No description available.

Previous studies showed that emotional pictures capture attention. Further, this effect was decreased by manipulating spatial attention. In contrast, studies produced mixed findings for effects of perceptual load on attention to emotional pictures. Emotional pictures can be phobic or nonphobic. Because phobia might be an evolutionary adaption, it is possible that effects of phobic pictures on attention differ from effects of nonphobic emotional pictures. The present thesis aimed at investigating attention in spider phobia. Attention to emotional pictures was operationalized as event-related potentials (ERPs) (P1, early posterior negativity [EPN,] and late positive potential [LPP]). Two research questions were formulated. First, do phobic pictures evoke larger ERPs than what can be expected from arousal and valence? Second, are effects of spatial attention and perceptual load on ERPs the same for phobic and nonphobic emotional pictures? To investigate this, phobic and nonphobic negative pictures were presented to spider phobic and nonphobic participants. To determine effects of spatial attention on ERPs, participants were instructed to divert attention to a single letter that was presented in the periphery. To determine effects of perceptual load on ERPs, participants were instructed to perform a letter discrimination task on one, two, or three letters that were presented in the periphery. Study 1 showed enhanced LPP amplitudes to phobic pictures independent of arousal and valence. Further, this effect was present in both phobic and nonphobic participants. Study 2 showed that there was no effect of perceptual load on LPP to phobic pictures. Study 3 showed that spatial attention reduced LPP amplitudes, and to a similar extent for both phobic and nonphobic pictures. Further, perceptual load did not reduce EPN or LPP amplitudes to either phobic or nonphobic pictures. To conclude, the results suggest that phobic pictures evoke larger ERP amplitudes than nonphobic pictures. Still, ERPs to phobic and nonphobic pictures are moderated similarly by spatial attention and perceptual load. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: Manuscript. Paper 3: Manuscript.</p>

The aim of this PhD thesis was to explore the way in which recognition memory changes over time. Of particular interest was how forgetting and systems level consolidation processes alter the qualitative nature of recognition judgments and the impact this has on event related potentials (ERPs) recorded during recognition. An emerging body of fMRI and animal work has started to suggest that changes to the neural basis of memory can be observed after intervals in the order of days and weeks. Although much research has examined the ERP correlates of recent recognition, there has been little attempt to compare this to remote recognition. This gap in the literature is investigated in the present PhD thesis over five ERP and two behavioural experiments. The first set of experiments investigated recognition success i.e. the subjective awareness that a stimulus has been encountered before. Previous work has associated familiarity-based recognition with an early midfrontal ERP effect whereas recollection-based recognition has been linked to a later onsetting parietal ERP effect. These effects were compared for recently studied stimuli and stimuli studied 1 week earlier. Results revealed an attenuation of the late parietal effect. This quantitative difference suggests that the neural networks underlying the ERPs for recent and remote recollection remain the same after a 1 week delay but may be less active after a period of forgetting. Behavioural work linked this to a drop in strength and episodic detail for remote recollection. Examining the midfrontal effect over time produced a more complex pattern of results. The effect was not reliable in Experiment 1 for remote familiarity judgments. In follow up experiments, however, midfrontal effects were reliable for week old memories but were not modulated by either delay or memory strength manipulations. These findings do not permit strong conclusions regarding the way familiarity memory and midfrontal ERPs vary over time, other than to say that the midfrontal effect is not a short lived correlate of recognition memory. A second set of experiments investigated how the length of the delay between study and test impacts on retrieval orientation and retrieval effort. Retrieval orientation refers to the way in which participants strategically alter how a memory cue is processed based on current task demands. Results showed ERP differences when remote memories were cued compared to when recent memories were cued. However, these differences were eliminated when recent and remote memory was matched for performance. This finding indicated that effort required at retrieval rather than memory age per se influenced differential cue processing. A follow up experiment supported this claim but found that participants may utilise delay information during recognition in a very general sense. In this experiment, ERPs indicated different cue processing when participants knew the age of the memories they were trying to retrieve compared to when they did not. Taken together, the results suggest that memory age does not influence the ERP correlates of recognition in a direct manner. More important are the indirect changes occurring over time, such as reduced memory strength, reduced episodic detail, slower reaction times and increased effort at retrieval. These variables, and possibly a range of others, should be controlled as far as possible in studies aiming to explore neural changes driven by systems consolidation. Prospective studies, where the learning phase can be controlled makes this aim feasible, as some of the experiments in this thesis have shown. Future work might benefit from focusing more on variations at encoding, rather than large differences in the length of the retention interval, as has been the traditional approach to this issue.

