Role of prefrontal cortex in generation of the contingent negative variation

Event-related potentials accompanying motor preparation and stimulus expectancy in the young, young-old and oldest-old

Although aging is accompanied by neurobiological changes and increased susceptibility to many neurological disorders, little is known about neurophysiological changes that start in old age. Here, neurophysiological changes during old age were assessed by recording brain potentials associated with motor preparation and stimulus expectancy (contingent negative variation, CNV) in young-old (60-69), oldest-old (85-98), and young (17-23) subjects. Individual trials began by a button press, followed 2.5 s later by either a low or high pitch tone. In the "motor" condition subjects responded following high pitch tones (P=0.20); in the "non-motor" condition subjects did not respond. Motor condition CNV amplitudes in the oldest old were more positive than the young and young-old groups, which were similar. In the non-motor condition, the young-old and oldest-old had similar CNV amplitudes that were positive in polarity, and were significantly different from young subjects. Motor potentials before button presses that started the trials were comparable among groups. Results show that neural activity associated with motor preparation and stimulus expectancy changes during advanced age, and that group differences can be modulated by task requirements.

Multisensory integration: methodological approaches and emerging principles in the human brain

Understanding the conditions under which the brain integrates the different sensory streams and the mechanisms supporting this phenomenon is now a question at the forefront of neuroscience. In this paper, we discuss the opportunities for investigating these multisensory processes using modern imaging techniques, the nature of the information obtainable from each method and their benefits and limitations. Despite considerable variability in terms of paradigm design and analysis, some consistent findings are beginning to emerge. The detection of brain activity in human neuroimaging studies that resembles multisensory integration responses at the cellular level in other species, suggests similar crossmodal binding mechanisms may be operational in the human brain. These mechanisms appear to be distributed across distinct neuronal networks that vary depending on the nature of the shared information between different sensory cues. For example, differing extents of correspondence in time, space or content seem to reliably bias the involvement of different integrative networks which code for these cues. A combination of data obtained from haemodynamic and electromagnetic methods, which offer high spatial or temporal resolution respectively, are providing converging evidence of multisensory interactions at both "early" and "late" stages of processing--suggesting a cascade of synergistic processes operating in parallel at different levels of the cortex.

Charting the maturation of the frontal lobe: An electrophysiological strategy

Tracking the functional development of specific regions of the prefrontal cortex in children using event-related potentials (ERPs) is challenging for both technical and conceptual reasons. In this paper we outline our strategy for studying frontal lobe development and present preliminary results from children aged 7-17 years and young adults using ERPs functionally associated with anterior cingulate and prefrontal cortex, especially the orbitofrontal, ventral, and medial portions. Our analysis of contingent negative variation, error-related negativity, and novelty P300 data show that the ERPs associated with these regions are still maturing into late adolescence, and that their amplitude has significant correlations with behavioral capacities.

Error detection in patients with lesions to the medial prefrontal cortex: an ERP study

When people detect their own errors in a discrimination task, a negative-going waveform can be observed in scalp-recorded EEG that has been coined the error-related negativity (Ne/ERN). Generation of the Ne/ERN has been associated with structures in the prefrontal cortex, especially the anterior cingulate region, but also the supplementary motor cortex and subcortical structures. There is some controversy as to whether the Ne/ERN is a necessary concomitant to error detection. We examined the Ne/ERN in five patients with damage to the medial prefrontal cortex, including the anterior cingulate region. Our findings support the implication of the rostral anterior cingulate in Ne/ERN production, but they also show that subjects can be aware of errors and yet not produce an Ne/ERN. Thus, error detection leads to the Ne/ERN process and damage to the anterior cingulate region may interrupt this relay, suggesting that error detection may be supported by circuits outside the anterior cingulate region.

