The Florey Institute of Neuroscience and Mental Health, University of Melbourne
In the living animal, sensory systems are generally not stimulated in isolation but are instead activated collectively. During this multi-sensory stimulation, pyramidal neurons in the primary somatosensory cortex receive both feedforward input from the thalamus and feedback input from other cortical areas. Since the synaptic location of the different input streams are morphologically and functionally isolated, how multi-sensory input is integrated and computed at the level of a single neuron is currently unknown. Here I will present recent results investigating dendritic activity in the hindpaw somatosensory cortex during hindpaw stimulation alone and during activation of additional sensory-evoked feedback input generated by forepaw stimulation. Using both single-cell electrophysiology and dendritic two-photon calcium imaging in vivo, we show that sensory input from the stimulation of the forepaw has different effects on the dendritic sub-domains of layer 2/3 pyramidal neurons. Namely, forepaw stimulation causes a decrease in the Ca2+ activity of apical tuft dendrites whereas there is an increase in synaptic input in proximal basal dendrites. Combined, these multi-sensory input streams led to a balancing of sensory information and had a negligible effect on the action potential output of the neuron. This balance between excitation and inhibition during multi-sensory information could be modulated by altering the strength of feedback input by photo-activation/inactivation of the forepaw somatosensory cortex. These results not only illustrate the counterbalancing interaction of multi-sensory input in cortical neurons but it also highlights the complexity of local dendritic activity during sensory perception.