Asked by Dr. Who
Changes in subjective sleepiness were shown to closely parallel changes in blood ammonia levels in both healthy volunteers and patients with cirrhosis in a study of induced hyperammonemia.
Hyperammonemia and sleepiness were also associated with changes in both the scalp distribution (spreading over the posterior–anterior axis) and the frequency (slowing) of the wake EEG. Slowing of the background alpha rhythm (9 to 8–8.5 Hz) and an increase in its amplitude along the posterior–anterior axis (anteriorization) are two of the neurophysiological characteristics of the transition from wake-to-sleep.
There are also behavioral similarities between the wake–sleep transition and Hepatic Encephalopathy (HE), which is characterized by sleepiness/lethargy, and diminished reactivity to external stimuli. All these characteristics seem to place HE at the very border between wakefulness and sleep.
Reference: Montagnese S, Turco M, Amodio P. Hepatic encephalopathy and sleepiness: an interesting connection? J Clin Exp Hepatol. 2015 Mar;5(Suppl 1):S49-53. doi: 10.1016/j.jceh.2014.06.006. Epub 2014 Jun 29. PMID: 26041958; PMCID: PMC4442851.
