Grey Matter: the graph

The concepts of Grey Matter and the questions that join them.

How can a cell record its own history without sending any data out? What does a seizure look like on an EEG, and what can the EEG miss? What is the difference between adrenaline and noradrenaline? Why does alcohol make walking unsteady and speech slurred? What happens to a person when the anterior cingulate cortex is damaged on both sides? Could a speech implant pick up words its user never meant to say aloud? Can fMRI decode what a person is thinking without their cooperation? Can a spreading depression stop a seizure that set it off? Can the light used in optogenetics change the brain it is meant to control? Can functional ultrasound decode what someone is about to do, and what would a wearable version mean for privacy? What part does the cerebellum play in learning a new skill? Does the cerebellum do anything for thinking, or only for movement? Why does the brain mostly use chemical synapses when electrical ones are faster? What does the chloride inside neurons have to do with seizures? What does a participant agree to when an implant is designed to stay in the body? What is hard about consent for implants scattered through the brain in hundreds? How can someone give informed consent to a brain-computer interface when they can barely communicate? How does cortisol switch off its own release, and what is the hippocampus doing in that loop? Could microwaves passed through the head read what a person is thinking? Which areas decide what you eat when you are hungry and a pastry is on offer? Do astrocytes feed neurons with lactate? Do neural data laws protect a raw recording, or only what is decoded from it? Does a long seizure burn the brain with its electricity? Does emotional arousal, through noradrenaline, push the cortex closer to a seizure? Does a wider data stream out of the brain expose more of the mind? Do the new neural data privacy laws cover the recordings from a Neuralink trial implant? Does the adult human brain make new neurons? Does the sodium-potassium pump power each action potential? Does the physics of the skull protect mental privacy? Why does each hemisphere's visual cortex see the opposite half of the world with both eyes? Why are emotional events remembered better than ordinary ones? Why do some synapses grow stronger during a burst while others grow weaker? What separates knowing a fact from remembering an event? How do the fast and the slow stress responses differ? Why do some receptors act in milliseconds and others over seconds or minutes? How can you jump at a shape in the grass before you know it is a stick? How does a fright become a racing heart and sweaty hands? Which areas work together when you search for the keys you put down somewhere? Why does damage to Wernicke's area leave speech fluent but full of wrong words? How can a wave in the cortex lead to a headache, if the brain itself feels no pain? What happens in the brain when frustration builds over a task that keeps failing? What do glutamate and GABA each do to the same neuron's membrane? What makes grey matter grey and white matter white at the level of cells? What is the difference between grey matter and white matter? How can someone hear sounds normally and still not recognise speech or a ringing phone? Why can a spinal injury high in the neck stop breathing when one lower down does not? Why is the hippocampus so often where focal seizures start? How does the hippocampus hand a memory over to the cortex? Which areas hold a phone number in mind for the seconds it takes to dial it? Which areas are working when you hold back an angry outburst? Why are oxytocin and vasopressin said to come from the pituitary when the hypothalamus makes them? How can a diet reduce seizures, and how well does it work? How does a dopamine neuron limit its own release? How can a nucleus of a few tens of thousands of neurons supply noradrenaline to the whole cortex? How does a spike arriving at a terminal turn into released transmitter? How can acetylcholine act both in milliseconds and over seconds? How does a busy patch of cortex get more blood within seconds? How can adrenaline strengthen memories if it does not cross the blood-brain barrier? How do the basal ganglia let one movement start and hold the others back? How does an implant send out the data of a thousand electrodes through the skin? How can a seizure that starts in the visual cortex spread to both hemispheres? How do benzodiazepines stop a seizure? How do Colorado and California define neural data, and what changes for a company that collects it? How could dopamine tell a synapse, seconds later, that it helped? How can dopamine turn a Hebbian rule into learning from reward? How do endocannabinoids send a message backwards across a synapse? How long does a spike take to cross the brain or reach a foot? How can GABA inhibit a neuron even when it barely changes the voltage? How do GABA-B receptors on a terminal reduce the transmitter it releases? How do gap junctions between interneurons help the cortex oscillate? How does too much glutamate kill a neuron? How does a deliberate action become an automatic habit? How can a minority of GABA interneurons hold back a majority of excitatory cells? How many electrodes does Neuralink's implant have, and how are they placed? How many synapses does a brain have, and how many does one neuron receive? How many vesicles does a single spike release? How do microglia decide which synapses to remove? How much power can an implant spend before it warms the brain by a degree? How much glutamate does one synaptic vesicle hold? How does a Neuropixels probe tell which neuron fired? How can nitric oxide signal without vesicles, receptors on the surface or a synapse? How does calcium through NMDA receptors make a synapse stronger? How does the NMDA receptor detect that two neurons fired together? How does one oligodendrocyte myelinate many axons at once? How can the same NMDA receptor make a synapse stronger or weaker? How could two brain areas use a