-white edge. The ratios of contour varied for each of the three problems, being respectively 3:1, 4:1 or 5:1. Following acquisition of the problems, posterior neocortical ablations were sustained by at least 30 animals in each group, the remainder serving as normal controls. When retested, normal animals retained the problem, while operated animals were unable to relearn the 3:1 or 4:1 ratio problems. Operated animals did relearn the 5:1 ratio contour problem, although they required more than twice as many trials than during original learning. These results suggest that rats deprived of visual cortex can make visual discriminations based upon differences other than total luminous flux. Density distributions of light or stimulus differences in amounts of darklight boundaries appear to be the likely parameters which, when large enough, permit discrimination of such problems.

Sodium appetite in rats after neocortical ablation.

Abstract Rats with ablations of either the entire neocortex or just the sensory cortex including the taste projection area responded to sodium depletion or mineralocorticoid treatment by increasing their intake of sodium chloride solution. The natrorectic response of the decorticate rats to sodium depletion was somewhat attentuated or delayed in comparison to intact controls but their response to mineralocorticoid treatment was normal.

Effects of cortical ablations upon recovery from the septal syndrome in hooded rats

The hyper-reactivity of the septal syndrome was produced in adult male Long-Evans rats by electrolytic lesions in the septal region. Various groups of the rats with septal lesions were handled postoperatively for either 5 or 18 days or left unhandled for 18 days. The operated control group was also not handled. Following these handling periods, the septal syndrome was found to have declined in both handled groups, and the animals were at normal reactivity levels. The unhandled group with septal lesions still displayed the syndrome. Neocortical ablations did not reinstate the syndrome in either handled group, nor did they change the reactivity level of the unhandled groups. The septal syndrome in another group of rats was reduced to normal levels by handling for 21 postoperative days. Spreading depression, induced by application of 25% KCl to the neocortex, did not reinstate the septal syndrome. These results differ from and restrict the generality of previous findings.

The consequences of septal and neocortical ablations upon learning a two-way conditioned avoidance response

Septal lesions facilitate acquisition of a CAR habit even in the absence of the anterior, posterior or entire neocortex. Small, but insignificant, deficits are found with anterior or posterior removals alone, but aspiration of all the neocortex severely impairs performance.

Neocortical projections to the pons and medulla of the nine-banded armadillo (Dasypus novemcinctus).

AbstractThe pattern of neocortical projections to the pons and medulla was determined by employing the Nauta‐Gygax technique ('54) on the brains of armadillos subjected to neocortical ablations. The results of this study indicate that the pretrigeminal basilar pontine gray receives input from a considerable portion of the neocortex. Degenerating fibers resulting from a lesion of the frontal tip of the neocortex terminated within the dorsal medial, the medial and the ventral medial areas of the rostral basilar pontine gray. Corticopontine fibers from the mid‐presupraorbital neocortex ended throughout the rostral to caudal extent of the basilar pontine gray, and terminated within the dorsal medial, the medial and the ventral medial areas; whereas degenerating fibers resulting from a lesion of the neocortex immediately rostral to the supraorbital sulcus terminated within the medial, the ventral and the ventral lateral areas of the basilar pontine gray. The neocortex immediately caudal to the supraorbital sulcus distributed corticopontine fibers to the ventral, the ventral lateral, the dorsal lateral and to the dorsal areas of the basilar pontine gray, while degenerating fibers resulting from lesions of the caudal one‐third and most caudal tip of the neocortex projected to the ventral and lateral portions of the basilar pontine gray.Neocortical projections to the pontine and medullary reticular formation originated mainly from cortical areas rostral and immediately caudal to the supraorbital sulcus. The neocortex rostral to the supraorbital sulcus distributed to the rostral and medial portions of the pontine reticular formation, whereas corticoreticular fibers from the neocortex immediately caudal to the suprarbital sulcus, also distributed degenerating fascicles to the spinal trigeminal nucleus, the nucleus of the solitary tract and to the nucleus cuneatus. No degenerating fibers were seen to terminate within motor nuclei of cranial nerves located within either the pons or medulla.

