The amygdala is a pair of almond-shaped clusters deep in the brain, one on each side, that tag what we see and hear with emotional importance. When both are damaged, a person usually thinks, reasons, and talks much as before, but their emotional reactions to the world change.1PubMed. Amygdala, affect and cognition: evidence from 10 patients with Urbach-Wiethe disease The best-known cases live ordinary-seeming lives yet fail to hold back from danger and from strangers, as if a protective brake had been removed.2PubMed. The primate amygdala and the neurobiology of social behavior: implications for understanding social anxiety How much changes depends heavily on whether one side or both are damaged, and at what age.
Fear of Outside Dangers Fades
The most studied woman, known as SM, shows a striking lack of fear around snakes, spiders, horror films, and even life-threatening events.3PubMed Central. Fear and panic in humans with bilateral amygdala damage Other people with similar damage on both sides have mostly shown the same pattern.4PubMed Central. Fear and panic in humans with bilateral amygdala damage The amygdala seems to be needed to turn an outside danger into a felt sense of fear.
Learning new fears is also impaired. People with this damage don’t learn to fear a warning signal that has been paired with something unpleasant.5PubMed Central. Fear and panic in humans with bilateral amygdala damage Even their quick protective reflexes, like the startle blink, fail to strengthen after such pairing.6PubMed Central. Impaired acquisition of classically conditioned fear-potentiated startle reflexes in humans with focal bilateral basolateral amygdala damage Their skin’s sweat response, a sign of alarm, often fails to build up to a warning signal.7Molecular Psychiatry. The amygdala: vigilance and emotion
In daily life, a person may walk up to a dangerous animal out of curiosity rather than freezing. They may not avoid a place or a person after a frightening encounter there. Family members may notice risky choices while the person feels no worry about them at all.
The body calms down too. In some people, damage to the left amygdala alone has lowered anxiety and slowed breathing while they waited for something unpleasant.8PubMed. Effects of left amygdala lesions on respiration, skin conductance, heart rate, anxiety, and activity of the right amygdala during anticipation of negative stimulus In one such person, heart rate and sweating while waiting also dropped.9PubMed. Effects of left amygdala lesions on respiration, skin conductance, heart rate, anxiety, and activity of the right amygdala during anticipation of negative stimulus
It is a common myth that these people feel no emotion at all. They still feel happiness, curiosity, and frustration. What fades is mainly fear set off by things outside the body.
Reading Fear in Faces and Voices
Damage to both amygdalae makes fearful faces hard to recognize, while the person still knows who the face belongs to.10PubMed Central. Fear and the human amygdala They seem insensitive to how intense the fear on a face is.11PubMed Central. Fear and the human amygdala After a brain infection that damaged the amygdala, three people read happiness, surprise, sadness, disgust, and anger normally but not fear.12PubMed. Face processing impairments after encephalitis: amygdala damage and recognition of fear A fourth person, whose amygdala was spared, read every emotion normally.13PubMed. Face processing impairments after encephalitis: amygdala damage and recognition of fear
A person with amygdala damage can name a friend instantly yet not notice that the friend looks scared. The problem is not poor eyesight or a failure to look at faces; the difficulty lies in turning what the eyes see into a sense of “this person is afraid.”
The effect varies from person to person. Among nine people with damage on both sides, fear recognition ranged from severely impaired to essentially normal.14PubMed. Recognition of facial emotion in nine individuals with bilateral amygdala damage Most also struggled with other negative emotions, but none had trouble recognizing happy faces.15PubMed. Recognition of facial emotion in nine individuals with bilateral amygdala damage In one person with right-side damage, recognizing disgust on faces was markedly reduced.16PubMed. Taste and olfactory status in a gourmand with a right amygdala lesion Damage on the left side alone weakened how the brain processes emotion in voices.17PubMed Central. Asymmetrical effects of unilateral right or left amygdala damage on auditory cortical processing of vocal emotions
A frightened face is a signal that something nearby is dangerous, so missing it means missing a warning others are giving. Caregivers may need to say worries out loud rather than rely on expressions.
Trusting Strangers and Standing Too Close
People with damage on both amygdalae rate unfamiliar faces as more approachable and trustworthy than others do.18Nature. The human amygdala in social judgment The gap is biggest for faces most people find untrustworthy-looking.19Nature. The human amygdala in social judgment
Personal space changes as well. SM lacks any sense of it.20PubMed Central. Personal Space Regulation by the Human Amygdala She is comfortable standing about one foot from someone, roughly half the two feet most people prefer.21The Transmitter: Neuroscience News and Perspectives. Amygdala found to govern notion of personal space In healthy people, the amygdala becomes active when someone gets too close, triggering discomfort.22PubMed Central. Personal Space Regulation by the Human Amygdala Without that signal, nothing tells her she has stepped in too far.
