Slow brain potentials in a visual-spatial memory task: topographic distribution and inter-laboratory consistency

A KCNJ6 gene polymorphism modulates theta oscillations during reward processing

Event related oscillations (EROs) are heritable measures of neurocognitive function that have served as useful phenotype in genetic research. A recent family genome-wide association study (GWAS) by the Collaborative Study on the Genetics of Alcoholism (COGA) found that theta EROs during visual target detection were associated at genome-wide levels with several single nucleotide polymorphisms (SNPs), including a synonymous SNP, rs702859, in the KCNJ6 gene that encodes GIRK2, a G-protein inward rectifying potassium channel that regulates excitability of neuronal networks. The present study examined the effect of the KCNJ6 SNP (rs702859), previously associated with theta ERO to targets in a visual oddball task, on theta EROs during reward processing in a monetary gambling task. The participants were 1601 adolescent and young adult offspring within the age-range of 17-25years (800 males and 801 females) from high-dense alcoholism families as well as control families of the COGA prospective study. Theta ERO power (3.5-7.5Hz, 200-500ms post-stimulus) was compared across genotype groups. ERO theta power at central and parietal regions increased as a function of the minor allele (A) dose in the genotype (AA>AG>GG) in both loss and gain conditions. These findings indicate that variations in the KCNJ6 SNP influence magnitude of theta oscillations at posterior loci during the evaluation of loss and gain, reflecting a genetic influence on neuronal circuits involved in reward-processing. Increased theta power as a function of minor allele dose suggests more efficient cognitive processing in those carrying the minor allele of the KCNJ6 SNPs. Future studies are needed to determine the implications of these genetic effects on posterior theta EROs as possible "protective" factors, or as indices of delays in brain maturation (i.e., lack of frontalization).

Deficient Event-Related Theta Oscillations in Individuals at Risk for Alcoholism: A Study of Reward Processing and Impulsivity Features

BACKGROUND

Individuals at high risk to develop alcoholism often manifest neurocognitive deficits as well as increased impulsivity. Event-related oscillations (EROs) have been used to effectively measure brain (dys)function during cognitive tasks in individuals with alcoholism and related disorders and in those at risk to develop these disorders. The current study examines ERO theta power during reward processing as well as impulsivity in adolescent and young adult subjects at high risk for alcoholism.

METHODS

EROs were recorded during a monetary gambling task (MGT) in 12-25 years old participants (N = 1821; males = 48%) from high risk alcoholic families (HR, N = 1534) and comparison low risk community families (LR, N = 287) from the Collaborative Study on the Genetics of Alcoholism (COGA). Impulsivity scores and prevalence of externalizing diagnoses were also compared between LR and HR groups.

RESULTS

HR offspring showed lower theta power and decreased current source density (CSD) activity than LR offspring during loss and gain conditions. Younger males had higher theta power than younger females in both groups, while the older HR females showed more theta power than older HR males. Younger subjects showed higher theta power than older subjects in each comparison. Differences in topography (i.e., frontalization) between groups were also observed. Further, HR subjects across gender had higher impulsivity scores and increased prevalence of externalizing disorders compared to LR subjects.

CONCLUSIONS

As theta power during reward processing is found to be lower not only in alcoholics, but also in HR subjects, it is proposed that reduced reward-related theta power, in addition to impulsivity and externalizing features, may be related in a predisposition to develop alcoholism and related disorders.

Reward processing deficits and impulsivity in high-risk offspring of alcoholics: A study of event-related potentials during a monetary gambling task

BACKGROUND

Individuals at high risk to develop alcoholism often manifest neurocognitive deficits as well as increased impulsivity. The goal of the present study is to elucidate reward processing deficits, externalizing disorders, and impulsivity as elicited by electrophysiological, clinical and behavioral measures in subjects at high risk for alcoholism from families densely affected by alcoholism in the context of brain maturation across age groups and gender.

METHODS

Event-related potentials (ERPs) and current source density (CSD) during a monetary gambling task (MGT) were measured in 12-25 year old offspring (N=1864) of families in the Collaborative Study on the Genetics of Alcoholism (COGA) Prospective study; the high risk (HR, N=1569) subjects were from families densely affected with alcoholism and the low risk (LR, N=295) subjects were from community families. Externalizing disorders and impulsivity scores were also compared between LR and HR groups.

