Event-related potential
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An event-related potential (ERP) is the measured brain response that is the direct result of a specific sensory, cognitive, or motor event.[1] 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 (EEG). The magnetoencephalography (MEG) equivalent of ERP is the ERF, or event-related field.[2] Evoked potentials and induced potentials 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 and colleagues began the modern era of ERP component discoveries when they reported the first cognitive ERP component, called the contingent negative variation (CNV).[3] Sutton, Braren, and Zubin (1965) made another advancement with the discovery of the P3 component.[4] 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 correlates of sensory, perceptual and cognitive activity associated with processing information.[5]
Nomenclature of ERP components
ERP waveforms consist of a series of positive and negative voltage deflections, which are related to a set of underlying components.[6] Though some ERP components are referred to with acronyms (e.g., contingent negative variation – CNV, error-related negativity – ERN, early left anterior negativity – ELAN, closure positive shift – CPS), 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. For example, the P300 component may exhibit a peak anywhere between 250ms – 700ms.[7]
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.[8]
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) are inherently limited by the slow speed of the BOLD 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.[1]
Cost
ERP research is much cheaper to do than other imaging techniques such as fMRI, PET, and MEG. This is because purchasing and maintaining an EEG system is less expensive than the other systems.
Clinical ERP
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:
- dementia[9]
- Parkinson's disease[10]
- multiple sclerosis[11]
- head injuries[12]
- stroke[13]
- obsessive-compulsive disorder[14]
Research ERP
ERPs are used extensively in neuroscience, cognitive psychology, 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. 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, 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.
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.[15]
Other ERPs used frequently in research, especially neurolinguistics research, include the ELAN, the N400, and the P600/SPS.
ERP software and training resources
- [1] – ERP Summer School 2017 will be held in The School of Psychology, Bangor University from 26th-30th 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
See also
- Bereitschaftspotential
- Brain vital signs
- C1 and P1
- Contingent negative variation
- Difference due to memory
- Early left anterior negativity
- Erich Schröger
- Error-related negativity
- Evoked potential
- Induced activity
- Lateralized readiness potential
- Mismatch negativity
- Negativity: N100 • Visual N1 • N170 • N200 • N2pc • N400
- Positivity: P200 • P300 • P3a • P3b • Late positive component • P600
- Somatosensory evoked potential
References
- ^ a b Luck, Steven J. (2005). An Introduction to the Event-Related Potential Technique. The MIT Press. ISBN 0-262-12277-4.
- ^ Brown, Colin M; Peter Hagoort (1999). "The cognitive neuroscience of language". In Colin M. Brown and Peter Hagoort (ed.). The Neurocognition of Language. New York: Oxford University Press. p. 6.
- ^ Walter, W.G; Cooper, R.; Aldridge, V.J.; McCallum, W.C.; Winter, A.L. (1964). "Contingent Negative Variation: an electric sign of sensorimotor association and expectancy in the human brain". Nature 203 (4943): 380–384.
- ^ Sutton, S., Braren, M., Zubin, J., & John, E.R. (1965). Evoked-Potential Correlates of Stimulus Uncertainty. Science, 150, 1187–1188
- ^ Handy, T. C. (2005). Event Related Potentials: A Methods Handbook. Cambridge, MA: Bradford/MIT Press.
- ^ Luck, S.J.; Kappenman, E.S., eds. (2012). The Oxford Handbook of Event-Related Potential Components. Oxford University Press. p. 664. ISBN 9780195374148.
- ^ For discussion of ERP component naming conventions see Luck, Steven (2005), An Introduction to the Event-Related Potential Technique, MIT Press, pp. 10–11.
- ^ Luck, Steven (2005). An Introduction to the Event-Related Potential Technique. MIT Press, pp. 21–23.
- ^ Boutros, N., et al. (1995). Evoked potentials in subjects at risk for Alzheimer's disease. Psychiatry Res, 57, (1), 57–63.
- ^ Prabhakar, S., Syal, P. and Srivastava, T. (2000). P300 in newly diagnosed nondementing Parkinson's disease: effect of dopaminergic drugs. Neurol India, 48, (3), 239- 242.
- ^ Boose, M. A. and Cranford, J. L. (1996). Auditory event-related potentials in multiple sclerosis. Am J Otol, 17, (1), 165–170.
- ^ Duncan, C. C., Kosmidis, M. H. and Mirsky, A. F. (2003). Event-related potential assessment of information processing after closed head injury. Psychophysiology, 40, (1), 45–59.
- ^ D'Arcy, R. C., et al. (2003). Electrophysiological assessment of language function following stroke. Clin Neurophysiol, 114, (4), 662–672.
- ^ Hanna, G.L., Carrasco, M., Harbin, S.M., Nienhuis, J.K., LaRosa, C.E., Chen, P., Fitzgerald, K.D., Gehring, W.J. (2012). Error-Related Negativity and Tic History in Pediatric Obsessive-Compulsive Disorder. Child Adolescent Psychiatry, 51, (9), 902–910.
- ^ Farwell, L.A.; Donchin E. (1988). "Talking off the top of your head: toward a mental prosthesis utilizing event-related brain potentials". Electroencephalogr Clin Neurophysiol. 70 (6): 510–23. doi:10.1016/0013-4694(88)90149-6. PMID 2461285.
Further reading
- Steven J. Luck: An Introduction to the Event-Related Potential Technique, Second edition. Cambridge, Mass.: The MIT Press, 2014. ISBN 9780262525855.
- Todd C. Handy: Event-Related Potentials : A Methods Handbook. Cambridge, Mass.: The MIT Press (B&T), 2004. ISBN 0-262-08333-7
- Luck, S.J., and Kappenman, E.S., ed. (2012). The Oxford Handbook of Event-Related Potential Components. Oxford University Press. pp. 664. ISBN 9780195374148.
- Monica Fabiani, Gabriele Gratton, and Kara D. Federmeier: "Event-Related Brain Potentials: Methods, Theory, and Applications". In Handbook of Psychophysiology, ed. by John T. Cacioppo, Louis G. Tassinary, and Gary G. Berntson. 3rd. ed. Cambridge: Cambridge University Press, 2007. ISBN 978-0-521-84471-0. pp. 85–119
- John Polich and Jody Corey-Bloom, Alzheimer's Disease and P300: Review and evaluation of Task and Modality. Current Alzheimer Research, 2005, 2, 515–525
- Zani A. & Proverbio A.M. (2003) Cognitive Electrophysiology of Mind and Brain. Academic Press/Elsvier.
- Kropotov J. (2009)" Quantitative EEG, Event-Related Potentials and Neurotherapy" Academic Press/Elsvier.