Infrequent Stimuli Research Articles

A systematic review of mobile brain/body imaging studies using the P300 event-related potentials to investigate cognition beyond the laboratory.

The P300 ERP component, related to the onset of task-relevant or infrequent stimuli, has been widely used in the Mobile Brain/Body Imaging (MoBI) literature. This systematic review evaluates the quality and breadth of P300 MoBI studies, revealing a maturing field with well-designed research yet grappling with standardization and global representation challenges. While affirming the reliability of measuring P300 ERP components in mobile settings, the review identifies significant hurdles in standardizing data cleaning and processing techniques, impacting comparability and reproducibility. Geographical disparities emerge, with studies predominantly in the Global North and a dearth of research from the Global South, emphasizing the need for broader inclusivity to counter the WEIRD bias in psychology. Collaborative projects and mobile EEG systems showcase the feasibility of reaching diverse populations, which is essential to advance precision psychiatry and to integrate varied data streams. Methodologically, a trend toward ecological validity is noted, shifting from lab-based to real-world settings with portable EEG system advancements. Future hardware developments are expected to balance signal quality and sensor intrusiveness, enriching data collection in everyday contexts. Innovative methodologies reflect a move toward more natural experimental settings, prompting critical questions about the applicability of traditional ERP markers, such as the P300 outside structured paradigms. The review concludes by highlighting the crucial role of integrating mobile technologies, physiological sensors, and machine learning to advance cognitive neuroscience. It advocates for an operational definition of ecological validity to bridge the gap between controlled experiments and the complexity of embodied cognitive experiences, enhancing both theoretical understanding and practical application in study design.

Development of Biomarkers Potentially Sensitive to Early Psychosis Using Mismatch Negativity (MMN) to Complex Pattern Deviations.

Infrequent stimulus deviations from repetitive sequences elicit mismatch negativity (MMN) even passively, making MMN practical for clinical applications. Auditory MMN is typically elicited by a change in one (or more) physical stimulus parameters (eg, pitch, duration). This lower-order simple MMN (sMMN) is impaired in long-term schizophrenia. However, sMMN contains activity from release from stimulus adaptation, clouding its face validity as purely deviance-related. More importantly, it is unreliably reduced in samples of first-episode psychosis, limiting its utility as a biomarker. Complex pattern-deviant MMN (cMMN) tasks, which elicit early and late responses, are based on higher-order abstractions and better isolate deviance detection. Their abstract nature may increase the sensitivity to processing deficits in early psychosis. However, both the early and late cMMNs are small, limiting separation between healthy and psychotic samples. In 29 healthy individuals, we tested a new dual-rule cMMN paradigm to assess additivity of deviance. Sounds alternated lateralization between left and right, and low and high pitches, creating a left-low, right-high alternating pattern. Deviants were a repeated left-low, violating lateralization and pitch patterns. Early and late cMMNs on the dual-rule task were significantly larger than those on the one-rule extra tone cMMN task (P < .05). Further, the dual-rule early cMMN was not significantly smaller than pitch or duration sMMNs (P > .48, .28, respectively). These results demonstrate additivity for cMMN pattern-violating rules. This increase in cMMN amplitude should increase group difference effect size, making it a prime candidate for a biomarker of disease presence at first psychotic episode, and perhaps even prior to the emergence of psychosis.

Influences of temporal and probabilistic expectation on subjective time of emotional stimulus.

Subjective time perception can change based on a stimulus's valence and expectancy. Yet, it is unclear how these two factors might interact to shape our sense of how long something lasts. Here, we conducted two experiments examining the effects of temporal and probabilistic expectancy on the perceived duration of images with varying emotional valence. In Experiment 1, we varied the temporal predictive cue with varying stimulus-onset asynchronies (SOAs), while in Experiment 2, we manipulated the cue-emotion probabilistic associations. Our results revealed that stimuli appearing earlier than anticipated were perceived as shorter, whereas less infrequent stimuli seemed to last longer. In addition, negative images were perceived longer than neural ones. However, no significant interaction between expectancy and stimulus valence was observed. We interpret these using the internal clock model, suggesting that while emotional stimuli primarily affect the pacemaker's rhythm through arousal, expectation steers attention, influencing how we register time's passage.

