Neuropsychological correlates of the P300 in patients with Alzheimer's disease

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.

TBX21, the Master regulator of the type 1 immune response, overexpresses in the leukocytes of peripheral blood in patients with late-onset Alzheimer's disease

BACKGROUND

The involvement of the peripheral immune system in the etiology of neurodegenerative diseases has recently been emphasized. Genome-wide association studies (GWAS) have recently identified several candidate immune genes linked to development of both Alzheimer's disease (AD) and depression. TBX21 (T-bet) which drives the Th1 immune response, is linked to the major depressive disorder (MDD) phenotype. This study investigated the association between the TBX21 immune gene and the possibility of late-onset Alzheimer's disease (LOAD) incidence in 194 LOAD and 200 control subjects using the real-time qPCR and the Tetra-ARMS-PCR methods. We also used an in silico approach to analyze the potential effects imparted by TBX21 rs17244587 and rs41515744 polymorphisms in LOAD pathogenesis.

RESULTS

We found that the TBX21 "immune gene" had significantly elevated mRNA expression levels in the leukocytes of peripheral blood in patients with LOAD (P < 0.0001). We also found an upward trend in TBX21 expression with increasing age in LOAD patients compared to the control group (P < 0.05; CI = 95%). We noticed that the TT genotype of rs41515744 plays a protective role in LOAD incidence, as it attenuates the expression of TBX21 in the control group. We observed that the dominant model of rs41515744 represented a substantial association with LOAD (P = 0.019).

CONCLUSIONS

Our results show for the first time the likely impact of the TBX21 (T-bet) immune gene in LOAD development and that the elevated TBX21 mRNAs in the WBCs of LOAD patients may represent a new easy diagnostic test for Alzheimer's disease.

Effect of aerobic exercise training on EEG: event-related potential and neuropsychological functions in depressed elderly with mild cognitive impairment

Increased depressive severity has been linked to neurocognitive impairment. Aerobic exercise (AE) is an efficient technique for improving cognitive function. However, studies indicating the importance of AE to neurophysiological and neuropsychological functions in the depressed elderly using event-related potentials (ERPs) are scarce.

Objectives

This study aimed to identify the potential benefits of AE on neurophysiological and neuropsychological functions.

Methods

A total of 30 depressed older adults (AE group: n=15; control group (CG): n=14) were recruited based on the inclusion and exclusion criteria. The AE group was subjected to an 8-week-period AE program (3 times/week for 30 min per session) at moderate intensity, determined using heart rate maximum (HRmax). The training intensity was set at 50% HRmax and increased by 5% in subsequent weeks. Pre- and post-training measures for neurophysiological function were tested using ERP-P300 (amplitude-μV and latency-ms) and also for neuropsychological functions using the trail making test (TMT), mini mental status examination (MMSE), and everyday cognition questionnaire (ECog).

Results

In the experimental group, statistically significant improvements were observed when analyzed for all 3 (group-by-time interaction effect, main effect of time, and main effect of group), in both neurophysiological functions (*p<0.001) and neuropsychological functions (*p<0.001), except for ECog scores, where the results were insignificant for the main effect of a group. Correlation analysis demonstrated no association between neurophysiological and neuropsychological functions (*p>0.05).

Conclusion

Findings showed that 8 weeks of AE training may be a promising approach to improve cognitive functions in depressed older adults. However, considering relatively small number of patients, the question arises for effectiveness in other populations.

Effect of repetitive transcranial magnetic stimulation combined with transcranial direct current stimulation on post-stroke dysmnesia: A preliminary study

OBJECTIVE

This study examined the effect of repetitive transcranial magnetic stimulation (rTMS) combined with transcranial direct current stimulation (tDCS) as a bimodal neuromodulatory approach for post-stroke dysmnesia.

METHODS

Thirty-four patients with post-stroke dysmnesia were randomly allocated into a sham group treated with neither rTMS nor tDCS, a group treated with rTMS, and a group treated with a combination of rTMS and tDCS. All three groups received cognitive rehabilitation training for 4 weeks. The memory function of each group before and after the intervention was assessed using the Montreal Cognitive Assessment (MoCA) and Rivermead Behavioral Memory Test (RBMT) scales, as well as in terms of the Mismatch Negativity（MMN）and P300 of event-related potentials.

RESULTS

The sham, rTMS, and rTMS-tDCS groups all showed improvement in the total MoCA score after the intervention. Delayed recall, a MoCA item, scored better in the rTMS-tDCS group than in the rTMS and sham groups. Delayed processing, an RBMT item, scored better in the rTMS-tDCS combination group than in the rTMS and sham groups. MMN and P300 latency was significantly shorter in the rTMS-tDCS combination group.

