Activity of attention related structures in multiple sclerosis patients.

Aims: It was investigated whether the cortical activity during tasks requiring focused or divided attention is reduced in multiple sclerosis patients with prominent deficits (MS(+D)) and increased in patients without impairment (MS(-D)) in these specific attention functions.
Methods: Six MS(+D) patients with attention deficits, six unimpaired MS(-D) patients, and age-, gender-, and education-matched healthy control subjects were examined with functional magnetic resonance imaging (fMRI). The experimental paradigm consisted of visual tasks requiring focused or divided attention.
Results: Performance accuracy and reaction times were impaired in MS(+D) patients. This subgroup showed reduced activation within superior and inferior frontal gyrus during focused attention. Under conditions of divided attention decreased activity was found within middle and inferior frontal gyrus, inferior parietal structures, and occipital areas. No compensatory activity was observed. MS(-D) patients did neither differ in behavioral data nor in cortical activity in attention related structures from control subjects.
Conclusions: The study found evidence for the neural correlate of attentional deficits in MS patients. In patients with specific attention deficits, reduced cortical activity in prefrontal and parietal areas, which are associated with attention and executive control, reflects the patients' reduced performance on a behavioral level. Our findings also suggest impaired top-down attentional control on sensory structures in these patients. In patients without verifiable attention deficits a normal functioning of structures relevant for executive attention was observed. Compensatory activity in these structures as a marker of reorganization in less pronounced stages of the disease was not found.