Somatosensory Mismatch Response in Patients with Cerebral Palsy

Background: Mismatch negativity (MMN), an event-related potential (ERP) component occurring at specific recording sites and latency, is associated with an automatic change detection response, generally elicited using oddball paradigms wherein infrequent stimuli are embedded in repeated, frequent stimuli. To verify the presence of mismatch-related ERP responses to somatosensory stimulation in individuals with cerebral palsy (CP), we conducted a preliminary study involving healthy participants and patients with CP. Methods: Both groups underwent ‘frequent’ and ’infrequent’ stimulation applied to the ring finger and thumb of their left hand, respectively. ERPs were recorded at frontal, central, and parietal scalp locations using electroencephalography. A healthy cohort tested the experimental protocol and showed evidence that mismatch-related ERP responses were observable. Subsequent analysis focused on the patient group. Results: Statistically significant differences between the two types of stimuli were observed on the frontocentral and parietal channels between 150 and 250 ms after the stimulus onset in the patient group. Furthermore, a late discriminative response was observed in the frontal and parietal channels. Conclusion: The results demonstrate the presence of mismatch-related ERP responses in individuals with CP.

ERP evidence of attentional somatosensory processing and stimulus-response coupling under different hand and arm postures.

We investigated (1) the effects of divided and focused attention on event-related brain potentials (ERPs) elicited by somatosensory stimulation under different response modes, (2) the effects of hand position (closely-placed vs. separated hands) and arm posture (crossed vs. uncrossed forearms) on the attentional modulation of somatosensory ERPs, and (3) changes in the coupling of stimulus- and response-related processes by somatosensory attention using a single-trial analysis of P300 latency and reaction times. Electrocutaneous stimulation was presented randomly to the thumb or middle finger of the left or right hand at random interstimulus intervals (700-900 ms). Subjects attended unilaterally or bilaterally to stimuli in order to detect target stimuli by a motor response or counting. The effects of unilaterally-focused attention were also tested under different hand and arm positions. The amplitude of N140 in the divided attention condition was intermediate between unilaterally attended and unattended stimuli in the unilaterally-focused attention condition in both the mental counting and motor response tasks. Attended infrequent (target) stimuli elicited greater P300 in the unilaterally attention condition than in the divided attention condition. P300 latency was longer in the divided attention condition than in the unilaterally-focused attention condition in the motor response task, but remained unchanged in the counting task. Closely locating the hands had no impact, whereas crossing the forearms decreased the attentional enhancement in N140 amplitude. In contrast, these two manipulations uniformly decreased P300 amplitude and increased P300 latency. The correlation between single-trial P300 latency and RT was decreased by crossed forearms, but not by divided attention or closely-placed hands. Therefore, the present results indicate that focused and divided attention differently affected middle latency and late processing, and that hand position and arm posture also differently affected attentional processes and stimulus-response coupling.

Short-term neuronal and synaptic plasticity act in synergy for deviance detection in spiking networks.

Sensory areas of cortex respond more strongly to infrequent stimuli when these violate previously established regularities, a phenomenon known as deviance detection (DD). Previous modeling work has mainly attempted to explain DD on the basis of synaptic plasticity. However, a large fraction of cortical neurons also exhibit firing rate adaptation, an underexplored potential mechanism. Here, we investigate DD in a spiking neuronal network model with two types of short-term plasticity, fast synaptic short-term depression (STD) and slower threshold adaptation (TA). We probe the model with an oddball stimulation paradigm and assess DD by evaluating the network responses. We find that TA is sufficient to elicit DD. It achieves this by habituating neurons near the stimulation site that respond earliest to the frequently presented standard stimulus (local fatigue), which diminishes the response and promotes the recovery (global fatigue) of the wider network. Further, we find a synergy effect between STD and TA, where they interact with each other to achieve greater DD than the sum of their individual effects. We show that this synergy is caused by the local fatigue added by STD, which inhibits the global response to the frequently presented stimulus, allowing greater recovery of TA-mediated global fatigue and making the network more responsive to the deviant stimulus. Finally, we show that the magnitude of DD strongly depends on the timescale of stimulation. We conclude that highly predictable information can be encoded in strong local fatigue, which allows greater global recovery and subsequent heightened sensitivity for DD.

