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PubMed2001

Imitation and matching of hand and finger postures.

Converging evidence from patients with unilateral brain lesions, from a patient with callosal disconnection, and from functional imaging in healthy subjects suggests different competencies of both hemispheres for imitation and matching of hand and finger postures. Whereas the left hemisphere is fully competent for processing hand postures, an additional right hemisphere contribution is needed for finger postures. I propose that the left hemisphere is responsible for coding gestures with reference to knowledge about the structure of the human body, whereas a right hemisphere contribution is needed for visuospatial exploration and analysis of gestures. Single case studies of patients with visuoimitative apraxia and results of functional imaging suggest a prominent role for left area 40 for body-part coding. Additional activation of left MT/V5 in the functional neuroimaging study may be related to processing of the motion implied by the gesture which is presented as a static image.

Attention↗
PubMed1998

Ultrastructural and temporal observations of the potyvirus cylindrical inclusions (Cls) show that the Cl protein acts transiently in aiding virus movement.

A systematic ultrastructural study across the edge of an advancing infection in pea seed-borne mosaic potyvirus-infected pea cotyledons showed the cylindrical inclusion (CI) protein to exist in transient functional states. Initially, the characteristic CI pinwheel inclusion bodies were positioned centrally over the plasmodesmal apertures (including those of plasmodesmata connected to the previously infected cell), in agreement with a proposed role in virus movement (Carrington et al., 1998, Plant J., 13, in press). The viral coat protein was associated with these structures and was seen within the modified plasmodesma, most notably in a continuous channel that passed along the axis of the pinwheel and through the plasmodesma. The CI protein was not detected within the plasmodesmal cavities. Later in the infection (i.e., behind the zone of active virus replication) the CI was no longer associated with cell walls, or with coat protein, and showed signs of structural degeneration. In contrast, the coat protein remained within plasmodesmal cavities. The role of the CI in assisting virus movement is not known but the presence of the CI was linked with an apparent transient reduction in callose in the vicinity of the plasmodesmata.

Inclusion Bodies, Viral↗
PubMed2005

Corpus callosum subdivision based on a probabilistic model of inter-hemispheric connectivity.

Statistical shape analysis has become of increasing interest to the neuroimaging community due to its potential to locate morphological changes. In this paper, we present the a novel combination of shape analysis and Diffusion Tensor Image (DTI) Tractography to the computation of a probabilistic, model based corpus callosum (CC) subdivision. The probabilistic subdivision is based on the distances of arc-length parameterized corpus callosum contour points to trans-callosal DTI fibers associated with an automatic lobe subdivision. Our proposed subdivision method is automatic and reproducible, Its results are more stable than the Witelson subdivision scheme or other commonly applied schemes based on the CC bounding box. We present the application of our subdivision method to a small scale study of regional CC area growth in healthy subjects from age 2 to 4 years.

Algorithms↗
PubMed1991

[Rethoracotomy after lung resection].

Postoperative complications after lung resection necessitating rethoracotomy are rare. The most common early complication is hemorrhage. Reintervention is indicated if bloody secretion of more than 250 ml/h persists over a period of hours. Any large intrapleural hematoma should be removed to avoid infection or development of pleural callosity. Further indications for rethoracotomy are: persistent parenchyma fistula, pneumothorax, residual cavity, pleural empyema, leakage of the bronchial stump and mechanical bronchial obstruction.

Bronchial Fistula↗
PubMed1987

Immunological studies in patients with central nervous system tumors.

