Cognitive Event-Related Potentials: Useful Clinical Information in Alzheimers Disease

Prefrontal intra-individual ERP variability and its asymmetry: exploring its biomarker potential in mild cognitive impairment

BACKGROUND

The worldwide trend of demographic aging highlights the progress made in healthcare, albeit with health challenges like Alzheimer's Disease (AD), prevalent in individuals aged 65 and above. Its early detection at the mild cognitive impairment (MCI) stage is crucial. Event-related potentials (ERPs) obtained by averaging EEG segments responded to repeated events are vital for cognitive impairment research. Consequently, examining intra-trial ERP variability is vital for comprehending fluctuations within psychophysiological processes of interest. This study aimed to investigate cognitive deficiencies and instability in MCI using ERP variability and its asymmetry from a prefrontal two-channel EEG device.

METHODS

In this study, ERP variability for both target and non-target responses was examined using the response variance curve (RVC) in a sample comprising 481 participants with MCI and 1,043 age-matched healthy individuals. The participants engaged in auditory selective attention tasks. Cognitive decline was assessed using the Seoul Neuropsychological Screening Battery (SNSB) and the Mini-Mental State Examination (MMSE). The research employed various statistical methods, including independent t-tests, and univariate and multiple logistic regression analyses. These analyses were conducted to investigate group differences and explore the relationships between neuropsychological test results, ERP variability and its asymmetry measures, and the prevalence of MCI.

RESULTS

Our results showed that patients with MCI exhibited unstable cognitive processing, characterized by increased ERP variability compared to cognitively normal (CN) adults. Multiple logistic regression analyses confirmed the association between ERP variability in the target and non-target responses with MCI prevalence, independent of demographic and neuropsychological factors.

DISCUSSION

The unstable cognitive processing in the MCI group compared to the CN individuals implies abnormal neurological changes and reduced and (or) unstable attentional maintenance during cognitive processing. Consequently, utilizing ERP variability measures from a portable EEG device could serve as a valuable addition to the conventional ERP measures of latency and amplitude. This approach holds significant promise for identifying mild cognitive deficits and neural alterations in individuals with MCI.

Adjunct Methods for Alzheimer's Disease Detection: A Review of Auditory Evoked Potentials

The auditory afferent pathway as a clinical marker of Alzheimer's disease (AD) has sparked interest in investigating the relationship between age-related hearing loss (ARHL) and AD. Given the earlier onset of ARHL compared to cognitive impairment caused by AD, there is a growing emphasis on early diagnosis and intervention to postpone or prevent the progression from ARHL to AD. In this context, auditory evoked potentials (AEPs) have emerged as a widely used objective auditory electrophysiological technique for both the clinical diagnosis and animal experimentation in ARHL due to their non-invasive and repeatable nature. This review focuses on the application of AEPs in AD detection and the auditory nerve system corresponding to different latencies of AEPs. Our objective was to establish AEPs as a systematic and non-invasive adjunct method for enhancing the diagnostic accuracy of AD. The success of AEPs in the early detection and prediction of AD in research settings underscores the need for further clinical application and study.

The Importance of Subjective Cognitive Decline Recognition and the Potential of Molecular and Neurophysiological Biomarkers-A Systematic Review

Subjective cognitive decline (SCD) and mild cognitive impairment (MCI) are early stages of Alzheimer's disease (AD). Neurophysiological markers such as electroencephalography (EEG) and event-related potential (ERP) are emerging as alternatives to traditional molecular and imaging markers. This paper aimed to review the literature on EEG and ERP markers in individuals with SCD. We analysed 30 studies that met our criteria, with 17 focusing on resting-state or cognitive task EEG, 11 on ERPs, and two on both EEG and ERP parameters. Typical spectral changes were indicative of EEG rhythm slowing and were associated with faster clinical progression, lower education levels, and abnormal cerebrospinal fluid biomarkers profiles. Some studies found no difference in ERP components between SCD subjects, controls, or MCI, while others reported lower amplitudes in the SCD group compared to controls. Further research is needed to explore the prognostic value of EEG and ERP in relation to molecular markers in individuals with SCD.

Functional changes in brain oscillations in dementia: a review

A growing body of evidence indicates that several characteristics of electroencephalography (EEG) and magnetoencephalography (MEG) play a functional role in cognition and could be linked to the progression of cognitive decline in some neurological diseases such as dementia. The present paper reviews previous studies investigating changes in brain oscillations associated to the most common types of dementia, namely Alzheimer's disease (AD), frontotemporal degeneration (FTD), and vascular dementia (VaD), with the aim of identifying pathology-specific patterns of alterations and supporting differential diagnosis in clinical practice. The included studies analysed changes in frequency power, functional connectivity, and event-related potentials, as well as the relationship between electrophysiological changes and cognitive deficits. Current evidence suggests that an increase in slow wave activity (i.e., theta and delta) as well as a general reduction in the power of faster frequency bands (i.e., alpha and beta) characterizes AD, VaD, and FTD. Additionally, compared to healthy controls, AD exhibits alteration in latencies and amplitudes of the most common event related potentials. In the reviewed studies, these changes generally correlate with performances in many cognitive tests. In conclusion, particularly in AD, neurophysiological changes can be reliable early markers of dementia.