Dissociating attentional capture from action cancellation during the inhibition of bimanual movement.

Inhibiting ongoing responses when environmental demands change is a critical component of motor control. Experimentally, the stop signal task (SST) represents the gold standard response inhibition paradigm. However, an emerging body of evidence suggests that the SST conflates two dissociable sources of inhibition, namely an involuntarily pause associated with attentional capture and the (subsequent) voluntary cancellation of action. The extent to which these processes also occur in other response tasks is unknown. Younger n = 24 (20-35 years) and older n = 23 (60-85 years) adults completed tasks involving rapid unimanual or bimanual responses to visual stimuli. A subset of trials required cancellation of one component of an initial bimanual response (i.e., selective stop task; stop left response, continue right response) or enacting an additional response (e.g., press left button as well as right button). Critically, both tasks involved some infrequent stimuli baring no behavioral imperative (i.e., they had to be ignored). EMG recordings of voluntary responses during stopping tasks revealed bimanual covert responses (muscle activation, which was suppressed before a button press ensued), consistent with a pause process, following both stop and ignore stimuli, before the required response was subsequently enacted. Critically, we also observed the behavioral consequences of a similar involuntary pause in trials where action cancellation was not part of the response set. Notably, the period over which movements were susceptible to response delays from additional stimuli was longer for older adults than younger adults. The findings demonstrate that an involuntary attentional component of inhibition significantly contributes to action cancellation processes.

Enhancing P300-Based Brain-Computer Interfaces with Hybrid Transfer Learning: A Data Alignment and Fine-Tuning Approach

A new approach is introduced to address the subject dependency problem in P300-based brain-computer interfaces (BCI) by using transfer learning. The occurrence of P300, an event-related potential, is primarily associated with changes in natural neuron activity and elicited in response to infrequent stimuli, which can be monitored non-invasively through an electroencephalogram. However, implementing P300-based BCI in real-time requires many training samples and time-consuming calibration, making it challenging to use in practical applications. To tackle these challenges, the proposed approach harnesses the high-level feature extraction capability of a deep neural network, achieved through fine-tuning. To ensure similar distributions of feature extraction data, the approach of aligning data in Euclidean space is employed, which is then applied to a discriminatively restricted Boltzmann machine with a single layer for P300 detection. The performance of the proposed method on the BCI Competition III dataset II and the BCI competition II dataset II, the state-of-the-art dataset, was evaluated and compared with previous studies. The results showed that robust performance could be achieved using a small number of training samples, demonstrating the effectiveness of the transfer learning approach in P300-based BCI applications.

Effects of volatile sesquiterpenes from Japanese cedarwood on visual processing in the human brain: an event-related potential study

Odor environments in living spaces can influence human physiological and psychological states. To elucidate the effect of volatile organic compounds (VOCs) of wood in living spaces on the modulations of cognitive processing, we built two experimental huts to simulate wooden construction living spaces. One hut was made of cedarwood (Cryptomeria japonica), and the other was made of resin. We used cedarwood and resin, because they are often used as construction materials in Japan. In both huts, we measured the participants’ first positivity in the early visual cortex (P1), the third positivity elicited by voluntary attention (P3b), and the automatic occipital negativity to infrequent visual stimuli in event-related potentials (ERPs), while they performed a visual discrimination task. The VOCs in both huts were measured by gas chromatography–mass spectrometry. The concentration of volatile sesquiterpenes was significantly increased in the cedarwood hut. Neither P1 nor P3b was affected by the cedarwood hut. Compared to the resin hut, we observed significantly larger occipital negativities to the infrequent stimuli in the cedarwood hut in the time windows of 280–300 ms at the mid-occipital region. These findings suggest that the increased concentration of volatile sesquiterpenes emitted from cedarwood facilitates the human brain’s response to changes in visual stimuli.

