How does type materialism identify pain with a physical process in the brain?

In the philosophy of mind, type materialism—or type-identity theory—identifies mental states, such as pain, with specific types of physical states within the brain or central nervous system.12

This perspective posits that every instance of a particular mental state is identical to a corresponding type of neurophysiological state. Proponents, such as J.J.C. Smart, argued that this identification functions similarly to how scientific discoveries equate phenomena like lightning with electrical discharge or water with $H_{2}O$. By reducing mental events to physical ones, the theory aims to unify causal claims, allowing mental states to interact with the physical world because they are, fundamentally, physical events themselves.12

However, this view has faced significant criticism. Critics argue that it is implausible to assume every instance of a mental state (like pain or belief) must correspond to the exact same type of neural activity, as this would exclude the possibility of different biological organisms—or even different human brains—sharing the same mental state despite having different physical compositions. Consequently, many philosophers have shifted toward "token-identity" theories or other frameworks like supervenience to address these complexities.12