shared rhythm to talk to each other? How small is the brain's signal at the scalp compared with the noise around it? How do the SNARE proteins and synaptotagmin divide the job of fusing a vesicle? How can a drug block sodium channels without stopping every normal spike? How stable are dendritic spines in the adult cortex, and does learning make new ones? How does a stressful thought end up raising cortisol in the blood? How do levetiracetam and brivaracetam reduce seizures by binding SV2A? How do Broca's and Wernicke's areas work together when you repeat a word you just heard? How does Synchron's Stentrode reach the motor cortex without opening the skull? How can stimulating a nerve in the neck reduce seizures in the brain? How well does removing part of the temporal lobe stop seizures? How does the hypothalamus give orders to the pituitary? Is an epileptic aura a warning before the seizure, or the seizure itself? Is a headband that measures blood oxygen in the cortex collecting neural data under the law? Is long-term potentiation the same thing as Hebb's rule? Is the brain really a reptilian core wrapped in a limbic layer and a rational neocortex? What happens in the brain when you get a joke and laugh? Why does a stroke in the left occipital lobe blind the right half of both eyes? What would it take to record every neuron in a human brain? What does a person without amygdalae fail to feel, and what can they still feel? What happens when the front of both temporal lobes degenerates? What happens, step by step, when blood stops reaching the brain? What makes a neuromodulator different from a fast transmitter like glutamate? What separates the strip that moves the body from the strip that feels it, and why are lips and hands so large on both maps? How does a piece of music produce chills of pleasure? Why does the nasal half of the retina see the outer half of the world? Was the Papez circuit the circuit of emotion, as first proposed? What did the iron bar through Phineas Gage's frontal lobe change, and how much of the story is true? How does a decision in the prefrontal cortex become a movement of the hand? Are some brain regions plastic and others fixed? What does the potassium that astrocytes buffer have to do with spreading depression? How does telling yourself it is only a film calm a frightened amygdala? What happens in the brain when you recognise a friend's face in a crowd? Why does imagining or remembering a scene activate the visual cortex? What makes consent delicate when a brain interface is tested during an operation the patient needs anyway? What does the right hemisphere add to language if the left does the words? Is there a simple rule of thumb for where a function lives in the brain? How can coloured lights from an occipital seizure be told apart from a migraine aura? Why did destroying the septal area make rats furious, while stimulating it made them seek more? What does the medial septum do for the hippocampus? How can someone with amnesia get better at a skill without remembering practising it? Why can a small lesion in the brainstem cause a coma when a large one in the cortex does not? Is there a mathematics area, or which areas solve a sum in your head? What happens when the corpus callosum is cut? What decides whether a perturbation in the cortex fades, becomes spreading depression or becomes a seizure? Does stimulating the brain from outside fall under the proposed right to mental integrity? How does the thalamus help produce the slow waves and spindles of sleep? Why does nearly every sense pass through the thalamus before reaching the cortex? How does daylight set the brain's clock, and why does the clock sit on top of the optic chiasm? What did Chile's Supreme Court order in the first case brought under the neurorights amendment? How do benzodiazepines, barbiturates and vigabatrin strengthen inhibition in different ways? What do the tonic and phasic modes of the locus coeruleus do to the cortex? What happens in the tonic and in the clonic phase of a convulsive seizure? Why can touching the face of someone who lost an arm be felt in the missing hand? What happens when the posterior pituitary stops releasing vasopressin? What does it mean when an EEG shows strong alpha or strong delta? What is a cortical column, and how large is it? What does a burst of dopamine signal? What does an implant over the motor cortex read when a paralysed person intends to move? What is a neuronal avalanche, and what does its power law say about the cortex? What does acetylcholine from the basal forebrain do to the cortex? What does a spike on the EEG between seizures say about the brain? What does a seizure in the visual cortex look like from the inside? What does an SSRI actually block? If Broca's area makes speech, why does a lesion confined to it rarely cause lasting Broca's aphasia? Why is the primary visual cortex called area 17? What physically changes at a synapse that has been potentiated? If consumer EEG is so noisy, how much can it reveal about its user? What does Chile's 2021 constitutional amendment protect? How is dopamine removed after release, and what do cocaine and amphetamine change? Why do implant studies such as Connect-One follow participants for years? What counts as a migraine aura, and how long does it last? What does the blood-brain barrier let through, and which cells build it? What does moving the electrodes from the scalp to the surface of the brain gain? How do potassium channels end each spike and decide how fast a neuron can fire? What happens to a neuron's membrane between −70 mV and +30 mV? What happens to the brain recordings that an implanted stimulator stores? What risks of a brain implant does a trial participant need to understand before agreeing? What happens to conduction when an axon loses its myelin? What does it mean for a brain to have a seizure threshold, and what lowers it? What is distinctive about Paradromics's Connexus implant? Which parts of the neuron make up grey matter, and why does it use most of the brain's energy? Why does a neuron either