The neural basis of the emotions
There has been major progress in elucidating the neural basis of the emotions and of emotional feelings. As a result of extensive animal and human studies, the best understood emotion is fear (Damasio, 1994/2005; Le Doux, 1996; Panksepp, 1998; Feinstein et al, 2010). Fear relative to external circumstances is triggered by the amygdalae, two sets of subcortical nuclei located in the depth of each temporal lobe. The amygdalae receive signals related to a certain situation, for example, a visually represented threat such as a looming shadow or an auditorily represented threat such as a high-pitched scream. When those signals have a suitable configuration, an appropriate context, and reach a workable threshold, i.e. when they are emotionally-competent, they activate nuclei in the hypothalamus and in the sector of the brain stem known as the periaqueductal gray.Working together those brain sites execute the requisite emotional actions — release of cortisol into the bloodstream, adjustment of heart rate, respiratory rate, degree of gut contraction, and fear-specific behaviors such as changes in facial expression and posture, and freezing in place or running away from danger. The ensemble of these actions constitutes the emotional state of fear. Thus, included in the emotional state are specific behaviors aimed at protecting the integrity of the individual, e.g. running away or freezing in place, and also a preparation of the organism meant to allow it to carry out those protective behaviors. When the situation is best handled by a flight response, the emotional state ensures that sources of energy are available in the blood stream and adjusts cardiac and respiratory functions so that they meet the metabolic needs ahead; the emotional state even provides for analgesia to offset the pain that might result from potential injuries.
In situations best dealt with by staying in place as inconspicuously as possible, the preparatory actions are radically different since no muscular effort will be needed and, immobility is instead the desired goal. The selection of fleeing or freezing responses is made automatically although humans may override the natural selection and decide for one of the other option. This fine-tuned mechanism calls for the engagement of different cellular columns of the periaqueductal gray.
Fear caused by internal events, for example, the extreme pain associated with myocardial infarction or the development of acidosis associated with CO2 inhalation, is probably triggered by chemoreceptors located subcortically, namely in the brain stem.
The emotion program of disgust is another good example of protection of the organism’s integrity. Disgust is triggered from a small region of the anterior insular cortex when certain stimuli are present, for instance, the sight of decomposing food or body waste, as well as tastes or odors from decomposing organic matter. The sight of body-boundary violations, as in a wound with blood, also causes disgust. The actions that constitute disgust include a typical facial expression and, for example, the rapid expulsion of the potentially offending food. As a result the subject will not ingest a potentially toxic food and other subjects may also be alerted to the potential danger (Harrison et al, 2010).
In the social emotion of contempt there is a rejection of certain behaviors or ideas rather than an expulsion of toxic substances or their tell-tale signs. Contempt can be seen as a biological metaphor for disgust. Significantly, we refer to actions that cause moral revulsion as “disgusting,” and the repertoire of facial expressions that accompanies a contemptuous judgment is similar to that of disgust. The advantages of contempt are apparent: the rejection of behaviors deemed dangerous to individuals or groups, and the social isolation of those who produce such behaviors.
Compassion is another emotion whose trigger region has been identified. The triggering site is located in the ventral and medial sector of the prefrontal cortex. When this region is activated by the sight of others facing a predicament, for example, an accident resulting in physical injury, facial expressions and even gestures meant to help the victims are rapidly deployed. Such actions benefit others and by extension the social group, but also result in personal benefits such as increased appreciation by others, gratitude, and thus enhanced reputation (Immordino Yang et al, 2009).
- source: scholarpedia.org
