The hippocampus makes a significant contribution to experience-dependent neocortical plasticity

Rats received unilateral hippocampal lesions before being placed in complex environments or standard lab housing. Three months later the brains were prepared for Golgi-Cox staining. Pyramidal cells in layer III of parietal cortex were analyzed bilaterally. The basilar dendrites of the parietal pyramidal cells in the intact hemisphere showed the expected changes in experience-dependent changes, including an increase in dendritic branching and length as well as spine density. In contrast, the basilar dendrites of the parietal neurons in the lesion hemisphere showed no significant effect of experience on dendritic branching or length and showed a decrease in spine density in the same neurons. The apical fields failed to show an effect of experience in either hemisphere. The hippocampus plays a crucial role in neocortical experience-dependent plasticity.