Depression as Episodic Dimensionality Collapse: The Hippocampal Substrate of Temporal Richness

This manuscript (December 2025) presents Depression as Episodic Dimensionality Collapse: The Hippocampal Substrate of Temporal Richness, a focused application of the Constraint Dynamics framework to major depressive disorder (MDD), with particular emphasis on the stress/inflammatory subtype (estimated 50–70% of cases). Constraint Dynamics models conscious experience as the active maintenance of three fundamental physical constraints under finite metabolic budgets: Λ (Lattice): Spatial coherence and navigable experiential structure (extended here to Λₑₚᵢₛₒdᵢc, governing temporal richness and episodic navigation) Γ (Strobe): Fast temporal binding and perceptual coherence within moments (largely preserved in depression) Θ (Anchor): Energetic and somatic grounding (secondarily dysregulated as a downstream consequence) The core thesis is that depression involves a progressive collapse of episodic dimensionality across past (overgeneral autobiographical memory), present (impaired scene construction), and future (prospection deficits). These capacities depend on shared hippocampal substrates—including dentate gyrus neurogenesis and CA1–CA3 pattern separation/completion—which are selectively vulnerable to chronic stress and inflammatory load. Damage to this substrate produces a state of phenomenological flattening without psychotic disorganization: a coherent but dimensionally impoverished experiential world (“coherent flatland”). Key contributions of the manuscript include: A principled distinction between fast perceptual binding failures (Γ collapse, characteristic of psychosis) and extended episodic navigation failures (Λₑₚᵢₛₒdᵢc collapse, characteristic of depression) A five-stage cascade model identifying a weeks-to-months intervention window prior to full phenomenological collapse A cross-disorder comparison framing depression and psychosis as distinct constraint vulnerabilities, rather than points on a single severity axis Testable predictions, including: episodic richness decline precedes mood relapse structural hippocampal recovery precedes subjective and affective improvement This manuscript builds on the phenomenological foundations introduced in The Geometry of Feeling (v6.0) and serves as a direct precursor to the fully developed, thermodynamically grounded framework presented in The Outlines of Sanity: A Constraint Dynamics Theory of Consciousness and Mental Illness (v10.0, January 2026). It is archived here for transparency, intellectual priority, and open access. Readers seeking the mature and consolidated formulation should consult: The Outlines of Sanity (v10.0)Zenodo DOI: https://doi.org/10.5281/zenodo.18204346Keywords: major depressive disorder, hippocampus, episodic memory, prospection, constraint dynamics, dimensional collapse, thermodynamic psychiatry Contact: matthewacator@gmail.com