Somatosensory event-related potentials (ERPs) in patients with different types of dementia

EEG measures for clinical research in major vascular cognitive impairment: recommendations by an expert panel

Vascular contribution to cognitive impairment (VCI) and dementia is related to etiologies that may affect the neurophysiological mechanisms regulating brain arousal and generating electroencephalographic (EEG) activity. A multidisciplinary expert panel reviewed the clinical literature and reached consensus about the EEG measures consistently found as abnormal in VCI patients with dementia. As compared to cognitively unimpaired individuals, those VCI patients showed (1) smaller amplitude of resting state alpha (8-12 Hz) rhythms dominant in posterior regions; (2) widespread increases in amplitude of delta (< 4 Hz) and theta (4-8 Hz) rhythms; and (3) delayed N200/P300 peak latencies in averaged event-related potentials, especially during the detection of auditory rare target stimuli requiring participants' responses in "oddball" paradigms. The expert panel formulated the following recommendations: (1) the above EEG measures are not specific for VCI and should not be used for its diagnosis; (2) they may be considered as "neural synchronization" biomarkers to enlighten the relationships between features of the VCI-related cerebrovascular lesions and abnormalities in neurophysiological brain mechanisms; and (3) they may be tested in future clinical trials as prognostic biomarkers and endpoints of interventions aimed at normalizing background brain excitability and vigilance in wakefulness.

Acute Effects of Aerobic Exercise on Somatosensory-Evoked Potentials in Patients with Mild Cognitive Impairment

Mild cognitive impairment (MCI) is becoming a serious problem for developing countries as the lifespan of populations increases. Exercise is known to be clinically beneficial for MCI patients. Somatosensory-evoked potentials (SEPs) may be a potential diagnostic and prognostic marker for this population. The objective of this study was to determine the acute effects of aerobic exercise on SEPs in patients with MCI, to test whether SEPs are sensitive enough to detect improvements in early somatosensory processing. The study had a randomized parallel-group design and included 28 MCI subjects (14 in the experimental group and 14 in the control group). The experimental intervention was 20 min of aerobic exercise using a stationary bicycle. The control intervention involved 20 min of movements and stretches. Subjects were assessed before and after a single intervention session. SEPs were recorded by stimulating the median nerve of the dominant hand. Analysis of normalized SEP peak amplitudes showed that a single session of aerobic activity significantly reduced the N30 peak at the F3 channel (p = 0.03). There were no significant effects of aerobic exercise on SEP peak latencies. The results indicate that 20 min of aerobic exercise has a significant effect on the N30 SEP peak amplitude in MCI patients. The results suggest that aerobic exercise is likely to provide sensory-enriching inputs that enhance sensorimotor integration. Future studies should assess the effects of aerobic exercise on somatosensory processing in progressive stages of Alzheimer’s disease, longer exercise durations, and multiple exercise sessions.

Relationship between somatosensory event-related potential N140 aberrations and hemispatial agnosia in patients with stroke: a preliminary study

PURPOSE

The somatosensory event-related potential N140 is thought to be related to selective attention. This study aimed to compare the somatosensory event-related potential N140 in healthy subjects to that in patients with stroke to determine whether N140 and attentiveness are associated in patients with stroke with or without hemispatial agnosia.

MATERIALS AND METHODS

Normal somatosensory event-related potential N140 values were determined using data from ten healthy subjects. Fifteen patients with stroke were divided into two groups based on the presence of hemispatial neglect. Somatosensory event-related potential N140 components were compared between the two groups.

RESULTS

Stimulation of the affected limb in the hemispatial agnosia group resulted in significantly longer N140 latency at the contralateral vs. the ipsilateral electrode. This was the inverse of the relationship observed in normal subjects, with stimulation of the intact side in patients with hemispatial agnosia, and with stimulation of both the intact and affected sides in patients without agnosia. In the hemispatial agnosia group, the peak latency of N140 following stimulation of the affected side was significantly longer than it was following stimulation of the intact side and when compared to that in patients without agnosia. In addition, abnormal N140 peak latencies were observed at the Cz and ipsilateral electrodes in patients with hemispatial agnosia following stimulation of the intact side.

CONCLUSIONS

These findings suggest that somatosensory event-related potential N140 is independently generated in each hemisphere and may reflect cognitive attention.

