Normal P300 following extensive damage to the left medial temporal lobe

A differential role for human hippocampus in novelty and contextual processing: Implications for P300

The role of the hippocampus in P300 has long been debated. Here, we present a theoretical framework that elucidates hippocampal contributions to scalp P300 based on intracranial and lesion research combined with emerging evidence on the role of the hippocampus in rapid statistical learning, memory, and novelty processing. The P300 has been divided in two subcomponents: a fronto-central P3a related to novelty and distractor processing, and a parietal P3b related to target detection. Interest in a role for hippocampus in scalp P300 was sparked by P3-like ERPs measured intracranially in human hippocampus. Subsequent medial temporal lobe lesion studies show intact scalp P3b, indicating that the hippocampus is not critical for P3b. This contrasts with the scalp P3a, which was significantly diminished in human patients with lesions in the posterior hippocampus. This suggests a differential role for hippocampus in P3a and P3b. Our framework purports that the hippocampus plays a central role in distractor processing that leads to P3a generation in cortical regions. We also propose that the hippocampus is involved at the end of the cognitive episode for both P3a and P3b implementing contextual updating. P3-like ERPs measured in hippocampus may reflect input signals from cortical regions implementing updates based on the outcome of cognitive processes underlying scalp P3, enabling a model update of the environment facilitated by the hippocampus. Overall, this framework proposes an active role for the hippocampus in novelty processing leading up to P3a generation, followed by contextual updating of the outcome of both scalp P3a and P3b.

Auditory Target and Novelty Processing in Patients with Unilateral Hippocampal Sclerosis: A Current-Source Density Study

The capacity to respond to novel events is crucial for adapting to the constantly changing environment. Here, we recorded 29-channel Event Related Brain Potentials (ERPs) during an active auditory novelty oddball paradigm and used for the first time Current Source Density-transformed Event Related Brain Potentials and associated time-frequency spectra to study target and novelty processing in a group of epileptic patients with unilateral damage of the hippocampus (N = 18) and in healthy matched control participants (N = 18). Importantly, we used Voxel-Based Morphometry to ensure that our group of patients had a focal unilateral damage restricted to the hippocampus and especially its medial part. We found a clear deficit for target processing at the behavioral level. In addition, compared to controls, our group of patients presented (i) a reduction of theta event-related synchronization (ERS) for targets and (ii) a reduction and delayed P3a source accompanied by reduced theta and low-beta ERS and alpha event-related synchronization (ERD) for novel stimuli. These results suggest that the integrity of the hippocampus might be crucial for the functioning of the complex cortico-subcortical network involved in the detection of novel and target stimuli.

Distributed cortical network for visual attention

The contribution of prefrontal and posterior association cortex to voluntary and involuntary visual attention was as sessed using electrophysiological techniques in patients with focal lesions in prefrontal (n = 11), temporal-parietal (n = 10), or lateral parietal cortex (n = 7). Subjects participated in a task requiring detection of designated target stimuli embedded in trains of repetitive stimuli. Infrequent and irrelevant novel visual stimuli were randomly interspersed with the target and background stimuli. Controls generated attention dependent N1 (170 msec) and N2 (243 msec) potentials maximal over extrastriate cortex. Anterior and posterior association cortex lesions reduced the amplitude of both the N1 and N2 potentials recorded over extrastriate cortex of the lesioned hemisphere. The pattern of results obtained reveals that an intrahemispheric network involving prefrontal and posterior association cortex modulates early visual processing in extrastriate regions. Voluntary target detection generated a parietal maximal P300 response (P3b) and irrelevant novel stimuli generated a more frontocentrally distributed P300 (P3a). Cortical lesions had differential effects on P3a and P3b potentials. The P3b was not significantly reduced in any cortical lesioned group. Conversely, the P3a was reduced by both prefrontal and posterior lesions with decrements most severe throughout the lesioned hemisphere. These data provide evidence that an association cortex network involving prefrontal and posterior regions is activated during orientation to novel events. The lack of a significant effect on the visual target P3b in patients with novelty P3a reductions supports the notion that different neural systems are engaged during voluntary vs involuntary atten- tion to visual stimuli.

Effect of emotional valence on episodic memory stages as indexed by event-related potentials

Several investigations have shown that emotional events show superior recall than non-emotional ones. However, the cortical mechanisms underlying the episodic recall of emotional scenes are still poorly understood. Our main aim was to compare the magnitude of the Event-Related brain Potentials (ERP) old-new effect related to emotionally unpleasant, pleasant and neutral photographic images. As expected, correct recognition of all types of images elicited three topographically distinct ERP components sensitive to the classical old-new recognition effect. The results revealed that the behavioral performances were mainly sensitive to arousal, while the ERP old/new effect over posterior regions (300 – 1000 ms) was exclusively affected by unpleasantness. A later component (1000 – 1400 ms) showed an inverted old/ new effect at parietal sites, which was also sensitive to unpleasantness. These results imply that ERP reflecting episodic conscious recollection and post-retrieval monitoring are clearly affected both by valence and arousal.

The brain's orienting response (novelty P3) in patients with unilateral temporal lobe resections

The brain's orienting response is a biologically primitive, yet critical cognitive function necessary for survival. Though based on a wide network of brain regions, the lateral prefrontal cortex and posterior hippocampus are thought to play essential roles. Indeed, damage to these regions results in abnormalities of the novelty P3 or P3a, an event-related potential (ERP) sign of the orienting response. Like other ubiquitous markers of orienting, such as the galvanic skin response, the P3a habituates when novel events are repeated. Here, we assessed habituation of the P3a in patients who had undergone unilateral anteromedial resection of the medial temporal lobe (AMTL), including the entire hippocampus, for relief of pharmacologically intractable epilepsy. Eight left- and 8 right-AMTL patients and 16 age- and education-matched controls heard frequent standard tones, infrequent targets (requiring reaction times) and equally infrequent, unique novel, environmental sounds. The novel sounds repeated 2 blocks after their first presentation. In controls, novel repetition engendered a reduction in P3a amplitude, but this was not the case in either left- or right-AMTL patients. We conclude that bilaterally intact hippocampi are necessary for the brain to appreciate that a repetition of a novel sound has occurred, perhaps due to disruptions in ipsilateral hippocampal-prefrontal pathways and/or between the left and right hippocampi.

