Brain

The brain is the highest energy organ per mass. It needs steady glucose, thyroid-driven respiration, CO2, and protective steroids (progesterone, pregnenolone). When energy fails, excitotoxicity, swelling, and functional loss follow.

Fuel and protection

The brain makes a large share of the body's CO2. Stress that raises lactic acid and free fatty acids injures neurons. Serotonin, excess estrogen, and high unsaturated free fats amplify that injury; progesterone and good oxidation oppose it.

See CO2, Progesterone, Glucose, Thyroid, Serotonin, PUFA.

Hypothyroidism cuts that fuel delivery: after thyroid hormone withdrawal, PET measured a 23.4% fall in regional cerebral blood flow and a 12.1% fall in cerebral glucose metabolism.

The brain's glucose dependence isn't just a modern fact, it may be what shaped it: at roughly 2% of adult body weight, the brain uses about 20% of resting metabolic rate in adults and 66% in a 5-year-old, and a 2026 modeling study across 4 million years of hominin evolution argues fruit and honey sugars, not meat, supplied the glucose that drove brain growth. See Human evolution.

About 35 hours without sleep raised amygdala activation to aversive pictures by about 60% and weakened medial-prefrontal-amygdala functional connectivity versus rested controls. See Sleep, Emotion.

One session of moderate resistance exercise (about 42 minutes of six machine lifts at 65%–75% of one-repetition maximum) sped executive-function responses in an acute randomized trial with a between-subjects design, in which 121 adults aged 18–50 lifted or watched a matched rest video. Flanker responses were about 18–19 ms faster after lifting versus about 6–7 ms after rest (between-group d = 0.37), Flanker P3 latency was shorter (d = 0.41), and 2-back response time fell within the lifting group (d = 0.46); accuracy and P3 amplitude showed no group-by-time effect. In exploratory mediation, the post-exercise systolic blood pressure rise (d = 0.99) statistically mediated the response-time gains, and the larger blood lactate rise (d = 2.06) did not. The trial covers a single session in adults who already exercised at least twice a week and did not test training or strength level. See Muscle.

When physically inactive, the brain consumes about 60% of the body's glucose, and that dependence makes it easily damaged by even short hypoglycemia. The blood-brain barrier depends on the body's energy reserves; when energy fails, barrier breakdown and excess permeability lead to diseases such as multiple sclerosis. Progesterone and pregnenolone improve all mental functions, including memory.

Memory

Memory depends on the brain's energy state. Thyroid-supported respiration, steady glucose, adequate CO2, and protective steroids support recall and learning. Low brain temperature and low energy production impair these functions.

In people with memory problems, memory improved when oral temperature rose from 96 or below 97°F toward 98 or 99°F.

Structural plasticity

Learning changes brain structure directly, not just brain activity.

If you simply change your mind, the limits of what is possible become undefined and very open. Changing your mind is the essence of living matter. Biology is changed by every experience. The brain is constantly in development, and that involves what you're learning. So what you learn changes your structure, and therefore your mind has changed. You're changing your past every time you learn something because you become a different organism.

— Ray Peat

First pregnancy reduces maternal gray matter volume in social-cognition regions for at least two years; the change classified pregnancy status from the scan alone, overlapped postpartum baby-response areas, and predicted maternal attachment. See Pregnancy.

In a cross-sectional study of 47 healthy 3-to-5-year-olds, higher screen-time exposure (via the ScreenQ composite score, based on American Academy of Pediatrics guidelines) was associated with lower white-matter integrity on diffusion tensor imaging in tracts supporting language, literacy, and executive function, along with lower expressive-language and literacy scores. Cross-sectional data like this can't establish that screen exposure caused the white-matter differences.

People with problematic internet use have less gray matter in frontal control regions than controls, in a meta-analysis of 15 cross-sectional MRI gray-matter studies (355 cases, 363 controls). Convergent clusters sat in the medial and superior frontal cortex (supplementary motor area), the left ACC (the front of the cortex arching over the corpus callosum), and the left dorsolateral prefrontal cortex, and every study contributing to those clusters showed less gray matter in cases. Most included studies examined internet gaming disorder in mostly male samples from China and South Korea, and the case-control design cannot show whether the differences preceded the heavy use or followed it.