Biomarkers for dementia and mild cognitive impairment in Parkinson's disease

Cognitive decline is one of the most frequent and disabling nonmotor features of Parkinson's disease. Around 30% of patients with Parkinson's disease experience mild cognitive impairment, a well-established risk factor for the development of dementia. However, mild cognitive impairment in patients with Parkinson's disease is a heterogeneous entity that involves different types and extents of cognitive deficits. Because it is not currently known which type of mild cognitive impairment confers a higher risk of progression to dementia, it would be useful to define biomarkers that could identify these patients to better study disease progression and possible interventions. In this sense, the identification among patients with Parkinson's disease and mild cognitive impairment of biomarkers associated with dementia would allow the early detection of this process. This review summarizes studies from the past 25 years that have assessed the potential biomarkers of dementia and mild cognitive impairment in Parkinson's disease patients. Despite the potential importance, no biomarker has as yet been validated. However, features such as low levels of epidermal and insulin-like growth factors or uric acid in plasma/serum and of Aß in CSF, reduction of cerebral cholinergic innervation and metabolism measured by PET mainly in posterior areas, and hippocampal atrophy in MRI might be indicative of distinct deficits with a distinct risk of dementia in subgroups of patients. Longitudinal studies combining the existing techniques and new approaches are needed to identify patients at higher risk of dementia. © 2016 International Parkinson and Movement Disorder Society.

Contact Heat Evoked Potentials (CHEPs) in Patients with Mild-Moderate Alzheimer's Disease and Matched Control--A Pilot Study

OBJECTIVE

Clinical studies have found that patients with Alzheimer's disease report pain of less intensity and with a lower affective response, which has been thought to be due to altered pain processing. The authors wished to examine the cerebral processing of non-painful and painful stimuli using somatosensory evoked potentials and contact heat evoked potentials in patients with Alzheimer's disease and in healthy elderly controls.

DESIGN

Case-control study

SETTING AND SUBJECTS

Twenty outpatients with mild-moderate Alzheimer's disease and in 17 age- and gender-matched healthy controls were included

METHOD

Contact heat evoked potentials and somatosensory evoked potentials were recorded in all subjects. Furthermore, warmth detection threshold and heat pain threshold were assessed. Patients and controls also rated quality and intensity of the stimuli.

RESULTS

The authors found no difference on contact heat evoked potential amplitude (P = 0.59) or latency of N2 or P2 wave (P = 0.62 and P = 0.75, respectively) between patients and controls. In addition, there was no difference in regard to pain intensity scores or pain quality. The patients and controls had similar warmth detection threshold and heat pain threshold. Somatosensory evoked potentials, amplitude, and latency were within normal range and similar for the two groups.

CONCLUSIONS

The findings suggest that the processing of non-painful and painful stimuli is preserved in patients with mild to moderate Alzheimer's disease.

The role of P300 event-related potentials in the cognitive recovery after the stroke

The aim of this study was to elucidate the effects of an ischemic stroke on the amplitude and latency of the P300 wave and evaluate their changes over a prospective 1-year follow-up period. We recorded the P300 wave using an auditory oddball paradigm in 60 consecutive brain infarct patients at baseline (i.e., within 4 weeks after the stroke), after 3 months, after 12 months and in 30 healthy control subjects. The P300 latencies in stroke patients were significantly longer and the P300 amplitudes were significantly smaller than those of the control group. The latency of P300 showed a highly significant average improvement 12 months after the stroke compared to the baseline. There was no significant change observed for the P300 amplitude during the same period. The P3 latency is initially more increased in the patients with hemispheric brain infarction but shows a better recovery compared to the patients with brainstem infarction. Also, the results of the P300 latency of patients with the left-sided lesions was significantly longer compared to the patients with right-sided lesions on the beginning of the study but not 3 and 12 months after the stroke. The results of our study show the importance of P300 event-related potentials in the detection and follow-up of cognitive changes after ischemic stroke.

Endogenous event-related potentials in patients with primary Sjögren's syndrome without central nervous system involvement

OBJECTIVES

Endogenous cognitive event-related potentials (CERPs) reflect higher-level processing of sensory information and can be used to evaluate cognitive functions. The aim of this paper was to determine whether there are any abnormalities in the electrophysiological parameters of CERPs in patients with primary Sjögren's syndrome (pSS) but without symptoms of central nervous system (CNS) involvement or mental disorder. The analysis of CERP parameters was then correlated with the clinical status of the patients and with some of the immunological parameters in the patient group.

METHOD

Thirty consecutive patients with pSS (29 females, one male) were included in the study. All the patients underwent CERP examination.

