Event-related Potential Recordings Research Articles

Olfactory function in patients with ischemic stroke: a pilot study

The aim of this pilot study was to investigate olfactory function in unselected, cooperative patients with ischemic stroke and to gain information about olfactory perception in patients with distinct stroke localizations. Three ischemic stroke patients underwent olfactory testing using the Sniffin' Sticks test and olfactory event-related potentials recording. All stroke patients were found to be normosmic or only slightly hyposmic when using a psychophysical testing device with age-adjusted norms. No responses or longer latencies on the affected side were found, however, when recording evoked potentials. This seems to argue for the idea that on the affected side it is often possible to document the objective lesion although the subjective perception of the patient appears normal.

Dysfunction in different phases of working memory in schizophrenia: Evidence from ERP recordings

The present study combined a time-locked paradigm and high-time-resolution event-related potential (ERP) recordings to examine different phases of working memory, including early visual processing and late memory-related processes of encoding, maintenance, and retrieval, in 67 adults with schizophrenia and 46 healthy controls. Alterations in ERP components were correlated with task performance. Patients performed significantly worse in the working memory task than healthy subjects, although all subjects' accuracy exceeded 80%. During encoding, the N1 and P2 component amplitudes were lower while the P300 amplitude was higher in schizophrenic patients compared to healthy controls. There were no differences between groups with respect to the mean amplitudes of the negative slow waves in the early stage (the first 400ms) of the maintenance phase. However, in the next 500-ms time window, the patients exhibited a more negative deflection in the middle fronto-central region than the control group. Likewise, a similar pattern was observed in the second 500-ms period in the middle fronto-central region, although the effect was marginally significant. There were no differences between groups in the remaining 1000ms. During retrieval, the P1, N1 and P2 amplitudes were lower while the P300 amplitude and latency were higher in schizophrenic patients. The present results indicate early visual deficits in the working memory task in adults with schizophrenia. Impairments in the maintenance phase were confined to the late rehearsal stage. The increased P300 amplitude at the fronto-central electrode sites along with the poorer behavioral performance suggests that schizophrenic patients have an inefficient working memory system.

TMS of the right angular gyrus modulates priming of pop-out in visual search: combined TMS-ERP evidence

During priming of pop-out, performance at discriminating a pop-out feature target in visual search is affected by whether the target on the previous trial was defined by the same feature as on the upcoming trial. Recent studies suggest that priming of pop-out relies on attentional processes. With the use of simultaneous, combined transcranial magnetic stimulation and event-related potential recording (TMS-ERP), we tested for any critical role of the right angular gyrus (rANG) and left and right frontal eye fields (FEFs)-key attentional sites-in modulating both performance and the ERPs evoked by such visual events. Intertrial TMS trains were applied while participants discriminated the orientation of a color pop-out element in a visual search array. rANG TMS disrupted priming of pop-out, reducing reaction time costs on switch trials and speeding responses when the color of the pop-out target switched. rANG TMS caused a negativity in the ERP elicited in response to the visual stimulus array, starting 210 ms after stimulus onset. Both behavioral and ERP effects were apparent only after rANG TMS, on switch trials, and when the target in the visual search array was presented in the left visual field, with no effects after left or right FEF TMS. These results provide evidence for an attentional reorienting mechanism, which originates in the rANG and is modulated by the implicit memory of the previous trial. The rANG plays a causal role on switch trials during priming of pop-out by interacting with visual processing, particularly in the ipsilateral hemisphere representing the contralateral hemifield.

Development of a minimally-invasive protocol for recording mismatch negativity (MMN) in the dog ( Canis familiaris) using electroencephalography (EEG)

Mismatch negativity (MMN), observed in event-related potentials (ERPs), constitutes a measurable change in electrophysiological brain activity occurring after exposure to a novel stimulus. In humans, MMN is considered to be related to stimulus discrimination at the cortical level. ERP recording in dogs may present an opportunity to increase understanding of cognitive processes without reliance on observable behaviour, which may be confounded by motivation or training. Preliminary data are presented suggesting the existence of MMN, recorded using a minimally-invasive procedure equivalent to that used in humans, in unrestrained, unanaesthetised dogs. This is the first example of this ERP component in dogs and the method has substantial utility for future research exploring auditory, olfactory, and visual discrimination tasks, development, and breed differences.

