Emotions are inferred states of overt behaviors exhibited after stimulus presentation. When stimulated, a peripheral neuron changes cell polarization causing the cell to fire and send a signal to the brain. Once received in the brain, the signal is processed for its meaning. From an evolutionary perspective, human and non-human behaviors are selected only if they are functionally adaptive and provide the individual with reproductive advantages. Emotional expressions are considered part of an individual's behavior repertoire. Studies ranging from ablasions in primates to temporal lobectomies in humans suggest similar phylogenetic structures are involved in emotional expressions. Because both humans and non-humans possess the neurological structures amygdala and hypothalamus, Darwin's position of comparative emotionality is supported by numerous studies.
A Comparative Look at the Neurobiology of Emotion
Emotions are inferred states resulting from behavioral changes exhibited by an organism after presentation of a stimulus. Whether the inferred emotion is stimulated from within the organism by an endogenous stimulus or triggered by an exogenous, environmental stimulus is inconsequential. What is important, however, is a behavioral change occurs. The physiology of these behavioral changes, according to Canon (1929) is defined in terms of homeostasis. Homeostasis is the ideal physiological and chemical balance within an organism and has survival value. Therefore, evolution selected organisms that possess optimal homeostatic internal and external conditions (Emerson, 1958).
When an organism's body senses a chemical imbalance in certain neurological processes, it triggers several responses. For instance, when sensory stimulation is presented to a peripheral neuron a change in cell polarization occurs causing the cell to fire and send a signal to the brain. Once received in the brain, the signal is processed for its meaning. It is at this point of the cycle that psychologists diverge on their interpretation of the evoked responses attributed to emotion.
Behaviorists, for instance, argue that emotions as a mental construct does not exist in any organism, rather the behaviors are simply unconditoned responses. Cognitive psychologists, in contrast, firmly insist that emotions are the essence and result of mental life.