Impairment of cell-mediated immunity in patients with primary central nervous system (CNS) tumors has repeatedly been reported but data to demonstrate the underlying immunological defect are not univocal. This report concerns a series of 31 patients harboring a glioma in which we studied: peripheral blood T-lymphocyte subpopulations by monoclonal antibody analysis; cellular responsiveness to mitogens; serum immunoglobulin values. The same parameters were also evaluated in 7 cases of intracranial meningioma and in 8 patients affected by non-proliferative, non-inflammatory CNS diseases. Thirty age-matched healthy volunteers formed the control group. Neither impairment of T-cells as regard to number, responsiveness and subsets, nor abnormal Ig values were found in these groups. However two patients, harboring respectively a third ventricle low grade astrocytoma and an anterior callosal glioblastoma, presented a striking T-cells impairment. These findings might suggest a correlation between hypothalamus and immune system, as already postulated by several previous experimental and clinical studies.

Adolescent↗
PubMed1993

Glucomannan synthesis in pea epicotyls: the mannose and glucose transferases.

Membrane fractions and digitonin-solubilized enzymes prepared from stem segments isolated from the third internode of etiolated pea seedlings (Pisum sativum L. cv. Alaska) catalyzed the synthesis of a beta-1,4-[14C]mannan from GDP-D-[U-14C]-mannose, a mixed beta-1,3- and beta-1,4-[14C]glucan from GDP-D-[U-14C]-glucose and a beta-1,4-[14C]-glucomannan from both GDP-D-[U-14C]mannose and GDP-D-[U-14C]glucose. The kinetics of the membrane-bound and soluble mannan and glucan synthases were determined. The effects of ions, chelators, inhibitors of lipid-linked saccharides, polyamines, polyols, nucleotides, nucleoside-diphosphate sugars, acetyl-CoA, group-specific chemical probes, phospholipases and detergents on the membrane-bound mannan and glucan synthases were investigated. The beta-glucan synthase had different properties from other preparations which bring about the synthesis of beta-1,3-glucans (callose) and mixed beta-1,3- and beta-1,4- glucans and which use UDP-D-glucose as substrate. It also differed from xyloglucan synthase because in the presence of several concentrations of UDP-D-xylose in addition to GDP-D-glucose no xyloglucan was formed. Using either the membrane-bound or the soluble mannan synthase, GDP-D-glucose acted competitively in the presence of GDP-D-mannose to inhibit the incorporation of mannose into the polymer. This was not due to an inhibition of the transferase activity but was a result of the incorporation of glucose residues from GDP-D-glucose into a glucomannan. The kinetics and the composition of the synthesized glucomannan depended on the ratio of the concentrations of GDP-D-glucose and GDP-D-mannose that were available. Our data indicated that a single enzyme has an active centre that can use both GDP-D-mannose and GDP-D-glucose to bring about the synthesis of the heteropolysaccharide.

Acetyl Coenzyme A↗
PubMed1996

Transcallosally mediated inhibition of interneurons within human primary motor cortex.

The objective of this study was to investigate interhemispheric transcallosal connections between primary motor cortices noninvasively in awake human subjects. For this purpose, focal transcranial magnetic stimulation was performed on eight healthy, right-handed subjects and one patient with congenital collosal agenesis. Using two magnetic stimulators, we investigated the effect of a conditioning magnetic stimulus applied to the motor cortex of one hemisphere on the duration of the silent period (SP) evoked in the first dorsal interosseus (FDI) muscle by a magnetic test stimulus given over the opposite motor cortex. It is well established that SP reflects activation of inhibitory interneurons within primary motor cortex. In all normal subjects, a conditioning stimulus to one hemisphere produced a significant shortening of SP evoked by the test stimulus when the conditioning-test-interval was 10-20 ms. The effect was also observed when an electrical test stimulus was used. The conditioning coil had to be placed over the hand motor area to obtain the maximal effect. The threshold for eliciting this decrease of SP duration was higher than the threshold for eliciting an early excitatory muscle response in the contralateral FDI. Increasing the intensity of the conditioning stimulus led to linear reduction of SP duration. In the patient with callosal agenesis, no such decreasing effect on SP duration was observed. These results suggest that inhibitory interneurons within primary hand motor cortex receive transcallosal inhibitory input from the opposite motor cortex. We propose that modulation of motor cortical interneurons via transcallosal pathways may provide a gain control for the motor cortical output system and subserve interhemispheric coordination in complex, nonsymmetrical bimanual movements.