The risks are practical. A trusting person is more likely to be exploited by scammers or manipulative people, and strangers may read close standing as rude or intrusive. Families can agree on simple rules, such as checking before giving out money or personal details. Since the person usually doesn’t feel anything is wrong, explanations tend to work better than warnings.
Taking Bigger Risks With Money
Most people feel a loss more sharply than an equal gain, so they turn down even-odds bets. Two people with amygdala damage showed no aversion to losing money at all.23California Institute of Technology. Caltech Neuroscientists Discover Brain Area Responsible for Fear of Losing Money They took risky gambles much more often than people of the same age and education.24California Institute of Technology. Caltech Neuroscientists Discover Brain Area Responsible for Fear of Losing Money Yet they still responded normally to changes in a gamble’s odds and payoff.25PubMed Central. Amygdala damage eliminates monetary loss aversion The amygdala seems to act as a brake on actions that could turn out badly.26PubMed Central. Amygdala damage eliminates monetary loss aversion It seems to supply the uneasy feeling that makes most people hesitate, so a person with this damage can calculate the chances correctly and still go ahead.
Families might notice bigger bets or impulsive purchases made without worry. Simple safeguards like spending limits help because understanding isn’t the problem.
Emotional Memories Lose Their Edge
Normally, emotionally charged events are remembered better than dull ones, because the amygdala flags them as important while they are being stored. People with damage on both amygdalae remember emotional material less well over the long term.27PubMed. Impaired declarative memory for emotional material following bilateral amygdala damage in humans People with damage on one side don’t show the usual stronger memory for the gist of an emotional scene.28PubMed. Amygdala damage impairs emotional memory for gist but not details of complex stimuli Ten people with Urbach-Wiethe disease, a rare condition that can damage both amygdalae, remembered both negative and positive pictures differently from others.29PubMed. Amygdala, affect and cognition: evidence from 10 patients with Urbach-Wiethe disease
Without the flag, an emotional event fades like an ordinary day. This is a weakening of the boost, not a loss of memory in general. Everyday facts and skills are generally remembered fine, and keeping notes of important emotional events can help fill the gap.
Even dreams change. People with amygdala damage report dreams that are more pleasant, shorter, and simpler than usual.30PubMed. The role of the basolateral amygdala in dreaming Their dreams still contain as much threat or danger as other people’s.31PubMed. The role of the basolateral amygdala in dreaming
What Stays the Same
Ten people with damage on both sides scored close to normal on thinking tests while differing emotionally.32PubMed. Amygdala, affect and cognition: evidence from 10 patients with Urbach-Wiethe disease Recognizing who a face belongs to stays intact.33PubMed Central. Fear and the human amygdala Reasoning, language, and general knowledge depend on other, much larger networks, so the change is easy to miss on first meeting.
Pain is still fully felt. A man with extensive damage to both amygdalae and nearby areas felt extreme pain with his hand in ice water.34PubMed Central. Preserved emotional awareness of pain in a patient with extensive bilateral damage to the insula, anterior cingulate, and amygdala He rated it at or near the maximum and was distressed by it.35PubMed Central. Preserved emotional awareness of pain in a patient with extensive bilateral damage to the insula, anterior cingulate, and amygdala
Panic from inside the body survives too. People with damage on both amygdalae panicked when they breathed air high in carbon dioxide, which feels like suffocating.36Translational Psychiatry. Acid–base dysregulation and chemosensory mechanisms in panic disorder: a translational update Their breathing and heart rate rose like those of people with panic disorder.37Translational Psychiatry. Acid–base dysregulation and chemosensory mechanisms in panic disorder: a translational update Fear of internal threats seems to run through other brain areas.38Translational Psychiatry. Acid–base dysregulation and chemosensory mechanisms in panic disorder: a translational update SM described her panic as new and terrifying, even though outside threats leave her calm.