Since its first use in human in 1929, the electroencephalogram (EEG) has become one of the most important diagnostic tool in clinical neurophysiology. However, their use in clinical studies is limited because the huge quantity of collected information is complicated to treat. Indeed, it is very difficult to have an overall picture of this multivariate problem. In addition to the impressive quantity of data to be treated, an intrinsic problem with electroencephalograms is that the signals are "contaminated" by body signals not directly related to cerebral activity. However, these signals do not interest us directly to evaluate treatment effect on the brain. Removing these signals known as "parasitic noise" from electroencephalograms is a difficult task. We use clinical data kindly made available by the pharmaceutical company Eli Lilly (Lilly Clinical Operations S.A., Louvain-la-Neuve, Belgium). Particular types of analyses were already carried out on these data, most based on frequency bands. They mainly confirmed the enormous potential of EEG in clinical studies without much insight in the understanding of treatment effect on the brain. The aim of this thesis is to propose and evaluate a panel of statistical techniques to clean and to analyze electroencephalograms. The first presented tool enables to align curves such as selected parts of EEGs before any further statistical treatment. Indeed, when monitoring some continuous process on similar units (like patients in a clinical study), one often notices a typical pattern common to all curves but with variation both in amplitude and dynamics across curves. In particular, typical peaks could be shifted from unit to unit. This complicates the statistical analysis of sample of curves. For example, the cross-sectional average usually does not reflect a typical curve pattern: due to shifts, the signal structure is smeared or might even disappear. Another of the presented tools is based on the preliminary linear decomposition of EEGs into statistically independent signals. This decomposition provides on the one hand an effective cleaning method and on the other hand a considerable reduction of the quantity of data to be analyzed. The technique of decomposition of our signals in statistically independent signals is a well-known technique in physics primarily used to unmix sound signals. This technique is named Independent Component Analysis or ICA. The last studied tool is functional ANOVA. The analysis of longitudinal curve data is a methodological and computational challenge for statisticians. Such data are often generated in biomedical studies. Most of the time, the statistical analysis focuses on simple summary measures, thereby discarding potentially important information. We propose to model these curves using non parametric regression techniques based on splines.

Source memory is defined as memory for not only the core aspect of some event, but additional contextual detail about that core aspect, or item. Source memory tasks are marked by their engagement of prefrontal cortex in addition to the brain circuits required by other episodic memory tasks. The dissertation examines the relationships among source memory accuracy, concurrent brain activity, and general cognitive principles derived from the study of episodic memory more generally. Electrical measures of brain activity (event-related potentials, ERPs) were recorded while manipulating factors hypothesized to improve or worsen source memory accuracy.The first experiment manipulated the task assigned during the encoding phase and its match to the retrieval demands of remembering objects (depicted in drawings) and their colors. As predicted by the principle of transfer-appropriate processing, source accuracy was higher when the encoding task fostered integration of the item (object) and source (color) attributes. Prefrontal activity during the retrieval phase was greatly reduced when retrieval could benefit from transfer-appropriate processing.In associative memory tasks, poor memory performance is observed when the to-be-retained stimuli share elements with other studied stimuli, as in a variety of interference paradigms. The second experiment thus examined the impact of feature overlap on source recognition by varying the quantitative mapping between the shape and color of an object depicted in a drawing. The results showed two frontal processes supporting source retrieval: an early differentiation between stimuli identical to those encoded and those that switch colors from study to test, and a later effect reflecting prolonged memory search that was truncated by reinstating unique object-color pairings at test.The final experiment compared conjunctions of "intra-item" versus "extra-item" features, by placing the features within a single visual object or distributing them across two visual objects. Source accuracy was worse when shape and color were spatially separated, but prefrontal activity did not vary. The insensitivity of prefrontal ERPs to this perceptual manipulation of difficulty stands in contrast to their sensitivity to encoding task. Individual variability in parietal ERPs was strongly correlated with source accuracy, and likely reflects a contribution of visual working memory to long-term memory.

