Infrequent Stimuli Research Articles

Neural substrates of normal and impaired preattentive sensory discrimination in large cohorts of nonpsychiatric subjects and schizophrenia patients as indexed by MMN and P3a change detection responses

Schizophrenia (SZ) patients have information processing deficits, spanning from low level sensory processing to higher-order cognitive functions. Mismatch negativity (MMN) and P3a are event-related potential (ERP) components that are automatically elicited in response to unattended changes in ongoing, repetitive stimuli that provide a window into abnormal information processing in SZ. MMN and P3a are among the most robust and consistently identified deficits in SZ, yet the neural substrates of these responses and their associated deficits in SZ are not fully understood. This study examined the neural sources of MMN and P3a components in a large cohort of SZ and nonpsychiatric control subjects (NCS) using Exact Low Resolution Electromagnetic Tomography Analyses (eLORETA) in order to identify the neural sources of MMN and P3a as well as the brain regions associated with deficits commonly observed among SZ patients. 410 SZ and 247 NCS underwent EEG testing using a duration-deviant auditory oddball paradigm (1-kHz tones, 500ms SOA; standard p=0.90, 50-ms duration; deviant tones P=0.10, 100-ms duration) while passively watching a silent video. Voxel-by-voxel within- (MMN vs. P3a) and between-group (SZ vs. NCS) comparisons were performed using eLORETA. SZ had robust deficits in MMN and P3a responses measured at scalp electrodes consistent with other studies. These components mapped onto neural sources broadly distributed across temporal, frontal, and parietal regions. MMN deficits in SZ were associated with reduced activations in discrete medial frontal brain regions, including the anterior-posterior cingulate and medial frontal gyri. These early sensory discriminatory MMN impairments were followed by P3a deficits associated with widespread reductions in the activation of attentional networks (frontal, temporal, parietal regions), reflecting impaired orienting or shifts of attention to the infrequent stimuli. MMN and P3a are dissociable responses associated with broadly distributed patterns of neural activation. MMN deficits among SZ patients appear to be primarily accounted for by reductions in medial prefrontal brain regions that are followed by widespread dysfunction across cortical networks associated with P3a in a manner that is consistent with hierarchical information processing models of cognitive deficits in SZ patients. Impairments in automatic stimulus discrimination may contribute to higher-order cognitive and psychosocial deficits in SZ.

Event-related potentials for 7-month-olds’ processing of animals and furniture items

Event-related potentials (ERPs) to single visual stimuli were recorded in 7-month-old infants. In a three-stimulus oddball paradigm, infants watched one frequently occurring standard stimulus (either an animal or a furniture item) and two infrequently occurring oddball stimuli, presenting one exemplar from the same and one from the different superordinate category as compared to the standard stimulus. Additionally, visual attributes of the stimuli were controlled to investigate whether infants focus on category membership or on perceptual similarity when processing the stimuli. Infant ERPs indicated encoding of the standard stimulus and discriminating it from the two oddball stimuli by larger Nc peak amplitude and late-slow-wave activity for the infrequent stimuli. Moreover, larger Nc latency and positive-slow-wave activity indicated increased processing for the different-category as compared to the same-category oddball. Thus, 7-month-olds seem to encode single stimuli not only by surface perceptual features, but they also regard information of category membership, leading to facilitated processing of the oddball that belongs to the same domain as the standard stimulus.

Methylphenidate Effects on Prefrontal Functioning During Attentional-Capture and Response Inhibition

Methylphenidate improves motor response inhibition, typically assessed with the stop-signal task. The exact underlying mechanism for this, however, remains unknown. In addition, recent studies highlight that stop signals can have a confounding attentional-capture effect because of their low frequency in the task. In the current study, we assessed the effects of methylphenidate on neural networks of inhibitory control and attentional-capture within the context of two inhibitory control tasks. The effects of methylphenidate (40 mg) were assessed using functional magnetic resonance imaging in 16 healthy volunteers in a within-subject, double-blind, placebo-controlled design. Methylphenidate significantly reduced activation of different regions within the right inferior frontal gyrus/insula to infrequent stimuli associated with successful inhibition, failed inhibition, and attentional capture. These inferior frontal gyrus regions showed different interregional connections with inhibitory and attention networks. For failed inhibitions, methylphenidate increased activation within performance-monitoring regions, including the superior frontal, anterior cingulate, and parietal-occipital cortices, but only after controlling for attentional capture. Our findings suggest that the improvement of response inhibition seen following methylphenidate administration is due to its influence on underlying attentional mechanisms linked to response control requirements.

