Automatic and effortful processing in aging and dementia: event-related brain potentials

Accelerometer-based and self-reported physical activity and sedentary time and their relationships with the P300 in a Go/No-Go task in older adults

Older adults who experience cognitive decline are more likely to have a reduced quality of life. Identifying lifestyle factors that may influence cognitive processing and in turn improve quality of life during older adulthood is an important area of interest. Cognitive function, as measured by the P300 event-related potential (ERP), has been noted to be modified by physical activity; however, no study to date has examined relationships between this neurophysiological measure and physical activity and sedentary time in older adults. Furthermore, there is a gap in understanding as to whether physical activity and sedentary time assessed using self-reported and accelerometer-based methods similarly relate to the P300. This study aimed to assess the P300 during a Go/No-Go task in relation to self-reported and accelerometer-based physical activity and sedentary time in a community sample of 75 older adults. Results indicated that participants engaging in more moderate-to-vigorous physical activity had larger P300 amplitudes across self-reported and accelerometer-based measurements; however, no relationships between sedentary time and P300 amplitude were observed. Notably, accelerometer-based moderate-to-vigorous physical activity explained P300 amplitudes over and above self-reported moderate-to-vigorous physical activity-an effect that remained significant even after accounting for age. Although these results highlight the importance of moderate-to-vigorous physical activity in relation to cognitive function, as measured via the P300 in older adults, a secondary analysis indicated that engaging in lifestyle activity may have similar effects on the P300 as moderate-to-vigorous physical activity. In sum, the present study highlights the role of habitual engagement in physical activity as a possible means for supporting cognitive function during the aging process.

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.

Naturalistic Assessment using a Simulated Environment: Cognitive Correlates and Relationship to Functional Status in Individuals with Neurologic Conditions

Objective

Research has shown that neurologic conditions, such as traumatic brain injury and multiple sclerosis, result in a number of cognitive and functional deficits. However, little is known about the relationship between various cognitive domains and ability to perform everyday activities. The Community Shopping Task (CST), a naturalistic assessment task conducted in a simulated environment, was used to examine functional abilities and cognitive correlates of everyday functioning in individuals with neurologic conditions.

Method

Thirty-four participants with neurologic conditions and 34 healthy controls completed the CST as well as traditional paper-pencil measures of cognition. In addition, all participants completed a questionnaire assessing instrumental activities of daily living (IADLs).

Results

The results indicated that participants with neurologic conditions required significantly more cues and time to complete the CST compared to control participants and that immediate memory and executive functioning were important predictors of CST performance. Furthermore, time to complete the CST accounted for a significant amount of variance in IADL performance, over and beyond the traditional measures of cognition.

Conclusions

These results provide evidence that a naturalistic task completed in an everyday environment can enhance our understanding of how daily functioning is impacted in individuals with neurologic conditions and subsequently inform rehabilitation strategies.

P300 Amplitude in Alzheimer's Disease: A Meta-Analysis and Meta-Regression

Alzheimer's disease accounts for 60% of all dementia. Numerous biomarkers have been developed that can help in making an early diagnosis. The P300 is an event-related potential that may be abnormal in Alzheimer's disease. Given the possible association between P300 amplitude and Alzheimer's disease and the need for biomarkers in early Alzheimer's disease, the main purpose of this meta-analysis and meta-regression was to characterize P300 amplitude in probable Alzheimer's disease compared to healthy controls. Using online search engines, we identified peer-reviewed articles containing amplitude measures for the P300 in response to a visual or auditory oddball stimulus in subjects with Alzheimer's disease and in a healthy control group and pooled effect sizes for differences in P300 amplitude between Alzheimer's disease and control groups to obtain summary effect sizes. We also used meta-regression to determine whether age, sex, educational attainment, or dementia severity affected the association between P300 amplitude and Alzheimer's disease. Twenty articles containing a total of 646 subjects met inclusion and exclusion criteria. The overall effect size from all electrode locations was 1.079 (95% confidence interval=0.745-1.412, P<.001). The pooled effect sizes for the Cz, Fz, and Pz locations were 1.226 (P<.001), 0.724 (P=.0007), and 1.430 (P<.001), respectively. Meta-regression showed an association between amplitude and educational attainment, but no association between amplitude and age, sex, and dementia severity. In conclusion, P300 amplitude is smaller in subjects with Alzheimer's disease than in healthy controls.

