LOW RESOLUTION ELECTROMAGNETIC TOMOGRAPHY (LORETA) ANALYSIS OF THE BRAINS ELECTROPHYSIOLOGICAL RESPONSE TO EMOTIONAL VISUAL STIMULI UNDER DIFFERING CONDITIONS

Current methods of diagnosing and monitoring stress include: observing changes in the severity of existing symptoms, the development of new symptoms, hormone level tests, and stress self-assessment surveys. Self-assessment surveys are subject to bias and false reporting. This project focuses on analyzing electroencephalogram (EEG) using Low Resolution Electromagnetic Tomography (LORETA) to identify differences within current source location of emotionally elicited event related potentials (ERPs), in order to aid physicians in stress diagnostics and management. For this study twenty-one participants took the Penn State Worry Questionnaire which classifies the participants into high-stress and low-stress groups. The individuals had their EEG recorded while viewing pleasant, neutral, and unpleasant stimuli. CURRY, the current reconstruction program, was used to filter, epoch, and average the data to obtain event related potentials (ERPs) for each participant. Using group-averaged ERPs as the data input, LORETA was used to calculate the current distribution within the brain. One and two-tailed t-tests were performed to examine for current source distribution differences between high-stress/low-stress conditions and pleasant, unpleasant and neutral stimuli. The results of the experiment indicate that there is a difference in current source location between high-stress and low-stress individuals. The current source distribution differences are within regions of the frontal lobe and the parietal lobe associated with emotional processing

Spatial filters yield stable features for error-related potentials across conditions

Error-related potentials (ErrP) have been increasingly studied in psychophysical experiments as well as for brain-machine interfacing. In the latter case, the generalisation capabilities of ErrP decoders is a crucial element to avoid frequent recalibration processes, thus increasing their usability. Previous studies have suggested that ErrP signals are rather stable across recording sessions. Also, studies using protocols of serial stimuli presentation show that these potentials do not change significantly with the presentation rate. Here we complement these studies by analysing the decoding generalisation capabilities. Using data from monitoring experiments, we evaluate how much the performance degrades when tested in a condition different than the one the decoder was trained with. Moreover, we compare different spatial filtering techniques to see which preprocessing steps yield less-sensitive features for ErrP decoding

Estimation of overlapped Eye Fixation Related Potentials: The General Linear Model, a more flexible framework than the ADJAR algorithm

The Eye Fixation Related Potential (EFRP) estimation is the average of EEG signals across epochs at ocular fixation onset. Its main limitation is the overlapping issue. Inter Fixation Intervals (IFI) - typically around 300 ms in the case of unrestricted eye movement- depend on participants’ oculomotor patterns, and can be shorter than the latency of the components of the evoked potential. If the duration of an epoch is longer than the IFI value, more than one fixation can occur, and some overlapping between adjacent neural responses ensues. The classical average does not take into account either the presence of several fixations during an epoch or overlapping. The Adjacent Response algorithm (ADJAR), which is popular for event-related potential estimation, was compared to the General Linear Model (GLM) on a real dataset from a conjoint EEG and eye-tracking experiment to address the overlapping issue. The results showed that the ADJAR algorithm was based on assumptions that were too restrictive for EFRP estimation. The General Linear Model appeared to be more robust and efficient. Different configurations of this model were compared to estimate the potential elicited at image onset, as well as EFRP at the beginning of exploration. These configurations took into account the overlap between the event-related potential at stimulus presentation and the following EFRP, and the distinction between the potential elicited by the first fixation onset and subsequent ones. The choice of the General Linear Model configuration was a tradeoff between assumptions about expected behavior and the quality of the EFRP estimation: the number of different potentials estimated by a given model must be controlled to avoid erroneous estimations with large variances

