Effects of passive heat stress and recovery on human cognitive function: An ERP study

Using event-related potentials (ERPs), we investigated the effects of passive heat stress and recovery on the human cognitive function with Flanker tasks, involving congruent and incongruent stimuli. We hypothesized that modulation of the peak amplitude and latency of the P300 component in ERP waveforms would differ with task difficulty during passive heat stress and recovery. Subjects performed the Flanker tasks before (Pre), at the end of whole body heating (Heat: internal temperature increase of ~1.2°C from the pre-heat baseline), and after the internal temperature had returned to the pre-heat baseline (Recovery). The internal temperature was regulated by a tube-lined suit by perfusing 50°C water for heat stress and 25°C water for recovery immediately after the heat stress. Regardless of task difficulty, the reaction time (RT) was shortened during Heat rather than Pre and Recovery, and standard deviations of RT (i.e., response variability) were significantly smaller during Heat than Pre. However, the peak amplitudes of the P300 component in ERPs, which involved selective attention, expectancy, and memory updating, were significantly smaller during Heat than during Pre, suggesting the impairment of neural activity in cognitive function. Notably, the peak amplitudes of the P300 component were higher during Recovery than during Heat, indicating that the impaired neural activity had recovered after sufficient whole-body cooling. An indicator of the stimulus classification/evaluation time (peak latency of P300) and the RT were shortened during Heat stress, but such shortening was not noted after whole-body cooling. These results suggest that hyperthermia affects the human cognitive function, reflected by the peak amplitude and latency of the P300 component in ERPs during the Flanker tasks, but sufficient treatment such as whole-body cooling performed in this study can recover those functions.

Extraction of the Major Features of Brain Signals using Intelligent Networks

The brain-computer interface is considered one of the main tools for implementing and designing smart medical software. The analysis of brain signal data, called EEG, is one of the main tasks of smart medical diagnostic systems. While EEG signals have many components, one of the most important brain activities pursued is the P300 component. Detection of this component can help detect abnormalities and visualize the movement of organs of the body. In this research, a new method for processing EEG signals is proposed with the aim of detecting the P300 component. Major features were extracted from the BCI Competition IV EEG data set in a number of steps, i.e. normalization with the purpose of noise reduction using a median filter, feature extraction using a recurrent neural network, and classification using Twin Support Vector Machine. Then, a series of evaluation criteria were used to validate the proposed approach and compare it with similar methods. The results showed that the proposed approach has high accuracy.

Two distinctive stages of novelty processing revealed by high-density EEG based source imaging

Novelty detection is an evolutionarily significant and ancient function as well as a relatively stable function whose early life status marks for long-term developmental outcomes and predicts a range of adult functions. While various brain regions have been shown to respond to environmental novelty, how different brain regions coordinate in novelty related information processing remains under-explored. Here using a combination of high-density EEG, second order blind identification (SOBI), and a standard visual oddball task, we test, in humans, a two-stage novelty processing hypothesis which states that two distinct stages of novelty processing exist, one involves early-occurring domain-specific neural activity in the sensory processing areas of the brain and the other involves later-occurring domain-general neural activity involving brain regions beyond the sensory cortices. We found that: (1) a significant Novelty effect (oddball effects) not only in the SOBI-recovered Late component (P300 component) but also in the Early component (N150 visual) offering first EEG evidence for oddball effect in the sensory domain; (2) a significant Stage (Early vs Late) by Frequency (delta, theta, alpha, beta, and gamma) interaction effect indicating two functionally dissociable mechanisms underlying novelty detection; (3) a significantly shorter latency in odd-ball related theta power increase in the Early visual than in the late P300 component. These results not only offer support for the two-stage novelty processing theory but also provide new evidence for an early involvement of theta power increase in the novelty processing.

Eye Fixation-Related Potentials during Visual Search on Acquaintance and Newly-Learned Faces

Searching familiar faces in the crowd may involve stimulus-driven attention by emotional significance, together with goal-directed attention due to task-relevant needs. The present study investigated the effect of familiarity on attentional processes by exploring eye fixation-related potentials (EFRPs) and eye gazes when humans searched for, among other distracting faces, either an acquaintance’s face or a newly-learned face. Task performance and gaze behavior were indistinguishable for identifying either faces. However, from the EFRP analysis, after a P300 component for successful search of target faces, we found greater deflections of right parietal late positive potentials in response to newly-learned faces than acquaintance’s faces, indicating more involvement of goal-directed attention in processing newly-learned faces. In addition, we found greater occipital negativity elicited by acquaintance’s faces, reflecting emotional responses to significant stimuli. These results may suggest that finding a familiar face in the crowd would involve lower goal-directed attention and elicit more emotional responses.

