What Traits Are Characteristic of a Sensitive Neurobiology?

Self-described ‘sensitives’ who completed the Environmental Sensitivity Survey(PDF, 10pp, 240KB) report, among other things:

These individuals also tend to report that immediate family members suffered from the same conditions. This raises the question of whether a genetic basis for extraordinary sensitivity may exist.

The Findings

The survey found 8 factors that appear to be significant in the profile of a sensitive person:

Synesthesia – the scientifically recognized condition of overlapping senses, such as hearing colors or tasting shapes – was reported by approximately 10% of the sensitive group but not at all among controls. This finding gives added weight to the possibility that anomalous perceptions stem from an underlying neurobiology of sensitivity. An individual’s neurobiology is shaped by nurture, too – which the survey findings affirm. Recall of a traumatic event in childhood was indicated by three times as many sensitives as controls. Furthermore, a startling 14% of sensitives reported having been struck by lightning or suffering an electrical shock, whereas none of the control group did.

The Implications

It seems likely that certain people are, from birth onward, disposed to a number of conditions, illnesses, and perceptions that, in novelty as well as intensity, distinguish them from the general population. If so, anomalous experience might have a bona fide neurobiological basis that makes it accessible to scientific inquiry.

The factors mentioned above, which appear to be significant in the makeup of a sensitive person, are consistent with a good deal of current knowledge. Science is determining, beyond the shadow of a doubt, that no two people live in the identical sensory world. How each of us is arrayed to process incoming stimuli – and the characteristic way we process feeling – will tell a highly individual tale.

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Gender Differences

Women predominate among all forms of environmental sensitivity. This should not be surprising since the female of the species is innately different than the male. In fact, the closer we look at gender, the more significant this basic biological difference becomes.

Women exhibit markedly greater sensitivity across all five senses. They have a lower threshold and tolerance for pain than men. They are also vastly more susceptible to a range of autoimmune diseases.

Many brain structures differ in size between the genders. The hippocampus (which has a role in memory) is larger in women, while the amygdala (the brain’s ‘alarm circuit’) is larger in men. Production of various neurotransmitters differs as well. Perhaps even more importantly, the back portion of the corpus callosum (an elongated bundle of nerve fibers carrying information between the brain's two halves) is wider and larger in women than in men. This latter fact supports the idea that, throughout their lives, females may boast greater communication between the hemispheres.

In general, men are wired to be more attuned to what’s going on outside of their body, while women are wired to be more vigilant to what’s happening inside. And study after study shows that women are more adept at remembering emotionally-tinged information.

Naturally, one might say, women are more prone than men to report anomalous perceptions.

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First-Born or Only Child

Some evidence suggests that first-borns are more likely to suffer from various allergies because they have a greater susceptibility determined in utero. Many children who have imaginary companions tend to be first-born or only children. These findings may help explain why a large proportion of self-described sensitives stated in the survey that they are first-born or only children.

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Being Single

The survey showed that sensitives are more likely than controls to be single or divorced/separated, and (the flip side) less likely to have ever been married. One interpretation is that sensitives tend to have personal issues that make marriage more problematic for both them and their partners. Alternately, since the average age of the control group was slightly higher, it could be that some of the sensitive respondents are approaching an age at which they get married, rather than being married already.

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Being Ambidextrous

Many more sensitive respondents than controls indicated they are ambidextrous. Given what we know of the corpus callosum, it’s distinctly possible that a greater degree of interchange exists between the hemispheres in persons who are sensitive. This would explain not only why women are disproportionately sensitive but why at least some sensitives tend to use both hands rather than preferring one.

Current research also suggests that persons with a higher degree of ‘mixed handedness’ show a greater tendency toward magical thinking (e.g., paranormal belief), a higher likelihood of experiencing déjà vu, and a greater benefit from placebo treatments. These personality traits could be manifestations of ‘hyperconnectivity’ in the mixed handed brain.

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Self-Assessment as Imaginative

The fact that sensitives (both men and women) rate themselves significantly higher on imagination makes perfect sense if we remember that sensitivity is likely associated with being thin boundary, fantasy-prone, inclined to absorption, and highly transliminal. These perceptual/Personality styles should indeed equate to viewing the world (not to mention oneself) quite differently. Imaginative? Creative? Artistic? You bet.

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Self-Assessment as Introverted

The survey item on self-assessment of temperament (introversion/extroversion) yielded an interesting gender difference. Sensitivity is evidently associated with the self-perception of introversion – but only for women. Men, especially among controls, apparently consider themselves introverted or restrained as a matter of course. This discrepancy, one could venture, has at least as much to do with learned style as innate biology.

