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An event-related potential (ERP) is the measured
brain The brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head ( cephalization), usually near organs for special ...
response that is the direct result of a specific
sensory Sensory may refer to: Biology * Sensory ecology, how organisms obtain information about their environment * Sensory neuron, nerve cell responsible for transmitting information about external stimuli * Sensory perception, the process of acquiri ...
,
cognitive Cognition refers to "the mental action or process of acquiring knowledge and understanding through thought, experience, and the senses". It encompasses all aspects of intellectual functions and processes such as: perception, attention, thought, ...
, or motor event. More formally, it is any stereotyped electrophysiological response to a stimulus. The study of the brain in this way provides a noninvasive means of evaluating brain functioning. ERPs are measured by means of
electroencephalography Electroencephalography (EEG) is a method to record an electrogram of the spontaneous electrical activity of the brain. The biosignals detected by EEG have been shown to represent the postsynaptic potentials of pyramidal neurons in the neocortex ...
(EEG). The magnetoencephalography (MEG) equivalent of ERP is the ERF, or event-related field. Evoked potentials and
induced potential Induce may refer to: * Induced consumption * Induced innovation * Induced character * Induced coma * Induced menopause * Induced metric * Induced path * Induced topology * Induce (musician), American musician See also * Inducement (disambiguatio ...
s are subtypes of ERPs.


History

With the discovery of the electroencephalogram (EEG) in 1924, Hans Berger revealed that one could measure the electrical activity of the human brain by placing electrodes on the scalp and amplifying the signal. Changes in voltage can then be plotted over a period of time. He observed that the voltages could be influenced by external events that stimulated the senses. The EEG proved to be a useful source in recording brain activity over the ensuing decades. However, it tended to be very difficult to assess the highly specific neural process that are the focus of cognitive neuroscience because using pure EEG data made it difficult to isolate individual neurocognitive processes. Event-related potentials (ERPs) offered a more sophisticated method of extracting more specific sensory, cognitive, and motor events by using simple averaging techniques. In 1935–1936, Pauline and Hallowell Davis recorded the first known ERPs on awake humans and their findings were published a few years later, in 1939. Due to World War II not much research was conducted in the 1940s, but research focusing on sensory issues picked back up again in the 1950s. In 1964, research by
Grey Walter William Grey Walter (February 19, 1910 – May 6, 1977) was an United States, American-born United Kingdom, British neurophysiologist, cybernetician and robotician. Early life and education Walter was born in Kansas City, Missouri, Kansas City, ...
and colleagues began the modern era of ERP component discoveries when they reported the first cognitive ERP component, called the
contingent negative variation The contingent negative variation (CNV) is a negative slow surface potential, as measured by electroencephalography (EEG), that occurs during the period between a warning stimulus or signal and an imperative ("go") stimulus. The CNV was one of the ...
(CNV). Sutton, Braren, and Zubin (1965) made another advancement with the discovery of the P3 component. Over the next fifteen years, ERP component research became increasingly popular. The 1980s, with the introduction of inexpensive computers, opened up a new door for cognitive neuroscience research. Currently, ERP is one of the most widely used methods in cognitive neuroscience research to study the
physiological Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemical ...
correlates of
sensory Sensory may refer to: Biology * Sensory ecology, how organisms obtain information about their environment * Sensory neuron, nerve cell responsible for transmitting information about external stimuli * Sensory perception, the process of acquiri ...
, perceptual and
cognitive Cognition refers to "the mental action or process of acquiring knowledge and understanding through thought, experience, and the senses". It encompasses all aspects of intellectual functions and processes such as: perception, attention, thought, ...
activity associated with processing information.


