Free The Pleasure Instinct: Why We Crave Adventure, Chocolate, Pheromones, and Music by Gene Wallenstein

characteristics that would have seemed familiar to Izidor. In his autobiography Abandoned for Life , he describes the morning-to-evening routine at the Sighetu Marmatiei orphanage: “Most of the time, the children did the same old thing; rock back and forth, sleep or hurt themselves. If they continued hurting themselves, the house nannies either gave the children more medication or put them into straight jackets.” With a ratio of one nanny for every 75 children during the day and one for every 150 children during the evening, there was not much time for the kinds of tactile stimulation—simple, loving touch—that are known to be so crucial for normal psychological and physical development. It is only in the past twenty years or so that scientists have begun to show that pleasurable touch during the early period of life is crucial for normal brain development and why its deprivation can produce autistic-like behaviors.
     
     
    Touch is often called the “mother of the senses” because it is believed to have been the first sensory ability to have evolved—the sense upon which all others have been based. Well before the appearance of primates and even before mammals, touch existed in the earliest unicellular organisms, such as the predecessors of the modern coliform bacteria E. coli . This phylogenetic observation has not been lost on developmental biologists, who point out that the skin is the first organ to develop embryologically in complex, multicellular organisms, and it is their first portal of communication. Touch, the sensation that is most intimately associated with the skin, is the earliest sense to develop in all species of mammals, birds, and fish. Before a primate embryo is even an inch long from head to rump—long before it has eyes and ears—it will respond to gentle stroking of its lips and outer nose by extending its trunk away from the source of stimulation.
    In the human embryo, tactile reactivity begins at about six weeks of gestation. As with all primates, a human embryo first responds to touch around its lips and nose, and gradually, with further development, begins to sense touch on other parts of its body. By nine weeks of gestation it will respond to touch of its fingers and hands, and by twelve weeks it will curl its toes if the soles of its feet are stroked. This well-known head-to-toe progression occurs in all primates and results from two important forces involving brain development.
    First, lower brain-stem regions develop and begin to function well before neocortical areas of the brain come online.This growth process limits the sensory and behavioral capabilities of the newborn to those supported by the brain regions that are developed and connected enough to show some degree of functionality. The reflexive turn of the embryo at six weeks of gestation is controlled predominantly by brain-stem circuits without any of the information being passed on to “higher” neocortical sites. In other words, the embryo will react when its mouth or nose is stroked at six weeks of gestation, but it will have no conscious perception of the experience. For touch to be perceived, the embryo will have to wait an additional six weeks for those higher sites to develop and begin to exhibit even the most basic physiological functions.
    The second constraint that influences the head-to-toe development of touch sensation is found in the way bodily sensations are mapped in the brain and how this organization changes with experience. Anyone who has taken an introductory psychology course has seen the grotesquely shaped homunculus with its exaggerated lips, nose, hands, and genitalia. The relative size of each body part is drawn to be proportional in size to the amount of cortex devoted to processing information from that area. The point is, not all portions of the body have equal representation in the brain—it is not a democracy. To understand how brain maps of the sensory world develop and how this process