Prefrontal EEG slowing, synchronization, and ERP peak latency in association with predementia stages of Alzheimer's disease

Background

Early screening of elderly individuals who are at risk of dementia allows timely medical interventions to prevent disease progression. The portable and low-cost electroencephalography (EEG) technique has the potential to serve it.

Objective

We examined prefrontal EEG and event-related potential (ERP) variables in association with the predementia stages of Alzheimer's disease (AD).

Methods

One hundred elderly individuals were recruited from the GARD cohort. The participants were classified into four groups according to their amyloid beta deposition (A+ or A-) and neurodegeneration status (N+ or N-): cognitively normal (CN; A-N-, n = 27), asymptomatic AD (aAD; A + N-, n = 15), mild cognitive impairment (MCI) with AD pathology (pAD; A+N+, n = 16), and MCI with non-AD pathology (MCI(-); A-N+, n = 42). Prefrontal resting-state eyes-closed EEG measurements were recorded for five minutes and auditory ERP measurements were recorded for 8 min. Three variables of median frequency (MDF), spectrum triangular index (STI), and positive-peak latency (PPL) were employed to reflect EEG slowing, temporal synchrony, and ERP latency, respectively.

Results

Decreasing prefrontal MDF and increasing PPL were observed in the MCI with AD pathology. Interestingly, after controlling for age, sex, and education, we found a significant negative association between MDF and the aAD and pAD stages with an odds ratio (OR) of 0.58. Similarly, PPL exhibited a significant positive association with these AD stages with an OR of 2.36. Additionally, compared with the MCI(-) group, significant negative associations were demonstrated by the aAD group with STI and those in the pAD group with MDF with ORs of 0.30 and 0.42, respectively.

Conclusion

Slow intrinsic EEG oscillation is associated with MCI due to AD, and a delayed ERP peak latency is likely associated with general cognitive impairment. MCI individuals without AD pathology exhibited better cortical temporal synchronization and faster EEG oscillations than those with aAD or pAD.

Significance

The EEG/ERP variables obtained from prefrontal EEG techniques are associated with early cognitive impairment due to AD and non-AD pathology. This result suggests that prefrontal EEG/ERP metrics may serve as useful indicators to screen elderly individuals' early stages on the AD continuum as well as overall cognitive impairment.

Treatment effects on event-related EEG potentials and oscillations in Alzheimer's disease

Alzheimer's disease dementia (ADD) is the most diffuse neurodegenerative disorder belonging to mild cognitive impairment (MCI) and dementia in old persons. This disease is provoked by an abnormal accumulation of amyloid-beta and tauopathy proteins in the brain. Very recently, the first disease-modifying drug has been licensed with reserve (i.e., Aducanumab). Therefore, there is a need to identify and use biomarkers probing the neurophysiological underpinnings of human cognitive functions to test the clinical efficacy of that drug. In this regard, event-related electroencephalographic potentials (ERPs) and oscillations (EROs) are promising candidates. Here, an Expert Panel from the Electrophysiology Professional Interest Area of the Alzheimer's Association and Global Brain Consortium reviewed the field literature on the effects of the most used symptomatic drug against ADD (i.e., Acetylcholinesterase inhibitors) on ERPs and EROs in ADD patients with MCI and dementia at the group level. The most convincing results were found in ADD patients. In those patients, Acetylcholinesterase inhibitors partially normalized ERP P300 peak latency and amplitude in oddball paradigms using visual stimuli. In these same paradigms, those drugs partially normalize ERO phase-locking at the theta band (4-7 Hz) and spectral coherence between electrode pairs at the gamma (around 40 Hz) band. These results are of great interest and may motivate multicentric, double-blind, randomized, and placebo-controlled clinical trials in MCI and ADD patients for final cross-validation.

Interval-based features of auditory ERPs for diagnosis of early Alzheimer's disease

INTRODUCTION

It has been demonstrated that event-related potentials (ERPs) mirror the neurodegenerative process of Alzheimer's disease (AD) and may therefore qualify as diagnostic markers. The aim of this study was to explore the potential of interval-based features as possible ERP biomarkers for early detection of AD patients.

METHODS

The current results are based on 7-channel ERP recordings of 95 healthy controls (HCs) and 75 subjects with mild AD acquired during a three-stimulus auditory oddball task. To evaluate interval-based features as diagnostic biomarkers in AD, two classifiers were applied to the selected features to distinguish AD and healthy control ERPs: RBFNN (radial basis function neural network) and MLP (multilayer perceptron).

RESULTS

Using extracted features and a radial basis function neural network, a high overall diagnostic accuracy of 98.3% was achieved.

DISCUSSION

Our findings demonstrate the great promise for scalp ERP and interval-based features as non-invasive, objective, and low-cost biomarkers for early AD detection.

