Neurobiologists have identified the neural circuits involved in fear learning and behavioral expression.
The frightened man begins to freeze like a statue, motionless and breathless, or crouches as instinctively to escape the gaze of others. The heart beats violently, and throbs or beats against the shore … The hairs on the skin stand, and the superficial muscles shiver. Because of the change in heart rate, respiration is accelerated … The mouth becomes dry and is often opened and closed.
Charles Darwin, The Expression of Emotions in Man and Animals.
One senses the fear in the presence or the prospect of danger. The physiological manifestations that accompany it, such as increased heart rate, the staring eyes, or the creepy, are due to release a hormone, adrenaline. These physiological changes can react quickly: the subject in danger prepares to flee or fight, thus ensuring his survival. However, some people suffer from exaggerated manifestations of fear such subjects quote drops till phobia, a posttraumatic stress disorder or anxiety disorders. They have abnormalities of certain neural circuits involved in fear, which causes anxiety reactions inadequate. But what are these channels?
Cyril Herry, INSERM Unit 862 of Neurocentre Magendie, Bordeaux, and several Swiss and German teams, have identified the first inhibitor of neuronal circuits involved in fear acquisition and expression of its behavioral responses. They are located in a region of the brain called amygdala (or amygdala) structure composed of several nuclei known to be the seat of fear.
The amygdala is the center of the brain circuitry of fear. Sensory information reaches the thalamus, a brain region central, then are analyzed – or not, depending on the seriousness and the imminence of the threat – by higher cortical structures and hippocampus, the seat of memory, before being transmitted to the amygdala. This then causes the behavioral response of the organism, via secretion of adrenaline.
Fear can be a learned response. For example, one can learn a rodent a painless stimulus – a sound – predicts an unpleasant event – an electric shock. At the beginning of the experiment, the animal shows no fear reaction when he hears the sound, but as he learns the association’s electric-shock, he is scared when the buzzer sounds and, for example, freezes. This fear conditioning involves the amygdala, particularly its lateral nucleus and the nucleus. We previously thought that the lateral nucleus was the region where the association of two stimuli – in this case, the sound and electric shock – was done and that the core was primarily involved in the behavioral expression of fear. It is indeed the core, particularly its middle part, leaving the fibers of the amygdala stimulates the hypothalamus and brainstem, which orchestrate the motor responses of fear and automatic (through the adrenaline).
Neurobiologists have identified the circuits of fear in the nuclei of the amygdala using two techniques, or they have blocked the amygdala neurons with pharmacological molecules, or they were excited after they have injected substances that boost neurons under the effect of light. Thus, by inactivating the lateral nucleus, they showed that rats only learned over the association between sound and electric shock. In contrast, inactivation of the middle part of the nucleus, where the information out, do not alter learning, but inhibits the behavioral response to fear (the rat came to rest over). Similarly, activation of the middle region causes a fear response in rats.
Furthermore, neurobiologists have recorded the electrical activity of neurons in the nucleus and identified the neural circuits involved in inhibiting behavioral fear. The lateral nucleus contains two distinct populations, but interconnected neurons, which inhibit the overall core income. On his “conditioning” the first active population, while it inhibits the second, and the first population may also inhibit the second. In fact, during conditioning, the researchers found that inhibition of the second population with the first lifts the inhibition on the overall core income, which causes an increase in conditioned responses to fear.
In parallel, neurobiologists have identified a U.S. cell types of the core side – that is inhibited by his conditioning – produces a particular protein kinase C delta. This is a molecular marker that allows scientists to “manipulate” these neurons and the expression of … fear. The identification of these circuits in the central nucleus of the amygdala should lead to new therapeutic approaches in patients who suffer from inadequate manifestations of anxiety.
|Category: Neuroscience||Tags: brain circuitry, heart beats violently, posttraumatic stress disorder|