Calculation

ERPs can be reliably measured using
electroencephalograph Electroencephalography (EEG) is a method to record an electrogram of the spontaneous electrical activity of the brain. The biosignals detected by EEG have been shown to represent the postsynaptic potentials of pyramidal neurons in the neocortex ...
y (EEG), a procedure that measures electrical activity of the brain over time using electrodes placed on the scalp. The EEG reflects thousands of simultaneously ongoing brain processes. This means that the brain response to a single stimulus or event of interest is not usually visible in the EEG recording of a single trial. To see the brain's response to a stimulus, the experimenter must conduct many trials and average the results together, causing random brain activity to be averaged out and the relevant waveform to remain, called the ERP. The random ( background) brain activity together with other bio-signals (e.g.,
EOG Electrooculography (EOG) is a technique for measuring the corneo-retinal standing potential that exists between the front and the back of the human eye. The resulting signal is called the electrooculogram. Primary applications are in ophthalmol ...
, EMG, EKG) and electromagnetic interference (e.g., line noise, fluorescent lamps) constitute the noise contribution to the recorded ERP. This noise obscures the signal of interest, which is the sequence of underlying ERPs under study. From an engineering point of view it is possible to define the
signal-to-noise ratio Signal-to-noise ratio (SNR or S/N) is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. SNR is defined as the ratio of signal power to the noise power, often expressed in deci ...
(SNR) of the recorded ERPs. Averaging increases the SNR of the recorded ERPs making them discernible and allowing for their interpretation. This has a simple mathematical explanation provided that some simplifying assumptions are made. These assumptions are: # The signal of interest is made of a sequence of event-locked ERPs with invariable latency and shape # The noise can be approximated by a zero-mean Gaussian random process of variance \sigma^2 which is uncorrelated between trials and not time-locked to the event (this assumption can be easily violated, for example in the case of a subject doing little tongue movements while mentally counting the targets in an experiment). Having defined k, the trial number, and t, the time elapsed after the kth event, each recorded trial can be written as x(t,k)=s(t)+n(t,k) where s(t) is the signal and n(t,k) is the noise (Note that, under the assumptions above, the signal does not depend on the specific trial while the noise does). The average of N trials is :\bar x(t) = \frac \sum_^N x(t,k) = s(t) + \frac \sum_^N n(t,k) . The
expected value In probability theory, the expected value (also called expectation, expectancy, mathematical expectation, mean, average, or first moment) is a generalization of the weighted average. Informally, the expected value is the arithmetic mean of a l ...
of \bar x(t) is (as hoped) the signal itself, \operatorname bar x(t)= s(t). Its variance is :\operatorname bar x(t)= \operatorname\left left(\bar x(t) - \operatorname[\bar x(t)right)^2\right">bar_x(t).html" ;"title="left(\bar x(t) - \operatorname[\bar x(t)">left(\bar x(t) - \operatorname[\bar x(t)right)^2\right= \frac \operatorname\left[\left(\sum_^N n(t,k)\right)^2\right] = \frac \sum_^N \operatorname\left[n(t,k)^2\right] = \frac. For this reason the noise amplitude of the average of N trials is expected to deviate from the mean (which is s(t)) by less or equal than \sigma/ in 68% of the cases. In particular, the deviation wherein 68% of the noise amplitudes lie is 1/ times that of a single trial. A larger deviation of 2 \sigma/ can already be expected to encompass 95% of all noise amplitudes. Wide amplitude noise (such as eye blinks or movement artifacts) are often several orders of magnitude larger than the underlying ERPs. Therefore, trials containing such artifacts should be removed before averaging. Artifact rejection can be performed manually by visual inspection or using an automated procedure based on predefined fixed thresholds (limiting the maximum EEG amplitude or slope) or on time-varying thresholds derived from the statistics of the set of trials.


Nomenclature

ERP waveforms consist of a series of positive and negative voltage deflections, which are related to a set of underlying components. Though some ERP components are referred to with acronyms (e.g.,
contingent negative variation The contingent negative variation (CNV) is a negative slow surface potential, as measured by electroencephalography (EEG), that occurs during the period between a warning stimulus or signal and an imperative ("go") stimulus. The CNV was one of the ...
 – CNV,
error-related negativity Error-related negativity (ERN), sometimes referred to as the Ne, is a component of an event-related potential (ERP). ERPs are electrical activity in the brain as measured through electroencephalography (EEG) and time-locked to an external event (e.g ...
 – ERN), most components are referred to by a letter (N/P) indicating polarity (negative/positive), followed by a number indicating either the latency in milliseconds or the component's ordinal position in the waveform. For instance, a negative-going peak that is the first substantial peak in the waveform and often occurs about 100 milliseconds after a stimulus is presented is often called the N100 (indicating its latency is 100 ms after the stimulus and that it is negative) or N1 (indicating that it is the first peak and is negative); it is often followed by a positive peak, usually called the P200 or P2. The stated latencies for ERP components are often quite variable, particularly so for the later components that are related to the cognitive processing of the stimulus. For example, the P300 component may exhibit a peak anywhere between 250 ms – 700 ms.


Advantages and disadvantages


Relative to behavioral measures

Compared with behavioral procedures, ERPs provide a continuous measure of processing between a stimulus and a response, making it possible to determine which stage(s) are being affected by a specific experimental manipulation. Another advantage over behavioral measures is that they can provide a measure of processing of stimuli even when there is no behavioral change. However, because of the significantly small size of an ERP, it usually takes a large number of trials to accurately measure it correctly.


