Removal Of Cortex Research Articles

Changes in inner plexiform layer thickness following neonatal visual cortical ablation in cats

The effect of visual cortex removal at 5–7 days of age on the development of the inner nuclear and inner plexiform layers of the cat's retina was examined in animals which had survived 9–36 months after the cortical removal. The lesions were unilateral so that only the nasal or the temporal region of each retina was affected, and the affected regions were positively identified by HRP injection into the optic tract either ipsilateral or contralateral to the ablated hemisphere. Small sections of retina straddling the naso-temporal boundary were then embedded in plastic and sectioned radially for analysis. In this way, comparisons could be made between areas of retina which were closely matched in terms of location as well as histological history. Cells in the inner nuclear layer in affected regions of retina appeared normal both in number and size, even though ganglion cell density in these areas was clearly reduced. This indicates that, at least at this age, the survival of inner nuclear layer cells does not depend on the availability of ganglion cells as synaptic targets. Paradoxically, in the affected regions of retina there was an increase in the width of the inner plexiform layer which was not associated with any change in the thickness of other, more distal retinal layers. This could be due either to an increased growth of surviving ganglion cells and/or inner nuclear layer cells, or to an increase in the survival of cells in the ganglion cell layer, perhaps displaced amacrine cells, which have a greater dendritic volume than the lost ganglion cells.

Importance of the projection from the sensory to the motor cortex for recovery of motor function following partial thalamic lesion in the monkey

Motor deficits produced by thalamic lesions were studied using adult cynomolgus monkeys. Lesioned areas included n. ventralis anterior (VA), ventralis lateralis (VL), n. ventralis posterolateralis pars oralis (VPLo), pars caudalis (VPLc) n. subthalamus (STN) and n. centrum medianum (CM). When the lesion included VA, VL, and VPLo, there was a cerebellar syndrome, i.e., ataxia and dysmetria. When the lesion included VPLo and VPLc, the animal was paralyzed. When the lesion included VPLo and rostral part of VPLc, there was loss of orientation in hand movement and clumsiness of finger manipulation. These motor deficits gradually disappeared within 1–2 weeks and the function recovered near to normal except for when VPLo and VPLc were totally destroyed. After recovery of motor function, the somatic sensory cortex (areas 1, 2, 3b) ipsilateral to the thalamic lesion was removed. Removal of the sensory cortex resulted in abolition of the recovered function, but when the border area between VPLo and VPLc was intact, the function recovered again. On the other hand, when the thalamic lesion included this border area, succeeding cortical lesion permanently abolished the recovered function or the reappeared function was substantially worse than that before the cortical lesion. Neuronal mechanisms subserving these differences are discussed and it is concluded that when direct sensory input to the motor cortex was interrupted by lesion of the border area between VPLo and VPLc, the lost function was compensated by reorganization of the projection from the sensory cortex to the motor cortex.

Diffusible proteins prolong survival of dorsal lateral geniculate neurons following occipital cortex lesions in newborn rats

Removal of the occipital cortex in newborn rats results in the rapid and nearly complete degeneration of the dorsal lateral geniculate nucleus (dLGN) in 5 days. In previous studies we have shown that transplants of embryonic posterior cortex neurons, which are allowed to develop in culture for 5 days prior to transplantation into the site of the lesion, prolong the survival of a particular population of host dLGN neurons for an additional week. In this study we tested the possibility that the transplant cells synthesize diffusible proteins which are responsible for this neurotrophic effect. Culture medium conditioned by explants of embryonic occipital cortex and diencephalon was concentrated by vacuum dialysis or ultrafiltration through membranes with at least a 10-kDa cut-off. This concentrated medium was loaded into polyacrylamide or sodium alginate gels which were then implanted into the cavity of the lesion. Five days after implantation, the alginate-conditioned-medium implants result in a 3-fold increase in dLGN survival compared to unconditioned medium controls, while a two-fold increase in survival of the nucleus is found with the polyacrylamide-conditioned-medium implants. Proteolysis of the conditioned medium eliminates all neurotrophic activity. The results suggest that the death of dLGN neurons following the cortical lesion is due to the loss of diffusible proteinaceous neurotrophic factors — factors that may operate during normal in vivo development of the geniculocortical pathway.