Tau phosphorylation and cochlear apoptosis cause hearing loss in 3×Tg-AD Mouse Model of Alzheimer's Disease

Clinically typical dementia Alzheimer's disease (AD) is associated with abnormal auditory processing. However, possible molecular mechanisms responsible for the auditory pathology of AD patients are not known. According to our past research findings that the thresholds of auditory brainstem response, but not distortion product otoacoustic emissions, were significantly increased in AD mice from 9 months of age and thereafter. Thus, we further explored the possible mechanism of auditory degradation of 3×Tg-AD mice in this study. Our histochemical staining evidence showed the cochlear spiral ganglion neurons (SGN), but not the cochlear hair cells, were lost significantly in the cochlea of 3×Tg-AD mice from 9 months of age and thereafter. Our immunostaining and western blotting evidence showed that phosphorylated tau protein (p-Tau), p-glycogen synthase kinase 3, neurofilament, and apoptosis-related p53, Bcl2-associated X protein, cytochrome c, caspase-9, and caspase-3 were gradually increased, but B-cell lymphoma 2 was gradually decreased with age growth in the cochlea of 3×Tg-AD mice. We suggested that tau hyperphosphorylation and p-Tau 181 aggregation, and mitochondria- and endoplasmic reticulum stress-mediated apoptosis may play a role in the degeneration of SGN in the cochlea. Progressive SGN degeneration in the cochlea may contribute to hearing loss of aging 3×Tg-AD mice.

Potential New Approaches for Diagnosis of Alzheimer's Disease and Related Dementias

Dementia is an umbrella term-caused by a large number of specific diagnoses, including several neurodegenerative disorders. Alzheimer's disease (AD) is now the most common cause of dementia in advanced countries, while dementia due to neurosyphilis was the leading cause a century ago. Many challenges remain for diagnosing dementia definitively. Some of these include variability of early symptoms and overlap with similar disorders, as well as the possibility of combined, or mixed, etiologies in some cases. Newer technologies, including the incorporation of PET neuroimaging and other biomarkers (genomics and proteomics), are being incorporated into revised diagnostic criteria. However, the application of novel diagnostic methods at clinical sites is plagued by many caveats including availability and access. This review surveys new diagnostic methods as well as remaining challenges-for clinical care and clinical research.

Dysfunction of attention switching networks in amyotrophic lateral sclerosis

OBJECTIVE

To localise and characterise changes in cognitive networks in Amyotrophic Lateral Sclerosis (ALS) using source analysis of mismatch negativity (MMN) waveforms.

RATIONALE

The MMN waveform has an increased average delay in ALS. MMN has been attributed to change detection and involuntary attention switching. This therefore indicates pathological impairment of the neural network components which generate these functions. Source localisation can mitigate the poor spatial resolution of sensor-level EEG analysis by associating the sensor-level signals to the contributing brain sources. The functional activity in each generating source can therefore be individually measured and investigated as a quantitative biomarker of impairment in ALS or its sub-phenotypes.

METHODS

MMN responses from 128-channel electroencephalography (EEG) recordings in 58 ALS patients and 39 healthy controls were localised to source by three separate localisation methods, including beamforming, dipole fitting and exact low resolution brain electromagnetic tomography.

RESULTS

Compared with controls, ALS patients showed significant increase in power of the left posterior parietal, central and dorsolateral prefrontal cortices (false discovery rate = 0.1). This change correlated with impaired cognitive flexibility (rho = 0.45, 0.45, 0.47, p = .042, .055, .031 respectively). ALS patients also exhibited a decrease in the power of dipoles representing activity in the inferior frontal (left: p = 5.16 × 10-6, right: p = 1.07 × 10-5) and left superior temporal gyri (p = 9.30 × 10-6). These patterns were detected across three source localisation methods. Decrease in right inferior frontal gyrus activity was a good discriminator of ALS patients from controls (AUROC = 0.77) and an excellent discriminator of C9ORF72 expansion-positive patients from controls (AUROC = 0.95).

INTERPRETATION

Source localization of evoked potentials can reliably discriminate patterns of functional network impairment in ALS and ALS subgroups during involuntary attention switching. The discriminative ability of the detected cognitive changes in specific brain regions are comparable to those of functional magnetic resonance imaging (fMRI). Source analysis of high-density EEG patterns has excellent potential to provide non-invasive, data-driven quantitative biomarkers of network disruption that could be harnessed as novel neurophysiology-based outcome measures in clinical trials.

Increased Amplitude of the P3a ERP Component as a Neurocognitive Marker for Differentiating Amnestic Subtypes of Mild Cognitive Impairment

The event-related potential (ERP) technique has been shown to be useful for evaluating changes in brain electrical activity associated with different cognitive processes, particularly in Alzheimer's disease (AD). Longitudinal studies have shown that a high proportion of people with amnestic mild cognitive impairment (aMCI) go on to develop AD. aMCI is divided into two subtypes according to the presence of memory impairment only (single-domain aMCI: sdaMCI) or impairment of memory and other cognitive domains (multi-domain aMCI: mdaMCI). The main aim of this study was to examine the effects of sdaMCI and mdaMCI on the P3a ERP component associated with the involuntary orientation of attention toward unattended infrequent novel auditory stimuli. Participants performed an auditory-visual distraction-attention task, in which they were asked to ignore the auditory stimuli (standard, deviant, and novel) and to attend to the visual stimuli (responding to some of them: Go stimuli). P3a was identified in the Novel minus Standard difference waveforms, and reaction times (RTs) and hits (in response to Go stimuli) were also analyzed. Participants were classified into three groups: Control, 20 adults (mean age (M): 65.8 years); sdaMCI, 19 adults (M: 67 years); and mdaMCI, 11 adults (M: 71 years). In all groups, the RTs were significantly longer when Go stimuli were preceded by novel (relative to standard) auditory stimuli, suggesting a distraction effect triggered by novel stimuli; mdaMCI participants made significantly fewer hits than control and sdaMCI participants. P3a comprised two consecutive phases in all groups: early-P3a (e-P3a), which may reflect the orienting response toward the irrelevant stimuli, and late-P3a (l-P3a), which may be a correlate of subsequent evaluation of these stimuli. The e-P3a amplitude was significantly larger in mdaMCI than in sdaMCI participants, and the l-P3a amplitude was significantly larger in mdaMCI than in sdaMCI and Control participants, indicating greater involuntary capture of attention to unattended novel auditory stimuli and allocation of more attentional resources for the subsequent evaluation of these stimuli in mdaMCI participants. The e-P3a and l-P3a components showed moderate to high sensitivity and specificity for distinguishing between groups, suggesting that both may represent optimal neurocognitive markers for differentiating aMCI subtypes.

