Late Positive Component
Encyclopedia
The 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 (relative to reference electrodes placed on the mastoid processes), 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 component that came to be called the LPC has been associated with episodic memory and was first described in ERP studies examining either repetition or recognition effects. In both paradigms, studies found that ERPs to repeated/recognized items differed from those to newly presented ones in several ways. In particular, second presentations of items were associated with increased positivity between 500 and 800 ms post-stimulus onset—an effect that came to be called the LPC. but also referred to as the P300
, late positivity or “parietal old/new effect”. In one of the earliest examples of such a study, Friedman (1990) presented test items in a continuous recognition paradigm (in which study and test trials are intermingled). Results showed that ERPs to old items were characterized by decreases in an negativity between 300 and 500 ms (N400
) and increases in a subsequent, partially overlapping positivity (LPC/P300
). The joint increase in positivity across these two responses was termed the "old/new" effect
, or Dm.
As described above, a variant of the study-test paradigm is a continuous recognition paradigm, in which subjects are asked to classify every item as new or old and "study" items (first presentations) and "test" items (second presentations) are intermingled.
Variants of the paradigm manipulate what subjects are doing at encoding (for example, through a levels of processing
manipulation, how long or how many times items are studied, what the delay between study and test is, and what kind of judgments subjects make at retrieval (for example, in addition to determining if an item is old or new, subjects might be asked to recall specific details of its learning context or to indicate their confidence in their memory judgments).
than implicit memory
. Although LPCs can be seen in repetition paradigms wherein items are repeated but subjects do not respond to those repetitions and are not asked to take note of them, LPC responses are bigger in tasks in which subjects make memory-related judgments. Rugg and colleagues (1998a) conducted a direct comparison of implicit and explicit retrieval ERPs. Specifically, in the explicit condition, participants performed an old/new recognition judgment on a list of words, half new and half repeated. In the implicit condition participants made living/nonliving judgment on the same material, so that repetition was task-irrelevant. Results revealed that repetition modulated LPC in the explicit task but not implicit task. Supporting evidence comes from studies of the effects of brain damage on the LPC, which have shown that the LPC effect is attenuated or eliminated in patients with bilateral hippocampal
damage or damage to the medial temporal lobe (similar damage does not disrupt the N400
part of the old/new effect, suggesting it is more related to implicit memory
).
There are many things that are known to change the amplitude
of the LPC. The amplitude increases with all of the following: study-test repetitions, words that are reported as being consciously remembered (versus being familiar), correctly recognized words that are then later recalled, and words for which the context at encoding is recalled with the word. Furthermore, LPC amplitude is also sensitive to levels of processing manipulation, being larger for more deeply encoded items.Thus, these data suggest that the LPC amplitude is closely allied with recollection and reflects successful retrieval.
The LPC is also sensitive to decision accuracy. It is larger in response to correctly identified old words than it is to incorrectly identified old words. For example, Finnigan and colleagues (2002) extended the traditional old/new effect paradigm by presenting new unstudied words and old words which had been presented at study either once (“weak”) or three times (“strong”). The probability of an “old” response was significantly higher for strong than weak words and significantly higher for weak than new words. Comparisons were made initially between ERPs to new, weak and strong words, and subsequently between ERPs associated with six strength-by-response conditions. Results showed the amplitude of LPC effect was sensitive to decision accuracy (and perhaps confidence). Its amplitude was larger in ERPs evoked by words attracting correct versus incorrect recognition decisions. The LPC effect had a left > right, centro-parietal scalp distribution (in ear-referenced ERPs). Therefore, in addition to the majority of studies in which interpreted LPC from the perspective of dual-process models (which dissociate familiarity and recollection), Finningan et al. (2002) provided alternative interpretations of LPC in terms of memory strength and decisional factors.
According to a study done by Mecklinger (1998), the scalp distribution of the LPC can vary with the type of material retrieved. When information was retrieved about an object, the distribution was right and centro-frontally centered. When the information retrieved was about spatial location, the distribution was bilaterally symmetric over the occipital lobe of the brain.
The difference in the response pattern of the LPC, in comparison with other components elicited in memory tasks, such as the N400
, has played an important role in debates about dual-process theories of memory, which postulate qualitatively different mechanisms underlying familiarity and recollection.
In terms of the neural source of the component, the characteristic scalp distribution of the LPC suggests that it might reflect neural activity generated in the lateral parietal cortex. Consistent with this hypothesis, fMRI studies report recollection-sensitive activity in this region. Furthermore, findings of direct functional parallels between these fMRI and ERP old/new effects give additional credence to the hypothesis that the ERP effect reflects activity in a recollection-sensitive region of the lateral parietal cortex. Results from studies of patients with brain damage, described above, indicate that medial temporal lobe areas and the hippocampus
contribute to the processes indexed by the LPC, although perhaps not directly to the recorded scalp activity.
