Written and reviewed by the InVivoLabs team, drawing on 15+ years of hands-on work in preclinical surgical models and CNS drug delivery. Last reviewed October 28, 2026.
Why electrophysiology matters in CNS drug discovery
Most CNS endpoints are indirect. Behavior is variable and slow to read out, and histology shows what happened after the fact. Electrophysiology measures the activity of neurons and circuits directly, in milliseconds, so it can show that a compound engages its target and changes neuronal function at a given concentration or exposure.
That makes it useful at every stage: confirming mechanism on a recombinant ion channel, showing that a compound restores synaptic function in tissue from a disease model, and demonstrating a dose-dependent change in brain activity in a living animal using a readout, such as EEG, that can be measured the same way in clinical trials.
Three levels of electrophysiology work
| Level | Typical preparations | Best for |
|---|---|---|
| In vitro, cell-based | Manual and automated patch clamp on cell lines; primary or iPSC-derived neurons on multi-electrode arrays (MEA) | Potency and mechanism at ion channels and receptors; screening many compounds; network activity and seizure-liability screens |
| Ex vivo | Acute brain or spinal cord slices; field potential and whole-cell recordings | Synaptic transmission and plasticity in an intact local circuit; disease-model phenotypes; tissue from dosed animals |
| In vivo | EEG/ECoG, local field potentials, single- and multi-unit recording, evoked potentials, spinal dorsal horn and peripheral nerve recording | Effects at real exposures in intact circuits; PK/PD; translational biomarkers; CNS safety |
Cell-based work: patch clamp and MEA
Patch clamp measures current through ion channels in a single cell. Automated platforms test many compounds against a recombinant target, such as a sodium, potassium or calcium channel, or a ligand-gated receptor such as GABA-A or NMDA, and report potency, state dependence and use dependence. Manual patch clamp is slower but gives the highest-quality data on difficult targets and native neurons. Cardiac hERG testing uses the same technology but is a separate safety assay; see our safety pharmacology CROs.
Multi-electrode arrays record spontaneous firing and network bursting from cultures of primary rodent neurons or human iPSC-derived neurons over days or weeks. They are used for phenotypic screening, for comparing patient-derived and control lines, and as an early screen for seizure liability.
Primary neuron data are only as good as the cultures. Ask how the lab controls culture age and density, and what positive controls it runs on every plate.
Ex vivo brain slice electrophysiology
Acute slices keep local circuits intact while giving direct access to identified neurons. Common readouts include field excitatory postsynaptic potentials and long-term potentiation (LTP) in the hippocampus, whole-cell recordings of synaptic currents and intrinsic excitability, and paired-pulse measures of release probability.
Slices can be used in two ways. Compounds can be applied to the bath at defined concentrations, which isolates mechanism. Or slices can be taken from animals dosed in vivo, which tests the effect of real brain exposure, an approach that pairs well with PK sampling from the same animals. Slices from transgenic or disease-model animals, for example models of Alzheimer’s disease, epilepsy or neurodevelopmental disorders, can show a synaptic deficit and whether a compound reverses it.
Slice health decides data quality. Ask about the dissection and cutting solutions the lab uses, how long after preparation slices remain usable, how many slices and animals contribute to each group, and whether recordings are analyzed blind to treatment.
In vivo electrophysiology
EEG and quantitative EEG
Electroencephalography in freely moving rodents, recorded by implanted telemetry or tethered systems, is the workhorse of in vivo CNS electrophysiology. Quantitative (pharmaco-)EEG analyzes the power in each frequency band and gives many drug classes a characteristic signature. The same recordings can score sleep–wake architecture and detect seizures or epileptiform activity. EEG is also recorded in larger species, including nonhuman primates, when a closer match to human brain anatomy or pharmacology is needed.
Single-unit, multi-unit and local field potential recording
Electrodes or silicon probes placed in a specific brain region record the firing of individual neurons and local oscillations, in anesthetized or freely moving animals. This shows how a compound changes activity in the circuit it is meant to act on, for example dopamine neuron firing or hippocampal oscillations.
Spinal cord and peripheral nerve recording
For pain programs, recordings from dorsal horn neurons measure how a compound alters responses to mechanical, thermal or electrical stimulation, a more direct readout than behavioral withdrawal tests alone. Nerve conduction velocity and amplitude are used to measure peripheral neuropathy, including chemotherapy-induced and diabetic neuropathy. Pair these with our list of pain model CROs.
Translational electrophysiology biomarkers
Some electrophysiological readouts can be measured in nearly the same way in animals and in people, which makes them useful bridges into phase 1. Examples include qEEG spectral changes, sleep architecture, and evoked responses such as auditory event-related potentials, mismatch negativity and the auditory steady-state response, which are used in schizophrenia and neurodevelopmental programs.
To get the most from them, record in the preclinical study with the montage, stimulus parameters and analysis methods you expect to use clinically, and collect plasma (and where possible brain or CSF) samples alongside the recordings so the effect can be tied to exposure.
Electrophysiology in CNS safety
Seizure liability is a common reason CNS programs stall. Cell-based MEA and brain slice assays can flag pro-convulsant activity early, and EEG in rodents or non-rodents confirms whether convulsions or subclinical epileptiform activity occur at relevant exposures. ICH S7A asks for CNS assessment in the safety pharmacology core battery; EEG is not routinely required, but it is often added when there is a signal or a mechanistic concern. See CNS safety CROs and our GLP toxicology guide.
Choosing an electrophysiology CRO
Many sponsors look for a lab that combines electrophysiology with neuropharmacology, so recordings, behavior, PK and histology come from the same animals and the same team. Others pair a specialist electrophysiology lab with a separate in vivo provider. Either way, ask:
- Which preparations and readouts have you run for our target class in the past year, and can you share example traces and baseline variability?
- For in vivo work: who performs the implant surgery, what are your implant success and attrition rates, and how long do implants remain usable?
- Which reference compounds do you use to show the assay responds as expected?
- How is analysis done: commercial software, in-house code, or manual scoring? Is it blind to treatment, and will we receive raw data files?
- Can PK samples be collected from the same animals and time points as the recordings?
- For translational readouts: can you match the recording montage and stimulus parameters planned for our clinical study?
Our CRO selection guide covers the broader questions on quality systems, capacity and contracting.
Frequently asked questions
Which CROs specialize in CNS electrophysiology for drug discovery?
Fewer labs offer electrophysiology than offer behavioral or histology endpoints, and most specialize in one level: cell-based patch clamp and MEA, ex vivo brain slice, or in vivo recording. Start with the CNS and neuroscience CROs in our directory, then ask each lab which preparations, species and readouts it has run in the past year, and request example traces and baseline data.
Should we use in vivo or ex vivo electrophysiology?
Ex vivo brain slice recording gives precise, mechanistic data on a defined circuit and is faster and cheaper per compound. In vivo recording shows what happens with real exposure, intact circuits and behavior, and EEG-based readouts translate to the clinic. Many programs use slice work to confirm mechanism, then in vivo EEG or evoked potentials to show target engagement at relevant exposures.
Can electrophysiology be run under GLP?
Efficacy and mechanism studies are normally non-GLP. Electrophysiological endpoints that support safety, such as EEG for seizure liability within a CNS safety pharmacology or toxicology study, can be run under GLP at labs that have validated the equipment and software.
How long does an in vivo EEG study take?
Allow for surgery, at least one to two weeks of recovery, and baseline recording before dosing starts. Crossover designs, where each animal receives vehicle and several doses, reduce animal numbers but add washout time.