Consequences of Magnocellular Dysfunction on Processing Attended Information in Schizophrenia

Schizophrenia is associated with perceptual and cognitive dysfunction including impairments in visual attention. These impairments may be related to deficits in early stages of sensory/perceptual processing, particularly within the magnocellular/dorsal visual pathway. In the present study, subjects viewed high and low spatial frequency (SF) gratings designed to test functioning of the parvocellular/magnocellular pathways, respectively. Schizophrenia patients and healthy controls attended to either the low SF (magnocellularly biased) or high SF (parvocellularly biased) gratings. Functional magnetic resonance imaging (fMRI) and recordings of event-related potentials (ERPs) were carried out during task performance. Patients were impaired at detecting low-frequency targets. ERP amplitudes to low-frequency gratings were diminished, both for the early sensory-evoked components and for the attend minus unattend difference component (the selection negativity), which is regarded as a neural index of feature-selective attention. Similarly, fMRI revealed that activity in extrastriate visual cortex was reduced in patients during attention to low, but not high, SF. In contrast, activity in frontal and parietal areas, previously implicated in the control of attention, did not differ between patients and controls. These findings suggest that impaired sensory processing of magnocellularly biased stimuli lead to impairments in the effective processing of attended stimuli, even when the attention control systems themselves are intact.

Dimension reduction: Additional benefit of an optimal filter for independent component analysis to extract event-related potentials

The present study addresses benefits of a linear optimal filter (OF) for independent component analysis (ICA) in extracting brain event-related potentials (ERPs). A filter such as the digital filter is usually considered as a denoising tool. Actually, in filtering ERP recordings by an OF, the ERP’ topography should not be changed by the filter, and the output should also be able to be modeled by the linear transformation. Moreover, an OF designed for a specific ERP source or component may remove noise, as well as reduce the overlap of sources and even reject some non-targeted sources in the ERP recordings. The OF can thus accomplish both the denoising and dimension reduction (reducing the number of sources) simultaneously. We demonstrated these effects using two datasets, one containing visual and the other auditory ERPs. The results showed that the method including OF and ICA extracted much more reliable components than the sole ICA without OF did, and that OF removed some non-targeted sources and made the underdetermined model of EEG recordings approach to the determined one. Thus, we suggest designing an OF based on the properties of an ERP to filter recordings before using ICA decomposition to extract the targeted ERP component.

Evaluation of auditory, visual and olfactory event-related potentials for comparing interspersed- and single-stimulus paradigms

Background An interspersed-stimulus paradigm (ISP) for event-related potential (ERP) recordings in which different sensory modality stimuli are presented within the same test session was developed to minimize recording time and facilitate modality comparison. The present study compared the ISP with a single-stimulus paradigm (SSP), using auditory, visual, and olfactory stimuli. Method Normal participants (n = 16) were assessed on two independent test occasions to obtain data on inter-paradigm and test–retest reliability. Peak amplitude/latency and area measures were obtained for the N1, P2 and P3 peaks for each paradigm. Results Except for larger auditory and visual P3 peaks and smaller visual P2 peaks in the ISP, no significant differences in amplitudes or latencies were found between the two paradigms. Correlation coefficients between paradigms were generally fairly high (amplitude mean r = 0.76; latency r = 0.42). Test–retest reliability within paradigms for amplitudes (ISP r = 0.70; SSP r = 0.68) and latencies (ISP r = 0.44; SSP r = 0.42) was similar across paradigms. Conclusion The findings suggest that the ISP, compared to the SSP, produces, in general, highly comparable auditory, visual, and olfactory peak amplitudes and latencies, and comparable reliability estimates, even though the ISP takes much less time to record (25 vs. 50 min). The larger auditory and visual P3 peaks and smaller visual P2 peaks in the ISP may be attributable to a less predictable stimulus environment. Thus, this method enables systematic comparisons of ERP peaks across sensory modalities while reducing testing time. Practical implications are discussed.

