The brain is plastic, and the internet is molding it

For most of the twentieth century, neuroscientists assumed the adult brain was essentially fixed — wired in childhood, then set. Carr opens by dismantling this. Research on neuroplasticity shows the brain continues rewiring itself throughout life, physically strengthening the circuits it uses and pruning the ones it doesn't, in response to whatever activities occupy it.

This is not a metaphor. London cab drivers who memorize the city's tangled streets show measurably enlarged hippocampal regions. Musicians who practice for years show expanded areas devoted to finger dexterity and sound processing.

Carr's leap, and the book's foundation, is that this same mechanism applies to how we read and think online. If practicing an instrument reshapes the brain, then practicing hours of skimming, clicking, and switching between tabs reshapes it too — just toward different capacities. You are not using the internet unchanged. It is quietly rewriting you.