Adult↗
PubMed1992

Projections from fetal neocortical transplants placed in the frontal neocortex of newborn rats. A Phaseolus vulgaris-leucoagglutinin tracing study.

Fetal rat neocortex grafted into lesion cavities made in the newborn rat neocortex can exchange multiple axonal connections with the host brain. Most previous studies demonstrating efferent transplant-to-host brain connections have used fluorescent retrograde tracers injected into the host brain (Castro et al. 1985, 1987; Floeter and Jones 1984; O'Leary and Stanfield 1989). Other studies have used anterograde axonal tracing with either tritium-labelled amino acids impregnating the transplant and its efferents (Floeter and Jones 1985) or horseradish peroxidase injected into the transplants (Chang et al. 1984, 1986). In the present study we used the anterograde axonal tracer Phaseolus vulgaris-leucoagglutinin (PHA-L) to examine in detail the course and termination of the efferent neocortical graft fibers. Twenty-six newborn rats had the right frontal cortex forepaw area removed by vacuum aspiration, while anesthetized by hypothermia. A piece of fetal frontal cortex 14-16 embryonic days old (E14-16) was immediately thereafter placed in the lesion, and the recipient rats allowed to survive for 5-7 months. At this time the rats were reoperated under sodium pentobarbital (Nembutal) anesthesia and the transplants iontophoretically injected with PHA-L. Two weeks later the animals were again anesthetized, perfused, and processed for PHA-L immunocytochemistry and routine histology. Analysis of acetylcholinesterase- (AChE) and Nissl-stained sections showed graft survival in 19 of the 26 animals used in this study. When these 19 brains were processed for PHA-L immunocytochemistry, 5 of them were found with certainty to have the PHA-L injection confined to the transplant. Based on these cases PHA-L-reactive fibers arising from labelled transplant neurons were traced into the ipsilateral host neocortex adjacent to the transplant and found to project through the subcortical white matter to the ipsilateral parietal neocortical area 1, and claustrum. Callosal fibers were traced to the contralateral frontal neocortical forelimb and parietal areas. Transplant fibers were also observed to descend through the caudate putamen in the dispersed fiber bundles of the internal capsule to distribute as terminal branches and varicose fibers within the mesencephalic periaqueductal gray, red nucleus, deep mesencephalic nucleus, and intermediate gray of the superior colliculus, as well as in the pontine gray. Similar fibers and terminations were present in the caudate putamen, the reticular, ventrobasal, centrolateral, posterior, and parafascicular thalamic nuclei.(ABSTRACT TRUNCATED AT 400 WORDS)

Acetylcholinesterase↗
PubMed1990

Human amblyopia: structure of the visual field.

Kittens raised with different kinds of abnormal early visual experience (monocular and binocular deprivation, convergent strabismus, eye rotation, asymmetric alternating occlusion, early callosal split) show systematic deficits in the nasal visual field of the affected eye. To test whether abnormal visual experience produces similar deficits in the human visual system, we measured the monocular visual field of humans with subnormal binocular vision (strabismic and anisometropic amblyopes, strabismics with alternating fixation). Eight amblyopes were tested with a computer-assisted static perimetry (Octopus 2000). Twenty other subjects were tested with kinetic perimetry (Goldmann 940), 11 subjects with static perimetry (Goldmann 940). In some of these subjects, we measured the latency of saccades and the accuracy of visually guided pointing toward stimuli presented in the peripheral visual field. Both strabismic and anisometropic amblyopes frequently showed deficits of visual sensitivity in the central part of the visual field, but no systematic deficits in the peripheral field of the amblyopic eyes. Strabismic alternators had practically equal fields in the two eyes. Neither saccadic latency nor pointing accuracy showed a systematic impairment in the nasal visual field. The discrepancy between the field losses in strabismic humans and in cats raised with a surgically induced squint cannot be due to methodological differences, but rather to anatomical differences, or to the different origin of strabismus in the two species.