In 5-to-7-year-olds, about 29 months of high weekly instrumental practice enlarged the anterior midbody of the corpus callosum relative to low-practice and control children; size did not differ at baseline, and weekly music exposure predicted both that change and motor-sequencing gains. Adult musicians who began before age seven show the same larger anterior corpus callosum pattern, and the child data favor training over preexisting anatomy as the cause. A 2005 review of that program also reported long-term visual-spatial, verbal, and mathematical gains after music training in children, alongside training-linked structural differences in adult musicians. See Children.

In aged rats, raising brain magnesium with magnesium L-threonate increased presynaptic bouton density in the hippocampal dentate gyrus and CA1 within 2 weeks, and density fell back to control levels 2 weeks after treatment stopped. T-maze working memory followed the same course, peaking 12 days after treatment began and returning to baseline 12 days after it ended.

Young men who practiced a falling-blocks video game for 4-8 weeks got more than seven times better at it while their cortex burned less glucose, and the best improvers showed the biggest drops.

Orienting reflex

The orienting reflex is the whole-organism response to novelty. It directs attention toward a new sound, sight, or smell and coordinates sensory, autonomic, and motor changes. It supports learning and exploration. The reticular activating system helps integrate this response, and environmental familiarity frees energy for new exploration.

Environment

The frontal cortex needs to run cooler than the rest of the brain to stay organized. The cortex has a temperature gradient, hot at the center and cooler toward the front, and keeping the forehead bare lets that gradient hold.

You can't think and plan if your frontal lobes are cool. It's just that it has to be cooler than all the rest of your brain and body. And the progesterone is part of maintaining that coolness by keeping the activity focused rather than tending in the direction of excitotoxicity and inflammation.

— Ray Peat

The frontal lobes are relatively uninsulated compared to the rest of the brain, which lets them run cooler even though the brain overall runs hot; progesterone stabilizes that balance, keeping the front from generating heat needlessly while keeping enough temperature for energy supply.

See Progesterone, Heat, Cold.

In a randomized crossover trial, adults 40 and older finished a planning and attention test faster after a month with a real HEPA air purifier at home than after a month with a sham unit; younger adults showed no change.

Practice

Keep blood sugar stable with regular carbohydrate. Support thyroid and sleep. Lower seed oils. Use light by day.

See Aging, Alzheimer's disease, Light, Red light, Stress.

Epilepsy

Epilepsy is recurring seizures from abnormal brain electrical activity. Progesterone has an anticonvulsant action and is a serious alternative or adjunct to conventional anticonvulsant drugs.

Progesterone's anticonvulsant action

Peat connected progesterone's calming, anesthetic-like effect on nerves (the same mechanism that reduces labor pain when levels are adequate) directly to suppressing seizure activity:

Progesterone, because of its normal anesthetic function (which prevents the pain of childbirth when its level is adequate), directly quiets nerves, and in this way suppresses many of the excitotoxic processes.

— Ray Peat

He made the case for progesterone use in women with seizure history was strong even independent of its anticonvulsant effect, given its other safety benefits over conventional drugs:

If progesterone's antiepileptic effectiveness were not enough (and it is very effective even in irrational pharmaceutical formulations), the fact that it reduces birth defects, and promotes brain development and nerve repair should assure its general use in women with a history of seizures.

— Ray Peat

Estrogen and seizure risk factors

In Ray Peat's framework, low thyroid and high estrogen connect to two recognized seizure risk factors, edema and low sodium (hyponatremia):

Low thyroid, high estrogen people have two of the conditions (edema and hyponatremia) known to predispose to seizures.

— Ray Peat

The link is not theoretical: in a case series of 5 patients with severe hyponatremia and active seizures, intravenous hypertonic saline (250 mmol given over 10 minutes) stopped seizures in all 5, raising mean serum sodium by 7.4 mmol/L; the one patient not treated promptly, who went into prolonged status epilepticus, was left with permanent neurological damage.

TLR4 after brain injury

Toll-like receptor 4 (TLR4), the innate immune receptor that senses endotoxin, increased calcium-permeable AMPA receptor currents in hippocampal dentate granule neurons after fluid-percussion brain injury in rats. Blocking TLR4 signaling shortly after injury reduced network excitability and seizure susceptibility, but blocking it after a delay did not. In uninjured controls, blocking TLR4 paradoxically raised excitability and seizure susceptibility.

