Why Couples Fight: Arousal, Memory, and the Missing Brake

by Stan Tatkin, PsyD, MFT

Introduction

PACT begins with a non-romantic premise: the human nervous system develops in attachment relationships and depends on co-regulation and social-emotional development for survival and functioning. However, under conditions of stress, the nervous system prioritizes survival and energy conservation over fairness, collaboration, and long-term thinking. Without structure, shared understanding, effective co-regulation, and practiced override, partners default to fast, automatic, self-protective responses.

The Locus Coeruleus and Arousal

The locus coeruleus (LC) plays a central role in this process. As the brain’s primary source of norepinephrine, it rapidly shifts the system into a threat-ready state. Attention narrows, vigilance increases, pain sensitivity rises, and the person orients toward self-protection and certainty. This shift occurs quickly and largely outside conscious awareness.

PACT has long taught that once this system takes over, relational cognition collapses. insight loses reliability. Then, empathy fluctuates, memory intrudes, and narrative hardens. PACT therefore never tries to reason couples out of dysregulation. 

You cannot out-think norepinephrine.

The Missing Brake

A recent Nature paper confirms something critical: the LC does not function as a pure accelerator. A specialized ring of inhibitory neurons called theperi-LC (pericoerulear) neurons surround it. These neurons release GABA and actively dampen LC-driven arousal. They function as a regulatory “dimmer switch" that modulates arousal rather than shutting it down.

This discovery confirms what PACT has always assumed: regulation can occur, but only with support.

Energy Conservation and LC-Driven Arousal

Energy conservation explains why partners drop formality, rely on habit instead of presence, become pro-self under stress, and insist they are right. The LC explains how this shift happens so quickly and so broadly. When norepinephrine floods the system, the brain favors speed over accuracy and certainty over cooperation.

The peri-LC system explains why some couples regulate successfully and why others fail. Inhibitory control exists, but it demands support, especially in long-term relationships with repeated stress. This is why PACT does not rely on goodwill, insight, or emotional intention. Instead, it requires deliberate design to compensate for predictable neurobiological failure.

Co-Regulation as External Inhibitory Control

Peri-LC neurons inhibit, quieting LC-driven arousal. In PACT terms, partners learn to function as external regulators that help dampen LC-driven arousal for one another when internal regulation falls short.

Eye contact, voice tone, proximity, predictable behavior, and touch act as biological inputs that dampen norepinephrine output. Pursuit, pressure, interrogation, moralizing, and emotional flooding do the opposite. These behaviors drive LC arousal higher and overwhelm inhibition.

When partners make each other worse, they do not fail at communication. They push each other into LC dominance.

Memory Under Arousal

High LC activation amplifies threat memory and pain sensitivity. The brain looks backward because it tries to predict danger, not understand the present. Memory shifts with state and becomes biased toward self-justification.

PACT therefore treats memory as unreliable under stress and insists that couples stay in the present, avoid past examples during conflict, and rely on prevention instead of post-hoc meaning.

Trauma Without Excuses

Arousal in itself does not activate the LC;  belongs to normal biology. The issue lies in poor inhibitory control. Trauma often sensitizes the LC and weakens the dimmer. But what happens in the brain is the cause and the limitation, but never an excuse for acting out or mistreating one's partner..

PACT maintains a clear position: Regardless of history, partners must avoid making each other worse. Structure, rehearsal, agreements, and consequences remain essential precisely because biology fails under threat.

Why Agreements Matter

Once LC dominance takes hold, the dimmer loses capacity, which is why PACT insists that agreements are made in calm states, rehearsed before stress, pre-authorized for enforcement, and followed with immediate cooperation.

Agreements do not manage dysregulation after it erupts. They prevent LC takeover. Defense, explanation, and delay prolong arousal and intensify threat bias.

Clinical Vignette: LC Takeover vs. Inhibitory Support

Jordan (Island) and Alex (Wave) discuss a missed text. In their therapy session, Jordan discusses ongoing exhaustion. In response, Alex’s body tightens and breathing shallows, following  an accusation. For both partners, LC-driven arousal surges and emory intrudes. Jordan hears threat, not information, and withdraws. Both nervous systems escalate.

The therapist interrupts to change state. The therapist directs eye contact, posture, and breathing. External support helps restore minimal regulation. The therapist blocks memory intrusion and keeps the couple in the present.

The therapist reframes responsibility and helps the couple design a simple agreement that prevents future LC spikes. The couple now has a structure to replace spinning out and they learn to prevent these moments, rather than repair them afterwards.

Teaching Takeaway

When couples show dysregulation, therapists must not chase meaning, explore history, or ask for empathy. Therapists must first support the dimmer.

Once LC inhibition returns, collaboration becomes possible again so that design can work.

PACT does not calm people down. It prevents predictable neurobiological failure through structure, rehearsal, and mutual responsibility.

Reference

Luskin, A. T., Li, L., Fu, X., et al. (2025). Heterogeneous pericoerulear neurons tune arousal and exploratory behaviours. Nature, 643, 437–447. https://doi.org/10.1038/s41586-025-08952-w