FOS and delirium: As studies have shown that delirium is associated with changes in neuronal activity patterns of the hippocampus [36,37] and that the severity and duration of aberrant neuronal activation are closely related to the outcome of the condition [38], brain samples from 48 HPT mice were subjected to immunochemical staining for c-Fos (a high-resolution marker for neural activity), NeuN (a neuronal marker), and Iba1.