Changes in attentional resources during the acquisition of laparoscopic surgical skills

Background Increasing familiarity and practice might free up mental resources during laparoscopic surgical skills training. The aim of the study was to track changes in mental resource allocation during acquisition of laparoscopic surgical skills. Methods Medical students with no previous experience in laparoscopic surgery took part in a 5-week laparoscopic training curriculum. At the beginning and end of the training period, one of the training tasks was combined with a secondary auditory detection task that required pressing a foot switch for defined target tones, creating a dual-task situation. During execution of the two concurrent tasks, continuous electroencephalographic measurements were made, with special attention to the P300 component, an index of mental resources. Accuracy and reaction times of the secondary task were determined. Results All 14 participants successfully completed the training curriculum. Target times for successful completion of individual tasks decreased significantly during training sessions (P <0.001 for all tasks). Comparing results before and after training showed a significant decrease in event-related brain potential amplitude at the parietal electrode cluster (P300 component, W = 67, P = 0.026), but there were no differences in accuracy (percentage correct responses: W = 48, P = 0.518) or reaction times (W = 42, P = 0.850) in the auditory detection task. Conclusion The P300 decrease in the secondary task over training demonstrated a shift of mental resources to the primary task: the surgical exercise. This indicates that, with more practice, mental resources are freed up for additional tasks.

Systematic review and meta-analysis of late auditory evoked potentials as a candidate biomarker in the assessment of tinnitus

Subjective tinnitus, the perception of sound in the absence of any sound source, is routinely assessed using questionnaires. The subjective nature of these tools hampers objective evaluation of tinnitus presence, severity and treatment effects. Late auditory evoked potentials (LAEPs) might be considered as a potential biomarker for assessing tinnitus complaints. Using a multivariate meta-analytic model including data from twenty-one studies, we determined the LAEP components differing systematically between tinnitus patients and controls. Results from this model indicate that amplitude of the P300 component is lower in tinnitus patients (standardized mean difference (SMD) = -0.83, p < 0.01), while latency of this component is abnormally prolonged in this population (SMD = 0.97, p < 0.01). No other investigated LAEP components were found to differ between tinnitus and non-tinnitus subjects. Additional sensitivity analyses regarding differences in experimental conditions confirmed the robustness of these results. Differences in age and hearing levels between the two experimental groups might have a considerable impact on LAEP outcomes and should be carefully considered in future studies. Although we established consistent differences in the P300 component between tinnitus patients and controls, we could not identify any evidence that this component might covary with tinnitus severity. We conclude that out of several commonly assessed LAEP components, only the P300 can be considered as a potential biomarker for subjective tinnitus, although more research is needed to determine its relationship with subjective tinnitus measures. Future trials investigating experimental tinnitus therapies should consider including P300 measurements in the evaluation of treatment effect.

The Effects of Acute Stress on the Neural Correlates of Decision-Making

Stress has been defined in many ways and is typically induced as a response to a threat to homeostasis. Stress affects decision-making, and the effects of stress on subcomponents of decision-making can be indirectly measured through EEG. The purpose of this study was to investigate the effects of acute stress on the neural correlates of decision-making. We hypothesized that acute stress would decrease the reward and attentional sensitivity, seen through reduced P300 and reward positivity component activity. The results were that the mean percent change from baseline for heart rate was higher for the stress condition during the TSST. The stress group also had decreased positive affect scores and increased negative affect scores for the STAI questionnaire and decreased positive affect scores for the PANAS questionnaire. Additionally, while not significant, there was a trend towards reduced P300 component activity in the stress condition, potentially indicative of reduced attentional sensitivity. Further research is needed to explore the implications for reward sensitivity, utilizing multiple tasks, and including cortisol measurement. Stress is common to everyday life and has been implicated chronically in numerous health conditions. Understanding how stress affects executive function, particularly decision-making, is therefore crucial in both the short- and long-term. Keywords: stress; decision-making; ERPs; P300 component; reward positivity component *This research was supported by a Jamie Cassels Undergraduate Research Award, University of Victoria.

Visual Search P300 Source Analysis Based On ERP-fMRI Integration

ABSTRACTAttention control can be achieved in two ways, stimulus-driven bottom-up attention and goal-driven top-down attention. Different visual search tasks involve different attention control. The pop-out task requires more bottom-up attention, whereas the search task involves more top-down attention. P300 which is the positive potential generated by the brain in the latency of 300-600 ms after the stimulus, reflects the processing of cognitive process and is an important component in visual attention. The P300 source is not consistent in the previous researches, our aim therefore, is to study the source location of P300 component based on visual search attention process. Here we use pop-out and search paradigm to get the ERP data of 13 subjects and the fMRI data of 25 subjects, and analyze the source location of P300 using the ERP-fMRI integration technology with high temporal resolution and high spatial resolution. The target differs from the distractor in color and orientation in the pop-out task, whereas the target and the distractor have different orientation and the same color in the search task. ERP results indicate that pop-out induces larger P300 concentrated in the parietal lobe, whereas search induced P300 is more distributed in the frontal lobe. Further ERP and fMRI integration analyses reveal that the left angular gyrus, right postcentral gyrus of parietal lobe and the left superior frontal gyrus (medial orbital) are the source of P300. Our study suggests the contribution of the frontal and parietal lobes to the P300 component.