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Author Topic: [BCI] An Overview of Event Related Potentials ("brain waves") such as the P300  (Read 3965 times)

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BCIs are Brain Computer Interfaces (like the EEG etc.) and anybody interested in what the future may be like using the concepts discussed below and could form vital neurological tools to understand both addiction and psychiatric dysfunctions at a far deeper level.

See P300 (neuroscience)Wiki also. This study, I believe, also determines much of our memory and action relationship.

Reduced P300 amplitude is an indicator of the broad neurobiological vulnerability that underlies disorders within the externalizing spectrum {and is of interest to me for: alcohol dependence, drug dependence, nicotine dependence, conduct disorder and adult antisocial behavior}.

P300 is an internal indication of auditory and visual stimui recognition and has been used in Criminal matters but isn't permissable in most judicial proceedings.

Event-related potential Overview

ElectroencephalographyWiki (EEG) provides an excellent medium to understand neurobiological dysregulation, with the potential to evaluate neurotransmission. Time-locked EEG activity or event-related potential (ERP) helps capture neural activity related to both sensory and cognitive processes. In this article, we attempt to present an overview of the different waveforms of ERP and the major findings in various psychiatric conditions.

Richard Caton (1842–1926), a medical lecturer at Liverpool, was the pioneer in the field of evoked potential. He observed that “feeble currents of varying direction pass through the multiplier when the electrodes are placed on two points of the external surface.” This sentence marked the birth of the electroencephalogram (EEG), though it was invented much later by Hans Berger, a German Psychiatrist, in 1929.


Event-related potentials (ERPs) are very small voltages generated in the brain structures in response to specific events or stimuli (Blackwood and Muir, 1990). They are EEG changes that are time locked to sensory, motor or cognitive events that provide safe and noninvasive approach to study psychophysiological correlates of mental processes. Event-related potentials can be elicited by a wide variety of sensory, cognitive or motor events.

They are thought to reflect the summed activity of postsynaptic potentials produced when a large number of similarly oriented cortical pyramidal neurons (in the order of thousands or millions) fire in synchrony while processing information (Peterson et al., 1995).

ERPs in humans can be divided into 2 categories:

1. The early waves, or components peaking roughly within the first 100 milliseconds after stimulus, are termed ‘sensory’ or ‘exogenous’ as they depend largely on the physical parameters of the stimulus.

2. In contrast, ERPs generated in later parts reflect the manner in which the subject evaluates the stimulus and are termed ‘cognitive’ or ‘endogenous’ ERPs as they examine information processing. The waveforms are described according to latency and amplitude.


P50 wave

The amount of attenuation in the neural response to the second of the two identical stimuli indexes the strength of the inhibitory pathway. This paradigm has been adapted as a test of sensory gating principally through the study of the P50 waveform. Sensory gating is crucial to an individual’s ability to selectively attend to salient stimuli and ignore redundant, repetitive or trivial information, protecting the brain from information overflow (Light and Braff, 2003). The most positive peak between 40 and 75 msec after the conditioning stimulus is the P50 (Olincy et al., 2005). The P50 amplitude is the absolute difference between the P50 peak and the preceding negative trough (Clementz et al., 1997). P50 can be elicited by either the “paired click” paradigm or the “steady-state” paradigm.

N100 or N1 wave

A negative deflection peaking between 90 and 200 msec after the onset of stimulus, is observed when an unexpected stimulus is presented. It is an orienting response or a “matching process,” that is, whenever a stimulus is presented, it is matched with previously experienced stimuli. It has maximum amplitude over Cz and is therefore also called “vertex potential.”

P200 or P2 wave

P200 or P2 wave refers to the positive deflection peaking around 100-250 msec after the stimulus. Current evidence suggests that the N1/P2 component may reflect the sensation-seeking behavior of an individual.

N200 or N2 wave

Is a negative deflection peaking at about 200 msec after presentation of stimulus.

There are 3 components of the N200 waveform —

1. N2a/ Mismatch negativity (MMN)
MMN is a negative component which is elicited by any discriminable change (Näätänen and Tiitinen, 1998) in a repetitive background of auditory stimulation (Winkler et al., 1996). MMN represents the brain’s automatic process involved in encoding of the stimulus difference or change.

2. N2b
It is slightly later in latency than the N2a and appears when changes in physical property of the stimulus are task relevant.

3. N2c
It is the classification N2, elicited when classification of disparate stimuli is needed.


N300 is a recent finding in the context of semantic congruity and expectancy.