Topographic abnormality of slow cortical potentials in schizophrenia

A recent study from our laboratory has provided evidence for the generation of slow potentials occurring in anticipation to task-performance feedback stimuli, in multiple association cortical areas, consistently including two prefrontal areas. In the present study, we intended to determine whether these slow potentials would indicate some abnormality (topographic) in schizophrenic patients, and thus serve as an indication of abnormal association cortex activity. We recorded slow potentials while subjects performed a paired-associates memory task. A 123-channel EEG montage and common average reference were used for 20 unmedicated schizophrenic (mean duration of illness: 11.3 +/- 9.2 years; mean number of previous hospitalizations: 1.2 +/- 1.9) and 22 healthy control subjects during a visual paired-associates matching task. For the topographic analysis, we used a simple index of individual topographic deviation from normality, corrected for absolute potential intensities. Slow potentials were observed in all subjects. Control subjects showed a simple spatial pattern of voltage extrema (left central positive and right prefrontal negative), whereas schizophrenic patients presented a more complex, fragmented pattern. Topographic deviation was significantly different between groups (P<0.001). The increased topographic complexity in schizophrenics could be visualized in grand averages computed across subjects. Increased topographic complexity could also be seen when grand averages were computed for subgroups of patients assembled either according to task-performance (high versus low) or by their scores on psychopathological scales. There was no significant correlation between topographic deviation and psychopathology scores. We conclude that the slow potential topographic abnormalities of schizophrenia indicate an abnormality in the configuration of large-scale electrical activity in association cortices.

Abnormal contingent negative variation in HIV patients receiving antiretroviral therapy

The contingent negative variation, an event-related potential related to neural activity in the frontal lobe and basal ganglia, neuropsychological tests and structural MRI were used to examine CNS function and structure in HIV-positive patients receiving antiretroviral therapy. Relative to controls, HIV patients had smaller thalamic volume and reduced late contingent negative variation amplitude that correlated with caudal atrophy. Behaviorally, viremic patients were more impaired than virally suppressed patients and controls on neuropsychological measures of psychomotor speed, selective attention and mental flexibility. These results suggest that antiretroviral therapy may not be effective in protecting cortical and subcortical structures against HIV-related neuropathology, regardless of immune function. However, the benefits of antiretroviral therapy on immune function appear to facilitate neurocognitive performance.

Abnormal CNV in chronic heavy drinkers

OBJECTIVE

We used the contingent negative variation (CNV), a slow negative shift in the human electroencephalogram, to investigate the effects of heavy chronic alcohol use on frontal lobe function.

METHODS

Event-related potentials (ERPs) were recorded from 30 heavy drinkers (HD) and 30 age-, sex-, and education-matched light or non-drinkers (LD), using a classical two-stimulus reaction time (RT) paradigm. Structural magnetic resonance images and neuropsychological tests were also administered.

RESULTS

The amplitude of the late CNV was significantly reduced in HD relative to light drinkers. Moreover, diminished CNV amplitudes in HD appear to be closely related to the amount of recent alcohol consumption. There were no significant differences in neuropsychological measures of frontal lobe function and frontal lobe volume between light and HD. However, in HD, reduced late CNV amplitudes were associated with decreased frontal lobe gray matter volume and poor performance on the Trail Making Test B. In LD but not in HD, late CNV amplitude correlated positively with RT, suggesting that the late CNV reflects some aspect of motor and cognitive preparation.

CONCLUSIONS

The inverse relationships between frontal lobe gray matter volume, performance on the Trail Making Test B, and late CNV amplitude in HD suggest that the ERP abnormalities observed in the current study may be indices of alcohol-related damage to the frontal lobe. The lack of a significant relationship between CNV amplitude and RT in HD suggests that chronic heavy alcohol use may disrupt response preparation.

Permanent or transitory effects on neurocognitive components of the CNV complex induced by brain dysfunctions, lesions and ablations in humans

