Electrophysiological Measurement of Noxious-evoked Brain Activity in Neonates Using a Flat-tip Probe Coupled to Electroencephalography
November 29th, 2017
Measuring pain in non-verbal patients is a challenge. In this study we combine EEG recording with stimulation using a flat-tip probe to detect noxious-evoked brain activity in an objective manner.
The overall goal of this electrophysiological measurement is to objectively asses nociception in newborn infants. This method can help answer key questions in the neonatal field such as how non-verbal patients perceive pain and how it differs in response to different conditions. The main advantage of this technique is that it can be used in neonates born at term or late pre-term starting at 34 weeks of gestational age.
The implications of this technique extends toward investigation of pain because it is the first objective measurement of nociception in non-verbal patients. Generally, individuals new to this method will struggle because experience with EEG is required. We first had the idea for this method when we observed after delivery different pain responses in neonates born spontaneously as compared to those born by elective ceasarean section.
But also at the neonatal intensive care unit, babies are exposed to so many potentially painful procedures. You don't know how much they perceive even when they are under analgesic drugs. Now we can objectively measure their noxious response.
Before starting, ensure the baby is quiet and settled. The baby can be asleep but sucking motion should be absent during the recording because of movement artifacts. Measure the neonate's head circumference with a measuring tape to define the size of the EEG cap.
Then identify the active electrode position by marking the middle point between nasion and inion and the middle point between left and right pre-auricular point with a skin marker pencil. A schematic of the electrode positions is shown here. Identify the positions for the ground electrode on the right forehead and for the reference electrode over the left mastoid.
Clean the three electrode sites using a cotton swab soaked in skin disinfectant. Then gently scrub the electrode sites with EEG prepping paste to lower the impedance and place the EEG cap with the electrodes attached on the neonate's head. Next, use a syringe with a short plastic needle to inject conductive EEG gel into the electrodes to optimize the contact between the electrodes and the scalp.
Then to ensure the impedance is below 50 kilo ohms, connect an impedance meter to the electrodes and set it below 50 kilo ohms. The light will turn green if the impedance is below 50 kilo ohms. After this, connect the electrodes to the amplifier.
Position a camera to record the neonate's facial expressions. Then connect the flat-tip probe to the contact trigger device which is fixed to the EEG recording device. Begin by choosing a new work file.
Set the sampling rate to 2, 000 Hertz. Set the low cutoff filter to a frequency of one Hertz. Set the high cutoff filter to 70 Hertz and the notch filter to 50 Hertz.
Select a study name to store the data. Start the EEG and the video recording. Whilst the neonate's right hand is held in a horizontal position, record background EEG activity.
Annotate the EEG recording manually to record periods where no stimuli are applied and the infant is resting. Once the background EEG is stable, administer the required amount of flat-tip probe stimuli to the neonate's right hand. Be careful to use the flat-tip probe perpendicularly to the neonate's hand so the tip does not bend and the correct force is applied.
When the flat-tip probe reaches the nominal force on the skin, a trigger signal is generated by the contact trigger device. This signal is sent to the computer tagging the EEG recording with the trigger mark. After the stimuli are administered, stop all the recordings and document the experimental setting details.
After taking off the electrodes at the infant's head, clean the scalp with a wet towel to remove any residuals. A flat-tip probe stimulus of 32 millinewtons was applied to the right hand of one patient. The shaded region shows the time window of interest which occurs 200 to 500 milliseconds after the stimulus.
After a single stimulus, the noxious-evoked response is visible at approximately 300 milliseconds post stimulus onset. The principle peak at 250 milliseconds is indicated with an arrow. This trace demonstrates the average response of 50 stimuli applied with a force of 32 millinewtons to the same patient.
Note that the noxious-evoked potential is clearer if more stimuli are applied. Woody filtering can be used to adjust for slight variability in the response latency. The predefined template shown in red is projected onto the EEG to calculate the magnitude of the noxious-evoked response.
Once mastered, this technique can be done in 15 minutes if it is performed properly. While attempting this procedure, it's important to remember to wait to apply the stimuli until the infant is calm. After watching this video, you should have a good understanding of how to objectively measure nociception at bedside.
View the full transcript and gain access to thousands of scientific videos
Overview
This study aims to objectively assess nociception in non-verbal patients, specifically newborn infants, using EEG recordings combined with noxious stimulation. This method provides insights into how these patients perceive pain under different conditions.
Key Study Components
Area of Science
- Neuroscience
- Pain perception
- Electrophysiology
Background
- Measuring pain in non-verbal patients is challenging.
- Understanding pain responses in neonates is crucial for neonatal care.
- The technique can be applied to neonates born at term or late pre-term.
- Previous observations indicated different pain responses based on delivery methods.
Purpose of Study
- To develop an objective measurement of nociception in non-verbal patients.
- To investigate how pain perception differs in various conditions.
- To enhance understanding of pain responses in newborns.
Methods Used
- EEG recording to measure brain activity.