Converting to Phacoemulsification (A Manual for the Surgeon in Transition)

This is a well-written monograph by an experienced phacoemulsification surgeon who is comfortable with the procedure and is pleased with the results in his patients. It is clearly written and very accurate in describing the stepwise sequence of the phacoemulsification procedure. There are chapters on the conjunctival flap, incision, capsulotomy, emulsification technology, nucleus handling, classic phacoemulsification maneuvers, cortex removal, intraocular implantation, wound closure, and complications. The illustrations are simplified line drawings and clearly illustrate the points that Dr Koch is making in describing the technique and pitfalls of this procedure. Although clear, the sketches are misleading as the depth of the anterior chamber is consistently sketched as deeper than normal, and this makes nucleus manipulation during emulsification look easier than it really is. The author discusses the rationale for small-incision surgery and points out that the incision heals faster, is ... an excellent guide for the surgeon who desires to master

Recovery from early cortical lesions in rats. III. Neonatal removal of posterior parietal cortex has greater behavioral and anatomical effects than similar removals in adulthood

The behavioral, anatomical, and electrophysiological effects of posterior parietal cortex lesions (Krieg's area 7) were compared in rats with removals at 1, 5, or 10 days of age or in adulthood. Behaviorally, the animals were administered several tests including grooming, beam walking, swimming, the Morris water task and a radial arm maze. Lesions at 10 days of age permitted behavioral sparing on most behavioral tasks, whereas lesions at 1 or 5 days of age allowed little sparing and even produced larger deficits than observed in adult operates on some tasks. Anatomical measures showed a direct relationship between cortical thickness and age of lesion: the earlier the lesion, the thinner the cortex. An analysis of postsurgical changes in cortical thickness showed only a small reduction in cortical thickness shortly after the lesions, with the major reduction occurring during adolescence. Electrophysiological recordings of cortical activity showed that rats with 1-day lesions had abnormal neocortical atropine-resistant activity and had an increased incidence of seizures. The results suggest that the neocortex of the rat may be particularly sensitive to perinatal injury.

Effects of occipital lobectomy upon eye movements in primate.

1. Eye movements were recorded before and after bilateral occipital lobectomy in six rhesus monkeys trained to fixate and to follow small targets. Striate cortex was completely removed in two animals; small islands islands remained in the others. In all animals portions of extrastriate cortex were also removed but the medial superior temporal area in the superior temporal sulcus was largely spared. Optokinetic nystagmus (OKN) was markedly altered but not abolished in all animals. The immediate pursuit component of OKN was eliminated leading to a poor response to stimuli comprised of high frequencies. The velocity-storage component of OKN was present, but the maximum value of OKN that could be achieved was decreased to 6 and 16 degrees/s in the two most severely affected animals (preop, 65-116 degrees/s). The residual OKN was similar to that of afoveate animals with a diminished response to high velocities of retinal-image motion and a temporal to nasal predominance during monocular viewing. 2. In the initial postoperative period all animals appeared completely blind. Within 1-6 mo, however, they regained an ability to make visually guided saccades to, and smooth pursuit of, small targets. Saccades were nearly as accurate as preoperatively, but saccade amplitudes were more variable and saccade latencies increased. In the two animals with a complete removal of striate cortex, gains (eye velocity/target velocity) of smooth pursuit during sinusoidal tracking (60 degrees/s, 0.5 Hz) were 0.9 and 0.95. During tracking of step-ramp (Rashbass) stimuli with 60 degrees/s ramps, the average acceleration of the eyes during the first 120 ms of smooth pursuit was 189-278 degrees.s-1.s-1 (preop range, 154-418 degrees.s-1.s-1). In other respects, though, smooth pursuit was not normal. Latencies were increased two- to threefold, and tracking was more variable. 3. Paradoxically, as visually guided saccades and pursuit recovered, some other ocular motor functions deteriorated. Spontaneous and gaze-evoked nystagmus developed 3-6 mo after occipital lobectomy; the time constant of the neural eye-position integrator dropped to values as low as 2.6-4.8 s. The maximum slow-phase velocity of OKN also decreased. 4. The findings immediately after occipital lobectomy indicate that in normal primates occipital cortex is necessary for visually guided saccades and smooth pursuit as well as for the immediate component of OKN. Occipital cortex also makes the predominant contribution toward the generation of the velocity-storage component of OKN.(ABSTRACT TRUNCATED AT 400 WORDS)

On the role of cortical area V4 in the discrimination of hue and pattern in macaque monkeys

