Brains are different like bikes are different.

The dominant analogy for the brain has tracked the leading technology of the day.

The human brain was like a clockwork, then a hydraulic system, then an electronic circuit, then a digital computer, then a computer network, – until the present day, when, according to Stephen Kosslyn & Wayne Miller, writing in the Wall Street Journal, the brain is like a bicycle:

Our brains are not engaged in some sort of constant cerebral tug of war, with one part seeking dominance over another. (What a poor evolutionary strategy that would have been!) Rather, they can be likened roughly to the parts of a bicycle: the frame, seat, wheels, handlebars, pedals, gears, brakes and chain that work together to provide transportation.

The distinguished scientist and journalist continue:

Although the ... parts of the brain are always used during all of our waking lives, people do not rely on them to an equal degree. To extend the bicycle analogy, not everyone rides a bike the same way. Some may meander, others may race.

To be sure, Kosslyn &  Miller are right: Brains are like bikes.

But Kosslyn &  Miller are wrong, in that brains are not different like bikers are different; brains are different like bikes are different.

The apt bike analogy for inter-individual differences in brain function is not inter-individual differences in how people ride bikes, but rather inter-individual differences in bikes. Road bikes, mountain bikes, cyclocross bikes, touring bikes, BMX bikes, commuters, recumbents, etc. – bikes are different.

Brains are like bikes, and brains are different from one another like bikes are different from one another – not like how cyclists ride differently from one another, okay?

Because otherwise, you're just putting Descartes in the saddle.