Attention impairment in temporal lobe epilepsy: a neurophysiological approach via analysis of the P300 wave

PURPOSE

Attention is often impaired in temporal lobe epilepsy (TLE). The P300 wave (an endogenous, event-related potential) is a correlate of attention which is usually recorded during an "oddball paradigm," where the subject is instructed to detect an infrequent target stimulus presented amongst frequent, standard stimuli. Modifications of the P300 wave's latency and amplitude in TLE have been suggested, but it is still not known whether the source regions also differ. Our hypothesis was that temporal lobe dysfunction would modify the P3 source regions in TLE patients.

METHODS

A comparative, high density, 128-channel electroencephalographic analysis of the characteristics of P300 (P3b latency and amplitude) was performed in 10 TLE patients and 10 healthy controls during auditory and visual oddball paradigms. The P3b sources were localized on individual 3D MR images using the LORETA method and intergroup statistical comparisons were performed using SPM2(R) software.

RESULTS

Our main results (in both individual analyses and intergroup comparisons) revealed a reduction in temporal (and more particularly mesiotemporal) sources and, to a lesser extent, frontal sources in TLE patients, compared with controls.

DISCUSSION

This reduction may reflect direct, local cortical dysfunction caused by the epileptic focus or more complex interference between epileptic networks and normal attentional pathways.

Disturbances in selective information processing associated with the BDNF Val66Met polymorphism: evidence from cognition, the P300 and fronto-hippocampal systems

In this study, we examined whether the Met allele of the BDNF Val66Met polymorphism is associated with selective disruptions to task-relevant information processing. In 475 non-clinical participants for whom BDNF genotype status was determined we used the 'IntegNeuro' computerized battery of neuropsychological tests to assess cognitive performance, an auditory oddball task to elicit the P300 event-related potential (ERP) and, in smaller subsets of these subjects, high resolution structural MRI imaging to quantify fronto-hippocampal grey matter (n=161), and functional magnetic resonance imaging to assess fronto-hippocampal BOLD activation (n=37). Met/Met (MM) homozygotes had higher verbal recall errors, in the absence of differences in attention, executive function, verbal ability or sensori-motor function. Further, MM homozygotes demonstrated a slowed P300 ERP during the oddball task, with corresponding alterations in hippocampal and lateral prefrontal activation, and a localized reduction in hippocampal grey matter. These results are consistent with a subtle impact of the Met allele on fronto-hippocampal systems involved in selective information processing of stimulus context and memory updating within the normal population. The findings also indicate that heritable endophenotypes such as the P300 have value in elucidating genotype-phenotype relationships.

Updating P300: an integrative theory of P3a and P3b

The empirical and theoretical development of the P300 event-related brain potential (ERP) is reviewed by considering factors that contribute to its amplitude, latency, and general characteristics. The neuropsychological origins of the P3a and P3b subcomponents are detailed, and how target/standard discrimination difficulty modulates scalp topography is discussed. The neural loci of P3a and P3b generation are outlined, and a cognitive model is proffered: P3a originates from stimulus-driven frontal attention mechanisms during task processing, whereas P3b originates from temporal-parietal activity associated with attention and appears related to subsequent memory processing. Neurotransmitter actions associating P3a to frontal/dopaminergic and P3b to parietal/norepinephrine pathways are highlighted. Neuroinhibition is suggested as an overarching theoretical mechanism for P300, which is elicited when stimulus detection engages memory operations.

Updating P300: an integrative theory of P3a and P3b

The empirical and theoretical development of the P300 event-related brain potential (ERP) is reviewed by considering factors that contribute to its amplitude, latency, and general characteristics. The neuropsychological origins of the P3a and P3b subcomponents are detailed, and how target/standard discrimination difficulty modulates scalp topography is discussed. The neural loci of P3a and P3b generation are outlined, and a cognitive model is proffered: P3a originates from stimulus-driven frontal attention mechanisms during task processing, whereas P3b originates from temporal-parietal activity associated with attention and appears related to subsequent memory processing. Neurotransmitter actions associating P3a to frontal/dopaminergic and P3b to parietal/norepinephrine pathways are highlighted. Neuroinhibition is suggested as an overarching theoretical mechanism for P300, which is elicited when stimulus detection engages memory operations.

Updating P300: an integrative theory of P3a and P3b

The empirical and theoretical development of the P300 event-related brain potential (ERP) is reviewed by considering factors that contribute to its amplitude, latency, and general characteristics. The neuropsychological origins of the P3a and P3b subcomponents are detailed, and how target/standard discrimination difficulty modulates scalp topography is discussed. The neural loci of P3a and P3b generation are outlined, and a cognitive model is proffered: P3a originates from stimulus-driven frontal attention mechanisms during task processing, whereas P3b originates from temporal-parietal activity associated with attention and appears related to subsequent memory processing. Neurotransmitter actions associating P3a to frontal/dopaminergic and P3b to parietal/norepinephrine pathways are highlighted. Neuroinhibition is suggested as an overarching theoretical mechanism for P300, which is elicited when stimulus detection engages memory operations.

