Insular cortex

The cortical home of interoception and the anatomical spine running through nearly every study in this wiki. Craig’s two papers (2002, 2009) established its organization; Seth, Critchley, and Damasio all build on it. See ad-craig.

The posterior→mid→anterior gradient

• Dorsal posterior insula — the primary interoceptive cortex: the topographic terminus of the lamina-i-spinothalamocortical-pathway (via VMpo/VMb). Objective bodily state (e.g., graded cooling) maps here linearly. Distinct from the parietal somatosensory cortices (S1/S2) — a neural separation of interoception from exteroception.
• Mid-insula — integrates the primary interoceptive image with emotionally salient environmental, multisensory, and hedonic input (amygdala, nucleus accumbens; see salience-network). Associated with body ownership/agency (e.g., rubber-hand-illusion activation).
• Anterior insular cortex (AIC) — the re-representation: subjective feeling (“how you feel”) rather than objective state. In humans this is lateralized (see asymmetry below) and is proposed as the seat of embodied-selfhood and, per Craig 2009, of awareness itself (the global-emotional-moment).

Limbic sensory cortex

Craig casts the insula as limbic sensory cortex (feeling) paired with the anterior-cingulate-cortex as limbic motor cortex (motivation/agency): insula + ACC = an emotion. The two are co-activated in nearly all emotion studies and interconnected by von-economo-neurons.

Human specificity

The AIC re-representation extends only to the middle of the insula in macaques but to the anterior limit in humans — Craig argues the human AIC “has no equivalent in the monkey.” Its expansion (and its VEN content) is proposed to underlie uniquely human self-awareness.

Forebrain emotional asymmetry (Craig 2009, Box 3)

Craig proposes the two AICs are functionally asymmetric, tied to autonomic opponency:

• Right AIC ↔ sympathetic / energy-expenditure / arousal / withdrawal (aversive) / individual-survival emotions (e.g., pain, anger, anxiety).
• Left AIC ↔ parasympathetic / energy-nourishment / relaxation / approach (appetitive) / affiliative emotions (e.g., maternal & romantic love, joy, smiling, pleasant music).

He grounds this in the asymmetric autonomic innervation of the heart and brain energy-optimization. It is a distinctive but contested claim (a hypothesis awaiting split-brain and direct-comparison tests), recorded here rather than given its own page.

The predictive fault line

Craig’s insular hierarchy is ascending re-representation with a comparator at the top (AIC). Seth (2013) adopts the same anatomy but reinterprets its computation as top-down predictive inference (predictions descend, prediction errors ascend). That is the core of feedforward-vs-predictive-interoception.