دانلود رایگان مقاله ایجاد تسکین رفتاری پس از ضایعه ناحیه هیپوکامپ

ABSTRACT

When parts of the brain suffer from damage, certain functional deficits or impairments are the expected and typical outcome. Amyriad of examples show such negative consequences, which afford the daily tasks of neurologists, neuropsychologists, and also behavioral neuroscientists working with experimental brain lesions. Compared to lesion-induced deficits, examples for functional enhancements or facilitation after brain lesions are rather rare and usually not well studied. Here, the mammalian hippocampus seems to provide an exception, since substantial evidence shows that its damage can have facilitatory behavioral effects under certain conditions. This review will address these effects and their possible mechanisms. It will show that facilitatory effects of hippocampal lesions, although mostly studied in rats, can be found in many mammalian species, that is, they are apparently not species-specific. Furthermore, they can be found with various lesion techniques, from tissue ablation, to neurotoxic damage, and from damage of hippocampal structure itself to damage of fiber systems innervating it. The major emphasis of this review, however, lies on the behavioral effects and their interpretations. Thus, facilitatory effects can be found in several learning paradigms, especially active avoidance, and some forms of Pavlovian and instrumental conditioning. These will be discussed in light of pertinent theories of hippocampal function, such as inhibition, spatial cognition, and multiple memory systems theories, which state that facilitatory effects of hippocampal lesions may reflect the loss of interference between hippocampal spatial and striatal procedural cognition. Using the example of the rat sequential reaction time task, it will also be discussed how such lesions can have direct and indirect consequences on certain behavioral readouts. A final note will advocate considering possible functional facilitation also in neurologic patients, especially those with hippocampal damage, since such a strategy might provide new avenues for therapeutic treatments.

9. Final thoughts

on basic research and its possible clinical relevance The studies outlined above, which almost exclusively depend on experimental lesions in laboratory animals, show that hippocampal lesions can have facilitatory functional effects which depend on certain demands of a given task. The question remains whether it is possible that patients with damage of the hippocampus, despite being deficient in a number of cognitive tasks, may not only be normal, but even superior in some other aspects compared to controls. Which tests should be used to test such a hypothesis? Based on the current literature, a general recommendation could be that such tests should have only few or even no spatial, relational, and explicit requirements, whereas they should rely on procedural aspects, specific cues, and action/outcome relationships. Even if substantial evidence in favor of certain facilitatory effects will be found in patients, the major question will probably remain, namely how such knowledge can be used for the good of the patients. There is currently no answer to this question, but finding one will surely require intense cooperation between neuroscientists working in basic research and clinical practitioners.