From amnesia to dementia: ERP studies of memory and language

Cognitive event-related potential (ERP) studies of memory and language impairments in amnesia and Alzheimer's disease (AD) are reviewed. Well-circumscribed lesions of the medial temporal lobe (MTL) or diencephalon causing an amnestic syndrome, an inability to encode and retrieve episodic memories beyond the brief duration of working memory, appear to produce altered plasticity of the late positive P600 component, but usually spare P300 and N400 components. The neuropathology of AD affects MTL and extends to neocortical association areas, causing deficits of episodic and semantic memory. In AD dementia, the P300, N400, and P600 all commonly show abnormalities. ERP studies of individuals with mild cognitive impairment may reveal neurophysiological changes prior to the emergence of clinical deficits, which could advance the early detection and diagnosis of AD.

Neuropsychology and neuropharmacology of P3a and P3b

Perspectives on the P300 event-related brain potential (ERP) are reviewed by outlining the distinction between the P3a and P3b subcomponents. The critical factor for eliciting P3a is how target/standard discrimination difficulty rather than novelty modulates task processing. The neural loci of P3a and P3b generation are sketched and a theoretical model is developed. P3a originates from stimulus-driven disruption of frontal attention engagement during task processing. P3b originates when temporal-parietal mechanisms process the stimulus information for memory storage. The neuropharmacological implications of this view are then outlined by evaluating how acute and chronic use of ethanol, marijuana, and nicotine affect P3a and P3b. The findings suggest that the circuit underlying ERP generation is influenced in a different ways for acute intake and varies between chronic use levels across drugs. Theoretical implications are assessed.

The p300: where in the brain is it produced and what does it tell us?

Intracranial recordings, lesion studies, and the combination of functional imaging with source analysis have produced a solid body of evidence about the generators of the P300 event-related potential. Although it is impossible to square all findings obtained across and within methodologies, a consistent pattern of generators has emerged, with target-related responses in the parietal cortex and the cingulate and novelty-related activations mainly in the inferior parietal and prefrontal regions. Stimulus modality-specific contributions come from the inferior temporal and superior parietal cortex for the visual and from the superior temporal cortex for the auditory modality. The P300 continues to be an important signature of cognitive processes such as attention and working memory and of its dysfunction in neurologic and mental disorders. It is increasingly being investigated as a potential genetic marker of mental disorders. Knowledge about the generators of the P300 will be crucial for a better understanding of its cognitive significance and its continuing clinical application.

An adaptive reflexive processing model of neurocognitive function: supporting evidence from a large scale (n = 100) fMRI study of an auditory oddball task

Recent hemodynamic imaging studies have shown that processing of low probability task-relevant target stimuli (i.e., oddballs) and low probability task-irrelevant novel stimuli elicit widespread activity in diverse, spatially distributed cortical and subcortical systems. The nature of this distributed response supports the model that processing of salient and novel stimuli engages many brain regions regardless of whether said regions were necessary for task performance. However, these latter neuroimaging studies largely employed small sample sizes and fixed-effect analyses, limiting the characterization and inference of the results. The present study addressed these issues by collecting a large sample size (n = 100) and employed random effects statistical models. Analyses were also conducted to determine the inter-subject reliability of the hemodynamic response and the effects of gender and age on target detection and novelty processing. Group data demonstrated highly significant activation in all 34 specified regions of interest for target detection and all 24 specified regions of interest for processing of novel stimuli. Neither age nor gender systematically influenced the results. These data are discussed within the context of a model that proposes that the mammalian brain has evolved to adopt a strategy of engaging distributed neuronal systems when processing salient stimuli despite the low probability that many of these brain regions are required for successful task performance. This process may be termed 'adaptive reflexive processing.' The implications of these results for interpreting functional MRI studies are discussed.

Abnormal hemodynamics in schizophrenia during an auditory oddball task

BACKGROUND

Schizophrenia is a heterogeneous disorder characterized by diffuse brain abnormalities that affect many facets of cognitive function. One replicated finding in schizophrenia is abnormalities in the neural systems associated with processing salient stimuli in the context of oddball tasks. This deficit in the processing of salience stimuli might be related to abnormalities in orienting, attention, and memory processes.

METHODS

Behavioral responses and functional magnetic resonance imaging data were collected while 18 patients with schizophrenia and 18 matched healthy control subjects performed a three-stimulus auditory oddball task.

RESULTS

Target detection by healthy participants was associated with significant activation in all 38 regions of interest embracing distributed cortical and subcortical systems. Similar reproducibility was observed in healthy participants for processing novel stimuli. Schizophrenia patients, relative to control subjects, showed diffuse cortical and subcortical hypofunctioning during target detection and novelty processing, including bilateral frontal, temporal, and parietal cortices and amygdala, thalamus, and cerebellum.

CONCLUSIONS

These data replicate and extend imaging studies of target detection in schizophrenia and present new insights regarding novelty processing in the disorder. The results are consistent with the hypothesis that schizophrenia is characterized by a widespread pathologic process affecting many cerebral areas, including cortical, subcortical, and cerebellar circuits.

Progression of P300 in a patient with bilateral hippocampal lesions

OBJECTIVE

To evaluate the effects of hippocampal damages on P300 of event-related potentials (ERPs).

METHODS

ERPs were recorded over about 8 months using the auditory oddball paradigm in a patient with bilateral hippocampal lesions confirmed on brain magnetic resonance imaging. Findings were compared with those from clinical electroencephalography (periodic lateralized epileptiform discharges (PLEDs) or bilateral independent PLEDs (BIPLEDs)). The patient displayed no marked clinical symptoms aside from mild memory impairment during this time, and was able to fully perform the oddball task.

RESULTS

Clearly identifiable P300 were present in all recordings. Furthermore, increases in the number of right PLEDs were significantly correlated with increases in P300 latency.

CONCLUSIONS

Two key results were apparent. First, the appearance of P300 in all ERP recordings supports the suggestion that the hippocampus is not indispensable for P300 generation. Second, the correlation between the number of PLEDs and P300 latency supports the suggestion that the hippocampus affect the components of P300 latency.