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In the United States, 12 percent of the population suffers from migraine. Women are three times as likely as men to be affected, though the disparity is not life long: it holds between the onset of puberty and the occurrence of menopause. Current thinking is that individual sufferers have a more sensitive nervous system than most. Factors that can bring on a headache include stress, noise, glare, certain odors or foods, and even weather conditions (changing temperature, humidity, barometric pressure, winds).

Individuals prone to migraine may also be extra sensitive to their own, internal ‘landscape’ of feeling. There is reason to believe that the dynamics of migraine effectively parallel those of emotion. Oliver Sacks, the renowned neurologist, asserts that migraine is “conspicuously a psychophysiological event...an oblique expression of feelings which are denied direct or adequate expression.” When a person is caught unawares by powerful feelings, and has no suitable way to acknowledge and/or discharge the inner agitation, a migraine may result.

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Role of Recollected Trauma

An especially noteworthy distinction between sensitives and controls relates to the recall of a traumatic event in childhood. To explain this, we might note that sensitives are also more apt to identify an immediate family member who suffered from alcoholism or depression/mood imbalance. If we assume that parents who are in the grip of these conditions are likelier to mistreat their children – or go into funks that precipitate a family crisis – then it only makes sense that these children should recollect traumatic experiences.

An alternate explanation draws from the understanding that some individuals are, from infancy, more excitable, more reactive, and more easily stressed than other people. As children, wouldn’t they be more likely to be adversely affected by events that, to less sensitive children, might not seem so ‘traumatic’? In other words, innate environmental sensitivities could be the driver of adult personality – rather than, as many researchers would have it, the other way around.

Near-death researcher Kenneth Ring holds a similar view. His survey respondents volunteered a greater incidence of childhood abuse, trauma, and illness than controls. On psychological profiles, they manifested greater dissociative tendencies. Ring’s opinion is that these individuals are “sensitives with low stress thresholds” who, through “their difficult and in some cases even tormented childhoods…have come to develop an extended range of human perception.”

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Perceived Electrical Sensitivity

One of the survey’s most interesting results is the extent to which persons who consider themselves sensitive claim that their very presence affects lights, computers, and other electrical appliances in an unusual way. This could, of course, be viewed as a manifestation of certain people’s tendency to apply highly improbable explanations to fairly typical events. Personality characteristics presumed to play a role include fantasy proneness, absorption, suggestibility, and transliminality.

However, as an unusually high percentage of the ‘sensitive’ survey respondents indicated that they’d been struck by lightning or otherwise suffered a severe electrical shock (a memorable and potentially verifiable event), electrical sensitivity could represent a bona fide aspect of sensitivity.

In the 1980s, British researcher Michael Shallis surveyed hundreds of people – the vast majority of them women – who’d claimed to be electrically sensitive. Certain associations jumped out: with allergy; (70% of Shallis’ sample); susceptibility to loud sounds and bright lights (70% again); a claim to have been struck by lightning (23%); to be affected by advancing thunderstorms (60%); and to have had a psychic experience (69%).

Shallis himself deduced a connection between strong feelings, electrical sensitivity, and reported anomalies. He acknowledges that we don’t know what we don’t know, remarking that electromagnetism -- "the physical force most apparent to us at the level at which we perceive the material world" – may be the vehicle for life forces that, at present, we simply do not comprehend.

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Synesthesia is the blending of senses that, in most people, are separate and distinct. While non-synesthetes may say metaphorically, "This wine tastes wonderfully dry" or "I sure feel blue today," the synesthete actually experiences such perceptions. For him/her, a taste can be round or pointy, a word can taste like potatoes, the sound of a violin can be felt on the face, a letter or number or even a smell can have its own vivid and recurring color.

What also makes synesthesia remarkable is its automatic and vivid nature. Synesthetes regard their co-mingled perceptions as real as anyone else’s; they are not merely imagined in the mind’s eye. Neuroimaging data bear this out. Nearly all synesthetes have experienced their impressions from an early age – and presumed that their families and friends did, too. Indeed, the phenomenon is known to run in families, suggesting that it is inherited.

The condition also has an oft-noted relationship with hypersensitivity. One synesthete puts it this way: “I tend to get overloaded quickly: like there's just too much sensory perception coming in at one time, and I have a hard time sorting it out and coping with it...Shopping can do it. Being in a store where there's a lot of noise, colors, smells - it's just too much.”

There’s also a tantalizing link with anomalous perception – first brought to light by researcher Richard Cytowic – and borne out by results of the Environmental Sensitivity Survey. (PDF, 10pp, 240KB)

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