Cortical visual area V4 in macaque monkeys has a large proportion of neurons that are sensitive to the wavelength or to the color of light. We tested its role in hue discrimination by removing it in macaque monkeys trained to discriminate small differences in hue. Hue discrimination thresholds were permanently elevated in 4 macaque monkeys in which V4 was removed bilaterally. In contrast, there was no impairment in achromatic intensity thresholds tested in an identical manner. However, the discrimination of pattern and orientation was also conspicuously impaired, indicating that area V4 is not concerned solely with processing information about wavelength. The multiple defect is consistent with evidence that V4 provides the major cortical visual input to the temporal lobe, where a large range of visual properties is registered. The performance of monkeys with V4 ablation was compared with that of unoperated control monkeys and monkeys with removal of cortex in the banks and floor of the rostral superior temporal sulcus (STS). Removal of STS had only slight effects on pattern discrimination and none of hue discrimination. To control for the possible effects of inadvertent damage to the visual radiations when removing V4, the lateral striate cortex was partially ablated bilaterally in a control monkey. This had no effect on any discrimination, despite producing more retrograde damage to the lateral geniculate nuclei than in any monkey with V4 ablation. The visual disorder following removal of visual area V4 strikingly resembles the clinical disorder of mild cerebral achromatopsia with associated apperceptive agnosia for objects and patterns.

Removal of Lens Epithelial Cells by Ultrasound in Endocapsular Cataract Surgery

A new method was developed to remove lens epithelial cells during endocapsular cataract surgery using a device with a tip that resembles the irrigating-aspirating tip for cortex removal by extracapsular cataract extraction. The tip has an opening on the side and end, both 0.20 mm in diameter, for aspiration. The opening at the end serves to remove the cells at the equator. The top of the tip is sandblasted to provide an abrasive surface. This tip is connected to a phacoemulsifier handle. After nucleus delivery and cortex removal, the tip is inserted beneath the inner surface of the anterior capsule. The cells are detached by the abrasive tip, which vibrates by ultrasound, and then aspirated. Histologic examination revealed that the cells can be removed completely, and that this method is more effective than vacuum cleaning.

The effects of cortical ablation on multiple unit activity in the striatum following dexamphetamine

Bilateral removal of the fronto-parietal cortex of the rat resulted in decreased spontaneous multiple-unit activity recorded in the striatum of freely-moving rats. Cortical ablations changed the neuronal response in the striatum to systemic administration of dexamphetamine (2.5 mg kg i.p.) from excitation in control animals (88%) to inhibition in ablated animals (61%). Furthermore, catalepsy, induced by haloperidol, but not by morphine, was markedly attenuated after cortical ablation. These changes were accompanied by a 23% decrease in the specific binding of [ 3H]spiperone in the striatum. The binding of [ 3H]met-enkephalin was unaffected by the cortical lesions. Levels of glutamate in the striatum decreased from 8.88 ± 0.5 μmols g in control animals to 6.93 ± 0.37 μmols g after bilateral cortical ablation. On the other hand, cortical ablations did not alter the content of either the γ-aminobutyric acid or glutamine of the striatum. It is concluded that the excitatory response, observed in striatal neurons in freely-moving animals, is dependent upon an intact cerebral cortex and requires intact cortico-striatal afferents. The results further suggest that neurons in the striatum are under the tonic influence of glutamate, released from cortico-striatal afferents. Lastly, some dopamine D 2 binding sites in the striatum are located on cortico-striatal afferent terminals and blockade of these striatal D 2 sites may be involved in the induction of catalepsy by neuroleptic drugs.

Reacquisition of classical conditioning after removal of cerebellar cortex.

We trained rabbits with white noise and light conditioned stimuli and a face shock unconditioned stimulus for classical conditioning of the nictitating membrane response and then removed the ipsilateral cerebellar cortex by aspiration. Larsell's hemisphere lobule VI was completely removed in 5 rabbits; the pattern of degeneration in the inferior olive matches the projections to HVI reported in experiments with horseradish peroxidase. All rabbits showed an initial abolition of conditioned responses but then relearned within two days. This indicates that cerebellar cortical lobule HVI normally is involved but is not necessary for classical conditioning.

Impact of neodecortication on colon motor response to a meal in the rat.