Since the mid-1960s, essentially using electrophysiological methods, our research group has examined the effects of different brain diseases in humans, both on first- and second-order conditioned responses and on some types of neurocognitive potentials of the CNV complex. This didactic lecture will focus on our various attempts to identify and understand the neuroanatomical and neurophysiological substrates involved in cognitive information processing followed by the conception and execution of sensory-motor and behavioural responses evoked by significant acoustic stimuli, in both pathological situations and normal control subjects. Great interest was, e.g. aroused in the early 1970s by the rare, fortunately unrepeatable, opportunity of examining the CNV patterns in various psychiatric patients treated with psychosurgical Freeman-Watts bilateral prefrontal 'radical' lobotomy, also with repeated recordings (The Responsive Brain (1976) 158; Multidisciplinary Perspectives in Event-Related Brain-Potentials Research (1978) 376) or bimedial bifrontal cingulotomy (Multidisciplinary Perspectives in Event-Related Brain Potential Research (1978) 383). In the same period, investigations into CNV activity recorded in patients submitted to complete callosotomy ('split brain': Attention and Performance, vol. IV (1972) 221; Electroenceph. Clin. Neurophysiol. Suppl. 33 (1973) 161) were also begun and were continued into the 1980s, also with regard to other types of ERP (Brain 111 (1988) 553; J. Cog. Neurosci. 2 (1990) 258). All these data furnished unique information about the sub-second dynamics of unilateral or bihemispheric cortico-cortical and cortico-subcortical interconnections in humans. In recent years, with a classic method of analysis based on sequential scalp-topographic bidimensional neuroelectric mapping and 21/19 electrodes connected to three different references, and binaural/monaural clicks as warning signals (S1), we have repeatedly examined the CNV activity of 11 selected patients submitted to complete ablation of the damaged cortical areas, with uni- or bilateral lesions restricted to the prefrontal or associative parieto-temporal areas. We have always used the standard CNV paradigm (S1-S2 motor-response) which evokes a complex of neurocognitive potentials, including the P300 from S1, which are well-known, since they are certainly among the most studied ERPs in the various ages and races of normal subjects, psychiatric patients and subjects with different brain diseases. The most important results have been, (1) In normal subjects the MRI and the latency differences of CNV component measurements along the bidirectional pathways functionally interconnecting ipsilateral distant associative cortical areas (e.g. the arcuate-superior longitudinal complex bundle) were accounted for by the transcortical conduction time, which varies in our scalp recordings from 1 cm/0.74 to 1.28 ms ( approximately 9.8 m/s). (2) Constantly, no true auditory S1-elicited N1a, b, c, P2, N2, P300 components or CNV slow waves (O- and E-wave) were recordable over the whole of the ablated cortical areas, but only clearly identifiable volume-conducted EP/ERPs generated in other hemispheric structures. (3) The post-S1 ERP/CNV complexes on the intact hemisphere were found to be within the normal limits. (4) Effects of severe disruption on the S1 ERP/CNV complexes evocable on the site and on remote ipsilateral apparently normal anatomo-functionally interconnected brain regions were observed in 5 patients, 4 of whom had extensive frontocortical ablations. In two of the latter the distant disruptive action on the CNV components over the neuroradiologically normal ipsilateral two-way connected post-rolandic sensory and association areas was seen to be partially reversible, showing aspects of a probable slowly evolving diaschisis-like effect. Similar deactivation of some ERP components was observed in reverse on the ipsilateral dorsolateral frontocortical region in the fifth patient with a large parieto-temporal cortex ablation. These data require confirmahese data require confirmation, and when this phenomenon is observable, it must be appropriately monitored with different methods of functional neuroimaging. This will serve not only for medical and neuropsychophysiological diagnosis purposes, but also particularly for a correct and really useful planning of neuro-rehabilitation activities in selected cases.

Multifocal slow potential generation revealed by high-resolution EEG and current density reconstruction

In this work we used high-resolution EEG (123 channels) and current density reconstruction (CDR) to analyze the generators of slow potentials (SPs) in 31 healthy individuals. SPs were obtained during a task-performance feedback anticipation paradigm. The task consisted of a visual paired-associate memory test, with correct performance on single trials indicated by pleasant visual stimuli and incorrect performance by an unpleasant sound. We used realistic models of each subject's head based on their magnetic resonance images (MRIs) to estimate the potentials in the intracranial compartments and to define the source space using individual cortical geometry. Source reconstruction was performed by an Lp-norm minimization algorithm. Results showed a multifocal pattern of current density foci in various association cortices, including prefrontal areas 9 and 10 of Brodmann in all subjects. Posterior cortical areas also contributed importantly to the SP, for instance extrastriate area 19 and parietal area 7, in 90% of the subjects. According to our modeling, we conclude that even the pure stimulus-anticipation SP obtained here, as opposed to traditional motor-task contigent negative variation (CNVs), is not exclusively prefrontal in origin, being generated by multiple association areas. We discuss our results with respect to new possibilities in large-scale cortical physiology and with respect to their application in psychiatry.

