A guide to techniques for measuring and stimulating the brain: what each technique measures or changes, its resolution, field of view, preparation and cost, with every value traced to its sources.
Core techniques
ASL perfusion: Arterial spin labeling is an MRI technique that uses radiofrequency inversion to magnetically tag water in the subject's own arterial blood as a tracer. After a delay that lets the tagged blood flow…
Two-photon calcium imaging: Two-photon calcium imaging is fluorescence microscopy in which a neuron's brightness reports its activity. Activity changes a cell's free calcium, and a genetically encoded sensor brightens when it…
CT (incl. perfusion, dual-energy): CT (computed tomography) sends X-rays through the patient from many angles and records the fraction of each beam that remains after passing through. From these measurements it reconstructs a map of…
DBS: Deep brain stimulation is a surgical therapy that stimulates the brain electrically without destroying tissue: an electrode implanted inside the skull, wired to an implanted pulse generator…
Direct electrical stimulation mapping: Direct electrical stimulation mapping (DES/ESM) is a temporary probe of brain function: brief current is passed through electrodes implanted on or in the brain, or through a handheld wand during…
DSA / catheter angiography: Cerebral digital subtraction angiography is an invasive imaging method that uses ionizing radiation. A contrast dye is injected through a catheter in a large artery, and an image taken before the…
Diffusion MRI (DWI/DTI): Diffusion tensor imaging is an MRI method that measures how water diffuses in brain tissue. Diffusion-encoding magnetic field gradients make the scan sensitive to diffusion along at least six…
ECoG: Electrocorticography (ECoG) is an invasive method in which electrode arrays are placed on the brain's surface, typically through surgery that opens the skull without crossing the brain's thin…
ECT: Electroconvulsive therapy (ECT) passes an electrical charge through the brain under brief general anaesthesia, with a muscle relaxant and oxygen. The charge is a train of brief electrical pulses…
EEG (scalp, wet): Conventional wet scalp EEG is a non-invasive recording of the brain's electrical activity through gel-coupled electrodes on the scalp. What it reads is the electric potential at the scalp, which…
EEG (dry electrode): Dry-electrode EEG is scalp EEG recorded through electrodes that use no conductive gel or paste. It reads the electrical activity of the cerebral cortex at the scalp. Without gel the electrode-skin…
Endovascular BCI (Stentrode): An endovascular brain-computer interface is an electrode array mounted on a stent and threaded through the jugular vein into the superior sagittal sinus, a large vein next to the motor cortex. From…
Expansion microscopy: Expansion microscopy is fluorescence imaging of fixed, post-mortem tissue that has been physically enlarged. Labels are linked to a swellable gel grown inside the specimen; after digestion or…
fMRI (7T): Functional MRI at 7 tesla is magnetic resonance imaging of the human brain that infers neuronal activity from blood oxygenation. In gradient-echo BOLD imaging the signal falls as local…
fMRI (BOLD, 3T): BOLD fMRI is a magnetic resonance imaging technique that detects changes in MRI signal intensity linked to blood oxygenation: paramagnetic deoxyhemoglobin alters local magnetic fields and T2/T2*…
fNIRS: fNIRS is a noninvasive optical brain-imaging method in which sensors on the scalp shine near-infrared light (650 to 950 nm) into the head and detect the light scattered back at several wavelengths…
fNIRS (wearable): Wearable fNIRS is near-infrared spectroscopy worn on the head, usually without fibre-optic bundles. Small light sources shine near-infrared light into the scalp and nearby detectors catch what…
Focused ultrasound (FUS) blood–brain barrier opening: Focused-ultrasound blood-brain barrier opening is image-guided sonication at low acoustic pressure, delivered together with injected gas-filled microbubbles. The sound makes the microbubbles in the…
Functional ultrasound (fUS): Functional ultrasound is an imaging method that sends ultrasound plane waves into the brain 1,000 times a second; the Power Doppler signal this yields is proportional to the volume of moving blood…
Gamma Knife radiosurgery: Gamma Knife radiosurgery is a device holding sealed cobalt-60 sources (192 in one version, 201 in another) whose gamma rays pass through circular tungsten openings, with nominal collimator sizes of…
HIFU ablation: High-intensity focused ultrasound (HIFU) ablation is non-invasive neurosurgery: a transducer array sends ultrasound through the skull and concentrates it on a small target inside the brain. What it…
ICMS: Intracortical microstimulation (ICMS) is the writing of small charge-balanced, current-controlled electrical pulses into brain tissue through microelectrode arrays implanted in the cortex. ICMS…