The colon motor response to a meal consisting of 100 mM of sodium oleate was assessed before and after neodecortication in male Sprague-Dawley rats. Recording probes were anchored surgically in the ascending and descending colon. Pressure changes were recorded on a dynograph using a low-compliance perfusion system. A motility index took into account the amplitude, duration, and frequency of contractions. Neodecortication increased the motility index of the distal colon in the fasting state. However, removal of the cerebral cortex did not affect significantly the colon motor response to a meal. Meal stimulation increased the motility index before and after neodecortication. These findings suggest that resting colonic motor activity is increased after neodecortication, probably through the loss of an inhibitory influence of the central nervous system; and the cerebral cortex is not required for the colon response to a meal in the rat.

Visual discrimination in the absence of visual cortex.

Normal rats and rats with devascularization lesions ranging from subtotal removals of striate cortex (Area 17) to complete removal of neocortex were trained in a horizontal/vertical stripe discrimination for a liquid reinforcer. Subgroups of animals were identified on the basis of size and location of lesion (with particular reference to striate cortex) as Subtotal, Striate, Posterior and Decorticate. Some animals in all of the lesion groups were able to acquire the discrimination, but there was a direct relationship between lesion size and number of training trials. Those animals which reached criterion on the original discrimination were trained on a second horizontal/vertical discrimination under either transfer or reversal conditions using 'rotated obliques' stimuli. Performance on this second discrimination indicated that animals from all lesion groups had been using visual stimuli based on stripe orientation in the original problem. Members of all lesion groups solved the rotated obliques problem under the transfer condition, though the speed and completeness with which they did so was again inversely related to lesion size. These data show high levels of visual competence in the absence of visual cortex even when stimuli thought to detect form discrimination are used and thus reinforce the view that superior colliculus may be a more significant visual area for the rat than was previously assumed. They also support other observations that animals do not use residual visual capacities without extensive experience and appropriate motivation.

Enrichment versus exercise effects on motor impairments following cortical removals in rats

Groups of rats were exposed to an enriched environment, given access to an activity wheel, or individually housed in wire mesh cages, impoverished. Rats were exposed in groups of four to the enriched environment or placed individually in the activity wheel for 2 h per day for 25 days preoperatively. Within each exposure group, rats sustained bilateral removals of sensorimotor cortex, or were sham-operated controls. Animals were trained preoperatively to locomote across a narrow elevated runway. Postoperatively, locomotor testing was initiated 17 days after surgery throughout which time all animals were maintained under impoverished conditions. Locomotor deficits following cortical damage were a function of preoperative exposure: enriched rats were least impaired; impoverished rats were most impaired. Rats allowed running wheel activity initially showed the same marked deficits as impoverished animals but recovered more rapidly. The opportunity for physical exercise afforded wheel animals preoperatively may have enhanced motor capabilities that aided recovery. However, physical activity alone did not yield the same protective effects from initial impairment as enrichment. Greater elaboration of neural structures associated with perceptual-motor enrichment probably accounted for the initial sparing of the enriched group.

Hippocampal, granule cell and CA 3–4 lesions impair formation of a place learning-set in the rat and induce reflex epilepsy

Rats were pretrained on a place learning-set task, in which a platform, submerged in a swimming pool filled with opaque water, was moved to a new location each day. Then they received either: (1) suction removal of the dorsal hippocampus, (2) intrahippocampal microinjections of colchicine to remove dentate gyrus granule cells, (3) kanic acid to remove CA 3–4 cells of the hippocampus proper, (4) suction removal of parietal cortex overlying the hippocampus, or (5) no surgery. Performance was then evaluated for 48 days. All lesion groups were chronically impaired with respect to the control group, but the rats with parietal cortex lesions retained the ability to solve the task, whereas rats with hippocampal damage did not. Training frequently induced task-related behavioural seizures in the rats with granule cell or CA 3–4 lesions. The results show that the hippocampus, including granule cell and CA 3–4 cell populations, is essential for the rapid acquisition of place responses in the swimming pool task. The finding that training on the task induced reflex epilepsy in granule cell and CA 3–4-damaged rats, but not those with aspirative removals, suggests that residual portions of the hippocampus are activated by training and are involved in production of the epileptic attacks.

On the role of posterior parietal and prefrontal cortex in visuo-spatial perception and attention.

Monkeys with bilateral removal of caudal prefrontal cortex (area 8) or dorso-lateral parietal cortex (areas 5 and 7) or the inferior temporal cortex (area TE) were presented with two versions of a go-left/go-right visuo-spatial discrimination. In the first task they had to displace either the left or right of two identical plaques according to whether both plaques were black or white respectively. There were no performance differences among groups. In the second task, the two plaques were always red and the appropriate response was indicated by whether a spatially remote third plaque was black or white. Both the prefrontal and parietal groups were impaired relative to the inferotemporal group on this task. The results indicate that whether an impairment occurs on a task that is thought to test the perception of egocentric space may depend on whether the animal has to notice and attend to a remote cue, and that an attentional disorder may also explain impairments reported on tests of allocentric perception where the critical cue is spatially remote from the response site.

