What does science say about high sensitivity? For the third time, leading names in research in this field came together. The first two editions had only taken place virtually. The third international conference on sensitivity research was held in person for the first time on May 23rd, 2025 at the University of Surrey in England. It was also streamed online. The host was Michael Pluess, who recently moved to Surrey from Queen Mary University in London. The keynote speech was followed by shorter study presentations and a concluding roundtable discussion on high sensitivity in relation to mental health. Terminologys: This article refers to both high sensitivity (HSP = highly sensitive persons) and sensory processing sensitivity (SPS). Both terms mean the same thing, but SPS is the more scientific term. The term environmental sensitivity is also increasingly used in research. In the following, all three terms are interchangeable. Please keep in mind that the following report by an online viewer does not purport to be complete or error-free.

Contents of Part 1

• The neurology of high sensitivity – research on humans and animals • High sensitivity and drugs – an animal experiment • Environmental sensitivity in connection with positive emotions, closeness to nature, climate anxiety • High sensitivity and digestion • High sensitivity in schoolchildren • Environmental sensitivity in Syrian refugee children • Influence of childhood irritability on the effect of parental education measures • Click here to go to part 2

Keynote: Neurology of high

sensitivity – research on

humans and animals

The first keynote speech was given by Prof. Judith Homberg from the Radboud University Medical Centre in the Netherlands. She is attempting to understand highly sensitive brains in humans and animals using the tools of brain research. What actually happens when a new sensory stimulus appears, e.g. a noise or a change in temperature? • The stimulus registers at the reception, so to speak. In the brain, this is the ‘salience network’. There, one of two possibilities is roughly examined: • Can the stimulus be ignored or processed by the brain's background functions? If so, it is passed on to the default mode network (mainly centred around the dorsal-medial prefrontal cortex). The stimulus is not consciously perceived. • Is action required because there could be a danger lurking, for example? If so, the reception centre passes the stimulus on to the frontoparietal network, better known as the central executive network. The stimulus is now consciously perceived. The insula or insular cortex is particularly responsible for integrating external sensory stimuli with internal emotions and feelings in the brain. A few interesting study results • HSP react more intensely than others to images with difficult content – but only if they had a good childhood! • In people with difficult to traumatic childhoods, there is no measurable difference in the reaction to difficult images between HSP and Non-HSP. • When an EEG (electroencephalogram) is used on people in a resting position, the brains of HSP remain more active than those of people with normal sensitivity, even when at rest – but only when their eyes are open! With their eyes closed, the EEG of both groups are comparable. Prof. Homberg also conducts a lot of research on animals. The problem is that animals cannot fill out high sensitivity self-evaluation questionnaires. So they have developed a model that looks for four signs of high sensitivity in animals: • Increased emotional reactivity • Deeper processing of sensory information • Greater attention to environmental stimuli • Increased tendency to overstimulation Test rats were sent through a maze. The rats presumed to be highly sensitive stood out due to the following behaviours: • frequent freezing, • increased startle response, • more observable inhibitions in behaviour. High sensitivity and drugs – an animal experiment Can high sensitivity and the associated tendency to overstimulation lead to increased consumption of alcohol and drugs? One experiment investigated this question. Test rats were placed under stress and ofered to supply themselves with any amount of cocaine they wanted. • Highly sensitive rats actually consumed measurably more cocaine. • In addition, a difference in neurotransmitters was found in highly sensitive rats: they had more glutamate and less GABA than rats with normal sensitivity. This indicates that high sensitivity may be associated with fewer GABA neurons – at least in rats. • Also interesting: the brain of a highly sensitive rat reacts more strongly to the same amount of cocaine than that of a rat with normal sensitivity. There is no explanation for this yet. It is suspected that highly sensitive rat brains have to work harder at self-regulation to maintain a balance between activation and inhibition in response to environmental stimuli. Applied to humans, this would mean: • Highly sensitive individuals are activated more intensely by sensory stimuli than those with normal sensitivity. They may have fewer inhibition mechanisms to cushion and filter out stimuli. They may have a narrower range for self-regulation between activation and inhibition in response to sensory stimuli. • Why does the activation threshold of the central executive network appear to be lower? One possible reason is that more of the neurotransmitter glutamate is available and less GABA. • More intense activation by stimuli from the external and internal world also means that the threshold of overstimulation is reached earlier. Activating vs. inhibiting neurons There are basically two types of neurons in the brain: activating and inhibiting neurons. They function a bit like the accelerator and brake in a car. The sum of the activating and inhibiting effects creates a balance at a certain level. In a coma, for example, the inhibiting neurons are overwhelmingly dominant. In a highly sensitive brain, the effect of the inhibiting neurons may be lower, while that of the activating neurons may be higher. Overall, a different baseline between activating and inhibiting neurons is established than in people with normal sensitivity. Do HSP see and feel more? Another question that comes up regularly is: Do highly sensitive people generally see and feel sensory stimuli more strongly? Or is the sensory stimulus initially the same as for others, and only the subsequent internal processing is different? The current consensus in research is: • HSP do not initially perceive sensory stimuli more intensely than people with normal sensitivity. • However, the subsequent processing of these stimuli may have fewer filters available.

