Role of the pulvinar in early visual cortical signaling in the macaque.

The function of the pulvinar, a thalamic structure richly interconnected with the neocortex, is poorly understood. The broad projections from pulvinar to cortex might broadcast common signals across cortical areas. Alternatively, the circuit connecting the cortex and pulvinar might be used to relay activity between cortical areas, complementing the interareal signaling through direct corticocortical circuits. We tested these proposed signaling motifs by performing simultaneous measurements of neuronal population spiking responses in two cortical areas-V1 and V2-and the pulvinar of anesthetized macaque monkeys. We show that corticopulvinar and corticocortical interactions involve distinct patterns of population spiking activity, consistent with the relay hypothesis. Signaling among these structures was biased in the feedforward direction, with V1 activity leading activity in the pulvinar which in turn led V2. Our work suggests that a primary function of the pulvinar is to communicate signals from lower cortical areas to higher areas.