Cross-modal recognition of familiar and unfamiliar objects by the monkey: the effects of ablation of polysensory neocortex or of the amygdaloid complex.

Nine rhesus monkeys were trained to a standard level of cross-modal recognition (CMR) in the directions vision to touch and touch to vision. Their level of performance remained essentially unchanged with unfamiliar objects. Five then received bilateral removals of frontal, temporal and parietal polysensory cortex in one stage or successively, and 4 underwent removal of the amygdaloid complex in one stage. All animals were retrained to criterion with familiar objects and then again tested with unfamiliar objects. Postoperatively, the monkeys with extensive neocortical removals were unimpaired or slightly impaired with familiar objects, and slightly impaired (in only one direction) with unfamiliar objects. The animals with amygdaloid ablations showed a different pattern of change: with familiar objects they were unimpaired (if removals were less extensive), or were severely but transiently impaired (if the removals of the amygdala were more extensive and/or other structures were involved); with unfamiliar objects they were unimpaired, tending to improve. The neocortical polysensory areas may be necessary for generating new visual representations during learning--a performance required only for the CMR of unfamiliar objects.

Visual cortex contribution to the organization of eye movements produced by local electrical stimulation of the cat lateral geniculate body

Eye movements evoked by local electrical stimulation of the dorsal nucleus of the lateral geniculate body were analyzed after removal of the visual cortex and in intact animals during trials on awake cats. No significant difference was observed between the eye movement patterns of the two animal groups evoked by electrical stimulation. These movements could be classed into three main groups: those unassociated with the starting position of the eyes in orbit (or unidirectional movements), goal-directed, and centered movements, with direction depending on the initial position of the eyes in their orbits. Our findings indicate that the cortical visual areas are neither the principal nor an indispensable link in the chain for transmitting signals evoked by (electrically) stimulating the geniculate body from the cortical structures of the direct visual pathway towards the operative links of the oculomotor system. Potential pathways for conducting information from the dorsal nucleus of the lateral geniculate body to oculomotor system structures are discussed.

Gonadal steroids influence axon sprouting in the hippocampal dentate gyrus: A sexually dimorphic response

Young adult Sprague-Dawley rats of either sex were randomly assigned to be gonadectomized or left intact. Capsules containing either testosterone or estrogen were implanted in animals in both categories. Fifteen days after removal of the entorhinal cortex, the brains were analyzed for changes in reactive outgrowth of the commissural-associational afferent fibers in the hippocampal dentate gyrus. Both male and female control subjects showed identical sprouting responses. Only female subjects were significantly affected by gonadectomy, resulting in significant decreases in reactive fiber outgrowth. Hormone replacement therapy resulted in a return to control values in castrated females but had no affect on castrated males. The results suggest that sex hormones may regulate axon sprouting in the mature central nervous system.

Quantitative measurement of interresponse times to assess forelimb motor function in rats

Eight rats were trained to use their left paw to rapidly press the right lever of an operant chamber once and the left lever twice to obtain a food reward. Between-levers interresponse times and same lever interresponse times were measured daily for several weeks before and after bilateral removal of frontal motor/sensory cortex. This surgery resulted in a permanent deficit in most rats' ability to rapidly alternate between levers, but resulted in only a temporary deficit in their ability to rapidly press the same lever. Sham surgery and removal of hindlimb motor cortex had little immediate effect on interresponse times. The data demonstrate that sequential motor behavior tested in the between-levers tasks is chronically affected by cortical lesions, but the speed of the same repetitive movement tested in the same lever task is not. Measuring the time to rapidly alternate between two different levers, therefore, provides a quantitative method for measuring acute and chronic forelimb motor deficits due to motor cortex injury in rats which could be applied to any mammal.

The hopping reaction in the rabbit after early and late removal of the motor cortex

Unilateral lesions of the sensorimotor cortex were made in rabbits either 24 h or 6 months after birth. Four months after the operation the hopping reaction in the leg contralateral to the lesion was still absent in the animals operated in adulthood. In the animals operated one day after birth a normal hopping reaction was found when tested 1.5 and 4 months after the operation.