CONCLUSION

rTMS-tDCS bimodal stimulation was more effective than cognitive rehabilitation or rTMS alone in treating patients with post-stroke dysmnesia, offering new possibilities for enhancing cognitive function and treating post-stroke dysmnesia.

Neuropsychological correlates of P300 parameters in individuals with aphasia

BACKGROUND

Aphasia is often accompanied by impairment of non-language cognitive functions. Assessment of cognitive capacity in people with aphasia (PWA) with standard neuropsychological methods may be problematic due to their language difficulties. Numerous experimental studies indicate that P300 may be considered as an index of cognitive capacity in both healthy and clinical samples. Accordingly, the measurement of event-related potentials enables the investigation of behaviourally non-observable mental processes underlying the cognitive functions that are assessed with neuropsychological tests.

AIMS

To investigate in PWA the relationship between P300 parameters and cognitive function efficiency measured with neuropsychological methods.

METHODS & PROCEDURES

A total of 25 PWA after left-hemispheric stroke participated in the study. Electrophysiological (EEG) signals were recorded during the performance of a visual Go-No Go task. P300 was identified on nine electrodes, which were then pooled in three lines: left (F3, C3, P3), central (Fz, Cz, Pz) and right (F4, C4, P4). The neuropsychological assessment of cognitive functions included mental speed, short-term memory, divided attention, executive functions, auditory language comprehension and expression.

OUTCOMES & RESULTS

P300 latency correlated with indices of several cognitive functions: temporal resolution, psychomotor speed, spatial short-term memory, planning, word and sentence comprehension, as well as verbal fluency. Shorter P300 latencies were accompanied by greater efficiency of the abovementioned functions. In contrast, significant correlations between P300 amplitudes and cognitive measures were fragmentary.

CONCLUSIONS & IMPLICATIONS

In PWA, P300 latency might be related to cognitive functioning, especially to measures that rely heavily on the speed of information processing. However, P300 seems to be unrelated to more complex cognitive functions. P300 latency may be used as a neurophysiological correlate of cognitive efficiency in PWA and might have potential applications in monitoring the effects of therapeutic interventions in this patient group.

WHAT THIS PAPER ADDS

What is already known on the subject P300 parameters have been reported to be associated with cognitive performance in both healthy individuals and clinical groups (e.g., patients with Alzheimer's disease). Previous studies show that the presence of P300 at the early post-stroke stage may be a predictor of better recovery of comprehension in PWA. What this paper adds to existing knowledge Our results show for the first time that P300 may be used as a neurophysiological correlate of cognitive efficiency in PWA. In our study, P300 latency was associated with several languages and non-language cognitive functions, especially with those whose effectiveness depends mainly on processing speed. In PWA, shorter latency corresponded to more efficient cognitive functioning. What are the potential or actual clinical implications of this work? P300 measurement may be potentially useful in assessing the efficiency of certain cognitive functions in PWA. It may be also used to monitor the recovery process of PWA and to verify the effects of therapeutic interventions.

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.

Developments in scalable strategies for detecting early markers of cognitive decline

Effective strategies for early detection of cognitive decline, if deployed on a large scale, would have individual and societal benefits. However, current detection methods are invasive or time-consuming and therefore not suitable for longitudinal monitoring of asymptomatic individuals. For example, biological markers of neuropathology associated with cognitive decline are typically collected via cerebral spinal fluid, cognitive functioning is evaluated from face-to-face assessments by experts and brain measures are obtained using expensive, non-portable equipment. Here, we describe scalable, repeatable, relatively non-invasive and comparatively inexpensive strategies for detecting the earliest markers of cognitive decline. These approaches are characterized by simple data collection protocols conducted in locations outside the laboratory: measurements are collected passively, by the participants themselves or by non-experts. The analysis of these data is, in contrast, often performed in a centralized location using sophisticated techniques. Recent developments allow neuropathology associated with potential cognitive decline to be accurately detected from peripheral blood samples. Advances in smartphone technology facilitate unobtrusive passive measurements of speech, fine motor movement and gait, that can be used to predict cognitive decline. Specific cognitive processes can be assayed using 'gamified' versions of standard laboratory cognitive tasks, which keep users engaged across multiple test sessions. High quality brain data can be regularly obtained, collected at-home by users themselves, using portable electroencephalography. Although these methods have great potential for addressing an important health challenge, there are barriers to be overcome. Technical obstacles include the need for standardization and interoperability across hardware and software. Societal challenges involve ensuring equity in access to new technologies, the cost of implementation and of any follow-up care, plus ethical issues.

