L’objectif général de cette thèse était de tester l’efficacité d’un entraînement exécutif ainsi que de tester les transferts des bénéfices de cet entraînement sur d’autres fonctions cognitives notamment la mémoire épisodique au niveau comportemental et électrophysiologique chez des adultes âgés. Pour cela, des effets test-retest ont été observés lors de la passation d’un même test de façon consécutive. Ainsi, la création de nouveaux tests pour confectionner le programme d’entraînement a été nécessaire pour ne pas avoir ces effets tests re-tests lors de la passation des pré-tests et des post-tests. Les entraînements exécutifs ont permis l’amélioration du fonctionnement exécutif mais aussi l’amélioration de la vitesse de traitement, et ces bénéfices ont permis l’annulation des effets d’âge dans le groupe entraîné sur une fonction exécutive : la mise à jour de la mémoire de travail. De plus, des effets de transfert ont été obtenus sur l’utilisation stratégique lors de l’encodage d’information en mémoire épisodique. Plus précisément, les adultes âgés entraînés utilisaient plus de stratégies d’encodages efficaces (encodage profond de type imagerie mentale ou phrase) après l’entraînement exécutif et l’utilisation de ces stratégies était plus efficace. Au niveau cérébral, l’entraînement exécutif semble engendrer des processus de spécialisation cérébrale se traduisant par une diminution de l’activité cérébrale de certaines zones cérébrales. Ce travail de thèse incite le développement de programmes d’entraînement des fonctions exécutives qui semblent permettre des effets de transfert à des tâches non entraînées et ces bénéfices semblent aussi modifier le fonctionnement cérébral, ce qui suppose un effet plus durable. Ceci confirme l’idée qu’un environnement stimulant cognitivement est en lien avec de bonnes capacités cognitives et contribue à un vieillissement réussi / The main objective of this thesis was to test the efficiency of an executive training program and the transfer effects of this program on other cognitive functions, in particular episodic memory strategies and performance. The present work was based on behavioral and electrophysiological data. Practice effects of executive tests have been first tested in young and older adults. Two tests have been practiced across ten practice sessions, and the results showed that the executive functions scores increased after practice, more for the older adults than for the younger ones. In order to develop an executive training program requiring several different tests, we have created new executive tests. The psychometric validity of these tests has been verified and confirmed. These tests have been used for our executive program. Thus, if training effects appeared following this program, they will not be due to the practice of a unique test. Eight sessions of executive stimulation with our new tests have allowed older adults increasing their executive functioning, measured by tests which were different from those employed in the training program (near transfer effects). Other cognitive functions were also improved, as processing speed and episodic memory. For the first time in the literature, far transfer effect have been found memory strategy efficiency and memory performance. More especially, the older adults trained group used more efficient memory strategies (mental imagery or making sentence with the words to be learnt) after the executive training program, and these strategies were more efficient to recall the words. Thus, the memory performance was increased in this group, in comparison the older adults group who did not participate to the training program. At a cerebral level, the executive training seems to decrease the duration of the cerebral activity for the same memory task. However, these results must to be taken with caution and require further analyses to be interpreted correctly. The results of this thesis encourages the development of training programs for executive functions which allows the transfer effects to untrained tasks. These benefits also appear to modify the brain functioning, which implies a longer lasting benefit effect. This work supports the idea that a cognitively stimulating environment is in line with higher cognitive abilities and contributes to successful aging

Two theories of consciousness have different ideas about when consciousness happens and what neural processes enable conscious experience. The recurrent processing theory supports an early onset of consciousness caused by recurring loops of information between sensory areas. Contrary to this belief, the global workspace theory claims that consciousness appears later, through global recurrent loops of information between sensory and higher order brain areas such as the visual cortex and frontoparietal areas. Electrophysiological studies have found an event-related negativity arising in primary visual areas around 200 ms that correlates to awareness. This activity suits the predictions of an early onset of consciousness made by the recurrent processing theory. It is followed by a later positive amplitude appearing around 400 ms. This activity is in line with predictions made by the global workspace theory. The current study transition from visual to auditory awareness research in order to find the neural correlates of consciousness in audition. A sound detection task with tones calibrated to each participants threshold value was used in the experiment and two electrophysiological measurements of auditory awareness were found. An auditory awareness negativity that appears around 200 ms after stimulus onset and a late positivity appearing around 400 ms. Researchers disagree about if these event-related potentials correlate with awareness or unrelated cognitive mechanisms. In order to solve this problem, the current experiment was devised to test if they were affected by response conditions. A no-response paradigm with reversed response conditions was used to separate pre- and post-conscious mechanisms from the auditory awareness negativity and the late positivity. Results showed that auditory awareness negativity was independent of response condition and thus free from post-perceptual processes. The late positivity amplitude seems to be dependent on response condition but the result was inconclusive.