RESULTS

There was a significant prolongation of the latency of P300 and N200 potentials in patients with pSS. Abnormalities in electrophysiological parameters of CERPs correlated with the duration of the disease, salivary gland abnormalities, and elevated erythrocyte sedimentation rate (ESR) values. Patients with coexisting chronic fatigue syndrome (CFS) had larger P300 amplitudes. There were no statistically significant changes in the electrophysiological parameters of CERPs in patients with pSS dependent on the presence of peripheral nervous system (PNS) lesions, skin changes, arthritis, abnormalities in white blood cells and the immune system or the levels of blood lipids.

CONCLUSIONS

The results of the study suggest the presence of a minor cognitive dysfunction in patients with pSS without symptoms of CNS involvement or mental disorder. Cognitive dysfunction correlated with the disease duration time and the severity of inflammatory changes (salivary gland abnormalities and inflammatory markers in the blood). Further and larger longitudinal studies are necessary for confirmation of this correlation.

Parkinson's disease dementia and potential therapeutic strategies

Dementia in Parkinson's disease (PD-D) has only been acknowledged in the recent three decades, but research in this field has accelerated. The purpose of this review was to discuss advances in PD-D regarding biomarker correlates and potential therapeutic targets. Attention and executive dysfunction, memory deficits that improve with cueing, and visual hallucinations are characteristic in PD-D. PD-D dramatically increases the disability and misery of the disease. Current treatment for PD-D is symptomatic, modest, and only transiently effective. There is wide agreement that more effective treatment is needed, but this will require more knowledge about PD-D pathophysiology. Advances in the pathogenesis of PD have focused on the substantia nigra, which is the location from where the pathophysiology of motor symptoms primarily arises in initial stages. In contradistinction, pathology studies have suggested that cognitive decline correlates with cortical and subcortical-cortical projection pathway abnormalities. There is evidence that substantia nigra mechanisms, including protein aggregation of α-synuclein (e.g., Lewy bodies) may also play a role in cortical neuron degeneration. Other different mechanisms, such as Alzheimer's disease pathology (e.g., Aβ aggregation) may be operant for PD-D. Biomarkers of various types are being proposed for the study of PD-D as well as for objective measures of PD-D prediction and progression. Therapeutic targets are currently derived mostly from general PD neurodegeneration research rather than cortical PD neurodegeneration per se. Protein aggregation, genes that are associated with PD, oxidative stress, inflammation, and trophic factors constitute the major classes of therapeutic targets for PD-D. More research is needed on the specific aspects of cortical dysfunction and degeneration that create PD-D.

Clinical diagnostic criteria for dementia associated with Parkinson's disease

Dementia has been increasingly more recognized to be a common feature in patients with Parkinson's disease (PD), especially in old age. Specific criteria for the clinical diagnosis of dementia associated with PD (PD-D), however, have been lacking. A Task Force, organized by the Movement Disorder Study, was charged with the development of clinical diagnostic criteria for PD-D. The Task Force members were assigned to sub-committees and performed a systematic review of the literature, based on pre-defined selection criteria, in order to identify the epidemiological, clinical, auxillary, and pathological features of PD-D. Clinical diagnostic criteria were then developed based on these findings and group consensus. The incidence of dementia in PD is increased up to six times, point-prevelance is close to 30%, older age and akinetic-rigid form are associated with higher risk. PD-D is characterized by impairment in attention, memory, executive and visuo-spatial functions, behavioral symptoms such as affective changes, hallucinations, and apathy are frequent. There are no specific ancillary investigations for the diagnosis; the main pathological correlate is Lewy body-type degeneration in cerebral cortex and limbic structures. Based on the characteristic features associated with this condition, clinical diagnostic criteria for probable and possible PD-D are proposed.

Assessing neurocognitive dysfunction in cranial radiotherapy: can cognitive event-related potentials help?

Cognitive changes are common sequelae of cancer and cancer treatment, particularly in patients receiving cranial radiotherapy (RT). These effects are typically assessed by subjective clinical examination or using objective neuropsychological tests. Biologically based neurophysiological methods have been increasingly applied to the study of cognitive processing in neuropsychiatric and neurological disorders and as objective measures of cognitive status for patients with dementia. These methods detect the activation of neural circuits that directly mediate cognitive function in the human brain and include metabolic and electrophysiology based techniques. Neuroimaging procedures such as 18FDG PET and more recently fMRI, which detect metabolic activation associated with cognitive processing, provide excellent spatial resolution and can be directly correlated with neuroradiological findings associated with cranial RT neurotoxicity. Clinical electrophysiology procedures such as cognitive event-related potentials (ERP), which detect the neuronal electrical activity associated with cognitive processing, offer excellent temporal resolution at low cost. Cognitive ERP techniques are already being used to assess severity and progression of cognitive dysfunction in patients with vascular and degenerative dementias, but have been largely overlooked in studies of radiation-related cognitive impairments. We review these various electrophysiological methods in the context of their relevance to assessing cranial RT effects on cognitive function, and provide recommendations for a neurophysiological approach to supplement current neuropsychological tests for RT cognitive impairments. This technology is well suited for clinical assessment of neurocognitive sequelae of cancer and should provide new insights into the mechanism of RT-related cognitive dysfunction.

