The cerebral cortex is connected to subcortical structures and is involved in higher cognitive functions; its thickness is most closely associated with which feature?

• A. Number of neurons in white matter
• B. Density of myelinated axons
• C. Layers of cell bodies and dendrites
• D. Amount of cerebrospinal fluid

Answer: (C)

Cortical thickness mainly reflects the structure within the cortical sheet itself—the density and arrangement of neuronal cell bodies across the six layers and the extent of their dendritic arbors. When there are more neurons packed into the layers and neurons with larger or more elaborate dendrites, the cortex appears thicker. The underlying white matter, made up of myelinated axons connecting regions, contributes to connectivity and conduction speed rather than to the thickness of the cortex. Fluids like cerebrospinal fluid define spaces around the brain, not the cortical mantle itself. So, the measure of how thick the cortex is aligns with the layers of cell bodies and dendrites, i.e., its cytoarchitecture.