The Electrical Basis of Consciousness

The posterior parietal cortex (PPC) is connected to the medial temporal lobe (MTL) is connected to the prefrontal cortex (PFC) all of which is goosed from below by the ascending reticular activating system (ARAS) rising up out of the brainstem. This crosstalking network keeps us alert and oriented. Per neuroscientists in Georgia and Tennessee, disruption of these circuits can take out IQ points in old folks and the seriously ill. Furthermore, if you happen to be both old and critically ill as in eligible for the ICU, the disruption of these connections takes delirium (temporarily out-to-lunch) and turns it into dementia (permanently out-to-lunch).

The matter with old gray matter is that it starts to dry up. The PPC, MTL, and the PFC all atrophy with age, leaving the ARAS in charge of activating increasingly balky connections. Pain medication, sedatives, and overwhelming systemic illness, however, cause the ARAS to falter. Once the critical threshold of normal functioning is passed, the very sick and the very old lose their tenuous hold on reality. Dr. Max Gunther and his colleagues theorize that this may be why delirium is common in the ICU.*

And I always thought it was the perpetual fluorescent lights, equipment alarms, and overhead pages that put patients over the ICU edge.
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*Gunther, ML et al. Medical Hypotheses Volume 69, Issue 6, 2007, Pages 1179-1182