Spatio-temporal representations during eye movements and their neuronal correlates

During fast ballistic eye movements, so-called saccades, our visual perception undergoes a range of distinct changes. Sensitivity to luminance contrasts is reduced (saccadic suppression) and the localization of stimuli can be shifted in the direction of a saccade or is compressed around the saccade target. The temporal order of two stimuli can be perceived as inverted and the duration in between can be underestimated. The duration of a target change close to the saccade target can be overestimated, when the change occurs during the saccade (chronostasis). In my thesis I investigated the spatial and temporal profiles of peri-saccadic changes in human visual perception and explored how these might result from changes in neural activity of the macaque middle temporal area (MT). I found that peri-saccadic contrast sensitivity was only reduced by a constant factor across space when the data was analyzed in retinal coordinates (as opposed to screen coordinates), indicating that saccadic suppression occurs in an eye-centered frame of reference. I demonstrated that the found variations of saccadic suppression with the location of the stimulus appear to cause variations in the spatio-temporal pattern of another peri-saccadic misperception: chronostasis. I was able to show that, unlike previously assumed, the saccadic overestimation of time is not a spatially localized disturbance of time perception but instead spans across the whole visual field. I further determined that chronostasis is not dependent on the eye movement itself, but is rather a consequence of the visual stimulation induced by it. This result clearly segregates chronostasis from other peri-saccadic perceptual changes like saccadic suppression and the compression of space. To relate these findings to a potential neuronal basis of saccadic suppression and time perception, I measured neuronal responses of single cells in MT of an awake behaving macaque. The results provide relevant insight into the processing of stationary stimuli and pairs of stimuli during fixation and saccades in MT. Responses to the second of a pair of stimuli were strongly suppressed and response latencies increased even at onset asynchronies of about 100ms. The increase in latency is an important difference to the temporal dynamics previously reported in other brain areas as the frontal eye field in the frontal cortex and the superior colliculus in the midbrain. During saccades, response latencies to single high luminance stimuli remained unchanged. For stimuli shown during the second half of the saccade, the average responses were reduced. By comparison with responses to single stimuli at different luminance levels during fixation, I was able to show that the peri-saccadic response reduction found in MT quantitatively fit to what could be expected from known psychophysical measurements of peri-saccadic contrast sensitivity. Responses that were already reduced due to a preceding stimulus were however not subject to further reductions, indicating a possible interaction of these two response modulations. Saccadic suppression occurs in an eye-centered frame of reference with changes in perception compatible to changes in single cell activity in the macaque monkey MT. The peri-saccadic overestimation of time is influenced by saccadic suppression and the saccade-induced visual changes, but is not dependent on eye-movement related signals

Spatiotemporal profile of peri-saccadic contrast sensitivity

Frank Bremmer Sensitivity to luminance contrast is reduced just before and during saccades (saccadic suppression), whereas sensitivity to color contrast is unimpaired peri-saccadically and enhanced post-saccadically. The exact spatiotemporal map of these perceptual effects is as yet unknown. Here, we measured detection thresholds for briefly flashed Gaussian blobs modulated in either luminance or chromatic contrast, displayed at a range of eccentricities. Sensitivity to luminance contrast was reduced peri-saccadically by a scaling factor, which was almost constant across retinal space. Saccadic suppression followed a similar time course across all tested eccentricities and was maximal shortly after the saccade onset. Sensitivity to chromatic contrast was enhanced post-saccadically at all tested locations. The enhancement was not specifically linked to the execution of saccades, as it was also observed following a displacement of retinal images comparable to that caused by a saccade. We conclude that luminance and chromatic contrast sensitivities are subject to distinct modulations at the time of saccades, resulting from independent neural processes

Neue Methode zur Erhebung von Aktivität, Insulintherapie und der Bewegungsfreundlichkeit der städtischen Umgebung von Jugendlichen mit T1DM - Machbarkeitsstudie zur Evaluation der Datenerhebung

