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When Fear Is Near: Threat Imminence Elicits Prefrontal-Periaqueductal Gray Shifts in Humans

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When Fear Is Near: Threat Imminence Elicits Prefrontal-Periaqueductal Gray Shifts in Humans

Type: paper Slug: when-fear-is-near-threat-imminence-elicits-prefrontal—hassabis Sources: when-fear-is-near-threat-imminence-elicits-prefrontal—hassabis Last updated: 2026-05-13

Summary

Mobbs et al. (2007) used an active-avoidance virtual-predator paradigm with fMRI to show that as threat proximity increases in humans, brain activity shifts from ventromedial prefrontal cortex (vmPFC) to the periaqueductal gray (PAG). This forebrain-to-midbrain shift mirrors the “predatory imminence continuum” from rodent defensive-systems models and has implications for understanding anxiety and panic disorder pathophysiology. Hassabis contributed as a co-author at UCL Wellcome Trust Centre for Neuroimaging.

Core content

Research question: Does the human brain exhibit a distal-to-proximal threat shift from prefrontal cortex to midbrain PAG, as predicted by animal defensive-systems models?

Method: 14 healthy subjects navigated a 2D maze while being pursued by a virtual predator (AI) that could capture and deliver pain (high: 3 shocks; low: 1 shock). High-resolution fMRI measured BOLD responses during cue phase (threat detection) and chase phase (active avoidance). Parametric regression between predator distance and BOLD signal tested the imminence hypothesis.

Key findings:

  • Threat detection (cue phase) activated rostral ACC, medial OFC, ventral ACC, and vmPFC (paper—when-fear-is-near-threat-imminence-elicits-prefrontal §2).
  • Distal threat during chase activated vmPFC/subgenual ACC; proximal threat activated PAG (paper—when-fear-is-near-threat-imminence-elicits-prefrontal §3).
  • PAG activity correlated with increased subjective dread and decreased confidence of escape (paper—when-fear-is-near-threat-imminence-elicits-prefrontal §4).
  • High-pain predator elicited longer avoidance times and faster movement than low-pain predator (paper—when-fear-is-near-threat-imminence-elicits-prefrontal §2).
  • Basolateral amygdala (BLA) was preferentially activated during distal threat; central nucleus/BNST during proximal threat (paper—when-fear-is-near-threat-imminence-elicits-prefrontal §4).

Significance: First demonstration in humans of the forebrain-to-midbrain defensive shift predicted by rodent models. Suggests panic and chronic anxiety may involve abnormal PAG-vmPFC balance — patients show decreased vmPFC but increased midbrain gray matter.

Connections- Theme: theme—hippocampal-construction — extends the UCL group’s work on neural circuitry supporting adaptive behaviour

  • Collaborators: Raymond Dolan (senior author context), Christopher Frith
  • Era: phd-period — conducted during Hassabis’s PhD at UCL
  • Venue: venue—Science

Honest Gaps

  • Hassabis’s specific intellectual contribution is unclear from the text — he appears in the author list and affiliation block but the paper does not delineate individual contributions.
  • The PDF extraction included a second unrelated paper (on pyruvate carboxylase) interleaved in pages 2–3 due to a scanning artefact — analysis is based only on the Mobbs et al. content.

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