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The chemosensory brain requires a distributed cellular mechanism to harness information and resolve conflicts – is consciousness the forum?

Behavioral and Brain Sciences; New York Vol. 39,  (2016). DOI:10.1017/S0140525X15002149

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It was previously argued (Merrick et al. 2014; Shepherd 2007) that olfaction is central to understanding consciousness. In the target article, Morsella et al. extend this framework and argue that consciousness “is for adaptive ‘voluntary’ action” (sect. 2.4, para. 1), including “action selection” and the integration of conflicting inputs. In addition, they assert that “olfaction provides the best portal for understanding the neural correlates of additions to the conscious field” (sect. 3.5, para. 9). Their account is very welcome; I suggest possible additions to their narrative that might strengthen their case.

That chemosensation, notably olfaction, is central to understanding brain function recognizes that the vertebrate brain has its evolutionary origins in a simple chemosensory epithelium (Nieuwenhuys et al. 1997). To this, one must add that a divergence occurred early in vertebrate evolution, with the olfactory/taste/vomeronasal systems becoming responsible for sensing external chemical stimuli (exteroception), whereas the limbic system (a derivative of the olfactory system) senses the internal milieu (Lathe 2001; Riss et al. 1969). This view (limbic enteroception) is supported by evidence that acquired responses can be guided by internal body states, which are abolished by hippocampal lesions, and by molecular evidence that the hippocampus is selectively adorned with receptors for hormones and metabolites (Lathe 2001). Therefore, if olfaction plays a central role in consciousness, so too must the limbic system (e.g., Behrendt 2013).

Regarding consciousness, we are undoubtedly “aware” of both external stimuli (tastes, smells) and internal stimuli (e.g., blood glucose and oxygen levels; see subsequent discussion). It should be noted that goal-oriented cravings of the hunger type are not restricted to calories (low blood glucose), and specific hungers can be driven by deficiencies in vitamins and specific minerals (Denton 1982). Other hippocampal inputs monitor other body states relevant to immunity and reproduction. However, exactly as for odors, perception of...