Recent research from the UIC group supports the hypothesis that oxytocin, acting in part through effects on the autonomic nervous system, might allow "immobility without fear." In other words, oxytocin may in general protect the nervous system from shutting down in the face of stressful circumstances, especially those that require holding still rather than fighting or fleeing. That includes even events that may seem positive from a societal standpoint, such as birth. One clue this may be so? Post-traumatic stress disorder is not usually associated with birth, although it's a tremendously stressful experience. Oxytocin plays an important role in helping females manage both emotional and physiological responses during life-altering events such as childbirth-converting potentially stressful experiences into opportunities for expressing joy and love.

Oxytocin, Fear, and the Amygdala

Function:

·         Arousal

·         Controls Autonomic Responses Associated with Fear

·         Emotional Responses

·         Hormonal Secretions

Location:

·     The amygdala is an almond shaped mass of nuclei located deep within thetemporal lobes, medial to the hypothalamus and adjacent to thehippocampus.

The amygdala is associated with a wide variety of psychiatric conditions in humans including anxiety disorders (PTSD, phobia, and panic), depression, schizophrenia, and autism, to name a few. Because the amygdala learns and stores information about emotional events, it is said to participate in emotional memory. Emotional memory is unconscious memory. In addition to its role in emotion and unconscious emotional memory, the amygdala is also involved in the regulation of numerous cognitive functions such as attention, perception, and explicit memory. The amygdala has a wide range of connections with other brain regions, allowing it to participate in a wide variety of behavioral functions. Most of the inputs to the amygdala involve excitatory pathways.  The common feel good neurotransmitters; norepinephrine, dopamine, serotonin, and acetylcholine are released in the amygdale. Numerous peptides receptors are also present in the amygdala, including receptors for opioid peptides, oxytocin, vasopressin, corticotripin releasing factor, and neuropetide Y, to name a few.

In the late 1930s, researchers observed damage to the temporal lobe resulted in profound changes in fear reactivity, feeding, and sexual behavior. Around mid century, it was determined that damage to the amygdala accounted for changes in emotional processing. Numerous studies subsequently attempted to understand the role of the amygdala in emotional functions, especially fear.

In the 1980s, researchers began to more fully understand the mechanisms of fear as it applies to the amygdale. We now know that the amygdala responds to severe traumas with an un-erasable fear response ("post-traumatic stress disorder", or PTSD; click for a superb site by the Madison Institute of Medicine on PTSD). 

Figure 1: Auditory fear conditioning pathways. The auditory conditioned stimulus (CS) and somatosensory (pain) unconditioned stimulus (US) converge in the lateral amygdala (LA). The LA receives inputs from each system via both thalamic and cortical inputs. CS-US convergence induces synaptic plasticity in LA such that after conditioning the CS flows through the LA to activate the central amygdala (CE) via intraamygdala connections. CE in turn controls the expression of behavioral (freezing), autonomic and endocrine responses that are components of the fear reaction. Other abbreviations: B, basal amygdal; CG, central gray; LH, lateral hypothalamlus; ITC, intercalated cells of the amygdala; PVN, paraventricular nucleus of the hypothalamlus.

But the amygdala is not all about fear. It is also implicated in aggressive, maternal, sexual, eating and drinking behaviors. Recent progress in functional imaging techniques has been a real help in understanding the amygdala. For example, we now know that a damage to the amygdala interferes with fear conditioning. Further, exposure to emotional faces potently activates the human amygdala. Both conditioned stimuli and emotional faces produce strong amygdala activation when presented unconsciously, emphasizing the importance of the amygdala as an implicit information processor and its role in unconscious memory.

Figure 4: Intracellular signal transduction pathways underlying auditory fear conditioning in LA cells.