section_path: Formation/Neurobiological explanation
section_name: Neurobiological explanation
paragraph_text: Neurobiological explanation
  
  Based on discoveries made through neural mapping of the limbic system, the neurobiological explanation of human emotion is that emotion is a pleasant or unpleasant mental state organized in the limbic system of the mammalian brain. If distinguished from reactive responses of reptiles, emotions would then be mammalian elaborations of general vertebrate arousal patterns, in which neurochemicals (for example, dopamine, noradrenaline, and serotonin) step-up or step-down the brain's activity level, as visible in body movements, gestures and postures. Emotions can likely be mediated by pheromones (see fear).
  
  For example, the emotion of love is proposed to be the expression of Paleocircuits of the mammalian brain (specifically, modules of the cingulate cortex (or gyrus)) which facilitate the care, feeding, and grooming of offspring. Paleocircuits are neural platforms for bodily expression configured before the advent of cortical circuits for speech. They consist of pre-configured pathways or networks of nerve cells in the forebrain, brainstem and spinal cord.
  
  Other emotions like fear and anxiety long thought to be exclusively generated by the most primitive parts of the brain (stem) and more associated to the fight-or-flight responses of behavior, have also been associated as adaptive expressions of defensive behavior whenever a threat is encountered. Although defensive behaviors have been present in a wide variety of species, Blanchard et al. (2001) discovered a correlation of given stimuli and situation that resulted in a similar pattern of defensive behavior towards a threat in human and non-human mammals.
  
  Whenever potentially dangerous stimuli are presented, additional brain structures activate that previous thought (hippocampus, thalamus, etc.). Thus, giving the amygdala an important role in coordinating the following behavioral input based on the presented neurotransmitters that respond to threat stimuli. These biological functions of the amygdala are not only limited to the "fear-conditioning" and "processing of aversive stimuli", but also are present on other components of the amygdala. Therefore, it can referred the amygdala as a key structure to understand the potential responses of behavior in danger like situations in human and non-human mammals.
  
  The motor centers of reptiles react to sensory cues of vision, sound, touch, chemical, gravity, and motion with pre-set body movements and programmed postures. With the arrival of night-active mammals, smell replaced vision as the dominant sense, and a different way of responding arose from the olfactory sense, which is proposed to have developed into mammalian emotion and emotional memory. The mammalian brain invested heavily in olfaction to succeed at night as reptiles slept – one explanation for why olfactory lobes in mammalian brains are proportionally larger than in the reptiles. These odor pathways gradually formed the neural blueprint for what was later to become our limbic brain.
  
  Emotions are thought to be related to certain activities in brain areas that direct our attention, motivate our behavior, and determine the significance of what is going on around us. Pioneering work by Paul Broca (1878), James Papez (1937), and Paul D. MacLean (1952) suggested that emotion is related to a group of structures in the center of the brain called the limbic system, which includes the hypothalamus, cingulate cortex, hippocampi, and other structures. More recent research has shown that some of these limbic structures are not as directly related to emotion as others are while some non-limbic structures have been found to be of greater emotional relevance.