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.

Auditory post-processing in a passive listening task is deficient in Alzheimer's disease

OBJECTIVE

To investigate whether automatic auditory post-processing is deficient in patients with Alzheimer's disease and is related to sensory gating.

METHODS

Event-related potentials were recorded during a passive listening task to examine the automatic transient storage of auditory information (short click pairs). Patients with Alzheimer's disease were compared to a healthy age-matched control group. A young healthy control group was included to assess effects of physiological aging.

RESULTS

A bilateral frontal negativity in combination with deep temporal positivity occurring 500 ms after stimulus offset was reduced in patients with Alzheimer's disease, but was unaffected by physiological aging. Its amplitude correlated with short-term memory capacity, but was independent of sensory gating in healthy elderly controls. Source analysis revealed a dipole pair in the anterior temporal lobes.

CONCLUSION

Results suggest that auditory post-processing is deficient in Alzheimer's disease, but is not typically related to sensory gating. The deficit could neither be explained by physiological aging nor by problems in earlier stages of auditory perception. Correlations with short-term memory capacity and executive control tasks suggested an association with memory encoding and/or overall cognitive control deficits.

SIGNIFICANCE

An auditory late negative wave could represent a marker of auditory working memory encoding deficits in Alzheimer's disease.

Cognitive function, physical activity, and aging: possible biological links and implications for multimodal interventions

Increasing evidence shows the positive effect of physical activity (PA) on maintaining cognitive function. Both processes seem intrinsically linked to each other. The most likely mechanism is a reciprocal stimulation of neuroplasticity. Based on extensive experimental work on animals and humans, the concept of an enriched environment, including PA and challenging cognitive tasks, has provided the basis to systematically assess possible interventions for successful aging. I will use recent findings on brain mechanisms associated with PA and its effects on higher cognitive function at a systems and molecular level to demonstrate the need to design effective interventions. Such interventions should be designed to take advantage of the presumed compensatory mechanisms of elderly individuals, thereby limiting functional decline in higher cognitive performance in aging people. My review of the most recent relevant publications concerning this topic supports the notion that it is a promising approach to provide cognitive training and PA in conjunction, since the combination may generate synergistic beneficial changes than either one individually. Multimodal training programs should therefore be tested. However, at present there is insufficient evidence to conclude that multimodal interventions are superior to isolated cognitive or physical exercise interventions, since major studies addressing this topic are lacking. These studies are needed to conclusively prove that both strategies will positively interact when used in combined interventions. Finally the use of modern technology for these interventions will be discussed.

Evaluation of event-related potentials in Klinefelter syndrome and idiopathic hypogonadotrophic hypogonadism

BACKGROUND

Many studies have evaluated patients with idiopathic hypogonadothropic hypogonadotropism (IHH), but few of these studies utilize event-related potentials (P300).

AIMS

To assess the cognitive functions of hypergonadotropic vs. hypogonadotropic patients.

SETTINGS AND DESIGN

The study group consisted of 41 untreated IHH patients, 32 untreated Klinefelter syndrome (KS) patients, and 30 healthy control subjects.

METHODS AND MATERIAL

In this study, the latency and amplitude of P300 was evaluated in 41 untreated IHH and 32 untreated KS patients and compared to healthy control subjects (average age: 30 years). Also evaluated were the patients' hormone levels.

RESULTS AND CONCLUSIONS

In this study, the amplitude of P300 was found to be reduced, and the latency prolonged in IHH patients in comparison to KS patients and control subjects. In KS patients, there was no difference in latency of P300, but the amplitude was reduced when compared with the control group. Cognitive dysfunction in patients with hypogonadotropism is related to androgen hormone levels. This deficiency can affect development of the central nervous system (CNS), causing defects of CNS to varying degrees during the perinatal period. Androgen deficiency is considered to exert its effects during the period of cognitive ability development, manifest in IHH patients but not KS patients.

