1,721,031 research outputs found
Electroencephalographic activity of the isolated hemicerebrum of the cat
No full textOne hemisphere was surgically isolated by combining midline bisection with a rostral hemisection of the brain stem. The EEG records from the isolated hemisphere showed almost continuous synchronization, typical of sleep or coma. However, brief periods of desynchronization up to 20 min could be brought about by olfactory and nociceptive stimuli. Episodes of a spontaneous form of desynchronization also occurred mostly during behavioral sleep. Even a small bridge of extrareticular tissue left intact in the brain-stem hemisection served to restore a normal wake-sleep cycle in the isolated hemisphere. © 1966
Some aspects of the history of the law of dynamic polarization of the neuron. From William James to Sherrington, from Cajal and van Gehuchten to Golgi.
No full textWilliam James was the first to suggest that propagation of impulses in the nervous system proceeds in one direction, from sensory to motor neurons, but not viceversa. His law of forward direction preceded the formulation of the law of dynamic polarization of van Gehuchten and Cajal, which assumed that nerve impulses are conducted cellulipetally along dendrites and cellulifugally along axons, based on different anatomo-functional properties of these neuronal components. Golgi did not accept the law of dynamic polarization because he believed that dendrites are involved in the nutrition of the neuron rather than in impulse propagation, and that impulses can travel in any direction in the axonal components of the diffuse nerve network. Sherrington in turn experimentally demonstrated that intraneuronic conduction is reversible, whereas, in accord with James's law, propagation of impulses along neuronal chains is irreversible, due to the valve-like action of synapses. The story of the law of dynamic polarization shows that neither Golgi nor Cajal paid much heed to Sherrington's findings and to neurophysiological studies in general, probably because they felt that histology alone could provide the key for understanding the general functioning of the nervous system. It is argued here that this attitude was detrimental to the progress of the neurosciences, because a multidisciplinary approach based on different techniques is inevitably called for in order to develop a plausible theory of the nervous system
Some effects of cortical and callosal damage on conscious and unconscious processing of visual information and other sensory inputs
No full textAlthough new methods of investigation from the molecular level to cognition are promoting major advances in the study of the functions of the human brain, the analysis of behavioral and psychological deficits following brain damage is still a major tool for the understanding of cerebral organization. The present paper reviews some aspects of work on functional losses and residual abilities following cortical damage that have allowed to distinguish conscious and unconscious levels of visual input processing. Attention is given to the possible contribution of residual conscious vision of color to unconscious form analysis in visual agnosia. The paper also reviews findings on temporary and permanent deficits that occur after selective lesions of a prominent input-output system of the cerebral cortex, the corpus callosum, with the aim of assessing the possibility of establishing a functional callosal topography
Integration of brain activities: the roles of the diffusely projecting brainstem systems and the corpus callosum
No full textRevisiting the 1981 Nobel Prize to Roger Sperry, David Hubel and Torsten Wiesel on the occasion of the centennial of the Prize to Golgi and Cajal
No full textIn 1981 the Nobel Prize for Medicine or Physiology was awarded to Roger Sperry for his work on the functional specialization of the cerebral hemispheres, and to David Hubel and Torsten Wiesel for their work on information processing in the visual system. The present paper points to some important links between the work of Sperry and that of Hubel and Wiesel and to their influences on neuroscience in the best tradition going back to Cajal
Sensory and attentional components of slowing of manual reaction time to non-fixated visual targets by ipsilateral primes
No full textReaction time (RT) for detecting extrafoveal targets is lengthened by a non-informative prime at the same location or in the same hemifield (RT inhibition). We assumed that sensory effects at primed locations should be the same for unilateral and bilateral primes, whereas systematic covert orienting to a primed location should occur only with unilateral primes. We found equal RT inhibition for both types of primes at 0.2 sec prime-target intervals (SOA), as contrasted with inhibition for unilateral but not bilateral primes at 0.6 sec SOAs. We conclude that RT inhibition involves a succession of sensory components and orienting-dependent components
Covert orienting to non-informative cues: reaction time studies
No full textLateralized, non-informative visual cues lengthen reaction time (RT) to successive targets flashed in the same hemified. Early ipsilateral RT facilitation is limited to the co-occurrence of cues and targets. Inhibition from visual cues has sensory components which do not depend on orienting, as well as attentional components which are limited to one side of the vertical meridian. An inhibition of RT to targets ipsilateral to the cues has been found with somatic or auditory cues and targets, and also when somatic targets follow visual cues or visual targets follow somatic cues. The results reviewed in this paper (1) are best accounted for by directional constraints in motor readiness which are induced by the voluntary suppression of an overt orienting toward the location of the cue; (2) indicate that similar mechanisms of covert orienting operate in the whole peripersonal and near extrapersonal space; and (3) point to a common neural substrate mediating both intramodal and cross-modal effects
Classical disconnection studies of the corpus callosum
No full textThe corpus callosum is one of the most prominent fiber systems of the mammalian brain. Early reports of animals in which the callosum was cut, often confused the effects attributable to callosum damage with those caused by lesions of other brain structures. Early clinical reports also failed to establish the role of the callosum in humans. Two sorts of evidence began to reveal the functions of the corpus callosum. People with callosal damage cannot read text presented in the left visual field, and animals in which the callosum is divided, and sensory input restricted to one hemisphere, fail to show interhemispheric transfer of learning. These functional findings are consistent with anatomical and physiological studies of the role of the corpus callosum in communication between the hemispheres
Binocularly driven neurons in visual cortex of split-chiasm cats
No full textIn cats with midsagittal section of the optic chiasm, some visual cortex neurons can be driven not only by the ipsilateral eye, through the direct geniculocortical pathways, but also by the contralateral eye, through the opposite visual cortex and corpus callosum. The receptive fields and the response characteristics observed upon stimulation of the contralateral eye are very similar to those observed upon stimulation of the ipsilateral eye; the two monocular receptive fields of a given cell lie in corresponding points of heteronymous halves of the visual field in close contact with the vertical meridian, thus adding in visual space and forming a binocular receptive area which crosses the vertical meridian and extends equally on either side of it
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