Les études en neurosciences cognitives ont mis en évidence des phénomènes de neuroréorganisation au cours du vieillissement et des corrélats neuronaux spécifiques à la maturation de l’enfant, lors de la réalisation de tâches de mémoire épisodique. Examiner l’évolution des corrélats neuronaux de la récupération en mémoire et déterminer si les patterns cérébraux spécifiques à l’enfant et à l’adulte âgé sont bénéfiques à la performance mnésique constituaient les objectifs majeurs de ce travail. Les résultats ont mis en évidence que les patterns de neuroréorganisation liés à l’âge (modèle PASA et modèle HAROLD) sont déjà présents chez l’adulte jeune et ne sont donc pas spécifiques au cerveau âgé. En accord avec l’hypothèse de compensation, la neuroréorganisation observée chez les adultes âgés, sous la forme d’un shift frontal, apparait bénéfique à la performance mnésique et est liée à un meilleur fonctionnement exécutif. Enfin, l’activité pariétale et frontale chez l’enfant est associée au processus de familiarité, alors que chez les adultes jeunes l’activité pariétale est liée à la remémoration. Chez les adultes âgés, l’activité frontale est associée au processus de remémoration, suggérant un phénomène compensatoire. / Studies in cognitive neurosciences have highlighted neural reorganization phenomena in aging and specific neural correlates associated with children’s maturation during episodic memory tasks. To examine the evolution of the neural correlates of the memory retrieval and to determine if brain patterns specific to children and older adults are beneficial to the memory performance, were the major objectives of this work. Results showed that age-related neural reorganization patterns (PASA model and HAROLD model) are already present in young adults, therefore they are not specific to the older brains. In agreement with the compensation hypothesis, the neural reorganization observed in older adults, taking the form of a frontal shift, appears to be beneficial to memory performance and associated with a better executive functioning. Finally, frontal and parietal activities in children are associated with the familiarity process, whereas in young adults the parietal activity is related to a recollection process. In older adults, the frontal activity is associated with a recollection process, suggesting a compensatory phenomenon.

Entgegen traditioneller Gesichtererkennungsmodelle konnte in einigen Studien gezeigt werden, dass die Erkennung des Emotionsausdrucks und der Bekanntheit interagieren. In dieser Dissertation wurde mit Hilfe von ereigniskorrelierten Potentialen untersucht, welche funktionalen Prozesse bei einer Interaktion moduliert werden. Teil I untersuchte, ob die Bekanntheit eines Gesichtes die Emotionsdiskrimination erleichtert. In mehreren Experimenten diskriminierten Versuchspersonen zwei Emotionen, die von bekannten und unbekannten Gesichtern praesentiert wurden . Dabei war die Entscheidung fuer persoenlich bekannte Gesichter mit froehlichem Ausdruck schneller und fehlerfreier. Dies zeigt sich in einer kuerzeren Latenz der P300 Komponente (Trend), welche die Dauer der Reizklassifikation auswies, sowie in einem verkuerzten Intervall zwischen Stimulus und Beginn des Lateralisierten Bereitschaftspotentials (S-LRP), welches die handspezifische Reaktionsauswahl anzeigt. Diese Befunde sprechen fuer eine Erleichterung der Emotionsdiskrimination auf spaeten perzeptuellen Verarbeitungsstufen bei persoenlich bekannten Gesichtern. In weiteren Experimenten mit oeffentlich bekannten, gelernten und unbekannten Gesichtern zeigte sich keine Erleichterung der Emotionsdiskrimination für bekannte Gesichter. Teil II untersuchte, ob es einen Einfluss des Emotionsausdrucks auf die Bekanntheitsentscheidung gibt. Eine Erleichterung zeigte sich fuer neutrale oder froehliche Emotionen nur bei persoenlich bekannten Gesichtern, nicht aber bei gelernten oder unbekannten Gesichtern. Sie spiegelt sich in einer Verkuerzung des S-LRP fuer persoenlich bekannte Gesichter wider, was eine Erleichterung der Reaktionsauswahl nahelegt. Zusammenfassend konnte gezeigt werden, dass eine Interaktion der Bekanntheit mit der Emotionserkennung unter bestimmten Bedingungen auftritt. In einer abschließenden Diskussion werden die experimentellen Ergebnisse in Beziehung gesetzt und in Hinblick auf bisherige Befunde diskutiert. / Contrasting traditional face recognition models previous research has revealed that the recognition of facial expressions and familiarity may not be independent. This dissertation attempts to localize this interaction within the information processing system by means of performance data and event-related potentials. Part I elucidated upon the question of whether there is an interaction between facial familiarity and the discrimination of facial expression. Participants had to discriminate two expressions which were displayed on familiar and unfamiliar faces. The discrimination was faster and less error prone for personally familiar faces displaying happiness. Results revealed a shorter peak latency for the P300 component (trend), reflecting stimulus categorization time, and for the onset of the lateralized readiness potential (S-LRP), reflecting the duration of pre-motor processes. A facilitation of perceptual stimulus categotization for personally familiar faces displaying happiness is suggested. The discrimination of expressions was not facilitated in further experiments using famous or experimentally familiarized, and unfamiliar faces. Part II raises the question of whether there is an interaction between facial expression and the discrimination of facial familiarity. In this task a facilitation was only observable for personally familiar faces displaying a neutral or happy expression, but not for experimentally familiarized, or unfamiliar faces. Event-related potentials reveal a shorter S-LRP interval for personally familiar faces, hence, suggesting a facilitated response selection stage. In summary, the results suggest that an interaction of facial familiarity and facial expression might be possible under some circumstances. Finally, the results are discussed in the context of possible interpretations, previous results, and face recognition models.