Brain event-related potentials: diagnosing early-stage Alzheimer's disease

A pattern of components from brain event-related potentials (ERPs) (cognitive non-invasive electrical brain measures) performed well in separating early-stage Alzheimer's disease (AD) subjects from normal-aging control subjects and shows promise for developing a clinical diagnostic for probable AD. A Number-Letter task elicited brain activity related to cognitive processes. In response to the task stimuli, brain activity was recorded as ERPs, whose components were measured by principal components analysis (PCA). The ERP component scores to relevant and irrelevant stimuli were used in discriminant analyses to develop functions that successfully classified individuals as belonging to an early-stage Alzheimer's disease group or a like-aged Control group, with probabilities of an individual belonging to each group. Applying the discriminant function to the developmental half of the data showed 92% of the subjects were correctly classified into either the AD group or the Control group with a sensitivity of 1.00. The two crossvalidation results were good with sensitivities of 0.83 and classification accuracies of 0.75-0.79. P3 and CNV components, as well as other, earlier ERP components, e.g. C145 and the memory "Storage" component, were useful in the discriminant functions.

Age-related change in neural processing of time-dependent stimulus features

Aging is associated with changes in automatic processing of task-irrelevant stimuli, and this may lead to functional disturbances including repeated orienting to nonnovel events and distraction from task. The effect of age on automatic processing of time-dependent stimulus features was investigated by measurement of the auditory mismatch negativity (MMN) in younger (18-23) and older (55-85) adults. Amplitude of MMN recorded during a paradigm involving low-probability deviation in interstimulus interval (from 500 ms to 250 ms) was found to be reduced in the older group at fronto-central sites. This effect was paralleled by, and correlated to, decreased sensory gating efficiency for component N1 recorded during a separate paradigm involving alternate presentation of auditory stimuli at long (9 s) and short (0.5 s) interstimulus intervals. Further, MMN amplitude was correlated to behavioral performance on a small subset of neuropsychological tests, including the Rey Auditory Verbal Learning Test, within a group of healthy older adults. The results support the hypothesis that aging is associated with declines in automatic processing of time-dependent stimulus features, and this is related to cognitive function. These conclusions are considered in the context of age-related declines in prefrontal cortex function and associated increases in susceptibility to task-irrelevant stimuli.

Clinical applications of cognitive event-related potentials in Alzheimer's disease

This article has reviewed several abnormalities in the cognitive ERPs of AD patients. These abnormalities are prominent from latencies of approximately 200 msec and later. In contrast, sensory-dependent evoked potentials, such as N100, are generally normal in AD. This finding is as one familiar with the neuropathology of AD would predict. Predilection sites in early AD include the medial temporal lobe, other limbic areas, and multimodal association cortices with sparing of primary sensory areas. Unimodal association cortex is involved in AD, but not as heavily as multimodal cortex. Particular advantages of studying a given ERP paradigm or component depend largely on the specific application or hypothesis being tested. A P300 paradigm can be useful in detecting a disorder of attention or in quantifying the effects of drugs that improve attention, such as the cholinesterase inhibitors. For the early diagnosis of AD or other memory disorders, a word-repetition paradigm with an explicit recognition task or one that fosters associative learning would be recommended. This article has discussed potential use of N400 in tracking disease progression. ERPs provide a flexible and powerful technique, with superb temporal resolution, which can be used as a probe into subtle "subclinical" abnormalities of cognitive processes. Despite being applied to AD for about 25 years since the early P300 studies, the full potential of ERPs in helping diagnose and treat AD patients has yet to be realized. In this era of rapidly evolving brain-imaging techniques, electrophysiologic data are important in advancing understanding of cognition. Brain-mapping techniques that can inform where and when key cognitive processes occur are finally emerging. A final example of potential clinical application of cognitive ERPs is in the development of rational combinational treatment of cognitive enhancing drugs. Along these lines, P300 investigations in epilepsy proved helpful in ranking the cognitive side effects of anticonvulsant drugs. Drug studies that use 2 x 2 combinational designs, which compare the effects of drug A, drug B, with A + B, are currently prohibitively expensive for full-scale clinical trials in AD. It is likely that precise ERP measures could hasten drug development in several ways. Smaller samples could be used, at lower cost, to test the cognitive effects of each specific drug combination. Optimal doses of combinational therapy perhaps could be identified by repeated within-subject ERP measures. Longitudinal changes in the ERP hold promise as a marker of individual responsivity to a particular agent, which could have diagnostic utility (eg, testing response to cholinergic or dopaminergic therapy). This horizon and many others remain wide open for well-planned explorations.

