Retrieval of recently acquired declarative memories depends on the hippocampus, but with time, retrieval is increasingly sustainable by neocortical representations alone. This process has been conceptualized as system-level consolidation. Using functional magnetic resonance imaging, we assessed over the course of three months how consolidation affects the neural correlates of memory retrieval. The duration of slow-wave sleep during a nap͞rest period after the initial study session and before the first scan session on day 1 correlated positively with recognition memory performance for items studied before the nap and negatively with hippocampal activity associated with correct confident recognition. Over the course of the entire study, hippocampal activity for correct confident recognition continued to decrease, whereas activity in a ventral medial prefrontal region increased. These findings, together with data obtained in rodents, may prompt a revision of classical consolidation theory, incorporating a transfer of putative linking nodes from hippocampal to prelimbic prefrontal areas.hippocampus ͉ retrograde amnesia ͉ sleep ͉ ventral medial prefrontal cortex ͉ recognition W e are able to recall memories from the remote past, suggesting a high-capacity system for long-term storage of declarative memories. Lesion studies suggest that declarative memory retrieval initially depends on the hippocampus, although, with time, stored information becomes reorganized in a way that makes retrieval gradually less dependent on the hippocampus (1-3). This pattern of findings has been conceptualized as system-level consolidation, a mnemonic process that leads to a shift from the hippocampus toward distributed neocortical traces (4-8). Although memory consolidation is a fundamental mnemonic operation, its neural correlates at the human brain-system level are not well understood. In particular, it is unknown whether the hippocampus participates under normal circumstances in remote memory retrieval or whether other brain regions take over putative linking nodes created initially in the hippocampus where they are used for recent memory retrieval.Sleep, in particular slow-wave sleep, appears to play a role in declarative memory consolidation in humans (9-15; but see ref.16). Moreover, animal studies have shown that during sleep, hippocampal and neocortical cell-assemblies reflecting recent events exhibit spontaneous coordinated reactivation (17)(18)(19)(20), that, thereby, may strengthen and͞or refine neocortical assemblies so that they can be used for retrieval without hippocampal engagement.The time course of declarative memory consolidation in humans is poorly defined. Estimates reach up to several decades, based on retrospective lesion and functional neuroimaging studies (1, 21). When investigated on a shorter time scale, prospective studies in rodents and nonhuman primates have revealed upperbound estimates of a few weeks (22-25); however, it remains to be determined whether these findings are related to a similar set of process...
Although the value of high-density surface electromyography (sEMG) has already been proven in fundamental research and for specific diagnostic questions, there is as yet no broad clinical application. This is partly due to limitations of construction principles and application techniques of conventional electrode array systems. We developed a thin, highly flexible, two-dimensional multielectrode sEMG grid, which is manufactured by using flexprint techniques. The material used as electrode carrier (Polyimid, 50 microm thick) allows grids to be cut out in any required shape or size. One universal grid version can therefore be used for many applications, thereby reducing costs. The reusable electrode grid is attached to the skin by using specially prepared double-sided adhesive tape, which allows the selective application of conductive cream only directly below the detection surfaces. To explore the practical possibilities, this technique was applied in single motor unit analysis of the facial musculature. The high mechanical flexibility allowed the electrode grid to follow the skin surface even in areas with very uneven contours, resulting in good electrical connections in the whole recording area. The silverchloride surfaces of the electrodes and their low electrode-to-skin impedances guaranteed high baseline stability and a low signal noise level. The electrode-to-skin attachment proved to withstand saliva and great tensile forces due to mimic contractions. The inexpensive, universally adaptable and minimally obstructive sensor allows the principal advantages of high-density sEMG to be extended to all skeletal muscles accessible from the skin surface and may lay the foundation for more broad clinical application of this noninvasive, two-dimensional sEMG technique.
An electromyography (EMG) system is presented that noninvasively records the electrical activity of a muscle with 126 densely spaced skin-surface electrodes. The electrodes are arranged in a two-dimensional array and integrated in a single container for ease of application. Signals are recorded “monopolarly”, with a reference electrode placed at a distance from the array. With this recording configuration, the surface EMG (sEMG) potential distribution can be described not only as a function of time, but also topographically. The availability of topographical information opens up a range of applications. Some of these have been described previously. However, the system presented is unique in that it allows exploration of all clinical and scientific possibilities of topographical sEMG. In its design, special attention was paid to user-friendliness and flexibility. With high-density multichannel sEMG, both the properties of a whole muscle and those of single motor units, the functional units of a muscle, can be studied. The latter belong to a realm that was long considered accessible only with needle-EMG, a conventional, invasive diagnostic technique. It is demonstrated that the additional topographical information can be used to characterize motor units in a way that is partially superior to needle EMG.
BTA is significantly more effective in the treatment of ICD, with less adverse effects.
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