The important point that the H gland introduces into future psychology is that the link between the psyche and the soma is full of unforeseeable events that are therefore difficult to master and understand. The connections between the body and the psyche that are made via the H gland are subject to a great variability quite close to random. The large number of variables that can influence this gland at a given moment make it such that a stimulus (an animal approaches) can provoke different reactions (fear, courage, indifference) in different persons or in a person at a different moment or even arouse the three passions at the same time.
Descartes also shows the enormous physiological mobilization that accompanies the slightest reflex, the slightest stimulation, and the fact that a stimulus can, in the same instance, introduce a quick behavioral reaction and slowly become a thought in the soul. In this system, there can easily be conflict between several drives, between drives and the desires of the soul, or between the will and the drives.26 The soul can also influence a drive to regulate another drive. A passion is in general a high stake for the body (what does the body good and what does the body ill) that transforms itself into a thought to recruit the help of the soul. At the same time, a passion recruits the resources of the organism so that the will of the soul might have the logistic support necessary to act.
No one believes that the H gland could be the connection between body and thoughts. The current theories lean more favorably toward the first point on Descartes’s list (the connection between the psyche and the organization of the organism). However, in showing all of the forces and stakes at play that could move this gland, Descartes finds a metaphor that makes it possible to show the extraordinary power of the interactions between the realm of thoughts, the sensorimotor circuits, and the affective dynamics. He also shows that these interactions mobilize, in a massive way, the collection of physiological mechanisms in other words, the assembling of the organs.â Today, the organization of the organs is on the verge of being detailed by research; it serves as a foundation for the idea that psychological dynamics inevitably interact with the powerful currents of the organism
A last important point in the mind of Descartes that will be taken up by Spinoza and in particular by Hume is that the domain of the passions play a crucial role in sorting out physiological mobilization, behavior, and thought.
Descartes shows how these systems are both heterogeneous and connected (linked notably by the blood). They are heterogeneous to the extent that they are constituted of materials so different that they do not have the same properties. The substances that link these systems (blood and nerve impulse) have properties that are their own. Finally, even in the soul, we find thoughts that have a different logistic support. The sensory data, the passions, and the instincts have distinct physiological mechanics that have different impacts on the soul and manifest differently thereon. The intellectual intuitions come from the soul, and they have an impact on the body that is not that of the perceptions, the passions, and the instincts.