Can a brain be modeled as a simplified interaction of different states and their triggers?
My answer is probably a weird hodgepodge of sometimes poorly explained stuff, but hopefully it's coherent enough :P

For many decades in psychology, we've had a mechanistic stimulus-organism-response understanding of the brain.  That is, a stimulus triggers an internal psychological process, which produces some behavioral response.  One of the major limitations of this kind of thinking is that it assumes that the mind is at rest until it's stimulated by something in the environment (even if we add a recursive component to it). However, this is fundamentally untrue. 

Instead, the brain is a predictive organ (e.g., Clark, 2013). It's loaded with prior knowledge about past experiences, which is constantly used to predict incoming sensory information. If there is a discrepancy between incoming information and past experience (i.e., prediction error), then our knowledge is updated. This is most clearly seen in the literature on vision, which shows how top-down expectations and prior knowledge robustly bias early visual activity, even in the absence of a visual stimulus (Summerfield &amp; de Lange, 2014). The trigger-state model could not easily account for this.

Moreover, dividing up the brain into mental states may not actually represent how the brain functions.  The brain isn't really faithful to the kinds of distinctions we make between cognition and emotion, for example (e.g., Barrett, 2009; Pessoa, 2008).  And not only that, those higher order states like anxiety and sexual arousal can be represented in the brain in many different ways. Indeed, there is no dedicated mechanism in the brain or body for producing states like anxiety or creative inspiration (e.g., Wager et al., 2015).  They're merely concepts for organizing and communicating our experience.  And even then, our brain may not really "have" concepts (see Laurence Barsalou's work; but see also Blouw, Solodkin, Thagard, &amp; Eliasmith, 2015), although it may have a conceptual system that allows us to conceptualize (e.g., Barsalou, 2005).

So I guess what I'm getting at is that brain function is nonlinear, spatiotemporally dynamic, and doesn't adhere to folk psychological categories. Thus, it would probably be difficult to understand the brain by attempting to reduce linear trigger-state relationships to the level of networks, regions, and cells. However, maybe (probably) someone has a better informed, more balanced answer than me! :)