How much of our brain do we really need?

Some time ago, I read a fascinating book called “The Brain” by David Eagleman. If there is one clear message from the book, it is that the brain exhibits remarkable plasticity. People talk of the brain as hard-wired, but it is the opposite of that. Eagleman describes some remarkable cases of people recovering from injury or operation and concludes: “The brain is fundamentally unlike the hardware in our digital computers. Instead, it’s ‘liveware’.”

He tells the remarkable story of a young girl called Cameron Mott who suffered so seriously from violent seizures, as a result of a rare form of epilepsy that would eventually lead to her death, that a team of neurosurgeons removed an entire half of her brain and, except for some weakness on one side of her body, she encountered no problems because the remaining half of her brain dynamically rewired to take over the missing functions. 

In this week’s “New Scientist” magazine, there is a piece about a teenager – known simply as C1 – who was born without the entire left hemisphere of her brain. The woman has been diagnosed with semi-hydranencephaly, an extreme;y rare condition in which a large part of the brain’s cortex is missing. C1 is now 18 years old and the right side of her brain has taken on some of the functions of the missing left side. Today she has average-to-high IQ and above-average readings skills. Indeed she plans to go university.

So, what exactly is the brain? Eagleman explains that an adult brain weighs three pounds (1.4 kilograms) and has the same number of cells as a child’s brain (in fact, a child of two has double the number of synapses of an adult prior to a process of neural “pruning”). We know that the typical brain has about 86 billion neurons and each neuron makes about 10,000 connections sending tens or hundreds of electrical pulses to thousands of other neurons every second. 

But we are only just beginning to understand how the brain works and why sometimes it does not (such as the growing problem of dementia).


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