Predictive Power of Cognitive Biomarkers in Neurodegenerative Disease Drug Development: Utility of the P300 Event-Related Potential

Neurodegenerative diseases, such as Alzheimer's disease (AD), and their associated deterioration of cognitive function are common causes of disability. The slowly developing pathology of neurodegenerative diseases necessitates early diagnosis and monitored long-term treatment. Lack of effective therapies coupled with an improved rate of early diagnosis in our aging population have created an urgent need for the development of novel drugs, as well as the need for reliable biomarkers for treatment response. These issues are especially relevant for AD, in which the rate of clinical trial drug failures has been very high. Frequently used biomarker evaluation procedures, such as positron emission tomography or cerebrospinal fluid measurements of phospho-tau and amyloid beta, are invasive and costly, and not universally available or accessible. This review considers the functionality of the event-related potential (ERP) P300 methodology as a surrogate biomarker for predicting the procognitive potential of drugs in clinical development for neurocognitive disorders. Through the application of standardized electroencephalography (EEG) described here, ERP P300 can be reliably measured. The P300 waveform objectively measures large-scale neuronal network functioning and working memory processes. Increased ERP P300 latency has been reported throughout the literature in disorders of cognition, supporting the potential utility of ERP P300 as a biomarker in many neurological and neuropsychiatric disorders, including AD. Specifically, evidence presented here supports ERP P300 latency as a quantitative, unbiased measure for detecting changes in cognition in patients with AD dementia through the progression from mild to moderate cognitive impairment and after drug treatment.

Event-related potential and neuropsychological function in depressed older adults with cognitive impairment: A correlational study

Background

Increased depression severity has been linked to cognitive functioning impairment, such as deficits in episodic memory and executive function, causing difficulties in planning strategies, which ultimately lead to impaired decision-making functions. There are number of ways to assess cognitive functions, two most important and routinely done tests are neuropsychological test battery (NBT) and event-related potentials (ERPs).

Objective

This study examines the relationship between conventional neuropsychological tests assessing various cognitive domains and an ERP-P300 in depressed older adults.

Methods

Forty-six depressed elderly subjects participated in the study. NBT (Pennsylvania's Penn Computerized Neurocognitive Battery [Penn CNP]) assessing attention, episodic memory, working memory, social cognition, complex cognition, and sensorimotor speed and ERP-P300 (amplitude μV and latency ms) was recorded using an auditory oddball paradigm.

Results

Correlation test was run and Pearson's analysis and revealed that there was a negative statistically significant linear correlation between working memory on NBT and P300 wave amplitude on ERP-P300 (r = -0.34, P = 0.021) and between complex cognition on NBT and P300 wave latency on ERP-P300 (r = -0.47, P < 0.001). No correlation was found between other tests on NBT and ERP-P300 wave characteristics. Further, the regression analysis (R ²) revealed that P300 amplitude was found to significantly predict the working memory (R ² = 0.116) and P300 latency was found to significantly predict the complex cognition (R ² = 0.224).

Conclusion

Therefore, we conclude that neurophysiological measurements cannot be substituted by neuropsychological tests or vice versa; rather, higher brain functions should be estimated by both of the methods.

A double-blind randomized controlled trial combining cognitive training (CoRe) and neurostimulation (tDCS) in the early stages of cognitive impairment

BACKGROUND

The prevalence of neurodegenerative diseases is expected to increase over the next years, therefore, new methods able to prevent and delay cognitive decline are needed.

AIMS

To evaluate the effectiveness of a combined treatment protocol associating a computerized cognitive training (CoRe) with anodal transcranial direct current stimulation (tDCS).

METHODS

In this randomized controlled trial, 33 patients in the early stage of cognitive impairment were assigned to the experimental group (CoRE + real tDCS) or control group (CoRE + sham tDCS). In each group, the intervention lasted 3 consecutive weeks (4 sessions/week). A neuropsychological assessment was administered at baseline (T0), post-intervention (T1) and 6-months later (T2).

RESULTS

The CoRE + real tDCS group only improved in working memory and attention/processing speed at both T1 and T2. It reported a stable MMSE score at T2, while the CoRE + sham tDCS group worsened. Age, mood, and T0 MMSE score resulted to play a role in predicting treatment effects.

CONCLUSION

Combined multi-domain interventions may contribute to preventing or delaying disease progression.

TRIAL REGISTRATION

Trial registration number (ClinicalTrials.gov): NCT04118686.

