How does the brain affect behavior and regulate emotional states?
Emotions are
regulated by the complex interaction between various brain components and
the environment 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, however,
the brain is more like a superhighway. This highway consists of a variety
of environmental inputs (some that are available to our consciousness but
many that are not) and our ultimate responses to those inputs.
Environmental inputs available to our consciousness are those that we
typically associate with the five senses: sight, smell, taste, hearing,
and touch. The mere words conjure up a myriad of emotional memories for
experiences that we have had in the past. 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 is caused by
actual structural changes in the brain. In fact, long-term memories are
long term because of those structural changes. The brain is not a
computer but is a dynamic organ that is capable of physical change
throughout one's life.
Although sensory inputs are generally obvious, a multitude of
environmental inputs occurs without conscious awareness. The brain is
also constantly monitoring our body's internal environment, the
available nutrients and chemicals, blood pressure, pulse, temperature,
and respiration, and it 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
make-up. Genes code for proteins, which are the building blocks for both
the structure and function of the human organism. Genes guide
neuroanatomy, and in turn, neuroanatomy and neurophysiology guide
actions. Past experiences, on the other hand, are literally carved into
brains through a process conceptualized as neuronal plasticity. Nerves
are literally 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. By the nature
of genetics and developmental experiences, people are biased 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 depression, it is merely biology's way of
simplifying behavioral strategies to create more rapid and efficient
actions. Without emotions, one cannot prioritize; priorities to action
must be linked to a preconceived template of what one considers important
in decision making. This is the bias based on one's 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 brainstem and basal ganglia, followed by the
limbic system and then the rational brain that is comprised of the
cortex. The first layer is that part responsible for self-preservation.
It is where the "fight or flight" response is generated in response to
perceived danger. The brainstem is also where control of certain visceral
or "vegetative" functions (sleep, appetite, libido, heart rate, blood
pressure, etc.), are generated. The limbic region (from the Latin word
limbus for, ring, or surrounding, as it forms a kind of border around
the brainstem) is better known as the reward center, where emotions or
feelings such as anger, fear, love, hate, joy, 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 cerebral region is
considered the "rational brain", which is capable of producing symbolic
language and developing intellectual tasks such as reading, writing, and
performing mathematical calculations. These neuroanatomic distinctions
are really not that distinct but are integrated into 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 structures are not hierarchical but
are egalitarian. Brain function is more akin to an orchestra rather than
the more common notion of a military command center, as each component is
required for the entire symphony to work where the conductor is merely a
"ghost in the machine".