Understanding the Pathophysiology of Alzheimer's Disease and Mild Cognitive Impairment: A Mini Review on fMRI and ERP Studies

The prevalence of Alzheimer's disease (AD) is predicted to increase rapidly in the coming decade, highlighting the importance of early detection and intervention in patients with AD and mild cognitive impairment (MCI). Recently, remarkable advances have been made in the application of neuroimaging techniques in investigations of AD and MCI. Among the various neuroimaging techniques, functional magnetic resonance imaging (fMRI) has many potential advantages, noninvasively detecting alterations in brain function that may be present very early in the course of AD and MCI. In this paper, we first review task-related and resting-state fMRI studies on AD and MCI. We then present our recent fMRI studies with additional event-related potential (ERP) experiments during a motion perception task in MCI. Our results indicate that fMRI, especially when combined with ERP recording, can be useful for detecting spatiotemporal functional changes in AD and MCI patients.

Ketamine effects on brain function — Simultaneous fMRI/EEG during a visual oddball task

Behavioral and electrophysiological human ketamine models of schizophrenia are used for testing compounds that target the glutamatergic system. However, corresponding functional neuroimaging models are difficult to reconcile with functional imaging and electrophysiological findings in schizophrenia. Resolving the discrepancies between different observational levels is critical to understand the complex pharmacological ketamine action and its usefulness for modeling schizophrenia pathophysiology. We conducted a within-subject, randomized, placebo-controlled pharmacoimaging study in twenty-four male volunteers. Subjects were given low-dose S-ketamine (bolus prior to functional imaging: 0.1mg/kg during 5min, thereafter continuous infusion: 0.015625mg/kg/min reduced by 10% every ten minutes) or placebo while performing a visual oddball task during simultaneous functional magnetic resonance imaging (fMRI) with continuous recording of event-related potentials (P300) and electrodermal activity (EDA). Before and after intervention, psychopathological status was assessed using the Positive and Negative Syndrome Scale (PANSS) and the Altered State of Consciousness (5D-ASC) Rating Scale. P300 amplitude and corresponding BOLD responses were diminished in the ketamine condition in cortical regions being involved in sensory processing/selective attention. In both measurement modalities separation of drug conditions was achieved with area under the curve (AUC) values of up to 0.8-0.9. Ketamine effects were also observed in the clinical, behavioral and peripheral physiological domains (Positive and Negative Syndrome Scale, reaction hit and false alarm rate, electrodermal activity and heart rate) which were in part related to the P300/fMRI measures. The findings from our ketamine experiment are consistent across modalities and directly related to observations in schizophrenia supporting the validity of the model. Our investigation provides the first prototypic example of a pharmacoimaging study using simultaneously acquired fMRI/EEG.

Brain Potentials Dissociate Emotional and Conceptual Cross-Modal Priming of Environmental Sounds

The attentional effects triggered by emotional stimuli in humans have been substantially investigated, but little is known about the impact of affective valence on the processing of meaning. Here, we used a cross-modal priming paradigm involving visually presented adjective-noun dyads and environmental sounds of controlled affective valence to test the contributions of conceptual relatedness and emotional congruence to priming. Participants undergoing event-related potential recording indicated whether target environmental sounds were related in meaning to adjective-noun dyads presented as primes. We tested spontaneous emotional priming by manipulating the congruence between the affective valence of the adjective in the prime and that of the sound. While the N400 was significantly reduced in amplitude by both conceptual relatedness and emotional congruence, there was no interaction between the 2 factors. The same pattern of results was found when participants judged the emotional congruence between environmental sounds and adjective-noun dyads. These results support the hypothesis that conceptual and emotional processes are functionally independent regardless of the specific cognitive focus of the comprehender.