Effect of hippocampal and neocortical ablation on scopolamine-induced activity in the rat

To test the hypothesis that the hippocampus may be an important site of action for anticholinergic drugs, scopolamine was administered to rats with hippocampal lesions produced by aspiration and to appropriate control groups, and their activity measured. The experimental design was a four-way analysis of variance with three lesion groups, three drug levels, eight measurements in a two-hour session, and four weeks. At the two higher drug doses (0.20 and 1.0 mg/kg), rats with hippocampal or cortical lesions had significantly greater activity than the sham operates (p<0.01 and p<0.05, respectively). A group of Ss with electrolytic hippocampal lesions tested at 0.20 mg/kg scopolamine had transitory activity increases. Therefore the hippocampus is not necessary for the motor activating effects of the drug nor is its ablation unique in producing increases in drug-induced activity.

Equivalence of simultaneous and successive neocortical ablations in production of impairments of retention of black-white habits in rats.

Equivalence of simultaneous and successive neocortical ablations in production of impairments of retention of black-white habits in rats.

Effects of simultaneous septal-visual, septal-anterior and anterior-posterior lesions upon relearning a black-white discrimination

Summary Rats were trained on a black-white discrimination task, and then were assigned to one of the following groups: (1) normal control S s; (2) S s with septal lesions; (3) S s with anterior neocortical ablations; (4) S s with visual neocortical ablations; (5) S s with anterior and visual neocortical ablations; (6) S s with anterior neocortical and septal lesions; (7) S s with visual neocortical and septal lesions. Following a 21 day recovery interval all S s were tested for retention of the black-white habit. Deficits of varying magnitude occured in operated groups. Data from the normal septal, anterior and visual groups replicated previous studies. S s with anterior neocortical and septal lesions behaved like S s with anterior neocortical lesions. S s with anterior and visual neocortical ablations and S s with visual neocortical and septal lesions relearned at about the same rate. The results suggested that the anterior neocortex and septal area might be components of the same system.

Responses to visual stimuli of units in the superior colliculus of rats and monkeys

Units in the superior colliculus of the rat responded primarily either to moving objects or to objects which, having moved, came to a stop in the receptive field. Small dark objects moving relatively slowly gave the best responses on the whole but there was considerable latitude in the range of effective stimuli; directional specificity was not found. The units fell into two major classes on the basis of size of receptive field, small-field units and large-field units. Anatomically, these corresponded to the two superficial layers of the colliculus, the stratum griseum superficiale, and the stratum opticum. Small fields, 2–15 deg across, were circular in shape. Large fields, 30–90 deg across at their widest point, were oval or irregular in shape, usually oriented horizontally, and often patchy as though made up of a conglomerate of smaller fields. Responses were frequently unstable in time and tended to wane with repeated stimulation. The over-all properties were unchanged by neocortical ablation. Units in the monkey likewise responded primarily to moving objects, although not to objects stopping in the field. Here, luminous objects were more effective than dark ones but again there was no great selectivity. The units did not fall into two classes on the basis of field size but there was a clear trend for field size to increase with depth. The range of field sizes was 2–90 deg across. The smaller fields were circular in shape; the largest approximated quadrants of the visual field. Here, too, responses were unstable. The results for the rat are strikingly like those reported for the frog optic tectum. It is argued that the present results together with those of other single unit studies point to a role for the mammalian colliculus in the detection and location of “evocative” visual stimuli, perhaps as part of a visual attention mechanism.

Emotionality changes following septal and neocortical ablations in the albino rat

Albino rats with neocortical-septal lesions exhibited the sustained emotionality following a three week recovery period that has been observed in hooded Ss. The maintenance of this behavior could not be accounted for in terms of locus or laterality of the neocortical lesion.

Visual cliff preferences following lesions of the visual neocortex in cats and rats

Normal cats, cats with lesions of the visual neocortex, normal rats, enucleated rats, and rats with lesions of the visual neocortex were tested on Gibson’s visual cliff for visual depth perception. All animals preferred the shallow side except rats that were enucleated and rats that sustained visual neocortical ablations.

Effects of neocortical ablations on relearning of a black-white discrimination habit by two strains of rats.

Effects of neocortical ablations on relearning of a black-white discrimination habit by two strains of rats.