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PubMed1998

Neural correlates of attention and arousal: insights from electrophysiology, functional neuroimaging and psychopharmacology.

Attention and arousal are multi-dimensional psychological processes, which interact closely with one another. The neural substrates of attention, as well as the interaction between arousal and attention, are discussed in this review. After a brief discussion of psychological and neuropsychological theories of attention, event-related potential correlates of attention are discussed. Essentially, attention acts to modulate stimulus-induced electrical potentials (N100/P100, P300, N400), rather than generating any unique potentials of its own. Functional neuroimaging studies of attentional orienting, selective attention, divided attention and sustained attention (and its inter-dependence on underlying levels of arousal) are then reviewed. A distinction is drawn between the brain areas which are crucially involved in the top-down modulation of attention (the 'sources' of attention) and those sensory-association areas whose activity is modulated by attention (the 'sites' of attentional expression). Frontal and parietal (usually right-lateralised) cortices and thalamus are most often associated with the source of attentional modulation. Also, the use of functional neuroimaging to test explicit hypotheses about psychological theories of attention is emphasised. These experimental paradigms form the basis for a 'new generation' of functional imaging studies which exploit the dynamic aspect of imaging and demonstrate how it can be used as more than just a 'brain mapping' device. Finally, a review of psychopharmacological studies in healthy human volunteers outlines the contributions of the noradrenergic, cholinergic and dopaminergic neurotransmitter systems to the neurochemical modulation of human attention and arousal. While, noradrenergic and cholinergic systems are involved in 'low-level' aspects of attention (e.g. attentional orienting), the dopaminergic system is associated with more 'executive' aspects of attention such as attentional set-shifting or working memory.

Animals↗
PubMed2003

Spatial attention: normal processes and their breakdown.

Although "attention" is a general term in everyday folk and psychologic use, using research from cognitive psychology allows a focus on the processes associated with attention. A process-oriented definition of attention [2] makes "attention" a concept that can be studied rigorously. Attention is necessary for eliminating unwanted sensory inputs or irrelevant behavioral tasks and is useful when some cognitive system or process receives too many inputs. Attention acts to restrict the number of inputs and allow processing to continue in an effective manner. Although there are many forms of attentional selection, spatial attention is the most studied and perhaps the best understood form of selection. Spatial attention is the variety of attention most widely studied in neuropsychologic populations. As was evident from the authors' review, different neuropsychologic syndromes can be characterized as involving different difficulties with the component processes of spatial attention. Different neural structures work in concert to produce normal spatial selection, and damage to any of these neural structures, including the parietal and frontal lobes, pulvinar, and superior colliculus, produce an attentional impairment. Attentional impairments often have been studied in cases of focal brain damage resulting from stroke, traumatic brain injury, tumor, and surgical resection. Focal or multifocal lesions caused by neurodegenerative impairments, such as PSP and AD, however, also have marked effects on neural processes of attention. Patients with AD exhibit a range of impairments in spatial attention, and these impairments have been studied relatively little. Despite the understanding of attention provided by various patient populations, gaps remain in knowledge of the mechanisms involved in attending to space. For example, most studies of neurologic patients have used a simple spatial cuing paradigm with highly predictive cues. Although this task yields robust results and can be adapted for use with many different patient groups, the spatial cuing effects produced by such tasks have multiple interpretations (e.g., allocation of resources versus reduction of decision noise). This review highlights the general point that different neural sites seem to be responsible for different forms of attentional control, such as object-based attention, attentional task switching, and the executive control of attention [8.33]. Understanding the integration of these neural sites and their relationship to cognitive processes and, ultimately, behavior, will increase understanding of normal and disordered attentional selection.

Alzheimer Disease↗
PubMed1996

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.

Adult↗