Descartes suggested that the pineal gland is "the seat of the soul" for several reasons. First, the soul is unitary, and unlike many areas of the brain the pineal gland appeared to be unitary (though subsequent microscopic inspection has revealed it is formed of two hemispheres). Second, Descartes observed that the pineal gland was located near the ventricles. He believed the cerebrospinal fluid of the ventricles acted through the nerves to control the body, and that the pineal gland influenced this process. Sensations delivered by the nerves to the pineal, he believed, caused it to vibrate in some sympathetic manner, which in turn gave rise to the emotions and caused the body to act.[26] Cartesian dualism set the agenda for philosophical discussion of the mind–body problem for many years after Descartes' death.