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Three different annual cycles in House Sparrows are described: temperate resident, subtropical resident, and temerpate migratory annual cycles. Photoperiodic control of the annual cycle is described, with the role of photoperiod in stimulating gonadal development discussed, along with photorefractoriness. The role of the circadian rhythm in mediating photoperiodic information is also discussed, along with the interaction of melatonin secretion by the pineal gland and the suprachiasmatic nuclei (SCN) of the hypothalamus in regulating this endogenous rhythm.

In his concise Cartesian textbook entitled Physiology (1641) Henricus Regius went beyond what could be found in Descartes’ published writings. There is no doubt that Regius completed some of its contents himself, but Descartes generously shared his (unpublished) views with him as well. This article investigates this tension on two specific points that relate to the function of the pineal gland and the animal spirits. First, did Descartes change his mind between the Treatise on Man and the Passions regarding the last step of sensory perception in the brain? It is argued he did not. Second, does the soul move or determine the movement of the animal spirits via the pineal gland? It is argued the soul determines the movement.

This chapter discusses Descartes thoughts on the seat of the soul or that part of the body which the soul is directly and intimately united. Descartes explains the simplicity principle: If the soul is simple, or indivisible, it can interact directly with only one object at once, thus indivisible. For example, if an animal's heart is taken and cut into pieces, the soul's indivisibility means that the soul cannot act directly upon the dissected parts of the heart. Descartes also consistently identified the pineal gland as the seat of the soul— partly because it was mobile, durable, protected from outside influence, and accessible to the nerves. It also explains that the mind is not affected by all parts of the body, but only the brain and one small part of the brain only where a certain part of the brain is affected while other parts are doing other things. This chapter finally reveals that the simplicity principle of Descartes will have strong difficulties in the final analysis in relation to the truth of God.

Electroconvulsive therapy is considered to be the most effective treatment for endogenous depression, but despite vigorous research there is no consensus on the mechanism of the antidepressant effect. One attempt to explain the mechanism uses a neuroendocrine hypothesis. Because it is generally accepted that the therapeutic effect of electroconvulsive shock (ECS) occurs after chronic (but not single) administration. In the past decade, evidence accumulated that depression might result from desynchronization of circadian rhythms. Such normalization is achieved simply by a single administration of the pineal gland hormone melatonin in rats. Also, administration of a single dose of melatonin has been reported to change circadian rhythms in humans. Elevation of human plasma melatonin levels was observed after a single dose of the heterocyclic antidepressants, desipramine and fluvoxamine, and of monoamine oxidase (MAO) inhibitors. If the stimulation of melatonin synthesis with consequent normalization of disrupted circadian rhythms is, indeed, the common denominator of the antidepressant effect, it is interesting to study the effect of ECS on melatonin synthesis.

The ways in which the Keplerian turn discussed in the previous chapter manifested itself during the seventeenth century is the subject of this chapter, which examines three particular developments influenced by that turn: the deployment and improvement of telescopes and microscopes; the emergence of new, mechanistic theories of light and color; and the resulting efforts to explain sensation, perception, and cognition on the basis of these new theories. One clear outcome of these efforts was a complete repudiation of the medieval “pictures-in-the-mind” approach to visual cognition, with its emphasis on animating spirits and intentional species, in favor of a more materialist approach based on physical impulses and reactions that correlate with such “pictures” without bearing any resemblance to them.