Direct electrical stimulation mapping

Implanted & surgical write · writes

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 surgery. The current acts most readily on axons and can inhibit or excite tissue nearby and at a distance; in a 2020 study of recorded neurons it most often inhibited, with excitation linked to high frequencies and sites near white matter. What is read is the response: movements, sensations or language changes, evoked potentials at other electrodes, and afterdischarges.

Spatial resolution: 10 mm
Temporal resolution: 10 ms (inter-pulse interval)
Field of view: 340–390 mm³ (suprathreshold volume)
Reads: motor responses; somatosensory responses (sensory changes during stimulation); temporal-lobe language-response thresholds; cortico-cortical evoked potentials (CCEPs) at other electrodes; after-discharge thresholds
Writes: neuronal excitation and inhibition; local and distant effects; functional-localization interference
Destructive?: minimally destructive
Prerequisites: surgery: For extraoperative ESM, implant subdural grids/strips by craniotomy or SEEG depth arrays through burr holes; intraoperative ESM may instead use a wand.; other: Use ECoG to monitor for afterdischarges.; anesthesia: Awake craniotomy is used for language DES.
Theoretical spatial resolution: 100 µm
Theoretical temporal resolution: 560 µs (inter-pulse interval)

Description

Direct electrical stimulation, also called electrical stimulation mapping (DES/ESM), is transient functional mapping of the brain: small bipolar currents inhibit or excite tissue while the responses are recorded. Extraoperative mapping delivers the current through implanted subdural grids or strips, or through stereo-EEG depth arrays placed through burr holes. Intraoperative mapping can use a handheld wand. Awake craniotomy is used for language mapping. The current acts most readily on axons: the axon initial segment and the nodes of Ranvier are the most excitable elements because they carry the most sodium channels. In quantitative models, high-frequency stimulation selectively activates low-threshold fibers of passage and axon terminals that low-frequency stimulation does not. Effects are both local and distant: stimulation activates sites the stimulated area projects to, in a pattern suggesting monosynaptic transmission, and the most common clinical effect is silencing of those areas. In a 2020 study of recorded neuronal activity, stimulation most often inhibited neurons; excitation most often came with high-frequency stimulation and with sites near white matter. What is read is the functional response: motor, somatosensory and language responses, cortico-cortical evoked potentials at other electrodes and afterdischarge thresholds. Electrocorticography monitors afterdischarges, which can confound localization. Extraoperative mapping uses 50 or 60 Hz trains of 0.2 to 0.3 ms pulses lasting 3 to 5 s, starting at 0.5 to 2 mA and rising by 0.5 to 1 mA until a response, an afterdischarge, a seizure or the device limit, with maxima of 10 to 20 mA for subdural electrodes and 3 to 8 mA for stereo-EEG.

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