Sensory gating, inhibition control and child intelligence: an event-related potentials study

The current study explored the relationship among sensory gating, inhibition control and human intelligence in two groups of children with different intellectual levels. A Go-Nogo task was adopted to investigate children's behavioral performances in inhibition control processing, and a paired-click paradigm with event-related potentials (ERP) recording was used to explore children's neural activation during sensory gating processing. The behavioral results showed that the intellectually gifted children committed significantly less commission error rate, which indicated that gifted children had better inhibition control than their average peers. The electrophysiological results showed that the gifted group had lower S2P50/S1P50 amplitude ratio than the average group and illustrated that gifted children had stronger sensory gating. The results of correlation analysis between inhibition control performances and sensory gating showed that children with stronger P50 suppression (lower S2/S1 latency ratio) in the fronto-central area and stronger N100 suppression (lower S2/S1 amplitude ratio) in the frontal and fronto-central areas had shorter reaction time in the Go-Nogo task. Moreover, the correlation patterns between sensory gating and inhibition control were different between two groups of children. The present findings further demonstrated the close relationship among sensory gating, inhibition control and human intelligence in children.

ERP evidence for selective drop in attentional costs in uncertain environments: Challenging a purely premotor account of covert orienting of attention

Several studies have proved that the reliability of endogenous spatial cues linearly modulates the reaction time advantage in the processing of targets at validly cued vs. invalidly cued locations, i.e. the “validity effect”. This would imply that with non-predictive cues, no “validity effect” should be observed. However, contrary to this prediction, one could hypothesize that attentional benefits by valid cuing (i.e. the RT advantage for validly vs. neutrally cued targets) can still be maintained with non-predictive cues, if the brain were endowed with mechanisms allowing the selective reduction in costs of reorienting from invalidly cued locations (i.e. the reduction of the RT disadvantage for invalidly vs. neutrally cued targets). This separated modulation of attentional benefits and costs would be adaptive in uncertain contexts where cues predict at chance level the location of targets. Through the joint recording of manual reaction times and event-related cerebral potentials (ERPs), we have found that this is the case and that relying on non-predictive endogenous cues results in abatement of attentional costs and the difference in the amplitude of the P1 brain responses evoked by invalidly vs. neutrally cued targets. In contrast, the use of non-predictive cues leaves unaffected attentional benefits and the difference in the amplitude of the N1 responses evoked by validly vs. neutrally cued targets. At the individual level, the drop in costs with non-predictive cues was matched with equivalent lateral biases in RTs to neutrally and invalidly cued targets presented in the left and right visual field. During the cue period, the drop in costs with non-predictive cues was preceded by reduction of the Early Directing Attention Negativity (EDAN) on posterior occipital sites and by enhancement of the frontal Anterior Directing Attention Negativity (ADAN) correlated to preparatory voluntary orienting. These findings demonstrate, for the first time, that the segregation of mechanisms regulating attentional benefits and costs helps efficiency of orienting in “uncertain” visual spatial contexts characterized by poor probabilistic association between cues and targets.

Probing consciousness with event-related potentials in the vegetative state

Probing consciousness in noncommunicating patients is a major medical and neuroscientific challenge. While standardized and expert behavioral assessment of patients constitutes a mandatory step, this clinical evaluation stage is often difficult and doubtful, and calls for complementary measures which may overcome its inherent limitations. Several functional brain imaging methods are currently being developed within this perspective, including fMRI and cognitive event-related potentials (ERPs). We recently designed an original rule extraction ERP test that is positive only in subjects who are conscious of the long-term regularity of auditory stimuli. In the present work, we report the results of this test in a population of 22 patients who met clinical criteria for vegetative state. We identified 2 patients showing this neural signature of consciousness. Interestingly, these 2 patients showed unequivocal clinical signs of consciousness within the 3 to 4 days following ERP recording. Taken together, these results strengthen the relevance of bedside neurophysiological tools to improve diagnosis of consciousness in noncommunicating patients.

Impaired preparatory re-mapping of stimulus–response associations and rule-implementation in schizophrenic patients—The role for differences in early processing

An accurate representation of task-set information is needed for successful goal directed behavior. Recent studies point to disturbances in the early processing stages as plausible causes for task-switching deficits in schizophrenia. A task-cueing protocol was administered to a group of schizophrenic patients and compared with a sample of age-matched healthy controls. Patients responded slower and less accurate compared with controls in all conditions. The concurrent recording of event-related brain potentials to contextual cues and target events revealed abnormalities in the early processing of both cue-locked and target-locked N1 potentials. Abnormally enhanced target-locked P2 amplitudes were observed in schizophrenic patients for task-switch trials only, suggesting disrupted stimulus evaluation and memory retrieval processes. The endogenous P3 potentials discriminated between task conditions but without further differences between groups. These results suggest that the observed impairments in task-switching behavior were not specifically related to anticipatory set-shifting, but derived from a deficit in the implementation of task-set representations at target onset in the presence of irrelevant and conflicting information.

