Non-spatial attention disorders in patients with frontal or posterior brain damage

The few studies that have looked at attention in patients with brain damage suggest a prominent role for the frontal lobe in nonspatial attentional control. However, the studies usually focus on one variety of attention and do not address the nature of the alteration of attention. In addition, the behavioural consequences of nonspatial attentional deficit remain unknown. The aim of this study was to evaluate the role of focal brain damage on divided and focused attention and the relationship between attention disorders and behavioural changes. The study group consisted of patients with lesions of the prefrontal and posterior cortices and control subjects. The assessment of attention used reaction time tests that evaluated the ability to divide attention between two sources (detection tests) and to focus attention on one source (Go/No-Go Tests). The response retardation of the 'frontal' group became more pronounced as the number of sources to be monitored increased, suggesting the presence of a deficit of divided attention. Focused attention deficit was demonstrated in the 'frontal' group by the more frequent responses to irrelevant stimuli on Go/No-Go Tests. Both focused and divided attention deficits were prominent when the lesion included the left dorsolateral prefrontal cortex and the caudate nucleus. Selective deficit of divided or focused attention was shown in a few patients. Finally, the clinically assessed distractibility was related to disorders of divided and focused attention. This study provides additional evidence for the prominent role of the frontal lobe in nonspatial attention regulation and shows that it also operates in elementary perceptuomotor processes. The relationship between distractibility and attention indexes supports the idea that attention disorders may have a functional counterpart that is clinically assessable. The demonstration of selective deficit of divided or focused attention suggests that nonspatial attention depends upon different mechanisms and that it is not an undifferentiated general purpose mechanism. Further studies addressing the nature of the interactions between attentional mechanisms and other cognitive processes are required.