Principles and clinical applications of auditory evoked potentials in the geriatric population

Age-related changes in auditory evoked potentials are complex and complicated by the confounding effects of gender; concomitant high-frequency hearing sensitivity loss; and, in the case of event-related responses, the nature of the task used to elicit the response. There is a tendency for amplitude to decline and latency to increase, but these trends are not always clear-cut. There is also a tendency for activation patterns to move forward from parietal to frontal areas as age increases. The dichotic listening tool has revealed age-related changes in interaural and interhemispheric asymmetries. These asymmetries seem to be related to loss in the efficiency of interhemispheric transfer via the corpus callosum.

Aging: A Switch From Automatic to Controlled Processing of Sounds?

In this article, the authors show that aging differentially affects peoples' ability to automatically and voluntarily process auditory information. Young, middle-aged, and older adults matched behaviorally in an auditory discrimination task showed similar patterns of neural activity indexing the voluntary and conscious detection of deviant (i.e., target) stimuli. In contrast, a negative wave indexing automatic processing (the mismatch negativity) was elicited only in young adults for near-threshold stimuli. These results indicate that aging affects the ability to automatically register small changes in a stream of homogeneous stimuli. However, this age-related decline in automatic detection of small change in the auditor environment can be compensated for by top-down controlled processes.

Effects of hormone replacement therapy on perceptual and cognitive event-related potentials in menopausal insomnia

The influence of a combined estrogen-progestin regimen (Climodien, Lafamme) on auditory event-related potentials (ERPs) was investigated in a double-blind, placebo-controlled, comparative, randomized 3-arm trial phase (Climodien 2/3=estradiol valerate 2 mg+the progestin dienogest 3 mg, EV=estradiol valerate 2 mg, and placebo), followed by an open-label phase in which all patients received Climodien 2/2 (estradiol valerate 2 mg+dienogest 2 mg). Both the double-blind and the open-label phase lasted 2 months. ERPs were recorded from 19 EEG leads in a two-tone odd-ball paradigm in 49 patients aged between 46 and 67 yr with the diagnosis of insomnia (G 47.0) related to postmenopausal syndrome (N 95.1). Climodien reduced standard N1 and target P300 latencies as compared to placebo, while EV did not affect N1 latency but similarly reduced P300 latency. Climodien increased N1, P2 and P300 amplitudes dose-dependently, predominantly at frontal leads. Estrogen alone had only minor effects on ERP amplitudes. The shortening of standard N1 latency and enhancement of N1 and P2 amplitudes indicates a positive effect of Climodien on perceptual processing, most likely due to vigilance improvements also observed in EEG mapping. Concerning target P300, it seems that estradiol is responsible for the improvement in stimulus evaluation time, as reflected by the shortening of the peak latency, while dienogest seems to account for the improvement in cognitive information processing capacity, whereby 3 mg induced a more pronounced augmentation of P300 amplitudes than 2 mg. Based on the spatial distribution of this increase, it can be speculated that Climodien mainly affects the more frontally distributed P3a subcomponent, which is associated with attention and orientation. Furthermore, the observed changes in ERP-components are consistent with recent studies showing significant positive effects of hormone replacement therapy on cholinergic functions. Thus, Climodien seems to be of interest in preventing cognitive decline and treating cognitive disorders in postmenopausal women. Indeed, there is increasing evidence of beneficial effects of estrogen in dementia. Our present findings suggest that the estrogen effects may be augmented by dienogest.

