SYNAPTIC AND DENDRITIC DYNAMICS DURING AN ATTENTION-SWITCHING TASK IN LAYER 2/3 NEURONS OF THE MOUSE VISUAL CORTEX

Attention has a powerful influence on sensory processing. In the visual cortex, neural activity can show enhanced response selectivity when stimuli are attended. However, the synaptic basis of attentional modulation in sensory neurons is poorly understood. Although neuronal spiking responses are shaped largely by inputs to the thousands of excitatory and inhibitory synapses located on their dendrites, it is not clear how changes in synaptic input patterns during attention-switching relate to changes in neuronal spiking output. Here we asked what synaptic dynamics are associated with stimulus selectivity changes in neurons modulated by attention, and whether changes in neural selectivity are reflected at the synaptic level. We performed dual colour 2-photon imaging of glutamate and calcium in spines and dendrites in layer 2/3 neurons of the visual cortex in mice performing an attention-switching task. Dendrites showed an average increase in stimulus selectivity during attention, similar to previous results in neuronal somata. While we found no average increase in stimulus selectivity in inputs to individual spines on either apical or basal dendrites, there was a significant positive correlation between the change in stimulus selectivity in dendrites and the change in stimulus selectivity in the inputs to spines on those dendrites. Our results constrain models of synaptic integration and reveal a distributed synaptic basis of attentional modulation in V1.​