Uncensored EEG: The role of DC potentials in neurobiology of the brain

Brain direct current (DC) potentials denote sustained shifts and slow deflections of cerebral potentials superimposed with conventional electroencephalography (EEG) waves and reflect alterations in the excitation level of the cerebral cortex and subcortical structures. Using galvanometers, such sustained displacement of the EEG baseline was recorded in the early days of EEG recordings. To stabilize the EEG baseline and eliminate artefacts, EEG was performed later by voltage amplifiers with high-pass filters that dismiss slow DC potentials. This left slow DC potential recordings as a neglected diagnostic source in the routine clinical setting over the last few decades. Brain DC waves may arise from physiological processes or pathological phenomena. Recordings of DC potentials are fundamental electro-clinical signatures of some neurological and psychological disorders and may serve as diagnostic, prognostic, and treatment monitoring tools. We here review the utility of both physiological and pathological brain DC potentials in different aspects of neurological and psychological disorders. This may enhance our understanding of the role of brain DC potentials and improve our fundamental clinical and research strategies for brain disorders.

Enhanced Feedback-Related Negativity in Alzheimer's Disease

Alzheimer’s disease (AD), the most common cause of dementia in the elderly, results in the impairment of executive function, including that of performance monitoring. Feedback-related negativity (FRN) is an electrophysiological measure reflecting the activity of this monitoring system via feedback signals, and is generated from the anterior cingulate cortex. However, there have been no reports on FRN in AD. Based on prior aging studies, we hypothesized that FRN would decrease in AD patients. To assess this, FRN was measured in healthy individuals and those with AD during a simple gambling task involving positive and negative feedback stimuli. Contrary to our hypothesis, FRN amplitude increased in AD patients, compared with the healthy elderly. We speculate that this may reflect the existence of a compensatory mechanism against the decline in executive function. Also, there was a significant association between FRN amplitude and depression scores in AD, and the FRN amplitude tended to increase insomuch as the Self-rating Depression Scale (SDS) was higher. This result suggests the existence of a negative bias in the affective state in AD. Thus, the impaired functioning monitoring system in AD is a more complex phenomenon than we thought.

A clinical trial to validate event-related potential markers of Alzheimer's disease in outpatient settings

INTRODUCTION

We investigated whether event-related potentials (ERP) collected in outpatient settings and analyzed with standardized methods can provide a sensitive and reliable measure of the cognitive deficits associated with early Alzheimer's disease (AD).

METHODS

A total of 103 subjects with probable mild AD and 101 healthy controls were recruited at seven clinical study sites. Subjects were tested using an auditory oddball ERP paradigm.

RESULTS

Subjects with mild AD showed lower amplitude and increased latency for ERP features associated with attention, working memory, and executive function. These subjects also had decreased accuracy and longer reaction time in the target detection task associated with the ERP test.

DISCUSSION

Analysis of ERP data showed significant changes in subjects with mild AD that are consistent with the cognitive deficits found in this population. The use of an integrated hardware/software system for data acquisition and automated data analysis methods make administration of ERP tests practical in outpatient settings.

Distinctive Effect of Donepezil Treatment on P300 and N200 Subcomponents of Auditory Event-Related Evoked Potentials in Alzheimer Disease Patients

Background

Latency of P300 subcomponent of event-related potentials (ERPs) increases in Alzheimer disease (AD) patients, which correlate well with cognitive impairment. Cholinesterase inhibitors (ChEIs) reduce P300 latency in AD patients with parallel improvement in cognition. It is not known whether N200 response to ChEIs is similar to that of P300.

The aim of this study was to evaluate and compare characteristics of P300 and N200 in AD patients, treatment-naïve and on stable donepezil treatment, matched by age, education, sex, and cognitive function.

Material/Methods

We recruited 22 consecutive treatment-naïve AD patients (AD-N group), 22 AD patients treated with a stable donepezil dose of 10 mg/day for at least 3 months (AD-T group), and 50 healthy controls were recruited. Neuropsychological testing (MMSE, ADAS-Cog, and additional tests) and ERP recording was performed and analyzed.

Results

All groups did not differ according to age, duration of education, or sex (p>0.05). AD-N and AD-T groups did not differ according to cognitive function. The AD-T group had longer duration of disease than the AD-N group (p<0.001). The AD-T and AD-N groups did not differ in P300 latencies (p=0.49). N200 latency was longer in the AD-T group (p<0.001). The general linear model showed that significant predictors of P300 latency were age (p=0.019) and AD treatment status (p<0.001). Duration of AD was a significant predictor of N200 latency (p=0.004).

