Event-related potential

As event- related potentials (ERP, English:. Event- related potentials, ERP) waveforms in the electroencephalogram (EEG ) are called, triggered either by sense perceptions ( evoked ) or with cognitive processes (such as attention and language processing ) are correlated.

Methodology

To make the niedrigamplitudigen ERPs in höheramplitudigen spontaneous EEG visible at all, many stimulus -related data epochs to be averaged. The event- independent portions of the EEG ( the spontaneous EEG, noise) submit emphasized here. In addition, alternative methods of signal analysis to be developed, which can be detected via the individual measurements, for example, changes in the vibration levels ( time-frequency analysis, wavelet analysis ), or in the synchronization of the coherence.

Depending on how long after an event a component (by a positive or negative latencies ) in the EEG occurs, you can assign these different brain areas. Early components (0-10 ms) are associated with the brain stem, medium components (up to 100 ms) the thalamus and late or slow components (up to 200 ms) the cortex.

In order to systematise individual components of the event-related potentials are referred to according to their polarity or seniority, position or latency. For example, the terms are used interchangeably P3 and P300 for one and the same component described, although the underlying principle is entirely different. P3 denotes the maximum of the third positive ERP while P300 denotes the positive maximum occurring 300 ms after the presentation of a stimulus.

ERPs can be obtained not only on the EEG, but also about the magnetoencephalography (MEG ).

Application

Applications of ERPs can be found in psychophysics and cognitive science. Lively discussion, the importance of ERPs when Libet experiment in particular. In psycholinguistics are examined ERPs, which are accompanied by difficulty in understanding sentences: For example, the N400 occurs ( voltage fluctuation negative polarity 0.4 seconds after a critical word) in semantic processing problems in, for example, if you set the " Hanna drinking a glass of concrete " hears or reads. The P600 is a positivity in the EEG, which occurs 0.6 seconds after a critical word and testimony of syntactic processing difficulties as "believes Hans that the discoverer of America told ," for example, the set evokes when we " the discoverer equate " of America " with " Columbus and expect its narrative.

In clinical psychology and psychiatry capture event Correlated potentials supports the diagnosis of patients. For example, a measurable difference was observed in schizophrenic ill people, which supports the hypothesis of facilitated facilitation in the semantic network in schizophrenia.

MMN

The so-called mismatch negativity ( MMN ) or N2a denotes a negative EKP component occurs only about 150-250 ms after the stimulus presentation when a new stimulus in comparison with previously presented, with regard to identical stimuli, frequency, duration, location or intensity differs. In part, the MMN is also supported by differences in complex stimuli, such as evoked in short melodies. For the first time they have been described by means of a passive - oddball designs of Näätänen, Gaillard and Mäntysalo for auditory stimuli in 1978. Whether the MMN occurring in other modalities is controversial.

For the auditory modality, the MMN occurs most prominently on at fronto- central electrodes and has a slight right hemisphere dominance. Dipolanalysen and converging research findings with imaging techniques show a supratemporal generator and create a second source close to prefrontal.

In contrast to components such as the P300, the MMN can be only partially influenced by the person himself, which is why it is regarded as transient exogenous component, and therefore, because it occurs only context-dependent. It seems reasonable to assume that the MMN therefore an expression of evolutionarily significant, pre- attentiven process that continuously detects the invariant acoustic environment and with different stimuli resources provides, so that attentional processes can handle separately the relevant stimulus. This theory was known by Risto Näätänen as Auditory - Trace Theory. Alternative hypotheses, such as the Refraktärhypothese by Erich Schröger who wanted to explain the MMN as a result of refractory groups of neurons are experimentally untenable. Näätänens theory is supported by findings that both the latency and the amplitude of MMN is strongly correlated with the individual Reizdiskrimationsschwelle and the physical stimulus difference. However, it is to note that in general, the MMN is confounded with other components, such as the N2b or the N1.

P300

The most common modalities well detectable P300, a positive wave, for example, in auditory stimulation a deviating tone or visual irritation heard about 300 ms after the stimulus, which is triggered by the fact that a rare target stimulus is applied, a different picture (so-called oddball paradigm ). The P300 but also occurs at the presentation of task- relevant stimuli, which is why it is divided into P3a and P3b. The P3b, which is an indicator of the stimulus meaning, has its maximum expression in the field of the parietal electrodes, whereas the P3a at the frontocentral electrodes is the most prominent and mainly reflects the charm of novelty.

Various theories such as the integrated, model triarchische Johnson (1986) postulate a function of the amplitude and latency of the P300 from the

• Information transfer
• Probability of the stimulus
• Of the importance of the stimulus

Under the prevailing theory of the Context Updating Hypothesis of Sutton and colleagues, it is assumed that the latency of the P300 reflects an update of the expectations regarding the probability of occurrence of certain events in the current context. Since this update can vonstattengehen only after a previous categorization, its latency depends on how long it takes this categorization / stimulus assessment to complete. The P300 is therefore often used as a measure of the time duration or latency of evaluation processes. To physiological or motor dimensions, such as the press of a lever, there is the advantage that in fact only the pure evaluation process, and not in addition, the time of transmission of the evaluation in a specific engine response (such as the movement of a finger on the key) is crucial. The Context Closure Hypothesis, however, describes the P300 as a component, which mainly occurs when the proffered stimulus embeds well in the context. The competition between these two conflicting hypotheses can dissolve when it associates each of the P3a and P3b of.

The P300 is also frequently used as an attention measure: As described above, the amplitude of the P300 can provide evidence of how a person categorizes stimuli and how their significance is assessed subjectively. However, the component appeared only when the person is active, ie, attentional, looking for charms. Farwell & Donchin (1991 ) have made this advantage, and the derivation of the P300 successfully used for lie detection. There were no false positive diagnoses. It is also used for diagnosing various pathological changes.