During development, nerve cells in the eye send messages to the thalamus, a region located deep within the brain. The thalamus then passes these messages on to the area of the outer cerebral cortex that deals with vision. The connection between the thalamus and cortex initially passes through a transient and seldom studied structure called the subplate. By removing parts of the subplate in cats, the HMS researchers have shown that this structure is a key component in strengthening the thalamus to cortex connection and in mapping out further cortical wiring patterns important for vision.
The subplate neurons are acting "kind of like teachers," says senior author Carla Shatz, the Nathan Marsh Pusey professor of neurobiology and head of the HMS Department of Neurobiology. "They're needed for the thalamic connections to strengthen and grow so that they can become strong enough to talk to the cortical neurons."
Shatz, who is also co-chair of the Harvard Center for Neurodegeneration and Repair (hcnr.med.harvard.edu), says that an intact subplate normally acts like a form of building scaffolding for the neural circuits, directing and strengthening important nerve signals, before disappearing. "You make sure all the connections in the building are really strong so the thing doesn't fall down, and then you remove the scaffolding." Once the brain is fully developed and the subplate neurons start to die, a hand-off of sorts occurs in which the thalamus starts sending its signals directly to the developing visual cortex, bypassing the dismantling subplate.