P3a

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The P3a, or novelty P3, [1] is a component of time-locked (EEG) signals known as event-related potentials (ERP). The P3a is a positive-going scalp-recorded brain potential that has a maximum amplitude over frontal/central electrode sites with a peak latency falling in the range of 250–280 ms. The P3a has been associated with brain activity related to the engagement of attention (especially orienting and involuntary shifts to changes in the environment) and the processing of novelty. [2]

Contents

History

In 1975 Squires and colleagues conducted a study attempting to resolve some of the questions surrounding what neural process the P300 reflects. At the time, several researchers suggested that there needed to be active attention towards the target stimuli in order to elicit a P300, in part because stimuli that were ignored resulted in a P300 with a smaller amplitude or no P300 at all. On the other hand, some research had shown that subjects exhibit a P300 to unpredictable stimuli in an ongoing repetitive series of stimuli, even when the stimuli were classified as irrelevant and subjects were asked to ignore them while completing another task (i.e. reading a book). It was intriguing that you could elicit a P300 in conditions with active attention and those of non-attention. Upon further investigation it turned out that when comparing the two types of P300 potentials, they differed in latency and scalp topography. This led Squires et al. to suggest that there were two distinct psycho-physiological entities that had been referred to collectively as the P300. [3]

More specifically, Squires et al. recorded EEG during an auditory odd-ball paradigm with various conditions. The two types of stimuli were 90 dB and 70 db tone bursts that occurred 1.1 sec apart. Loud tones occurred with a probability of .9, .5, or .1, while the soft tones occurred with complementary probability. In addition, subjects completed blocks of stimuli under instruction to count the number of loud tones, count the number of soft tones, or ignore the tones and quietly read. Therefore, each set of instructions was performed at each of the probability combinations. Squires et al. found that when subjects were told to ignore the tones, the less frequent or rare tone (probability of .1) elicited a positive-going potential which occurred between 220 and 280 ms. They termed this potential the P3a in order to distinguish it from its relative, the P3b, which was a positive-going potential that occurred at 310–380 ms when the infrequent tones were attended to. Scalp distribution helped them differentiate the two potentials as well. The newly coined "P3a" had a peak amplitude occurring at frontal midline sites while the P3b peak amplitude occurred over parietal midline sites. [3]

Component characteristics

Consistent with this historical separation of the two components, typically if a stimulus is a rare non-target then the recorded EEG waveform has characteristics associated with the P3a, whereas attended targets elicit a P3b. With now-extensive research, it is also possible to dissociate these components even when the experimental context is different and/or less well-studied. P3a amplitudes tend to be maximal over frontal/central sites on the scalp, such as FCz/Cz in the international 10-20 system, which is the standard electrode placement system of many ERP labs around the world. P3b amplitudes are generally greater at sites like Pz. [1] Latency is another distinguishing characteristic. While many things can affect the latency of the P3b, [2] P3a latencies often occur 75-100 ms earlier than P3b peak latencies, and around 250-280 ms. [3] Finally, the two responses have different functional sensitivities and associated psychological correlates.

Main paradigms

The 3-stimulus oddball paradigm is one of the primary paradigms used to elicit a prominent P3a. As the name implies, the paradigm includes three types of stimuli: frequent, attended "standards", less frequent, attended "target" stimuli and a third "deviant" stimulus type. This paradigm is a modification of the oddball task that is used to elicit a P3b. In this task, infrequent-nontarget stimuli are dispersed throughout a sequence of task-relevant target and standard stimuli. When these infrequent, novel stimuli (for example, the sound of dog barks or color forms) are presented in the series of more typical target and standard stimuli (for example, tones or letters of the alphabet), a P3a that is larger over the frontal and central areas of the brain is produced in response to auditory, visual, and somatosensory stimuli. Deviant stimuli from auditory, visual, and somatosensory modalities are all sufficient for eliciting a P3a. [1] For example, Grillon and colleagues used this design when they tested for the effects of rare non-target (deviant) auditory stimuli on subjects' EEG activity. They used 1600 Hz tones as the standard stimuli, while a 900 Hz tone represented the rare target stimuli. In the “Novel” condition, they added a rare non-target tone at 700 Hz. In their results it was apparent that the P300 they recorded to the rare non-target tones was in fact a P3a. The rare non-target tones resulted in a P300 (P3a) with a shorter latency that was distributed more towards the front of the scalp when compared to the P300 (P3b) elicited by rare target stimuli. [4]

