The Shallows

My life, like the lives of most Baby Boomers and Generation Xers, has unfolded like a two-act play. It opened with Analogue Youth and then, after a quick but thorough shuffling of the props, it entered Digital Adulthood.

Virtually all of our neural circuits—whether they’re involved in feeling, seeing, hearing, moving, thinking, learning, perceiving, or remembering— are subject to change

The genius of our brain’s construction is not that it contains a lot of hardwiring but that it doesn’t. Natural selection, writes the philosopher David Buller in Adapting Minds, his critique of evolutionary psychology, “has not designed a brain that consists of numerous prefabricated adaptations” but rather one that is able “to adapt to local environmental demands throughout the lifetime of an individual, and sometimes within a period of days, by forming specialized structures to deal with those demands.”

Extensive, perpetual plasticity has been documented in healthy, normally functioning nervous systems, leading neuroscientists to conclude that our brains are always in flux, adapting to even small shifts in our circumstances and behavior. “We have learned that neuroplasticity is not only possible but that it is constantly in action,” writes Mark Hallett, head of the Medical Neurology Branch of the National Institutes of Health. “That is the way we adapt to changing conditions, the way we learn new facts, and the way we develop new skills.”26

As a result of such experiments, it’s now believed that the sensations of a “phantom limb” felt by amputees are largely the result of neuroplastic changes in the brain.

Neurons seem to ‘want’ to receive input,” explains Nancy Kanwisher of MIT’s McGovern Institute for Brain Research: “When their usual input disappears, they start responding to the next best thing.”

By monitoring slugs’ nervous systems, Kandel discovered that “this learned change in behavior was paralleled by a progressive weakening of the synaptic connections” between the sensory neurons that “feel” the touch and the motor neurons that tell the gill to retract. In a slug’s ordinary state, about ninety percent of the sensory neurons in its gill have connections to motor neurons. But after its gill is touched just forty times, only ten percent of the sensory cells maintain links to the motor cells. The research “showed dramatically,” Kandel wrote, that “synapses can undergo large and enduring changes in strength after only a relatively small amount of training.”

Today, scientists sum up the essential dynamic of neuroplasticity with a saying known as Hebb’s rule: “Cells that fire together wire together.”

Our neurons are always breaking old connections and forming new ones, and brand-new nerve cells are always being created. “The brain,” observes Olds, “has the ability to reprogram itself on the fly, altering the way it functions.”

Virtually all of our neural circuits—whether they’re involved in feeling, seeing, hearing, moving, thinking, learning, perceiving, or remembering— are subject to change. The received wisdom is cast aside