Electrically evoked compound action potential artifact rejection by independent component analysis: Technique validation

The electrically-evoked compound action potential (ECAP) is the synchronous whole auditory nerve activity in response to an electrical stimulus, and can be recorded in situ on cochlear implant (CI) electrodes. A novel procedure (ECAP-ICA) to isolate the ECAP from the stimulation artifact, based on independent component analysis (ICA), is described here. ECAPs with artifact (raw-ECAPs) were sequentially recorded for the same stimulus on 9 different intracochlear recording electrodes. The raw-ECAPs were fed to ICA, which separated them into independent sources. Restricting the ICA projection to 4 independent components did not induce under-fitting and was found to explain most of the raw-data variance. The sources were identified and only the source corresponding to the neural response was retained for artifact-free ECAP reconstruction. The validity of the ECAP-ICA procedure was supported as follows: N(1) and P(1) peaks occurred at usual latencies; and ECAP-ICA and artifact amplitude-growth functions (AGFs) had different slopes. Concatenation of raw-ECAPs from multiple stimulus currents, including some below the ECAP-ICA threshold, improved the source separation process. The main advantage of ECAP-ICA is that use of maskers or alternating polarity stimulation are not needed

Objective Measures of Emotion Related to Brand Attitude: A New Way to Quantify Emotion-Related Aspects Relevant to Marketing

With this study we wanted to test the hypothesis that individual like and dislike as occurring in relation to brand attitude can be objectively assessed. First, individuals rated common brands with respect to subjective preference. Then, they volunteered in an experiment during which their most liked and disliked brand names were visually presented while three different objective measures were taken. Participant's eye blinks as responses to acoustic startle probes were registered with electromyography (EMG) (i) and their skin conductance (ii) and their heart rate (iii) were recorded. We found significantly reduced eye blink amplitudes related to liked brand names compared to disliked brand names. This finding suggests that visual perception of liked brand names elicits higher degrees of pleasantness, more positive emotion and approach-oriented motivation than visual perception of disliked brand names. Also, skin conductance and heart rate were both reduced in case of liked versus disliked brand names. We conclude that all our physiological measures highlight emotion-related differences depending on the like and dislike toward individual brands. We suggest that objective measures should be used more frequently to quantify emotion-related aspects of brand attitude. In particular, there might be potential interest to introduce startle reflex modulation to measure emotion-related impact during product development, product design and various further fields relevant to marketing. Our findings are discussed in relation to the idea that self reported measures are most often cognitively polluted

Neuropsychological and electrophysiological biomarkers of the schizophrenia spectrum

Schizophrenia is a neuropsychiatric disorder lying at the extreme of a spectrum of disorders that possibly share a common abnormality in neural connectivity. Efforts to reverse the core cognitive manifestations of schizophrenia using drug treatments have so far been unsuccessful. This thesis investigates the cognitive abnormalities and their electrophysiological correlates across the schizophrenia spectrum in order to identify and validate biomarkers for proof of concept studies of cognitive enhancers. Such studies in milder disorders of the schizophrenia spectrum such as schizotypal personality trait may be a crucial method in identifying new effective compounds, as reviewed in Chapter 3, and tested in Chapter 4. The latter features the results of a large three-centre study which probed the sensitivity of several neuropsychological measures to the schizotypy phenotype, as well as to the effects of amisulpride, risperidone and nicotine. Schizotypal volunteers showed impaired performance only on the more difficult tasks. The most consistent pharmacological finding was that amisulpride tended to improve performance in the high schizotypy group but to impair it in the average schizotypy controls. One interpretation is that the ability of low dose amisulpride to enhance dopamine function in frontal cortex reversed an impairment of dopamine function present in the high schizotypes which is thought to occur in schizophrenia. Chapter 5 explored the methodological question of whether low or average schizotypy individuals should be used as controls in cognitive comparisons versus high schizotypy. The results suggest that low schizotypes have the most intact cognitive performance and are therefore the control group of choice. Chapters 6, 7 and 8 tested the hypothesis that cognitive deficits are part of a larger information processing abnormality in the schizophrenia spectrum. In accordance, both high schizotypy and schizophrenia patients exhibited reduced amplitude of an early visual evoked potential P1 (Chapters 6 and 8, respectively) and disruptions of the underlying evoked neural oscillations (Chapters 7 and 8). The pattern of abnormalities suggested an inefficient top-down modulation of perception in the schizophrenia spectrum. These data argue that cognitive abnormalities and their electrophysiological correlate may be sensitive biomarkers of the core dysconnectivity deficit in schizophrenia. This thesis supports their use in proof of concept studies to foster the development of cognitive enhancers.EThOS - Electronic Theses Online ServiceThe University of ManchesterP1vitalGBUnited Kingdo

A comparison between the neural correlates of laser and electric pain stimulation and their modulation by expectation