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
potential (ERP)
Event-related potential
An event-related potential is any measured brain response that is directly the result of a thought or perception. More formally, it is any stereotyped electrophysiological response to an internal or external stimulus....
component that has been important in studies of explicit recognition memory
Memory
In psychology, memory is an organism's ability to store, retain, and recall information and experiences. Traditional studies of memory began in the fields of philosophy, including techniques of artificially enhancing memory....
. It is generally found to be largest over parietal scalp sites (relative to reference electrodes placed on the mastoid processes), 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
P3b
The P3b is a subcomponent of the P300, an event-related potential component that can be observed in human scalp recordings of brain electrical activity...
, P300
P300 (neuroscience)
The P300 wave is an event related potential elicited by infrequent, task-relevant stimuli. 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 the stimulus. More specifically, the P300 is thought to...
, and P600
P600
The P600 is an event-related potential , or peak in electrical brain activity measured by electroencephalography . It is a language-relevant ERP and is thought to be elicited by hearing or reading grammatical errors and other syntactic anomalies...
. Here, we use the term “LPC” in reference to this late positive component.
History
In psychological literature on memory, long term memory (LTM) is commonly divided into two types: semantic and episodic. Semantic memories are memories that are stored in LTM without specific encoding information linked to them, and thus represent general knowledge about the world that a person has acquired across the lifespan. Episodic memories are memories that are stored in long term memory as specific “episodes” and that, therefore, have some sort of specific context information associated with them, such as where or when they were encoded. At retrieval, episodic memories are often divided into two different categories based on how much information is available about the “episode.” These two categories are recollection and familiarity. Recollection is when certain information about the context of the memory at encoding, for instance when or where a memory was encoded, is recalled. Familiarity is a general sense that a person has seen something before without any other details about the event. Even though they are divided into two categories, it is currently debated whether they are separate entities controlled by different brain functions or just a graded continuum of the same function.The component that came to be called the LPC has been associated with episodic memory and was first described in ERP studies examining either repetition or recognition effects. In both paradigms, studies found that ERPs to repeated/recognized items differed from those to newly presented ones in several ways. In particular, second presentations of items were associated with increased positivity between 500 and 800 ms post-stimulus onset—an effect that came to be called the LPC. but also referred to as the P300
P300 (neuroscience)
The P300 wave is an event related potential elicited by infrequent, task-relevant stimuli. 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 the stimulus. More specifically, the P300 is thought to...
, late positivity or “parietal old/new effect”. In one of the earliest examples of such a study, Friedman (1990) presented test items in a continuous recognition paradigm (in which study and test trials are intermingled). Results showed that ERPs to old items were characterized by decreases in an negativity between 300 and 500 ms (N400
N400
The N400 is a component of time-locked EEG signals known as event-related potentials . 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...
) and increases in a subsequent, partially overlapping positivity (LPC/P300
P300 (neuroscience)
The P300 wave is an event related potential elicited by infrequent, task-relevant stimuli. 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 the stimulus. More specifically, the P300 is thought to...
). The joint increase in positivity across these two responses was termed the "old/new" effect
Main paradigms
The main paradigm that is used to elicit and study the LPC involves a two part, study-test design. In the "study" phase, the participant is given a list of words or other items to be remembered, presented one at a time. The participant may be told to try to remember these items for later ("intentional" encoding), or may be asked to make judgments about the item without realizing that there will later be a memory test for the items ("incidental" encoding). Then, after some amount of time, the studied ("old") items are re-presented to the subjects, mixed with never before presented foils ("new" items), and subjects are asked to classify the items as old or new. During this test or retrieval phase, ERPs are recorded and the brain responses to both new and old words are analyzed. The results typically show a larger LPC for old than for new words. Note that if ERPs are also recorded during the study phase of the experiment, then responses during the test phase can be used to look at factors that predict later memory; this effect is known as the Difference due to MemoryDifference due to Memory
Difference due to Memory 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...
, or Dm.
As described above, a variant of the study-test paradigm is a continuous recognition paradigm, in which subjects are asked to classify every item as new or old and "study" items (first presentations) and "test" items (second presentations) are intermingled.
