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Στόχος της παρούσας διπλωματικής είναι η παρουσίαση σύγχρονων μεθόδων μελέτης των διεγχειρητικών προκλητών δυναμικών και η χρήση των μεθόδων αυτών για την ανάλυση σημάτων που προέρχονται από πραγματικές μετρήσεις κατά τη διάρκεια εγχειρήσεων στη σπονδυλική στήλη. Πριν όμως παρουσιαστούν οι μέθοδοι αυτές, είναι χρήσιμη μια γενική αναφορά στην έννοια της διεγχειρητικής παρακολούθησης, των προκλητών δυναμικών και στη χρήση των τελευταίων για την παρακολούθηση της κατάστασης του ασθενή κατά τη διάρκεια μιας εγχείρησης. Οι έννοιες αυτές αποτελούν τη βάση του παρόντος κεφαλαίου. Στη συνέχεια, στο κεφάλαιο 2 αναλύονται οι σύγχρονες μέθοδοι ανάλυσης των προκλητών δυναμικών και ολοκληρώνεται κατ’αυτό τον τρόπο το θεωρητικό υπόβαθρο στο οποίο στηρίζεται η παρούσα εργασία. Στο κεφάλαιο 3 παρουσιάζεται η εφαρμογή MATLAB η οποία υλοποιήθηκε για την ανάλυση των προκλητών δυναμικών. Η εφαρμογή δίνει τη δυνατότητα στο χρήστη να «φορτώσει» ένα σήμα, να εξάγει κάποια χαρακτηριστικά του χρησιμοποιώντας τρεις διαφορετικούς τρόπους ανάλυσης και στη συνέχεια να αποθηκεύσει τα αποτελέσματα σε tab-delimited αρχεία κειμένου. Στο κεφάλαιο 4 παρουσιάζονται τα αποτελέσματα που εξήχθησαν από την επεξεργασία των σημάτων που είχαμε στη διάθεσή μας. Τα σήματα αφορούσαν μετρήσεις σε διαφορετικούς ασθενείς κατά τη διάρκεια εγχειρήσεων ιππουρίδας και το αποτέλεσμα της εγχείρησης ήταν γνωστό (πρόκληση ή μη βλάβης σε μία ή και στις δύο πλευρές του σώματος). Στόχος του κεφαλαίου είναι να κάνει μια πρώτη παράθεση των αποτελεσμάτων και να διευκολύνει την εξαγωγή συμπερασμάτων όσον αφορά στην ακρίβεια των μεθόδων. Στο κεφάλαιο 5 ακολουθεί μια συζήτηση που στόχο έχει να συνοψίσει τα βασικά στοιχεία των αποτελεσμάτων ενώ τέλος στο κεφάλαιο 6 παρατίθενται τα συμπεράσματα της εργασίας. Μετά τα συμπεράσματα ακολουθεί το παράρτημα Α στο οποίο εμφανίζονται σε πίνακες των αποτελεσμάτων που προέκυψαν για τα διαθέσιμα σήματα εκτελώντας ανάλυση στο πεδίο του χρόνου, στο πεδίο της συχνότητας και στο πεδίο χρόνου- συχνότητας. / -

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Psychopathy is a complex personality disorder denned by a constellation of affective and behavioral characteristics. There is accumulating behavioral evidence suggesting that the condition is associated with impairments in affective, cognitive, and language functions. However, relatively little is known regarding the neural systems underlying these abnormalities. The present thesis is comprised of five experiments designed to elucidate and characterize the abnormal functional architecture underlying these abnormalities in psychopathic criminals. In Experiments 1 and 2, functional magnetic resonance imaging (fMRI) was used to elucidate the neural systems underling abnormal semantic and affective processes in these individuals. In Experiments 3, 4 and 5, event-related potentials (ERPs) were used to characterize the temporal features of cognitive and language functions in psychopaths. The results from Experiment 1 revealed that compared to control participants, psychopaths performed more poorly and failed to showed the appropriate neural differentiation between abstract and concrete stimuli during a lexical decision task. These deficits were located in the right anterior superior temporal gyrus. The results from Experiment 2 indicated that psychopaths, relative to control participants, showed less activation for processing affective stimuli than for neutral stimuli in several neural regions, including the right amygdala/hippocampal formation, left parahippocampal gyrus, ventral striatum, and in the anterior and posterior cingulate. Psychopaths did show greater activation for processing affective than for neutral stimuli in regions located outside the limbic system, including bilateral inferior frontal gyrus. These latter data suggesting that psychopaths used different neural systems than did controls for performing the task. The