The relationship of age to prepulse inhibition and habituation of the acoustic startle response

Prepulse inhibition (PPI) of the startle response reflects an early stage of information processing that is abnormal in schizophrenia and certain other specific neuropsychiatric disorders that are distinguished by the inability to inhibit redundant or relatively irrelevant sensory, cognitive, or motor information. The goal of the present study was to characterize the effect of normal aging on PPI and habituation of the startle response and to examine the hypothesis that normal aging is characterized by a global decline in inhibitory function. Ninety-seven non-psychiatric controls (age range 18-88) were tested for startle eyeblink response using electromyogram (EMG) recording. Startle magnitude decreased and startle latency increased with aging. PPI demonstrated an inverted U-shaped function with age (greatest PPI at intermediate ages) while there was no significant effect of age on startle habituation. The results do not support the theory that aging is associated with a general decline in inhibitory function and contrast with previous studies that have compared only extreme age groups and have found no effects of age on PPI.

Identification of diagnostic evoked response potential segments in Alzheimer's disease

Evoked response potentials (ERPs) to brief flashes of light were analyzed for constituent features that could be used to distinguish individuals with Alzheimer's disease (AD, n = 15) from matched control subjects (n = 17). Statistical k nearest-neighbor methods distinguished AD from control with a maximum sensitivity of 29% and false alarm rate of 12%. The comparable sensitivity/false-alarm values for a statistical projection pursuit method and an extended projection pursuit method, which selectively identify discriminative features for classification, were 75%/18% and 100%/6%, respectively. The results demonstrate that combinations of selected ERP time segments across different electrodes contain signal features that discriminate AD from control subjects with high sensitivity and specificity.

Electrophysiological analysis of cognitive slowing in subjects with mitochondrial encephalomyopathy

Mitochondrial encephalomyopathies (MEs) are multisystemic inherited disorders affecting tissues with high energy requirement such as the muscle, retina and central nervous system. Progressive external ophthalmoplegia and myopathy are the most common features in adults, and cognitive impairment is rare. In many neurodegenerative disorders, ERPs have been effectively performed to record cognitive slowing on tasks with different amount of information. To analyze the evidence for possible cognitive slowing, a standard auditory oddball paradigm with a button-press response was applied. Participants were 11 non-demented patients affected by mitochondrial encephalomyopathy and 14 age-matched normal controls. This hypothesis was tested using two tasks of different difficulty (pure tone vs. phonetic stimuli). Reaction time (RT), performance (P) and event-related potentials (ERPs) were measured. RT and P were not significantly different between the groups. Patients showed significantly increased N2 latency and reduced P3 amplitude on both tasks. No difference was found in pure tone and phonetic task conditions. Results were interpreted as electrophysiological signs of cognitive slowing--particularly in relation to stimulus evaluation--irrespective of sensory problems, response selection and cognitive load. These findings suggest that in ME patients, there may be a possible dysfunction of neural mechanisms underlying cognitive events and ERP generation.

Visual event-related potential in mild dementia of the Alzheimer's type

Visual event-related potentials (ERP) and behavioral measures were recorded during a geometrical-figure discrimination task to examine sensory processing in 10 patients with mild dementia of the Alzheimer's type (DAT) and 10 age-matched controls. No difference existed between the groups in P1, N1, and P2 potentials, which reflects the early stage of sensory processing, as well as in NA potential, which reflects pattern recognition. The patients showed reduced amplitude of P3 potential, retarded reaction time, and increased behavioral errors compared to controls. These findings suggest that the patients with mild DAT were intact in early sensory processing including pattern recognition but were selectively compromised in higher-level processing, including integration of information and memory matching, which may influence behavioral deviation.

N1 and P300 abnormalities in patients with schizophrenia, epilepsy, and epilepsy with schizophrenialike features

BACKGROUND

The scalp-recorded N1 and P300 components of the event-related brain potential (ERP) are commonly reduced in patients with schizophrenia but not in patients with epilepsy. Epilepsy patients with interictal chronic schizophrenialike features (EPI-SZ) provide a comparison group for determining whether the ERP amplitude abnormalities seen in schizophrenic patients are associated with shared clinical features of EPI-SZ and schizophrenic patients or overlapping pathophysiologies, or are specific to a distinct schizophrenia etiology.