We examined relations between eye movements (single-fixation durations) and RSVP-based event-related potentials (ERPs; N400’s) recorded during reading the same sentences in two independent experiments. Longer fixation durations correlated with larger N400 amplitudes. Word frequency and predictability of the fixated word as well as the predictability of the upcoming word accounted for this covariance in a path-analytic model. Moreover, larger N400 amplitudes entailed longer fixation durations on the next word, a relation accounted for by word frequency. This pattern offers a neurophysiological correlate for the lag-word frequency effect on fixation durations: Word processing is reliably expressed not only in fixation durations on currently fixated words, but also in those on subsequently fixated words.

Remembering previously experienced events can happen as a result of an effortful retrieval attempt. At other occasions, a memory can enter our minds without any apparent effort – or, indeed, intention - to retrieve. Although it has long been appreciated that retrieval from episodic memory is intertwined with cognitive control, the neural mechanisms of memory-control interactions remain unclear. In this thesis I have used functional magnetic resonance imaging (fMRI) and scalp-recorded event-related potentials (ERP) to study the neural basis of episodic retrieval at varying levels of cognitive control. The dorsolateral prefrontal cortex (dlPFC) has been suggested to support a cognitive control mechanism (context processing) which is relevant during various situations that demand maintenance of current goals and rules. Although increased dlPFC recruitment with increasing context processing demands has been demonstrated during episodic retrieval, there are relatively few studies directly comparing the engagement of dlPFC during episodic retrieval with that during other task domains. In Study I, context processing demands were amplified in episodic retrieval, auditory attention and emotion regulation tasks. This led to overlapping dlPFC recruitment in the first two domains and a divergent reliance on ventromedial prefrontal cortex in the emotion domain. Thus, when selection between competing representations needs to be carried out in accordance with the currently relevant goals and task rules, the episodic memory system interacts with domain-general cognitive control mechanisms. Studies II and III explored the reactive nature of retrieval-specific control mechanisms: can we flexibly switch between semantic and episodic retrieval based on the information extracted from a retrieval cue? This was studied using a recognition memory task where the relevant information could with equal probability be supplied by the semantic or the episodic memory system. The fMRI results (Study II) showed that the brain activation during the ‘episodic’ but not the ‘semantic’ trials was expressed in the right prefrontal cortex. As the order of trials was unpredictable, the corresponding changes in brain activation might be evoked by differences in early cue-trace interactions. An event-related potential study (Study III) with the same experimental protocol as in Study II showed that neural processing corresponding to the two trial types diverged as early as in the time window 100-140 ms post-cue onset, thus highlighting the importance of early cue-trace matching in the selection of further retrieval processing. Study IV explored incidental episodic retrieval. Although this form of retrieval is a common experience in everyday life and a disturbing symptom in some psychiatric conditions, it is not clear how such spontaneous expressions of memory are initiated and to what extent the prefrontal cortex is engaged. The fMRI results showed, consistent with Study I, that dlPFC is specifically associated with the intention to retrieve, independently of success. Retrieval success engaged similar networks for incidentally as well as intentionally retrieved memories, comprising the hippocampus, precuneus, ventrolateral PFC, and the anterior cingulate cortex. Collectively, the fMRI and ERP results indicated that incidental retrieval was initiated by early (< 200 ms) oldness estimation carried out on the semantic information extracted from the retrieval cues. Taken together, the results of this thesis indicate that episodic retrieval can be initiated via two routes:  a bottom-up input rising early during the cue processing, and a top-down input provided by the cognitive control processes mediated by the prefrontal cortex.