The P3 wave was discovered by Sutton et al. in 1965 and since then has been the major component of research in the field of ERP. For auditory stimuli, the latency range is 250-400 msec for most adult subjects between 20 and 70 years of age. The latency is usually interpreted as the speed of stimulus classification resulting from discrimination of one event from another. Shorter latencies indicate superior mental performance relative to longer latencies. P3 amplitude seems to reflect stimulus information such that greater attention produces larger P3 waves.

A wide variety of paradigms have been used to elicit the P300, of which the “oddball” paradigm is the most utilized where different stimuli are presented in a series such that one of them occurs relatively infrequently — that is the oddball. The subject is instructed to respond to the infrequent or target stimulus and not to the frequently presented or standard stimulus.

Reduced P300 amplitude is an indicator of the broad neurobiological vulnerability that underlies disorders within the externalizing spectrum {alcohol dependence, drug dependence, nicotine dependence, conduct disorder and adult antisocial behavior} (Patrick et al., 2006).


It is a negative wave first described in the context of semantic incongruity, 300–600 msec post-stimulus (Kutas and Hillyard, 1980). N400 is inversely related to the expectancy of a given word to end a sentence.


In the domain of language processing, a P600 effect occurs to sentences that (a) contain a syntactic violation, (b) have a nonpreferred syntactic structure or (c) have a complex syntactic structure (Osterhout and Holcomb, 1992).

Movement-related cortical potentials

MRCPs denote a series of potentials that occur in close temporal relation with movement or movement-like activity. These may occur before/during or after the movement and they refer to the associated preparedness for movement in the cortex. Kornhuber and Deecke (1965) distinguished 4 components of the MRCPs, viz., (1) Bereitschafts potential, (2) Reafferent potential, (3) Pre-motion positivity and (4) Motor potential.

Contingent negative variation

Richard Caton in 1875 first used the term negative variation while describing electrical activity of gray matter, while Walter (1964) coined the term contingent negative variation (CNV). CNV can be elicited by a standard reaction time paradigm (S1-S2-motor response) or only by paired stimuli without any motor response (S1-S2 paradigm). A first stimulus (S1) serves as a preparatory signal for an imperative stimulus (S2) to which the subject must make a response. In the S1-S2 interval, there are early and late CNV components. Early CNV is considered as indicator of arousal processes, and late CNV is associated with attention to the experimental task.

Post-imperative negative variation

PINV is the delay in CNV resolution, that is, negativity continues after S2. PINV is a marker of sustained cognitive activity.


Alcohol dependence syndrome

N1 P2

Alcohol-induced attenuation of N1 and P2 amplitudes has been consistently reported. The N1 amplitude was dose-dependently suppressed by alcohol, and the N1 peak latency was prolonged by the higher (0.85 g/ kg) dose of ethanol, thus supporting the previous observations.

There is increase in the latency of N200.

Acute ethanol intake is seen to reduce P300 amplitude. However, wave abnormalities have also been seen in abstinent individuals and in the first-degree relatives of patients (Patrick et al., 2006).

Decreased amplitude of CNV and MRCP denoting deficits in executive functioning in alcoholic patients has been reported.


One of the most robust neurophysiological findings in schizophrenia is decrease in P300 amplitude. P300 is often smaller in amplitude and longer in latency in patients who have been ill longer. P300 latency was found to be increased in schizophrenic patients but not in their first-degree relatives (Simlai& Nizamie, 1998). In longitudinal analyses, P300 amplitude is sensitive to fluctuations in the severity of positive symptoms, independent of medication, and to the enduring level of negative symptom severity (Mathalon et al., 2000).

Diminished P50 suppression has been reported in patients with schizophrenia (Bramon et al., 2004) and in their non-psychotic relatives (Clementz et al., 1998).

N1, P2, N2
Schizophrenia patients have demonstrated reduced N100, P200 and N200 amplitudes (O’Donnell et al., 2004).

There is decreased MMN amplitude, as well as abnormal MMN topographical distribution, in treatment-refractory patients with schizophrenia (Milovan, 2004).

CNV amplitude was noted to be shorter and latency longer, localized to the left central region, in schizophrenia patients. BP interval and amplitude were found to be increased when compared to controls (Simlai& Nizamie, 1998). BP latency was found to be decreased in patients denoting impairment in planning movement and decision making (Duggal& Nizamie, 1998).

Late components


There is an increase in N400 and P600 latencies in schizophrenic patients.

Bipolar affective disorder

P50 suppression deficits have been found in patients with bipolar disorder with psychotic symptoms, as well as in their unaffected first-degree relatives, suggesting P50 to be an endophenotypic marker for the illness (Schulze et al., 2007).