Induction of Psychosis byΔ9-Tetrahydrocannabinol Reflects Modulation of Prefrontal and Striatal Function During Attentional Salience Processing

The aberrant processing of salience is thought to be a fundamental factor underlying psychosis. Cannabis can induce acute psychotic symptoms, and its chronic use may increase the risk of schizophrenia. We investigated whether its psychotic effects are mediated through an influence on attentional salience processing. To examine the effects of Δ9-tetrahydrocannabinol (Δ9-THC) and cannabidiol (CBD) on regional brain function during salience processing. Volunteers were studied using event-related functional magnetic resonance imaging on 3 occasions after administration of Δ9-THC, CBD, or placebo while performing a visual oddball detection paradigm that involved allocation of attention to infrequent (oddball) stimuli within a string of frequent (standard) stimuli. University center. Fifteen healthy men with minimal previous cannabis use. Symptom ratings, task performance, and regional brain activation. During the processing of oddball stimuli, relative to placebo, Δ9-THC attenuated activation in the right caudate but augmented it in the right prefrontal cortex. Δ9-Tetrahydrocannabinol also reduced the response latency to standard relative to oddball stimuli. The effect of Δ9-THC in the right caudate was negatively correlated with the severity of the psychotic symptoms it induced and its effect on response latency. The effects of CBD on task-related activation were in the opposite direction of those of Δ9-THC; relative to placebo, CBD augmented left caudate and hippocampal activation but attenuated right prefrontal activation. Δ9-Tetrahydrocannabinol and CBD differentially modulate prefrontal, striatal, and hippocampal function during attentional salience processing. These effects may contribute to the effects of cannabis on psychotic symptoms and on the risk of psychotic disorders.

Does the visual mismatch negativity (vMMN) care about eye-of-origin information?

Event Abstract Back to Event Does the visual mismatch negativity (vMMN) care about eye-of-origin information? Bradley N. Jack1*, Urte Roeber2, 3, 4 and Robert P. O'Shea1 1 Southern Cross University, Discipline of Psychology and Cognitive Neuroscience Research Cluster, School of Health and Human Sciences, Australia 2 University of Leipzig, Institute for Psychology, Germany 3 University of Sydney, Discipline of Biomedical Science, Australia 4 Southern Cross University, Discipline of Psychology, School of Health and Human Sciences, Australia When the eyes are simultaneously presented with dissimilar images, the images alternate in visual perception—binocular rivalry—and an observer cannot tell which image is presented to his or her left or right eye—failure of utrocular discrimination. We wondered if infrequently swapping binocular rivalry stimuli between the eyes would yield the visual mismatch negativity (vMMN)—a negative component of the event-related potential (ERP) technique. The vMMN usually occurs about 150-250 ms after the presentation of an infrequent stimulus (a “deviant”) embedded in a sequence of frequent stimuli (a “standard”). We presented 80% of binocular rivalry standards—one grating to one eye and an orthogonal grating to the other, and 20% of deviants—either by swapping the gratings between the eyes or by rotating the gratings by 45°. We measured ERPs to a 180° phase shift of both gratings (along with the change to the deviant set) every 500 ms. Sixteen participants pressed buttons to record their experiences of binocular rivalry. We made two key findings. First, there was no difference between the standard and the eye-swap deviant in the vMMN range, suggesting that the vMMN does not care about eye-of-origin information. Second, there was a bigger P1, an ERP component between 80-100 ms after onset of the event, for the standard than for either deviant. The P1 reflects sensory and perceptual processing; in this case we suspect it is because of the 180° phase shift of stimuli. We conclude that the vMMN does not care about eye-of-origin information. Keywords: Binocular Rivalry, visual mismatch negativity (vMMN), event-related potential (ERP), Utrocular Discrimination, Visual perception in humans Conference: ACNS-2012 Australasian Cognitive Neuroscience Conference, Brisbane, Australia, 29 Nov - 2 Dec, 2012. Presentation Type: Poster Presentation Topic: Sensation and Perception Citation: Jack BN, Roeber U and O'Shea RP (2012). Does the visual mismatch negativity (vMMN) care about eye-of-origin information?. Conference Abstract: ACNS-2012 Australasian Cognitive Neuroscience Conference. doi: 10.3389/conf.fnhum.2012.208.00152 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 13 Oct 2012; Published Online: 17 Nov 2012. * Correspondence: Mr. Bradley N Jack, Southern Cross University, Discipline of Psychology and Cognitive Neuroscience Research Cluster, School of Health and Human Sciences, Coffs Harbour, Australia, bradley.jack@scu.edu.au Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Bradley N Jack Urte Roeber Robert P O'Shea Google Bradley N Jack Urte Roeber Robert P O'Shea Google Scholar Bradley N Jack Urte Roeber Robert P O'Shea PubMed Bradley N Jack Urte Roeber Robert P O'Shea Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