Variants of the paradigm manipulate what subjects are doing at encoding (for example, through a levels of processing
Levels-of-processing effect
The levels-of-processing effect, identified by Fergus I. M. Craik and Robert S. Lockhart in 1972, describes memory recall of stimuli as a function of the depth of mental processing. Depth of processing falls on a shallow to deep continuum. Shallow processing leads to a fragile memory trace that...
manipulation, how long or how many times items are studied, what the delay between study and test is, and what kind of judgments subjects make at retrieval (for example, in addition to determining if an item is old or new, subjects might be asked to recall specific details of its learning context or to indicate their confidence in their memory judgments).
Component characteristics
As reviewed by Friedman and Johnson, the LPC is typically seen in the form of a broad positivity between 400 and 800 ms post-stimulus onset. It is largest over medial, posterior scalp sites, and tends to be bigger over left hemisphere recording sites. It is larger for items that have been seen before, especially those correctly classified as "old", as compared with those correctly classified as "new". LPCs have been recorded to words, line drawings, sounds, and meaningless shapes, and it is seen in both long and short term memory paradigms. It is believed to index recollective processes.Functional sensitivity
The LPC has been more associated with explicit memoryExplicit memory
Explicit memory is the conscious, intentional recollection of previous experiences and information. People use explicit memory throughout the day, such as remembering the time of an appointment or recollecting an event from years ago....
than implicit memory
Implicit memory
Implicit memory is a type of memory in which previous experiences aid in the performance of a task without conscious awareness of these previous experiences. Evidence for implicit memory arises in priming, a process whereby subjects show improved performance on tasks for which they have been...
. Although LPCs can be seen in repetition paradigms wherein items are repeated but subjects do not respond to those repetitions and are not asked to take note of them, LPC responses are bigger in tasks in which subjects make memory-related judgments. Rugg and colleagues (1998a) conducted a direct comparison of implicit and explicit retrieval ERPs. Specifically, in the explicit condition, participants performed an old/new recognition judgment on a list of words, half new and half repeated. In the implicit condition participants made living/nonliving judgment on the same material, so that repetition was task-irrelevant. Results revealed that repetition modulated LPC in the explicit task but not implicit task. Supporting evidence comes from studies of the effects of brain damage on the LPC, which have shown that the LPC effect is attenuated or eliminated in patients with bilateral hippocampal
Hippocampus
The hippocampus is a major component of the brains of humans and other vertebrates. It belongs to the limbic system and plays important roles in the consolidation of information from short-term memory to long-term memory and spatial navigation. Humans and other mammals have two hippocampi, one in...
damage or damage to the medial temporal lobe (similar damage does not disrupt the N400
N400
The N400 is a component of time-locked EEG signals known as event-related potentials . 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...
part of the old/new effect, suggesting it is more related to implicit memory
Implicit memory
Implicit memory is a type of memory in which previous experiences aid in the performance of a task without conscious awareness of these previous experiences. Evidence for implicit memory arises in priming, a process whereby subjects show improved performance on tasks for which they have been...
).
There are many things that are known to change the amplitude
Amplitude
Amplitude is the magnitude of change in the oscillating variable with each oscillation within an oscillating system. For example, sound waves in air are oscillations in atmospheric pressure and their amplitudes are proportional to the change in pressure during one oscillation...
of the LPC. The amplitude increases with all of the following: study-test repetitions, words that are reported as being consciously remembered (versus being familiar), correctly recognized words that are then later recalled, and words for which the context at encoding is recalled with the word. Furthermore, LPC amplitude is also sensitive to levels of processing manipulation, being larger for more deeply encoded items.Thus, these data suggest that the LPC amplitude is closely allied with recollection and reflects successful retrieval.
The LPC is also sensitive to decision accuracy. It is larger in response to correctly identified old words than it is to incorrectly identified old words. For example, Finnigan and colleagues (2002) extended the traditional old/new effect paradigm by presenting new unstudied words and old words which had been presented at study either once (“weak”) or three times (“strong”). The probability of an “old” response was significantly higher for strong than weak words and significantly higher for weak than new words. Comparisons were made initially between ERPs to new, weak and strong words, and subsequently between ERPs associated with six strength-by-response conditions. Results showed the amplitude of LPC effect was sensitive to decision accuracy (and perhaps confidence). Its amplitude was larger in ERPs evoked by words attracting correct versus incorrect recognition decisions. The LPC effect had a left > right, centro-parietal scalp distribution (in ear-referenced ERPs). Therefore, in addition to the majority of studies in which interpreted LPC from the perspective of dual-process models (which dissociate familiarity and recollection), Finningan et al. (2002) provided alternative interpretations of LPC in terms of memory strength and decisional factors.
According to a study done by Mecklinger (1998), the scalp distribution of the LPC can vary with the type of material retrieved. When information was retrieved about an object, the distribution was right and centro-frontally centered. When the information retrieved was about spatial location, the distribution was bilaterally symmetric over the occipital lobe of the brain.