High sensitivity in connection

with positive emotions,

closeness to nature, climate

anxiety

Dr Annalisa Setti from University College Cork (Ireland) is investigating high sensitivity in combination with positive emotions and the role of closeness to nature. Her current work asks the following key question: How exactly does our connection to nature work? And how does it help to improve our well-being and cognition? Here are a few findings that are supported by both quantitative and qualitative data: • On average, highly sensitive people have a stronger connection to nature than people with normal sensitivity. • HSP often exhibit more environmentally- conscious behaviour, but also more climate anxiety. This may be related to the fact that HSP are more prone to rumination. • HSP are more severely affected in their well- being than people with normal sensitivity when they are in a chaotic environment. However, this negative effect is less pronounced when there is a stronger connection to nature. Interestingly, this positive effect is stronger in older people (over 60) than in younger ones. • HSP react more positively than others when watching a beautiful nature video. • When people have little connection to nature, this has a more negative effect on HSP than on people with normal sensitivity. This confirms how important the presence of nature is for HSP. In the subsequent short Q&A session, the question came up as to whether HSP also tend to be more likely to be climate activists due to their more intense reaction to climate change. The answer is not known. However, every form of activism brings its own challenges, which HSP may be more reluctant to face.

High sensitivity and digestion

Dr Shuhei Iimura from Soka University in Tokyo (Japan) spoke about the links between high sensitivity and digestion in teenagers. It has long been known that highly sensitive people are likely to be more vulnerable in terms of their mental health. In particular, they appear to have an increased proclivity towards anxiety and depression. But what about physical health? For some time now (Benham, 2006), researchers have been investigating a link between high sensitivity and more frequently having certain physical symptoms. These include aches in back, stomach and head diarrhoea and sleep disorders. However, the research on physical symptoms is less clear than on psychological symptoms. In particular, there is a lack of meta reviews. Dr. Iimura has supervised three studies and gained the following insights: • When asked about any digestive problems experienced in the last seven days, HSP report reflux, irritable stomach, abdominal pain, constipation and diarrhoea more often than others. • When there is little diversity in the microbiome, high sensitivity correlates with elevated inflammation markers (high levels of C-reactive protein = CRP). Elevated inflammation markers are also often found in people with depression. • HSP have higher levels of inflammation than other people when their microbiome contains low levels of the bacteria of the types Marinifilaceae and Butyricimona. However, there is no evidence that HSP have a fundamentally different composition of the microbiome than other people. The importance of the microbiome – in connection with depression, for example – has been demonstrated in astonishing experiments: stool samples were taken from depressed people and transplanted into healthy mice. The mice then also developed signs of depression. Incidentally, people with autism also report digestive problems more often than others. Taking certain dietary supplements may improve mental health. In any case, a healthy digestive system improves the overall health of HSP – both physically and mentally.

