In3 pigeons ablation of the posterodorsolateral neostriatum impaired delayed alternation without affecting visual discrimination. In mammals the same selective deficit is produced by lesions in the prefrontal system. The presently ablated neostriatal region resembles the mammalian prefrontal cortex also by being richly innervated with dopaminergic fibers. This region is clearly separated from paleostriatum augmentatum and archistriatum which also have a strong dopaminergic innervation. The presence of a prefrontal cortex-like formation in a bird species raises the possibility that all higher vertebrates are equipped with this neural device.
A new method for monitoring neuromuscular function based on measurement of acceleration is presented. The rationale behind the method is Newton's second law, stating that the acceleration is directly proportional to the force. For measurement of acceleration, a piezo-electric ceramic wafer was used. When this piezo electrode was fixed to the thumb, an electrical signal proportional to the acceleration was produced whenever the thumb moved in response to nerve stimulation. The electrical signal was registered and analysed in a Myograph 2000 neuromuscular transmission monitor. In 35 patients anaesthetized with halothane, train-of-four ratios measured with the accelerometer (ACT-TOF) were compared with simultaneous mechanical train-of-four ratios (FDT-TOF). Control ACT-TOF ratios were significantly higher than control FDT-TOF ratios: 116 +/- 12 and 98 +/- 4 (mean +/- s.d.), respectively. In five patients not given any relaxant during the anaesthetic procedure (20-60 min), both responses were remarkably constant. In 30 patients given vecuronium, a close linear relationship was found during recovery between ACT-TOF and FDT-TOF ratios. It is concluded that the method fulfils the basic requirements for a simple and reliable clinical monitoring tool.
Studies addressing cerebral functional localization face methodological and theoretical problems. Lesion experiments expect that when a functionally specialized structure is missing, its function can be deduced from the resulting impairments. Mostly, however, initial impairments are partially or fully eliminated through functional recovery. Apparently, such a recovery contradicts the notion of functional localization. In order to understand the mechanisms of recovery, improved methodology and a new theoretical framework are required. Insights into the mechanisms of recovery can be achieved by using ''challenge'' techniques, where functionally recovered individuals are exposed to organic and behavioral challenges, e.g. pharmacological manipulations or additional lesions, as well as modified test situations. Using such methods, a number of principles of functional recovery have emerged. We evaluate some of the available theories of post-traumatic recovery against these principles and find that none of them can account for the principles.
In the search for a neural substrate of cognitive processes, a frequently utilized method is the scrutiny of post-traumatic symptoms exhibited by individuals suffering focal injury to the brain. For instance, the presence or absence of conscious awareness within a particular domain may, combined with knowledge of which regions of the brain have been injured, provide important data in the search for neural correlates of consciousness. Like all studies addressing the consequences of brain injury, however, such research has to face the fact that in most cases, post-traumatic impairments are accompanied by a “functional recovery” during which symptoms are reduced or eliminated. The apparent contradiction between localization and recovery, respectively, of functions constitutes a problem to almost all aspects of cognitive neuroscience. Several lines of investigation indicate that although the brain remains highly plastic throughout life, the post-traumatic plasticity does not recreate a copy of the neural mechanisms lost to injury. Instead, the uninjured parts of the brain are functionally reorganized in a manner which – in spite of not recreating the basic information processing lost to injury – is able to allow a more or less complete return of the surface phenomena (including manifestations of consciousness) originally impaired by the trauma. A novel model [the Reorganization of Elementary Functions-model] of these processes is presented – and some of its implications discussed relative to studies of the neural substrates of cognition and consciousness.
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