There are limits. They may notice their own heartbeat or breathlessness less, and one person who didn’t panic felt no breathlessness at all.39PubMed Central. Panic Anxiety in Humans with Bilateral Amygdala Lesions: Pharmacological Induction via Cardiorespiratory Interoceptive Pathways
One Side Versus Both, and Childhood Versus Adulthood
Trouble recognizing fearful faces appears with damage to both amygdalae but not one.40PubMed Central. Fear and the human amygdala Each person has two, and the intact one may carry out much of the work, which helps explain why one-sided damage is usually milder. It is not harmless, though. Weaker emotional processing of voices follows left-side damage.41PubMed Central. Asymmetrical effects of unilateral right or left amygdala damage on auditory cortical processing of vocal emotions
Age at damage matters too. One-sided damage early in life, but not in adulthood, removes the usual stronger memory for emotional material.42PubMed. A critical period for the impact of amygdala damage on the emotional enhancement of memory? People damaged early, especially with childhood seizures, struggled to catch irony, tactless remarks, and non-literal speech.43PubMed. The impact of early and late damage to the human amygdala on ‘theory of mind’ reasoning People who lost an amygdala as adults, usually in epilepsy surgery, understood others’ thoughts and feelings normally.44PubMed. The impact of early and late damage to the human amygdala on ‘theory of mind’ reasoning
For a child, that may mean extra help learning social cues like sarcasm. The brain seems to need the amygdala while learning these skills, not afterward.45PubMed. Increased social fear and decreased fear of objects in monkeys with neonatal amygdala lesions
Mood After Epilepsy Surgery That Removes an Amygdala
Temporal lobe epilepsy surgery treats seizures that begin in the temporal lobe, usually in people whose seizures haven’t been controlled well by medication. The aim is to remove or destroy the small area where seizures start, and because the amygdala sits close by, it is often taken along with neighboring tissue.46PubMed. The impact of early and late damage to the human amygdala on ‘theory of mind’ reasoning The operation can remove tissue or use a laser to destroy it through a small opening.
Many people feel better afterward. Six months after laser surgery of this kind, depression and anxiety scores dropped on average.47PubMed Central. Psychiatric changes after stereotactic laser amygdalohippocampotomy for medial temporal lobe epilepsy In another group, mood improved in 56% of people after surgery.48medRxiv. Right amygdala lesions are associated with improved mood after epilepsy surgery Improvement was most linked to removal of the right amygdala.49medRxiv. Right amygdala lesions are associated with improved mood after epilepsy surgery
Some feel worse. In the same group, 38% had worse mood afterward.50medRxiv. Right amygdala lesions are associated with improved mood after epilepsy surgery In two other groups, 14% and 22% had a significant drop in mood.51PubMed Central. Predicting Mood Decline Following Temporal Lobe Epilepsy Surgery in Adults Any psychiatric history tripled the odds of a mood drop,52PubMed Central. Predicting Mood Decline Following Temporal Lobe Epilepsy Surgery in Adults and surgery on the side of the brain that handles language nearly doubled them.53PubMed Central. Predicting Mood Decline Following Temporal Lobe Epilepsy Surgery in Adults
If you or a relative faces this surgery, tell the team about any past depression or anxiety, even if mild. Ask which side is being operated on and whether it handles language. Plan mood check-ins in the months afterward. Changes are usually subtler than in people missing both amygdalae.
What Causes Amygdala Damage
Urbach-Wiethe disease, a rare inherited condition, damages both amygdalae symmetrically in more than half of those affected.54PubMed. Amygdala, affect and cognition: evidence from 10 patients with Urbach-Wiethe disease A brain infection (encephalitis) can damage the amygdala.55PubMed. Face processing impairments after encephalitis: amygdala damage and recognition of fear Epilepsy surgery removes one amygdala in many patients.56PubMed. The impact of early and late damage to the human amygdala on ‘theory of mind’ reasoning Damage has followed cancer treatment,57PubMed. Klüver-Bucy syndrome after bilateral selective damage of amygdala and its cortical connections and Alzheimer’s disease can affect the amygdala.58PubMed Central. Alzheimer Abnormalities of the Amygdala With Klüver-Bucy Syndrome Symptoms
Most of these causes don’t harm the amygdala alone, so a person’s changes may come from the amygdala plus nearby tissue. Urbach-Wiethe disease is unusual because it can damage both amygdalae while leaving much else intact.
Severe damage on both sides, usually also involving nearby temporal lobe tissue, can cause Klüver-Bucy syndrome, a cluster of behavior changes first described in the 1930s.59PubMed Central. Alzheimer Abnormalities of the Amygdala With Klüver-Bucy Syndrome Symptoms It includes heightened sex drive, putting objects in the mouth, failing to recognize familiar things by sight, and compulsively exploring everything seen.60PubMed Central. Alzheimer Abnormalities of the Amygdala With Klüver-Bucy Syndrome Symptoms Apathy and withdrawal can occur too.61PubMed Central. Alzheimer Abnormalities of the Amygdala With Klüver-Bucy Syndrome Symptoms One person developed these signs plus memory problems after cancer treatment damaged both amygdalae.62PubMed. Klüver-Bucy syndrome after bilateral selective damage of amygdala and its cortical connections
Sudden loss of fear, odd trust in strangers, or new mouthing behavior warrant a visit to a neurologist, and changes after a brain infection or surgery should be reported. Brain scans can show amygdala damage. Treatment targets the underlying cause and safety, since the amygdala doesn’t regrow.