It has been argued that targets within contralesional regions may not be detected in neglect due to competition from stimuli in the ipsilesional space being stronger. The balance of inter-hemisphere competition is off-set towards the non-damaged hemisphere and therefore the ipsilesional region of space (Harding & Riddoch; Kinsbourne, 1977; Polanowska et al., 2009; Sparing et al., 2009). It has been proposed that the activation of the damaged hemisphere through FES increases the weighting of contralesional space and this can result in an improvement in the detection and recognition of stimuli in the left hemispace (Harding and Riddoch, 2009).
It was predicted that if there was a sampling deficit present in neglect that limb stimulation treatment would reduce its extent. This prediction was based on previous research demonstrating that limb activation, due to increasing contralesional attention through activating the right parietal regions, improves scanning of the contralesional side of space (Eskes et al., 2003). Increased sampling of the left by SS was apparent in Session 3 for all the tasks (either demonstrated in the proportion of gazes and/or fixation time), although to a lesser extent in the letter cancellation task, partly due to there being an increase in eye movements made to the left in Session 2 of this task.
The treatment appeared to increase contralesional target identification in the star and line cancellation tasks. In the star cancellation task, increased sampling of the left after treatment resulted in more contralesional targets being identified in this session than previously. Thus, for the star cancellation task, the treatment not only aided sampling of the left region but also processing of information in the left region, which was shown to be deficient in the first two sessions. Additionally, inflated processing time on the left and hyper-attention to the right mitigated after treatment in the line cancellation task. These findings together suggest that limb stimulation may aid attention to, and processing of, contralesional information.
In contrast to performance in the star and line cancellation tasks, treatment did not affect contralesional TIA in the letter cancellation task. For this task, even though the sampling deficit was alleviated in Session 3, neglect remained to the same extent as in the previous sessions. It has been suggested that the effectiveness of treatment in ameliorating neglect depends upon the measures used to assess the extent of neglect recovery (Bowen & Lincoln, 2007; Bonato, 2012). Brown et al. (1999) also found that limb activation had an impact on performance in neglect in particular tasks. Fewer errors were made for reading
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words presented on the left of a sentence by the neglect patients during a limb activation condition compared to a neutral condition. However, limb activation did not improve detection of briefly presented contralesional stimuli or on contralesional saccadic eye movements. They concluded that limb activation improved performance on tasks that required voluntary eye movements to be made to the left but not for those tasks that required initiation of reflexive eye movements to be made. Therefore, voluntary eye movements may be improved by limb activation in neglect. However, as all of the tasks that were used in the present study required voluntary eye movements to be made into contralesional space, this cannot explain the differences found for the effectiveness of the treatment on performance for the different tasks. As the letter cancellation task was the most difficult task and neglect of contralesional targets during completion of this task in neglect persisted, it is likely that the factor that is moderating the effect of the treatment is related to task complexity, which has been discussed earlier in great detail.
It has been suggested that in order for FES treatment to have long term effects in neglect it would appear that cortical reorganisation of the damaged hemisphere is promoted (Polanowska et al., 2009; Rushton, 2003). It has, however, so far only been established that FES improves performance in neglect patients who are in their acute phase of stroke recovery (Eskes et al., 2003; Harding & Riddoch, 2009; Polanowska, 2009). The present study demonstrated that FES treatment can aid contralesional target identification in a chronic neglect patient, which means that some cortical reorganisation may still be enabled by FES treatment a year post-stroke.
It is important to note that the treatment effects of the present study cannot solely be related to the effect of FES. Due to the inclusion of iterative sessions of tracking a moving sphere within the contralesional field and the use of the robotic arm to support movements within that region of space, these factors could have also affected performance. It may be that SS was, albeit implicitly, trained to scan the contralesional side of space during the training trials where she was required to guide her affected arm within the contralesional regions of space. Therefore, any relief in the sampling deficit apparent in the initial sessions may not be a direct result of FES but also that of implicit scanning training. However, Polanowska et al. (2009) found that one-month of scanning training alone was far less effective in ameliorating neglect than the combination of this training alongside FES treatment. It may be that scanning training needs to be combined with other
treatments in order for any processing deficit of contralesional information to be alleviated so that increased sampling can improve contralesional target identification.
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Unfortunately no follow up assessment was obtained for patient SS. It would have been beneficial to determine whether the effects of the FES treatment on sampling and processing were maintained 3 and 6 months after the treatment was completed. This is required to assess the effectiveness of the treatment in mitigating neglect and determining whether this type of treatment affects the underlying causes of neglect and not just
symptomology (which may demonstrate improvement in the short term). Both scanning training and prismatic adaption have demonstrated mitigation of neglect after treatment but often neglect is present again on testing 3 or 6 months later. Follow up after FES requires further investigation to establish whether it targets the underlying causes of neglect. Harding and Riddoch’s (2009) study suggested that this was the case, as the patients whose neglect had mitigated after treatment was still diminished at 6 month follow up (Harding & Riddoch, 2009).
In summary, it seems as though the underlying deficits in neglect can be revealed by detailed inspection of measures of eye movements exhibited during cancellation tasks. It was clear that initially the neglect participant displayed a sampling deficit, not fixating the contralesional side less often or for less time as the ipsilesional regions. It was also apparent, though, that SS did sample the left side of the stimulus and, on some occasions, to the same extent as the control participants. Importantly, this did not always result in that information being processed, or there was an associated delay in processing contralesional targets before treatment was administered. The task demands also affected sampling and processing of contralesional information and moderated the effect of limb stimulation treatment on these factors. Given that many patients present with hemiplegia (and
therefore cannot move their affected arm), it would appear that FES, which enables passive movement of the arm, could be a clinically applicable tool, even in chronic cases of neglect, to aid sampling and processing of contralesional space during completion of simple tasks.
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