Salisbury et al. (1999) have recently noted P300 reduction in manic psychosis. Latency prolongation and amplitude reduction were seen in chronic bipolar patients (O’Donell et al., 2004).


Reduced amplitude of P300 has been seen in depressed patients, mainly with suicidal ideations, psychotic features or severe depression (Hansenne et al., 1996).



Studies show that individuals with spider and snake phobias showed significantly larger P300 amplitudes than healthy controls when exposed to pictures of their feared objects, indicating enhanced processing of stimuli that reflect critical fear concerns (Miltner et al., 2000).

Panic disorder

An enlarged frontal P3a to distractor stimuli among patients has been reported using a three-tone discrimination task, supporting the hypothesis of dysfunctional prefrontal-limbic pathways. In addition, a longer P3b latency in drug-free patients than in unaffected controls has also been reported as possible evidence of a dysfunctional hippocampus and amygdala (Turan et al., 2002).

Generalized anxiety disorder

ERPs elicited by threat-relevant stimuli support the existence of an attentional bias, showing larger amplitude of P300 and slow waves in response to fear-related words or pictures in subjects with high-trait anxiety or anxiety disorders when compared with healthy controls (De Pascalis et al., 2004).

Obsessive compulsive disorder

N2, P3
OCD patients are seen to have significantly shorter P300 and N200 latencies for target stimuli and greater N200 negativity when compared with normal controls. However, there are no significant relationships between these ERP abnormalities in OCD patients and the type or severity of their OCD symptoms. Paul and Nizamie (1999) found increased P300 latency in OCD patients but no difference in amplitude.

Posttraumatic stress disorder

There are reports of a reduction of the P50 suppression response in persons with posttraumatic stress disorder (PTSD) (Neylan et al., 1999; Skinner et al., 1999).

The most common finding is reduced P300 amplitudes (Metzger et al., 1997).

Dissociative disorder

Patients showed significant reduction in the amplitudes of P300 during dissociative disorders compared with the levels at remission. The latency of P300 remained unchanged. The amplitudes of P300 might be a state-dependent biological marker of dissociative disorders.

Personality disorders

In healthy subjects, several studies have reported some relationships between N200, P300 and personality. A consistent result of these studies is that introverts exhibit higher P300 amplitude than extroverts. P300 amplitude is weakly correlated (positively) to the self-directedness dimension; and CNV, to cooperativeness. Longer N200 latency may be associated with higher harm avoidance score. N200 amplitude is negatively correlated to persistence. This indicates that lower N200 amplitude may be related to a higher persistence score.


ERP constitutes a millisecond-by-millisecond record of neural information processing, which can be associated with particular operations such as sensory encoding, inhibitory responses and updating working memory. Thus it provides a noninvasive means to evaluate brain functioning in patients with cognitive disorders and is of prognostic value in few cases. ERP is a method of neuropsychiatric research which holds great promise for the future.

EDIT: This may also help you


A study of event related potential frequency domain coherency using multichannel electroencephalogram subspace analysis is available at

Event related potentials (ERP) are time-locked electrical activities of the brain in direct response to a specific sensory, cognitive, or motor stimulus. ERP components, such as the P300 wave, which are involved in the process of decision-making, help scientists diagnose specific cognitive disabilities.

In this study, we utilize the angles between multichannel electroencephalogram (EEG) subspaces in different frequency bands, as a similarity factor for studying the spatial coherency between ERP frequency responses. A matched filter is used to enhance the ERP from background EEG.

While previous researches have focused on frequencies below 10 Hz, as the major frequency band of ERP, it is shown that by using the proposed method, significant ERP-related information can also be found in the 25-40 Hz band. These frequency bands are selected by calculating the correlation coefficient between P300 response segments and synthetic EEG, and ERP segments without P300 waves, and by rejecting the bands having the most association with background EEG and non-P300 components.

The significance of the results is assessed by real EEG acquired in brain computer interface experiments versus synthetic EEG produced by existing methods in the literature, to assure that the results are not systematic side effects of the proposed framework.

The overall results show that the equivalent dipoles corresponding to narrow-band events in the brain are spatially coherent within different (not necessarily adjacent) frequency bands. The results of this study can lead into novel perspectives in ERP studies.

A study on Decomposing stimulus and response component waveforms in ERP is available at

Event-related potentials (ERPs) are evoked brain potentials that are averaged across many trial repetitions with individual trials aligned (i.e. time-locked) to a specific behavioral event, typically the onset of the stimulus (s-lock) or the onset of the behavioral response (r-lock).

