Arousal (responsiveness to stimuli) is required for attention, but the ability to focus and sustain attention may be impaired with normal immediate responsiveness to stimuli. The most anterior part of the frontal cortex is called prefrontal cortex. The cortex deep in the fissure between the cerebral hemispheres, just superior to the band of white matter that connects the hemispheres, is called the cingulate cortex. These areas are important for the ability to focus and sustain attention, but many other cortical and subcortical areas also play a role. Dysfunction of these structures may cause impaired attention, which can be tested by tasks such as serial arithmetic problems or spelling words forward and backward.
Parietal association cortices on the nondominant side also play a role in attention to the contralateral body and environment. Nondominant parietal cortical dysfunction may cause hemineglect, where there is less responsiveness to visual, auditory, or somatosensory stimuli on the contralateral side. Severe hemineglect is usually obvious, but mild hemineglect may only be detected by presenting bilateral simultaneous stimuli, which are then not perceived on the neglected side; this is called extinction. Dominant parietal cortical dysfunction rarely causes hemineglect.
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Introduction to Neurology 