The brain is the body’s command centre, the headquarters in our head. Scary when you consider how small it seems, weighing roughly 1.3 kilograms, compact enough to perch in a cupped palm. Yet the key word here is compact. While the organ may resemble a small parboiled cabbage, there is a lot to see if you know where to look.

Take the outer layer encasing the cabbage’s bulk. This is the cortex, Latin for ‘bark’, the actual grey matter we use as colloquial shorthand for the brain itself. The cortex is responsible for all manner of vital functions, from memory to attention, from language to awareness: the core skills a puzzle demands. It’s no thicker than leather, only 2.5 millimetres deep on average, but critically, unlike leather, the cortex is convoluted: a crinkled mass of ridges (gyri) and furrows (sulci), plus the deeper indents known as fissures. Together, these corrugations allow humans to out-think any other species. Courtesy of crinkling, we can even keep a few moves ahead of chimpanzees, whose brains, while superficially humanoid, contain fewer convolutions, meaning three-quarters less surface area should the cabbage ever be pulled taut.

Size, of course, isn’t everything. This is especially true for intelligence, when trying to gauge a creature’s smarts by virtue of their brain’s weight and mass. A sperm whale’s brain, say, is six times heavier than ours. This is impressive, sure, but the more meaningful metric is the body-to-brain-mass ratio, and here Moby Dick fares poorly. Dolphins and humans, on the other hand, have much denser cortices.

Furthermore, this density is twofold, the cortex encased by a left and a right hemisphere. To the naked eye the hemispheres seem identical, and yet each of us has a degree of lateral dominance, a workload bias across the divide. Nine in ten right-handers, for example, have their speech centres located in the left hemisphere, and the remaining one in ten in the right. By contrast, 65 per cent of left-handers have speech centres in the left, a further 20 per cent are located in the right, and the remainder claim bilateral speech centres. That’s just a single snapshot of our inner complexity, and each brain is unique, with its own maze of pathways and hubs. But for now, let’s continue with our tour.

The cortex is sealed together by a fibrous band called the corpus callosum, or ‘tough body’. Just as sticky-tape adheres to giftwrap, this C-shaped strip runs from nose to nape, both fastener and neural thoroughfare between the hemispheres.

Digging deeper, we enter the inmost lobes, the four segments making up the cerebrum, the brain’s upper bulk, where each precinct has its own set of roles to play.

If one lobe is the boss, then the frontal lobe is your forerunner. Occupying the skull’s anterior arc, that curve above your brow, this segment governs many of the body’s voluntary movements. This includes walking and also where to walk, as the prefrontal cortex is tied up with decision-making as well as problem-solving. Mood and speech are also traced here, making this segment a cornerstone of who we are.

When comparing the evolution of species over millennia, humans have enjoyed the greatest expansion in this brain segment. Since antiquity, the feline brain’s frontal lobe has only expanded by 3 per cent, against a massive 29 per cent in our own species. Homo sapiens, it could be said, climbed to the top of the zoological pile thanks to that development.

Below the prefrontal cortex is the temporal lobe, named for the skull’s two temples that defend the area. Language dwells here, in tandem with the senses, notably hearing. New memories are captured here too. Time and deeper processing may etch these so-called working memories into established data, whether that’s declarative (recalling a name, a fact) or procedural (like riding a bike). More on both later, in the chapter ‘Memory’—for now, let’s keep the tour rolling.

Climbing back into the upper reaches, at the rear of the skull you’ll find the parietal lobe. The word stems from ‘paries’ in Latin, or ‘wall’. As you’re reading this sentence, the parietal is in full swing, as focus mainly dwells here. Numbers and logic swim nearby too, along with language, a crossover from the temporal, in league with sorting sensory input from touch to taste. Pain is registered here as well. And when gurus advocate mindfulness—see the chapter ‘Focus’—the parietal is the one lobe we most heavily draw upon.

Last lobe but not least is the occipital. Despite sitting furthest from your eyes, lining the posterior bulge above your nape, this brain section supervises sight. The same lobe also handles spatial duties, the kind you’ll need for the upcoming matchstick puzzles. In keeping with space and sight, the occipital—Latin for ‘the back of the head’—is also vital in recognising shapes and colours, making this bundle of neurons the skull’s fashionista of the foursome.

