Amygdala
Referenced across the wiki long before it had a page. Three of this wiki’s sources characterize it incompatibly, which makes it a useful place to see locationist-vs-constructionist-brain-emotion play out on one structure.
Three readings
1. Fear centre (locationism). The canonical mapping fear → amygdala, inherited from the basic-emotions tradition and the fear-conditioning literature. This is the target Lindquist et al. (2012) set out to test — and it is not a position LeDoux endorses, despite his identification with amygdala fear research.
2. Salience detector (constructionism). Lindquist et al.’s meta-analysis found the amygdala functionally selective for fear perception (and disgust experience) but not functionally specific — it responds comparably to novel, uncertain, arousing, or salient stimuli of any valence. Reframed as a domain-general salience detector and folded into the core affect network. See also salience-network, where the amygdala is a node of the AIC/ACC-anchored network.
3. Nucleus-specific survival circuit component (LeDoux). LeDoux (2012) rejects “the amygdala” as an explanatory unit at all. The relevant objects are nuclei within specific circuits, and they differ by trigger modality and by learned vs. innate status. See survival-circuits, pavlovian-defense-conditioning.
The nucleus-level anatomy (LeDoux 2012, Figure 1)
| Pathway | Route |
|---|---|
| Unconditioned olfactory threat | vomeronasal → MEA → VMH → PMH → dorsal PAG |
| Unconditioned non-olfactory threat | sensory → LA → ABA → VMH-PM-PAG |
| Conditioned threat (any modality) | sensory → LA → (direct, and via BA/ABA/ITC) → CEA → medial CEA → ventrolateral PAG → freezing |
Different subnuclei of MEA, PMH, and PAGd handle conspecific vs. predatory threat. Damage to PAGvl disrupts freezing while PAGdl lesions enhance it, implying interaction between the regions. Homologous circuitry is reported in rabbits, nonhuman primates, reptiles, and birds; human imaging and lesion work supports an amygdala role in defense conditioning “at least to a first approximation,” though at resolution that “obscures circuit details.”
Appetitive functions, and the argument they support
The amygdala is not defense-only: LA/BA/ABA process learned food cues and relay to lateral hypothalamus, where sufficiently potent cues stimulate eating even in sated animals. CEA outputs suppress feeding to an aversive CS; MEA threat-odor areas suppress reproduction via VMH.
LeDoux uses this to make a methodological point aimed squarely at reading (2): that the amygdala serves both appetitive and aversive functions does not mean it processes them alike. Primate unit recordings show appetitive and aversive signals handled by distinct neuronal populations in lateral/basal amygdala (Paton et al. 2006; Belova et al. 2007, 2008; Morrison & Salzman 2010), and molecular imaging shows area-level activation similarity concealing microcircuit-level difference (Lin et al. 2011). His charge is that fMRI-based claims of shared mechanism — Lindquist’s and Barrett’s — outrun the resolution of the method.
This is the sharpest live methodological disagreement in the wiki’s emotion-anatomy material: selectivity-without-specificity at the voxel level (Lindquist) vs. specificity at the cellular level invisible to voxels (LeDoux). Both are consistent with the imaging data. They differ on what imaging data can license.
Route to arousal and the body
Central amygdala outputs drive the brain-wide neuromodulator systems and, peripherally, the sympathetic ANS (adrenal medulla) and the hpa-axis (cortisol) — the mechanism by which a detected threat becomes a whole-body global organismic state rather than a local response.