SIGNIFICANCE

This case thus offers very suggestive evidence regarding the generation of P300.

Hippocampal involvement in detection of deviant auditory and visual stimuli

Recent models of hippocampal function have emphasized its role in processing sequences of events. In this study, we used an oddball task to investigate hippocampal responses to the detection of deviant "target" stimuli that were embedded in a sequence of repetitive "standard" stimuli. Evidence from intracranial event-related potential studies has suggested a critical role for the hippocampus in oddball tasks. However, functional neuroimaging experiments have failed to detect activation in the hippocampus in response to deviant stimuli. Our study aimed to resolve this discrepancy by using a novel functional magnetic resonance imaging (fMRI) technique that drastically improves signal detection in the hippocampus. Significant hippocampal activation was observed during both auditory and visual oddball tasks. Although there was no difference in the overall level of hippocampal activation in the two modalities, significant modality differences in the profile of activation along the long axis of the hippocampus were observed. In both left and right hippocampi, an anterior-to-posterior gradient in the activation (anterior to posterior) was observed during the auditory oddball task, whereas a posterior-to-anterior gradient (posterior to anterior) was observed during the visual oddball task. These results indicate that the hippocampus is involved in the detection of deviant stimuli regardless of stimulus modality, and that there are prominent modality differences along the long axis of the hippocampus. The implications of our findings for understanding hippocampal involvement in processing sequences of events are discussed.

Functional and anatomical memory indices in patients with or at risk for Alzheimer's disease

We investigated the sensitivity of the P300 event-related brain potential (ERP) recorded during a memory-demanding task to memory function in subjects with dementia of the Alzheimer's type (DAT), those with mild cognitive impairment (MCI), and normal elderly controls. We also explored the ability of neuropsychological (delayed verbal memory), neuroanatomical (MRI-based hippocampal volume), and electrophysiological (memory search P300 amplitude) memory measures to distinguish between the three subject groups using discriminant function analyses. Fourteen patients with DAT, 16 with MCI, and 15 age- and education-matched controls were tested. P300 amplitude was reduced in DAT subjects at all levels of memory load; however, it did not differ between MCI and control subjects. Delayed verbal memory performance best discriminated DAT from MCI and control subjects, while delayed verbal memory and hippocampal volume best discriminated MCI subjects from controls. These results support the utility of neuropsychological and neuroanatomical measures in diagnosing dementia and do not support the notion that P300 amplitude is sensitive to mild memory dysfunction when measured using the current task.

Clinical applications of event-related potentials in brain injury

ERPs may extend the battery of neurophysiologic tests currently available for determining the functional integrity of the central nervous system and the capacity of cognition in patients with brain injury. The use of stimuli relevant for the patient can enhance the probability to record these waves in unconscious patients and in patients with cognitive impairment and enhance the predictive value on outcome. The experimental data in these patients still are not sufficient, however, to standardize the indications of ERPs in clinical practice. Their limitations, mainly the variability also present in normal individuals and the limited standardization and validation, must be considered, and they must be judged cautiously as a prognostic index. Nevertheless, ERPs might be applied as a useful supplement to neuropsychologic assessment.

Differential activation in the medial temporal lobe during a sound-sequence discrimination task across age in human subjects

To elucidate the brain mechanisms to encode sequential events, event-related potentials (ERPs) were recorded during a sound-sequence discrimination task using young and middle-aged adult subjects. In the task, a series of six or 12 kinds of natural sounds were sequentially presented; 70-80% of the stimuli were presented in a fixed order (Non-target), but the remaining stimuli, in a random order (Target). The subjects were instructed to detect the Targets and press a button at the end of each Target. In a control task, the same sounds were randomly presented (Control), and they were instructed to press the button at the end of each sound. Behavioral results indicated that the young subjects learned the task faster than did the middle-aged subjects. Positive ERP waves were evoked by Targets and Non-targets in the parieto-occipital area around 300-700 ms after stimulus onset. The mean amplitudes during this period in the young subjects were larger in Target than Control conditions, and those in Target condition were larger in the young than middle-aged subjects. Furthermore, the mean amplitudes in the Target condition were significantly correlated with behavioral performance. Equivalent dipoles for the ERPs evoked by Targets were estimated in the medial temporal lobe including the hippocampal formation and parahippocampal gyrus. The results suggest that the ERPs around 300-700 ms latency are involved in sound-sequence information processing. Furthermore, decrease in amplitudes of this positivity in the middle-aged subjects suggests that age-related memory decline is associated with deficits in encoding and retrieval of unfamiliar sequence.

Investigating the generators of the scalp recorded visuo-verbal P300 using cortically constrained source localization

Considerable ambiguity exists about the generators of the scalp recorded P300, despite a vast body of research employing a diverse range of methodologies. Previous investigations employing source localization techniques have been limited largely to equivalent current dipole models, with most studies identifying medial temporal and/or hippocampal sources, but providing little information about the contribution of other cortical regions to the generation of the scalp recorded P3. Event-related potentials (ERPs) were recorded from 5 subjects using a 124-channel sensor array during the performance of a visuo-verbal Oddball task. Cortically constrained, MRI-guided boundary element modeling was used to identify the cortical generators of this target P3 in individual subjects. Cortical generators of the P3 were localized principally to the intraparietal sulcus (IPS) and surrounding superior parietal lobes (SPL) bilaterally in all subjects, though with some variability across subjects. Two subjects also showed activity in the lingual/inferior occipital gyrus and mid-fusiform gyrus. A group cortical surface was calculated by non-linear warping of each subject's segmented cortex followed by averaging and creation of a group mesh. Source activity identified across the group reflected the individual subject activations in the IPS and SPL bilaterally and in the lingual/inferior occipital gyrus primarily on the left. Activation of IPS and SPL is interpreted to reflect the role of this region in working memory and related attention processes and visuo-motor integration. The activity in left lingual/inferior occipital gyrus is taken to reflect activation of regions associated with modality-specific analysis of visual word forms.