Conclusions

The response of N200 latency to donepezil treatment differs from the response of P300. P300 is a better marker of ChEI treatment-dependent cognitive functions. N200 is more dependent on the duration of AD.

Potential cognitive decline linked to angiotensin-converting enzyme gene but not hypertension: Evidence from cognitive event-related potentials

OBJECTIVES

The aims of the present study were to investigate the effect of hypertension and angiotensin-converting enzyme (ACE) genotypes on cognitive event-related potentials (ERPs), and whether the impact of ACE genotypes on P300 is related to the influence of hypertension.

METHODS

Using the Cognitive Abilities Screening Instrument (CASI), we recruited 97 mentally healthy middle-aged and older adults. Medical histories were collected, and blood pressure, ACE insertion/deletion polymorphisms and ERPs in an auditory oddball task were measured for all participants.

RESULTS

When the participants were stratified according to the presence or absence of hypertension, there were no differences in CASI score, percentage of ACE genotypes and ERPs. The subjects with the D/D homozygote displayed lower amplitude and longer latency of P300, although there were no differences in CASI score and the percentage of hypertension.

CONCLUSIONS

The subjects with the D/D genotype tended to have decreased amplitude and prolonged latency of P300 ERPs which reflected subtle cognitive impairment. There were no associations between hypertension, CASI score and P300 measurements.

SIGNIFICANCE

Using ERPs, potential cognitive decline was linked to ACE genotypes, independently of the effect of hypertension.

Parallel improvement of cognitive functions and P300 latency following donepezil treatment in patients with Alzheimer's disease: a case-control study

PURPOSE

To evaluate the effect of donepezil, one of the cholinesterase inhibitors, on P300 measurements in patients with Alzheimer's disease (AD) and investigate the relationship between the subfactors of cognitive performance and P300 components.

METHODS

One hundred outpatients with AD were evaluated for cognitive function (cognitive ability screening instrument) and event-related potentials before and after 22 to 23 weeks of treatment with donepezil (5 mg/day). Twenty age-matched normal control subjects were recruited.

RESULTS

The patients with AD showed prolonged P300 and N200 latency, no significant differences in N100 and P200 components, and poor performance in neuropsychological assessments compared with control subjects at baseline. After donepezil treatment, the patients with AD had reduction in P300 latency at Pz lead, which was associated with a parallel improvement in cognitive function in terms of remote memory, recent memory, visual instruction, and orientation. The pre-post treatment difference of P300 latency significantly correlated with the cognitive ability screening instrument score difference and recent memory score difference, respectively.

CONCLUSIONS

The patients with AD still had intact early sensory processing but impaired higher-level cognitive processes that could influence behavior deviation. The donepezil treatment, which enhances higher-level cognitive processing time, revealed that P300 latency decreases as cognitive capability increases, especially improved in recent memory.

Evaluation of P300 components for emotion-loaded visual event-related potential in elderly subjects, including those with dementia

AIM

In the present study, the P300 component of the emotion-loaded visual event-related potential in response to photographs of babies crying or smiling was measured to evaluate cognitive function in elderly subjects, including those with dementia.

METHODS

The subjects were 48 elderly people who consulted a memory disorder clinic. The visual event-related potential was measured using oddball tasks. Brain waves were recorded from four sites. We analyzed the P300 amplitude and latency. Subjects were divided into three groups (the dementia with Alzheimer's disease group [ADG]; the intermediate group [MG], and the healthy group [HG]) based on the Revised Hasegawa Dementia Scale, Mini-mental State Examination scores and the Clinical Dementia Rating.

RESULTS

For all subjects, there was a significant positive correlation between P300 latency and Z-score of voxel-based specific regional analysis for Alzheimer's disease for crying or smiling faces. There was a negative correlation between P300 amplitude and Z-score for the crying face. MG subjects were divided into two groups (high risk: HRMG, low risk: LRMG) based on Z-scores (HRMG ≥ 2.0). The P300 amplitude of ADG was significantly smaller than that of HG, and the P300 latency of ADG was significantly longer than those of other groups for crying or smiling faces. The P300 latency of HRMG was significantly longer than that of LRMG for the smiling face. Furthermore, the P300 latency for the crying face was significantly shorter than that for the smiling face in HG and ADG.

CONCLUSION

These findings suggest that analysis of P300 components of the emotion-loaded visual event-related potential may be a useful neuropsychological index for the diagnosis of Alzheimer's disease and high-risk subjects.

The clinical utility of the auditory P300 latency subcomponent event-related potential in preclinical diagnosis of patients with mild cognitive impairment and Alzheimer's disease

The present meta-analysis investigated the clinical utility of the auditory P300 latency event-related potential in differentiating patients with Alzheimer's disease (AD), patients with mild cognitive impairment (MCI), and unaffected controls. Effect size estimates were computed from mean P300 latency measurements at midline electrodes between patients and unaffected controls using the random effects restricted maximum likelihood model. The effects of clinical and ERP/EEG methological variables were assessed in a moderator analysis. P300 latency was found to be significantly prolonged in patients with AD (and MCI) compared to unaffected controls. Shortened P300 latencies were observed when comparing patients with MCI to patients with AD. Clinically relevant differences in P300 latency effect sizes were associated with mean age, interstimulus interval, stimulus difference, target frequency, reference electrode, and sampling rate. The meta-analytic findings provide robust statistical evidence for the use of the auditory P300 latency subcomponent as a biological marker of prodromal AD.

