The complex interaction between various brain components and the environment regulates emotions in a feedback loop that allows for both the environment to impact brain structure and function and the brain to impact on the environment through action.  More than being a two-way street, though, the brain is more like a superhighway consisting of a variety of environmental inputs (some of which are available to our consciousness but many of which are not) and our ultimate responses to those inputs.  Environmental inputs available to our consciousness are those we typically associate with the five senses: sight, smell, taste, hearing, and touch.  The mere words conjure up a myriad of emotional memories for past experiences.  A certain odor or song can suddenly take a person back to a previous relationship or situation.  The connection between a current environmental cue and memories are due to actual structural changes in the brain.  In fact, longterm memories are long term because of those structural changes.  The brain is not a computer but a dynamic organ capable of physical change throughout one's life.

 

Although sensory inputs are generally obvious, a multitude of environmental inputs occur without conscious awareness.  The brain is constantly monitoring our body's internal environment--the available nutrients and chemicals, blood pressure, pulse, temperature, and respiration--and adjusts itself accordingly.  It is also monitoring the external environment in ways that are not immediately apparent.  These unconscious inputs can affect the emotional state in ways that are not always obvious.

 

Interpretations of these inputs that prompt actions are also influenced by two important factors influencing the brain long before inputs are received.  Built into the brain are sets of biases, some of which are determined by genes and the biological (uterine) environment in which development occurs, and others by past experiences.  Although genes do not cause behavior, they are the foundation for a person's entire organic makeup.  Genes code for proteins, and proteins are the building blocks for both the structure and function of the human organism.  Genes guide neuroanatomy, and inturn neuroanatomy and neurophysiology guide actions.  Past experiences, on the other hand, are carved into the brain through a process known as neuronal plastiity.  Nerves are pruned away like tree branches through learning and experience as the brain attempts to create more efficient and faster communication pathways through those repeated experiences.  The nature of genetics and developmental experiences cause people to respond to the environment in certain ways.  Although bias can predispose people toward negative actions and may be one of the mechanisms behind the development of some types of mental illness, it is merely biology's way of simplifying behavioral strategies to create more rapid and efficient action.  Without emotions you cannot prioritize; priorities to action must be linked to a preconceived template of what you consider important in decision making.  This bias is based on your emotional experiences and constitutional nature (genes and non-genetic biological effects).

 

In terms of defining the specific areas of the brain, or the anatomical locations, that control emotions, the division of regions is not clear-cut.  One of the oldest and easiest to understand (but not necessarily the most accurate) theories divides the brain into three regions or layers.  The most primitive is the brain stem and basal ganglia, followed by the limbic system, and then the rational brain composed of the cortex.  The first layer, the brain stem, is responsible for self-preservation.  It is where the "fight or flight" response is generated in response to perceived danger.  The brain stem is also where control of certain visceral or "vegatative" functions (sleep, appetite, libido, heart rate, blood pressure, and so on) are generated.  The limbic region (from the Latin word "limbus" for ring, or surrounding, because it forms a kind of border around the brain stem) is better known as the reward center, where emotions or feelings like anger, fear, love, hate, ojoy, and sadness originate.  The limbic system is also responsible for some aspects of personal identity as related to the emotional power of memory.  The third cerebal region is considered the "rational brain," capable of producing symbolic language and developing intellectual tasks such as reading, writing, and performing mathematical calculations.  These neuroanatomical distinctions are really not that distinct but instead function as a unified whole, such that an assumption cannot be made of any one system taking priority over the other.  The notions of brain regions as "primitive versus advanced" and "inferior versus superior" have not been supported by modern science.  Brain stuctures are not hierarchical but egalitarian.  Brain function is more akin to an orchestra than a military command center, as each component is required for the entire symphony to work, and the conductor is merely a "ghost in the machine."