The enhanced processing of visual novel events in females: ERP correlates from two modified three-stimulus oddball tasks

The ability to detect and cope with unpredictable novel events is fundamental for adapting to a rapidly changing environment and ensuring the survival of the organism. Despite knowledge of gender differences in emotional processing, little is currently known about the impact of gender on neural processing of emotion-irrelevant, novel stimuli. Using two modified three-stimulus oddball tasks and event-related potentials (ERPs), the present study investigated the impact of sex on brain processing of novel events and the associated neurophysiological correlates. With novel and non-novel control stimuli used as task-irrelevant distracters, Experiment 1 showed higher novelty rating scores and larger size of novelty effects in brain potentials at 200–300ms and 300–430ms time intervals in females compared to males. After excluding the contribution of stimulus probability, Experiment 2 continued to display significant novelty effects in the response times and the amplitudes of the 130–500ms time windows. Most importantly, females displayed a sustained novelty effect in the late positive component (LPC) amplitudes of the 500–600ms interval, which was not observed in males. Therefore, Experiment 1 and 2 demonstrated that females are equipped with enhanced brain processing of emotion-irrelevant, novel stimuli. This phenomenon is independent of the established gender difference in infrequent stimulus processing. We suggest that our findings reflect the differential adaptive demands on females and males during evolution.

Roles of the medial frontal cortices in the selection, storage and retrieval of response tactics in a voluntary arm-reaching task

Response inhibition and salience detection are among the most studied psychological constructs of cognitive control. Despite a growing body of work, how inhibition and salience processing interact and engage regional brain activations remains unclear. Here, we examined this issue in a stop signal task (SST), where a prepotent response needs to be inhibited to allow an alternative, less dominant response. Sixteen adult individuals performed two versions of the SST each with 25% (SST25) and 75% (SST75) of stop trials. We posited that greater regional activations to the infrequent trial type in each condition (i.e., to stop as compared to go trials in SST25 and to go as compared to stop trials in SST75) support salience detection. Further, successful inhibition in stop trials requires attention to the stop signal to trigger motor inhibition, and the stop signal reaction time (SSRT) has been used to index the efficiency of motor response inhibition. Therefore, greater regional activations to stop as compared to go success trials in association with the stop signal reaction time (SSRT) serve to expedite response inhibition. In support of an interactive role, the dorsal anterior cingulate cortex (dACC) increases activation to salience detection in both SST25 and SST75, but only mediates response inhibition in SST75. Thus, infrequency response in the dACC supports motor inhibition only when stopping has become a routine. In contrast, although the evidence is less robust, the pre-supplementary motor area (pre-SMA) increases activity to the infrequent stimulus and supports inhibition in both SST25 and SST75. These findings clarify a unique role of the dACC and add to the literature that distinguishes dACC and pre-SMA functions in cognitive control.

