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New research from Germany shows that the subcortex of the brain affects selective visual attention. The discovery comes from a study by Fimm et al of 15 patients (10 with bleeding: five right sided and five left and five with infarction: three right and two left) with enclosed lesions exclusively in the subcortex, as determined by CT scanning on referral and confirmed by MRI 14–28 days after clinical onset.
Patients' performance in two computerised tests of visual attention—a searching and a detection test—compared with that of 200 controls against whom the tests had been standardised showed clear differences between those with right sided and those with left sided lesions. Most patients (seven of eight) with right sided lesions were much slower or missed the target more often when scanning across a 5×5 matrix of squares when the target was in one of the left columns. However, their performance was as good as that of the controls in the test of visual hemineglect in detecting dots presented simultaneously in the left and right visual hemispace. Only two of seven patients with left sided lesions showed impairment in the searching or detection test.
The results confirm right brain dominance for spatial attention. This extends to the subcortex, independent of the cortex, and in these patients involves lesions in the basal ganglia, internal capsule, and thalamus—particularly the putamen and posterior limb of the internal capsule.