Relative to other neurophysiological measures


Invasiveness

Unlike microelectrodes, which require an electrode to be inserted into the brain, and PET scans that expose humans to radiation, ERPs use EEG, a non-invasive procedure.


Spatial and temporal resolution

ERPs provide excellent temporal resolution—as the speed of ERP recording is only constrained by the sampling rate that the recording equipment can feasibly support, whereas hemodynamic measures (such as fMRI, PET, and
fNIRS Functional near-infrared spectroscopy (fNIRS) is an optical brain monitoring technique which uses near-infrared spectroscopy for the purpose of functional neuroimaging. Using fNIRS, brain activity is measured by using near-infrared light to estimat ...
) are inherently limited by the slow speed of the
BOLD In typography, emphasis is the strengthening of words in a text with a font in a different style from the rest of the text, to highlight them. It is the equivalent of prosody stress in speech. Methods and use The most common methods in W ...
response. The spatial resolution of an ERP, however, is much poorer than that of hemodynamic methods—in fact, the location of ERP sources is an inverse problem that cannot be exactly solved, only estimated. Thus, ERPs are well suited to research questions about the speed of neural activity, and are less well suited to research questions about the location of such activity.


Cost

ERP research is much cheaper to do than other imaging techniques such as fMRI, PET, and
MEG Meg is a feminine given name, often a short form of Megatron, Megan, Megumi (Japanese), etc. It may refer to: People *Meg (singer), a Japanese singer *Meg Cabot (born 1967), American author of romantic and paranormal fiction *Meg Burton Cahill ( ...
. This is because purchasing and maintaining an EEG system is less expensive than the other systems.


Clinical

Physicians and neurologists will sometimes use a flashing visual checkerboard stimulus to test for any damage or trauma in the visual system. In a healthy person, this stimulus will elicit a strong response over the primary visual cortex located in the occipital lobe, in the back of the brain. ERP component abnormalities in clinical research have been shown in neurological conditions such as: * AD/HD * Dementia * Parkinson's disease *
Multiple sclerosis Multiple (cerebral) sclerosis (MS), also known as encephalomyelitis disseminata or disseminated sclerosis, is the most common demyelinating disease, in which the insulating covers of nerve cells in the brain and spinal cord are damaged. This d ...
* Head injuries * Stroke * Obsessive-compulsive disorder * Schizophrenia * Depression * Autism Spectrum Disorder


Research

ERPs are used extensively in neuroscience,
cognitive psychology Cognitive psychology is the scientific study of mental processes such as attention, language use, memory, perception, problem solving, creativity, and reasoning. Cognitive psychology originated in the 1960s in a break from behaviorism, which ...
, cognitive science, and psycho-physiological research. Experimental psychologists and neuroscientists have discovered many different stimuli that elicit reliable ERPs from participants. The timing of these responses is thought to provide a measure of the timing of the brain's communication or timing of information processing. For example, in the checkerboard paradigm described above, healthy participants' first response of the visual cortex is around 50–70 ms. This would seem to indicate that this is the amount of time it takes for the transduced visual stimulus to reach the cortex after light first enters the
eye Eyes are organs of the visual system. They provide living organisms with vision, the ability to receive and process visual detail, as well as enabling several photo response functions that are independent of vision. Eyes detect light and conv ...
. Alternatively, the P300 response occurs at around 300ms in the oddball paradigm, for example, regardless of the type of stimulus presented: visual, tactile, auditory,
olfactory The sense of smell, or olfaction, is the special sense through which smells (or odors) are perceived. The sense of smell has many functions, including detecting desirable foods, hazards, and pheromones, and plays a role in taste. In humans, it ...
, gustatory, etc. Because of this general invariance with regard to stimulus type, the P300 component is understood to reflect a higher cognitive response to unexpected and/or cognitively salient stimuli. The P300 response has also been studied in the context of information and memory detection. In addition, there are studies on abnormalities of P300 in depression. Depressed patients tend to have a reduced P200 and P300 amplitude and a prolonged P300 latency. Due to the consistency of the P300 response to novel stimuli, a brain–computer interface can be constructed which relies on it. By arranging many signals in a grid, randomly flashing the rows of the grid as in the previous paradigm, and observing the P300 responses of a subject staring at the grid, the subject may communicate which stimulus he is looking at, and thus slowly "type" words. Another area of research in the field of ERP lies in the efference copy. This predictive mechanism plays a central role in for example human verbalization. Efference copies, however, do not only occur with spoken words, but also with inner language - i.e. the quiet production of words - which has also been proven by event-related potentials. Other ERPs used frequently in research, especially neurolinguistics research, include the
ELAN Elan or Élan may refer to: People *Elan Atias (born 1975), American singer-songwriter *Elán (musician) (born 1983), Mexican singer * Poets of Elan, a group of Ecuadorian poets Fictional characters * Elan (Order of the Stick), a character in th ...
, the N400, and the P600/SPS. The analysis of ERP data is also increasingly supported by machine learning algorithms.