An Event-Related fMRI Study of Visual and Auditory Oddball Tasks

Abstract Whole brain event-related functional magnetic resonance imaging (fMRI) techniques were employed to elucidate the cerebral sites involved in processing rare target and novel visual stimuli during an oddball discrimination task. The analyses of the hemodynamic response to the visual target stimuli revealed a distributed network of neural sources in anterior and posterior cingulate, inferior and middle frontal gyrus, bilateral parietal lobules, anterior superior temporal gyrus, amygdala, and thalamus. The analyses of the hemodynamic response for the visual novel stimuli revealed an extensive network of neural activations in occipital lobes and posterior temporal lobes, bilateral parietal lobules, and lateral frontal cortex. The hemodynamic response associated with processing target and novel stimuli in the visual modality were also compared with data from an analogous study in the auditory modality ( Kiehl et al., 2001 ). Similar patterns of activation were observed for target and novel stimuli in both modalities, but there were some significant differences. The results support the hypothesis that target detection and novelty processing are associated with neural activation in widespread neural areas, suggesting that the brain seems to adopt a strategy of activating many potentially useful brain regions despite the low probability that these brain regions are necessary for task performance.

Multimodal P3 under different attentional states in mesial temporal lobe epilepsy

BACKGROUND

Several studies demonstrate that the P3 component of the event-related potentials (ERP) is generated by mesial temporal structures. The P3 is considered as endogenous information processing component independent from modality.

PURPOSE

The aim of this investigation was to study whether the P3 latency elicited by auditory and visual stimuli under different attentional states is influenced by the mesial temporal lobe epilepsy (mTLE).

METHODS

The event related P3 component of 10 right handed patients (7 m/3 f, mean age 31.3 years (SD 7.3), median 31.5, range 20-47) with unilateral mTLE were studied and compared with 10 age matched controls (5 m/5 f, mean age 36.6 years (SD 12.6), median 32.1, range 22-48). Diagnosis of mTLE was based on seizure description, clinical history and examination, prolonged video-EEG monitoring, magnetic resonance imaging (MRI), interictal and ictal SPECT. P3 potentials were elicited with a visual and auditory three stimulus discrimination paradigm.

RESULTS

The latency of the P3 response to the auditory stimulus under automatic and effortful attention was delayed (423.3 ms (SD 60.4) and 436.9 ms (SD 83.4)) compared with a control group (359 ms (SD 42.4) and 354.2 ms (SD 39.7); P = 0.039 and P = 0.012, ANOVA), while the P3 latencies to visual stimuli under both tested attentional states (407.3 ms (SD 52.9) and 390.6 ms (SD 40.2)) did not differ from controls (378.2 ms (SD 48.6) and 378.2 ms (SD 55.4)). P3 latencies to auditory novel paradigm in patients with right sided mTLE, but not left sided mTLE, differed significantly from controls (P = 0.01).

CONCLUSION

The results suggest a modality dependence of the P3 component in patients with mTLE. The novelty processing of auditory stimuli is disturbed in patients with right sided mTLE.

[The recording of cognitive evoked potentials during and after transient global amnesia: report of three cases]

It is of interest to record event-related potentials in the course of transient global amnesia (TGA) because the hippocampus and diencephalon, generally considered to be the sites of the dysfunction responsible for the amnesic episodes are also considered as two possible generators of the P300 wave. However, the only four cases reported so far in the literature showed an intact auditive P300 in three cases and an intact auditive P300 with reduction of visual P300 in one case. Here are reported four new cases. The P300 wave was readily identifiable in all four cases, without any amplitude reduction, thus suggesting that the condition did not entail inactivation or functional depression of P300 generators. Concerning P300 latency, in one case it was delayed but became normal after the ictus. In the second case, the latency, although within normal limits, shortened after the ictus. In the third and the fourth cases, the latency, initially within normal limits, remained unchanged. These apparently disparate results should be analysed in the light of the results of isotope measurement of cerebral blood flow during the amnesia, which are also inconsistent but most frequently indicate bilateral temporal or thalamic flow reduction. It remains to be determined in the future whether the stability or change in the P300 will make it possible to predict the brain region involved in transient global amnesia, which could perhaps vary from one patient to another.

The neurophysiological meaning of auditory P300 in subtypes of schizophrenia

Event-related potentials are a powerful tool to investigate the real-time course of brain electrical mass activation during cognitive processing. In several psychiatric disorders, differences compared to healthy subjects have been reliably described. The specificity and the pathophysiological meaning of the findings were unclear in most studies, however. This review summarizes methodological aspects and findings, in healthy subjects and psychiatric patients, of investigations based on the auditory oddball paradigm, which evokes the P300 component of event-related potentials. Recent convergent results from P300 and brain imaging studies allowed the interpretation of P300 findings in psychotic disorders in terms of different specific and meaningful neurophysiological disturbances. Namely, core schizophrenia is characterized by a left-temporal dysfunction associated with deficits in verbal processing. Acute remitting schizophrenia-like psychoses (cycloid psychosis, ICD-10 F23), on the other hand, show normal hemispheric balance but consistent signs of cerebral hyperarousal. Recent studies further indicate that the drive for action of manic patients does not rely on over-excitation but rather on frontal disinhibition. The findings may help to further advance the understandings and sub-grouping of functional psychoses based on pathophysiological mechanisms.