Adult↗
PubMed1991

Bi-versus monohemispheric performance in split-brain and partially split-brain macaques.

Experiments comparing binocular with monocular abilities of monkeys working on visual mnemonic tasks were performed. First, it was shown that even in split-brain monkeys performance was more accurate when both hemispheres were utilized than when the task was performed with only the single (better) hemisphere. Some form of noncommissural integration is thus possible. However, when the forebrain commissures are present, as in four other animals (with only optic chiasm transected) it was shown that integration occurs via callosal mechanisms as well. This was demonstrated by the fact that here, too, binocular performance was normally more accurate than monocular performance, but when different images to be remembered were presented concurrently to the two eyes, the binocular advantage was lost. Finally, in three monkeys with only the anterior commissure allowing interhemispheric communication the superiority of binocular assessment remained even when the two hemispheres simultaneously received such differing images.

Animals↗
PubMed1992

The effects of monocular enucleation on visual topography in area 17 in the rabbit.

The effects of neonatal monocular enucleation on the topographic representation of the ipsilateral visual field in the visual cortex of the rabbit were investigated, using electrophysiological recordings of multi-unit activity in area 17. Topography of receptive fields was determined in normal adult rabbits, adult rabbits monocularly enucleated on the day of birth and adult rabbits monocularly enucleated as adults. In normal rabbits and in adult enucleates, the projection from the ipsilateral eye is represented by a strip of cortex extending approximately 2 mm from the 17/18 border. In neonatal enucleates, the width of the area of cortex in which the projection from the ipsilateral eye is represented was approximately twice as large as normal. Visual topography was normal in the superior-inferior axis but was distorted in the nasotemporal axis. Our data suggest that the abnormal topography observed in the visual cortex of neonatally enucleated rabbits may play a major role in shaping the abnormal visual callosal projections observed in these animals. In addition, our data indicate that, following neonatal monocular enucleation, developmental abnormalities in the topography of geniculocortical projections can occur independently of any alteration in the retinogeniculate projection patterns.

Animals↗
PubMed1981

Intracellular studies on cortical synaptic plasticity. Conditioning effect of antidromic activation on test-EPSPs.

1. An intracellular study on pyramidal tract (PT) neurons in the cat's motor cortex was carried out to examine whether their antidromic activation would be able to induce plastic changes in the efficacy of the synapses situated on their membrane. 2. The experimental paradigm was based on the principles of classical conditioning. It included habituation, pseudoconditioning, conditioning and extinction procedures. The antidromic spike was regarded as an unconditioned stimulus while excitatory postsynaptic potentials (EPSPs) evoked by thalamic (n. ventralis lateralis), callosal and somatosensory afferents served as conditioned stimuli. Stimulus pairs were given, consisting of EPSPs and antidromic spikes with various time intervals, and the stimulus sequences were at a 0.2--1.0/s frequency. 3. Reversible, short-term (3--28 min) enhancement of synaptic excitability was observed in 27% of the PT cells after conditioning with 60--150 stimulus pairs. 4. EPSP-spike and spike-EPSP sequences were equally effective, but plastic changes were induced only by stimulus pairs with less than 100 ms interstimulus intervals. 5. Facilitated EPSP states were frequently accompanied by changes in membrane potential, membrane resistance and firing activity. 6. In repeated conditioning series, the temporal parameters of conditioning changes, the number of stimuli necessary for full development of facilitation, and some membrane parameters showed marked alterations. 7. Conditioned plastic changes in synaptic efficacy showed analogies with associative learning: (a) they were specific to the pairing procedure, because randomized presentation of EPSPs and antidromic spikes never produced synaptic facilitation; (b) unpaired spike trains used as unconditioned stimuli (of 10--200/s frequency and 1--20 s duration) caused only a minor degree of facilitation as compared with EPSP-spike pairings; (c) changes in synaptic efficacy were subject to extinction. 8. The present findings indicate that the plastic changes in synaptic transmission may be localized to the postsynaptic membrane of the conditioned PT cells.

