Which of the following is not a subdivision of Layer IV?

Which of the following is not a subdivision of Layer IV?

• A. IVA
• B. IVB
• C. IV C
• D. IVD

Answer: (D)

Layer IV is the granular input layer of the neocortex and is commonly divided into sublayers that reflect distinct thalamic inputs and local circuitry. In many sensory areas, the accepted subdivisions are IVA, IVB, and IV C, with the C subdivision often split further into IV Cα and IV Cβ. A subdivision labeled IVD is not a recognized part of Layer IV in standard cortical lamination schemes, so it does not belong to Layer IV. The other subdivisions (IVA, IVB, IV C) are established parts of Layer IV, which is why IVD stands out as the non-existent subdivision.

Layer IV is the granular input layer of the neocortex and is commonly divided into sublayers that reflect distinct thalamic inputs and local circuitry. In many sensory areas, the accepted subdivisions are IVA, IVB, and IV C, with the C subdivision often split further into IV Cα and IV Cβ. A subdivision labeled IVD is not a recognized part of Layer IV in standard cortical lamination schemes, so it does not belong to Layer IV. The other subdivisions (IVA, IVB, IV C) are established parts of Layer IV, which is why IVD stands out as the non-existent subdivision.