Visual stimulus-dependent changes in interhemispheric EEG coherence in humans.

We analyzed the coherence of electroencephalographic (EEG) signals recorded symmetrically from the two hemispheres, while subjects (n = 9) were viewing visual stimuli. Considering the many common features of the callosal connectivity in mammals, we expected that, as in our animal studies, interhemispheric coherence (ICoh) would increase only with bilateral iso-oriented gratings located close to the vertical meridian of the visual field, or extending across it. Indeed, a single grating that extended across the vertical meridian significantly increased the EEG ICoh in normal adult subjects. These ICoh responses were obtained from occipital and parietal derivations and were restricted to the gamma frequency band. They were detectable with different EEG references and were robust across and within subjects. Other unilateral and bilateral stimuli, including identical gratings that were effective in anesthetized animals, did not affect ICoh in humans. This fact suggests the existence of regulatory influences, possibly of a top-down kind, on the pattern of callosal activation in conscious human subjects. In addition to establishing the validity of EEG coherence analysis for assaying cortico-cortical connectivity, this study extends to the human brain the finding that visual stimuli cause interhemispheric synchronization, particularly in frequencies of the gamma band. It also indicates that the synchronization is carried out by cortico-cortical connection and suggests similarities in the organization of visual callosal connections in animals and in man.

The Rank Lecture: Has imaging told us anything new about human visual organisation?

The functional architecture of the occipital cortex is being studied with increasing detail. Functional and structural MR based imaging are altering views about the organisation of the human visual system. Recent advances have ranged from comparative studies with non-human primates to predictive scanning. The latter multivariate technique describes with sub-voxel resolution patterns of activity that are characteristic of specific visual experiences. One can deduce what a subject experienced visually from the pattern of cortical activity recorded. The challenge for the future is to understand visual functions in terms of cerebral computations at a mesoscopic level of description and to relate this information to electrophysiology. The principal medical application of this new knowledge has focused to a large extent on plasticity and the capacity for functional reorganisation. Crossmodality visual-sensory interactions and cross-correlations between visual and other cerebral areas in the resting state are areas of considerable current interest. The lecture will review findings over the last two decades and reflect on possible roles for imaging studies in the future.

Estudio de la agudeza visual final en correlación con variables anatómicas y funcionales objetivas en pacientes con desprendimiento de retina primario

Estudi de cohort de pacients amb despreniment de retina primaris, intervinguts per vitrectomia posterior i agudesa visual final superior a 0,1. Es recullen 23 pacients i es practica un tall de mesura longitudinal a la cohort, recollint paràmetres demogràfics, agudesa visual final, tomografia de coherència òptica i electrorretinograma multifocal. S'estudien associacions entre l'agudesa visual final i les proves objectives anatòmiques i funcionals.

Repercusión visual posterior al explante de lente intraocular opacificada

INTRODUCCIÓ: Valorar els resultats funcionals i quirúrgics posteriors a l’explant de la lent intraocular H60M opacificada. MATERIAL I MÈTODES: Estudi retrospectiu de vint-i-cinc ulls sotmesos a intercanvi de H60M opacificada. Anàlisi dels resultats visuals i complicacions, abans, durant i després de l’explante. RESULTATS: Trobarem millors resultats visuals i una menor taxa de complicacions quan no associem vitrectomia anterior a la cirurgia, així como amb la col•locació de la lent secundaria a sulcus. CONCLUSIÓ: L’intercanvi de la LIO Hidroview opacificada suposa un risc quirúrgic addicional, que podem minimitzar durant el període intraoperatori intentant preservar les estructures oculars el més anatòmicament possible.

Dynamic visual information plays a critical role for spatial navigation in water but not on solid ground.

In the Morris water maze (MWM) task, proprioceptive information is likely to have a poor accuracy due to movement inertia. Hence, in this condition, dynamic visual information providing information on linear and angular acceleration would play a critical role in spatial navigation. To investigate this assumption we compared rat's spatial performance in the MWM and in the homing hole board (HB) tasks using a 1.5 Hz stroboscopic illumination. In the MWM, rats trained in the stroboscopic condition needed more time than those trained in a continuous light condition to reach the hidden platform. They expressed also little accuracy during the probe trial. In the HB task, in contrast, place learning remained unaffected by the stroboscopic light condition. The deficit in the MWM was thus complete, affecting both escape latency and discrimination of the reinforced area, and was thus task specific. This dissociation confirms that dynamic visual information is crucial to spatial navigation in the MWM whereas spatial navigation on solid ground is mediated by a multisensory integration, and thus less dependent on visual information.