RESULTS

HR offspring from older (16-25 years) male and younger (12-15 years) female subgroups showed lower P3 amplitude than LR subjects. The amplitude decrement was most prominent in HR males during the loss condition. Overall, P3 amplitude increase at anterior sites and decrease at posterior areas were seen in older compared to younger subjects, suggesting frontalization during brain maturation. The HR subgroups also exhibited hypofrontality manifested as weaker CSD activity during both loss and gain conditions at frontal regions. Further, the HR subjects had higher impulsivity scores and increased prevalence of externalizing disorders. P3 amplitudes during the gain condition were negatively correlated with impulsivity scores.

CONCLUSIONS

Older male and younger female HR offspring, compared to their LR counterparts, manifested reward processing deficits as indexed by lower P3 amplitude and weaker CSD activity, along with higher prevalence of externalizing disorders and higher impulsivity scores.

SIGNIFICANCE

Reward related P3 is a valuable measure reflecting neurocognitive dysfunction in subjects at risk for alcoholism, as well as to characterize reward processing and brain maturation across gender and age group.

Modulation of ERP components by task instructions in a cued go/no-go task

The present study investigated how components of ERPs are modulated when participants optimize speed versus accuracy in a cued go/no-go task. Using a crossover design, 35 participants received instructions to complete the task prioritizing response speed in half of the task, and accurate responding in the other half of the task. Analysis was performed on the contingent negative variation (CNV), P3go, and P3no-go and the corresponding independent components (IC), as identified by group independent component analysis. After speed instructions, the IC CNV(late), P3go(anterior), P3no-go(early), and P3no-go(late) all had larger amplitudes than after accuracy instructions. Furthermore, both the IC P3go(posterior) and IC P3go(anterior) had shorter latencies after speed than after accuracy instructions. The results demonstrate that components derived from the CNV and P3 components are facilitated when participants optimize response speed. These findings indicate that these ERP components reflect executive processes enabling adjustment of behavior to changing demands.

Neuropsychological parameters indexing executive processes are associated with independent components of ERPs

Lesion studies have indicated that at least the three executive processes can be differentiated in the frontal lobe: Energization, monitoring and task setting. Event related potentials (ERPs) in Go/NoGo tasks have been widely used in studying executive processes. In this study, ERPs were obtained from EEG recorded during performance of a cued Go/NoGo task. The Contingent Negative Variation (CNV) and P3NoGo waves were decomposed into four independent components (ICs), by applying Independent Component Analysis (ICA) to a collection of ERPs from 193 healthy individuals. The components were named IC CNVearly, IC CNVlate, IC P3NoGoearly and IC P3NoGolate according to the conditions and time interval in which they occurred. A sub-group of 28 individuals was also assessed with neuropsychological tests. The test parameters were selected on the basis of studies demonstrating their sensitivity to executive processes as defined in the ROtman-Baycrest Battery for Investigating Attention (ROBBIA) model. The test scores were categorized into the domain scores of energization, monitoring and task setting and correlated with the amplitudes of the individual ICs from the sub-group of 28 individuals. The energization domain correlated with the IC CNVlate and IC P3NoGoearly. The monitoring domain correlated with the IC P3NoGolate, while the task setting domain correlated with the IC CNVlate. The IC CNVearly was not correlated with any of the neuropsychological domain scores. The correlations between the domains and ICs remained largely unchanged when controlling for full-scale IQ. This is the first study to demonstrate that executive processes, as indexed by neuropsychological test parameters, are associated with particular event-related potentials in a cued Go/NoGo paradigm.

What MEG can reveal about inference making: the case of if...then sentences

Characterizing the neural substrate of reasoning has been investigated with regularity over the last 10 years or so while relying on measures that come primarily from positron emission tomography and functional magnetic resonance imaging. To some extent, these techniques—as well as those from electroencephalography—have shown that time course is equally worthwhile for revealing the way reasoning processes work in the brain. In this work, we employ magnetoencephalography while investigating Modus Ponens (If P then Q; P//Therefore, Q) in order to simultaneously derive time course and the source of this fundamental logical inference. The present results show that conditional reasoning involves several successive cognitive processes, each of which engages a distinct cerebral network over the course of inference making, and as soon as a conditional sentence is processed.

Planning: fixed-foreperiod event-related potentials during the Tower of London task

Slow wave ERPs were recorded from 28 young adults as they generated plans for various difficulty levels of a fixed-foreperiod version of the Tower of London task. The resulting waveform included three segments: (1) a left-lateralized negative early-interval wave, which was frontally maximal but not sensitive to difficulty, (2) a right-lateralized frontally maximal mid-interval wave, which was more positive for more difficult problems, and (3) a left lateralized centrally maximal negative-ramping contingent negative variation (CNV) late wave, which was more negative for more difficult problems. The current study adds to the current literature in that it finds that the frontal and central neural utilization with difficulty changes across plan generation. This suggests that plan generation should be considered in terms of when component processes of planning are differentially utilized as plan generation unfolds.

