It has been proposed that visual-memory traces are located in the temporal lobes of the cerebral cortex, as electric stimulation of this area in humans results in recall of imagery. Lesions in this area also affect recognition of an object after a delay in both humans and monkeys, indicating a role in short-term memory of images. Single-unit recordings from the temporal cortex have shown that some neurons continue to fire when one of two or four colours are to be remembered temporarily. But neuronal responses selective to specific complex objects, including hands and faces, cease soon after the offset of stimulus presentation. These results led to the question of whether any of these neurons could serve the memory of complex objects. We report here a group of shape-selective neurons in an anterior ventral part of the temporal cortex of monkeys that exhibited sustained activity during the delay period of a visual short-term memory task. The activity was highly selective for the pictorial information to be memorized and was independent of the physical attributes such as size, orientation, colour or position of the object. These observations show that the delay activity represents the short-term memory of the categorized percept of a picture.
Extracellular phospholipase A2 was purified about 1.7 X 10(5) fold to near homogeneity from human synovial fluid of rheumatoid arthritis by sequential use of column chromatographies on heparin-Sepharose, butyl-Toyopearl, and reversed-phase HPLC. The final preparation showed a single band on SDS-polyacrylamide gel electrophoresis, and its molecular mass was estimated to be approximately 13,700 daltons. The purified enzyme had a pH optimum of 9.0 and required Ca2+ for maximum activity. It hydrolyzed phosphatidyl-ethanolamine more effectively than phosphatidylserine and phosphatidylcholine. These properties were similar to those of an extracellular phospholipase A2 detected in the peritoneal cavity of caseinate-treated rats.
Objectives: Despite many hypotheses, the pathophysiology of syringomyelia is still not well understood. In this report, the authors propose a hypothesis based on analysis of cerebrospinal fluid dynamics in the spine. Methods: An electric circuit model of the CSF dynamics of the spine was constructed based on a technique of computational fluid mechanics. With this model, the authors calculated how a pulsatile CSF wave coming from the cranial side is propagated along the spinal cord. Results: Reducing the temporary fluid storage capacity of the cisterna magna dramatically increased the pressure wave propagated along the central canal. The peak of this pressure wave resided in the mid-portion of the spinal cord. Conclusions:The following hypotheses are proposed. The cisterna magna functions as a shock absorber against the pulsatile CSF waves coming from the cranial side. The loss of shock absorbing capacity of the cisterna magna and subsequent increase of central canal wall pressure leads to syrinx formation in patients with Chiari I malformation. S yringomyelia is a disease that produces fluid containing cavities in the parenchyma of the spinal cord. Most often it is associated with Chiari type I malformation with a herniation of cerebellar tonsils through the foramen magnum. In 1958, Gardner described his hypothesis on the pathophysiology of this disease 1 ; he considered that an obstruction of the cerebrospinal fluid (CSF) outflow from the fourth ventricle diverts the CSF pulse waves into the central canal. His hypothesis was thus called the "water-hammer theory". 2Based on his theory, suboccipital craniectomy with plugging of the obex, obstructing the opening of the central canal, became common. Recently, however, most surgeons agree that bony decompression of the foramen magnum together with some form of dural decompression is all that is required to treat this type of syringomyelia.3-6 Gardner's theory is difficult to reconcile with this operation because, if the obex is not plugged, CSF pulses will be propagated down the central canal.Ball and Dayan 7 proposed that the CSF enters the syrinx through the enlarged Virchow-Robin space in the spinal cord. Although several other authors agree with this hypothesis, their opinions differ about specific mechanisms. Ball and Dayan hypothesised that the CSF is driven into the VirchowRobin space when the spinal subarachnoid pressure is increased during coughing or straining. They postulated that this increased pressure is caused by a one way valve-like mechanism at the craniovertebral junction, which blocks the upward CSF movement. Heiss et al 8 thought that the piston-like movement of the herniated tonsils is responsible for producing downward pulse waves in the subarachnoid space, which contribute to the downward progression of the syrinx. Stoodley et al, 9 10 on the other hand, considered that increased compliance of the spinal subarachnoid space increases the arterial pulse dependent CSF flow through the Virchow-Robin space.In this report, we took a different approa...
Our findings suggest that the function of lumbosacral nerve roots is altered in patients with lumbarized S1 so that the S1 nerve root serves the usual function of the L5 nerve root.
Objective : To apply a theoretical model to analyse the derangement of cerebrospinal fluid (CSF) dynamics in syringomyelia associated with adhesive arachnoiditis. Methods: An electrical circuit model of CSF dynamics in the spine was used. With this model, the derangement of CSF dynamics in adhesive arachnoiditis was simulated. The effects of various surgical procedures were then analysed, such as syringo-subarachnoid shunting, subarachnoid bypass, and foramen magnum decompression. Results: When CSF flow in the subarachnoid space was obstructed at a certain point, the pressure inside the spinal cord increased in the segment immediately distal to the blockage. This location of increased pressure corresponded to the preferred site of syrinx formation in adhesive arachnoiditis. Syringosubarachnoid shunting, subarachnoid bypass, and foramen magnum decompression were all effective at reducing this pressure gradient. Conclusions: Blockage of the spinal subarachnoid CSF pathway produces a relative increase in the pressure inside the spinal cord distal to the blockage point. Repetitive formation of this pressure gradient then induces CSF leakage into the spinal parenchyma, leading to the formation of syringomyelia. Using this model, alternative surgical procedures could be suggested that might be effective in treating this disease.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.