Stimulus-driven changes in the gain of sensory neurons are well-documented, but relatively little is known about whether analogous gain-control can also be effected in a top-down manner. A recent psychophysical study demonstrated that sensitivity to luminance contrast can be modulated by a priori knowledge (de la Rosa et al., in press). In the present study, event-related potentials were used to resolve the stages of information processing that facilitate such knowledge-driven adjustments. Groupwise independent component analysis identified two robust spatiotemporal patterns of endogenous brain activity that captured experimental effects. The first pattern was associated with obligatory processing of contextual information, while the second pattern was associated with selective initiation of contrast gain adjustment. These data suggest that knowledge-driven contrast gain control is mediated by multiple independent electrogenic sources.

Stimulus-driven changes in the gain of sensory neurons are well-documented, but relatively little is known about whether analogous gain-control can also be effected in a top-down manner. A recent psychophysical study demonstrated that sensitivity to luminance contrast can be modulated by a priori knowledge (de la Rosa et al., in press). In the present study, event-related potentials were used to resolve the stages of information processing that facilitate such knowledge-driven adjustments. Groupwise independent component analysis identified two robust spatiotemporal patterns of endogenous brain activity that captured experimental effects. The first pattern was associated with obligatory processing of contextual information, while the second pattern was associated with selective initiation of contrast gain adjustment. These data suggest that knowledge-driven contrast gain control is mediated by multiple independent electrogenic sources.

The ability to correct balance disturbances is essential for maintaining upright stability. Recent literature highlights a potentially important role for the cerebral cortex in controlling compensatory balance reactions. The objective of this research was to provide a more detailed understanding of the specific neurophysiologic events occurring at the cortex following balance disturbances. More specifically, the focus was to determine whether the N1, a cortical potential evoked during balance control, and the error-related negativity (ERN), a cortical potential measured in response to errors during cognitive tasks, have similar cortical representation, revealing a similar link to an error detection mechanism. It was hypothesized that the N1 and ERN would have the same generator located in the anterior cingulate cortex (ACC). Fourteen healthy young adults participated in a balance task (evoked N1) and a flanker task (evoked ERN). Temporally unpredictable perturbations to standing balance were achieved using a lean and release cable system. Electromyography and centre of pressure were measured during the balance task. Reaction times and error rates were measured during the flanker task. Electroencephalography was recorded during both tasks. Source localization was performed in CURRY 6 using a single fixed coherent dipole model to determine the neural generator of the N1 and ERN. The results revealed that the locations of the N1 and ERN dipoles were different. The mean (n=9) distance between N1 and ERN dipoles was 25.46 ± 8.88 mm. The mean Talairach coordinates for the ERN dipole were (6.47 ± 3.08, -4.41 ± 13.15, 41.17 ± 11.63) mm, corresponding to the cingulate gyrus (Brodmann area 24). This represents the ACC, supporting results from previous literature. The mean Talairach coordinates for the N1 dipole were (5.74 ± 3.77, -11.81 ± 10.84, 53.73 ± 7.30) mm, corresponding to the medial frontal gyrus (Brodmann area 6). This is the first work to localize the source of the N1. It is speculated that the generator of the N1 is the supplementary motor area and that it represents the generation of a contingency motor plan to shape the later phases of the compensatory balance response based on sensory feedback from the perturbation.

Several lines of evidence from rapid serial visual presentation, attentional blink, and dual-task interference phenomena propose that human beings have a significant limitation on the short-term consolidation process. Short-term consolidation is transferring early representations to more durable forms of memory. Although previous research has shown that masks presented after targets interrupt the consolidation process of information, there is not enough evidence for the role of attention in consolidation for episodic memory. One electrophysiological and five behavioral experiments were conducted to investigate the effects of attention and stimulus onset asynchrony (SOA) between targets and masks on episodic memory. Masks were presented after targets with varying SOAs. The participants in the divided attention condition but not the ones in the full attention condition performed the attention-demanding secondary task after the presentation of the masks. The results showed that reducing SOA between targets and masks caused an impairment in memory performance for divided attention but not for full attention, providing evidence for the necessity of attention for the short-term consolidation process. Electrophysiological results demonstrated that this impairment did not result from perceptual processes.