Photophobia as the presenting visual symptom of chiasmal compression.

Five patients with a chief visual complaint of photophobia were subsequently found to have compressive lesions of the optic chiasm. Visual acuity and visual field deficits were often subtle. Magnetic resonance imaging scanning revealed large suprasellar masses, including three pituitary adenomas, a craniopharyngioma, and a clivus chordoma. Photophobia resolved in all patients following treatment of the tumors. A compressive lesion of the optic chiasm should be considered in patients who experience persistent photophobia unexplained by ocular abnormalities.

Penetrance of marked cognitive impairment in older male carriers of the FMR1 gene premutation.

BACKGROUND: Male carriers of the FMR1 premutation are at risk of developing the fragile X-associated tremor/ataxia syndrome (FXTAS), a newly recognised and largely under-diagnosed late onset neurodegenerative disorder. Patients affected with FXTAS primarily present with cerebellar ataxia and intention tremor. Cognitive decline has also been associated with the premutation, but the lack of data on its penetrance is a growing concern for clinicians who provide genetic counselling. METHODS: The Mattis Dementia Rating Scale (MDRS) was administered in a double blind fashion to 74 men aged 50 years or more recruited from fragile X families (35 premutation carriers and 39 intrafamilial controls) regardless of their clinical manifestation. Based on previous publications, marked cognitive impairment was defined by a score <or=123 on the MDRS. RESULTS: Both logistic and survival models confirmed that in addition to age and education level, premutation size plays a significant (p<0.01 and p<0.03 for logistic and survival model, respectively) role in cognitive impairment. The estimated penetrance of marked cognitive impairment in our sample (adjusted for the mean age 63.4 years and mean education level 9.7 years) for midsize/large (70-200 CGG) and small (55-69 CGG) premutation alleles was 33.3% (relative risk (RR) 6.5; p = 0.01) and 5.9% (RR 1.15; p = 0.9) respectively. Penetrance in the control group was 5.1%. CONCLUSIONS: Male carriers of midsize to large premutation alleles had a sixfold increased risk of developing cognitive decline and the risk increases with allele size. In addition, it was observed that cognitive impairment may precede motor symptoms. These data provide guidance for genetic counselling although larger samples are required to refine these estimates.

Perioperative visual loss: a rare complication of general surgery

BACKGROUND: Perioperative visual loss (PVL) refers to the loss of vision following surgery performed at distance from the visual pathways. An ischemic optic neuropathy (ION) is the most frequent clinical presentation of PVL, and can be bilateral. PATIENTS AND METHODS: A retrospective chart review of 11 consecutive patients with PVL examined between 2002 and 2007 was undertaken. RESULTS: An ION was found in all 11 cases: 8 were anterior (AION) and 3 were posterior (PION). Visual loss was bilateral in 9 patients. Mean visual acuity (VA) was 0.2 on the Snellen chart (0.74 LogMAR). Most frequently an arcuate/altitudinal visual field defect was present. PVL followed orthopedic (6), spinal (1), cardiac (2) and vascular (2) procedures. The average delay between surgery and visual loss was 32 hours (range: 0-96 hours). Average lowest perioperative hemoglobin level was 75 g/L. Average follow-up time was 14.7 months. VA improved by at least 2 Snellen lines in 5/20 eyes (25 %). CONCLUSIONS: PVL is a rare but dreadful complication of surgery, and is usually associated with severe anemia. Like other causes of ION, there is no specific therapy. Prompt correction of the anemia might decrease the rate of this complication

Language and syntactic impairment following stroke in late bilingual aphasics.

