Dynamik und Kontextabhängigkeit in den Antworteigenschaften tectaler Neurone und im Orientierungsverhalten des Salamanders Plethodon shermani durch unterschiedliche Merkmale visueller Stimuli

Abstract

The appearance of an object in the visual field induces eye- and head movements towards the object. These orienting responses represent a basic type of directed attention and serve for a gross categorization of objects. Such visuomotor abilities were tested in a behavioral task and the results were used as a basis for physiological experiments.In behavioral experiments, animated prey-dummies differing in features such as size and contrast were presented pairwise on a screen. Orienting responses of animals were evaluated and a preference scale of stimuli was established. Size and velocity appeared to be dominant features, movement pattern, shape and contrast was less important. The findings favor the view that in amphibians prey recognition is guided by a number of visual features depending on the attentional states and individual experience. The tectum of salamanders integrates visual information for the generation of goal-directed orienting movements. Response characteristics of tectal neurons were investigated by single cell recordings. Stimuli with different preferences in behaviour were taken for stimulation. Stimuli were presented single and pairwise. In the majority of tectal neurons, single presentation revealed that the higher the preference in behavior, the more spikes are discharged. At paired stimulus presentation, effect of stimuli presented outside the RF depends on preference in behavior. A reverse correlation analysis revealed differences in RF size depending on the context of stimulation. In summary, the results suggest that in salamanders discharge rates of tectal neurons are highly dynamic as is found in the visual system of mammals. Changes in spike activity depend on the state of activity of surrounding neuronal populations, which code visual features of competing stimuli in the visual field. Local horizontal interactions of tectal neurons as well as afferent systems of bulbar and thalamic centers are regarded to control these dynamic changes.