C145 as a short-latency electrophysiological index of cognitive compensation in Alzheimer's disease

Brain plasticity and cognitive compensation in the elderly are of increasing interest, and Alzheimer's disease (AD) offers an opportunity to elucidate how the brain may overcome damage. We provide neurophysiological evidence of a short-latency event-related potential (ERP) component (C145) linked to stimulus relevancy that may reflect cognitive compensation in early-stage AD. Thirty-six subjects with early-stage, mild AD and 36 like-aged normal elderly (controls) had their EEG recorded while performing our Number-Letter task, a cognitive/perceptual paradigm that manipulates stimulus relevancies. ERP components, including C145, were extracted from ERPs using principal components analysis. C145 amplitudes and spatial distributions were compared among controls, AD subjects with high performance on the Number-Letter task, and AD subjects with low performance. Compared to AD subjects, control subjects showed enhanced C145 processing of visual stimuli in the occipital region where differential processing of relevant stimuli occurred. AD high performers recruited central brain areas in processing task relevancy. Controls and AD low performers did not show a significant task relevancy effect in these areas. We conclude that short-latency ERP components can detect electrophysiological differences in early-stage AD that reflect altered cognition. Differences in C145 amplitudes between AD and normal elderly groups regarding brain locations and types of task effects suggest compensatory mechanisms can occur in the AD brain to overcome loss of normal functionality, and this early compensation may have a profound effect on the cognitive efficiency of AD individuals.

Vagus somatosensory evoked potentials--a possibility for diagnostic improvement in patients with mild cognitive impairment?

OBJECTIVE

Vagus somatosensory evoked potentials (VSEP) are far-field potentials probably generated in nuclei of then. vagus in the lower brainstem. They represent a putative, easily applicable method for discrimination between patients with Alzheimer's disease (AD), patients with mild cognitive impairment (MCI), and healthy controls (HC).

METHODS

Thirteen patients with AD, 12 with MCI, and 27 age- and gender-matched HC were investigated by stimulating the cutaneous branch of the n. vagus; 8, 6, and 20, respectively, were included in the main part of the analysis.

RESULTS

In fronto-central recordings (electrode positions Fz-F4) a grading from HC over MCI to AD could be found, with a significant linear trend over the three groups and significantly increased latencies of the cognitively impaired patients but no significant difference between MCI and AD.

CONCLUSION

The results indicate that the method of VSEP is able to discriminate between cognitively declined patients and HC, whereas no clear-cut differences were detected between MCI and AD.

P300 and neuropsychological assessment in mild cognitive impairment and Alzheimer dementia

Only a small proportion of individuals with Mild Cognitive Impairment (MCI) will convert to dementia. Methods currently available to identify risk for conversion do not combine enough sensitivity and specificity, which is even more problematic in low-educated populations. Current guidelines suggest the use of combined markers for dementia to enhance the prediction accuracy of assessment methods. The present study adhered to this proposal and investigated the sensitivity and specificity of the electrophysiological component P300 and standard neuropsychological tests to assess patients with Alzheimer's disease (AD) and MCI recruited from a low-income country. The neuropsychological battery comprised tests of memory, attention, language, praxis, and executive functions. The P300 was recorded using a classical visual odd-ball paradigm. Three variables were found to achieve sensitivity and specificity values above 80% (Immediate and Delayed recall of word list - CERAD - and the latency of P300) for both MCI and AD. When they entered the model together (i.e., combined approach) the sensitivity for MCI increased to 96% and the specificity remained high (80%). Our preliminary findings suggest that the combined use of sensitive neuropsychological tasks and the analysis of the P300 may offer a very useful method for the preclinical assessment of AD, particularly in populations with low socioeconomic and educational levels. Our results provide a platform and justification to employ more resources to convert P300 and related parameters into a biological marker for AD.

Brain event-related potentials associated with psychiatric symptoms in amphetamine-type stimulant dependent patients

OBJECTIVE

To explore the correlation between brain event-related potentials (ERPs) and psychiatric symptoms in patients with amphetamine-type stimulants (ATS) dependence.

METHOD

Using Galileo Sirius 32-channels digital-evoked potential system, we measured the auditory P300 ERP in 40 ATS dependence subjects and 30 normal controls, respectively. Symptom Checklist 90 (SCL-90) was used to rate the psychiatric symptoms in the subjects.

RESULTS

In ATS dependence subjects, the latency of N2, latency of P3, and inter-peak latency of P2-N2 were significantly longer than those in controls, respectively (P < 0.05). The amplitude of P300 in ATS dependence subjects was significantly lower than that in controls (P < 0.01). Besides, significantly lower amplitude of P3 and longer latency of P3 were found in ATS dependence subjects suffering from psychiatric symptoms than those without psychotic symptoms (P < 0.05). Furthermore, in ATS dependence subjects, the latency of N2 was negatively correlated with the scores of anxiety factor (r = -0.366) and paranoid ideation factor of SCL-90; the latency of P3 negatively correlated with the scores of psychoticism (r = -0.430) and somatization (r = -0.397) factor; also, the amplitude of P3 was negatively correlated with the score ofpsychoticism factor (r = -0.486).

