The neural mechanisms of selective attention : Investigation of insect selective attention during visual object tracking using neurophysiology, neuroanatomy, computational modelling

Sammanfattning: The brain simulates the world around us using sensory information and provides an estimation of reality in which actions can be executed. This estimation of reality is controlled by attention which decides which information is accepted, further processed and ignored. The process of attending a certain part of the sensory information while ignoring other parts is called selective attention. I have studied visual selective attention on a neuronal level in hoverflies and dragonflies. These insects are highly skilled at object tracking in behaviors related to defending territories, mating or hunting prey. They have very small brains with few neurons compared to mammals and yet execute object tracking tasks with impressive accuracy. In Paper 1 we compare insect brain tissue preparation techniques for optimizing the amount of neuronal morphology details that can be captured during microscopy imaging. We then use these techniques to acquire a highly detailed neuron morphology and further apply the techniques in the other papers. In Paper 2 we captured the morphology of a hoverfly target-tracking neuron using techniques from Paper 1. I measured a type of short-term memory called response facilitation in a population of these hoverfly target-tracking neurons. This was measured by comparing the response of long (primed) versus short (unprimed) target traveling paths. In the next experiment I measured the neuronal response while distracting the neuron with another target moving outside the part of the visual field in which that neuron responds. Both primed and unprimed distractors reduced the response, indicating that the attention was sometimes moved to the distractor. This phenomenon could potentially be implemented using long range inhibition as part of an attention mechanism. Paper 3 & 4 involved computational modeling of target tracking neurons using a neuronal morphology from the dragonfly. We show that a receptor (N-methyl-D-aspartate receptor), known for its involvement in short term memory processing, have some of the properties required to generate facilitation. Altogether, the results of this thesis have improved our knowledge and understanding of the neural mechanisms of selective attention in hoverflies and dragonflies. It has also paved the way for future studies to further expand on this knowledge and understanding.