LAUSR

Significance Neuroanatomical tracing provides just a partial picture of information flow in the brain, because excitatory synapses are not all equal. Some strongly drive postsynaptic targets to transfer information, whereas others weakly modulate their responsiveness. Here, we show conserved patterns of synaptic function across somatosensory and visual thalamocortical circuits in mice involving higher-order thalamic nuclei. These nuclei serve as hubs in transthalamic or cortico-thalamo-cortical pathways. We report that feedforward transthalamic circuits in the somatosensory and visual systems operate to efficiently transmit information, whereas feedback transthalamic circuits act to modulate their target areas. These patterns may generalize to other brain systems and show how methods of synapse physiology and molecular biology can inform the exploration of brain circuitry and information processing.