The input-output transfer function of brain circuits

Abstract

We aim to understand how the brain works. Specifically, we aim to answer how different brain circuits, learn, memorise or process information that result to changes in behaviour or muscle action. To answer this question, we isolate single neurons from a rat brain and study how different inputs of a single neuron translate to an output. To study the neuron's input-output transfer function, we have custom-built a unique two-photon laser microscope, which makes use of a holographic projector that transforms the incident laser into multiple foci at the sample volume. The hologram is programmable so we can position the different foci anywhere around the neuron in 3D. Each focus can be used to trigger an input or record an output. This means we can stimulate and probe the activity from multiple locations within the neuron’s dendritic tree using light. For triggering inputs, a focal stimulation represents a synaptic input. For recording, a laser focus excites a fluorescence marker that changes in fluorescence whenever the neuron is active. Using this technique, we have now identified a novel function of a specific set of dendrites that can have a significant role in learning and memory. The set of dendrites we are probing are currently unexplored due to their very thin morphology. We were able to see observe unique properties that allow these dendrites to be more receptive to inputs whenever the neuron fires an output. Hence, they have a functional role in the brain's capacity to learn and memorise. Understanding the different roles of the dendrites could provide us with a better understanding of how these neurons function as tiny computers in the brain.