Early contingent negative variation of the EEG and attentional flexibility are reduced in hypotension

This study explored the question as to whether hypotension is related to decreased attentional performance and reduced cortical activation. A total of 50 females aged 19-44 years participated in the study. Attentional performance was assessed using three subtests of the Attentional and Cognitive Efficiency (ACE) battery. Contingent negative variation (CNV) as a measure of cortical activation was registered during a constant fore-period reaction time paradigm: two conditions were defined using tones as S1 (80 or 60 dB) and S2 (70 dB). The following results were obtained. Hypotensive patients performed significantly more poorly on one subtest of the ACE, which indicates a reduced speed for switching from a routine to a controlled response (quantifying attentional flexibility). They also had longer reaction times and revealed a significantly smaller amplitude of the early CNV component. In addition, a significant correlation was observed between systolic blood pressure and the amplitude of the early CNV component. The data support previous findings that hypotension can be related to lowered cortical activation and indicate that specific aspects of attentional performance might be negatively affected by hypotension.

Frontal and parieto-temporal cortical ablations and diaschisis-like effects on auditory neurocognitive potentials evocable from apparently intact ipsilateral association areas in humans: five case reports

The aim of this study was to investigate the effects of disruption on the warning auditory S1-elicited ERP and CNV complexes recordable on the site and on remote ipsilateral apparently normal anatomo-functionally interconnected brain regions. These effects in some cases showed aspects of a probable diaschisis-like phenomenon, due to resections of extensive frontal association cortex or of primary and secondary sensory parieto-temporal areas damaged by differing pathological processes. Using a standard CNV paradigm, 21/19 EEG electrodes connected with three different references, and scalp-topographic bidimensional mapping analysis, the S1 auditory binaural/monaural clicks N1a,b,c, P2, N2, P3 and CNV waves were recorded in 10 normal subjects and 11 patients. Nine of the latter had been submitted to unilateral frontal dorsolateral cortex ablation, one to bihemispheric dorsomedial cortex ablation, and one to unilateral ablation of sensory parieto-temporal cortex and underlying white matter, verified through CT/MRI examinations. No true S1ERP/CNV components were recordable over the ablated cortical areas, whereas normal ERP/CNV complexes were observable on the intact hemispheres. In five patients, four of whom with frontocortical ablations, the S1 ERP/CNV complexes appeared severely diminished or disrupted, in two cases in a slow, partially-reversible manner, also in the neuroradiologically normal ipsilateral functionally-connected post-rolandic sensory and association areas. Similar deactivation of some ERP components was observed in reverse on the unilateral dorsolateral frontocortical region in the fifth patient with parieto-temporal cortex ablation. Even when they are partially reversible, these ipsilateral remote ERP changes in apparently intact brain regions, due to ablations of functionally-interconnected cortical formations, probably reflect cortical deactivation or simply dysfacilitation deriving from functional unilateral diaschisis. If these changes are instead irreversible they may probably be interpreted as transneuronal degeneration phenomena, though they are not at present easy to document either neuroradiologically or electroclinically.

P3 topographical change with task familiarization and task complexity

The P3 event-related potential (ERP) component is usually reported as having a centro-parietal maximum. However, a more frontal P3 topography is also evident in early-session trials which may be masked by averaging over the entire session, and is also present longer in elderly subjects. This maintenance of hyperfrontal topography is interpreted as a sign of reduced prefrontal adaptive functioning. In the present study, P3 amplitude was examined in young adults to determine: (1) how early in the test session the reduction in hyperfrontality occurs; and (2) the effect of task complexity on the P3 amplitude across electrode sites (Fz, Cz, Pz). ERPs were elicited using a working memory n-back task. Single-trial ERP waveforms were averaged in successive blocks of five trials. There was a greater decrease in P3 amplitude at Fz compared to Cz and Pz sites after the first block, and the decrease reached an asymptote by the third block. The results are interpreted as indicating rapid decrease in initial P3 hyperfrontality for a simple task in young adults, and an increased ratio of P3 amplitude at frontal versus posterior sites in more complex tasks.