The 3 stimulus oddball paradigm provides a flexible way to examine the P3a across stimulus modality and tasks. Yamaguchi and Knight conducted a study using mechanical tactile stimuli (finger taps) and electric shocks to the wrist within a 3-stimulus oddball paradigm. They were interested in seeing if subjects would elicit a P3a to novel somatosensory stimuli. They devised a design wherein subjects would receive finger taps to hand digits 2-5 and electric shocks to the wrist. Taps on the 2nd finger were considered standards (76% probability) while taps on the 5th finger were targets (12% prob.). Taps occurring on the 3rd and 4th digits were considered “tactile novel” stimuli (6% prob.) and electric shocks to the wrist were shock novels (6% prob.). They found that both types of the novel somatosensory stimuli did in fact produce P3a’s that had a more frontal distribution than responses to target stimuli. Shock novels also resulted in a significantly shorter P3a latency. [5]

Functional sensitivity

Two important factors for determining the amplitude of the P3a include habituation and target discrimination. One major difference between the P3b and the P3a is that only the P3a habituates with repeated presentation. The habituation indicates that some sort of memory encoding for the event has been created, and for this reason the event no longer generates a response when repeated. Each time a novel event is experienced, it is compared to the previously created neural representation, and, if it is sufficiently deviant, then the process begins again. If this event is not sufficiently deviant (i.e., it is the same) then habituation occurs. The P3a's rapid amplitude reduction with exposure to repeated trials of novel stimuli supports the idea that the P3a is the electrophysiological representation of the orienting response (which also habituates in behavior). [6] For example, Grillon and colleagues used a 3 stimulus odd-ball paradigm wherein they presented subjects with a condition in which the deviant stimuli were constant and a condition in which the deviant stimuli were always novel. Their results showed the largest P3a amplitude in response to deviant stimuli that were novel. [4]

Another factor that affects P3a amplitude is target discrimination. It is interesting that although the P3a is elicited by non-target deviant stimuli, the nature of the target stimuli affect the P3a response. It seems that the amplitude of the P3a may be affected by an individual’s ability to distinguish target stimuli from standard stimuli. When this discrimination is easy, non-target deviant stimuli produce a P300 that is smaller than the target P3b and is largest over parietal sites. However, if target discrimination is difficult, the P3a to non-target stimuli is larger and more frontally-skewed with a shorter latency—in other words, the more "canonical" P3a response [2]

Although the P3a has been dissociated from the P3b, its amplitude and latency may be affected by factors that also modulate the P3b. Some of these factors include stimulus probability, stimulus evaluation difficulty, natural state variables (such as circadian and menstrual cycles), and environmentally induced state variables (such as drugs and exercise). John Polich and Albert Kok have written up an extensive review that covers many of these variables. [7]

Theory

The P3a has been linked with novelty or orienting and involuntary shifts to changes in the environment. Some have suggested that the P3a and P3b are variants of the same ERP response that varies in scalp topography as a function of attention and task demands. [8] In other cases, however, the two can be dissociated: for example, patients with temporal-parietal lesions and an absent visual P3a response have partial preservation of their visual target P3b. These results indicate that at least partially non-overlapping neural circuits may be engaged during P3a and P3b generation. [5]

Neural sources of the P3a have been hypothesized to arise from frontal lobe functioning and to involve frontal lobe attention mechanisms. Magnetic resonance imaging (MRI) studies looking at gray matter volume and P3a amplitude show stronger correlations when non-target, startling stimuli are viewed. [1] Lesion studies indicate that prefrontal and temporal-parietal cortex contribute to auditory P3a generation. [9] [10] The P3a is suspected to also reflect interactions between the frontal lobe and the hippocampus, as patients with focal hippocampal lesions have reduced P3a amplitude from novel distracters. [8]

See also

Related Research Articles

An evoked potential or evoked response is an electrical potential in a specific pattern recorded from a specific part of the nervous system, especially the brain, of a human or other animals following presentation of a stimulus such as a light flash or a pure tone. Different types of potentials result from stimuli of different modalities and types. Evoked potential is distinct from spontaneous potentials as detected by electroencephalography (EEG), electromyography (EMG), or other electrophysiologic recording method. Such potentials are useful for electrodiagnosis and monitoring that include detections of disease and drug-related sensory dysfunction and intraoperative monitoring of sensory pathway integrity.