Spatiotemporal brain mapping of spatial attention effects on pattern‐reversal ERPs

Recordings of event-related potentials (ERPs) were combined with structural and functional magnetic resonance imaging (fMRI) to investigate the timing and localization of stimulus selection processes during visual-spatial attention to pattern-reversing gratings. Pattern reversals were presented in random order to the left and right visual fields at a rapid rate, while subjects attended to the reversals in one field at a time. On separate runs, stimuli were presented in the upper and lower visual quadrants. The earliest ERP component (C1, peaking at around 80 ms), which inverted in polarity for upper versus lower field stimuli and was localized in or near visual area V1, was not modulated by attention. In the latency range 80-250 ms, multiple components were elicited that were increased in amplitude by attention and were colocalized with fMRI activations in specific visual cortical areas. The principal anatomical sources of these attention-sensitive components were localized by fMRI-seeded dipole modeling as follows: P1 (ca. 100 ms-source in motion-sensitive area MT+), C2 (ca. 130 ms-same source as C1), N1a (ca. 145 ms-source in horizontal intraparietal sulcus), N1b (ca. 165 ms-source in fusiform gyrus, area V4/V8), N1c (ca. 180 ms-source in posterior intraparietal sulcus, area V3A), and P2 (ca. 220 ms-multiple sources, including parieto-occipital sulcus, area V6). These results support the hypothesis that spatial attention acts to amplify both feed-forward and feedback signals in multiple visual areas of both the dorsal and ventral streams of processing.

A Longitudinal Twin Study of Effects of Adolescent Alcohol Abuse on the Neurophysiology of Attention and Orienting

Long-term functional brain effects of adolescent alcohol abuse remain uncertain, partially because of difficulties in distinguishing inherited deficits from neuronal effects of ethanol and by confounds associated with alcohol abuse, especially nicotine exposure. We conducted a longitudinal twin study to determine neurocognitive effects of adolescent alcohol abuse, as measured with the auditory event-related potential (ERP) component P3, a putative marker of genetic vulnerability to alcoholism. Twin pairs (N=177; 150 selected for intrapair concordance/discordance for alcohol-related problems at age 18½) were recruited from ongoing studies of twins born 1975-1979 in Finland. Alcohol and tobacco use were assessed with questionnaires at ages 16, 17, 18½, and ~25, and by a structured psychiatric interview concurrent with the ERP testing at mean age 25.8. During ERP recordings, subjects were instructed to detect target tones within a train of frequent "standards" and to ignore occasional "novel" sounds. To distinguish familial factors from ethanol effects, ERP and self-reported alcohol use measures were incorporated into hierarchical multiple regression (HMR) analysis, and intrapair differences in ERP were associated with intra-pair differences in alcohol variables. Novel-sound P3 amplitude correlated negatively with self-reported alcohol use in both between- and within-family analyses. No similar effect was observed for target-tone P3. HMR results suggest that twins' similarity for novel-sound P3 amplitude is modulated by their alcohol use, and this effect of alcohol use is influenced by genetic factors. Our results, from a large sample of twins selected from a population-based registry for pairwise concordance/discordance for alcohol problems at 18½, demonstrate that adolescent alcohol abuse is associated with subtle neurophysiological changes in attention and orienting. The changes are reflected in decreased novel-sound P3 amplitude and may be modified by genetic factors.

P300 auditory event-related potentials in children with obesity: is childhood obesity related to impairment in cognitive functions?