Abstract Background Pain is modulated by expectation. Event-related potential (ERP) studies of the influence of expectation on pain typically utilise laser heat stimulation to provide a controllable nociceptive-specific stimulus. Short painful electric stimulation has a number of practical advantages, but is less nociceptive-specific. We compared the modulation of electric versus laser-evoked pain by expectation, and their corresponding pain-evoked and anticipatory ERPs. New Method We developed understanding of recognised methods of laser and electric stimulation. We tested whether pain perception and neural activity induced by electric stimulation was modulated by expectation, whether this expectation elicited anticipatory neural correlates, and how these measures compared to those associated with laser stimulation. We elicited cue-evoked expectations of high and low pain and compared subjective ratings and corresponding ERPs in response to the delivery of laser and electric stimulation in a within-participant design. Results Despite sensory and affective differences between laser and electric pain, intensity ratings and pain-evoked potentials were modulated equivalently by expectation, though ERPs only correlated with pain ratings in the laser pain condition. Anticipatory correlates significantly differentiated pain intensity expectation to laser but not electric pain. Comparison with Existing Method Previous studies have consistently shown that laser-evoked potentials are modulated by expectation. We extend this by showing electric pain-evoked potentials are equally modulated by expectation, within the same participants. We also show a difference between the pain types in anticipation. Conclusions Though laser-evoked potentials express a stronger relationship with pain perception, both laser and electric stimulation may be used to study the modulation of pain-evoked potentials by expectation. Anticipatory-evoked potentials are elicited by both pain types, but they may reflect different processes and did not correlate with pain perception.This work was supported by a studentship grant from the Medical Research Council, UK. We would like to acknowledge the Medical Physics team at Salford Royal Foundation Trust, especially P. Samraj and S. Watson, for their technical assistance in building the Labview program to operate the laser. We thank T. Rainey for his technical expertise and assistance. WeD acknowledges the support of CONICYT, Chile, Basal project FB0008 and FONDECYT project 1161378

Self-regulation learning as active inference: dynamic causal modeling of an fMRI neurofeedback task

IntroductionLearning to self-regulate brain activity by neurofeedback has been shown to lead to changes in the brain and behavior, with beneficial clinical and non-clinical outcomes. Neurofeedback uses a brain-computer interface to guide participants to change some feature of their brain activity. However, the neural mechanism of self-regulation learning remains unclear, with only 50% of the participants succeeding in achieving it. To bridge this knowledge gap, our study delves into the neural mechanisms of self-regulation learning via neurofeedback and investigates the brain processes associated with successful brain self-regulation.MethodsWe study the neural underpinnings of self-regulation learning by employing dynamical causal modeling (DCM) in conjunction with real-time functional MRI data. The study involved a cohort of 18 participants undergoing neurofeedback training targeting the supplementary motor area. A critical focus was the comparison between top-down hierarchical connectivity models proposed by Active Inference and alternative bottom-up connectivity models like reinforcement learning.ResultsOur analysis revealed a crucial distinction in brain connectivity patterns between successful and non-successful learners. Particularly, successful learners evinced a significantly stronger top-down effective connectivity towards the target area implicated in self-regulation. This heightened top-down network engagement closely resembles the patterns observed in goal-oriented and cognitive control studies, shedding light on the intricate cognitive processes intertwined with self-regulation learning.DiscussionThe findings from our investigation underscore the significance of cognitive mechanisms in the process of self-regulation learning through neurofeedback. The observed stronger top-down effective connectivity in successful learners indicates the involvement of hierarchical cognitive control, which aligns with the tenets of Active Inference. This study contributes to a deeper understanding of the neural dynamics behind successful self-regulation learning and provides insights into the potential cognitive architecture underpinning this process

Neuropsychological and electrophysiological biomarkers of the schizophrenia spectrum

Schizophrenia is a neuropsychiatric disorder lying at the extreme of a spectrum of disorders that possibly share a common abnormality in neural connectivity. Efforts to reverse the core cognitive manifestations of schizophrenia using drug treatments have so far been unsuccessful. This thesis investigates the cognitive abnormalities and their electrophysiological correlates across the schizophrenia spectrum in order to identify and validate biomarkers for proof of concept studies of cognitive enhancers. Such studies in milder disorders of the schizophrenia spectrum such as schizotypal personality trait may be a crucial method in identifying new effective compounds, as reviewed in Chapter 3, and tested in Chapter 4. The latter features the results of a large three-centre study which probed the sensitivity of several neuropsychological measures to the schizotypy phenotype, as well as to the effects of amisulpride, risperidone and nicotine. Schizotypal volunteers showed impaired performance only on the more difficult tasks. The most consistent pharmacological finding was that amisulpride tended to improve performance in the high schizotypy group but to impair it in the average schizotypy controls. One interpretation is that the ability of low dose amisulpride to enhance dopamine function in frontal cortex reversed an impairment of dopamine function present in the high schizotypes which is thought to occur in schizophrenia. Chapter 5 explored the methodological question of whether low or average schizotypy individuals should be used as controls in cognitive comparisons versus high schizotypy. The results suggest that low schizotypes have the most intact cognitive performance and are therefore the control group of choice. Chapters 6, 7 and 8 tested the hypothesis that cognitive deficits are part of a larger information processing abnormality in the schizophrenia spectrum. In accordance, both high schizotypy and schizophrenia patients exhibited reduced amplitude of an early visual evoked potential P1 (Chapters 6 and 8, respectively) and disruptions of the underlying evoked neural oscillations (Chapters 7 and 8). The pattern of abnormalities suggested an inefficient top-down modulation of perception in the schizophrenia spectrum. These data argue that cognitive abnormalities and their electrophysiological correlate may be sensitive biomarkers of the core dysconnectivity deficit in schizophrenia. This thesis supports their use in proof of concept studies to foster the development of cognitive enhancers.EThOS - Electronic Theses Online ServiceThe University of ManchesterP1vitalGBUnited Kingdo