Die Bewegungsfreundlichkeit („Walkability“) der alltäglichen Umgebung eines Menschen hat einen positiven Einfluss auf die Qualität und Quantität der körperlichen Aktivität - Das interdisziplinäre Forschungsvorhaben zielt darauf ab, neue Methoden zu entwickeln, um Einflüsse der städtischen Umgebung (wie Dichte und Nutzung der gebauten Umgebung, Zugang zu Grünzonen und gesundem Essen) auf die individuelle Diabetestherapie analysieren und visualisieren zu können. In Rahmen einer zweiwöchigen Machbarkeitsstudie mit acht jugendlichen T1DM Patienten (12-15 Jahre, 4 weiblich) im Großraum Stuttgart, sollte das zur Datenerhebung benutzte System auf dessen Usability evaluiert werden und der Vorgang der Datenerhebung aus Sicht der Probanden festgehalten werden. Der Prototyp besteht aus einem Sensor zur Aktivitätserkennung (sog. Wearable) (Fig. 2) und einem Smartphone zum Dokumentieren der Diabetestherapie und der GPS-Koordinaten (Ground Truth) der besuchten Orte (Fig. 3). Zusätzlich wurde ein NEWS-Fragebogen zur Erhebung der Bewegungsfreundlichkeit (Walkability) (Rosenberg, Ding, Sallis et al., 2009) eingesetzt und durch Fragebogen und persönliche Gespräche mit den Probanden die Instrumente der Datenerhebung evaluiert. Alle acht Probanden führten das Projekt zu Ende. Die Sensoren wurden dauerhaft getragen und stellten keine größere Beeinträchtigung dar (Fig. 4). Von den acht ausgegebenen Sensoren zeichneten sechs Stück über den gesamten Versuchszeitraum körperliche Aktivität auf (Fig. 5). Die Dokumentation der Insulintherapie, Blutzuckerwerte und Mahlzeiten mithilfe der App „mySugr“ klappte bei allen Probanden problemlos. Die Annotation der aufgezeichneten GPS Koordinaten (z.B. „Schule“) durch den Nutzer klappt mit Einschränkungen (keine Differenzierung zwischen Schulunterricht und Hausaufgaben möglich). Die Kombination aus aufgezeichneten Positionen und Diabetesdaten lässt sich in Excel exportieren, z.B. durch Nutzungskategorien wie FourSquaire API (Noulas, Scelatto, Mascolo et al., 2011) anreichern und in Geo Informations System (GIS) Software darstellen (Fig. 6). Die Machbarkeitsstudie zeigt, dass das System (Wearable in Verbindung mit Smartphone) gut von Jugendlichen mit Typ-1 Diabetes angenommen wird und die daraus erhobenen Daten als Grundlage der Analyse und Visualisierung des Einflusses der städtischen Umgebung auf körperliche Aktivität geeignet sind. Dabei bewährte sich die Organisationsstruktur der Studie in zwei Workshops zu Anfang und Ende des Testzeitraumes, um die Erhebung und den Rücklauf der Daten zu ermöglichen. Die Studie wurde durch die Stiftung „Das zuckerkranke Kind in der Deutschen Diabetes Stiftung“ (DDS) sowie durch die Projektmittel „Gesundheitsförderung“ der Stadt Stuttgart gefördert. Die GIS Visualisierung (Fig. 6) wurde von Dipl.-Ing. Christian Wagner erstellt

The molecular tweezer CLR01 inhibits Ebola and Zika virus infection.

Ebola (EBOV) and Zika viruses (ZIKV) are responsible for recent global health threats. As no preventive vaccines or antiviral drugs against these two re-emerging pathogens are available, we evaluated whether the molecular tweezer CLR01 may inhibit EBOV and ZIKV infection. This small molecule has previously been shown to inactivate HIV-1 and herpes viruses through a selective interaction with lipid-raft-rich regions in the viral envelope, which results in membrane disruption and loss of infectivity. We found that CLR01 indeed blocked infection of EBOV and ZIKV in a dose-dependent manner. The tweezer inhibited infection of epidemic ZIKV strains in cells derived from the anogenital tract and the central nervous system, and remained antivirally active in the presence of semen, saliva, urine and cerebrospinal fluid. Our findings show that CLR01 is a broad-spectrum inhibitor of enveloped viruses with prospects as a preventative microbicide or antiviral agent

The molecular tweezer CLR01 inhibits Ebola and Zika virus infection.

Ebola (EBOV) and Zika viruses (ZIKV) are responsible for recent global health threats. As no preventive vaccines or antiviral drugs against these two re-emerging pathogens are available, we evaluated whether the molecular tweezer CLR01 may inhibit EBOV and ZIKV infection. This small molecule has previously been shown to inactivate HIV-1 and herpes viruses through a selective interaction with lipid-raft-rich regions in the viral envelope, which results in membrane disruption and loss of infectivity. We found that CLR01 indeed blocked infection of EBOV and ZIKV in a dose-dependent manner. The tweezer inhibited infection of epidemic ZIKV strains in cells derived from the anogenital tract and the central nervous system, and remained antivirally active in the presence of semen, saliva, urine and cerebrospinal fluid. Our findings show that CLR01 is a broad-spectrum inhibitor of enveloped viruses with prospects as a preventative microbicide or antiviral agent