Uncoupling of contingent negative variation and alpha band event-related desynchronization in a go/no-go task

OBJECTIVES

To examine how the differences in the sequences of brain activation during the go/no-go delayed response choice reaction time (RT) task are reflected into two concurrent methods of measuring brain electrical activity, the alpha band event-related desynchronization (alpha ERD) and the contingent negative variation (CNV).

METHODS

alpha ERD and CNV were calculated using appropriate techniques from the same samples of electroencephalographic activity recorded during performance of a cued choice go/no-go delayed response RT task (i.e. S1 (go/no-go)--S2 paradigm) in 8 healthy subjects.

RESULTS

All segments of the CNV traces were different in the go and the no-go conditions. The go CNV traces displayed a typical pattern of slow rising negativity reflecting the build-up of attentional resources necessary for adequate performance of the task. On the other hand, the no-go traces remained close to zero reflecting the 'withdrawal' of further preparation after evaluation of S1. During the same period, both go and no-go ERD traces showed a gradual decrease in alpha band power (desynchronization) that was evident until shortly before the presentation of S2. It was only in the 500 ms before S2 presentation that there was any indication that the go and no-go ERD traces were different, but this did not reach statistical significance.

CONCLUSIONS

Our data show that the pattern of the go/no-go difference in alpha ERD traces does not correspond to the pattern that can be seen in the CNV traces. This suggests that there is no direct coupling of CNV and alpha ERD, most probably because they measure different aspects of cortical electrical activity. In addition, the extent of the no-go alpha ERD reveals that refraining from performance of a pre-programmed movement is by no means a passive/inactive process.

Error-negativity and positivity as they relate to other ERP indices of attentional control and stimulus processing

We compared individual differences in the ERP associated with incorrect responses in a discrimination task with other ERP components associated with attentional control and stimulus discrimination (N2, P3, CNV). Trials with errors that are detected by the subject normally produce a negativity (N(E)) immediately following the response followed by a positivity (P(E)). The morphology of the N(E) and the P(E) is similar to that of the standard N2-P3 complex on correct discrimination trials. Our findings suggest that the P(E) is a P3 response to the internal detection of errors. The N(E), however, appears to be distinct from the N2. Finally, even though both the contingent negative variation (CNV) and the N(E) are associated with prefrontal cortex and the allocation of attention to response accuracy, the N(E) and CNV did not relate to one another.

Electrophysiological evidence for the cumulative effects of concussion

PURPOSE

A study was initiated with the intent of demonstrating the cumulative effects of concussion in junior hockey players using visual event-related potentials and post-concussion syndrome (PCS) self-reports.

METHODS

Players were assessed at the beginning of the season (pre-injury) and at various times post-injury.

RESULTS

The results suggest that players with three or more concussions differed significantly on the several cognitive PCS symptoms as well as for the latency of the P3 response compared to those with no concussion history.

DISCUSSION

Event-related potentials are useful indices of the cumulative damage that can occur following multiple concussions. These measures correlate significantly with cognitive self-reports of PCS symptoms.

CONCLUSIONS

This pattern of results is consistent with the position that each concussion potentially causes brain damage. Cumulative damage can be detected using electrophysiological measures of brain function.

High resolution spatiotemporal analysis of the contingent negative variation in simple or complex motor tasks and a non-motor task

OBJECTIVES

Since the characteristics of the Bereitschaftspotential (BP) - voluntary movement paradigm of internally-driven movements - have been established recently by our group using high resolution DC-EEG techniques, it was of great interest to apply similar techniques to the other slow brain potential--contingent negative variation (CNV) of externally-cued movements--with the same motor tasks using the same subjects.