These evoked potential averages may reflect brain activities during the stimulus encoding/analyzing stage (stimulus component waveform, or 'S-component'), during the response preparation/production stage (response component waveform, or 'R-component'), or a combination thereof. In the stimulus-locked average of the ensemble of the recorded waveforms (i.e. in the s-locked ERP), the contribution of an R-component will be convoluted, due to the trial-by-trial variance in reaction time (RT): so will an S-component in the r-locked ERP.

It is shown here that the knowledge of (1) the s-locked and r-locked ERP waveforms constructed from the same ensemble of trials and (2) the RT distribution of this ensemble allows us to determine whether the recorded potential results from a single S-component, a single R-component, or a single intermediate ('decisional' or D-) component related to the transition of the two stochastically independent stages.

If it can be assumed that the evoked potential is the result of a linear summation of an S-component and an R-component, then there is a unique recovery into these two components, such that the reconstructed waveform on an individual trial is a superposition of the two components with their relative offset determined by the RT of that trial and the ensemble average is the experimentally obtained s-locked and r-locked ERP waveforms.

Two independent methods can be used to recover those components, one based on Fourier transform techniques which was first proposed by Hansen (1983) in the context of ERP component isolation and the other based on a recursive iteration approach through which the contamination of the R or S-component is successively removed from the s-locked or r-locked ERP waveforms, respectively.

The iterative procedure is analytically proven to converge to the Fourier-based solution, demonstrating the equivalence of the two approaches. Finally, if the condition of a single intermediate D-component is satisfied, then one can recover this component waveform along with the probability distributions of the relative durations of the two underlying linear stages; however, there is always an equivalent pair of S- and R-component which also satisfy the same data set (s-locked and r-locked ERP waveforms and the overall RT distribution).

In this case, the S/R-component assumption and the D-component assumption cannot be distinguished solely on the ground of the available data set. The technique developed here outlines the assumptions and the boundary conditions upon which ensemble ERP waveforms are to be analyzed and interpreted in terms of processing mechanisms related to stimulus, to response, or to the transition between the two.

a study on Event-related EEG/MEG synchronization and desynchronization: basic principles is available at

An internally or externally paced event results not only in the generation of an event-related potential (ERP) but also in a change in the ongoing EEG/MEG in form of an event-related desynchronization (ERD) or event-related synchronization (ERS). The ERP on the one side and the ERD/ERS on the other side are different responses of neuronal structures in the brain. While the former is phase-locked, the latter is not phase-locked to the event. The most important difference between both phenomena is that the ERD/ERS is highly frequency band-specific, whereby either the same or different locations on the scalp can display ERD and ERS simultaneously. Quantification of ERD/ERS in time and space is demonstrated on data from a number of movement experiments.

a study on Long-term stability and consistency of EEG event-related (de-)synchronization across different cognitive tasks is available at

We examined whether task-related band power changes (event-related desynchronization/synchronization; ERD/ERS) that have been linked to individual differences in cognitive ability demonstrate satisfying temporal stability and cross-situational consistency.

Multi-channel EEG recordings from 29 adults, assessed at three different occasions over 2 years were examined. Between-session correlations and consistency coefficients (Cronbach's alpha) across the three experiments were evaluated for both, spectral power features of the resting EEG and ERD/ERS estimates while the participants performed some cognitive task (i.e. different elementary cognitive tasks that put comparable demands on the participants).

ERD/ERS values, while subjects performed a cognitive task, demonstrated satisfactory stability and consistency (i.e. >0.7), whereby the degree of consistency varied as a function of frequency band and brain region. Highest consistency was found for the 8-10 Hz ERD in parieto-occipital recording sites (i.e. >0.9). In resting EEG, mean alpha (gravity) frequency was the most stable EEG feature.

The present data suggest that ERD/ERS phenomena in different narrow frequency bands are rather stable over time and across different situations. The relatively high reproducibility of ERD/ERS promotes the usefulness of this measure in assessing individual differences of physiological activation patterns accompanying cognitive performance.

This study addresses the issue of reproducibility of EEG in general and ERD/ERS experiments in particular, which is a prerequisite for both basic research and clinical studies.

A study on Intracerebral ERD/ERS in voluntary movement and in cognitive visuomotor task is available at

In order to study cerebral activity related to preparation and execution of movement, evoked and induced brain electrical activities were compared to each other and to fMRI results in voluntary self-paced movements. Also, the event-related desynchronization and synchronization (ERD/ERS) were studied in complex movements with various degrees of cognitive load.

The Bereitschaftspotential (BP) and alpha (8-12 Hz) and beta (16-24 Hz) ERD/ERS rhythms in self-paced simple movements were analyzed in 14 epilepsy surgery candidates. In previous studies, the cortical sources of BP were consistently displayed contralateral to the movement in the primary motor cortex and primary somatosensory cortexWiki, and bilateral in the supplementary motor area (SMA) and in the cingulate cortexWiki.