fire a full spike or none at all? What does MEG see that EEG does not, and the other way round? What does oxygen actually do in a neuron, and why does losing it stop the brain within seconds? What does prolonged high cortisol do to neurons? What can someone who is blind from damage to both visual cortices still do with their eyes? What does the brain run on during a long fast? How does the cerebellum correct a movement before the error shows? What are the vesicle pools, and what happens when the ready one runs out? What did UNESCO adopt on neurotechnology in 2025, and does it bind anyone? What happens to a person's brain implant when the study that placed it ends? What happens to people with implants if the company that made them stops supporting the device? When does measuring a brain become changing it, and which proposed right covers that? Where does the brain's serotonin come from, and how does it reach so many regions? How does inhibition set the pace of fast brain rhythms? Where does sound reach the cortex, and how is it laid out there? Which part of the brain holds most of its neurons? Where in the release machinery does SV2A sit, and what is it known to do? Where on a neuron does the action potential start, and why there? Where does the time go between a spike reaching a terminal and the next cell responding? Where do the brain's 20 watts go? Where do the signals of the two eyes first meet in a single neuron? Which rights have been proposed to protect the mind, and where does mental privacy sit among them? What removes glutamate after it is released, and why does the speed matter? Would a record of activity written inside brain cells count as neural data? What does Precision Neuroscience's 30-day clearance allow, and why does it matter? Why can a neuron not fire again immediately after a spike, and why does the spike travel only one way? Why is the inside of a resting neuron about 70 mV negative? Why do absence seizures appear as 3 Hz spike-and-wave over both hemispheres at once? Why does Alzheimer's disease often first show as asking the same question again? If SSRIs raise serotonin within hours, why do they take weeks to work? Why are benzodiazepines the first treatment for status epilepticus, and why do they work less the later they are given? Why does blocking CGRP prevent migraine attacks? Why does botulinum toxin paralyse muscles while tetanus toxin makes them rigid? How much ATP does one glucose give, and why does the brain need oxygen to get it? Why are calcium channels anchored within nanometres of the vesicles they trigger? Why is calcium imaging done almost only in animals? Why does deep brain stimulation for epilepsy target the thalamus? Why does EEG record synaptic currents of pyramidal cells and miss their action potentials? Why does a lack of energy turn into a flood of glutamate? Why does a rise of potassium outside the cells make every neuron nearby easier to fire? Why is a convulsive seizure that lasts more than five minutes treated as an emergency? Why can light flashing at 15 to 25 times a second trigger seizures in photosensitive people? Why can GABA excite the neurons of a newborn's brain? Why does GABA produce both a fast and a slow inhibition? Why is the spinal cord's grey matter inside, the reverse of the brain's cortex, and what does it do there? If most of the body's serotonin is made in the gut, why does it not reach the brain? Why did the patient H.M. keep his old memories but form no new ones? Why do brain implant trials enrol only people with severe paralysis? Is language on the left side of the brain in everyone? Why can near-infrared light read only the outer centimetre or two of the brain? If thick axons are faster, why are most axons in the brain thin and slow? Why does wrapping an axon in myelin make the signal so much faster? Why does damage to the right parietal lobe make people ignore the left side, while left damage rarely does the reverse? Why is neural data treated as more sensitive than other personal data? Why are neurons especially vulnerable to misfolded proteins? Why are neuropeptides released only when a neuron fires hard? Why does the NMDA receptor need glycine as well as glutamate? Why do older antihistamines make people drowsy while newer ones do not? Why does a pituitary tumour take away the outer half of vision in both eyes? Why does a small change in calcium entry change transmitter release so much? If running near a critical point is useful, how does it relate to a seizure? Why can a full helmet of MEG sensors still not say for certain where a signal came from? What does sleep do for the transfer of memories to the cortex? Why do sleep loss and the first hour after waking matter so much in juvenile myoclonic epilepsy? Why are sodium channels packed into the nodes of Ranvier? Why does the order of two spikes, a few milliseconds apart, decide whether a synapse strengthens or weakens? Why must spikes be sampled tens of thousands of times a second while EEG makes do with hundreds? Why does a stroke in the left hemisphere weaken the right side of the body? Why does strychnine cause violent muscle spasms? Why does a tool that can switch chosen neurons on raise questions of mental integrity? Why is synchrony, rather than just more firing, the signature of a seizure? Why is the AMPA current over within a few milliseconds of glutamate release? Why does a migraine aura drift slowly across the visual field? Why does the brain probably not learn by backpropagation as artificial networks do? Why does the brain use about a fifth of the body's oxygen at about 2 % of its mass? Why is the hippocampus the most common starting point of focal epilepsy that resists drugs? How does a racing heart become the feeling of being anxious? Why does a migraine scotoma grow as it moves toward the edge of vision? Why has one small array from Utah carried most human brain-computer interface research? Why does myelin make white matter conduct signals so much faster? How do optogenetics and calcium imaging divide the work of writing to neurons and reading them?