Predicting Dementia With Prefrontal Electroencephalography and Event-Related Potential

Objective: To examine whether prefrontal electroencephalography (EEG) can be used for screening dementia.

Methods: We estimated the global cognitive decline using the results of Mini-Mental Status Examination (MMSE), measurements of brain activity from resting-state EEG, responses elicited by auditory stimulation [sensory event-related potential (ERP)], and selective attention tasks (selective-attention ERP) from 122 elderly participants (dementia, 35; control, 87). We investigated that the association between MMSE and each EEG/ERP variable by using Pearson’s correlation coefficient and performing univariate linear regression analysis. Kernel density estimation was used to examine the distribution of each EEG/ERP variable in the dementia and non-dementia groups. Both Univariate and multiple logistic regression analyses with the estimated odds ratios were conducted to assess the associations between the EEG/ERP variables and dementia prevalence. To develop the predictive models, five-fold cross-validation was applied to multiple classification algorithms.

Results: Most prefrontal EEG/ERP variables, previously known to be associated with cognitive decline, show correlations with the MMSE score (strongest correlation has |r| = 0.68). Although variables such as the frontal asymmetry of the resting-state EEG are not well correlated with the MMSE score, they indicate risk factors for dementia. The selective-attention ERP and resting-state EEG variables outperform the MMSE scores in dementia prediction (areas under the receiver operating characteristic curve of 0.891, 0.824, and 0.803, respectively). In addition, combining EEG/ERP variables and MMSE scores improves the model predictive performance, whereas adding demographic risk factors do not improve the prediction accuracy.

Conclusion: Prefrontal EEG markers outperform MMSE scores in predicting dementia, and additional prediction accuracy is expected when combining them with MMSE scores.

Significance: Prefrontal EEG is effective for screening dementia when used independently or in combination with MMSE.

Cognitive and neuroimaging markers for preclinical vascular cognitive impairment

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Explores the cognitive correlates of midlife risk factors of pre-clinical vascular cognitive impairment.

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Midlife cardiovascular risks associated with reduces neural integrity in parietal to anterior structures and may identify at-risk individuals.

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Novel experimental investigation testing fronto-parietal structures is required to increase specificity and sensitivity to pre-clinical VCI and inform clinical testing and diagnostic pathways of at-risk individuals.

Detection of incipient cognitive impairment and dementia pathophysiology is critical to identify preclinical populations and target potentially disease modifying interventions towards them. There are currently concerted efforts for such detection for Alzheimer's disease (AD). By contrast, the examination of cognitive markers and their relationship to biomarkers for Vascular Cognitive Impairment (VCI) is far less established, despite VCI being highly prevalent and often concomitantly presenting with AD. Critically, vascular risk factors are currently associated with the most viable treatment options via pharmacological and non-pharmacological intervention, hence early identification of vascular factors have important implications for modifying dementia disease trajectories. The aim of this review is to examine the current evidence of cognitive marker correlates to VCI pathology. We begin by examining midlife risk factors that predict VCI. Next, discuss preclinical cognitive hallmarks of VCI informed by insights from neuropsychological assessment, network connectivity and ERP/EEG experimental findings. Finally, we discuss limitations of current cognitive assessments and the need for future cognitive test development to inform diagnostic assessment. As well as, intervention outcome measures for preclinical VCI. In turn, these tests will inform earlier detection of vascular changes and allow implementation of disease intervention approaches.

Investigating Auditory Electrophysiological Measures of Participants with Mild Cognitive Impairment and Alzheimer's Disease: A Systematic Review and Meta-Analysis of Event-Related Potential Studies

BACKGROUND

Objectively measuring auditory functions has been proposed as an avenue in differentiating normal age-related cognitive dysfunction from Alzheimer's disease (AD) and its prodromal states. Previous research has suggested auditory event-related potentials (AERPs) to be non-invasive, cost-effective, and efficient biomarkers for the diagnosis of AD.

OBJECTIVE

The objective of this paper is to review the published literature on AERPs measures in older adults diagnosed with AD and those at higher risk of developing AD, i.e., mild cognitive impairment (MCI) and subjective cognitive decline.

METHODS

The search was performed on six major electronic databases (Ovid MEDLINE, OVID EMBASE, PsycINFO, PubMed, Scopus, and CINAHL Plus). Articles identified prior to 7 May 2019 were considered for this review. A random effects meta-analysis and analysis of between study heterogeneity was conducted using the Comprehensive Meta-Analysis software.

