In vivo functional mapping of single synapses in the vibrissal cortex of the mouse

Single neurons, which represent the elementary units of brain function, organize into larger circuits that integrate external and internal brain signals.To understand the operation of these cortical circuits it is essential to identify the functional connections among the neurons.Recently, in vivo two-photon calcium imaging made it possible to identify the location of these connections by imaging dendrites and spines of single neurons.In this study, an improved procedure of two-photon imaging was applied to map the distribution of inputs on the dendrites of neurons in the whisker representation part of the primary somatosensory cortex of the mouse.This cortical region is widely used to study circuit functions because the functional representation of single whiskers is tightly linked to the anatomical structures of defined barrels.Thus, mapping the distribution of sensory stimulation-evoked inputs on the dendrites of the neurons located here allows studying the interaction of functional connections and anatomy.In this study, sensory stimulation-evoked inputs were mapped on the dendrites of neurons residing in the upper half of the vibrissal cortex.These neurons are responsible for the initial steps in the processing of sensory signals in the cortex, thereby determining the structure and timing of the incoming sensory information.Together, this study gives insight in sensory signal processing at the level of single synapses in anatomically organized cortical region.