However, neat as any cranial diagram strives to be, the brain can adjust and reinvent itself. This is the concept of neuroplasticity, theorised in the last fifty years. Should damage occur to one lobe, another lobe might well compensate over time, forging new circuitry to bypass the deficit. Likewise, to say that memory, for one, resides in a single lobe is to ignore the constellation effect at large in the brain, where recall is steeped throughout the network. Aside from the survival basics located in the hindbrain alone—the reptilian pith in charge of breathing and heartrate, wakefulness and sleep—there is no fixity within the infinity.

So there you have it, the basic itinerary. I’ve neglected several key regions—notably the hippocampus and so-called subcortical level, including the basal ganglia and thalamus (the system’s sensory router, which we’ll meet at various points in the chapters to come). Nevertheless, I hope you have a better understanding of your attic’s layout now—a grey-blueprint of your brain—before we explore the same organ under pressure, seeing how your cabbage copes (and flourishes) with the input of puzzles.

Neural pathways

Q: What’s the difference between brain and mind?

Not a riddle, but a genuine question. Often we use the two words interchangeably, but they are in fact distinct: the brain is the physical organ, while the mind is its mental dimension, what we do with our skull’s contents. American novelist Jeffrey Eugenides believes, ‘Biology gives you a brain. Life turns it into a mind.’

Or, if you like, the brain is the hardware to the mind’s software. Memory, insight and every other function comprise the programs, so to speak—specific tasks performed by the cerebrum. In the meantime, the components—the folds and fissures and corpus callosum—entail the organic hardware. You can’t have one without the other. Both are there to serve its ally, which is why the words are often swapped, except in the anatomy lab.

The reason I make this distinction is to help you think about thinking, the mechanics behind cognition. We peered deep inside our skulls a moment ago to reveal the city map inside our heads. But what about the traffic? How does a burnt finger send pain to the parietal lobe? How does a riddle, once heard, arrive in the temporal region, level with your eyebrow, then pass upwards to the problem-solving frontal lobe?

A vital component is axons, wisps of fibre running the length of cells, serving as chutes for the incoming signals. But the heroes are the neurons. You have some 100 billion of them in your cortex, and each carry their own relay equipment. To receive signals, every neuron owns a set of tiny branches radiating from either end, called the dendrites. Named after tree in Greek, the dendrites serve as receivers, awaiting any trace of the brain’s electrical flow.

In simple terms, this electricity is generated by a constant imbalance of ions. At rest, neurons have negatively charged innards. An incoming signal sparks the opening and closing of ion-channel floodgates, transiently flipping the internal charge to positive. This change in voltage is called the action potential, faithfully relaying the message.

Amazing, don’t you think? All these invisible transactions go on to not only solve a jigsaw, per se, but en masse they could also power a low-watt bulb. To further your amazement, every neuron is isolated by the tiniest gap, some 20 nanometres wide—a gap we call the synapse, making the neurons one vast archipelago.

Synapse, I should explain, derives from ‘synapsis’ in Greek, or ‘connection’. But how can a gap translate as a connection? How can neurons communicate if each cell is marooned by its own private moat?

The answer lies in neurotransmitters. An action-potential surge streaks from a neuron cell body to the outermost tips of its axon, stirring the neurotransmitters into life. Much like chemical couriers, the transmitters loiter at the end of the axons, working as messengers-for-hire across the extracellular fluid.

As the neuron emits electricity, the transmitters kick into action, including amino acids and peptides, or what I call the mule molecules. (Hmm, the mulecules?) As a thought flashes across the cerebrum, these proteins are recruited, and different chemicals react to different charges.

Multiply that action a million times, a billion times, and you have a picture of your brain at work. And at play. Let’s say I asked you to name Santa’s nine reindeers. Countless neurons would spark into action, the entire pathway a warp-speed alternation of neural signals, switching from electrical to chemical in nature, all in the name of retrieving trivia. I only hope you get the answer right.

The more we learn about the brain—the least trivial thing we own—the more questions we generate. In the grand scheme of things, neuroscience is a relative newcomer compared to other disciplines. In the Iron Age, around 500BC, humans believed the brain did nothing more than cool the blood. Now we know the brain to be a universe we’re only just beginning to map, an evolutionary marvel that guards its secrets closely. Study by study, however, we are gaining more clues, deciphering the wonder, learning how to use it more wisely. To renew it. To maximise it. And in that spirit lie the challenges at the core of each coming chapter, where we turn to puzzles to understand the inmost puzzle that is the brain.