Individual Differences in Impulsivity Predict Anticipatory Eye Movements

Impulsivity is the tendency to act without forethought. It is a personality trait commonly used in the diagnosis of many psychiatric diseases. In clinical practice, impulsivity is estimated using written questionnaires. However, answers to questions might be subject to personal biases and misinterpretations. In order to alleviate this problem, eye movements could be used to study differences in decision processes related to impulsivity. Therefore, we investigated correlations between impulsivity scores obtained with a questionnaire in healthy subjects and characteristics of their anticipatory eye movements in a simple smooth pursuit task. Healthy subjects were asked to answer the UPPS questionnaire (Urgency Premeditation Perseverance and Sensation seeking Impulsive Behavior scale), which distinguishes four independent dimensions of impulsivity: Urgency, lack of Premeditation, lack of Perseverance, and Sensation seeking. The same subjects took part in an oculomotor task that consisted of pursuing a target that moved in a predictable direction. This task reliably evoked anticipatory saccades and smooth eye movements. We found that eye movement characteristics such as latency and velocity were significantly correlated with UPPS scores. The specific correlations between distinct UPPS factors and oculomotor anticipation parameters support the validity of the UPPS construct and corroborate neurobiological explanations for impulsivity. We suggest that the oculomotor approach of impulsivity put forth in the present study could help bridge the gap between psychiatry and physiology

Velocity memory

It is known that primates are sensitive to the velocity of moving objects. We can also remember velocity information after moving objects disappear. This cognitive faculty has been investigated before, however, the literature on velocity memory to date has been fragmented. For example, velocity memory has been disparately described as a system that controls eye movements and delayed discrimination. Furthermore, velocity memory may have a role in motion extrapolation, i.e. the ability to judge the position of a moving target after it becomes occluded. This thesis provides a unifying account of velocity memory, and uses electroencephalography (EEG) to explore its neural basis. In Chapter 2, the relationship between oculomotor control and motion extrapolation was investigated. Two forms of motion extrapolation task were presented. In the first, participants observed a moving target disappear then reappear further along its path. Reappearance could be at the correct time, too early or too late. Participants discriminated reappearance error with a two-alternative forced choice button press. In the second task, participants saw identical targets travel behind a visible occluder, and they attempted to press a button at the exact time that it reached the other side. Tasks were completed under fixation and free viewing conditions. The accuracy of participant's judgments was reduced by fixation in both tasks. In addition, eye movements were systematically related to behavioural responses, and small eye movements during fixation were affected by occluded motion. These three results imply that common velocity memory and pre-motor systems mediate eye movements and motion extrapolation. In Chapter 3, different types of velocity representation were explored. Another motion extrapolation task was presented, and targets of a particular colour were associated with fast or slow motion. On identical-velocity probe trials, colour still influenced response times. This indicates that long-term colour-velocity associations influence motion extrapolation. In Chapter 4, interference between subsequently encoded velocities was explored. There was robust interference between motion extrapolation and delayed discrimination tasks, suggesting that common processes are involved in both. In Chapter 5, EEG was used to investigate when memory-guided tracking begins during motion extrapolation. This study compared conditions where participants covertly tracked visible and occluded targets. It was found that a specific event related potential (ERP) appeared around 200 ms post occlusion, irrespective of target location or velocity. This component could delineate the onset of memory guided tracking during occlusion. Finally, Chapter 6 presents evidence that a change in alpha band activity is associated with information processing during motion extrapolation tasks. In light of these results, it is concluded that a common velocity memory system is involved a variety of tasks. In the general discussion (Chapter 7), a new account of velocity memory is proposed. It is suggested that a velocity memory reflects persistent synchronization across several velocity sensitive neural populations after stimulus offset. This distributed network is involved in sensory-motor integration, and can remain active without visual input. Theoretical work on eye movements, delayed discrimination and motion extrapolation could benefit from this account of velocity memory.EThOS - Electronic Theses Online ServiceGBUnited Kingdo