The third problem is vital and perhaps the most complex. Attention has been suggested as a mediator of conscious states. Focusing of attention has been shown to increase neuronal firing, increase cerebral blood flow, and elicit gamma-oscillatory responses.3,10 Lesions in the medial reticular formation, nucleus reticularis of the thalamus, superior colliculus, intralaminar complex, and parietal lobes have all been associated with decreased attentional responses to external stimuli. Decreased attention is among the symptoms of many neurological disorders of consciousness, including blindsight, neglect, prosopagnosia, pure alexia, and optic aphasia.3 Lesions in many of these cases lead to only a partial loss of consciousness and are thus qualitatively different from lesions associated with comatose states. The existence of a gradient suggests that consciousness is a state regulated by specific neuronal processes rather than an epiphenomenon of coordinated brain activity.