A Cerebral Cortex Makes Animals Programmable
As we ascend the scale of cerebral development the possibility of teaching increases. It becomes possible to domesticate and train these higher-brain animals in just the measure that their brains are developed. You can teach very little to a fish or a reptile, but directly you come to the higher cerebral mammals you are confronted by the new possibility of establishing an artificial, taught, motive system to control, supplement or altogether replace natural instinct. You must catch them young...
notes Sexual Selection in Penises and Clitori
In species that do not use copulatory thrusting, especially
insects, penises evolve more obvious tactile stimulators: nubs, spikes, ridges, curls, barbs, hooks, and flagella. Male insects often try to push each other off during copulation, so copulatory thrusting would risk disengagement. Better to lock the genitals together and have internal flagella to excite the female. With primates, it is not so common for male rivals to swarm over females knocking each other off. This allows couples a ... notesFemale sexual preferences may have guided the evolution of these sexual organs.
NgR1 Improves Brain Plasticity in Adult Mice
Experience rearranges anatomical connectivity in the brain, but such plasticity is suppressed in adulthood. We examined the turnover of dendritic spines and axonal varicosities in the somatosensory cortex of mice lacking Nogo Receptor 1 (NgR1). Through adolescence, the anatomy and plasticity of ngr1 null mice are indistinguishable from control, but suppression of turnover after age 26 days fails to occur in ngr1?/? mice. Adolescent anatomical plasticity can be restored to 1-year-old mice by c...
1 The plasticity lost from our youth is revived in mice by deletion of Nogo-A ligand.
Sound Localization
One trick our brains use to figure out the location of a sound is to compare the time it takes to reach each ear. For example, sound waves emanating from a wind chime located to your right will reach your right ear a few milliseconds earlier than they reach your left ear, and the brain uses this small timing difference to compute exactly how far to your right the chime is located. Researchers have capitalized on this timing difference to test sound localization, using a special experimental t... notesHow the brain localizes the origin of a sound by calculating the difference in time between the soundwaves hitting one ear versus the other.
Hyperacuity and Obligatory Looking
Beginning about four months of age, the perception of detail takes another leap forward with the emergence of hyperacuity: the ability to discriminate features that are up to ten times finer than the size of the photoreceptors should theoretically permit. It is this ultrafine discrimination that allows us, for instance, to see a very slight glitch in an otherwise straight line. even though the size of the glitch is below our eyes' limit of resolution. It is not yet known how our brains perfor... notesTwo visual phenomena in the developing infant. One is the ability to make out visual details for which the eye does not appear physically capable of registering and the other is a conflict between the visual cortex and the brain stem that gets the baby stuck staring at something.
The Importance of Tactile Experience in Infants
Nonetheless, our early touch experiences determine the extent of possible tactile sensitivity. They also play a surprisingly potent role in the overall quality of brain development. We have already seen in Chapter 2 how rats raised in a highly enriched environment develop a thicker cerebral cortex and are actually cleverer than rats raised in a standard laboratory environment. A good share of this enriching experience involves tactile sensation. When young rats are provided with new toys, the...
1 Rats provided with a variety of constantly changed toys to play with and those touched by their mothers have larger brains and are more cognitively prepared for the world.
Mother's Hormones Impact a Child's Propensity for Shyness
As we learn more about maternal hormones and their influence on the developing brain, scientists are beginning to propose actual biological mechanisms for the kind of folk prophecies that have been around for ages. One recent study, for instance, suggests that a child's shyness is determined, in part, by maternal hormone fluctuations during gestation. Researchers who interviewed several thousand preschoolers in both the United States and New Zealand noted a significant relationship between th... notesThere appears to be a correlation between the amount of sunlight to which a mother is exposed mid-pregnancy and how shy her children are later on.
How Brains Grow Into Bodies
Brain wiring begins with the outgrowth of axons. Once a newborn neuron has migrated, planting its cell body in a permanent position, it sends out a fine axon shoot with an enlarged tip known as a growth cone. At the end of the growth cone are about a dozen long tentacles that shoot out in all directions and act like radar, picking up all manner of navigational signals. They feel out the best-textured surfaces, sniff around for chemical cues, and even use tiny electrical fields to help the axo...Best description yet of the synaptic "pruning" human brains go through as the brain wires up to the body and best reason yet for why children should have rich, mentally-nourishing environments in which to grow so that their synapses don't get unnecessarily pruned, resulting in smaller brains.
Ontogeny Recapitulates Phylogeny
The similarity between different vertebrate embryos is indeed remarkable. Since the early 1800s, embryologists have been struck by the parallel between early development in various animal species and their evolutionary relationship, a resemblance conveniently abbreviated by the saying "ontogeny recapitulates phylogeny." Of course, each of us does not really pass through a "lizard" stage on our way to a fully developed human form. But it is true that animals who are more closely related in ter...Living things go through the forms of their ancestors, not specifically but generally, because it is easier for evolution to add a mutation to the end of a complex sequence of developments than to re-engineer earlier in the process.
