Attention and Arousal Systems

Attention and arousal systems set the brain's overall level of activation and selectively prioritize behaviourally relevant information. Arousal reflects the global state of wakefulness and alertness maintained by ascending brainstem and hypothalamic systems, while attention is the set of mechanisms that select among competing inputs and guide processing toward goals.

Definition

Arousal is the global state of physiological and cortical activation underlying wakefulness and responsiveness, regulated by the ascending reticular and neuromodulatory systems; attention is the set of selective mechanisms by which the nervous system prioritizes some sources of information over others for further processing.

Scope

This entry covers the ascending arousal system that controls wakefulness, and the attention networks that select information, including the distinction between goal-directed and stimulus-driven attention. It is reference-educational and does not address the diagnosis or treatment of disorders of attention, arousal, or consciousness.

Core questions

• How is the global state of wakefulness and cortical activation generated and maintained?
• How does the brain select relevant information from competing inputs?
• How do goal-directed and stimulus-driven forms of attention differ in their neural substrates?
• How are attention and arousal related to each other?

Key concepts

• Ascending reticular activating system
• Wakefulness and cortical activation
• Goal-directed (top-down) attention
• Stimulus-driven (bottom-up) attention
• Dorsal and ventral attention networks
• Neuromodulatory arousal systems

Key theories

Two attention networks (dorsal and ventral)

Corbetta and Shulman proposed that attention is supported by a dorsal frontoparietal network mediating voluntary, goal-directed orienting and a more ventral, right-lateralized network that detects salient or unexpected stimuli and reorients attention.

Mechanisms

Arousal depends on ascending projections from the brainstem reticular formation and associated neuromodulatory nuclei to the thalamus and cortex; Moruzzi and Magoun showed that stimulating the brainstem reticular formation produces cortical activation of the kind seen in waking, defining the ascending reticular activating system. Hypothalamic circuits, summarized by Saper and colleagues, regulate the switch between wakefulness and sleep and impose circadian structure on arousal. Attention operates on this background state: Posner and Petersen outlined separable attentional functions, Knudsen organized attention into fundamental components such as working memory, competitive selection, top-down sensitivity control, and salience filtering, and Corbetta and Shulman distinguished a dorsal network for voluntary orienting from a ventral network for detecting salient events.

Clinical relevance

Disorders of arousal range from coma to disturbances of sleep and wakefulness, while disorders of attention include neglect after parietal damage and clinical inattention syndromes, so the normal organization of these systems is central to clinical neurology and psychiatry. This entry describes that normal organization for educational reference and is not a basis for diagnosing or treating any condition.

Evidence & guidelines

Understanding of arousal and attention rests on lesion and stimulation studies, electrophysiology, and human neuroimaging. The ascending arousal concept derives from Moruzzi and Magoun, hypothalamic sleep-wake control from work synthesized by Saper and colleagues, and the network architecture of attention from the frameworks of Posner and Petersen, Knudsen, and Corbetta and Shulman.

History

The modern understanding of arousal began with Moruzzi and Magoun's 1949 demonstration of the ascending reticular activating system. The cognitive neuroscience of attention developed from the 1980s onward, with Posner and Petersen's influential decomposition of attention into separable systems, and was extended by human neuroimaging into the dorsal and ventral network account of Corbetta and Shulman and the componential framework of Knudsen, while hypothalamic sleep-wake circuitry clarified the state-control side of arousal.

Key figures

• Giuseppe Moruzzi
• Horace Magoun
• Michael Posner
• Maurizio Corbetta
• Clifford Saper

Seminal works

• moruzzi-magoun-1949
• posner-petersen-1990
• corbetta-shulman-2002

Frequently asked questions

How do attention and arousal differ?

Arousal is the global level of wakefulness and cortical activation that sets the brain's overall responsiveness, whereas attention is the selective prioritization of particular information; attention operates against the background state established by arousal.

What is the difference between top-down and bottom-up attention?

Top-down (goal-directed) attention voluntarily directs processing toward task-relevant information and is associated with a dorsal frontoparietal network, while bottom-up (stimulus-driven) attention is captured by salient or unexpected events and is associated with a more ventral network, as described by Corbetta and Shulman.