How does interactionism explain the connection between a decision and a bodily movement?

In the philosophy of mind, interactionism is a form of mind-body dualism that posits that the mind and body are distinct substances that nevertheless exert causal influence on one another.1

According to this view, a mental event—such as a decision or an act of will—functions as the direct cause of a physical action. For example, if an individual wills to move their leg, that mental state initiates the physical movement of the limb.1

While this theory provides an intuitive explanation for how our intentions translate into actions, it faces significant philosophical challenges:

• The Problem of Interaction: Because the mind and body are considered fundamentally different in quality, it is difficult to explain how a nonphysical entity can influence a physical one.1
• Scientific Consistency: A mechanistic interpretation of physical science suggests that the physical world, including the brain, operates as a closed system, leaving no clear mechanism for nonphysical "intrusions".1

Historically, René Descartes famously struggled to identify the site of this interaction, speculatively pointing to the pineal gland.1