Herpes Simplex Encephalitis

Chapter 4 endnote 55, from How Emotions are Made: The Secret Life of the Brain by Lisa Feldman Barrett.
Some context is:

Consider the case of Roger, a fifty-six-year-old patient whose relevant circuitry was destroyed by a rare illness.

Herpes Simplex Encephalitis (HSE) is an extremely rare disease that infects only two people per million and mysteriously attacks only limbic tissue, leaving adjacent brain cells intact. Also, the hypothalamus and below remain intact. Roger’s damaged limbic tissue included all of his cortical limbic tissue and his amygdala (but not his hypothalamus and brainstem or Roger would be dead, suffering from “locked in syndrome”, or he wouldn’t remain conscious or in control of his body functions). The damaged regions were the regions that were originally believed to be part of the mythical "limbic system."

Overall, Roger can seem completely emotionally normal if you don’t know that he has extensive brain damage.

Several prominent scientists, including Antonio Damasio and the neuroscientist Bjorn Merker (who has written about the affectivity of children who are born without a cerebral cortex), have asserted that conscious feeling requires only circuitry in the brainstem, and that cortical regions are not required. This might explain why Roger and other similar patients with HSE are conscious and have affective feelings. The neuroscientist Bud Craig argues, however, that Roger (and patients like him) might have some intact limbic tissue in the ventral anterior insula, and presents an alternative view for the anterior insula as the brain basis of conscious feeling.

While it is tempting to hypothesize that the anterior insula or other cortical regions are unimportant for feeling (or are the locus of feeling), the idea of a single “source” of feeling is essentialism. If you instead consider feelings as arising from both predictions and incoming sensory input, then degeneracy is possible, and patients like Roger can be understood without essentializing.