The relationship between multisensory associative learning and multisensory integration

Integrating sensory information from multiple modalities leads to more precise and efficient perception and behaviour. The process of determining which sensory information should be perceptually bound is reliant on both low-level stimulus features, as well as multisensory associations learned throughout development based on the statistics of our environment. Here, we explored the relationship between multisensory associative learning and multisensory integration using encephalography (EEG) and behavioural measures. Sixty-one participants completed a three-phase study. First, participants were exposed to novel audiovisual shape-tone pairings with frequent and infrequent stimulus pairings and completed a target detection task. EEG recordings of the mismatch negativity (MMN) and P3 were calculated as neural indices of multisensory associative learning. Next, the same learned stimulus pairs were presented in audiovisual as well as unisensory auditory and visual modalities while both early (<100 ms) and late neural indices of multisensory integration were recorded. Finally, participants completed an analogous behavioural speeded-response task, with behavioural indices of multisensory gain calculated using the Race Model. Significant relationships were found in fronto-central and occipital areas between neural measures of associative learning and both early and late indices of multisensory integration in frontal and centro-parietal areas, respectively. Participants who showed stronger indices of associative learning also exhibited stronger indices of multisensory integration of the stimuli they learned to associate. Furthermore, a significant relationship was found between neural index of early multisensory integration and behavioural indices of multisensory gain. These results provide insight into the neural underpinnings of how higher-order processes such as associative learning guide multisensory integration.

The Effect of a Short Mindfulness Meditation on Somatosensory Attention

ObjectivesMindfulness training has been theorised to have beneficial effects on mental health through initially changes in attention mechanisms. The aim of the present study was to assess the impact of a short mindfulness meditation on the P300 event-related potential (ERP), a neural marker of attention, in meditation-naïve participants.MethodsAs mindfulness practice is based on monitoring bodily sensations and breathing, we applied somatosensory stimuli to investigate attention changes. We employed an oddball paradigm with frequent tactile stimuli delivered to the tip of the index finger and infrequent stimuli to the base of the index and the little finger of the right hand to elicit the somatosensory P300. Forty-six participants counted the infrequent stimuli in two separate sessions before and after a 10-min guided meditation, or a control audio clip. We also measured participants’ trait mindfulness (FFMQ) and anxiety (STAI-T) to ensure similar levels in the meditation and control group prior to the intervention.ResultsIn line with previous research, we show decreased somatosensory P300 amplitudes to infrequent tactile target stimuli after compared to before the audio clip in the control group. Such a decrease in P300 amplitudes was not present in the mindfulness meditation group as confirmed in a significant group by time interaction.ConclusionsEven a short mindfulness meditation leads to preservation of attention resources in meditation-naïve participants. The preservation (or lack of habituation) of the amplitude of the somatosensory P300 across repeated presentations may reflect the underlying, early neural mechanism by which mindfulness meditation training modulates executive attention.Trial RegistrationOpen Science Framework: https://osf.io/pkxm3.

Emotional Reactivity and Inhibitory Control in Nonsuicidal Self-Injury Adolescence: Divergence Between Positive and Negative Emotions.

Nonsuicidal self-injury (NSSI) is prevalent in adolescents and is often linked to emotion dysregulation. However, it remains unknown which specific processes of emotion regulation and under what emotional context these processes are related to the risk for NSSI in samples of community-based adolescents. This study used two laboratory tasks to examine whether adolescents with a history of NSSI displayed difficulties in emotional reactivity and inhibitory control in response to negative and positive emotions. In Study 1, adolescents with/without a history of NSSI (N = 64; MAge = 13.45 ± 0.50; 53% female) completed a picture perception task in which they were asked to judge the valence and arousal of images. In Study 2, adolescents with/without a history of NSSI (N = 74; MAge = 13.49 ± 0.80; 50% female) were given a two-choice emotional oddball task that required them to differentially respond to frequent stimuli (images of an object) and infrequent stimuli (affective images). The results showed that adolescents with a history of NSSI showed decreased emotional sensitivity and lower levels of inhibitory control in response to images depicting negative emotional content but not to those depicting positive emotional content. Furthermore, affective inhibitory control problems were significantly positively related to the severity of NSSI, especially in the context of negative emotions. These findings suggest that there is a divergence between positive and negative emotions in both emotional reactivity and affective inhibitory control processes on NSSI. Specifically, relative to adolescents with no history of NSSI, adolescents with a history of NSSI showed lower emotional awareness and behavioral inhibitory control when processing negative emotions, but these distinctions were not found in contexts involving positive emotions. Additionally, the results suggest that affective inhibitory control deficits specific for negative emotions may result in vulnerability to increased NSSI severity.