In animal experiments the estrogen-to-progesterone ratio governs nerve-cell stability; when it is too high, slight stimulation can set off seizures, and raising progesterone and clearing estrogen faster corrects it. The brain makes large amounts of DHEA, progesterone and pregnenolone, which have a quieting effect; glutamic acid, aspartic acid, cysteine and tryptophan are the worst amino acids for lowering the seizure threshold.

Magnesium deficiency increases susceptibility to seizures, and hypothyroidism reduces the ability of cells to retain magnesium; thyroid keeps estrogen and adrenal hormones low, raises progesterone and pregnenolone, and helps retain magnesium and sodium. Hypoglycemia with raised cortisone probably accounts for the nighttime incidence of seizures.

Practice (Epilepsy)

This is not a substitute for anticonvulsant medication in diagnosed epilepsy, abrupt medication changes carry real seizure risk. See Progesterone, Hyponatremia, Thyroid for the supporting framework, and consult a neurologist before changing seizure medication.

Excitotoxicity

Excitotoxicity is neuron injury from excess excitatory amino acid signaling, classically driven by glutamate and aspartate causing calcium overload. Damage requires both stimulation and difficulty maintaining adequate energy production; the combination causes calcium uptake and lipid peroxidation.

Excitotoxicity, in its simplest sense, is the harmful cellular effect (death or injury) caused by an excitatory transmitter such as glutamate or aspartate acting on a cell whose energetic reserves aren't adequate to sustain the level of activity provoked by the transmitter.

— Ray Peat

Once an excitotoxic state exists, cell exhaustion can spread to other cells, since excitation can trigger a cascade of other excitatory processes.

Mechanism

As calcium enters cells and potassium leaves, enzymes are activated that produce free fatty acids (linoleic and arachidonic) and prostaglandins, which activate lipid peroxidation and free radical production. Estrogen supports acetylcholine release, which increases extracellular potassium and excitatory amino acids, and also stimulates free radical production directly.

Carbon dioxide is tied directly to excitotoxicity: ammonia produced by stimulated nerves normally helps clear glutamate and aspartate through urea synthesis, but that process consumes CO2. A CO2 deficiency, which itself constricts blood vessels and reduces oxygen delivery, therefore also reduces the clearance of excitatory amino acids through the Krebs cycle, so as energy becomes deficient, excitation is promoted. This is part of why seizures can be triggered by hypoxia.

At resting membrane potential, extracellular magnesium blocks the channel of the NMDA-type glutamate receptor, and depolarization relieves the block; removing physiological magnesium (about 1 mM) greatly reduced the voltage sensitivity of NMDA currents in mouse spinal cord neurons.

Protective factors

Sugar, magnesium, sodium (balancing calcium and potassium), thyroid and progesterone (by increasing energy production), and CO2 all help control excitotoxic processes. Aspirin lowers free radical production by inhibiting prostaglandin synthesis. Progesterone directly quiets nerves through its anesthetic function and has direct protective effects on mitochondria. In cultured hippocampal neurons, pretreating with progesterone (10 ng/mL) before a 200 µmol/L glutamate exposure significantly reduced cell damage; in rats, 16 mg/kg progesterone given after traumatic brain injury reduced hippocampal neuronal damage and improved cognitive outcome. Minimizing dietary PUFA matters here specifically because unsaturated fats and the free radicals they generate are involved in the excitotoxic cascade; even years after removing them from the diet, their slow release from tissue storage can prolong susceptibility.

Glutamate and aspartate

Glutamate and aspartate are the excitatory amino acids most directly implicated. Bacterial endotoxin from the bowel can also contribute to nerve instability, so supporting gut health (see Gut health) is part of the same picture.

Excitotoxin exposure through diet (monosodium glutamate and related food additives) is a topic covered in detail by neurosurgeon Russell Blaylock. Total excitability load (low energy, low progesterone, high estrogen, PUFA, poor CO2 status) matters more than isolated MSG avoidance.

Glutamate as a metabolic intermediate

Beyond its excitatory role, glutamate is also a metabolic intermediate. Dietary free glutamate (including some food additives) is one input among many; energy failure and barrier problems raise risk more than a single meal. Balanced protein, gelatin glycine, and good oxidation support safer handling of glutamate load.

See also

• GABA
• Mitochondria