Action Potentials↗
PubMed1981

The role of the corpus callosum and some subcortical commissures in interocular transfer in the hooded rat.

The effect of sectioning the corpus callosum on interocular transfer of a brightness and a horizontal/vertical discrimination was examined in hooded rats. Lesions of the posterior portion of the callosum usually led to moderate transfer deficits, but considerable individual variation was found. Lesions involving only the anterior part of the callosum had little effect on transfer. This suggests a functional localisation in the corpus callosum of the rat similar to that seen in higher mammals. Section of the posterior and tectal commissures and the thalamic massa intermedia in addition to the callosum had no greater effect on transfer thatn callosal section alone. It is therefore unlikely that these structures play a crucial role in interocular transfer in the rat.

Animals↗
PubMed1983

Physiological and morphological properties of identified basket cells in the cat's visual cortex.

In 87 cells studied physiologically, and filled intracellularly with horseradish peroxidase (HRP), we have found four cells which make multiple contacts with the perikarya of their post-synaptic targets. These cells are all multipolar non-pyramidal neurones with elongated smooth dendrites. Three resemble the classical "basket cells" of Ramón y Cajal (1911), having widely distributed axons which contribute to the "nids pericellulaires" around pyramidal cell perikarya. The fourth cell has a much more restricted axon virtually confined to layer 4 and appears to contact principally small, probably non-pyramidal, cells. Two of the basket cell axons have been examined by electron microscopy and make symmetrical, Gray's type II contacts with the perikarya and apical and basal dendrites of pyramidal cells. Ten percent of the synapses are on dendrites of non-pyramidal cells. The axon arborizations of all four cells are distributed in a patchy fashion. In two cells examined for the purpose, very few boutons were found within 100 micron of the cell body and a radially aligned cylinder of the same diameter extending from the cell body to the pial surface. The physiological properties of these structurally similar cells are far from uniform. They can be activated mono- or polysynaptically, by X- or Y-type lateral geniculate input, and can have S or C type receptive fields. Two were activated, probably monosynaptically, via callosal afferents. These cells may play an important role in the inhibitory mechanisms of the cortex.

Animals↗
PubMed1983

Motor representation in the rostral portion of the cat corpus callosum as evidenced by microstimulation.

In six chronic cats experiments were carried out to examine the motor effects elicited by microstimulation of the rostral portion of the corpus callosum (CC) which contains fibres interconnecting the motor cortices of the two hemispheres. Serial dorso-ventral penetrations were stereotaxically performed along the rostro-caudal extent of the CC at 0.25-0.5 mm intervals. Motor responses, consisting of very discrete contractions of shoulder, whisker and eyelid muscles, were obtained upon stimulation of about the most rostral 4 mm at intensities lower than 50 microA. At threshold the responses appeared in only one body region and were often unilateral. A light increase in current gave rise to symmetrical bilateral effects. Thresholds were the lowest in the middle of CC and gradually rose towards its dorsal and ventral surfaces. In the course of a penetration an effect once elicited persisted until either the threshold became higher than 50 microA or the ventral edge was reached. All motor effects had thresholds higher than 10 microA. Contractions of shoulder, whisker and eyelid muscles at a threshold lower than 20 microA were obtained in 62.7%, 25.7% and 54.3% of penetrations, respectively. Shoulder and eyelid muscles were represented in the rostral and caudal half of the effective zone, respectively, whereas the representation of whisker muscles overlapped with the other two in the rostral third or the middle part of the effective zone. Single fibres driven by palpation of muscles responding to microstimulation or by movements of the joint mobilized by microstimulation were found at the most rostral sites, whereas units responding to hair displacement over or around the affected muscles were isolated mainly at the most caudal sites. It was inferred that functionally homogeneous callosal fibres are clustered in bundles arranged in dorso-ventrally oriented laminae. The somatotopic representation of the motor effects elicited by microstimulation along the rostro-caudal extent of the effective zone should be the consequence of the serial arrangement of these partially overlapping laminae.

