How does identity theory connect a thought or feeling to an event in the brain?

In the philosophy of mind, identity theory asserts that mental states—such as thoughts or feelings—are identical to physical states of the brain or central nervous system. Proponents, such as J.J.C. Smart, argue that this connection is similar to how lightning is identical to an electrical discharge; the mental state is not merely caused by the brain event, but is the very same physical event viewed from a different perspective.123

Historically, this was framed as "type-type" identity, suggesting every instance of a specific mental state (like pain) corresponds to a specific type of neural state. However, due to the concern that different beings might experience the same mental state through different physical configurations, many philosophers shifted to "token-token" identity. This view posits that each individual occurrence of a thought or feeling is identical to a specific, unique physical event in the brain. Despite its goal of unifying the mental and physical, the theory faces significant challenges, including the difficulty of locating abstract thoughts in physical space and the "explanatory gap" regarding how physical matter gives rise to conscious experience.234