CONCLUSIONS

These findings suggest cognitive dysfunction may be one of results of ATS dependence.

Cognitive event-related potentials: biomarkers of synaptic dysfunction across the stages of Alzheimer's disease

Cognitive event-related brain potential (ERP) studies of decision-making and attention, language, and memory impairments in Alzheimer's disease (AD) and mild cognitive impairment (MCI) are reviewed. Circumscribed lesions of the medial temporal lobe (MTL), as may be the case in individuals with amnestic MCI, generally produce altered plasticity of the late positive P600 component, with relative sparing of earlier sensory ERP components. However, as the neuropathology of AD extends to neocortical association areas, abnormalities of the P300 and N400 (and perhaps even P50) become more common. Critically, ERP studies of individuals at risk for AD may reveal neurophysiological changes prior to clinical deficits, which could advance the early detection and diagnosis of "presymptomatic AD".

The mismatch negativity (MMN)--a unique window to disturbed central auditory processing in ageing and different clinical conditions

In this article, we review clinical research using the mismatch negativity (MMN), a change-detection response of the brain elicited even in the absence of attention or behavioural task. In these studies, the MMN was usually elicited by employing occasional frequency, duration or speech-sound changes in repetitive background stimulation while the patient was reading or watching videos. It was found that in a large number of different neuropsychiatric, neurological and neurodevelopmental disorders, as well as in normal ageing, the MMN amplitude was attenuated and peak latency prolonged. Besides indexing decreased discrimination accuracy, these effects may also reflect, depending on the specific stimulus paradigm used, decreased sensory-memory duration, abnormal perception or attention control or, most importantly, cognitive decline. In fact, MMN deficiency appears to index cognitive decline irrespective of the specific symptomatologies and aetiologies of the different disorders involved.

Event-related potentials for the diagnosis of mild cognitive impairment and Alzheimer's disease

INTRODUCTION

Alzheimer's disease (AD) and the nosological entity of mild cognitive impairment (MCI) constitute a major public health concern. The diagnostic approach and therapeutic management of these disorders may be significantly improved by recent advances in the field of event-related potentials (ERPs).

AREAS COVERED

The authors performed a PubMed search in order to identify full-length, original research articles on the experimental and clinical application of ERPs in AD and MCI. The major part of the retrieved articles concerns the application of auditory and, to a lesser extent, visual ERPs for the early diagnosis of AD and MCI. Particular emphasis was placed on the role of ERPs in identifying the subgroup of MCI patients who will subsequently convert to AD. Other areas covered include the contribution of ERPs in the differential diagnosis of dementia types, the utility of ERPs for monitoring pharmacological treatment in AD and the correlation between ERPs and the results of neuropsychological testing.

EXPERT OPINION

The reviewed evidence suggests that ERPs hold promise as an electrophysiological tool for the early and accurate diagnosis of AD and MCI. However, certain methodological issues need to be resolved before ERPs enter the arena of clinical practice.

More potential in statistical analyses of event-related potentials: a mixed regression approach

Despite many developments in the methods of event-related potentials (ERPs), little attention has gone out to the statistical handling of ERP data. Trials are often averaged, and univariate or repeated measures of analysis of variance (ANOVA) are used to test hypotheses. The aim of this study was to introduce mixed regression to ERP research and to demonstrate advantages associated with this method. Eighty-five healthy subjects received electrical pain stimuli with simultaneous electroencephalography (EEG) registration. Analyses first showed that results obtained with mixed regression analyses are highly comparable to those using repeated measures of ANOVA. Second, important advantages of the mixed regression technique were demonstrated by allowing the inclusion of persons with missing data, single trial analysis, non-linear time effects, time×person effects (random slope effects) and a within-subject covariate. Among others, the results showed a strong trial (habituation) effect, which contraindicates the common procedure of averaging of trials. Furthermore, the regression coefficients for intensity and trial varied significantly between persons, indicating individual differences in the effect of intensity and trial on the ERP amplitude. In conclusion, using mixed regression analysis as a statistical technique in ERP research will advance the science of unravelling mechanisms underlying ERP data.

Event-related potential markers of brain changes in preclinical familial Alzheimer disease

OBJECTIVES

Event-related potentials (ERPs) can reflect differences in brain electrophysiology underlying cognitive functions in brain disorders such as dementia and mild cognitive impairment. To identify individuals at risk for Alzheimer disease (AD) we used high-density ERPs to examine brain physiology in young presymptomatic individuals (average age 34.2 years) who carry the E280A mutation in the presenilin-1 (PSEN1) gene and will go on to develop AD around the age of 45.

METHODS

Twenty-one subjects from a Colombian population with familial AD participated: 10 presymptomatic subjects positive for the PSEN1 mutation (carriers) and 11 siblings without the mutation (controls). Subjects performed a visual recognition memory test while 128-channel ERPs were recorded.

RESULTS

Despite identical behavioral performance, PSEN1 mutation carriers showed less positivity in frontal regions and more positivity in occipital regions, compared to controls. These differences were more pronounced during the 200-300 msec period. Discriminant analysis at this time interval showed promising sensitivity (72.7%) and specificity (81.8%) of the ERP measures to predict the presence of AD pathology.

