The Highly Sensitive Brain

Humans and other animals deal to the environment around them by developing two response strategies: “pause and acting”, or “approaching quickly”. This response depends on the traits that configure our personality. The highly sensitive persons (HSP) possess a personality trait named “sensory processing sensitivity”. This trait makes them process the environment around them (physical, social, emotional, etc.) with a greater attention and awareness. They process the environment more deeply and also doing it with a great amount of detail. As they have greater emotional activation are more perceptive and they are able to integrate information and to respond to the affective states of others, especially people known or familiar in front of the “strangers / novelties”.

The SPS trait has also been studied at the genetic level, some genetic studies have found relationships between the level of sensitivity and a polymorphism of the 5HTTLPR gene (short allele) involved in the transport of a neurotransmitter called serotonin. 5HTTLPR is related to increased sensitivity to the environment. It has also been related to superior performance in perceptual tasks and a higher level of reflection when making decisions. Likewise, relationships have been found between the SPS trait and the levels of dopamine, another brain neurotransmitter, especially in the precuneus, which is a brain region related to the integration of visuospatial information, episodic memory and emotional stimuli.

HSP brain activity have been studied using neuroimaging techniques (fMRI). Regarding the level of deep processing and detection of subtleties, it was found that when they were presented with images in which they had to find differences (obvious vs. subtle), those higher on SPS spent more time processing the images with subtle differences and responded better finding these differences between the two images. However, when the images being compared had obvious differences, there were no differences between HSPs depending on their level of sensitivity. This means that the higher the score on high sensitivity scale the more aware they were of visual subtleties. Cerebral activation was found mainly on high visual processing areas such as left middle-temporal gyrus, greater activation of the right claustrum, right subgyral temporal lobe and right declive of the cerebellum. An important fact is that this activation was not explained by the scores of the participants in other equally measured personality traits that are related to the SPS such as introversion and negative affectivity or neuroticism.

In another fMRI study, HSP were presented with faces with positive and negative expressions from close people (their romantic partner) and strangers (as control). The objective was to study aspects such as highly sensitive people process social stimuli in this case associated with emotions.

The results found showed that people scoring high on a high-sensitive-scale (11 items of Aaron and Aaron; 1997) showed greater activation in regions related to awareness, integration of sensory information, empathy and regions that are activated when we prepare ourselves for the emotional response in relation to social stimuli. They also showed increased activation in the ventral tegmental area (midbrain), an area very rich in dopamine, a neurotransmitter that is activated in brain reward processes. In relation to the “pause and acting” strategy typical of highly sensitive people, it was found greater activation in areas of the premotor cortex. Of special interest was that the greater activation of the medial temporal gyrus explained not only the processing of stimuli at the physical level but more importantly related to the processing of the mood of the other. It was shown that relative to the detection of emotions a greater activation was collected in the insula, a very active area in relation to emotions, their detection and interpretation. Finally, it was shown that highly sensitive people tend to dedicate more time processing positive emotions (vs. negative or neutral) due to the higher activation of the inferior frontal gyrus. This inferior frontal gyrus is part of a more complex brain system named mirror neuron system. A brain system of core importance regulating our emotional social life. This system allows us to quickly capture the emotional life of others, intuit the sense of what they do and their goals. In the case of highly sensitive people, this activation is even greater. Highly sensitive people activate brain areas to a greater extent to interpret in great depth and detail the information of the affective and emotional states of the people around them, especially those close to them.

From a neurobehavioral point of view, research has been showing how certain personality traits are reflected in brain systems that are activated to a greater or lesser extent depending on the “amount” of trait that one possesses. In this sense, we talk about the Eysenck personality model that proposes areas of the cerebral cortex and cortico-limbic areas as a reflection of the individual differences in the traits of Introversion-Extroversion and Neuroticism-Stability.

In the case of highly sensitive people, research has also shown that different brain areas are activated in a greater extent as a person score higher on sensibility scales. Research have shown that this area are: Precuneus (self-related mental representation), Sensory cortices (perception), Cingulate cortex (attention), prefrontal cortex (cognitive processing and control), inferior frontal gyrus (response inhibition), claustrum (sensory integration), insula (interception, empathy), amygdala and hippocampus (emotion and memory).

We can conclude that there is a HSP brain configuration that have to do with the deep and subtle processing of information and emotional information. A high sensitive person identify not only the moods of the people around them but also the emotional charge of those emotional states, being more aware of these emotional states when emotions are positive and when came from familiar people.