Number of Trials

A common issue in ERP studies is whether the observed data have a sufficient number of trials to support statistical analysis. The background noise in any ERP for any individual can vary. Therefore simply characterizing the number of ERP trials needed for a robust component response is inadequate. Therefore, ERP researchers can use metrics like the standardized measurement error (SME) to justify the examination of between-condition or between-group differences or estimates of internal consistency to justify the examination of individual differences.


See also

*
Bereitschaftspotential In neurology, the Bereitschaftspotential or BP (German for "readiness potential"), also called the pre-motor potential or readiness potential (RP), is a measure of activity in the motor cortex and supplementary motor area of the brain leading up to ...
* C1 and P1 * Contingent negative variation *
Difference due to memory Difference due to memory (Dm) indexes differences in neural activity during the study phase of an experiment for items that subsequently are remembered compared to items that are later forgotten. It is mainly discussed as an event-related potential ...
* Early left anterior negativity *
Erich Schröger Erich Schröger (born 11 November 1958, in Munich) is a German psychologist and neuroscientist. Biography Erich Schröger studied philosophy and psychology at the Munich School of Philosophy and at the Ludwig Maximilians University (LMU) in Mun ...
*
Error-related negativity Error-related negativity (ERN), sometimes referred to as the Ne, is a component of an event-related potential (ERP). ERPs are electrical activity in the brain as measured through electroencephalography (EEG) and time-locked to an external event (e. ...
* Evoked potential *
Induced activity Neural oscillations, or brainwaves, are rhythmic or repetitive patterns of neural activity in the central nervous system. Neural tissue can generate oscillatory activity in many ways, driven either by mechanisms within individual neurons or by ...
*
Lateralized readiness potential In neuroscience, the lateralized readiness potential (LRP) is an event-related brain potential, or increase in electrical activity at the surface of the brain, that is thought to reflect the preparation of motor activity on a certain side of the bo ...
* Mismatch negativity * Negativity: N100
Visual N1 The visual N1 is a visual evoked potential, a type of event-related electrical potential (ERP), that is produced in the brain and recorded on the scalp. The N1 is so named to reflect the polarity and typical timing of the component. The "N" indic ...
N170 The N170 is a component of the event-related potential (ERP) that reflects the neural processing of faces, familiar objects or words. Furthermore, the N170 is modulated by prediction error processes. When potentials evoked by images of faces are ...
N200
N2pc N2pc refers to an ERP component linked to selective attention.Luck, S. J. (2005). "The operation of attention—millisecond by millisecond—over the first half second." In H. Ogmen & B. G. Breitmeyer (Eds.), ''The first half second: The microgene ...
N400 * Positivity: P200P300P3aP3b
Late positive component The late positive component or late positive complex (LPC) is a positive-going event-related brain potential (ERP) component that has been important in studies of explicit recognition memory.Munte, T. F., Urbach, T. P., Duzel, E., & Kutas, M., (200 ...
P600 *
Somatosensory evoked potential Somatosensory evoked potential (SEP or SSEP) is the electrical activity of the brain that results from the stimulation of touch. SEP tests measure that activity and are a useful, noninvasive means of assessing somatosensory system functioning. By co ...


References


Further reading

* * * * * *


External links



– ERP Summer School 2017 was held in The School of Psychology, Bangor University from 25–30 June 2017
EEGLAB Toolbox
– A freely available, open-source, Matlab toolbox for processing and analyzing EEG data
ERPLAB Toolbox
– A freely available, open-source, Matlab toolbox for processing and analyzing ERP data
The ERP Boot Camp
– A series of training workshops for ERP researchers led by Steve Luck and Emily Kappenman
Virtual ERP Boot Camp
– A blog with information, announcements, and tips about ERP methodology {{DEFAULTSORT:Event-Related Potential Evoked potentials Electroencephalography Neurophysiology fr:Event-Related Potential pl:Potencjały wywołane zh:事件相关电位