Visual Attention Study in Youth With Spastic Cerebral Palsy Using the Event-Related Potential Method

Youth with mild spastic cerebral palsy (n = 14) and a peer control group were compared on an oddball paradigm. Here, visual stimuli were presented with low and high probability and participants were instructed to count in silence the number of rare stimuli. The infrequent stimulus typically elicits an enhanced frontal central N2 and a centroparietal P300 event-related brain potential, reflecting orientation and evaluation of stimulus novelty. No differences in latency and amplitude of the N2-P300 complex were found between the 2 groups, indicating that some fundamental attention processes are intact in youth with mild spastic cerebral palsy.

Electrical neuroimaging of early sensory processing in first-episode psychosis

Event Abstract Back to Event Electrical neuroimaging of early sensory processing in first-episode psychosis Jean-François Knebel1*, Lucas Spierer1, Philippe Baumann1, Carina Ferrari1, Andrea Polari1, Tanja Teichmann1, Kim Q. Do1, Philippe Conus1 and Micah M. Murray1 1 CHUV/UNIL, Switzerland Low-level, early auditory and visual impairments have been documented in patients with schizophrenia and their first-degree relatives. More recently, such findings have been extended to first-episode psychotics. At present, it remains under-determined the precise mechanism leading to these impairments, including but not limited to whether any impairments reflect general sensory processing deficits or specific functional deficits in processing particular stimulus properties, as well as whether impairments in one sensory modality are co-occur with those in another sensory modality. We performed electrical neuroimaging analyses of event-related potentials recorded from 16 (all males; 13 right-handed) first-episode psychosis patients and 14 (10 males; 12 right-handed) age-matched controls. The visual task entailed the presentation of Kanizsa-type illusory contour stimuli, allowing for the parallel investigation of impairments in visual sensory processing and completion processes. The auditory task entailed an oddball paradigm. The frequent stimulus (70% of trials) was a 1000Hz centrally-presented sound of 100ms duration. The infrequent stimuli (10% of trials each) varied in pitch (1200Hz), perceived lateralization (700µs), or duration (150ms) Remaining parameters matched the frequent stimulus. While we were able to replicate prior findings of impaired early visual responses in first-episode patients using analyses of individual scalp electrodes, this was not evident in analyses of global features of the electric field. By contrast, there was evidence for sensory and functional auditory processing impairments at all levels of analysis. We discuss our findings in the context of attempts to establish biomarkers of psychosis. Funding: NCCR “SYNAPSY”-National Science Foundation (n° 51AU40_125759)- the SNF (to MMM)-the Leenaards Foundation-the Loterie Romande. Keywords: Auditory and visual impairments, Perception Conference: XI International Conference on Cognitive Neuroscience (ICON XI), Palma, Mallorca, Spain, 25 Sep - 29 Sep, 2011. Presentation Type: Poster Presentation Topic: Poster Sessions: Neurophysiology of Sensation and Perception Citation: Knebel J, Spierer L, Baumann P, Ferrari C, Polari A, Teichmann T, Do KQ, Conus P and Murray MM (2011). Electrical neuroimaging of early sensory processing in first-episode psychosis. Conference Abstract: XI International Conference on Cognitive Neuroscience (ICON XI). doi: 10.3389/conf.fnhum.2011.207.00478 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 25 Nov 2011; Published Online: 28 Nov 2011. * Correspondence: Dr. Jean-François Knebel, CHUV/UNIL, Lausanne, Switzerland, jean-francois.knebel@chuv.ch Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Jean-François Knebel Lucas Spierer Philippe Baumann Carina Ferrari Andrea Polari Tanja Teichmann Kim Q Do Philippe Conus Micah M Murray Google Jean-François Knebel Lucas Spierer Philippe Baumann Carina Ferrari Andrea Polari Tanja Teichmann Kim Q Do Philippe Conus Micah M Murray Google Scholar Jean-François Knebel Lucas Spierer Philippe Baumann Carina Ferrari Andrea Polari Tanja Teichmann Kim Q Do Philippe Conus Micah M Murray PubMed Jean-François Knebel Lucas Spierer Philippe Baumann Carina Ferrari Andrea Polari Tanja Teichmann Kim Q Do Philippe Conus Micah M Murray Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