Tc-99m HMPAO brain SPECT findings in mild and moderate Alzheimer's disease: Correlation with event related potentials

We investigated whether brain SPECT findings show any differences between patients with mild and moderate Alzheimer's disease (AD) and to compare results with event related potentials (ERPs). Twenty-two patients with mild to moderate AD diagnosed according to NINCDS-ADRDA criteria and 10 age-matched control subjects were included in this prospective study. All subjects underwent ERP recordings and Tc-99m HMPAO brain SPECT study. Cortical perfusion index (CPI) was calculated as the ratio of cortical activity to the cerebellum activity. CPI was found to be statistically lower in bilaterally posterolateral temporal cortex and precuneus in the moderate AD compared to the control group. There was no statistically significant difference between the mild AD and control groups for CPI in any cortical areas. The mean P300 latency was statistically prolonged in the mild and moderate AD compared to the control group. In addition, in moderate AD P300 latency was longer than in mild AD. While the mean P300 amplitude was statistically reduced in moderate AD compared to the control and mild AD, there was no statistically significant difference between the mild AD and control groups. There was a strong negative correlation between P300 latency and CPI in the right and left precuneus in the moderate AD group. The present study suggested that Tc-99m HMPAO SPECT study is the more appropriate technique for patients with moderate AD rather than mild AD. Our results indicated that alterations in ERPs, especially prolongation of P300 latency could be a finding that occurred earlier than the deterioration in cerebral blood flow. We thought that precuneus is closely related to cognitive function and may have an important role in the pathophysiology of AD.

Cognitive Event-Related Potential and Neuropsychological Findings in Behcet's Disease without Neurological Manifestations

Behcet's disease (BD) is a multisystem inflammatory disorder characterized by recurrent oral and genital ulcers and uveitis. BD patients without neurological involvement frequently have mild neurological symptoms. The aim of this study was to evaluate whether BD patients without neurological involvement have any changes in cognitive functions. Twenty BD patients without neurological involvement and 13 control subjects were included in the study and were analyzed by neurophysiological and neuropsychological examinations. The cognitive event-related potentials (P300) were recorded from the frontal, central and parietal areas of the right and left hemispheres of the patients and control subjects. Likewise, all individuals were evaluated with neuropsychological tests. In contrast to a study with similar design, we did not find any difference between the cognitive event-related potentials values of BD patients without neurological involvement and the control subjects. All BD patients without neurological involvement exhibit normal results of the neuropsychological test. In conclusion, the results of neuropsychological tests and cognitive event-related potentials values in BD patients without neurological involvement are indistinguishable from those in control subjects and no alteration of cognitive functions is present.

Clinical and neuroimaging correlates of abnormal short-latency Somatosensory Evoked Potentials in elderly vascular dementia patients: A psychophysiological exploratory study

Background

Short Latency Somatosensory Evoked Potentials (SEPs) may serve to the testing of the somatosensory tract function, which is vulnerable and affected in vascular encephalopathy. The aim of the current study was to search for clinical and neuroimaging correlates of abnormal SEPs in vascular dementia (VD) patients.

Materials and Methods

The study included 14 VD patients, aged 72.93 ± 4.73 years, and 10 controls aged 71.20 ± 4.44 years. All subjects underwent a detailed clinical examination, blood and biochemical testing, brain MRI and were assessed with the MMSE. SEPs were recorded after stimulation from upper and lower limbs. The statistical Analysis included 1 and 2-way MANCOVAs and Factor analysis

Results

The N13 latency was significantly prolonged, the N19 amplitude was lower, the P27 amplitude was lower and the N11-P27 conduction time was prolonged in severely demented patients in comparison to controls. The N19 latency was prolonged in severely demented patients in comparison to both mildly demented and controls. The same was true for the N13-N19 conduction time, and for the P27 latency. Patients with subcortical lesions had all their latencies prolonged and lower P27 amplitude.