RESULTS

The search identified 1,076 articles; 74 articles met the full inclusion criteria and were included in the systematic review, and 47 articles were included into the analyses. Pooled analysis suggests that AD participants can be differentiated from controls due to significant delays in ABR, N100, P200, N200, and P300 latencies. P300 amplitude was significantly smaller in AD participants compared to controls. P300 latencies differed significantly between MCI participants and controls based on the pooled analysis.

CONCLUSION

The findings of this review indicate that some AERPs may be valuable biomarkers of AD. In conjunction with currently available clinical and neuropsychological assessments, AERPs can aid in screening and diagnosis of prodromal AD.

Psychometric Properties of NASA-TLX and Index of Cognitive Activity as Measures of Cognitive Workload in Older Adults

Cognitive workload is increasingly recognized as an important determinant of performance in cognitive tests and daily life activities. Cognitive workload is a measure of physical and mental effort allocation to a task, which can be determined through self-report or physiological measures. However, the reliability and validity of these measures have not been established in older adults with a wide range of cognitive ability. The aim of this study was to establish the test-retest reliability of the National Aeronautics and Space Administration Task Load Index (NASA-TLX) and Index of Cognitive Activity (ICA), extracted from pupillary size. The convergent validity of these measures against event-related potentials (ERPs) was also investigated. A total of 38 individuals with scores on the Montreal Cognitive Assessment ranging between 17 and 30 completed a working memory test (n-back) with three levels of difficulty at baseline and at a two-week follow-up. The intraclass correlation coefficients (ICC) values of the NASA-TLX ranged between 0.71 and 0.81, demonstrating good to excellent reliability. The mean ICA scores showed fair to good reliability, with ICCs ranging between 0.56 and 0.73. The mean ICA and NASA-TLX scores showed significant and moderate correlations (Pearson's r ranging between 0.30 and 0.33) with the third positive peak of the ERP at the midline channels. We conclude that ICA and NASA-TLX are reliable measures of cognitive workload in older adults. Further research is needed in dissecting the subjective and objective constructs of cognitive workload.

Reliability of P3 Event-Related Potential During Working Memory Across the Spectrum of Cognitive Aging

Event-related potentials (ERPs) offer unparalleled temporal resolution in tracing distinct electrophysiological processes related to normal and pathological cognitive aging. The stability of ERPs in older individuals with a vast range of cognitive ability has not been established. In this test-retest reliability study, 39 older individuals (age 74.10 (5.4) years; 23 (59%) women; 15 non β-amyloid elevated, 16 β-amyloid elevated, 8 cognitively impaired) with scores on the Montreal Cognitive Assessment (MOCA) ranging between 3 and 30 completed a working memory (n-back) test with three levels of difficulty at baseline and 2-week follow-up. The main aim was to evaluate stability of the ERP on grand averaged task effects for both visits in the total sample (n = 39). Secondary aims were to evaluate the effect of age, group (non β-amyloid elevated; β-amyloid elevated, cognitively impaired), cognitive status (MOCA), and task difficulty on ERP reliability. P3 peak amplitude and latency were measured in predetermined channels. P3 peak amplitude at Fz, our main outcome variable, showed excellent reliability in 0-back (intraclass correlation coefficient (ICC), 95% confidence interval = 0.82 (0.67-0.90) and 1-back (ICC = 0.87 (0.76-0.93), however, only fair reliability in 2-back (ICC = 0.53 (0.09-0.75). Reliability of P3 peak latencies was substantially lower, with ICCs ranging between 0.17 for 2-back and 0.54 for 0-back. Generalized linear mixed models showed no confounding effect of age, group, or task difficulty on stability of P3 amplitude and latency of Fz. By contrast, MOCA scores tended to negatively correlate with P3 amplitude of Fz (p = 0.07). We conclude that P3 peak amplitude, and to lesser extent P3 peak latency, provide a stable measure of electrophysiological processes in older individuals.

Cognitive Impairment, P300, and Transforming Growth Factor β1 in Different Forms of Dementia

BACKGROUND

There are currently few biomarkers to assist in early diagnosis of dementias.

OBJECTIVE

To distinguish between different dementias: Alzheimer's disease (AD), vascular dementia (VaD), and Parkinson's disease dementia (PDD) using simple neurophysiologic (P300) and laboratory markers (transforming growth factor β1 "TGF-β1").

METHODS

The study included 15 patients for each type of dementia and 25 age- and sex-matched control subjects. Dementia patients were diagnosed according to the Diagnostic and Statistical Manual of Mental Disorders 4th edition-revised (DSM-IV-R). Modified Mini-Mental State Examination (3MS), Memory Assessment Scale (MAS), P300, and TGF-β1 were examined for each participant.