Serial Recall Order of Category Fluency Words: Exploring Its Neural Underpinnings.

Background: Although performance on the category fluency test (CFT) is influenced by many cognitive functions (i.e., including language, executive functioning and speed of processing), item-level scoring methods of CFT performance might be a promising way to capture aspects of semantic memory that are less influenced by intervenient abilities. One such approach is based on the calculation of correlation coefficients that quantify the association between item-level features and the serial order with which words are recalled (SRO).Methods: We explored the neural underpinnings of 10 of these correlational indices in a sample of 40 healthy adults who completed a classic 1-min CFT and an MRI protocol inclusive of T1-weighted (analysed with voxel-based morphometry) and resting-state fMRI sequences for the evaluation of the default-mode network (DMN). Two sets of linear models were defined to test the association between neural maps and each correlational index: a first set in which major demographic and clinical descriptors were controlled for and a second set in which, additionally, all other 9 correlational indices were regressed out.Results: In the analysis of the DMN, ‘SRO-frequency’, ‘SRO-dominance’ and ‘SRO-body-object interaction’ correlational indices were all negatively associated with the anterior portion of the right temporoparietal junction. The ‘SRO-frequency’ correlational index was also negatively associated with the right dorsal anterior cingulate and the ‘SRO-dominance’ correlational index with the right lateral prefrontal cortex. From the second set of models, the ‘SRO-typicality’ correlational index was positively associated with the left entorhinal cortex. No association was found in relation to grey matter maps.Conclusion: The ability to retrieve more difficult words during CFT performance as measured by the correlational indices between SRO and item-level descriptors is associated with DMN expression in regions deputed to attentional reorienting and processing of salience of infrequent stimuli and dominance status. Of all item-level features, typicality appears to be that most closely linked with entorhinal functioning and may thus play a relevant role in assessing its value in testing procedures for early detection of subtle cognitive difficulties in people with suspected Alzheimer’s degeneration. Although exploratory, these findings warrant further investigations in larger cohorts.

Outcome valence and stimulus frequency affect neural responses to rewards and punishments.

The Reward-Positivity (RewP) is a frontocentral event-related potential elicited following reward and punishment feedback. Reinforcement learning theories propose the RewP reflects a reward prediction error that increases following more favorable (vs. unfavorable) outcomes. An alternative perspective, however, proposes this component indexes a salience-prediction error that increases following more salient outcomes. Evidence from prior studies that included both reward and punishment conditions is mixed, supporting both accounts. However, these studies often varied how feedback stimuli were repeated across reward and punishment conditions. Differences in the frequency of feedback stimuli may drive inconsistencies by introducing salience effects for infrequent stimuli regardless of whether they are associated with rewards or punishments. To test this hypothesis, the current study examined the effect of outcome valence and stimulus frequency on the RewP and neighboring P2 and P3 components in reward, punishment, and neutral contexts across two separate experiments that varied how often feedback stimuli were repeated between conditions. Experiment 1 revealed infrequent feedback stimuli generated overlapping positivity across all three components. However, controlling for stimulus frequency, experiment 2 revealed favorable outcomes that increased RewP and P3 positivity. Together, these results suggest the RewP reflects some combination of reward- and salience-prediction error encoding. Results also indicate infrequent feedback stimuli elicited strong salience effects across all three components that may inflate, eliminate, or reverse outcome valence effects for the RewP and P3. These results resolve several inconsistencies in the literature and have important implications for electrocortical investigations of reward and punishment feedback processing.

Neural Representation of the English Vowel Feature [High]: Evidence From /ε/ vs. /ɪ/.