The role of complexity of the infrequently presented irrelevant stimuli in orientation

Event Abstract Back to Event The role of complexity of the infrequently presented irrelevant stimuli in orientation I. Barkaszi1, 2*, I. Czigler1 and L. Balázs1 1 Hungarian Academy of Sciences, Institute for Psychology, Hungary 2 Debrecen University, Institute of Psychology, Hungary The orienting response is an involuntary shift of attention to new, unexpected or unpredictable stimuli, enabling the event to enter the consciousness. If the event is deemed significant, this could lead to appropriate behavioral action. The neurocognitive changes induced by the orienting response enable the organism to respond appropriately to a variety of familiar or unfamiliar environmental events. The brain electrical activity correlates of this response is a component (P3a) elicited by task irrelevant stimuli that is of maximum amplitude over the frontal/central areas with a peak latency of 300‑400 ms. This component is typically obtained in response to task irrelevant stimuli. In our experiments participants were asked to perform auditory and visual discrimination tasks. All subjects were given 3 task conditions in each modality. In the conditions 1. and 2. the tasks consisted of simple standards (80%) and targets (10%) and the task irrelevant stimuli were more complex. In condition 1. complex stimuli were similar, however in condition 2. they were different each time. In contrast in condition 3. the standards and targets were more complex and the task irrelevant infrequent stimuli were similar and more simple.The irrelevant infrequent stimuli elicited P3a component in the 1. and 2. but not in the 3. conditions.Our results show that the infrequency and the irrelevance is not enough to elicit orienting response per se, there is a significant role of complexity. Keywords: Sensory and motor activity, Neuroscience Conference: 13th Conference of the Hungarian Neuroscience Society (MITT), Budapest, Hungary, 20 Jan - 22 Jan, 2011. Presentation Type: Abstract Topic: Sensory and motor activity Citation: Barkaszi I, Czigler I and Balázs L (2011). The role of complexity of the infrequently presented irrelevant stimuli in orientation. Front. Neurosci. Conference Abstract: 13th Conference of the Hungarian Neuroscience Society (MITT). doi: 10.3389/conf.fnins.2011.84.00092 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 03 Mar 2011; Published Online: 23 Mar 2011. * Correspondence: Dr. I. Barkaszi, Hungarian Academy of Sciences, Institute for Psychology, Budapest, Hungary, barkaszi.iren@ttk.mta.hu Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers I. Barkaszi I. Czigler L. Balázs Google I. Barkaszi I. Czigler L. Balázs Google Scholar I. Barkaszi I. Czigler L. Balázs PubMed I. Barkaszi I. Czigler L. Balázs Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Cortical dynamics of the visual change detection process

In this study, the cortical dynamics of the visual change detection process were investigated using an oddball paradigm similar to that used in auditory mismatch negativity studies. When subjects watched a silent movie, color stimuli were presented using 280 dual color LEDs arranged along the frame of the video screen. Task-irrelevant red and blue color stimuli were presented randomly at a probability of 10% and 90%, respectively, in one session and vice versa for the other one, and we traced brain responses using magnetoencephalography. Results show that activation in the middle occipital gyrus (MOG) was significantly enhanced for the infrequent stimulus, while early activities in Brodmann's area 17/18 were comparable for the frequent and infrequent stimuli. These results suggest that automatic visual change detection is associated with the MOG activity.