Despite the vast number of studies that have examined the relationship between human memory and learning, few have examined learning and memory in more realistically valid environments. The current study examines learning memory in a classroom environment, specifically with students enrolled in a medical anatomy course. In addition to behavioral data, this study also uses electroencephalography (EEG) to examine the neural correlates of successful learning in medical students. A total of 37 students over 2 years was recruited from the Boston University School of Medicine to participate in this study. In the study, medical students were tested on a set of anatomical terms that they learned in the anatomy course. Testing occurred in three sessions: prior to the start of the course, immediately after the completion of the course, and 5 months after the completion of the course. In the experiment itself, students were presented with 176 anatomical terms (132 terms learned in the course and 44 terms deemed outdated) and then given three response choices: whether they "Can Define", are "Familiar" with, or "Don't Know" the term. While testing, the subject's scalp EEG was recorded to measure the brain's neural activity in response to anatomical terms displayed on the computer screen. Resulting EEG waveforms were separated and then averaged based on the response type in order to analyze the difference in amplitude for three neural correlates across distinct scalp sites when the students could define, were familiar with, or did not know the term. Results showed a higher amplitude in ERP readings for "Can Define" and "Familiar" responses for the early frontal effect, which is correlated with memorial familiarity. A higher "Don't Know" ERP wave was observed for the late parietal effect, which reflects memorial recollection. Lastly, a larger ERP amplitude was detected for "Familiar" and "Don't Know" responses for the late frontal effect, which is associated with post memory retrieval processing. Both Pearson correlation and multiple linear regression analyses were then run to investigate if any significant relationship between ERP amplitude and grades existed, and if so, the degree to which these electrophysiological responses can predict the course grades received. Final results found that the early frontal effect for the Can Define responses over the Right Posterior Superior scalp region is the best predictor variable, among the ones tested in the study, for student performance in the medical anatomy course. This finding has the potential to determine whether the information learned in a classroom environment has in fact been incorporated into long-term or even semantic memory. Through the findings of this study, we hope to determine if this method of measuring learning through EEG can be used as a useful indicator of long-lasting learning in classroom environments.

When stimuli processing time varies in an oddball paradigm, the latency of the P300 will vary across trials. In an oddball task requiring difficult response selections, as the variation of stimuli processing time increases, so does the variation of the P300 latency, causing latency jitters in the measurement. Averaging the P300 across different trials without adjusting this latency jitter will lead to diminished P300 amplitude, resulting in inaccurate conclusions from the data. Verleger et al. (2014) reported a diminished P300 amplitude in a difficult oddball task that required subjects to make response selections among stimuli that are difficult to distinguish, but his work did not correct for any latency jitter observed within his sample. The current study replicated the easy and hard oddball tasks conducted in Verleger et al.. Raw ERPs obtained from 16 subjects indicated a successful replication of the study. An examination of the behavioral data showed that there was substantial variation in the P300 during the hard oddball tasks, and a latency jitter correction was applied in the analysis. Results indicated that there was a significant increase in the amplitude of P300 after latency jitter correction, and that this P300 amplitude did not differ significantly between easy and hard oddball tasks. These results suggest that difficult decision requirement does not reduce the amplitude of the P300, and that latency jitter should be accounted for when analyzing data from tasks involving a difficult decision requirement.