<span class="mw-page-title-main">Event-related potential</span> Brain response that is the direct result of a specific sensory, cognitive, or motor event

An event-related potential (ERP) is the measured brain response that is the direct result of a specific sensory, cognitive, 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.

The orienting response (OR), also called orienting reflex, is an organism's immediate response to a change in its environment, when that change is not sudden enough to elicit the startle reflex. The phenomenon was first described by Russian physiologist Ivan Sechenov in his 1863 book Reflexes of the Brain, and the term was coined by Ivan Pavlov, who also referred to it as the Shto takoye? reflex. The orienting response is a reaction to novel or significant stimuli. In the 1950s the orienting response was studied systematically by the Russian scientist Evgeny Sokolov, who documented the phenomenon called "habituation", referring to a gradual "familiarity effect" and reduction of the orienting response with repeated stimulus presentations.

The N400 is a component of time-locked EEG signals known as event-related potentials (ERP). It is a negative-going deflection that peaks around 400 milliseconds post-stimulus onset, although it can extend from 250-500 ms, and is typically maximal over centro-parietal electrode sites. The N400 is part of the normal brain response to words and other meaningful stimuli, including visual and auditory words, sign language signs, pictures, faces, environmental sounds, and smells.

<span class="mw-page-title-main">P300 (neuroscience)</span> Event-related potential

The P300 (P3) wave is an event-related potential (ERP) component elicited in the process of decision making. It is considered to be an endogenous potential, as its occurrence links not to the physical attributes of a stimulus, but to a person's reaction to it. More specifically, the P300 is thought to reflect processes involved in stimulus evaluation or categorization.

The mismatch negativity (MMN) or mismatch field (MMF) is a component of the event-related potential (ERP) to an odd stimulus in a sequence of stimuli. It arises from electrical activity in the brain and is studied within the field of cognitive neuroscience and psychology. It can occur in any sensory system, but has most frequently been studied for hearing and for vision, in which case it is abbreviated to vMMN. The (v)MMN occurs after an infrequent change in a repetitive sequence of stimuli For example, a rare deviant (d) stimulus can be interspersed among a series of frequent standard (s) stimuli. In hearing, a deviant sound can differ from the standards in one or more perceptual features such as pitch, duration, loudness, or location. The MMN can be elicited regardless of whether someone is paying attention to the sequence. During auditory sequences, a person can be reading or watching a silent subtitled movie, yet still show a clear MMN. In the case of visual stimuli, the MMN occurs after an infrequent change in a repetitive sequence of images.

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 first event-related potential (ERP) components to be described. The CNV component was first described by W. Grey Walter and colleagues in an article published in Nature in 1964. The importance of this finding was that it was one of the first studies which showed that consistent patterns of the amplitude of electric responses could be obtained from the large background noise which occurs in EEG recordings and that this activity could be related to a cognitive process such as expectancy.

The P600 is an event-related potential (ERP) component, or peak in electrical brain activity measured by electroencephalography (EEG). It is a language-relevant ERP component and is thought to be elicited by hearing or reading grammatical errors and other syntactic anomalies. Therefore, it is a common topic of study in neurolinguistic experiments investigating sentence processing in the human brain.

In neuroscience, the N100 or N1 is a large, negative-going evoked potential measured by electroencephalography ; it peaks in adults between 80 and 120 milliseconds after the onset of a stimulus, and is distributed mostly over the fronto-central region of the scalp. It is elicited by any unpredictable stimulus in the absence of task demands. It is often referred to with the following P200 evoked potential as the "N100-P200" or "N1-P2" complex. While most research focuses on auditory stimuli, the N100 also occurs for visual, olfactory, heat, pain, balance, respiration blocking, and somatosensory stimuli.

