Final answer:
Layer IV is the most developed neocortical layer in the primary sensory cortex.
Step-by-step explanation:
The most developed layer in the primary sensory cortex is Layer IV. Layer IV contains a high density of synapses and receives direct input from the thalamus, allowing it to play a central role in sensory processing. It acts as a relay station, transmitting information from the thalamus to other layers of the neocortex.