Memorial Symposium for Ruxandra Sireteanu

Organizer: Ute Leonards, Maria Fronius, Hans Strasburger

Chair: Wolf Singer

Programme:

3.00 pm Wolf Singer, "Ruxandra Sireteanu"
3.20 pm Maria Fronius, "Amblyopia – a model of plasticity of the visual system. A retrospective and a look at present research"

A retrospective on many years of amblyopia research with Ruxandra Sireteanu and an account of the influence of that work on the present research in our Child Vision Research Unit at the University of Frankfurt will be presented. The early work utilised psychophysical methods in the central and peripheral visual field of adult amblyopes (grating acuity, interocular transfer of contrast adaptation, binocular summation, motion-in-depth). A later focus was on spatial localization in adults and children with strabismic amblyopia. These correlative studies demonstrated the role of interocular suppression and anomalous correspondence for the deficits occurring in amblyopia and the capability of the visual system to selectively exclude or preserve information. The influence of occlusion treatment in children (enforced use of the amblyopic eye) was a next step to explore the potential and limits of plasticity of the visual system, followed by investigations of training in adult amblyopia. Our current research aims at differentiating the influence of plasticity and compliance with treatment (electronically monitored with the Occlusion Dose Monitor, ODM) in older children and adolescents. This sheds light on the amount of residual plasticity beyond the once defined sensitive period and on the practice of age limits of amblyopia treatment.

3.40 pm Aylin Thiel, "Spatial and temporal distortions in human amblyopes"

Amblyopia (“lazy eye”) is a non-organic visual impairment of one or (less often) both eyes which is caused by a disturbed view in the development of the visual system during early childhood. The impairment resulting from amblyopia is devastating and may concern visual acuity, binocular interaction and contrast sensitivity. Additionally, spatial misperception of visual stimuli, heavy spatial distortions and temporal instability can occur (Sireteanu, 2000). We investigated 22 amblyopic or alternating amblyopes with the qualitative detection of visual amblyopic perception at four standardized stimulus patterns. Distortions were observed in all participants and were most distinct in the group of strabismic amblyopes, but still observed distortions were weaker than described in the literature. Regardless of the etiology, severe amblyopia showed the greatest extent of distortion. Four of the five categories proposed by Barrett et al. (2003) were replicated, and the range of distortion pattern was extended by some more categories. The results of the study confirm the known limitations of the ventral visual pathway and also suggest a dysfunction of the dorsal visual pathway.
3.50 pm Lars Muckli, "Experience dependent cortical development of the visual system"
Experience dependent cortical development of the visual system was one of the major focuses of Ruxandra Sireteanu's research. Ruxandra was interested in the early visual development of humans and animals. When functional brain imaging methods became available Ruxandra was immediately attracted and amongst the first to initiate fMRI research on human Amblyopia as a model of experience dependent cortical plasticity. In Amblyopic subjects we found a transmission failure between strong amblyopic eye activation in early visual areas and reduced activation of higher visual areas in the ventral processing stream (Muckli et al. 2006). We concluded that this transmission failure in amblyopia is experience dependent and has been acquired early in life. More recently we had a chance to investigate a very different and very early experience dependent plasticity in a patient who was born with only one cerebral hemisphere. Early in the embryonic development the formation of AH's right brain hemisphere ceased. Retinal ganglion-cells changed their predetermined crossing pattern in the optic chiasm, and grew to the left brain to form new maps in the LGN and the visual cortex (V1, V2, V3). This reorganisation allows patient AH's surprisingly normal visual abilities in both visual fields.
4.10 pm Alina Jurcoane, Bhaskar Choubey, Donka Mitsieva, Lars Muckli and Ruxandra Sireteanu, "On fMRI interocular transfer"

We investigated fMRI adaptation for oriented gratings with emphasis on the amount of adaptation that is transferred interocularly. In normally sighted humans (n=10) interocular transfer was present both in early (striate) as well as later visual areas (extrastriate). In contrast, amblyopic subjects (n=10) did not show any interocular transfer regardless of which eye was adapted. There are three main outcomes of this study: 1. Interocular transfer of adaptation can be measured with fMRI. 2. The method might provide an insight into the binocular interaction in normally-sighted subjects. 3. The abnormal pattern of interocular transfer in amblyopia might be related to disturbed binocular integration. The method may further be used to address more subtle aspects of the neurobiological substrate of interocular transfer.
4.20 pm Ingo Rentschler and Martin Juettner, "Gravel or the Dalmatian’s tail? – Four decades in search of lost Gestalt"

In the early Seventies, Wolf Singer drew attention to the “binding problem” by asking how a visual neuron could know whether it is seeing parts of the gravel background or of the dog’s tail. This led Ruxandra to address in collaboration with Wolf the issue of “morphic insensitivities” in amblyopic vision and, more generally, in visual development. Similarly, the Dalmatian binding paradigm was at the roots of our interest in feature integration. While she preferred to pursue this from a physiological point of view, we sought to better understand it using more formal approaches from systems theory. Ruxandra’s studies opened many useful perspectives for clinicians; ours tended to puzzle them. Thus, we left the track of amblyopia research and got involved with structure-based normal pattern and object recognition. Two years ago Ruxandra and we discussed the possibility of combining these different perspectives in the sense of Ernst Mach’s (1865) original concept of Gestalt perception. Unfortunately enough, her untimely death prevented the possible re-union from taking place.
4.40 pm Janette Atkinson and Oliver Braddick, "Visual development in infancy: work in the spirit of Ruxandra Sireteanu"

Ruxandra Sireteanu, our friend and colleague, was among the first in Europe to take up work on visual development in infancy with a strong base in visual neuroscience. We will discuss our parallel findings in two areas where our work converged.
In parallel with Ruxandra’s group, we investigated young infants’ ability to segment visual arrays through differences in oriented textures, publishing adjacent papers in Behavioural Brain Research (1992). Ruxandra’s group concentrated on pop-out, visual attention, and perceptual learning, while our work focussed on global perceptual organization in dorsal and ventral stream development, dorsal stream vulnerability and the definition of objects in infancy. We discuss how these lines of work relate, in particular with respect to the role of attention.

Ruxandra had a major interest in amblyopia and strabismus. She collaborated with us in a videorefractive screening programme, across 6 European centres to identify amblyogenic and strabismogenic risk factors. We review findings from our controlled trials of 9000 typically developing 9-month-olds, showing that significant infant hyperopia predicts strabismus and amblyopia, reduced by early spectacle refractive correction, and that infant hyperopia correlates with delays in visual cognition and attention in preschool years.
5.00 pm Lamberto Maffei, Nicoletta Berardi, "Enrich the environment to empower the brain"

Environmental enrichment (EE) has long been exploited to investigate the influence of the environment on brain structure and function. Robust morphological and functional effects elicited by EE at the neuronal level have been reported to be accompanied by improvements in cognitive performance. Recently, EE has been shown to accelerate the development of the visual system and to enhance visual-cortex plasticity in adulthood, promoting recovery from amblyopia. EE acts by modulating the level of endogenous factors such as BDNF, IGF-1 and intracortical inhibition. These findings underline the importance of the environment as a driving force in early postnatal development and highlight the potential of EE as a promising non-invasive strategy to ameliorate deficits in the maturation of the nervous system and to promote recovery of normal sensory functions in pathological conditions affecting the adult brain.