Aberrant Frequency Related Change-Detection Activity in Chronic Tinnitus

Tinnitus is the perception of sound without the occurrence of an acoustic event. The deficit in auditory sensory or echoic memory may be the cause of the perception of tinnitus. This study considered the mismatch negativity (MMN) to investigate the potential difference between and within groups of persons with normal hearing (NH) and tinnitus. Using an auditory multi-feature paradigm to elicit the MMN, this study considered the MMN peak amplitude at two central frequencies for two MMN subcomponents. These central frequencies were 1 and 5 kHz, which the latter was closer to the perceived tinnitus frequency in the group with tinnitus. The deviants were higher frequency, lower frequency, higher intensity, lower intensity, duration, location (left), location (right), and gap. The pure tone audiometry (PTA) test and distortion product otoacoustic emissions (DPOAE) test showed no meaningful difference between the two groups. For the frontal subcomponent, the mean amplitudes of the MMN peak for the two groups illustrated less negative meaningful MMN peak amplitudes in the group of persons with tinnitus. For the supratemporal component at 5 kHz central frequency, amplitudes were lower for the group of persons with tinnitus, whereas for the central frequency of 1 kHz, most deviants exhibited meaningful differences. Additionally, within-group comparisons indicated that mean amplitudes for both groups were more negative at the central frequency of 1 kHz for the frontal MMN subcomponent. In comparison, the supratemporal component illustrated a lower peak amplitude at 5 kHz central frequency in the group of persons with tinnitus and no difference in the NH group, which is a unique observation of this study. Results of the between-groups are in accordance with previous studies and within-group comparisons consider the probability of decreasing the change detection capability of the brain. The results of this study indicate that increasing the frequency of the stimuli close to the tinnitus perceived frequencies decreases the prediction error, including the prediction error of the silence. Such a decrease may cause the prediction error of the spontaneous neural activity in the auditory pathway to exceed the silence prediction error, and as a result, increases the probability of occurrence of tinnitus in higher frequencies according to the predictive coding model. © Copyright © 2020 Asadpour, Jahed and Mahmoudian

Error Commission and Aging: Using Single-Trial Movement Kinematics to Decode the Time-Course of Response Monitoring Processes during Complex Decisions in Older and Younger Adults

We are constantly making decisions in everyday life that involve interactions with our environment: from simple behaviors like deciding to reach for your cup of coffee to complex behaviors like deciding which route to take to work. It is well known that these decisions require constant monitoring, such that decision-making is not a discrete event and requires initiation, monitoring, and evaluation for success. This process can be seen during error-corrections, in which an initial plan was implemented, an error was recognized, and a new plan was implemented to correct the initial response. While we have learned a great deal about response monitoring processes over three decades of research in cognitive neuroscience, most of the literature has used button-presses, which does not permit evaluation of the processes involved in the monitoring, cancellation, or correction of erroneous behaviors. Understanding the neural correlates of the response monitoring process may contribute to an improved understanding of cognitive aging as the natural aging process has revealed to impact this decision-making process, as older adults commit more errors than younger adults on cognitive tasks, as well as experience slower correct responses compared to younger adults. However, the current literature regarding what neurological processes are impaired as a result of the natural aging process remains to be unknown. Purpose: The primary aims of this study were (1) to delineate the neural correlates of response-monitoring process during correct, incorrect, and corrected trials as indicated by kinematic markers of the decision-making processes, and (2) to determine the integrity of these neural responses in older adults. Results reveal that the ERN, Pe, and medial-frontal theta oscillations are highly correlated with response cancellation in only younger adults, and these correlations significantly differ between older and younger adults such that older adults had significantly reduced correlations. Source localization also further confirm that the ERN and Pe are related to caudal anterior cingulate cortex activation (ACC) in both older and younger adults

Comparison of Averaging and Regression Techniques for Estimating Event Related Potentials

Abstract — The traditional method of estimating an Event Related Potential (ERP) is to take the average of signal epochs time locked to a set of similar experimental events. This averaging method is useful as long as the experimental procedure can sufficiently isolate the brain or non-brain process of interest. However, if responses from multiple cognitive processes, time locked to multiple classes of closely spaced events, overlap in time with varying inter-event intervals, averaging will most likely fail to identify the individual response time courses. For this situation, we study estimation of responses to all recorded events in an experiment by a single model using standard linear regression (the rERP technique). Applied to data collected during a Rapid Serial Visual Presentation (RSVP) task, our analysis shows: (1) The rERP technique accounts for more variance in the data than averaging when individual event responses are highly overlapping; (2) the variance accounted for by the estimates is concentrated into a fewer ICA components than raw EEG channel signals. I