The Brain Reacts To Threat Before It Identifies One

Recognition Is Not Where The Reaction Begins

LeDoux Measured That Order In The Rat Amygdala

Timing Is Only Half Of What The Research Has Looked At

The Other Half Is Whether The Structures Themselves Differ

Not Every Difference Followed The Trauma

This Part Covers What Changes And What Does Not

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OKAY BACK FROM THE SCAN 🧠

A Trigger Begins As Ordinary Sensory Information

Sound And Sight Enter The Thalamus

The Thalamus Passes Signals To The Cortex And The Amygdala

Joseph LeDoux Studied The Direct Thalamus To Amygdala Link

His Team Paired Tones With Foot Shocks In Freely Moving Rats

Conditioning Changed Responses Under 15 Milliseconds

Those Short Responses Point To The Thalamus Not The Cortex

The Amygdala Handles Threat Detection And Fear Conditioning

LeDoux Has Since Argued Against The Fear Wording

He Wrote That The Term Fear Conditioning Should Be Given Up

Threat Conditioning Is The Name He Prefers

LeDoux And Daniel Pine Split Threat Response From Felt Fear

Behavioral Reactions And Conscious Feelings Are Separate

PTSD Includes Distress From Harmless Things That Resemble The Trauma

Researchers Call That Pattern Overgeneralization

A Minnesota Team Tested It With Rings Of Graded Size

An Extreme Size Was Paired With A Shock

Middle Sizes Formed A Range Between Danger And Safety

Veterans With PTSD Generalized More Than Trauma Controls

Their Insula And Hippocampus Responses Followed The Same Pattern

Symptom Severity Correlated With Generalization At Two Sites

Triggers Look Arbitrary From Outside For That Reason

The Hippocampus Encodes The Context Of A Memory

Many Studies Report Smaller Hippocampi In PTSD

A Consortium Pooled Brain Scans From 1868 People

That Sample Included 794 PTSD Patients From 16 Cohorts

The Hippocampus Was Smaller In Current PTSD

That Difference Equals A Cohen's D Of 0.17

Whether Trauma Caused That Difference Is Not Settled

Twin Research Suggests The Opposite

Investigators Scanned Identical Twins Discordant For Trauma

The Final Sample Included 17 PTSD Pairs And 23 Control Pairs

PTSD Severity In One Twin Correlated With The Other Twin's Volume

The Correlation Was Negative 0.70

Severe Pairs Had Smaller Hippocampi Including The Unexposed Twin

Those Authors Described It As A Pre Existing Vulnerability Factor

The Ventromedial Prefrontal Cortex Restrains The Amygdala

Extinction Means Learning That A Feared Cue Is Now Safe

That Learning Depends On The Ventromedial Prefrontal Cortex

Milad And Colleagues Tested Extinction Recall In A Scanner

Recall Of Extinction Was Impaired On Day 2

Activity In The Ventromedial Prefrontal Cortex Fell

The Dorsal Anterior Cingulate Was More Active Instead

Insula Activity Reflects The Internal State Of The Body

One Meta Analysis Compared PTSD With Two Other Anxiety Disorders

Greater Amygdala And Insula Activity Appeared In All Three

The Locus Coeruleus Supplies Most Forebrain Noradrenaline

Spinal Fluid Noradrenaline Was Higher In Chronic PTSD

Symptom Severity Rose With Those Levels

The Hypothalamus Starts The Cortisol Sequence

It Releases Corticotropin Releasing Hormone Or CRH

CRH Prompts The Pituitary To Release A Second Hormone

That Second Hormone Makes The Adrenal Cortex Produce Cortisol

Cortisol Findings In PTSD Have Been Inconsistent

Bremner And Colleagues Measured CRH In Spinal Fluid

Patients Averaged 29.0 Picograms Per Milliliter

Comparison Subjects Averaged 21.9

A Later Team Sampled CRH Hourly For 6 Hours

CRH Was Higher In 11 Veterans Than In 12 Volunteers

Urinary Cortisol Did Not Differ Between The Groups

That Cortisol Correlated Negatively With Symptom Severity

A Meta Analysis Of 37 Studies Found No Overall Difference

Another Meta Analysis Of 47 Studies Disagreed

Daily Cortisol Output Was Lower In Those PTSD Groups

The Cortisol Literature Stays Mixed

Treatment Did Not Wait For That Question To Settle

Exposure Therapy Repeats The Feared Cue Until Response Drops

EMDR Stands For Eye Movement Desensitization And Reprocessing

Those Eye Movements Load Working Memory During Recall

Recall Also Returns A Fear Memory To A Changeable State

A Phase Three Trial Randomized 90 Participants

MDMA Therapy Reduced Symptom Scores More Than Placebo

That Trial Paired The Drug With Preparatory And Integrative Therapy

The United States Food And Drug Administration Declined To Approve It

Another Phase Three Trial Was Requested

Treatment Works On The Learning Rather Than The Chemistry