Figure 5. Drawing from the De Homine of Descartes (1662), showing the pathway of the light through the ocular globe, retina, and collaterals of the optic nerves (corresponding to the retino-hypothalamic tract) that project to the 3rd ventricle (i.e., to the suprachiasmatic nucleus – SCN), to stimulate the pineal gland to release the animal spirit (corresponding to the nerve impulse) to the peripheral striatal muscles. Indeed, we currently know that the photic stimuli may not only activate a hypothalamic-medullary-epithalamic pathway for melatonin release (see Circadian Rhythm section) and thus signal the day/night shift to SCN-dependent pituitary secretions, but also trigger the lateral habenular nucleus. The lateral habenular nucleus receives projections from the SCN directly through the stria medullaris of the thalamus, and indirectly via the superior colliculi by lateral hypothalamic efferents. It influences brainstem motor centers like the substantia nigra and reticular raphe nuclei, to regulate body movement in relation to visual clues. In addition, melatonin acts on skeletal muscle as an ergogenic factor, favoring aerobic motor performance. Thus, Descartes view of the hypothalamic-pineal connection is partly consistent with evidence that light impulses transmitted through the hypothalamus may influence motor activity via the pineal gland and related epithalamus. (From Toni R. “Il sistema ipotalamo-ipofisario nell’antichità [The hypothalamic-pituitary system in the antiquity] – Dedicato alla memoria del Prof. Aldo Pinchera [Dedicated to the memory of Prof. Aldo Pinchera], In: L’Endocrinologo, Per una Storia dell’Endocrinologia [For a History of Endocrinology], 13, suppl. to n. 6, 1-11, 2012.