- Stimulation using a flat-tip probe to evoke noxious responses.
- Application of the method starting at 34 weeks of gestational age.
- Comparison of pain responses in different neonatal delivery scenarios.
Main Results
- The method provides the first objective measurement of nociception in non-verbal patients.
- Different pain responses were observed in neonates based on delivery method.
- The technique is applicable to a wide range of neonatal patients.
- Experience with EEG is necessary for effective implementation.
Conclusions
- This technique represents a significant advancement in pain assessment for non-verbal patients.
- It opens avenues for further research into pain perception in neonates.
- Understanding nociception can improve neonatal care practices.
Frequently Asked Questions
Executive Industry Relevance
Objective measurement of nociception in non-verbal neonatal patients addresses a critical gap in preclinical analgesic development, enabling direct assessment of central pain processing without reliance on behavioral proxies. This electrophysiological approach supports mechanistic de-risking of analgesic candidates by providing quantifiable, reproducible biomarkers of noxious-evoked brain activity. Applicable from 34 weeks gestational age, the method facilitates early translational continuity in neonatal pain model validation and analgesic efficacy screening.
Strategic Applications in Biopharma R&D
Early Discovery & Target Validation
- Scientific Value: Enables interrogation of therapeutic hypotheses by measuring cortical nociceptive responses as a direct readout of central pain pathway engagement.
- Operational Value: Provides standardized, reproducible noxious-evoked potentials via flat-tip probe stimulation, reducing variability in target validation assays.
- Predictive Value: Supports lead identification by allowing objective comparison of analgesic efficacy across compounds through consistent EEG-based nociception metrics.
Screening & Assay Development
- Assay Readiness: Generates quantitative dependent variable measurements (e.g., peak amplitude at 300 ms post-stimulus) enabling dose-response characterization of analgesic candidates.
- Reproducibility: Requires impedance below 50 kΩ and fixed stimulus parameters (32 mN force, perpendicular application) to ensure consistent signal acquisition across runs.
- Scalability: Protocol completion in ~15 minutes per session supports high-throughput screening readiness when integrated with automated stimulus delivery and EEG acquisition systems.
Translational & Preclinical Research
- Disease-Relevant System: Models human neonatal nociception in infants ≥34 weeks gestational age, offering translational fidelity for perinatal analgesic development.
- Preclinical Continuity: Enables longitudinal assessment of nociceptive trajectory from discovery through preclinical validation by tracking evoked potential maturation.
- Risk-Adjusted Advancement: Objective nociception metrics inform go/no-go decisions by reducing reliance on indirect physiological or behavioral pain indicators with known limitations in non-verbal models.
Pipeline & Workflow Integration
The method fits within the early discovery to preclinical continuum, serving as a discovery biology tool for target engagement confirmation and a translational bridge for analgesic efficacy evaluation in neonatal-relevant systems.
- Discovery Biology: Supports hypothesis testing of analgesic targets by measuring noxious-evoked cortical responses as a functional biomarker of pathway modulation.
- Screening: Delivers assay-standardized, quantitative EEG outputs (e.g., evoked potential magnitude via template projection) enabling compound comparison and hit-to-lead progression.
- Analytics: Requires predefined time-locked analysis windows (200–500 ms post-stimulus) and Woody filtering for latency adjustment to ensure consistent quantitative readouts.
- Translational Research: Connects to preclinical continuity through gestational age–aligned applicability, allowing extrapolation of analgesic effects from neonatal models to clinical pain assessment.
- Enterprise Reuse: Establishes a reusable electrophysiological platform for nociception assessment across analgesic classes, reducing redundant assay development in neonatal pain programs.
Operational & Enterprise Impact
- Scientific Value: Provides mechanistic de-risking by isolating central nociceptive processing from confounding peripheral or behavioral variables in pain assessment.
- Operational Value: Ensures reproducibility through standardized stimulus delivery (flat-tip probe, contact trigger) and EEG preprocessing (impedance <50 kΩ, gel injection, site prep).
- Strategic Value: Improves capital efficiency by enabling early, objective go/no-go decisions on analgesic candidates based on central nervous system engagement.
- Portfolio Impact: Supports risk-adjusted prioritization by quantifying target modulation efficacy in a disease-relevant neonatal nociception system.
Implementation Considerations
- Requires expertise in EEG electrode placement, impedance monitoring, and neonatal signal artifact mitigation (e.g., excluding sucking motion).
- Dependent on EEG amplifier capable of 2000 Hz sampling, 1–70 Hz bandpass, and 50 Hz notch filtering as specified in the protocol.
- Necessitates cross-team standardization of stimulus application (perpendicular flat-tip probe at 32 mN) and trigger synchronization with EEG acquisition.
- Adaptation considerations include adjusting stimulus intensity for age-dependent skin thickness while maintaining noxious-evoked potential detectability.
- Practical limitation: Movement artifacts from infant motion necessitate quiet/sleeping state during recording, constraining throughput in agitated neonates.
