Auswahlmechanismen im Sehsystem der Katze

The research projects reported in this thesis aimed at the demonstration and description of important mechanisms of response selection operating in the visual system of the cat.The first project focused on selection mechanisms on the cellular level. In the anesthetized preparation, cortical cell groups were stimulated electrically during presentation of a light stimulus to the eyes of the cat. Collicular cells responded to this combined stimulation with amplitudes depending on the match of their visual input to the receptive field characteristics of the cortical cells stimulated electrically. Compartmentalized dendritic input processing within single collicular cells seems to cause this selective facilitation of matching inputs with respect to others. First results from a related project show that these cells can also act as detectors of the temporal match (i.e. coincidence) of incoming signals.The two following chapters of this work are dedicated to the hypothesis of the temporal stucture of neural activity as a carrier of information in the brain. Microelectrodes were implanted in the visual cortex of cats. During recordings, these cats were exposed to incongruently moving grating stimuli presented simultaneously but separately to the two eyes. The animals perceived only one of the two stimuli at a time. The analysis of the neural data showed that during this so-called binocular rivalry the strength of neural synchronization, a prominent form of temporal structure, correlated well with perception.In strabismic cats displaying a different perceptual performance of the two eyes it has been shown that synchronization is reduced among cells in primary visual cortex that represent the weak, so-called amblyopic eye. The results of a fourth project measuring firing rates in higher visual areas of such cats confirm the expectation that reduced synchrony on one level of neural processing should be followed by reduced firing rate on the next level.