Event Related Potentials Archives

Researchers studying the nervous system have a host of physiological signals at their disposal to provide critical data on neurological function. Various signals present advantages and disadvantages, depending on the demands of the research being conducted. Evoked potentials offer a particularly effective means of measuring the nervous system’s response to certain stimuli, notably visual and auditory cues.

Evoked potentials are employed in both research and clinical settings to measure electrical activity in the central nervous system. Stimulation of specific sensory neural pathways produces this electrical activity, allowing researchers to see the speed and thoroughness with which these signals reach the brain. Evoked potentials provide researchers with heightened precision when isolating and localizing a participant’s response to stimuli.

Because evoked potential amplitudes tend to be low, from less than one to just a few microvolts, these signals can be difficult to differentiate from other higher amplitude signals and background noise. This is resolved by using signal averaging to separate the low-amplitude signals from the noise. Multiple readings are taken with evoked potential signals time-locked to the stimulus. Averaging these measurements allows the evoked potential to be filtered from the random signal noise.

Along with providing useful data for research, evoked potential tests are commonly used in clinical settings to diagnose and explore treatments for a range of disorders such as multiple sclerosis (MS), epilepsy, glaucoma, neuropathies, Alzheimer’s, and others. In both research and clinical applications, evoked potential tests provide several advantages over using other approaches since they are noninvasive, painless, and provide results more quickly than other neurological scans, such as MRI. Types of evoked potentials can be categorized by the stimuli with which they are associated. Visual evoked potentials (VEP) are triggered by visual stimuli such as light flashes or by participants viewing certain patterns. Auditory evoked potentials (AEP) measure responses to sound stimuli such as clicks. Somatosensory evoked potentials (SEP) are triggered by electrical stimulation of peripheral nerves.

A 2022 study by researchers at the Autonomous University of Aguascalientes in Mexico evaluated the effectiveness of using VEP waveforms embedded in electroencephalographic (EEG) signals to determine the health of the optic nerve. The team employed an MP36 data acquisition system connected to an SS2LB lead set to record EEG signals from study participants. The signal data were used to create a database of VEPs that could be processed with analysis software for the early detection of glaucoma and other optic nerve-related illnesses.

A similar study combined the use of EEG signals with VEP to examine how participants recognize em otion in others. Researchers from two universities in China relied on a variation of VEP known as steady-state visual evoked potential (SSVEP), which exhibits distinctive frequency and phase properties. EEG signals were recorded via a BIOPAC data acquisition unit while participants were shown flickering images representing three emotional states—delight, sadness, and anger. The study found a positive correlation between SSVEP amplitude, alpha-frequency entrainment, and accurate identification of emotion.

These are just a few examples of how evoked potentials provide researchers with valuable insight into the central nervous system’s response to stimuli and its relationship to a wide range of physiological states. For additional information on how to use BIOPAC hardware and AcqKnowledge to stimulate a range of senses using electrical, auditory, visual, haptic, scent, and thermal stimuli and record evoked potentials, check out our webinar on Exogenous and Stimulus-related Evoked Potentials.

To learn more about how your study can benefit from using BIOPAC hardware and software to record and analyze evoked potential data, contact your local sales representative.

By Alan Macy, BIOPAC Systems, Inc.

This blog is a continuation of the previous discussion of Electroencephalography or EEG. Short-term Electroencephalography or EEG measurements are typically focused on the nature of cognition. These types of recordings are typically performed in synchrony with well-controlled, environmental, stimuli. Signal-averaging measurements, of this type, are known as Event Related Potentials (ERPs). There are a range of ERP signals, stretching between 50 ms to many seconds, with respect to the occurrence of the event. ERPs require signal averaging methods, to be observed, because their amplitude levels (0.2-2 uV) are usually lower than the ambient EEG signal level.

ERPs can be generated by a wide range of stimuli. The stimulus event can be targeted to any specific human sense or combination of senses (auditory, visual, olfactory, touch or taste). ERPs indicate the superimposed potentials of neuronal activity that synchronously generate when a subject processes sensory information. There are two general types of human subject ERPs. Early ERP wave components occur before 100 milliseconds after the stimulus. Late ERP components occur after 100ms after the stimulus. Early ERPs are known as exogenous potentials and late ERPs are known as endogenous potentials. Exogenous potentials depend on neuronal sensory structure responses that occur prior to cognition. Endogenous potentials depend on cognitive responses to the sensory stimuli.

Slow Cortical Potentials (SCPs) are a class of ERPs that are characterized by slowly-moving, stimulus-related changes in the EEG signal. SCPs originate in cell concentrations in the top cortical layer of the brain. SCP waves (0.01-3 Hz) are EEG signals that occur before and after stimulus presentation. They encompass such pre-stimulus measures as Contingent Negative Variation (CNV) and Readiness Potential (RP). The CNV is a slow-changing negative potential that happens between an initial warning and a “go” stimulus. NV amplitude depends on the subject’s expectation of an imagined, forthcoming event. The RP is associated with the beginning of movement. The RP precedes movement and is identified as a slow-changing negative potential that maximizes with movement onset. The RP is observed when signal averaging the EEG, from the motor cortex, synchronously with movement.

EEG can be useful to:

Monitor alertness and conscious states
Evaluate inhibitory control over behavior
Locate areas of neural damage
Establish levels of cognitive engagement
Investigate brain disorders, such as Alzheimer’s, epilepsy and seizures
Establish brain / computer interfaces
Monitor sleep

For more information on BIOPAC’s wide range of tools for recording, displaying, and analyzing EEG signals from human and animal subjects, including automated EEG analysis, seizure detection, evoked responses and many others, visit BIOPAC’s EEG Analysis page or view BIOPAC’s full line of electrodes, amplifiers, and wearable, wireless transmitters and loggers.

BIOPAC Systems, Inc. provides life science researchers and educators with data acquisition and analysis systems that inspire people and enable greater discovery about life. Visit us at www.biopac.com.