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 (ERP) effect that appears in studies employing a subsequent memory paradigm, in which ERPs are recorded when a participant is studying a list of materials and trials are sorted as a function of whether they go on to be remembered or not in the test phase. For meaningful study material, such as words or line drawings, items that are subsequently remembered typically elicit a more positive waveform during the study phase. This difference typically occurs in the range of 400–800 milliseconds (ms) and is generally greatest over centro-parietal recording sites, although these characteristics are modulated by many factors.

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 after the onset of some external stimulus. This component is often distributed around the centro-frontal and the parieto-occipital areas of the scalp. It is generally found to be maximal around the vertex of the scalp, however there have been some topographical differences noted in ERP studies of the P2 in different experimental conditions.

<span class="mw-page-title-main">Visual N1</span>

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" indicates that the polarity of the component is negative with respect to an average mastoid reference. The "1" originally indicated that it was the first negative-going component, but it now better indexes the typical peak of this component, which is around 150 to 200 milliseconds post-stimulus. The N1 deflection may be detected at most recording sites, including the occipital, parietal, central, and frontal electrode sites. Although, the visual N1 is widely distributed over the entire scalp, it peaks earlier over frontal than posterior regions of the scalp, suggestive of distinct neural and/or cognitive correlates. The N1 is elicited by visual stimuli, and is part of the visual evoked potential – a series of voltage deflections observed in response to visual onsets, offsets, and changes. Both the right and left hemispheres generate an N1, but the laterality of the N1 depends on whether a stimulus is presented centrally, laterally, or bilaterally. When a stimulus is presented centrally, the N1 is bilateral. When presented laterally, the N1 is larger, earlier, and contralateral to the visual field of the stimulus. When two visual stimuli are presented, one in each visual field, the N1 is bilateral. In the latter case, the N1's asymmetrical skewedness is modulated by attention. Additionally, its amplitude is influenced by selective attention, and thus it has been used to study a variety of attentional processes.

The N200, or N2, is an event-related potential (ERP) component. An ERP can be monitored using a non-invasive electroencephalography (EEG) cap that is fitted over the scalp on human subjects. An EEG cap allows researchers and clinicians to monitor the minute electrical activity that reaches the surface of the scalp from post-synaptic potentials in neurons, which fluctuate in relation to cognitive processing. EEG provides millisecond-level temporal resolution and is therefore known as one of the most direct measures of covert mental operations in the brain. The N200 in particular is a negative-going wave that peaks 200-350ms post-stimulus and is found primarily over anterior scalp sites. Past research focused on the N200 as a mismatch detector, but it has also been found to reflect executive cognitive control functions, and has recently been used in the study of language.

Somatosensory evoked potential 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 combining SEP recordings at different levels of the somatosensory pathways, it is possible to assess the transmission of the afferent volley from the periphery up to the cortex. SEP components include a series of positive and negative deflections that can be elicited by virtually any sensory stimuli. For example, SEPs can be obtained in response to a brief mechanical impact on the fingertip or to air puffs. However, SEPs are most commonly elicited by bipolar transcutaneous electrical stimulation applied on the skin over the trajectory of peripheral nerves of the upper limb or lower limb, and then recorded from the scalp. In general, somatosensory stimuli evoke early cortical components, generated in the contralateral primary somatosensory cortex (S1), related to the processing of the physical stimulus attributes. About 100 ms after stimulus application, additional cortical regions are activated, such as the secondary somatosensory cortex (S2), and the posterior parietal and frontal cortices, marked by a parietal P100 and bilateral frontal N140. SEPs are routinely used in neurology today to confirm and localize sensory abnormalities, to identify silent lesions and to monitor changes during surgical procedures.

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. It is generally found to be largest over parietal scalp sites, beginning around 400–500 ms after the onset of a stimulus and lasting for a few hundred milliseconds. It is an important part of the ERP "old/new" effect, which may also include modulations of an earlier component similar to an N400. Similar positivities have sometimes been referred to as the P3b, P300, and P600. Here, we use the term "LPC" in reference to this late positive component.

The C1 and P1 are two human scalp-recorded event-related brain potential components, collected by means of a technique called electroencephalography (EEG). The C1 is named so because it was the first component in a series of components found to respond to visual stimuli when it was first discovered. It can be a negative-going component or a positive going component with its peak normally observed in the 65–90 ms range post-stimulus onset. The P1 is called the P1 because it is the first positive-going component and its peak is normally observed in around 100 ms. Both components are related to processing of visual stimuli and are under the category of potentials called visually evoked potentials (VEPs). Both components are theorized to be evoked within the visual cortices of the brain with C1 being linked to the primary visual cortex of the human brain and the P1 being linked to other visual areas. One of the primary distinctions between these two components is that, whereas the P1 can be modulated by attention, the C1 has been typically found to be invariable to different levels of attention.

