The medial SuM, or SuMM, is made of smaller cells which release dopamine and give input to the lateral septal nucleus.
[1] Although the exact function of the supramammillary nucleus is still not clear, it is known that the SuM plays a role in modulating theta frequencies.
The axons of SuM neurons make monosynaptic connections to granule cells and GABAergic interneurons in the dentate gyrus.
Although it will not cause an action potential alone, SuM neurons can have excitatory impact on granule cells with the help of perforant path inputs.
Ultimately, the SuM will modulate the granule cell outputs causing it to influence the dentate gyrus information processing.