The current study used event-related potentials (ERPs) to investigate how motivational salience in the form of expectation violation influences spatial attention. The medial frontal negativity (MFN) ERP indexes expected value, being negative to unexpected punishments and positive to unexpected rewards. The P1 and N1 ERPs index spatial attention, being larger to stimuli in attended locations. This design attached motivational value to locations by making one visual hemifield economically rewarding (greater probability of a rewarding outcome) and the other punishing (greater probability of a punishing outcome). Keypresses to a dot probe following a reward-signifying stimulus were awarded money if correct, and penalized following a punishment-signifying stimulus if incorrect. We predicted that salience would be attached to visual hemifield, thus the MFN would be most negative to punishing outcomes in the rewarding hemifield and most positive to rewarding outcomes in the punishing hemifield. We also predicted that attention would be allocated to a location where expectation was violated, thus the P1 and N1 ERPs would be larger and RTs (reaction times) faster to dot probes appearing in the same side as an outcome that violated expected value. In a sample of 36 participants, there were no significant effects on the MFN, although the means were in the predicted direction, suggesting a lack of power. Contrary to our hypothesis, keypresses were slower, P1 smaller, and N1 larger to probes opposite the location where an expectation violation occurred. This suggested that expectation violation did not direct attention to a particular location, but produced general interference.

Investigations into the cognitive effects of tobacco smoking have generally focused on nicotine and its effect on nicotinic acetylcholine receptors (nAChRs) in the brain. However, it is now known that chronic smokers exhibit robust inhibition of the monoamine oxidase (MAO) enzyme through the actions of non-nicotine components in tobacco smoke. Therefore, the primary aim of this thesis is to elucidate the effects of nicotine and MAO-inhibition on electroencephalographic (EEG) and event-related potential (ERP) measures of cognition. 24 healthy nonsmoking males were administered 75 mg of moclobemide, and chewed 6 mg nicotine gum, in order to simulate the effects of acute smoking. Four experimental conditions included placebo, nicotine, moclobemide, and a combination of nicotine and moclobemide. Early auditory ERPs were used as measures of cognition, such as the auditory P50 sensory gating paired-stimulus paradigm, the acoustic-change-elicited mismatch-negativity (MMN), the novel sound-elicited P3a, and the target sound-elicited P3b. Three minutes of eyes closed EEG were also recorded. Because these ERPs are often identified as biomarkers for schizophrenia, drug effects were also measured after individuals were stratified for low-baseline amplitude of each ERP measure, as a laboratory model of cognitive deficits in schizophrenia. Overall results showed a synergistic improvement in sensory gating via nicotine combined with moclobemide, accompanied by a reduction in theta band power. Nicotine in the absence of moclobemide increased P3b amplitude, accompanied by an increase in alpha2 band power. Moclobemide in the absence of nicotine increased P3a amplitude, accompanied by a decrease in beta2 power. Stratifying participants by placebo amplitude revealed both nicotine and moclobemide exhibited an inverted-U pattern of effect, i.e. showing greater amplitude increases in individuals with the lowest baseline amplitudes. Overall, this thesis demonstrates how these two components of tobacco smoke affect different facets of auditory processing in different ways, with synergistic effects in some paradigms but antagonizing effects in others. Therefore, chronic smokers and schizophrenia patients who seek transient cognitive improvement through smoking may actually experience cognitive detriments overall, possibly contributing to withdrawal symptoms and/or an exacerbation of already-present psychiatric symptoms.

The measurement of electrical activity at the scalp using EEG can provide great insight into cognition and information processing. For example, event-related potentials (ERPs) are positive or negative deflections that correspond to a stimulus or event. These ERPs can reflect error processing and attentional processes associated with a stimulus. Specifically, error-related negativity and feedback-related negativity (ERN, FRN), are related to performance/conflict monitoring. Furthermore, the P300 ERP reflects attentional processes in response to target stimuli. Previous research examining the P300 component on a complex learning task has demonstrated increased P300 amplitude in response to violations of participants’ expectations about task events. The current study extends this research by examining ERN and FRN amplitudes on trials with incorrect behavioral responses throughout the same learning task. Pilot data has been collected from four participants. Participants wore an electrode cap with 32 electrodes to record EEG data while completing a paired associate task. Pilot data has demonstrated an increased ERN amplitude 50ms after error commission on incorrect trials. The ERN and FRN amplitudes were greater for incorrect trials than for correct trials. Larger P300 amplitudes were also observed for the incorrect trials than for the correct trials. This extension upon previous findings provides further insight into the role of performance monitoring and error processing in learning.