Animals↗
PubMed1986

Stereoperception in cats following section of the corpus callosum and/or the optic chiasma.

The spatial separation of the eyes in animals with overlapping visual fields means that parts of a three dimensional object project to slightly disparate retinal points in each eye. This disparity, once interpreted by the brain, is thought to be a sufficient condition for stereoperception. In the present experiment, stereopsis based on spatial disparity cues was evaluated in cats using Julesz random-dot stereograms before and after sections of the optic chiasm, the corpus callosum or both. Normal cats were able to solve the random-dot problem. Optic chiasm transection drastically diminished this ability, callosal section had little effect and combined lesions of these two structures abolished stereoperception. These results suggest that central stereopsis based on spatial disparity is mainly mediated by binocular cortical cells receiving their input via the ipsilateral and the through-the-chiasm contralateral thalamo-cortical pathways.

Animals↗
PubMed1995

Spatially distributed responses induced by contrast reversal in cat visual cortex.

Field potentials were recorded from cat striate cortex, either between an epidural screw electrode and a cannula-electrode inserted deep in the gray matter (transcortical recording) or with a pair of metal microelectrodes. Electrodes were placed bilaterally near the cortical projection of the area centralis. The horizontal separation of the recording tips was approximately 2 mm and approximately 300 microns, respectively. The area of the visual field providing input to the recording site (receptive field) was determined by measuring the field potentials generated by contrast reversal of high-contrast, achromatic bar gratings. Five-degree-diameter grating patches were presented individually over a large area of the visual field. The gratings were contrast-reversed at 4, 6 or 10 Hz, while also being swept in spatial frequency between 0.56 and 5.24 c/deg. The receptive fields were approximately 20 deg across or more, substantially larger than expected on the basis of cortical retinotopy. Responses were also elicited by stimulation of the hemi-field contralateral to that contributing to the classical receptive field, implicating the presence of a callosal projection. The large, spatially distributed receptive fields consisted of patches of high and low sensitivity. Continuous cortical infusion of either 100 microM tetrodotoxin or 10 mM muscimol at the recording site totally suppressed the transcortically recorded field potentials, proving that the local field potentials were generated postsynaptically. The present findings suggest that a cluster of cortical cells near the projection site of the area centralis receives input from remote cortical regions to an extent that is comparable with that of anatomically demonstrated long-range lateral connections.

Animals↗
PubMed1988

Local connections in transplanted and normal cerebral cortex of rats.

Injections of the fluorescent tracer Fluoro-Gold were made in transplanted and normal cerebral cortex of rats in order to investigate and compare the local connectivities of both. In the normal somatosensory cortex, small injections in superficial layers (I to III) produced retrograde cell labeling below the injection site in two bands: in layer V and in the deep part of layer VI. Pieces of embryonic rat neocortical tissue were transplanted into a cavity made in the somatosensory cortex of young adult rats. After a survival period of 2-3 months, small injections of Fluoro-Gold were made in the superficial part of the grafts. These injections revealed multiple clusters of intratransplant-projecting cells. No callosal or thalamic neurons were labeled in these experiments. On occasion, a bilaminated pattern of retrograde cell labeling was observed inside the transplants. In both transplanted and normal cortices, pyramidal and non-pyramidal cells were retrograde-labeled. We conclude that in the neocortical transplants there is a pattern of local connectivity that is reminiscent of the pattern of intracortical connectivity in the normal neocortex in at least two aspects: first, the retrograde-labeled cells tended to form clusters or bands; second, both pyramidal and non-pyramidal cells were labeled.

Animals↗