results from Experiments 3 and 4 indicated that psychopathy is associated with abnormalities in the P3 ERP component elicited by target stimuli during visual and auditory oddball tasks. In addition, the psychopaths' ERPs to visual and auditory target stimuli were characterized by large fronto-central negativities in the 350-600 millisecond time window. These fronto-central ERP negativities are similar to those observed for patients with temporal lobe damage. In Experiment 5, using a standard sentence processing paradigm, no group differences were observed between psychopaths and nonpsychopaths in the amplitude of the N400 potential elicited by terminal words of sentences that were either congruent or incongruent with the previous sentence context. These results indicate that the abnormal fronto-central ERP negativities observed in previous studies of language function in psychopaths are not related to processes involved in the generation of the N400. Taken together, these data suggest that one of the cardinal abnormalities in psychopathy is abnormal semantic processing of conceptually abstract information and affective information and that these abnormalities are related to the function of neural circuits in the anterior temporal lobes and lateral frontal cortex.

The experiments in this thesis used behavioural measures and event-related potentials (ERPs) to investigate the influence of race on face processing in the brain. Previous behavioural research has highlighted an own-race effect in face processing, whereby individuals are more accurate at recognizing own-race compared to other-race faces. The current Thesis examined the own-race effect at perceptual and neural levels. Social influences on the own-race effect were also investigated, such as other-race experience, anxiety and implicit social bias, as these may account for differential own- versus other-race face processing. The main aim of the experiments contained in this thesis was to delve deeper into the examination of own and other-race face perception through a series of original experiments. Participants performed a variety of perceptual discrimination and identification tasks, and completed measures of explicit other-race experience and implicit racial bias to record their perceptions of other-race individuals. Chapters 2-4 saw the development of a new paradigm that tested the own-race effect in perception, in contrast to traditional recognition memory investigations. In Chapter 2 the own-race effect was investigated developmentally and found across three age-groups, and was larger in the two older age-groups. Chapters 3 and 4 found that the own-race effect differed across racial groups, and that social variables such as other-race experience influenced the strength of the own-race effect. In the latter experimental chapters, ERPs revealed that the behavioural own-race effect was evident at a neural level. Chapter 7 demonstrated that face-related stages of processing in the brain were sensitive to race of face. In Chapters 8 and 9, the sensitivity of face processing to own and other-race emotional expression processing was also examined. The additional social factor of emotional expression was explored in order to further the investigation of socially relevant information processing from the face. Findings from the last two experimental chapters demonstrated differential emotional face processing for own- versus other-race faces. Confirming the findings of the behavioural experiments, own- versus other-race emotion processing varied across racial groups and was subject to social influences such as other-race experience, intergroup anxiety and implicit racial bias. Overall, behavioural and neural investigations of the own-race effect demonstrated the influence of social variables such as other-race experience, intergroup anxiety and implicit racial bias on the way in which individuals processed own- versus other-race faces in the human brain.