<span class="mw-page-title-main">P3b</span>

The P3b is a subcomponent of the P300, an event-related potential (ERP) component that can be observed in human scalp recordings of brain electrical activity. The P3b is a positive-going amplitude peaking at around 300 ms, though the peak will vary in latency from 250 to 500 ms or later depending upon the task and on the individual subject response. Amplitudes are typically highest on the scalp over parietal brain areas.

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.

N2pc refers to an ERP component linked to selective attention. The N2pc appears over visual cortex contralateral to the location in space to which subjects are attending; if subjects pay attention to the left side of the visual field, the N2pc appears in the right hemisphere of the brain, and vice versa. This characteristic makes it a useful tool for directly measuring the general direction of a person's attention with fine-grained temporal resolution.

The oddball paradigm is an experimental design used within psychology research. Presentations of sequences of repetitive stimuli are infrequently interrupted by a deviant stimulus. The reaction of the participant to this "oddball" stimulus is recorded.

References

  1. 1 2 3 4 Comerchero, M. D.; Polich, J. (1999). "P3a and P3b from typical auditory and visual stimuli". Clinical Neurophysiology. 110 (1): 24–30. CiteSeerX   10.1.1.576.880 . doi:10.1016/S0168-5597(98)00033-1. PMID   10348317. S2CID   17357823.
  2. 1 2 3 Polich, J. (2003). Overview of P3a and P3b. In J. Polich (Ed.), Detection of Change:Event-Related Potential and fMRI Findings (pp. 83-98). Kluwer Academic Press: Boston.
  3. 1 2 3 Squires, N. K.; Squires, K. C.; Hillyard, S. A. (1975). "Two varieties of long-latency positive waves evoked by unpredictable auditory stimuli in man". Electroencephalography and Clinical Neurophysiology. 38 (4): 387–401. CiteSeerX   10.1.1.326.332 . doi:10.1016/0013-4694(75)90263-1. PMID   46819.
  4. 1 2 Grillon, C.; Courchesne, E.; Ameli, R.; Elmasian, R.; Braff, D. (1990). "Effects of rare non-target stimuli on brain electrophysiological activity and performance". International Journal of Psychophysiology. 9 (3): 257–267. doi: 10.1016/0167-8760(90)90058-L . PMID   2276944.
  5. 1 2 Yamaguchi, S.; Knight, R. T. (1991). "P300 generation by novel somatosensory stimuli". Electroencephalography and Clinical Neurophysiology. 78 (1): 50–55. doi:10.1016/0013-4694(91)90018-Y. PMID   1701715.
  6. ↑ Soltana, M., & Knight, R. (2000). "Neural origins of the P300". Critical Reviews in Neurobiology. 14 (3): 199–224. PMID   12645958.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  7. ↑ Polich, J.; Kok, A. (1995). "Cognitive and biological determinants of P300: an integrative review". Biological Psychology. 41 (2): 103–146. doi:10.1016/0301-0511(95)05130-9. PMID   8534788. S2CID   20671251.
  8. 1 2 Polich, J. (2007). "Updating P300: An integrative theory of P3a and P3b". Clinical Neurophysiology. 118 (10): 2128–2148. doi:10.1016/j.clinph.2007.04.019. PMC   2715154 . PMID   17573239.
  9. ↑ Knight, R. T. (1984). "Decreased response to novel stimuli after prefrontal lesions in man". Electroenceph. Clin. Neurophysiol. 59 (1): 9–20. doi:10.1016/0168-5597(84)90016-9. PMID   6198170.
  10. ↑ Knight, R. T.; Scabini, D.; Woods, D. L.; Clayworth, C. C. (1989). "Contributions of temporal-parietal junction to the human auditory P3". Brain Res. 502 (1): 109–116. doi:10.1016/0006-8993(89)90466-6. PMID   2819449. S2CID   11156612.
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