Event-related brain potentials reveal the time-course of language change detection in early bilinguals

Using event-related brain potentials, we investigated the temporal course of language change detection in proficient bilinguals as compared to matched controls. Welsh–English bilingual participants and English controls were presented with a variant of the oddball paradigm involving picture-word pairs. The language of the spoken word was manipulated such that English was the frequent stimulus (75%) and Welsh the infrequent stimulus (25%). We also manipulated semantic relatedness between pictures and words, such that only half of the pictures were followed by a word that corresponded with the identity of the picture. The P2 wave was significantly modulated by language in the bilingual group only, suggesting that this group detected a language change as early as 200 ms after word onset. Monolinguals also reliably detected the language change, but at a later stage of semantic integration (N400 range), since Welsh words were perceived as meaningless. The early detection of a language change in bilinguals triggered stimulus re-evaluation mechanisms reflected by a significant P600 modulation by Welsh words. Furthermore, compared to English unrelated words, English words matching the picture identity elicited significantly greater P2 amplitudes in the bilingual group only, suggesting that proficient bilinguals validate an incoming word against their expectation based on the context. Overall, highly proficient bilinguals appear to detect language changes very early on during speech perception and to consciously monitor language changes when they occur.

Electrophysiological evidence for effects of color knowledge in object recognition

Knowledge about the typical colors associated with familiar everyday objects (i.e., strawberries are red) is well-known to be represented in the conceptual semantic system. Evidence that such knowledge may also play a role in early perceptual processes for object recognition is scant. In the present ERP study, participants viewed a list of object pictures and detected infrequent stimulus repetitions. Results show that shortly after stimulus onset, ERP components indexing early perceptual processes, including N1, P2, and N2, differentiated between objects in their appropriate or congruent color from these objects in an inappropriate or incongruent color. Such congruence effect also occurred in N3 associated with semantic processing of pictures but not in N4 for domain-general semantic processing. Our results demonstrate a clear effect of color knowledge in early object recognition stages and support the following proposal-color as a surface property is stored in a multiple-memory system where pre-semantic perceptual and semantic conceptual representations interact during object recognition.

Automatic change detection during the performance of a continuous visual task

The brain's automatic detection of change within the visual environment can be examined by recording visual mismatch negativity (vMMN), a negative deflection in the visual event-related potential evoked by infrequent deviant stimuli presented within a sequence of common standard stimuli. In this study, we examine whether automatic visual change detection occurs even when the visual cortex is concurrently processing other visual information at the focus of attention. We ensured that attention was strongly engaged upon a highly demanding and continuous central task, while at the same time presenting in the peripheral field a sequence of task-irrelevant standard stimuli interspersed by infrequent deviant stimuli. A significant vMMN was evoked. However, decreasing the rarity of deviation resulted in the abolition of the vMMN response.

ERPs to infrequent auditory stimuli in two- and three-stimulus versions of the inter-modal oddball task

Previous research has shown that auditory targets in inter-modal oddball conditions are processed in two stages, an early modality-specific and a later context-dependent stage. The aim of this study was to investigate how the processing of auditory target stimuli is affected by the inclusion of an additional infrequent auditory non-target stimulus in inter-modal oddball conditions. 17 subjects received 300 stimuli in each of a two- and a three-stimulus version of the inter-modal oddball task. Both tasks included 240 (80%) presentations of a counter-phasing checkerboard randomly interspersed with 60 presentations of an auditory stimulus. In the two-stimulus condition subjects received 60 (20%) target stimuli. In the three-stimulus condition subjects received 30 (10%) target and 30 (10%) non-target stimuli. ERPs to the two target stimuli and ERPs to targets and auditory non-targets in the three-stimulus condition were investigated. Early components N100 and P200 were larger to non-targets than targets. N140, an additional frontal negativity in inter-modal oddball conditions, was larger in the three-stimulus compared with the two-stimulus condition. Targets produced two late positive components (P250/P3a and P300). In the three-stimulus task the P250/P3a was enhanced frontally and P300 was enhanced in right parietal regions. Non-target auditory stimuli produced a broad negativity (N285) at this latency. All stimuli produced a late positivity (P350) that demonstrated task-related topographic differences. The results are interpreted with respect to previous inter-modal oddball findings and research into auditory processing.

Spectrum of neurocognitive impairment in cirrhosis: Implications for the assessment of hepatic encephalopathy

Spectrum of neurocognitive impairment in cirrhosis: Implications for the assessment of hepatic encephalopathy

Infrequent stimuli increase demands on alertness network

Infrequent stimuli increase demands on alertness network

Can illusory deviant stimuli be used as attentional distractors to record vMMN in a passive three stimulus oddball paradigm?

