Life, Death & the Neuroscience of Your Unique Experience | Dr. David Linden

KEYPOINTS

• 01

  Krause corpuscles are finally confirmed as the nerve endings for sexual touch

  German anatomist Krause described these endings in the penis and clitoris in 1860. They also appear in the nipples, lips, cornea and joint linings, so their role was never clear. A preprint from David Ginty's lab at Harvard showed in mice that they're mechanical sensors. Switching them on with light-activated (optogenetic) tools caused erections, and switching them off reduced mounting and ejaculation in males and receptivity in females.

• 02

  Sexual sensation may vary between people and fade with age

  Linden speculates that individual differences in Krause corpuscle structure might help explain why people like different kinds of touch, and that their loss with age could parallel the known age-related loss of fine-touch endings (Merkel and Meissner) in fingertips. He notes that chronic masturbation is known to desensitize the penis, which is more likely a change in receptor function than in structure.

• 03

  Smell is where humans differ most, and it's highly suggestible

  We have about 400 functional odor receptors, and any two people differ in about 30% of them (work by Leslie Vosshall's group at Rockefeller). Androstenone smells like nothing, grass or urine depending on a single receptor gene. Linden calls humans the 'anti-pandas': we live everywhere and eat everything, so few smells are innately aversive (exceptions include the rotting-meat compounds cadaverine and putrescine), and most smell preferences are learned culturally.

• 04

  Perception is inference

  Linden's broader theme is that no sense delivers an objective world. Smell, taste, sight, balance and fullness are all shaped by experience, expectation and context, which makes it 'almost a miracle' that we agree on a shared reality at all.

• 05

  Early-life experience can set traits that look genetic

  Children who spend little time outdoors in their first five years or so are more likely to become nearsighted, because light appears to drive growth factors that control how much the eyeball elongates. Linden calls this 'news you can use': get kids outside. Heat tolerance is another example (see below).

• 06

  Most traits are partly heritable, and heritability depends on circumstances

  Wet versus dry earwax (the ABCC11 gene) is 100% heritable, while accent is 0% heritable and comes mainly from peers. Height is about 85% heritable in the US but only about 50% in rural Bolivia or India, where poor nutrition and disease keep people from reaching their genetic potential. IQ shows the same pattern: roughly 60–70% heritable in affluent settings and lower where schooling and care are poor. 'Genes don't code for traits, they code for proteins.'

• 07

  Family environment explains surprisingly little of personality

  In the Minnesota Study of Twins Reared Apart, the 'Big Five' personality traits were about 50% heritable, but family upbringing contributed almost nothing to the rest. Linden attributes much of the remainder to the random nature of development: the genome isn't a wiring diagram for trillions of connections. Parents still shape values, religion and career choices.

• 08

  Inheriting trauma through DNA marks across generations isn't proven in mammals

  It has been shown convincingly in worms and plants. The human evidence comes largely from famine records in Överkalix, Sweden, which Linden criticizes for having no known mechanism and for running many comparisons without correction (hypothesizing after the results are known). 'You may well inherit your grandma's trauma, but probably socially.' Effects within a single pregnancy are better established.

• 09

  Inflammation and depression are linked, but simple fixes haven't worked

  About a third of people with depression benefit significantly from SSRIs, a third slightly and a third not at all. An inflammatory cytokine once used to treat hepatitis C made nearly everyone depressed, and multiple sclerosis (with high IL-6) carries far more depression than spinal cord injury does. Yet giving anti-inflammatory drugs to depressed people in general hasn't helped. There are hints they may help SSRI non-responders, but the evidence is 'right on the edge'.

• 10

  Mind-to-body effects need clear biological pathways

  Nerves that grow into melanomas release CGRP, which suppresses the immune cells attacking the tumor and worsens prognosis. Linden floats, and labels as without evidence, the hypothesis that meditation could slow such tumors through a defined neural pathway. He argues researchers should take mind-body claims back from 'nonsense' by testing them rigorously. Breathing rhythms show up throughout the brain, which makes effects of breathwork plausible.

• 11

  The cerebellum predicts the next second or two

  The cerebellum is known for motor coordination; damage causes clumsiness and overshooting, not paralysis. Through connections to the thalamus and frontal cortex, its predictive computation also supports social judgments, such as whether someone is a friend or a threat, and other non-motor tasks.