RESULTS

There were no significant differences between groups as regard to age, sex, and education, social, and economic levels. Significant differences between groups were observed in registration and naming variables of the 3MS. Compared with the control group, P300 latency was prolonged in all groups, although to a greater extent in AD and PDD than in VaD. A serum level of TGF-β1 was significantly elevated in all groups but was significantly higher in AD and VaD than in PDD. 3MS tended to correlate with P300 more than TGF-β1, and to be stronger in AD than the other groups.

CONCLUSION

Measurements of P300 latency and serum levels of TGF-β1 can help distinguish AD, PDD, and VaD. P300 was more prolonged in AD and PDD than VaD whereas TGF-β1 was significantly higher in AD and VaD than PDD. Thus P300 and TGF-β1 may be useful biomarkers for detection and evaluation of the extent of cognitive dysfunction.

Transcranial Alternating Current Stimulation (tACS) as a Tool to Modulate P300 Amplitude in Attention Deficit Hyperactivity Disorder (ADHD): Preliminary Findings

Studies examining event-related potentials (ERP) in patients affected by attention deficit/hyperactivity disorder (ADHD) have found considerable evidence of reduced target P300 amplitude across different perceptual modalities. P300 amplitude has been related to attention-driven context comparison and resource allocation processes. Altered P300 amplitude in ADHD can be reasonably assumed to be related to ADHD typical cognitive performance deficits. Transcranial alternating current stimulation (tACS) can increase the amplitude of endogenous brain oscillations. Because ERP components can be viewed as event-related oscillations (EROs), with P300 translating into the delta (0–4 Hz) and theta (4–8 Hz) frequency range, an increase of delta and theta ERO amplitudes by tACS should result in an increase of P300 amplitudes in ADHD patients. In this pilot study, 18 adult ADHD patients (7 female) performed three consecutive blocks of a visual oddball task while the electroencephalogram (EEG) was recorded. Patients received either 20 min of tACS or sham stimulation at a stimulation intensity of 1 mA. Individual stimulation frequency was determined using a time–frequency decomposition of the P300. Our preliminary results demonstrate a significant increase in P300 amplitude in the stimulation group which was accompanied by a decrease in omission errors pre-to-post tACS. However, studies including larger sample sizes are advised.

Associations of event-related brain potentials and Alzheimer's disease severity: A longitudinal study

BACKGROUND

So far, no cost-efficient, widely-used biomarkers have been established to facilitate the objectivization of Alzheimer's disease (AD) diagnosis and monitoring. Research suggests that event-related potentials (ERPs) reflect neurodegenerative processes in AD and might qualify as neurophysiological AD markers.

OBJECTIVES

First, to examine which ERP component correlates the most with AD severity, as measured by the Mini-Mental State Examination (MMSE). Then, to analyze the temporal change of this component as AD progresses.

METHODS

Sixty-three subjects (31 with possible, 32 with probable AD diagnosis) were recruited as part of the cohort study Prospective Dementia Registry Austria (PRODEM). For a maximum of 18 months patients revisited every 6 months for follow-up assessments. ERPs were elicited using an auditory oddball paradigm. P300 and N200 latency was determined with regard to target as well as difference wave ERPs, whereas P50 amplitude was measured from standard stimuli waveforms.

RESULTS

P300 latency exhibited the strongest association with AD severity (e.g., r = -0.512, p < 0.01 at Pz for target stimuli in probable AD subjects). Further, there were significant Pearson correlations for N200 latency (e.g., r = -0.407, p = 0.026 at Cz for difference waves in probable AD subjects). P50 amplitude, as measured by different detection methods and at various scalp sites, did not significantly correlate with disease severity - neither in probable AD, possible AD, nor in both subgroups of patients combined. ERP markers for the group of possible AD patients did not show any significant correlations with MMSE scores. Post-hoc pairwise comparisons between baseline and 18-months follow-up assessment revealed significant P300 latency differences (e.g., p < 0.001 at Cz for difference waves in probable AD subjects). However, there were no significant correlations between the change rates of P300 latency and MMSE score.

CONCLUSIONS

P300 and N200 latency significantly correlated with disease severity in probable AD, whereas P50 amplitude did not. P300 latency, which showed the highest correlation coefficients with MMSE, significantly increased over the course of the 18 months study period in probable AD patients. The magnitude of the observed prolongation is in line with other longitudinal AD studies and substantially higher than in normal ageing, as reported in previous trials (no healthy controls were included in our study).