Many studies have observed modulation of the amplitude of the neural index mismatch negativity (MMN) related to which member of a phoneme contrast [phoneme A, phoneme B] serves as the frequent (standard) and which serves as the infrequent (deviant) stimulus (i.e., AAAB vs. BBBA) in an oddball paradigm. Explanations for this amplitude modulation range from acoustic to linguistic factors. We tested whether exchanging the role of the mid vowel /ε/ vs. high vowel /ɪ/ of English modulated MMN amplitude and whether the pattern of modulation was compatible with an underspecification account, in which the underspecified height values are [−high] and [−low]. MMN was larger for /ε/ as the deviant, but only when compared across conditions to itself as the standard. For the within-condition comparison, MMN was larger to /ɪ/ deviant minus /ε/ standard than to the reverse. A condition order effect was also observed. MMN amplitude was smaller to the deviant stimulus if it had previously served as the standard. In addition, the amplitudes of late discriminative negativity (LDN) showed similar asymmetry. LDN was larger for deviant /ε/ than deviant /ɪ/ when compared to themselves as the standard. These findings were compatible with an underspecification account, but also with other accounts, such as the Natural Referent Vowel model and a prototype model; we also suggest that non-linguistic factors need to be carefully considered as additional sources of speech processing asymmetries.

Attentional salience and the neural substrates of response inhibition in borderline personality disorder.

Impulsivity is a central symptom of borderline personality disorder (BPD) and its neural basis may be instantiated in a frontoparietal network involved in response inhibition. However, research has yet to determine whether neural activation differences in BPD associated with response inhibition are attributed to attentional saliency, which is subserved by a partially overlapping network of brain regions. Patients with BPD (n = 45) and 29 healthy controls (HCs; n = 29) underwent functional magnetic resonance imaging while completing a novel go/no-go task with infrequent odd-ball trials to control for attentional saliency. Contrasts reflecting a combination of response inhibition and attentional saliency (no-go > go), saliency processing alone (oddball > go), and response inhibition controlling for attentional saliency (no-go > oddball) were compared between BPD and HC. Compared to HC, BPD showed less activation in the combined no-go > go contrast in the right posterior inferior and middle-frontal gyri, and less activation for oddball > go in left-hemispheric inferior frontal junction, frontal pole, superior parietal lobe, and supramarginal gyri. Crucially, BPD and HC showed no activation differences for the no-go > oddball contrast. In BPD, higher vlPFC activation for no-go > go was correlated with greater self-rated BPD symptoms, whereas lower vlPFC activation for oddball > go was associated with greater self-rated attentional impulsivity. Patients with BPD show frontoparietal disruptions related to the combination of response inhibition and attentional saliency or saliency alone, but no specific response inhibition neural activation difference when attentional saliency is controlled. The findings suggest a neural dysfunction in BPD underlying attention to salient or infrequent stimuli, which is supported by a negative correlation with self-rated impulsiveness.

Pre-attentive Visual Processing in Alzheimer's Disease: An Event-related Potential Study.

While identifying Alzheimer's Disease (AD) in its early stages is crucial, traditional neuropsychological tests tend to lack sensitivity and specificity for its diagnosis. Neuropsychological studies have reported visual processing deficits of AD, and event-related potentials (ERPs) are suitable to investigate pre-attentive processing with superior temporal resolution. This study aimed to investigate visual attentional characteristics of adults with AD, from pre-attentive to attentive processing, using a visual oddball task and ERPs. Cognitively normal elderly controls (CN) and patients with probable AD (AD) were recruited. Participants performed a three-stimulus visual oddball task and were asked to press a designated button in response to the target stimuli. The amplitudes of 4 ERPs were analyzed. Mismatchnegativity (vMMN) was analyzed around the parieto-occipital and temporo-occipital regions. P3a was analyzed around the fronto-central regions, whereas P3b was analyzed around the centro-parietal regions. Late vMMN amplitudes of the AD group were significantly smaller than those of the CN group, while early vMMN amplitudes were comparable. Compared to the CN group, P3a amplitudes of the AD group were significantly smaller for the infrequent deviant stimuli, but the amplitudes for the standard stimuli were comparable. Lastly, the AD group had significantly smaller P3b amplitudes for the target stimuli compared to the CN group. Our findings imply that AD patients exhibit pre-attentive visual processing deficits, known to affect later higher-order brain functions. In a clinical setting, the visual oddball paradigm could be used to provide helpful diagnostic information since pre-attentive ERPs can be induced by passive exposure to infrequent stimuli.

