How we see spatially
Spatial vision depends on certain nerve cells: Ruhr University Bochum and biologists in Paris identify the responsible neurons. How is it actually possible to purposefully reach for a cup when drinking coffee in the morning without taking your eyes off the editorial? A significant step towards clarifying this question has recently been taken by scientists at the Paris Collège de France, including the Bochum neurobiologist Dr. Frank Bremmer (employee of Prof. Dr. Klaus-Peter Hoffmann, Chair of General Zoology and Neurobiology, Faculty of Biology at the Ruhr University Bochum. They have been able to identify certain nerve cells (neurons) in the brain of primates that determine the position of an object in the environment always show the same despite different perspectives. These neurons have been identified in an area of the macaque brain termed the ventral intraparietal area (VIP). In further investigation steps, it should now be clarified which coordinate system is the basis of this non-retina-centric coding. Their findings are published in the October 23, 1997 issue of NATURE.
How does the brain process spatial relationships
The scientists' investigations de alt with the question of how information about spatial relationships is processed in the brains of primates. Previous work had pointed to the importance of a specific area of the cerebrum (cortex), an area called the parietal or parietal cortex. Damage to the right posterior parietal cortex (PPC) in humans causes massive, mostly permanent disorders of perception and orientation in space (exploration of the contralateral extrapersonal hemisphere). Humans cannot avoid obstacles in this area, cannot reach for objects in this area, etc. Injuries to the right as well as the left PPC in non-human primates cause similar deficits. Only within the last 10 years, however, have studies using functional magnetic resonance imaging in particular been able to show direct analogies between the structures of the so-called occipital and parietal areas of the human neocortex and those of non-human primates (macaques). Macaques as an animal model for the study of the parietal cortex therefore appear justified and particularly necessary, since, for example, the necessary behavioral studies can only be carried out on them.
Head or body centered coordinate system
More detailed investigations on parietal cortex patients could show that the processing of sensory information of different modalities regarding an abstract concept, a so-called head- or body-centered, internal coordinate system is disturbed. For the neurobiologists from Paris and Bochum, the most important question to be answered on the way to a better understanding of how the brain works was therefore to investigate whether there are explicit neuronal correlates to such coordinate systems.
Excited cells and their disproportion to the coffee cup
Visual information is first displayed on the retina, like a camera. This leads to the excitation of nerve cells, so-called neurons, which forward the information to the cortex for further processing by means of electrical impulses. The reference or coordinate system for the visual information is therefore the eye. If we change our line of sight, the same objects in the environment, such as a coffee cup, are imaged on different areas of the retina. Other cells in the retina are excited and send information to her. Now the disproportion arises between a displacement of the coffee cup on the retina and its constant location in the environment. If a command to reach for the coffee cup were based solely on visual information related to the retina, we would miss the coffee cup every time we looked.
The responsible cells
So somewhere in the course of processing visual information there must be a calculation step, i.e. an area in the cortex that calculates the change of gaze when evaluating the incoming visual signals and explicitly encodes the location of an object in the environment in a retina-independent coordinate system. The researchers at the Paris Collège de France were able to find exactly such an area. In an area of the macaque brain known as the ventral intraparietal area (VIP), they were able to identify neurons that always indicate the position of an object in the environment in the same way despite different viewing directions. In further investigation steps, it should now be clarified which coordinate system is the basis of this non-retina-centric coding.
Basic research with long-term hope for brain injured
The primary goal of the outlined project was to improve our understanding of the functioning of the primate posterior parietal cortex. In the long term, however, the further development of diagnoses or even therapies for parietal cortex patients based on the results of the project cannot be ruled out.