Two functional channels from primary visual cortex to dorsal visual cortical areas

Relationships between the M and P retino-geniculo-cortical visual pathways and "dorsal" visual areas were investigated by measuring the sources of Local excitatory input to individual neurons in Layer 4B of primary visual cortex. We found that contributions of the M and P pathways to Layer 4B neurons are dependent on cell type. Spiny stellate neurons receive strong M input through Layer 4C alpha and no significant P input through Layer 4C beta. In contrast, pyramidal neurons in Layer 4B receive strong input from both Layers 4C alpha and 4C beta. These observations, along with evidence that direct input from Layer 4B to area MT arises predominantly from spiny stellates, suggest that these different cell types constitute two functionally specialized subsystems.