Effects of Electrolytic Lesions of the Reuniens and Rhomboid Nuclei on cognitive behaviors using the Intradimensional Extradimensional (IED) task in Rats

Reuniens and rhomboid nuclei (RE/RH) of the ventral midline thalamus compose a relay between the medial prefrontal cortex (mPFC) and the hippocampus (HPC). Recent behavioral studies have shown that RE/RH is critical in cognitive tasks that involve both the HPC and mPFC. Lesion and inactivation studies of the RE/RH, however, do not affect hippocampal dependent spatial behaviors. Here, we examined the effects of electrolytic lesions of RE/RH on an odor-texture discrimination task sensitive to faculties of orbitomedial prefrontal cortices. Rats with RE/RH lesions exhibited small deficits in reversal stages compared to controls. Reversal learning has been found to be anatomically and chemically dependent on normal functioning of the prefrontal cortex. Excitatory input from reuniens to the prefrontal cortex may be involved in mediating behavioral flexibility, the lack of which is a symptom of behavioral disorders such as Alzheimer’s and Parkinson’s diseases.