Introduction: Psychophysical and electrophysiological techniques have shown that chromatic contrast sensitivity improves between infancy and adolescence. In adults, electrophysiological and psychophysical methods usually agree. However, in infants electrophysiological techniques may underestimate ability to see chromatic contrast (Suttle et al., 2002). It is not known if the discrepancy between electrophysiological and psychophysical methods continues during childhood nor whether the chromatic VEP can be used as an indicator of colour perception in children. Purpose: To investigate the transient L-M chromatic visual evoked potential and its ability to indicate perception (psychophysical thresholds) of chromatic stimuli in children and adults. In particular, to determine whether a discrepancy between VEP and psychophysical L-M thresholds exists during childhood and if so, to gain some understanding about the nature of the discrepancy. Methods: Transient chromatic VEPs were recorded in children (aged 4.5-13 years) and adults (aged 20-40 years). VEP thresholds were compared with psychophysical thresholds (within-subjects comparison). Because the VEPs of the children were less intra-individually repeatable in morphology than those of the adults, post-hoc objective analysis of the VEPs, linear (Fourier) and nonlinear dynamical (Grassberger and Procaccia's (1983) correlation dimension) analyses, was conducted. Results: VEP and psychophysical estimates of chromatic contrast thresholds agreed using a variety of methods in the adults. In the children, however, the objective methods of assessment (extrapolation from Fourier-derived amplitudes and the correlation dimension) were more accurate than the methods that employed subjective evaluations of VEP morphology. Conclusion: The L-M transient chromatic VEPs of both children (aged 4.5-13 years) and adults appear to contain chromatic information, even in the absence of repeatable VEP morphology and should therefore be able to indicate chromatic perception (psychophysical thresholds). However, the chromatic information may be present as a nonlinear dynamical signal, which may require objective methods (Fourier analysis, the correlation dimension) to reveal the chromatic signal. The greater intra-individual variability of VEP morphology in children compared to adults may reflect poorer precision when switching between cortical states in children's brains. Alternatively, interactions between the immature visual system of the children and their general EEG may occur. Children's VEPs should therefore be interpreted differently to adult VEPs.

Previous studies have found that spatial processing in children and adults with Down syndrome is different in comparison to the normal population. Some previous studies have also found that there is a high prevalence of colour vision deficiencies in people with Down syndrome. The aim of the present study was to use an objective test, the transient visual evoked potential (VEP), to assess achromatic and chromatic visual processing in adults with Down syndrome. Achromatic VEPs were recorded in response to black-white stimuli presented in patternreversal mode. Chromatic VEPs were recorded in response to two types of colour pattern, presented in pattern onset-offset mode. The two colour types were intended to preferentially stimulate the two principal chromatic pathways of the visual system, the ???redgreen??? and ???blue-yellow??? colour-opponent pathways. These stimuli are here termed the ???LM??? and ???S-(L+M) stimuli, respectively, reflecting the cone types that input to the pathways they are intended to stimulate. Each subject also completed two subjective colour vision tests, the Colour Vision Test Made Easy (CVTME) and the City University Colour Vision Test (CUT). Morphology of the achromatic and chromatic VEPs was found to differ between the group with Down syndrome and an age-matched control group. The latency of the P100 component of the achromatic VEP was found to be significantly later in the group with Down syndrome compared to the control group (the N75 latency was earlier in the group with Down syndrome, but not significantly so). The group-averaged peak-to-peak amplitude of the achromatic VEP was significantly lower in the group with Down syndrome compared to the control group. The major positive component of the VEP in response to the L-M stimulus was of significantly longer latency compared to that of the control group. The major negative component and the peak-to-peak amplitude of this response were not significantly different between the groups. For the response to S-(L+M) stimuli, the latency of the major negativity was significantly earlier in the group with Down syndrome and the major positivity was later, but not significantly so. Amplitude of this response was significantly higher in adults with Down syndrome compared to the control group. Most subjects in both groups passed both the CVTME and CUT. Our findings indicate that chromatic VEPs are abnormal in Down syndrome, and this may reflect abnormal processing of chromatic stimuli in this population. Alternatively, these abnormalities may arise due to abnormal cortical morphology, which may occur with normal or abnormal processing of chromatic signals. These findings further indicate that abnormality of chromatic VEPs may be expected in Down syndrome, and is not necessarily indicative of pathology or other abnormal function that is unrelated to the syndrome.