METHODS

Patients with schizophrenia (n = 24) were compared with normal control subjects (n = 32) and patients with epilepsy syndromes on visual and auditory oddball ERP paradigms. Epilepsy patients included those with chronic interictal schizophrenialike features (n = 6) and those without (n = 16).

RESULTS

Auditory P300 amplitude was reduced in both schizophrenic and EPI-SZ patients, whose positive or negative symptoms did not differ. In contrast, N1 amplitude was reduced only in schizophrenic patients. Delays in both N1 and P300 were associated with epilepsy patients and EPI-SZ but not schizophrenic patients.

CONCLUSIONS

The schizophrenialike symptoms in epilepsy probably represent a phenocopy of schizophrenia with common clinical features and some common pathophysiologies but distinct etiologies. P300 amplitude appears to be sensitive to schizophrenialike features, regardless of whether they occur in the context of schizophrenia or epilepsy. N1 amplitude reduction appears to be specific to schizophrenia, suggesting its sensitivity to the distinct etiology of schizophrenia.

The auditory event-related potential is a stable and reliable measure in elderly subjects over a 3 year period

OBJECTIVES

Valid markers of psychobiological processes, including changes over the lifespan, must be reliable. This study investigated the reliability of the auditory event-related potential (ERP) over a 3 year period.

METHODS

Predictable and unpredictable rare tones were embedded in common-to-rare sequences at 3 different ratios (2:3, 2:5 and 2:8). Forty-six older (mean age 72.3 years) volunteers pressed a key to the rare tones, and ERPs (Fz, Cz and Pz) and reaction time (RT) were measured. Reliability across years was assessed using 3 methods: (1) determination of the stability of waveform components (P1, N1, P2, N2 and P3); (2) cross-correlation of successive 15 ms epochs of within-subject ERPs; and (3) cross-correlation of 15 ms epochs of between-subject ERPs.

RESULTS

With all analyses, the ERP was stable. Analysis of the scored components indicated that P3 was especially stable in the unpredictable rare (2:8) condition. Earlier components were equally stable across all conditions. Analysis of 15 ms ERP epochs indicated significant ERP stability 60 ms after stimulation, lasting over 640 ms.

CONCLUSIONS

Robust within-subject reliability of the ERP strengthens its potential use for detecting preclinical changes in at-risk elderly populations.

Comparison of endogenous event-related potentials in attend and non-attend conditions: latency changes with normal aging

OBJECTIVE

Endogenous event-related potential (ERP) components have been observed under both attend and non-attend conditions, but it appears that at least some of the attend and non-attend components are functionally and topographically distinct. Also, under active task conditions, motivational and attentional variations may modulate the amplitude of the ERP. These various effects of attention on the ERP can complicate comparisons of the ERPs of normal subjects with the ERPs of clinical subjects, who may have reduced attentional capabilities. The experiment reported here sought to develop a non-task paradigm that reliably produces the same ERP components typically seen under task conditions.

METHODS

Using rare auditory stimuli that were discrepant from the frequent stimuli both in frequency and intensity, stimuli were presented under non-attend instructions and under instruction to count the rare stimuli. The ERPs in these two conditions were compared with ERPs in a standard oddball paradigm which used stimulus parameters comparable to those of most previous experiments on ERPs in aging. Fifty subjects, ranging in age from 20 to 77, participated.

RESULTS

The ERPs to the DISCREPANT oddball stimuli under non-task conditions were similar in scalp distribution to the ERPs to the same stimuli in the ATTEND condition and to the ERPs in the STANDARD/ATTEND condition. Furthermore, there were no significant differences in the age-related increase in ERP latencies among the DISCREPANT/IGNORE, the DISCREPANT/ATTEND, and the STANDARD/ATTEND conditions.

CONCLUSION

The results indicate that increases in ERP latencies with aging can be assessed in the absence of task requirements, and that the paradigm described here may prove useful in investigating cognitive processing speed in clinical populations.