ASYMMETRY OF SELECTIVE ATTENTION IN HEALTHY SUBJECTS AND PATIENTS WITH CERVICAL FOCAL DYSTONIA

The environment continuously provides a wealth of information through our senses. This poses a major challenge to our brains to effectively process the relevant pieces of information over space and time, involving attentional processes. Attention selects, modulates and sustains focus on information most relevant for behaviour going beyond our limited capacity to process competing options. Voluntary allocation of attention to features, objects, or regions in space is controlled by top-down mechanisms. On the other hand, salient stimuli can automatically attract attention, even though the subject does not have intentions to attend to these stimuli. A key question is how attention is shaped by the presence of objects, in particular with respect to object exposure time. In healthy subjects, it is well known that the spatial features of objects influence attention processes. It has been shown that visuospatial attention is asymmetrically distributed with a systematic bias towards the left visual field. In contrast, there seems to be a rightward bias for audiospatial attention, yet this notion is controversial. In patients with idiopathic focal dystonia, processing of spatial and temporal information has been shown to be impaired, but it remains unclear how much impaired sensory processing is linked to abnormal biases in spatial attention. This thesis explored the role of selective attention in healthy subjects and dystonic patients employing novel paradigms which require shifts of spatial and temporal processing in response to visual and auditory cues. The results obtained in healthy subjects showed a rightward bias for auditory attention. Together with the evidence of a leftward bias for visuospatial attention, the results support the idea of modality-specific auditory and visual attentional systems. Furthermore, the experiments provided evidence that temporal attention may be spatially driven, again, expressing a leftward bias for the visual modality and a rightward bias for the auditory modality. In contrast to healthy individuals, patients with idiopathic cervical dystonia and prominent torticollis displayed a consistent leftward bias for visual stimuli. This was also the case in patients in whom dystonia was worse on the right side of the body. This abnormal leftward attentional bias in dystonic patients with torticollis indicates an aberrant hemispheric lateralization of the visuospatial attentional system in idiopathic cervical dystonia. Finally, attentional processes were influenced by the “phenotype” of idiopathic cervical dystonia. We found a double dissociation in the performance between patients presenting with laterocollis or torticollis. The laterocollis sub-group showed a significant alteration of auditory processing, whereas temporal processing was impaired in the torticollis sub-group. In conclusion, this work suggests that differences in deployment of auditory attention are related to individual differences in visuospatial attentional processing. Moreover, it is especially important to design rehabilitation treatment for individuals who have sustained damage to portions of the parietal-basal ganglia-cerebellum network and may be suffering from various attentional disorders.