Their analyses of connectivity, developed from examining correlations of blood oxygen levels between various brain regions in resting-state fMRI scans, show that the brain in delirium patients has disrupted connectivity between the dorsal lateral prefrontal cortex and the posterior cingulate cortex. The authors suggest that the persistence of this physiological disruption beyond the resolution of acute delirious symptoms accounts for patients' problems in attentiveness that often outlast their acute hospitalization. A disruption of the connectivity of key subcortical regions, such as the intralaminar thalamus, from brainstem and midbrain nuclei was also observed. The disrupted connectivity includes the mesencephalic tegmentum, which relays brainstem reticular activation, the midbrain nucleus basalis, the source of cholinergic innervation, and the midbrain ventral tegmental area, the source of dopaminergic innervation. Unlike the cortical connections, these subcortical connections recover more quickly, perhaps because they reflect the transient effects of the anticholinergic drugs from anesthesia and the antidopaminergic drugs used for acute behavioral control. The resolution of connectivity between the mesencephalic tegmentum and the thalamus may account for the early restoration of alertness, although higher brain neocortical functions remain altered. Strengths of this study include the scanning of patients both during the acute episode and after its resolution; weaknesses include the a priori assumption about the role of the posterior cingulate cortex and the modest sample size. The patients' use of medication also confounds results but is clinically unavoidable.