To investigate alterations in P300 auditory event-related potentials in children with obesity to detect changes in cognitive functions. A total of 50 children with obesity and 23 age- and sex-matched healthy control subjects were included in the study. Laboratory tests were performed to detect dislipidemia and insulin resistance (IR). The latencies and amplitudes of P300 waves were measured in healthy and obese subjects with or without IR. The oddball paradigm was used in recordings of P300 auditory event-related potentials. A significant difference was observed between groups regarding latency and amplitude of P300 component obtained from central (Cz) electrode. The grand means of P300 latency were longer, and amplitude decreased significantly in obese group compared to that of healthy controls. When the obese group was divided into two different subgroups, those with IR and without IR, the grand means of P300 latency were longer and the amplitude decreased significantly in subjects with IR compared to those without IR. Both decreased amplitude and prolonged latency of P300 are associated with IR in children with obesity, which shows the impairment of neural activity associated with sensory and cognitive information processing in these children. Further studies are necessary to strengthen the current findings and to determine the exact mechanism of cognitive impairment in obese children.

Impaired engagement of the ventral attentional pathway in ADHD

In the cognitive theories of Attention Deficit Hyperactivity Disorder (ADHD) impaired behavioral adjustment has been linked to a deficit in learning to detect regularities or irregularities in the environment. In the neural level, the P3 component of event-related potential (ERP) is modulated by stimulus probability and has been suggested to index activation of the ventral attention network, which constitutes the reorienting system of the human brain. To explore the cortical basis of late positive ERP components and the engagement of the ventral attentional pathway in ADHD, we used ERP recordings complemented by spatiotemporally sensitive magnetoencephalography (MEG) measurements. We followed the activation evoked by frequent Go and infrequent NoGo stimuli in 10 ADHD adults and 13 control subjects. In the ERP recordings, a prominent positive deflection was detected after the infrequent visual stimuli (late positive component, LPC) in both subject groups. In ADHD adults the difference between the responses evoked by infrequent NoGo and frequent Go stimuli was markedly reduced compared to the control group during the LPC. The MEG recordings revealed that the activation detected during the LPC was localized bilaterally in the posterior temporal cortex. Activation of the left and right temporal regions was enhanced after infrequent NoGo stimuli in both subject groups. In ADHD adults, however, the effect of stimulus frequency was less pronounced. We suggest that the activation in the superior temporal cortices during the LPC reflects the action of ventral attention network. The engagement of this stimulus-driven reorienting system is defective in ADHD.

ERP evidence of a meaningfulness impact on visual global/local processing: When meaning captures attention

Event-related potentials (ERPs) were recorded to investigate whether the meaningfulness of experimental stimuli impacted performances during global/local visual tasks. Participants were presented with compound stimuli, based on either meaningful letters, meaningful objects, or meaningless non-objects. The ERP recordings displayed typical early components, P1 and N1, evoked by task-related processes that affected global and local processes differently according to the meaningfulness of the stimuli. The effect of meaningfulness of the stimuli during global processing showed that P1 amplitudes were larger in response to objects and non-objects compared to letters, while letters and objects elicited larger N1 amplitudes than non-objects. Second, during local processing, the mean amplitudes of the ERPs recorded for object and letter stimuli were systematically smaller than the amplitudes recorded for non-object stimuli for both P1 and N1 components. In addition, object and letter stimuli elicited comparable mean ERP responses during local processing. These results are discussed in terms of the influences of both attentional and top–down identification processes. Taken together, these findings suggested that looking for meaning is crucial in the perception of visual scenes and that the meaningfulness nature of the stimuli should be taken into account in future studies.

Classification of Error-Related Negativity (ERN) and Positivity (Pe) potentials using kNN and Support Vector Machines

Error processing in subjects performing actions has been associated with the Event-Related Potential (ERP) components called Error-Related Negativity (ERN) and Error Positivity (Pe). In this paper, features based on statistical measures of the sample of averaged ERP recordings are used for classifying correct from incorrect actions. Three feature selection techniques were used and compared. Classification was done by means of a kNN and a Support Vector Machines (SVM) classifier. The use of a leave-one-out approach in the feature selection provided sensitivity and specificity values concurrently higher than or equal to 87.5%, for both classifiers. The classification results were significantly better for the time window that included only the ERN, as compared to time windows including also Pe.