METHODS

The CNV for simple bimanual sequential movements (task 1), complex bimanual sequential movements (task 2) and a non-motor condition (task 3) was recorded on the scalp using a 64 channel DC-EEG in 16 healthy subjects, and the data were analyzed with high resolution spatiotemporal statistics and current source density (CSD).

RESULTS

(1) The CNV was distributed over frontal, frontocentral, central and centroparietal regions; a negative potential was found at the frontal pole and a positive potential was found over occipital regions. (2) CNV amplitudes were higher for task 2 than for task 1, and there was no late CNV for task 3. (3) A high resolution spatiotemporal analysis revealed that during the early CNV component, statistical differences existed between the motor tasks (tasks 1 and 2) and the non-motor task (task 3), which occurred at frontocentral, central, centroparietal, parietal and parieto-occipital regions. During the late CNV component, additional significant differences were found not only between the motor tasks and the non-motor task but also between motor task 1 and task 2 at frontocentral, central and centroparietal regions. (4) Comparison of the CNV between the frontomesial cortex (situated over the supplementary/cingulate areas, SCMA) and both lateral pre-central areas (situated over the primary motor areas, MIs) showed that there was no statistically significant difference between the two cortical motor areas except for the early CNV. (5) Comparison of the CNV between the 3 tasks over the cortical motor areas showed that there were significant differences between the motor tasks and the non-motor task regarding the auditory evoked potential (AEP) and the early CNV component, and between all 3 tasks in the late CNV, the visual evoked potential (VEP(2)) and the N-P component. (6) The ranges and the densities of the CSD maps were larger and higher for complex than for simple tasks. The current sinks of the AEP and the early CNV were located at Fz, the late CNV at FCz and surrounding regions. As to be expected, current sources of the VEPs were located at the occipital lobes. The CNV was a current sink (negative) except for the VEP's main component which was a current source (positive).

CONCLUSIONS

(1) The CNV topography over the scalp varied with the complexity of motor tasks and between motor and non-motor conditions. (2) The origin of the early CNV may rest in the frontal lobes, while the late CNV may stem from more extensive cortical areas including SCMA, MIs, etc. (3) The late CNV component is not identical with the BP.

Prefrontal modulation of visual processing in humans

Single neuron, evoked potential and metabolic techniques show that attention influences visual processing in extrastriate cortex. We provide anatomical, electrophysiological and behavioral evidence that prefrontal cortex regulates neuronal activity in extrastriate cortex during visual discrimination. Event-related potentials (ERPs) were recorded during a visual detection task in patients with damage in dorsolateral prefrontal cortex. Prefrontal damage reduced neuronal activity in extrastriate cortex of the lesioned hemisphere. These electrophysiological abnormalities, beginning 125 ms after stimulation and lasting for another 500 ms, were accompanied by behavioral deficits in detection ability in the contralesional hemifield. The results provide evidence for intrahemispheric prefrontal modulation of visual processing.

Neuromagnetic localization of CMV generators using incomplete and full-head biomagnetometer

Contingent magnetic variation (CMV) data were recorded in three healthy male subjects using a 2 x 37 biomagnetometer system. The experiment was repeated for one of the subjects using a 151 whole-head biomagnetometer; the same auditory GO/NOGO choice reaction time paradigm as in the first experiment was used, extended to include repetitions of identical runs and additional control conditions. Magnetic field tomography was applied to the averaged data of each subject, for each run and condition (e.g., GO/NOGO). An independent estimate of the current density in the brain was obtained every few milliseconds. The slow components were emphasized by integrating the square of the current density vector, pixel by pixel, revealing in each subject activity in the auditory cortex, sensorimotor cortex, inferior prefrontal area, and posterior inferior parietal area. The intersubject variability was large, but looking across subjects the auditory and sensorimotor cortex (which were best covered by the two probes) were consistently identified in each subject as contributing to the generation of the early and late slow CMV components. These findings were confirmed by the whole-head single-subject experiment, in which slow activity was also identified in the supplementary motor area (SMA) and posterior cingulate cortex (PCC), areas very likely missed in the first experiment because of the limited view of the twin system. The PCC and particularly the SMA activations were substantially reduced when identical runs were repeated.