Neurophysiological markers of network dysfunction in neurodegenerative diseases

There is strong clinical, imaging and pathological evidence that neurodegeneration is associated with altered brain connectivity. While functional imaging (fMRI) can detect resting and activated states of metabolic activity, its use is limited by poor temporal resolution, cost and confounding vascular parameters. By contrast, electrophysiological (e.g. EEG/MEG) recordings provide direct measures of neural activity with excellent temporal resolution, and source localization methodologies can address problems of spatial resolution, permitting measurement of functional activity of brain networks with a spatial resolution similar to that of fMRI. This opens an exciting therapeutic approach focussed on pharmacological and physiological modulation of brain network activity. This review describes current neurophysiological approaches towards evaluating cortical network dysfunction in common neurodegenerative disorders. It explores how modern neurophysiologic tools can provide markers for diagnosis, prognosis, subcategorization and clinical trial outcome measures, and how modulation of brain networks can contribute to new therapeutic approaches.

On the use of the P300 as a tool for cognitive processing assessment in healthy aging: A review

Changes in patterns of performance for the cognitive functions of memory, processing speed, and focused attention are expected in old age.

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.

Cortical function in Alzheimer's disease and frontotemporal dementia

Objectives

Alzheimer’s disease (AD) and the behavioral variant of frontotemporal dementia (bvFTD) are the most common causes of dementia; however, their overlapping clinical syndromes and involved brain regions make a differential diagnosis difficult. We aimed to identify the differences in the cognition and motor cortex excitability between AD and bvFTD patients.

Methods

Twenty-seven AD patients and 30 bvFTD patients were included in the study. Each participant received a neurological evaluation. Cognitive event-related potentials (P300) were recorded during an auditory oddball task. Next, the excitability of the motor cortex, including the resting, facilitated motor threshold (RMT and FMT) and cortical silent period (CSP), were assessed during transcranial magnetic stimulation (TMS).

Results

The bvFTD patients exhibited significantly longer P300 latencies compared with AD patients. There was a significant negative correlation between cognition and P300 latency in the bvFTD group. The AD patients showed significantly reduced RMT and FMT values compared to the bvFTD group; however, no significant correlation was found between AD severity and the excitability of the motor cortex.

Conclusions

Cognition and motor cortical functions are different between AD and bvFTD patients. Noninvasive electrophysiological examinations have the potential to identify unique pathophysiological features that can be used to differentially diagnose AD and bvFTD patients.

Event-related Potential Patterns Reflect Reversed Hemispheric Activity during Visual Attention Processing in Children with Dyslexia: A Preliminary Study

Objective

Individuals with dyslexia experience reading difficulties, whereas their other cognitive abilities seem normal. The purpose of this study was to investigate the event-related potential (ERP) patterns of children with dyslexia during a target-detection task.

Methods

Seventeen children with dyslexia and 18 children without this disorder participated in this study. We evaluated their writing and reading ability, symptoms of attention-deficit/hyperactivity disorder, and intelligence quotient. ERPs were recorded while participants performed a target-detection task, and the peak amplitude and latency of P100 and P300 were analyzed. The lateral asymmetry index (LAI) was calculated for each ERP component.

Results

The dyslexic group exhibited longer reaction times and larger P100 amplitudes than the non-dyslexic group in the right hemisphere. The P100 latency was also significantly delayed in the right hemisphere of those in the dyslexic group compared with those in the non-dyslexic group. The P300 amplitude was larger in the right hemisphere compared with left hemisphere in the dyslexic group, whereas no interhemispheric differences were observed with respect to the P300 latency. The LAI for P100 showed a significant right hemispheric dominance, whereas the LAI for P100 was significantly correlated with the accuracy of target detection in children with dyslexia.

Conclusion

Our results suggest that right hemispheric dominance acts as an ancillary system that compensates for poor reading in children with dyslexia.

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.

A double-blind randomized clinical trial on the efficacy of cortical direct current stimulation for the treatment of Alzheimer's disease

Background: The purpose of this study was to investigate the long-term efficacy of transcranial direct current stimulation (tDCS) in the neurorehabilitation of Alzheimer’s disease (AD).

Methods: Thirty-four AD patients were randomly assigned to three groups: anodal, cathodal, and sham tDCS. Stimulation was applied over the left dorsolateral prefrontal cortex for 25 min at 2 mA, daily for 10 days. Each patient was submitted to the following psychometric assessments: mini-mental state examination (MMSE) and Wechsler adult intelligence scale-third edition at base line, at the end of the 10th sessions and then at 1 and 2 months after the end of the sessions. Motor cortical excitability and the P300 event-related potential were assessed at baseline and after the last tDCS session.