EEG event related potentials in sustained, focused and divided attention tasks: Potential biomarkers for cognitive impairment in HIV patients

ObjectivesThe objective of this study was to assess the usability of event-related-potentials (ERPs) during sustained, focused, and divided attention tasks as biomarkers for cognitive decline in HIV patients. MethodsEEG was acquired using a mobile/wireless 9-channel system in 39 persons with HIV, with well-controlled immune function and 63 healthy control participants (HCs) during three ERP tasks: sustained attention, focused attention, and divided attention. ResultsThe HIV-group evidenced smaller late positive potential (LPP) and larger P200 amplitudes across the tasks compared to the HC group. P200 amplitude was correlated (r = 0.56) with the estimated duration of infection. Both groups showed higher P200 and LPP amplitudes in response to infrequent stimuli; this effect was not significantly different between groups. In the sustained attention task, the HIV-group showed significantly slower reaction time than controls while maintaining the same level of accuracy. In the divided attention task, the HIV-group showed a trend towards faster/less accurate responses. ConclusionsHIV seropositive participants receiving anti-retroviral treatment (ART) demonstrated significantly larger P200 amplitude during three different attention tasks. This may reflect attentional deficits characterized by over-attending to non-target/distracting stimuli. SignificanceThese findings demonstrate the potential benefits of EEG-ERP metrics derived from attention tasks as neurocognitive biomarkers for HIV. This approach may reveal underlying causes of attentional deficits in HIV patients.

MEG reveals preference specific increases of sexual-image-evoked responses in paedophilic sexual offenders and healthy controls

Objectives Paedophilic disorder is characterised by sexual attraction towards children. Classification of a counterpart as sexually attractive likely occurs rapidly, and involves both conscious and unconscious attentional and cognitive processes. Magnetoencephalography (MEG) is an imaging method especially well-suited to examine visual and attentional processes triggered by sexual images within the range of milliseconds. Methods We investigated brain responses to sexual images depicting adults (frequent) and children (infrequent stimulus) in seventeen paedophilic patients with a history of child sexual offending (P + CSO) and twenty healthy controls (HC) during a passive visual oddball paradigm. Event-related fields (ERF) were measured to extract the magnetic visual mismatch negativity (vMMNm), and how it relates to the processing of different classes of sexual stimuli. Results P + CSO exhibited significantly longer vMMNm latencies (100–180 ms post-stimulus) than HC. Moreover, P + CSO showed widespread increased amplitudes in response to child images starting from P3a and P3b components and lasting up to 400 ms post-stimulus presentation localised in frontal and temporal brain regions. Conclusions This study uncovers the first MEG differences in automatic change detection between P + CSO and HC during the presentation of subliminal sexual images of adults and children, contributing towards a better understanding of the neurobiological processes of P + CSO.

P300 response modulation reflects breaches of non-probabilistic expectations

In oddball paradigms, infrequent stimuli elicit larger P300 event related potentials (ERPs) than frequent ones. One hypothesis is that P300 modulations reflect the degree of “surprise” associated with unexpected stimuli. That is the P300 represents how unlikely the stimulus is and this signal is then used to update the observer’s expectations. It could be hypothesized that P300 is modulated by any factor affecting an observer’s expectations, not only target probability. Alternatively, the P300 may reflect an evaluative process engaged whenever a discrepancy between task context and sensory inputs arises, irrespective of the latter probability. In previous ERP studies, stimulus probability was often the only determinant of task set confounding the effects of stimulus probability and set stimulus discrepancy. In this study, we used a speeded luminance detection task. The target was preceded by a central cue that predicted its location. The probability that the target was valid, i.e. would appear at the cued location was manipulated by varying the reliability of the cue. Reaction times were modulated by probabilistic expectations based on cue reliability and target validity while P300 was affected by target validity only. We conclude that increased P300 amplitude reflects primarily breaches of non-probabilistic expectations, rather than target probability.