Research gap at a glance
- Question: What are the multisynaptic routes by which organ signals pass through the nucleus of the solitary tract and parabrachial nucleus to cortex in humans, given that human data cover cortex well and animal data cover the body-to-brainstem stage well?
- Why it matters: Most theories in the wiki join rodent brainstem circuitry to human cortical findings by inference, so the middle of the interoceptive hierarchy is assumed rather than observed. Mapping it would constrain predictive accounts, neuromodulation targets such as vagal stimulation, and claims about where feelings are constituted.
- Theme: Anatomy and physiology
- Status: open
What the wiki already knows
- Berntson and Khalsa diagram an evidence asymmetry: human work characterises cortical and limbic levels, animal work details the body-to-brainstem stage, and neither covers the join; three of their four outstanding questions are versions of this (Berntson & Khalsa (2021)).
- The NIH review describes current human methods as a handful of mostly correlational approaches and nominates Microneurography as the one recent addition offering objectivity (Chen et al. (2021), Interoceptive taxonomy (Farb et al. Box 1)).
- Reviews quote rodent circuit work alongside human patient findings and mix species in functional claims (Bonaz et al. (2021), Quigley et al. (2021)).
- Mouse insular cortex shifts its hunger and thirst activity in anticipation of expected satiety, the only manipulable-animal evidence for anticipatory interoceptive representation in the wiki (Berntson & Khalsa (2021), inferential?).
What would answer it
- Pair human methods that can reach the brainstem (high-field brainstem fMRI during controlled visceral stimulation, with Microneurography recording the afferent input) with homologous rodent experiments using the same stimuli, so that responses in the nucleus of the solitary tract and parabrachial nucleus can be traced to insular and cingulate cortex in both species.
Connections
- Raised on: Berntson & Khalsa (2021), Chen et al. (2021)
- Related concepts: Central autonomic network, Lamina I spinothalamocortical pathway, Insular cortex, Interoceptive sensors
- Related debates: inferential?, Can we know whether other animals have conscious feelings?
Berntson and Khalsa (2021) supply the wiki’s anatomical floor plan and, with it, a clear statement of what is not known: the multisynaptic organ-to-cortex maps, the relay from brainstem to cortex in humans, how signals with different time courses are integrated, and what determines whether any of it reaches awareness. Their central figure is not a brain but a table of evidence: the two halves of the hierarchy are known in different species, and the middle is inferred.
The wiki has met the consequences piecemeal. Bonaz et al. build a clinical neuraxis argument in which rodent and human data sit in the same paragraph, Quigley et al. mix species in functional claims, and the strongest animal evidence for anticipatory interoceptive coding (mouse insula) cannot be checked against a human brainstem-to-insula pathway because that pathway has not been mapped in humans.
The question also touches Can we know whether other animals have conscious feelings?. Berntson and Khalsa note there are currently no animal models of interoceptive awareness, and Craig argued that the direct lamina I to insula route exists only in primates (Craig (2002)). Both arguments compare species at levels where one species is well mapped and the other is not, which is the same missing join.