The activation of the habenula inhibits or deactivates the dopamine neurons in the substantia nigra and ventral tegmental area, and, conversely excites or activates them when it is deactivated. This has profound implications for PD, as this points to the possibility that it is not cell death which causes the issues in PD, but chronic activation of the habenula permanently switching off the cells in the substantia nigra from producing dopamine. This is a more hopeful hypothesis, as it means the cells are just dormant, not dead. If we can figure out how to deactivate the habenula, this could provide significant symptom reduction.