CONCLUSIONS

Presymptomatic PSEN1 mutation carriers show changes in brain physiology that can be detected by high-density ERPs. The relative differences observed showing greater frontal positivity in controls and greater occipital positivity in carriers indicates that control subjects may use frontally mediated processes to distinguish between studied and unstudied visual items, whereas carriers appear to rely more upon perceptual details of the items to distinguish between them. These findings also demonstrate the potential usefulness of ERP brain correlates as preclinical markers of AD.

The role of event-related potentials in cognitive decline in Alzheimer's disease

OBJECTIVES

Early diagnosis and monitoring of disease progression have become vital in clinical practice as disease modifying treatments for Alzheimer's disease (AD) become available. This one-year prospective study aimed to clarify the usefulness of event-related potentials (ERPs) in cognitive decline and elucidate their cognitive significance in AD.

METHODS

Using the Cognitive Abilities Screening Instrument (CASI) and ERPs, probable AD patients, mild cognitive impairment (MCI) patients, and normal controls were recruited.

RESULTS

The AD and MCI patients had significantly decreased cognitive function and manifested a delay of P300 latency. The P300 latencies demonstrated significantly more prolongation than their baseline values in probable AD and MCI patients, although their CASI scores showed no statistically significant decline. Whereas N100, P200, and N200 components did not reach statistical differences between groups either in the baseline or follow-up assessments and did not show significant change on follow-up.

CONCLUSION

The combination of neuropsychological tests and P300 measurements proved useful in improving reliability and increasing sensitivity to early cognitive decline or disease progression in AD patients.

SIGNIFICANCE

The P300 latency may reflect cognitive decline more sensitively than neuropsychological tests in the longitudinal follow-up of AD patients.

The effect of aging on auditory components of event-related brain potentials

OBJECTIVE

To describe auditory perceptual, pre-attentive, attention-related and cognitive processes along lifespan in normal people by a simple auditory oddball paradigm easily usable in clinical practice.

METHODS

ERPs were recorded in 72 normal subjects. Four blocks of tones were delivered (20% rare 2,000 Hz and 80% frequent 1,000 Hz). In the former two blocks, subjects performed a concomitant distracting visual search task (distracted condition); in the latter two blocks, they had to attend the occurrence of the rare tones (active condition). Latency and amplitude of ERPs were analyzed according to age, gender, educational level and repetition.

RESULTS

N100 amplitude was greater in active than in distracted condition. MMN amplitude decreased with age. N2b and P300 latencies increased with age, while their amplitudes decreased. Females produced greater P300 than males. In the elderly, P300 latency was found to be longer in the second block than in the first one.

CONCLUSIONS

N100 and MMN were found to be less affected by age than N2b and P300. When repeated, P300 showed increased latency in elderly subjects.

SIGNIFICANCE

The protocol detected the higher influence of aging on late cognitive processes than on the perceptual and pre-attentive ones. Age-adjusted normative data were produced.

Clinical neurophysiology of aging brain: from normal aging to neurodegeneration

Physiological brain aging is characterized by a loss of synaptic contacts and neuronal apoptosis that provokes age-dependent decline of sensory processing, motor performance, and cognitive function. Neural redundancy and plastic remodelling of brain networking, also secondary to mental and physical training, promotes maintenance of brain activity in healthy elderly for everyday life and fully productive affective and intellectual capabilities. However, age is the main risk factor for neurodegenerative disorders such as Alzheimer's disease (AD) that impact on cognition. Oscillatory electromagnetic brain activity is a hallmark of neuronal network function in various brain regions. Modern neurophysiological techniques including electroencephalography (EEG), event-related potential (ERP), magnetoencephalography (MEG), and transcranial magnetic stimulation (TMS) can accurately index normal and abnormal brain aging to facilitate non-invasive analysis of cortico-cortical connectivity and neuronal synchronization of firing and coherence of rhythmic oscillations at various frequencies. The present review provides a perspective of these issues by assaying different neurophysiological methods and integrating the results with functional brain imaging findings. It is concluded that discrimination between physiological and pathological brain aging clearly emerges at the group level, with applications at the individual level also suggested. Integrated approaches utilizing neurophysiological techniques together with biological markers and structural and functional imaging are promising for large-scale, low-cost and non-invasive evaluation of at-risk populations. Practical implications of the methods are emphasized.

Reductions in levels of the Alzheimer's amyloid beta peptide after oral administration of ginsenosides

For millennia, ginseng and some of its components have been used to treat a wide variety of medical conditions, including age-related memory impairment. Because of its purported effects and apparently low rate of side effects, ginseng remains one of the top selling natural product remedies in the United States. Given its potential role for improving age-related memory impairments and its common use in China for the treatment of Alzheimer's disease-like symptoms, we analyzed the effects of commercially available preparations of ginseng on the accumulation of the Alzheimer's amyloid beta peptide (Abeta) in a cell-based model system. In this model system, ginseng treatment resulted in a significant reduction in the levels of Abeta in the conditioned medium. We next examined the effects of several compounds isolated from ginseng and found that certain ginsenosides lowered Abeta concentration in a dose-dependent manner with ginsenoside Rg3 having an approximate IC50 of under 25 microM against Abeta42. Furthermore, we found that three of these isolated components, ginsenoside Rg1, Rg3, and RE, resulted in significant reductions in the amount of Abeta detected in the brains of animals after single oral doses of these agents. The results indicate that ginseng itself, or purified ginsenosides, may have similarly useful effects in human disease.