PubMed · 8311337
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E I Eger, R B Weiskopf. 1994. Sympathetic hyperactivity during desflurane anesthesia.. https://doi.org/10.1097/00000542-199402000-00039
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By means of their small receptive fields (RFs), neurons in primary visual cortex perform highly localized analyses of the visual scene, far removed from our normal unified experience of vision. Local image elements coded by the RF are put into more global context, however, by means of modulation of the responses of the V1 neurons. Contextual modulation has been shown to follow closely the perceptual interpretation of the scene as a whole. This would suggest that some aspects of contextual modulation can be recorded only in awake and perceiving animals. In this study, multi-unit activity was recorded with implanted electrodes from primary visual cortex of awake, fixating monkeys viewing textured displays in which figure and ground regions were segregated by differences in either orientation or motion. Contextual modulation was isolated from local RF processing, by keeping RF stimulation identical across trials while sampling responses for various positions of the RF relative to figure and ground. Contextual modulation was observed to unfold spatially and temporally in a way that closely resembles the figure-ground percept. When recording was repeated, but with the animals anesthetized, the figure-ground related modulatory activity was selectively suppressed. RF tuning properties, however, remained unaffected. The results show that the modulatory activity is functionally distinct from the RF properties. V1 thus hosts distinct regimes of activity that are mediated by separate mechanisms and that depend differentially on the animal being awake or anesthetized.
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The evolution of hepatic cryotherapy as an accepted treatment for patients with non-resectable hepatic malignancy has required concurrent evaluation and development of perioperative anesthetic management of these cases. Review of published and institutional experience demonstrates that hepatic cryotherapy presents the anesthesiologist with an array of challenges, all of which are not intuitively apparent. Specifically, such issues as management of coexisting physiologic perturbations of the oncology patient, heat conservation during the procedure, and readiness for a more extensive procedure would be readily anticipated by most clinicians. Description and reasonable management of problems ranging from mild or moderate postoperative thrombocytopenia to the so-called cryoshock syndrome with the possibility of severe postoperative coagulopathy, renal dysfunction, and pulmonary complications, however, could emerge only with the education of experience. The goal of this article is to address the key issues faced by anesthesiologists consulted in the perioperative care of patients undergoing hepatic cryotherapy.