PURPOSE: Bilingual aphasia generally affects both languages. However, the age of acquisition of the second language (L2) seems to play a role in the anatomo-functional correlation of the syntactical/grammatical processes, thus potentially influencing the L2 syntactic impairment following a stroke. The present study aims to analyze the influence of late age of acquisition of the L2 on syntactic impairment in bilingual aphasic patients. METHODS: Twelve late bilingual participants (speaking French as L2 and either English, German, Italian or Spanish as L1) with stroke-induced aphasia participated in the study. The MAST or BAT aphasia batteries were used to evaluate overall aphasia score. An auditory syntactic judgement task was developed and used to test participants syntactic performance. RESULTS: The overall aphasia scores did not differ between L1 and L2. In a multiple case analysis, only one patient had lower scores in L2. However, four patients presented significantly lower performances in syntactic processing in the late L2 than in their native language (L1). In these four patients the infarct was localized, either exclusively or at least partially, in the pre-rolandic region. CONCLUSION: This pilot study suggests that, in late bilingual aphasics, syntactic judgment abilities may be more severely impaired in L2, and that this syntactic deficit is most likely to occur following anterior lesions.

Visual representation of food in the brain : effects of repeated exposure and gut hormone secretion

The thesis at hand is concerned with the spatio-temporal brain mechanisms of visual food perception as investigated by electrical neuroimaging. Due to the increasing prevalence of obesity and its associated challenges for public health care, there is a need to better understand behavioral and brain processes underlying food perception and food-based decision-making. The first study (Study A) of this thesis was concerned with the role of repeated exposure to visual food cues. In our everyday lives we constantly and repeatedly encounter food and these exposures influence our food choices and preferences. In Study A, we therefore applied electrical neuroimaging analyses of visual evoked potentials to investigate the spatio-temporal brain dynamics linked to the repeated viewing of high- and low-energy food cues (published manuscript: "The role of energetic value in dynamic brain response adaptation during repeated food image viewing" (Lietti et al., 2012)). In this study, we found that repetitions differentially affect behavioral and brain mechanisms when high-energy, as opposed to low-energy foods and non-food control objects, were viewed. The representation of high-energy food remained invariant between initial and repeated exposures indicating that the sight of high-energy dense food induces less behavioral and neural adaptation than the sight of low-energy food and non-food control objects. We discuss this finding in the context of the higher salience (due to greater motivation and higher reward or hedonic valuation) of energy- dense food that likely generates a more mnemonically stable representation. In turn, this more invariant representation of energy-dense food is supposed to (partially) explain why these foods are over-consumed despite of detrimental health consequences. In Study Β we investigated food responsiveness in patients who had undergone Roux-en-Y gastric bypass surgery to overcome excessive obesity. This type of gastric bypass surgery is not only known to alter food appreciation, but also the secretion patterns of adipokines and gut peptides. Study Β aimed at a comprehensive and interdisciplinary investigation of differences along the gut-brain axis in bypass-operated patients as opposed to weight-matched non-operated controls. On the one hand, the spatio-temporal brain dynamics to the visual perception of high- vs. low-energy foods under differing states of motivation towards food intake (i.e. pre- and post-prandial) were assessed and compared between groups. On the other hand, peripheral gut hormone measures were taken in pre- and post-prandial nutrition state and compared between groups. In order to evaluate alterations in the responsiveness along the gut-brain-axis related to gastric bypass surgery, correlations between both measures were compared between both participant groups. The results revealed that Roux-en- Y gastric bypass surgery alters the spatio-temporal brain dynamics to the perception of high- and low-energy food cues, as well as the responsiveness along the gut-brain-axis. The potential role of these response alterations is discussed in relation to previously observed changes in physiological factors and food intake behavior post-Roux-en-Y gastric bypass surgery. By doing so, we highlight potential behavioral, neural and endocrine (i.e. gut hormone) targets for the future development of intervention strategies for deviant eating behavior and obesity. Together, the studies showed that the visual representation of foods in the brain is plastic and that modulations in neural activity are already noted at early stages of visual processing. Different factors of influence such as a repeated exposure, Roux-en-Y gastric bypass surgery, motivation (nutrition state), as well as the energy density of the visually perceived food were identified. En raison de la prévalence croissante de l'obésité et du défi que cela représente en matière de santé publique, une meilleure compréhension des processus