Prefrontal cortical involvement in visual working memory

Studies of human amnesia provide evidence for a short-term memory store with information transfer to long term memory occurring within 60 s of sensory encoding. Human and nonhuman primate research has shown that maintenance of this short-term or working memory store is dependent upon frontal cortical activation, although the critical temporal parameters of frontal involvement throughout this 60-s window are undetermined. We examined prefrontal contributions to rapid (under 2 s) and sustained (over 4 s) visual working memory by recording behavioral performance and event-related potentials (ERPs) in patients with lesions in dorsolateral frontal cortex and age-matched control subjects. Prefrontal lesioned patients generated a reduced sustained frontal positivity at all delays. At short delays, patients generated reduced performance to stimuli presented in the contralesional field. Patients generated a negative potential (N400), greatest to contralesionally presented stimuli, that was observed in the control subjects only at long delays. The results indicate that prefrontal lesions impair the frontal component of an anterior-posterior working memory network activated during rapid and sustained visual memory processing. Frontal patients may require activation of limbic cortex, indexed by N400, for maintenance of both rapid and sustained working memory.

The Contingent Magnetic Variation in Migraine

Abstract Migraine is characterized by an increased contingent negative variation. Separate comparisons of the early and late component showed that it was the former rather than the latter that was elevated. The function and localization of the early component are as yet poorly understood. The magneto-encephalogram was recorded in 16 patients with migraine and 17 healthy control subjects during a forewarned reaction time task. Neuromagnetic data were recorded with a 37-channel neuromagnetometer with the sensors being placed above the left hemisphere contralaterally to the side of the acoustic stimulation and the motor reaction. Subjects responded to the second of two low intensity sound stimuli that were administered with an interval of 4.5 s. Migraine patients exhibited a significantly higher amplitude of the early component of the contingent magnetic variation (CMV) than controls. Groups did not differ with regard to the amplitude of the late component. Modeling the sources with a single moving equivalent current dipole (ECD) provided a high goodness of fit for the M100 (magnetic N1) in both groups and for the early component of the CMV in migraineurs but not controls. The activity of the early component was centered medially with respect to the M100-ECDs and more laterally so in migraine patients than in controls.

Correlation between contingent negative variation and regional cerebral blood flow

The relationship between contingent negative variation (CNV) and regional cerebral blood flow was investigated, using the stable xenon computed tomography method. Seventeen cases of chronic multiple cerebral infarction in the perforating artery areas (vascular dementia, mean age 67.0), 6 cases of Alzheimer's disease (mean age 69.5) and 8 healthy controls (mean age 62.5) were studied. Regional cerebral blood flows in the frontal, temporal, parietal and occipital cortex, frontal, temporal and occipital white matter, caudate nucleus, putamen and thalamus were measured. The amplitude of early CNV was significantly smaller in the vascular dementia group than in the healthy control group. The blood flows in the parietal cortex and thalamus were significantly lower in the vascular dementia group than in the healthy control group. There was a significant positive correlation between the amplitude of early CNV and frontal cortex blood flow. No significant correlations were present between the CNV and the other regional cerebral blood flows nor in healthy controls. The amplitude of CNV has been reported to be decreased in dementia. From the present study, the amplitude of early CNV was considered to be influenced by the blood flow in the frontal cortex.

Source monitoring: ERP evidence for greater reactivity to nontarget information in older adults

Event-Related Potentials (ERPs) were collected concurrently with stimulus presentation during a source monitoring task. Younger adults were less likely than older adults to make source monitoring errors and their ERP records showed far greater discrimination between target stimuli and familiar but nontarget foils. Older adults not only made more source errors but produced high amplitude late positivities to the nontarget foils even when these foils were correctly rejected. Under divided attention conditions, younger adults performance was similar to that of the older adults both behaviorally and electrophysiologically. These data illustrate the role that attentional resources play in the ability to inhibit response tendencies and suggest that age differences in source monitoring may be more related to attentional control than inefficiencies in the encoding of contextual information. As well, they suggest that the ERP late positivity may represent a more general response to item salience rather than serve as an index of recollection as is the current view.