Theory and sources
As reviewed by Rugg and Curran, the precise functional significance of the LPC continues to be debated. One early suggestion was that the effect reflects processes that contribute to the representation of recollected information. Alternatively, the effect might index attentional orienting to recollected information, rather than processes supporting its representation or maintenance. It has recently been argued that findings indicating that the effect varies according to the amount of information recollected are more consistent with the first of these two proposals.The difference in the response pattern of the LPC, in comparison with other components elicited in memory tasks, such as the N400
N400
The N400 is a component of time-locked EEG signals known as event-related potentials . 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...
, has played an important role in debates about dual-process theories of memory, which postulate qualitatively different mechanisms underlying familiarity and recollection.
In terms of the neural source of the component, the characteristic scalp distribution of the LPC suggests that it might reflect neural activity generated in the lateral parietal cortex. Consistent with this hypothesis, fMRI studies report recollection-sensitive activity in this region. Furthermore, findings of direct functional parallels between these fMRI and ERP old/new effects give additional credence to the hypothesis that the ERP effect reflects activity in a recollection-sensitive region of the lateral parietal cortex. Results from studies of patients with brain damage, described above, indicate that medial temporal lobe areas and the hippocampus
Hippocampus
The hippocampus is a major component of the brains of humans and other vertebrates. It belongs to the limbic system and plays important roles in the consolidation of information from short-term memory to long-term memory and spatial navigation. Humans and other mammals have two hippocampi, one in...
contribute to the processes indexed by the LPC, although perhaps not directly to the recorded scalp activity.
See also
- Somatosensory evoked potentialSomatosensory Evoked PotentialSomatosensory Evoked Potentials 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...
- C1 and P1C1 & P1 (Neuroscience)The C1 and P1 are two human scalp-recorded event-related brain potential components, collected by means of a technique called electroencephalography . 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...
- Visual N1Visual N1The Visual N1 is a visual evoked potential, a type of event-related electrical potential , 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...
- Mismatch negativityMismatch negativityThe mismatch negativity or mismatch field is a component of the event-related potential 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...
- N100
- N200N200 (neuroscience)The N200, or N2, is an event-related potential component. An ERP can be monitored using a non-invasive electroencephalography cap that is fitted over the scalp on human subjects...
- N2pcN2pcN2pc 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...
- N170N170The N170 is a component of the event-related potential that reflects the neural processing of faces.When potentials evoked by images of faces are compared to those elicited by other visual stimuli, the former show increased negativity 130-200 ms after stimulus presentation...
- P200P200In neuroscience, the visual P200 or P2 is a waveform component or feature of the event-related potential 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...
- N400
- P300 (neuroscience)P300 (neuroscience)The P300 wave is an event related potential elicited by infrequent, task-relevant stimuli. 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 the stimulus. More specifically, the P300 is thought to...
- P3aP3aThe P3a, or novelty P3, is a component of time-locked signals known as event-related potentials . 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...
- P3bP3bThe P3b is a subcomponent of the P300, an event-related potential component that can be observed in human scalp recordings of brain electrical activity...
- Difference due to MemoryDifference due to MemoryDifference due to Memory 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...
- Contingent negative variationContingent negative variationThe contingent negative variation was one of the first event-related potential components to be described. The CNV component was first described by Dr. W. Grey Walter and colleagues in an article published in Nature in 1964...
- Error-related negativityError-related negativityError-related negativity , , is a component of an event-related potential . ERPs are electrical activity in the brain as measured through electroencephalography and time-locked to an external event...
- BereitschaftspotentialBereitschaftspotentialIn neurology, the Bereitschaftspotential or BP , also called the pre-motor potential or readiness potential , is a measure of activity in the motor cortex of the brain leading up to voluntary muscle movement. The BP is a manifestation of cortical contribution to the pre-motor planning of volitional...
- Lateralized readiness potentialLateralized readiness potentialIn neuroscience, the lateralized readiness potential is an event-related brain potential, or increase in electrical activity at the surface of the brain, that is thought to reflect the preparation of motor activity on a certain side of the body; in other words, it is a spike in the electrical...
- Early left anterior negativityEarly left anterior negativityThe early left anterior negativity is an event-related potential in electroencephalography , or component of brain activity that occurs in response to a certain kind of stimulus...
- P600P600The P600 is an event-related potential , or peak in electrical brain activity measured by electroencephalography . It is a language-relevant ERP and is thought to be elicited by hearing or reading grammatical errors and other syntactic anomalies...