You can monitor the amount of cortical damage by looking at the extent of retrograde degeneration in the thalamus.

Ablation of area 17 leads to almost total loss of cells in the dorsal lateral geniculate body, a process known as retrograde degeneration.

The slowed conduction of action potentials in axons causes segmental demyelination extending proximally; this is also known as retrograde degeneration.

After injury, the proximal end swells and experiences some retrograde degeneration, but once the debris is cleared, it begins to sprout axons and the presence of growth cones can be detected.

For example, the neocortex is connected to the thalamus in such a way that destruction of part of the cortex causes cells in a corresponding part of the thalamus to die, a process known as 'retrograde degeneration'.