High sensitivity in

schoolchildren

Dr. Monika Baryła-Matejczuk (University of Economics and Innovation in Lubin, Poland) studied primary school children in the first three years of school from five schools in central and eastern Poland. The groups were also checked for various forms of neurodiversity to avoid confusing high sensitivity with other personality traits. This confirmed numerous known or suspected characteristics of highly sensitive children in various areas of experience: • Physical: heightened body awareness, a tendency to experience physical symptoms when stressed, more intense feelings of discomfort, more intense reactions to noise, light, textures and sensory overload, need for a structured environment with built-in breaks in a low-stimulus environment. Interestingly, they often develop strategies all by themselves to cope better with sensory overload. • Relationships: tendency to be alone or in very small groups. They observe interpersonal situations for a while before engaging and often appear shy or withdrawn to outsiders. They are socially engaged, but selective in their choices of activities. They tend to stand up for others and prefer authentic relationships. They often seek the approval of others, tend to want to please authority figures, and are sensitive to criticism or rejection. • Emotions: Emotions are often held back until they become overwhelming. They may appear calm on the outside, even though they are experiencing many emotions. They seek emotional security and predictability and can become anxious in new or unstructured situations. Clear expectations and routines are helpful. When emotional reactions arise, they come quickly, sometimes seem exaggerated, and these children need support in self-regulation. Spending time in nature has a supportive and soothing effect on their emotional self-regulation. These children often show empathy for animals and the environment. They can react intensely to the feelings and emotions of others, often worry about their well-being, and can literally soak up an emotional atmosphere. • Cognition: Learning processes are approached slowly. Step-by-step instructions are preferred. Increased ability to process information in depth, analyse and think critically, increased sense of justice and ethics. They are curious, self-reflective, value intellectual challenges and find creative solutions. Self-critical, tendency towards perfectionism, fear of making mistakes. In the artistic field, there is often a great deal of creativity and imagination in thinking and expression, and art can be used as a means of processing impressions and expressing oneself. These observations provide lessons for dealing with highly sensitive children in schools. In particular, it is important that teachers are informed and trained about the characteristics of high sensitivity and how to deal with these children. This will enable highly sensitive children to feel safe and flourish. Adjustments are desirable in the following areas: • immediate environment (classroom), • extended environment (school, structures, timetables, breaks, curricula, protocols, emotional support for children and teachers, etc.). Ideally, teachers and parents should work together to coordinate the entire daily routine in both the school and private spheres.

Environmental sensitivity in

Syrian refugee children

Dr Andrew May from the University of Surrey looked for characteristics that indicate environmental sensitivity in Syrian refugee children. He is aware of the many unknowns in the following areas of knowledge: • What is the genetic contribution to environmental sensitivity? • How is environmental sensitivity “calibrated” during childhood? A total of 1,409 children with an average age of 11 were observed and 40 variables were taken into account. The children's sensitivity was assessed through self-reporting. The hypothesis was that highly sensitive children react more strongly to a negative environment. This search was part of a larger study called BIOPATH (Biological Pathways of Risk and Resilience Study). The results for children with increased environmental sensitivity: • Lower sensitivity thresholds in children correlate with their own experiences of war, but also with post-traumatic stress disorders in their mothers. • They also react more strongly than other children to a particularly stressful environment, but also, conversely, have a stronger positive reaction to a particularly supportive environment. Further studies will focus in particular on the spontaneous strategies these children use to cope with circumstances. Michael Pluess added in the subsequent discussion that one study shows that high sensitivity is the most significant factor in predicting low resilience. In other words, HSP seem to have less resilience on average than others.

Influence of childhood irritability

on the effect of parental

educational measures

Dr. Danni Liu is currently conducting an ongoing study to investigate how supportive or punitive parental educational measures (e.g. praise, affirmation, scolding, punishment, teaching by example, etc.) affect children with different levels of irritability. Irritability does not mean sensitivity. It is well established that parenting programmes are effective when they are based on psychological findings, especially when it comes to addressing disruptive early childhood behaviour. This allows the reciprocal coercive interventions as described by Gerald Patterson to be replaced by more appropriate interventions. In Patterson's cycle, disruptive child behaviour leads to parental punishment, to which the child reacts with even more intense behaviour, resulting in a recurring cycle of escalation. These cycles then become established as recurring, automatic processes in the family system. They can be replaced, for example, with processes in which parents take non-violent measures and positively reinforce and affirm positive behaviour in their children in order to encourage that same behaviour. The example set by the parents‘ own behaviour also has an effect here. The hypothesis for the current study is as follows: • Highly sensitive children may respond more strongly to parenting programmes if they are also above average in terms of irritability. • Children with low irritability are likely to respond less because they are better able to adapt to parental behaviour. Children with medium irritability are likely to respond the least because their behaviour is the most difficult to change. At the time of presentation, no final results were available. Continued: Click here to go to part 2 Read also: • Coaching for highly sensitive people • High sensitivity in the workplace and in leadership and management • The dark side of high sensitivity • Further articles and blogs • How does a coaching session look like? • Contact and appointment