Detection and transmission in the visual pathway

The early visual pathway has two distinct functions: the detection of salient stimuli in the visual field and the transmission of detailed features of these stimuli for analysis in higher brain areas. To successfully perform these functions, the encoding properties of the early visual pathway must be dynamically adjusted. In this thesis, two aspects of encoding in the early visual pathway are investigated: the adaptation of encoding properties during the transmission of nonstationary stimuli and the activation of the burst response mechanism during detection.; During transmission, adaptation maximizes the differential sensitivity of a neuron over the current statistical distribution of the stimulus by adjusting encoding properties such as gain and baseline membrane potential on multiple time scales. Here, a new framework for the functional characterization of visual adaptation during nonstationary stimulation is developed. Within this framework, adaptive changes in visual encoding properties can be tracked during a single stimulus/response trial and the function of multiple adaptive encoding mechanisms can be uniquely characterized. The framework is applied to responses to nonstationary stimuli to demonstrate how receptive field (RF) structure and baseline membrane potential interact to control the encoding properties of visual neurons.; To facilitate detection, neurons in the lateral geniculate nucleus (LGN) of the thalamus utilize a burst response mechanism, which causes all stimuli that trigger a response to evoke a stereotyped high-frequency burst of spikes. Here, the role of the burst response mode in the encoding of natural stimuli is investigated. The stimuli that trigger burst responses are characterized and a functional model for predicting the LGN response during both tonic and burst firing is developed. The model is used to simulate the LGN response to the appearance of stimulus features with and without the burst mechanism, and the results reveal that the amplification properties of the burst mechanism greatly enhance the detection of specific stimulus features. Together, the results presented in this thesis describe a strategy implemented by the visual system to perform the tasks of detection and transmission with limited processing resources.