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In neuroscience, the visual P200 or P2 is a waveform component or feature of the event-related potential (ERP) measured at the human scalp. Like other potential changes measurable from the scalp, this effect is believed to reflect the post-synaptic activity of a specific neural process. The P2 component, also known as the P200, is so named because it is a positive going electrical potential that peaks at about 200 milliseconds (varying between about 150 and 275 ms) after the onset of some external stimulus . The distribution of this component in the brain, as measured by electrodes placed across the scalp, is located around the centro-frontal and the parieto-occipital region. It is generally found to be maximal around the vertex (frontal region) of the scalp, however there have been some topographical differences noted in ERP studies of the P2 in different experimental conditions. Research on the visual P2 is at an early stage compared to other more established ERP components and there is much that we still do not know about it. Part of the difficulty of clearly characterizing this component is that it appears to be modulated by a large and diverse number of cognitive tasks. Functionally, there seems to be partial agreement amongst researchers in the field of cognitive neuroscience that the P2 represents some aspect of higher-order perceptual processing, modulated by attention. It is known that the P2 is typically elicited as part of the normal response to visual stimuli and has been studied in relation to visual search and attention, language context information, and memory and repetition effects. The amplitude of the peak of the waveform may be modulated by many different aspects of visual stimuli, which allow it to be used for studies of visual cognition and disease. In general, the P2 may be a part of cognitive matching system that compares sensory inputs with stored memory.〔Freunberger, R., Klimiesch, W., Doppelmayr, M & Holler, Y. (2007). Visual P2 component is related to theta phase-locking. Neuroscience Letters, 426, 181-186.〕〔Luck, S. J., & Hillyard, S. A. (1994). Electrophysiological correlates of feature analysis during visual search. Psychophysiology, 31, 291-308.〕 ==History== The first mentions of an ERP component similar to that of the modern P2 were characterized in studies of basic visual and auditory evoked potentials. One of the first of such studies involved the presentation of flashing lights. Using this method, researchers found that a series of potential changes were consistently observed across repeated trials. These would later be classified as components of the visual evoked response (VER), part of which includes the P2. The P2 follows the visual N1 (or auditory N100) and P1 waveforms (negativity and positivity at 150 and 100ms respectively) and is followed by the N200, P3, and N400 waveforms. Other components may overlap with the P2 to some extent, making it difficult to distinguish clearly between them, depending on the location of measurement. Originally, the P2 was characterized as a sub-component of a complex involving the N1, P1 and P2, which was known as the vertex potential and which was classically studied as a unitary phenomenon. In particular, the relationship between the N1 and P2 was thought to be important. The difference between the N1 and P2, known as the vertex amplitude, was found to be significantly larger for target than non-target stimuli and for rapid attention switching task.〔Furutsuka, T. (1989). Effects of rapid attention switching on the N1-P2 amplitude of the visual event-related potentials. Research and Clinical Center for Child Development Annual Report, 11, 55-64.〕 Further studies have subsequently examined the P2 separately from the N1 and have found that the amplitude of the P2 itself is larger for target stimuli that are less frequent. This is similar to the P3, though the P2 is usually seen for more simple features than the P3.〔〔Crowley, K. E., & Colrain, I. M. (2004)〕 In the auditory domain, there is evidence of enhanced P2 amplitudes even when a target stimuli is not embedded in a series of identical stimuli. In these instances, enhanced P2 amplitudes have been associated with auditory learning and repeated stimulus exposure.〔Tremblay et al. 2001 Central auditory plasticity: Changes in the N1-P2 complex after speech-sound training. Ear and Hearing 22,79-90〕 Enhanced P2 amplitudes have been reported in musicians with extensive listening experience 〔Shahin et al. 2003, Enhancement of Neuroplastic P2 and N1c Auditory Evoked Potentials in Musicians, Journal of Neuroscience, 2 July 2003, 23(13):5545-5552〕 as well as laboratory based auditory training experiments.〔Tremblay et al. 2009, Auditory training alters the physiological detection of stimulus-specific cues in humans. Clinical Neurophysiology. 120,128–135〕 A significant finding is that P2 amplitude changes are sometimes seen independent of N1 amplitude changes,〔Ross and Tremblay 2009. Stimulus experience modifies auditory neuromagnetic responses in young and older listeners. Hearing Research, Feb;248(1-2):48-59〕 again suggesting some degree of independence of N1, and P2 latencies and amplitudes appear to be affected by old age.〔Tremblay et al. 2003 Effects of age and age-related hearing loss on the neural representation of speech cues. Clin Neurophysiol. Jul;114(7):1332-43〕〔A review of the evidence for P2 being an independent component process: age, sleep and modality. Clinical Neurophysiology, 115, 732-744.〕 In terms of modality, the visual P2 is similar to the auditory P2 and both have been studied in similar contexts. There are most likely multiple distinct P2s in different modalities, including both frontal and posterior visual P2s, which may or may not have similar origins or functional similarities. It is not yet understood whether the visual, auditory or other P2s reflect the same functional and neural activities. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「P200」の詳細全文を読む スポンサード リンク
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