Discussion

The results of the current study suggest that there are significant differences between patients suffering from VD and healthy controls in SEPs, but these are detectable only when dementia is severe or there are lesions located in the subcortical regions. The results of the current study locate the abnormal SEPs in the white matter, and are in accord with the literature.

Enhancement of the somatosensory N140 component during attentional training after stroke

OBJECTIVE

To evaluate the training effect on the N140 component of the somatosensory event related potential in patients suffering from first ever stroke in the middle cerebral artery area and prove the influence, if any, on a component related to spatial attention.

METHODS

Forty patients were studied. Twenty were enrolled in a daily discrimination training task using an oddball paradigm with cutaneous electrical stimuli. The training period was 3 weeks. Twenty control patients were untrained. Electroencephalographic signals were recorded from scalp electrodes during each training session. In the controls, only two recordings were made, at baseline and after 3 weeks. Disability at the time of admission and discharge were evaluated using the functional independence measure (FIM). Twenty healthy control volunteers were also studied.

RESULTS

During training, event related potentials took the form of a large positive-negative complex over the period 106-160ms after the stimulus, followed by a smaller P300 component. The amplitude of the responses was smaller over the affected hemisphere (P<0.05). In the treatment group, N140 was present in 3 patients from the beginning and in 16 after training. Four of the untrained control patients showed a N140 at baseline, whereas it was seen in only 6 after 3 weeks (Chi-square 8.1; P<0.001).

CONCLUSIONS

In stroke patients, training improved the recovery of N140. That potential was prognostic of general outcome since its presence at baseline was correlated with a higher FIM score on discharge.

Do Event-Related Brain Potentials Reflect Mental (Cognitive) Operations?

Abstract Most cognitive psychophysiological studies assume (1) that there is a chain of (partially overlapping) cognitive processes (processing stages, mechanisms, operators) leading from stimulus to response, and (2) that components of event-related brain potentials (ERPs) may be regarded as manifestations of these processing stages. What is usually discussed is which particular processing mechanisms are related to some particular component, but not whether such a relationship exists at all. Alternatively, from the point of view of noncognitive (e. g., “naturalistic”) theories of perception ERP components might be conceived of as correlates of extraction of the information from the experimental environment. In a series of experiments, the author attempted to separate these two accounts, i. e., internal variables like mental operations or cognitive parameters versus external variables like information content of stimulation. Whenever this separation could be performed, the latter factor proved to significantly affect ERP amplitudes, whereas the former did not. These data indicate that ERPs cannot be unequivocally linked to processing mechanisms postulated by cognitive models of perception. Therefore, they cannot be regarded as support for these models.

P300 in Behcet's patients without neurological manifestations

OBJECTIVE

Behcet's disease is the association of recurrent aphthous stomatitis with genital ulceration and eye disease. Neurologic involvement patterns include meningomyelitis, a brain stem syndrome, pyramidal and extrapyramidal abnormality and stroke. In the present study, subclinical involvement was investigated by using P300 in Behcet's patients without neurological manifestation.

METHODS

Fifteen patients and 15 healthy volunteers were accepted for the study. P300 from vertex (Cz) electrode sites of the 10-20 system using electrodes and motor response time were recorded.

RESULTS

Patients had significantly prolonged latencies of P300 as compared to normal controls (p=0.013) but no significant differences in amplitude (p=1.000). Patients showed a significantly delayed motor response time than controls (p=0.006). Nine patients (60%) had P300 latency and eight patients (53.3%) had motor response time values exceeding the mean of controls by two standard deviations.

CONCLUSION

The findings suggest that the P300 measures and motor response time may reflect subclinical neurologic involvement in Behcet's disease.

Age and stage dependency of P300 latency alterations in non-demented Parkinson's disease patients without therapy