Results: Significant treatment group × time interactions were observed for the MMSE and performance IQ of the WAIS. Post hoc comparisons showed that both anodal and cathodal tDCS (ctDCS) improved MMSE in contrast to sham tDCS. Whereas, this was only true for ctDCS in the performance IQ. Remarkably, tDCS also reduced the P300 latency, but had no effect on motor cortex excitability.

Conclusion: Our findings reveal that repeated sessions of tDCS could not only improve cognitive function but also reduce the P300 latency, which is known to be pathologically increased in AD.

Menopause Analytical Hormonal Correlate Outcome Study (MAHCOS) and the association to brain electrophysiology (P300) in a clinical setting

Various studies have demonstrated that increased leptin levels and obesity are inversely related to cognitive decline in menopausal women. It is hypothesized that adiposity is inversely correlated with cognitive decline, as women with increased weight are less vulnerable to diminishing cognition. However, it is increasingly observed that menopausal women, even with increased adiposity, experience significant cognitive decline. Positron emission tomography (PET) has been used to analyze cognitive function and processing in menopausal women. Evoked potentials (P300) and neurophysiologic tests have validated brain metabolism in cognitively impaired patients. Post-hoc analyses of 796 female patients entering PATH Medical Clinic, between January 4, 2009 and February 24, 2013, were performed as part of the "Menopause Analytical Hormonal Correlate Outcome Study" (MAHCOS). Patient age range was 39-76 years (46.7 ± 0.2). P300 latency and amplitude correlated with a number of hormones: follicle stimulating hormone (FSH), luteinizing hormone (LH), estradiol, estrone, estriol, DHEA, pregnenolone, progesterone, free and total testosterone, thyroid stimulating hormone (TSH), Vitamins D 1.25 and D 25OH, leptin, and insulin-like growth factor-binding protein 3 (IGF-BP3). Corrected statistics did not reveal significant associations with P300 latency or amplitude for these hormones except for leptin plasma levels. However, factor analysis showed that FSH and LH clustered together with Vitamin D1.25 and Vitamin D25OH, P300 latency (not amplitude), and log leptin were found to be associated in the same cluster. Utilizing regression analysis, once age adjusted, leptin was the only significant predictor for latency or speed (p = 0.03) with an effect size of 0.23. Higher plasma leptin levels were associated with abnormal P300 speed (OR = 0.98). Our findings show a significant relationship of higher plasma leptin levels, potentially due to leptin resistance, and prolonged P300 latency. This suggests leptin resistance may delay electrophysiological processing of memory and attention, which appears to be the first of such an association.

Identification of BDNF sensitive electrophysiological markers of synaptic activity and their structural correlates in healthy subjects using a genetic approach utilizing the functional BDNF Val66Met polymorphism

Increasing evidence suggests that synaptic dysfunction is a core pathophysiological hallmark of neurodegenerative disorders. Brain-derived neurotropic factor (BDNF) is key synaptogenic molecule and targeting synaptic repair through modulation of BDNF signalling has been suggested as a potential drug discovery strategy. The development of such "synaptogenic" therapies depend on the availability of BDNF sensitive markers of synaptic function that could be utilized as biomarkers for examining target engagement or drug efficacy in humans. Here we have utilized the BDNF Val66Met genetic polymorphism to examine the effect of the polymorphism and genetic load (i.e. Met allele load) on electrophysiological (EEG) markers of synaptic activity and their structural (MRI) correlates. Sixty healthy adults were prospectively recruited into the three genetic groups (Val/Val, Val/Met, Met/Met). Subjects also underwent fMRI, tDCS/TMS, and cognitive assessments as part of a larger study. Overall, some of the EEG markers of synaptic activity and brain structure measured with MRI were the most sensitive markers of the polymorphism. Met carriers showed decreased oscillatory activity and synchrony in the neural network subserving error-processing, as measured during a flanker task (ERN); and showed increased slow-wave activity during resting. There was no evidence for a Met load effect on the EEG measures and the polymorphism had no effects on MMN and P300. Met carriers also showed reduced grey matter volume in the anterior cingulate and in the (left) prefrontal cortex. Furthermore, anterior cingulate grey matter volume, and oscillatory EEG power during the flanker task predicted subsequent behavioural adaptation, indicating a BDNF dependent link between brain structure, function and behaviour associated with error processing and monitoring. These findings suggest that EEG markers such as ERN and resting EEG could be used as BDNF sensitive functional markers in early clinical development to examine target engagement or drug related efficacy of synaptic repair therapies in humans.

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.