Common Blood Flow Changes across Visual Tasks: I. Increases in Subcortical Structures and Cerebellum but Not in Nonvisual Cortex

Nine positron emission tomography (PET) studies of human visual information processing were reanalyzed to determine the consistency across experiments of blood flow increases during active tasks relative to passive viewing of the same stimulus array. No consistent blood flow increases were found in cerebral cortex outside of the visual system, but increases were seen in the thalamus and cerebellum. Although most tasks involve increases in arousal, establishing an intention or behavioral goal, setting up control structures for sequencing task operations, detecting targets, etc., these operations do not produce blood flow increases, detectable with the present methods, in localized cortical regions that are common across tasks. Common subcortical regions, however, may be involved.

A left cerebellar and a medial cerebellar focus reflected motor-related processes. Blood flow increases in these regions only occurred in experiments in which the subject made an overt response and were largest when the response was made in the active but not passive condition. These motor-related processes were more complex than simple motor execution, however, since increases were still present when the response was made in both the active and passive conditions. These cerebellar increases may reflect processes related to response selection.Blood flow increases in a right cerebellar region were not motor-related. Increases were not modulated by the presence or absence of motor responses during either the active or passive conditions, and increases were sensitive to within-experiment variables that held the motor response constant. Increases occurred in both language and nonlanguage tasks and appeared to involve a general nonmotor process, but the nature of that process was difficult to specify.

A right thalamic focus was sensitive to variables related to focal attention, suggesting that this region was involved in attentional engagement. Right thalamic increases were also correlated over conditions with increases in the left and medial cerebellum, perhaps reflecting additional contributions from motor-related nuclei receiving cerebellar projections.

Blood flow increases in a left thalamic focus were completely uncorrelated over conditions with increases in the right thalamus, indicating that it was involved in different functions. Both the left thalamus and right cerebellum yielded larger blood flow increases when subjects performed a complex rather than simple language task, possibly reflecting a language-related pathway. Blood flow increases in the left thalamus were also observed, however, during nonlanguage tasks.

Prefrontal and posterior cortical activation during auditory working memory

The present study investigated brain mechanisms underlying auditory memory. In a modified Sternberg memory scanning task, 11 subjects indicated whether a probe sound was part of a previously presented 4-item memory set by a button press. Behaviorally, subjects responded fastest and most accurately to probes that matched the last memory set items and slowest and least accurately to negative probes and to positive probes to the first two memory set items. Electrophysiologically, probes to the last memory set items elicited the largest amplitude and earliest latency P3 components while other probes elicited smaller amplitude, prolonged P3s as well as a negativity around 400 ms. These results suggest that subjects utilized a trace strength/self-terminating search model to perform the memory scanning task. Subjects only generated the P3 component during the matching phase of the auditory memory task while a sustained frontal negativity was elicited during both the encoding and matching phase. Taken together these findings provide evidence of differential activation of distributed neural activity during non-linguistic auditory memory.

Auditory event-related potentials dissociate early and late memory processes

Event-related potentials (ERPs) to environmental sounds were recorded from 15 young control subjects in an auditory recognition memory task. Subjects listened to a continuous string of binaurally presented sounds, 20% of which were presented once and 80% were repeated. Of the repeated sounds, some repeated immediately after the initial presentation (2 sec; short delay repetition) while others repeated after 2-6 intervening sounds (4-12 sec; long delay repetition). Subjects were instructed to indicate whether they had heard the sounds before by pressing a "yes" or "no" button. The initial stimulus presentation and long delay repetition stimuli generated both an N4 component and a prolonged latency P3 component while the short delay repetition stimuli elicited no N4 component and an earlier latency P3 component. Subjects' responses were faster and more accurate for short delay repetition. All stimuli generated a sustained frontal negative component (SFN). These data indicate that auditory recognition memory for environmental sounds may involve two processes. The P3 generated by both short and long delay repetition stimuli may index activation of a neocortical template matching system. The N4 generated by initial stimulus presentations and long delay repetition is proposed to measure additional activation of limbic memory systems at long retention intervals.