Acoustic P300 was recorded from Fz, Cz and Pz by means of an 'odd-ball' paradigm in 44 non-demented de novo Parkinson's disease patients (PD) or PD patients under treatment withdrawal, and in 31 age-matched normal subjects, to evaluate whether a P300 latency increase was present in PD patients. The influence of age and disease stage on latency was successively verified by subgrouping PD patients according to different age ('young' and 'old') and disease stage ('early' or 'advanced'). PD patient data were compared to data of normal subjects subgrouped into 'young' and 'old' or, to eliminate the age-dependent shift of latency, this latter was adjusted to 60 years in all the examined subjects. A significant increase of latency has been found in Fz and Cz in the 'old' group of PD patients (n = 23) but not in the 'young' group (n = 21) utilising both methods. Moreover, a significant latency increase was also present in Fz and Cz in the group of 'advanced' PD patients (n = 8), but not in the group of 'early' PD patients (n = 36) utilising age-adjusted measurements. When the 'early' PD patient group was divided into 'young' (n = 20) and 'old' (n = 16), the 'early old' group displayed significantly increased latencies in Fz compared with normal subjects. Abnormal P300 latencies were observed, at least in one electrode, by analysing the raw data, in 5.0% of the 'early young', 43.7% of the 'early old' and up to 62.7% of the 'advanced' patients. Fz represented the site in which abnormal P300 latencies were most often observed. Moreover, in the total group of PD patients, the P300 delay was significant only on the frontal (Fz) site when compared with normal subjects. The reported findings were interpreted as if PD produces a sort of 'accelerated effect of age' on the cognitive functions, presumably produced by a mechanism different from that producing motor impairment since no clear correlation could be detected between P300 latency and motor score. The frontal impairment of P300 is in line with previous neuropsychological findings obtained in these patients. Considering that about 30% of PD patients develop dementia during their disease progression, a border-line or abnormal P300 latency observed at disease onset may represent a predictive marker of this evolution.

Generators for human P300 elicited by somatosensory stimuli using multiple dipole source analysis

Cognitive event-related potentials, such as P300, are sensitive to manipulations of psychological variables and may provide evidence to support theories of brain mechanisms involved in cognition. However, the relationship between event-related potentials and the active neural structures is not yet understood. Electrical stimulation of the index and little fingers of the left hand in the context of a somatosensory target discrimination task, performed by healthy human subjects, elicited the middle-latency component of somatosensory evoked potentials, N60, the long-latency component, N140, and the P300 component. Identification of the generators for both the earlier components and P300, using equivalent electrical dipole modeling, was performed. Individual spatiotemporal seven-dipole models were developed in order to suggest locations of the sources generating each subject's scalp-recorded wave forms. Three dipoles with fairly weak moments, located in the primary and secondary sensory areas, explained the middle- and long-latency somatosensory evoked potential components, and the remaining four dipoles (4-7), with stronger dipole moments, were active during P300. There was a clear temporal separation of dipole activity between the somatosensory evoked potential components and the P300 component. Dipoles 4 and 5 were found quite symmetrically in the parahippocampal areas of the two hemispheres, while dipoles 6 and 7 were slightly asymmetrical. Dipole 7 was found in the left hippocampal area. Dipole 6 appeared in the right insular cortex. The locations of the four dipoles implicated in the generation of the somatosensory P300 were compared with the locations of four dipoles accounting for the auditory evoked P300 described in our previous paper [Tarkka et al. (1995) Electroenceph. clin. Neurophysiol. 96, 538-545]. No substantial difference in source locations of the P300 was found between auditory and somatosensory modality other than an asymmetrical activity in the somatosensory modality contralateral to the stimulated hand.

Meta-analysis of P300 normative aging studies

The theoretical and empirical backgrounds for the utility of the P300 event-related potential (ERP) as a measure of cognitive aging are summarized. P300 latency data from 32 different normative aging studies are then reviewed and assessed with meta-analytic procedures. Evaluation of moderator variables indicates that sample characteristics, stimulus factors, and task conditions contribute significantly to the "normal" change in peak latency that occurs with aging. These findings are critiqued in the context of previous reports, and implications are outlined for future applications of ERPs to normative aging. It is concluded that P300 latency can provide useful information about cognitive aging but that specific variables must be considered to obtain more precise results.

Effects of intravenous L-dopa on P300 and regional cerebral blood flow in parkinsonism

The P300 and regional cerebral blood flow were measured before and after intravenous injection of L-dopa in 10 patients with idiopathic Parkinson's disease and 10 patients with vascular parkinsonism. The P300 was measured with an evoked potential recorder using an oddball paradigm and the regional cerebral blood flow was measured using the stable xenon computed tomography method. The P300 latency was significantly longer and the regional cerebral blood flow in the cerebral cortex and basal ganglia was significantly lower in the Parkinson's disease group and the vascular parkinsonism group than in the age-matched healthy control group. The intravenous injection of L-dopa improved these abnormalities significantly in the Parkinson's disease group but did not improve these abnormalities in the vascular parkinsonism group. Cognitive function is considered to be impaired in Parkinson's disease and vascular parkinsonism and L-dopa is considered to improve it in Parkinson's disease.