Delayed visual P3 in unilateral thalamic stroke

The P3 potential is accepted as a neurophysiological correlate of memory and attention. Delayed latencies were reported in different forms of dementias. Although the generator sites are still under debate, the thalamus may play a crucial role. The aim of this study was to investigate the influence of an unilateral thalamic ischaemic infarction on P3 generation. The event-related P3 component of six patients (2 male, four female; mean age 47 years, range 22-63 years) with unilateral thalamic ischaemic infarction was studied and compared to age-matched controls (five male, nine female; mean age 45.8 years; range 22-69 years). All patients underwent full clinical examination, CCT, and MRI scan. P3 potentials were recorded with a visual three stimulus discrimination paradigm. The mean P3 latency of the patient group to the target stimulus was delayed (469.7 ms, SD = 36.8) compared with the controls (378.8 ms, SD = 51.5; P < 0. 05). The mean P3 latency to the unexpected stimulus was delayed in patients with thalamic infarction compared with controls [477 ms (SD = 46.6) vs. 381.2 ms (SD = 48.5); P < 0.001). Delayed P3 components of the event-related potential (ERP) were recorded in six patients with unilateral thalamic infarction, suggesting an important role of the thalamus in the generation of the P3 potential.

[The p300 cognitive event-related potential. I. Theoretical and psychobiologic perspectives]

The P300 is a positive wave which arises when an attended stimulus is detected. Its parameters depend on a number of variables, in particular the subject's mental state, the task that has to be accomplished, the significance of the stimulus, and the degree of attention. It can be recorded with accuracy, and the different stages of information processing can therefore be analyzed. The P300 wave shows the modifications in neuronal activity which take place during the cognitive process: P300 latency provides an indirect indication of the duration of the processes involved in stimulus discrimination while its amplitude, which is influenced by a number of variables, provides an index of the intensity of the energetic activation or arousal involved. The P300 wave consists of several components which reflect distinct information-processing events (P3a, P3b, P3e, P-SR, P-CR). According to the theoretical models, it is hypothesized that P300 could either represent the adaptation of the working memory to further environmental input ('context updating'), or indicate a closing process ('context closure') in information processing. As regards the physiological aspect of P300 and its association with cortical networks, various studies have suggested that several cortical generators of P300 may co-exist: the medial temporal lobe, the temporo-parietal junction, and the medial and lateral frontal lobe. Psychopharmacological studies have shown that different neurotransmitter systems are involved in the generation and modulation of P300, namely the cholinergic, noradrenergic, dopaminergic, serotoninergic and gabaergic systems. It appears that the noradrenergic agonists increase the amplitude of P300, dopaminergic agonists may have a biphasic effect (increase/reduction), while cholinergic antagonists and gabaergic agonists reduce P300 amplitude and prolong its latency.

Auditory event-related potentials in an amnesic patient with a left temporal lobe lesion

We studied auditory event-related potentials (ERPs) in correlation with Rey's auditory verbal learning test (AVLT) in an amnesic patient with a left temporal lobe lesion. On the AVLT, the number of words recalled was limited to immediate memory capacity (nine words) throughout five trials, and recall after interference was remarkably decreased. In the ERPs, the P300 component was elicited normally, but no N400 component was apparent. Present findings suggest that these two ERP components may be associated with independent processes and support the view that the N400 may index a neural process involved in transfer of information from immediate memory to long-term storage.

Event related potentials recorded in patients with locked-in syndrome

OBJECTIVE

To determine the possibility of recording "cognitive" event related potentials (ERPs) in locked-in patients and therefore to determine whether ERPs can have a role in differential diagnosis of coma.

METHODS

ERPs to classic auditory or visual "odd ball paradigms" were recorded three to four days, seven to eight days, and 30 to 60 days after admission to the intensive care unit, in four patients affected by basilar artery thromboembolism resulting in locked-in syndrome. Two patients (one 32 year old man, one 31 year old woman) could move the eyes laterally and vertically spontaneously and on command. One patient (a 39 year old man) had a "one and half syndrome", one patient (a 40 year old woman) could only elevate the left eyelid and eye. Results were compared with data from 30 age matched controls. In the last recording session a letter recognition paradigm was applied, in which ERPs were produced by the identification of letters forming a word. Results were compared with five age matched controls. Brainstem lesions extending to the pontomesencephalic junction were found on MRI and CT.

RESULTS

ERPs to the oddball paradigms were recorded in three patients in the first recording session, in all patients in the second recording session. Latency, amplitude, and topographic distribution of ERP components were inside normal limits. With the letter recognition paradigm the patients could emit a P3 component to correspond with target letters, with the same margin of error as controls.

CONCLUSION

It is possible to record ERPs in patients with locked-in syndrome shortly after the acute ischaemic lesion, and therefore to assess objectively cognitive activities. Furthermore the letter recognition paradigm could be implemented to facilitate linguistic communication with patients with locked-in syndrome.

Event-related potentials in brain-injured patients with neuropsychological disorders: a review

Investigations using event-related potentials (ERPs) in brain-injured patients affected by neuropsychological disorders of perception, attention, memory, and language, and other special syndromes such as blind-sight, neglect, prosopagnosia, and apraxia are reviewed. These electrophysiological techniques can be used to assess the integrity of specific brain processes during the performance of cognitive tasks in which behavioral impairments are observed. A special feature of ERP technique is that it reveals ongoing and covert processing which may not be fully assessed by measuring only overt behavioral performance.

