Thalamic activation of the visual cortex at the single-synapse level

Deciphering thalamocortical (TC) activation at the level of individual synapses is essential to understanding how the cortex processes sensory information. In this work, we studied TC computation underlying the emergence of orientation selectivity in the mammalian primary visual cortex (V1). Using two-photon glutamate imaging and optogenetic cortical silencing in vivo, we identified and characterized TC synapses onto mouse V1 layer 4 neurons. We found that TC- but not corticocortical-recipient spines lacked postsynaptic Ca²⁺ signals. Our results directly validate the core predictions of Hubel and Wiesel's feedforward model and reveal distinctive synaptic properties that are critical for cortical computation and plasticity.