Neural generators of sustained activity differ for stimulus-encoding and delay maintenance

The ability to maintain information online beyond sensory stimulation is regarded as a key contribution of working memory to goal-directed behaviour. It is widely accepted that sustained neural activity is a key mechanism of stimulus maintenance, but it is unclear to what extent the neural generators of sustained activity change from stimulus-encoding to maintenance. Using event-related potentials in humans, we show that, in a delayed match-to-sample task, slow shifts over parieto-occipital electrode sites had a different topography and polarity during encoding and delay maintenance of images depicting scenes. This clearly demonstrates that neural generators of sustained activity associated with stimulus-encoding and delay maintenance differed, and that the change between these generators occurred time-locked to the onset of the delay period. We also investigated how monetary reward incentives modulated the amplitude and topography of sustained delay activity and the ability to suppress irrelevant distracting information during the delay. Reward incentives improved maintenance performance and this was correlated with an expansion of the parieto-occipital electrode sites that were entrained into sustained delay activity (rather than improved distractor suppression), suggesting that under the influence of reward, the parieto-occipital regions that contributed to delay maintenance expanded in size.

What's behind an inference? An EEG study with conditional arguments

Conditional reasoning studies typically involve presenting a major conditional premise (If P then Q), a minor premise (P) and a conclusion (Q). We describe how most fMRI studies investigate reasoning and point out that these studies neglect to take into consideration the temporal sequence of cognitive steps generated by the interaction of the premises. The present study uses EEG to address this issue and compares the processing of the minor premise P when it is presented before vs. after the conditional statement (P; If P then Q vs. If P then Q; P). When the minor premise comes after the conditional statement and matches the antecedent its processing results in a P3b component, known to reflect the satisfaction of expectations, and in two later components, a PSW component and a CNV component. These two components are discussed in light of a conclusion generation phase and a maintenance phase. We also investigated the effect of violating expectations through the presentation of a minor premise that mismatches the antecedent of the conditional statement (If P then Q; R). The data indicate that the processing of such a premise yields an N2 component which is known to reflect perceptual conflict.

The topography of the scalp-recorded visual N700

OBJECTIVE

To describe the topography of the N700 component of the scalp-recorded visual event-related potential (ERP) and to provide fundamental knowledge of the conditions under which it occurs.

METHODS

We examined the time-course of visual ERP in response to the short (100ms) and prolonged (7s) presentation of simple salient visual stimuli separated by long interstimulus intervals employing high-resolution 64-channel DC-EEG. Current source density (CSD) mapping and spatio-temporal dipole source analysis were performed.

RESULTS

CSD analysis revealed highly significant bilateral current sinks over occipito-temporal areas from about 450ms up to 1s after stimulus offset (visual N700). CSD topography and dipole source analysis suggested late prolonged activation of extrastriate visual areas which did not depend merely upon a stimulus offset response, afterimages or blinking, as confirmed by control conditions.

CONCLUSIONS

Our findings provide basic knowledge about the time-course of sensory activation. We found that passive watching of rare salient short stimuli automatically evoked sustained activity in the extrastriate visual cortex up to 1s after stimulus offset.

SIGNIFICANCE

Visual N700 provides a promising tool for important insights into the cortical mechanisms of stimulus post-processing. Its role in associative learning of temporally non-overlapping stimuli (automatic ultra-short-term sensory memory) should be explored.

Meditation states and traits: EEG, ERP, and neuroimaging studies

Neuroelectric and imaging studies of meditation are reviewed. Electroencephalographic measures indicate an overall slowing subsequent to meditation, with theta and alpha activation related to proficiency of practice. Sensory evoked potential assessment of concentrative meditation yields amplitude and latency changes for some components and practices. Cognitive event-related potential evaluation of meditation implies that practice changes attentional allocation. Neuroimaging studies indicate increased regional cerebral blood flow measures during meditation. Taken together, meditation appears to reflect changes in anterior cingulate cortex and dorsolateral prefrontal areas. Neurophysiological meditative state and trait effects are variable but are beginning to demonstrate consistent outcomes for research and clinical applications. Psychological and clinical effects of meditation are summarized, integrated, and discussed with respect to neuroimaging data.