Working memory in temporal lobe epilepsy: an event-related potential study

Event-related potentials (ERPs) were recorded to a digit-probe identification and matching task (modified 'Sternberg paradigm') in 29 patients with temporal lobe epilepsy (TLE) and 26 healthy subjects. Our main aim was to identify the neurophysiological correlates of abnormal short term memory function in patients with TLE. Neuropsychological tests allowed the definition and comparison of two patient groups according to the presence or absence of memory dysfunction. These two groups did not differ significantly in mean age, education years, IQ, seizure duration, seizure frequency, anti-epileptic drug (AED) regimes, or on findings on neuroimaging. ERPs recorded under different levels of memory load were analysed both by conventional component identification and by an objective computer method of determining mean amplitudes of multiple 50 ms epochs (MMA analysis). We found that some significant abnormalities were common to both groups of patients; these included slow reaction times, a reduced amplitude of the N170 wave (and the corresponding 157-210 ms epoch in the MMA analysis) and a broad late negative shift between 577 and 735 ms. Other findings, including a significantly reduced performance accuracy as the level of memory load increased, were restricted to patients with abnormal memory function. The ERP changes that were specific to these patients occurred within a latency band of 200-420 ms and included a relatively preserved, but delayed P250 component and a delayed and attenuated N290 wave. When compared with either healthy subjects or with patients with normal memory, the responses in patients with abnormal memory showed an abnormal 'positive shift' between 262 and 315 ms after probe presentation and a further positive shift between 315 and 420 ms as memory load increased. These abnormalities of 'memory scanning' ERPs in patients with TLE which paralleled neuropsychological and behavioural evidence of memory dysfunction, and which occurred in the section of the response that is sensitive to memory loading in healthy subjects, provide further objective evidence that abnormalities of short term memory processes contribute to the memory deficits of TLE.

Dipole-modeling of the visual evoked P300

We collected visual event-related potentials (ERPs) from 6 normal subjects using an "oddball" paradigm. Subjects were required to count the occurrences of matching shapes presented in the left and right visual field. Shapes matched on 20% of trials. ERPs were recorded from 20 or 43 electrodes distributed over the scalp. A multiple spatio-temporal equivalent dipole (ED) model was used to fit the early sensory and P300 component. A latency window to analyze the P300 was determined using the global field power statistic. The spatial topography of the P300 over this window was characterized by a midline positivity that decreased in amplitude with spatial distance from the peak. After sensory components were fit, the source of P300 could be accounted for by 1 or 2 EDs, which were usually located near medial temporal areas. This result is at odds with evidence from depth recordings during the oddball paradigm, showing that multiple regions of the brain are active during this interval.

Transient P300 abnormality of event-related potentials following unilateral temporal lobectomy

Event-related potentials (ERP) were recorded during auditory oddball tasks for a patient prior to and soon after left anterior temporal lobectomy. The N100 amplitude decreased bilaterally although the latency did not change after the lobectomy. The P300 amplitude decreased in the left hemisphere at 1 and 2 weeks after surgery, then recovered to the pre-operative level at 4 weeks. These findings suggest that the medial temporal structure participates in the generating system of P300.

P300 asymmetries in focal brain lesions are reference dependent

In 6 patients with lesions of frontal, parietal and temporal lobe, in 4 patients affected by primary progressive aphasia (PPA) and in 56 age-matched controls, event-related potentials (ERPs) to an auditory odd-ball paradigm were recorded with the linked earlobe reference (LER) and with a computer calculated average reference (AR), excluding the two linked earlobe derivations. Latencies, amplitudes and scalp distribution of the earlier ERP components (P1, N1, P2, N2) were within normal limits for both LER and AR recordings. P300 scalp distribution in patients was normal when LER was used. When P300 was recorded using AR, the scalp distribution was statistically different from normal distributions in all patients. A negativity, instead of the positive P300 observed in controls, was recorded in patients from leads corresponding to the affected hemisphere.

P300 in Alzheimer's disease: relationships to dementia severity and glucose metabolism

In 45 patients (aged 48-85 years) with probable Alzheimer's disease (AD) according to current research criteria (NINCDS-ADRDA) with different stages of dementia severity (Mini Mental Status Examination (MMSE) 7-27) the auditory evoked P300 waves were mapped and regional cerebral metabolic rates of glucose were measured by positron emission tomography of 2-[18F]fluoro-2-deoxy-D-glucose. Age adjusted P300 latency was significantly correlated to dementia severity (r = -0.33, p = 0.028), but no significant relationships were found for P300 amplitudes. Dependencies existed among cortical glucose metabolic rates and MMSE with the highest correlation coefficient for the metabolic ratio of regions typically affected and non-affected in AD (r = 0.75, p = 0.0001). A significant correlation was also calculated between P300 latency and metabolic ratio (r = -0.44, p = 0.002), but no relationships were observed among P300 amplitudes and glucose metabolic rates of individual brain regions. These results indicate that P300 latency and metabolic rates but not P300 amplitudes qualify as measures of severity in AD. The lack of regional correlations among P300 amplitudes and glucose metabolism is not consistent with a cortical contribution to P300 generation.

Reduction of P3b in patients with temporo-parietal lesions

By recording event-related EEG potentials from patients with frontal, parietal, or temporo-parietal lesions, we wanted to determine the cortical area that is relevant to the P3b component, replicating the approach used by Knight and associates who found reduced P3bs in patients with temporo-parietal lesions. They used auditory and somatosensory stimuli. We wanted to replicate their findings in auditory and visual oddball tasks and analysed potentials evoked by targets and by standard stimuli. Temporo-parietal patients' P3bs were reduced with auditory targets and lacked a distinct Pz maximum with visual targets. Further, auditory N1 was reduced both with targets and standards, P3 to visual standards and P2 to auditory standards were reduced. Parietal patients' P3bs differed only slightly from the control group, being somewhat reduced over the lesioned hemisphere with visual stimuli. Their P3 to visual standards was, however, reduced to the same extent as was the temporo-parietal patients'. Frontal patients did not differ from the control group both in their P3b and in their P3 to standards but had a number of conspicuous features in modality-specific components. In sum, our results on P3b (as well as on N1) replicate Knight's findings, confirming his conclusion that integrity of the temporo-parietal junction is critical for P3b. Implications for hypotheses on P3 are discussed.