A passive three stimulus oddball paradigm was used to investigate Visual Mismatch Negativity (vMMN) a component of the Event Related Potential (ERP) believed to represent a central pre-attentive change mechanism. Responses to a change in orientation were recorded to monochrome stimuli presented to subjects on a computer screen. One of the infrequent stimuli formed an illusory figure (Kanizsa Square) aimed to capture spatial attention in the absence of an active task. Nineteen electrodes (10-20 system) were used to record the electroencephalogram in fourteen subjects (ten females) mean age 34.5 years. ERPs to all stimuli consisted of a positive negative positive complex recorded maximally over lateral occipital areas. The negative component was greater for deviant and illusory deviant compared to standard stimuli in a time window of 170-190 ms. A P3a component over frontal/central electrodes to the illusory deviant but not to the deviant stimulus suggests the illusory figure was able to capture attention and orientate subjects to the recording. Subtraction waveforms revealed visual discrimination responses at occipital electrodes, which may represent vMMN. In a control study with 13 subjects (11 females; mean age 29.23 years), using an embedded active attention task, we confirmed the existence of an earlier (150-170 ms) and attenuated vMMN. Recordings from an intracranial case study confirmed separation of N1 and discrimination components to posterior and anterior occipital areas, respectively. We conclude that although the illusory figure captured spatial attention in its own right it did not draw sufficient attentional resources from the standard-deviant comparison as revealed when using a concurrent active task.

Frequency-domain analysis of fast oddball responses to visual stimuli: A feasibility study

Event-related potential responses to oddball stimuli, including the P300 component, have been proposed as a diagnostic tool for discerning psychiatric or higher-level neural disorders from malingering, for instance in cases of unexplained visual loss. For clinical use, short recording durations and easy statistical assessment are highly desirable. With this aim, we investigated the feasibility of recording oddball responses in a fast steady-state regime. We used gratings with two possible orientations in a rapid oddball paradigm with an inter-stimulus interval of 214 ms. Six consecutive presentations of one stimulus type (frequent) were followed by a single presentation of the other (infrequent) stimulus type. Subjects were attending to the rare stimulus type. The electroencephalographic recordings were analyzed in the frequency domain. All subjects produced significant harmonic responses related to the processing of the rare stimulus, demonstrating the feasibility of the technique, with the potential of reducing recording times substantially compared to conventional slow stimulation. We furthermore found that the regularity of the occurrence of infrequent stimuli, which is necessary for frequency-domain analysis, does not per se reduce the P300 responses, as would have been expected in the framework of some hypotheses regarding the role of the P300.

Preattentive auditory information processing under exposure to the 902 MHz GSM mobile phone electromagnetic field: A mismatch negativity (MMN) study

Previous studies on the effects of the mobile phone electromagnetic field (EMF) on various event-related potential (ERP) components have yielded inconsistent and even contradictory results, and often failed in replication. The mismatch negativity (MMN) is an auditory ERP component elicited by infrequent (deviant) stimuli differing in some physical features from the repetitive frequent (standard) stimuli in a sound sequence. The MMN provides a sensitive measure for cortical auditory stimulus feature discrimination, regardless of attention and other contaminating factors. In this study, MMN responses to duration, intensity, frequency, and gap changes were recorded in healthy young adults (n = 17), using a multifeature paradigm including several types of auditory change in the same stimulus sequence, while a GSM mobile phone was placed on either ear with the EMF (902 MHz pulsed at 217 Hz; SAR(1g) = 1.14 W/kg, SAR(10g) = 0.82 W/kg, peak value = 1.21 W/kg, measured with an SAM phantom) on or off. An MMN was elicited by all deviant types, while its amplitude and latency showed no significant differences due to EMF exposure for any deviant types. In the present study, we found no conclusive evidence that acute exposure to GSM mobile phone EMF affects cortical auditory change detection processing reflected by the MMN.