How to Create a Mind: The Secret of Human Thought Revealed

by Ray Kurzweil

This thin structure is basically made up of six layers, numbered I (the outermost layer) to VI. The axons emerging from the neurons in layers II and III project to other parts of the neocortex. The axons (output connections) from layers V and VI are connected primarily outside of the neocortex to the thalamus, brain stem, and spinal cord. The neurons in layer IV receive synaptic (input) connections from neurons that are outside the neocortex, especially in the thalamus. The number of layers varies slightly from region to region. Layer IV is very thin in the motor cortex, because in that area it largely does not receive input from the thalamus, brain stem, or spinal cord. Conversely, in the occipital lobe (the part of the neocortex usually responsible for visual processing), there are three additional sublayers that can be seen in layer IV, due to the considerable input flowing into this region, including from the thalamus.