Symposien Samstag

The discovery of the retinotopic map in visual cortex came from examination of soldiers wounded in battle, not from patients with a history of stroke. Embolic stroke produces a limited and stereotypic repertoire of visual field defects, constrained by the organization of the blood supply of the occipital lobe with respect to the retinotopic map. This talk will explain – in terms of the arrangement and plasticity of the cortical map, why some patterns of visual field loss and recovery following stroke are common, whereas others are essentially impossible.

Whereas regenerative plasticity is limited in the primary visual cortex, compensative plasticity can be utilized and enhanced. Spontaneous adaptive mechanisms in hemianopia – such as fixational eye movements towards the blind side – can be supported: With an explorative saccadic training, scanning of the blind hemifield and improved utilization of the total field of gaze is being trained. Even in longstanding visual field defects improvement of exploration, spatial orientation and therefore quality of life is achievable.

An overview will be given of dominant notions concerning the plasticity of the brain with a focus on the human (sensory) motor system. It will be shown that the system is extremely adaptive although there are clear limitations. Mechanisms of recovery and relearning will be discussed. It will be shown how close brain and body are linked in the continuous attempt to survive in an ever changing environment.

At birth, visual resolution is around 0.01, increasing fast through maturation and perceptual learning, to almost 2.0 for healthy adults, corresponding to 0.5 arc min, or 30 arc sec. But in stereoscopic vision, positional differences between the images of the two eyes can be used that are 10 times smaller than conventional two-point acuity, namely around 3-5 arc sec! I will explain how perceptual learning can achieve such ‘hyperacuity’ by clever computations in the brain.