comportementaux et cérébraux liés à la nourriture sont nécessaires. En particulier, cette thèse se concentre sur l'investigation des mécanismes cérébraux spatio-temporels liés à la perception visuelle de la nourriture. Nous sommes quotidiennement et répétitivement exposés à des images de nourriture. Ces expositions répétées influencent nos choix, ainsi que nos préférences alimentaires. La première étude (Study A) de cette thèse investigue donc l'impact de ces exposition répétée à des stimuli visuels de nourriture. En particulier, nous avons comparé la dynamique spatio-temporelle de l'activité cérébrale induite par une exposition répétée à des images de nourriture de haute densité et de basse densité énergétique. (Manuscrit publié: "The role of energetic value in dynamic brain response adaptation during repeated food image viewing" (Lietti et al., 2012)). Dans cette étude, nous avons pu constater qu'une exposition répétée à des images représentant de la nourriture de haute densité énergétique, par opposition à de la nourriture de basse densité énergétique, affecte les mécanismes comportementaux et cérébraux de manière différente. En particulier, la représentation neurale des images de nourriture de haute densité énergétique est similaire lors de l'exposition initiale que lors de l'exposition répétée. Ceci indique que la perception d'images de nourriture de haute densité énergétique induit des adaptations comportementales et neurales de moindre ampleur par rapport à la perception d'images de nourriture de basse densité énergétique ou à la perception d'une « catégorie contrôle » d'objets qui ne sont pas de la nourriture. Notre discussion est orientée sur les notions prépondérantes de récompense et de motivation qui sont associées à la nourriture de haute densité énergétique. Nous suggérons que la nourriture de haute densité énergétique génère une représentation mémorielle plus stable et que ce mécanisme pourrait (partiellement) être sous-jacent au fait que la nourriture de haute densité énergétique soit préférentiellement consommée. Dans la deuxième étude (Study Β) menée au cours de cette thèse, nous nous sommes intéressés aux mécanismes de perception de la nourriture chez des patients ayant subi un bypass gastrique Roux- en-Y, afin de réussir à perdre du poids et améliorer leur santé. Ce type de chirurgie est connu pour altérer la perception de la nourriture et le comportement alimentaire, mais également la sécrétion d'adipokines et de peptides gastriques. Dans une approche interdisciplinaire et globale, cette deuxième étude investigue donc les différences entre les patients opérés et des individus « contrôles » de poids similaire au niveau des interactions entre leur activité cérébrale et les mesures de leurs hormones gastriques. D'un côté, nous avons investigué la dynamique spatio-temporelle cérébrale de la perception visuelle de nourriture de haute et de basse densité énergétique dans deux états physiologiques différent (pre- et post-prandial). Et de l'autre, nous avons également investigué les mesures physiologiques des hormones gastriques. Ensuite, afin d'évaluer les altérations liées à l'intervention chirurgicale au niveau des interactions entre la réponse cérébrale et la sécrétion d'hormone, des corrélations entre ces deux mesures ont été comparées entre les deux groupes. Les résultats révèlent que l'intervention chirurgicale du bypass gastrique Roux-en-Y altère la dynamique spatio-temporelle de la perception visuelle de la nourriture de haute et de basse densité énergétique, ainsi que les interactions entre cette dernière et les mesures périphériques des hormones gastriques. Nous discutons le rôle potentiel de ces altérations en relation avec les modulations des facteurs physiologiques et les changements du comportement alimentaire préalablement déjà démontrés. De cette manière, nous identifions des cibles potentielles pour le développement de stratégies d'intervention future, au niveau comportemental, cérébral et endocrinien (hormones gastriques) en ce qui concerne les déviances du comportement alimentaire, dont l'obésité. Nos deux études réunies démontrent que la représentation visuelle de la nourriture dans le cerveau est plastique et que des modulations de l'activité neurale apparaissent déjà à un stade très précoce des mécanismes de perception visuelle. Différents facteurs d'influence comme une exposition repetee, le bypass gastrique Roux-en-Y, la motivation (état nutritionnel), ainsi que la densité énergétique de la nourriture qui est perçue ont pu être identifiés.

Olfactory and/or visual cues for spatial navigation through ontogeny: olfactory cues enable the use of visual cues

This study analyzed the spatial memory capacities of rats in darkness with visual and/or olfactory cues through ontogeny. Tests were conducted with the homing board, where rats had to find the correct escape hole. Four age groups (24 days, 48 days, 3-6 months, and 12 months) were trained in 3 conditions: (a) 3 identical light cues; (b) 5 different olfactory cues; and (c) both types of cues, followed by removal of the olfactory cues. Results indicate that immature rats first take into account olfactory information but are unable to orient with only the help of discrete visual cues. Olfaction enables the use of visual information by 48-day-old rats. Visual information predominantly supports spatial cognition in adult and 12-month-old rats. Results point out cooperation between vision and olfaction for place navigation during ontogeny in rats.