Reduction of visual P300 during transient global amnesia

Transient global amnesia (TGA) is a syndrome of selective loss of recent memory without other neurological deficits. Auditory and visual P300s were recorded during and after TGA to investigate the contribution of the short-term memory system to P300 generation. The auditory P300 during TGA was comparable to that recorded 1 week and 9 months after TGA. In contrast to the auditory modality, the visual target P300 was reduced in amplitude during TGA and at 1 week after the attack. The P300 to novel visual stimuli was also reduced during TGA. Both target and novelty visual P300 recovered by 9 months after TGA. The results support the notion that the neuronal networks responsible for P300 generation are modality dependent and that brain structures perfused by the posterior circulation are involved in visual P300 generation.

Focal abnormalities of P3 ERPs unveiled in patients with cortical lesions and primary progressive aphasia by average reference recordings

Event related potentials (ERPs) to an auditory odd-ball paradigm were recorded with the linked earlobe reference (LER) and with a computer calculated average reference (AR), excluding the two linked earlobe derivations. The study was performed in 30 patients with lesions of frontal, parietal, occipital cortex, unilateral and bilateral lesions of the medial temporal lobe (MTL), in four patients affected by Primary Progressive Aphasia (PPA) and in 56 age matched controls. Latencies, amplitudes and scalp distribution of the earlier ERP components (P1, N1, P2, N2) were within normal limits for both LER and AR recordings. P3 scalp distribution in patients was normal when LER was used, with the exception of two patients affected by bilateral MTL lesions. When P3 was recorded using AR, the scalp distribution was statistically different from normal distributions in all patients. A negativity, instead of the positive P3 observed in controls, was recorded in patients from leads corresponding to the affected areas. This finding might have clinical applications, and confirms earlier studies suggesting that P3 is generated simultaneously from different cortical areas.

The relationship between P300 amplitude and regional gray matter volumes depends upon the attentional system engaged

Event-related potentials (ERPs) and brain magnetic resonance images (MRIs) were acquired from 28 normal men, age 21-60 years. ERPs were recorded during 3 paradigms designed to elicit automatic or effortful attention, and a combination of both. MRI-derived measures of brain gray matter, white matter and cerebral spinal fluid (CSF) volumes were computed from frontal, parietal and temporal lobes. P300 amplitude correlated significantly with gray matter volumes but not with white matter or CSF volumes. Furthermore, the relationships between P300 amplitude and gray matter volumes reflected functional rather than direct topographical relationships: P300 recorded at Pz during automatically elicited attention correlated significantly with frontal but not parietal lobe gray matter volumes, P300 recorded during effortful attention correlated significantly with parietal but not frontal lobe gray matter volumes, and P300 recorded when both types of attention were invoked correlated significantly with both frontal and parietal gray matter volumes. Startle blinks, also elicited during automatic attention-engaging paradigms, were significantly correlated with frontal but not parietal lobe gray matter volumes. There was no evidence for a direct spatial relationship between P300 amplitude and the gray matter volumes underlying the recording electrode.

Electrical source analysis of auditory ERPs in medial temporal lobe amnestic syndrome

Auditory event-related potential (ERP) components have been anatomically linked to temporal lobe structures and functionally related to attentional and memory processes. We recorded auditory ERPs using an "oddball" paradigm from two patients with amnestic syndromes secondary to medial temporal lobe encephalitic infections. The oddball paradigm elicits the exogenous N1 and P2 components, and the endogenous N2 and P3 components. Electrical source analysis was used to test for alterations in source strength and orientation in these patients compared to control subjects. Symmetric dipoles placed in the temporal lobe region were used to measure ERP component activity. In the patient with a lesion confined to the left, medial temporal lobe, including the posterior hippocampus, dipole orientation was displaced anteriorally. In the patient with lesions to the anterior medial temporal lobe, temporal poles, and orbital frontal cortex, the negative components of the ERP (N1 and N2) were reduced in the right hemisphere, accompanied by disturbed orientation. These findings are consistent with other evidence that the different components of the auditory ERP can be dissociated on the basis of lesion effects, and that the antero-posterior extent of encephalitic lesions may play an important role in modulating ERP abnormalities.

P300 from amnesic patients with bilateral hippocampal lesions

P3(00) event-related brain potentials (ERPs) were recorded using auditory and visual stimuli from 5 amnesic patients with confirmed (n = 4) or suspected (n = 1) bilateral damage to the hippocampal formation without skull defects. Four normal control subjects were matched to each amnesic patient with respect to age, sex, education, and IQ subtest scores (n = 20 total controls). All 5 amnesic patients exhibited ERPs, and no reliable differences in P3 amplitude or latency could be detected between the patients and the control subjects in either modality. The findings indicate that the hippocampal formation does not contribute significantly to the scalp-recorded P3 from auditory and visual target stimuli, a conclusion also supported by additional recent findings from studies of patients with extensive bilateral medial temporal lobe damage studies. The significance of the P3 component for cognitive processing is discussed.

On the neural generators of the P300 component of the event-related potential

The triarchic model of P300 amplitude (Johnson, 1986, 1988a) postulated that the overall amplitude of the P300 recorded at any given electrode site represented the summation of activity from different neural generators, each related to the processing of a different type of information. However, neither of these original accounts provided an explicit description of the methods required to establish experimentally the presence of multiple neural sources. This paper reviews the triarchic amplitude model, the subsequently obtained data that support the postulated presence of multiple generators underlying the P300, and the methods used to demonstrate the presence of these multiple sources. These methods are straightforward because it is only necessary to show that the portions of P300 amplitude associated with different experimental variables have different scalp distributions. The implications of the multiple-generator basis of P300 on such factors as component definition, neural source analyses, and the cognitive processes underlying its activity are discussed.