Translaminar imaging of calcium signals evoked by sensory stimuli in Etruscan shrew somatosensory cortex

Abstract

The Etruscan shrew, Suncus etruscus, is the smallest terrestrial mammal with a body weight of ~ 2 g and a body length of ~ 4 cm. The small size of the Etruscan shrew’s brain offers particular advantages for imaging, as the entire cortical sheet as well as somatosensory cortex are on average less than 500 µm thick. Here we show that in this animal two photon imaging allows to visualize all cortical layers, which is typically difficult to do in rodents or other mammals. Although much is known about the activity of individual cells, the pattern of activity across an entire column during sensory stimulation is less well understood. Using bulk loading of calcium indicators in the somatosensory cortex of anaesthetized shrews, we aim to describe the cellular activity of populations of neurons in somatosensory cortex across different layers. We characterize single-neuron and multi-neuron responses to whisker stimuli using optically recorded calcium transients. Our preliminary data indicate that responses are heterogeneous in Etruscan shrew cortex. Much like observed previously in rodent somatosensory cortex there is little spontaneous activity and even powerful stimuli (air puffs) evoke only sparse responses