There’s more than one way to carve up a human brain. We could draw lines based on what we see with the naked eye: your brain has two hemispheres, left and right. Or we could peer more deeply with a powerful microscope or sophisticated brain-imaging tools: your brain is a network of nearly 200 billion interconnected brain cells. About two-thirds of them, called neurons, continually talk to each other via electrical and chemical signals throughout the network. The other third, called glial cells, have multiple functions that scientists are still learning about.
We could examine a brain structurally. Neurons can be organised in layers, like in the cerebral cortex, which is traditionally divided into different lobes — frontal (at the front), occipital (at the back), temporal (roughly over your ears), and parietal (the rest).
Neurons can also be organised into clumps, which scientists call nuclei, that sit beneath the cerebral cortex; for example, you might recognise the name ‘amygdala’, which is actually a cluster of 13 nuclei deep within each temporal lobe of your brain. We can also carve a brain up by looking at genetic material inside the brain cells, which reveals something about how your brain evolved and how it was assembled when you were a developing embryo.
Another popular way to slice and dice the brain is by function. An obvious approach is to search for the bits of the brain that allow you to think thoughts, feel emotions, see and read these words, hear music, move your arms and legs, and do all the other things that make you who you are.
Thousands of studies reveal that this approach has not worked well, because these sorts of functional designations — such as cognition, emotion, perception, action, and so on — do not represent firm boundaries in the brain. The left side of your brain is not the source of logic, and the right side is not the wellspring of creativity. Rationality does not live in your cerebral cortex, and emotions are not lurking in an ancient beast within the subcortical parts of your brain.
At this point, it’s fairly safe to say that no psychological function lives in a single part of your brain. Most of your neurons do more than one thing, psychologically speaking. For example, the parts of your brain most associated with your ability to see, known as the visual cortex (in your occipital lobe), also carry information about hearing and touch. Likewise, some neurons outside of your visual cortex help you to see. Thoughts, emotions, perceptions, imagination, dreams and the rest are better viewed as whole-brain events.
Still, it’s possible to carve up a brain by function, but in a different way, based on the information that neurons send and receive. For example, a part of your frontal lobe called the anterior insula routinely plays a role in making your emotions, deciding between options, paying attention to certain things and ignoring others, being aware of yourself, and a host of other mental events.
Whatever these neurons are doing, they are always integrating sight, sound, smell, touch, taste, and all the sensations from inside your body, into multisensory summaries that allow your brain to regulate the systems of your body to keep you alive and well.
No matter which way you carve up a brain, it’s important to realise that none of these organisations is ‘true’ in any absolute way. Each organisation is better or worse, depending on the goal you have in mind and what you want to explain. And no organisation alone tells the full story of how your brain, in constant conversation with your body and the world around you, creates your mind.
- This article first appeared in issue 371 of BBC Science Focus Magazine – find out how to subscribe here
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