There were also small and inconstant BP generators in the ipsilateral sensorimotor, premotor, and dorsolateral prefrontal cortex. Alpha and beta ERD/ERS were also observed in these cortical regions. The distribution of contacts showing ERD or ERS was larger than of those showing BP. In contrast to BP, ERD, and ERS frequently occurred in the orbitofrontal, lateral and mesial temporal cortices, and inferior parietal lobule.

The spatial location of brain activation for self-paced repetitive movements, i.e., writing simple dots, was studied using event-related functional MRI (fMRI) in 10 healthy right-handed subjects. We observed significant activation in regions known to participate in motor control: contralateral to the movement in the primary sensorimotor and supramarginal cortices, the SMA and the underlying cingulate, and, to a lesser extent, the ipsilateral sensorimotor region.

When the fMRI was compared with the map of the brain areas electrically active with self-paced movements (intracerebral recordings; Rektor et al., 1994, 1998, 2001b, c; Rektor, 2003), there was an evident overlap of most results. Nevertheless, the electrophysiological studies were more sensitive in uncovering small active areas, i.e., in the premotor and prefrontal cortices.

The BP and the event-related hemodynamic changes were displayed in regions known to participate in motor control. The cortical occurrence of oscillatory activities in the alpha-beta range was clearly more widespread. Four epilepsy surgery candidates with implanted depth brain electrodes performed two visuomotor-cognitive tasks with cued complex movements: a simple task--copying randomly presented letters from the monitor; and a more complex task--writing a letter other than that which appears on the monitor.

The second task demanded an increased cognitive load, i.e., of executive functions. Alpha and beta ERD/ERS rhythms were evaluated. Similar results for both tasks were found in the majority of the frontal contacts, i.e., in the SMA, anterior cingulate, premotor, and dorsolateral prefrontal cortices. The most frequent observed activity was ERD in the beta rhythm; alpha ERS and ERD were also present. Significant differences between the two tasks appeared in several frontal areas--in the dorsolateral and ventrolateral prefrontal and orbitofrontal cortices (BA 9, 45, 11), and in the temporal neocortex (BA 21). In several contacts localized in these areas, namely in the lateral temporal cortex, there were significant changes only with the complex task--mostly beta ERD.

Although the fMRI results fit well with the map of the evoked activity (BP), several discrepant localizations were displayed when the BP was compared with the distribution of the oscillatory activity (ERD-ERS). The BP and hemodynamic changes are closely related to the motor control areas; ERD/ERS represent the broader physiological aspects of motor execution and control. The BP probably reflects regional activation, while the more widespread ERD/ERS may reflect the spread of task-relevant information across relevant areas.

In the writing tasks, the spatial distribution of the alpha-beta ERD/ERS in the frontal and lateral temporal cortices was partially task dependent. The ERD/ERS occurred there predominantly in the more complex of the writing tasks. Some sites were only active in the task with the increased demand on executive functions. In the temporal neocortex only, the oscillatory, but not the evoked, activity was recorded in the self-paced movement.

The temporal appearance of changes of oscillatory activities in the self-paced movement task as well as in the cued movement task with an increased load of executive functions raises the interesting question of the role of this region in cognitive-movement information processing.

A study on the cortical activation model (CAM) is available at

The Cortical Activation Model (CAM) is an attempt to explain whether an internally or externally paced event reveals an event-related desynchronization (ERD) or event-related synchronization (ERS) in a specific frequency band.

It is assumed that the amplitude of network-specific oscillations depends on, in addition to other factors, the number of neurons available for synchronization and the excitability level of neurons and forms a bell-shaped curve with a maximum of oscillatory activity at a certain balance of both factors. Depending on the baseline level of cortical activation (CA) and the location of the "working point" (WP), a sudden change of activation can induce either ERD or ERS in a given area.



The human cerebral cortex divided into Brodmann areas on the basis of cytoarchitecture.
Cytoarchitecture (Greek κύτος= "cell" + ἀρχιτεκτονική= "architecture"), also known as cytoarchitectonics, is the study of the cellular composition of the central nervous system's tissues under the microscope.

Cytoarchitectonics is one of the ways to parse the brain, by obtaining sections of the brain using a microtomeWiki and staining them with chemical agents which reveal where different neurons are located.

more on this and related topics can be accesssed via the source links top rightmost frame of the article
« Last Edit: June 17, 2019, 08:47:44 AM by Chip »
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