Intracortical arrays: Intracortical microelectrode arrays are tiny penetrating electrodes implanted into the cortex, the brain's outer layer, on a small silicon array or on flexible threads. They record the electrical…
LITT: Laser interstitial thermal therapy (LITT) is an MRI-guided treatment in which a thin laser fiber is placed into the brain along a stereotactic path. The fiber delivers continuous or pulsed…
MEG (OPM): OPM-MEG uses small quantum sensors worn directly on the scalp, recording inside a magnetically shielded room without cryogenic cooling, though each sensor's vapor cell is heated to about 150°C. It…
MEG (SQUID): SQUID-based (cryogenic) MEG is a helmet of superconducting sensors kept near -270 °C by liquid helium; in 2018 commercial systems held about 300 sensors in such a cooled container. It reads the…
Low-field MRI: Low-field MRI is a form of magnetic resonance imaging that uses weaker magnets, below about 1.5 tesla and down to 0.05 tesla, so scanners can be placed at the point of care. Like conventional MRI…
Structural MRI: Structural MRI is nuclear magnetic resonance imaging: a strong static magnetic field lines up the protons in the body's water, and a brief radio-frequency pulse tips them out of alignment. The…
MR spectroscopy: Proton MR spectroscopy (¹H MRS) is a noninvasive MRI-based method that estimates tissue metabolite profiles from proton signals, which are separated by their chemical shift. It chiefly detects NAA…
Neuropixels: A Neuropixels probe is a 10-mm silicon shank (70×20 µm in cross-section) inserted into brain tissue, carrying 960 closely spaced titanium nitride electrode sites, 384 of which can be used at once…
Open microsurgical resection: Open surgical resection is brain surgery that cuts into, removes or disconnects brain tissue, for example taking out a tumour or parts of the temporal lobe; one variant, hemispherotomy, disconnects…
Optogenetics: Optogenetics is neural stimulation by light: a delivered gene makes chosen neurons express a light-gated ion channel, and illumination opens it. In mammalian neurons, switched light controlled…
PET: PET is molecular imaging that uses radioactive tracers. It detects pairs of 511 keV photons produced when positrons and electrons annihilate, mapping where the tracer is concentrated. Depending on…
Photoacoustic microscopy: Short laser pulses are absorbed mainly by haemoglobin in blood, briefly heating it so it emits ultrasound pressure waves. A detector picks up these generated waves, and their one-way acoustic travel…
Photoacoustic tomography: Photoacoustic brain imaging sends brief laser pulses into tissue; light absorbed, mostly by haemoglobin, briefly heats and expands it, emitting ultrasound that surrounding detectors record to…
RNS (responsive neurostimulation): Responsive neurostimulation (RNS) is a closed-loop device implanted in the skull, with leads placed deep in the brain and/or as strips on its surface, each lead having four contacts. It records…
sEEG: Stereo-EEG is an invasive method that implants thin, cylindrical electrodes into the brain with stereotactic guidance, reaching deep, folded and both-sided regions without an open craniotomy…
Temporal interference: Temporal interference stimulation is noninvasive deep-brain electrical stimulation through pairs of scalp electrodes. Each pair passes current at a slightly different kilohertz frequency, too fast…
tES (tDCS / tACS / tRNS): Transcranial electrical stimulation (tES) passes a weak electric current between electrodes on the scalp. In tDCS the current is constant, and at 1–2 mA it sets up a cortical field of up to about…
Transcranial focused ultrasound: Transcranial focused ultrasound (tFUS) is ultrasound aimed through the skull, without surgery, onto targets at the brain's surface or deep inside it. At low intensity, with little heating, the…
TMS: Transcranial magnetic stimulation (TMS) is a noninvasive method in which a coil on the scalp sends pulsed magnetic fields that induce electric fields in the brain. It writes by altering neurons'…
Ultrasound localization microscopy: Ultrasound localization microscopy is a super-resolution ultrasound method mapping the brain's blood vessels. Gas-filled microbubbles in the bloodstream are imaged at raw frame rates of hundreds per…
VNS (implanted): Implanted vagus nerve stimulation uses a pulse generator placed below the collarbone, wired to a coil-shaped cuff wrapped around the left vagus nerve in the neck. It writes by electrically…
Voltage imaging (GEVI): Voltage imaging with genetically encoded indicators is fluorescence microscopy of neurons that carry a protein sensor whose brightness changes with membrane voltage; two-photon excitation reaches…
Volume EM connectomics: Volume electron microscopy is electron imaging of fixed, heavy-metal-stained tissue, serial section by serial section, stitched into a three-dimensional volume; the short wavelength of electrons…