From adolescence onwards we all begin to lose brain cells. As a consequence our brains gradually and inexorably shrink (compare the “old” brain on the left to the “young” brain on the right). In fact by the age of 80 your brain will occupy 15% less of the space within your skull than in the prime of life. Yet over the course of adulthood, as our brains are losing more and more cells, our knowledge and repertoire of skills nonetheless continues to grow as we accumulate more and more experience. How is this possible? Well, despite the incremental decrease in quantity of brain cells over the years connections between neuronal networks that are in regular and intensive communication with each other are selectively reinforced. This enables increased efficiency in execution of the mental processes that those networks support. Hence we can do more with less as we age. Sadly, for all of us, there will always come a time when the degree of brain cell loss is such that mental function begins to decline. In other words, if we all could live forever, dementia will inevitably strike at some point in time.
Although we cannot halt the process of grey matter loss completely, the good news is that we can slow down its progression. This month a study conducted at the University of Pittsburgh and published in the journal “Neurology” describes the influence of regular exercise on the rate of reduction of brain volume and cognitive function in 299 elderly individuals.
It was observed that those individuals of this group of average age 78 who walked in excess of 6 miles per week had a significantly reduced rate of grey matter loss and consequently a lesser degree of cognitive decline. The greater the distance walked each week, the smaller the reduction in volume over a 9 year period within their frontal lobe, occipital lobe, entorhinal cortex and critically, in the hippocampus. My post last month described the vital role that the hippocampus plays in the creation and recall of long term memories.
This begs the question – how and why does exercise slow down the rate at which grey matter shrinks? An exciting possibility is that all that walking might actually increase the rate at which new brain cells are created; a process known as neurogenesis. This boost in the creation of new brain cells might help to compensate for the loss of old brain cells. Evidence to support this hypothesis comes from research conducted over a decade ago suggesting, in the mouse brain at least, that exercise does indeed increase the rate of neurogenesis.
Exactly why this happens is unclear, but I would propose that, given the hippocampus is heavily involved in navigation, particularly when it comes to flexibility in finding the best route from A to B, it would make sense for physical activity to trigger production of new cells in this brain area. A greater number of hippocampal neurons would presumably support a greater capacity to memorise routes and landmarks encountered whilst exploring the environment. This could feasibly convey a critical survival advantage by helping to prevent people from getting lost. Over the thousands of years of our species evolultion, getting lost was probably an excellent way of deleting oneself from the gene pool and so those with movement-triggered hippocampal neurogenesis may have been more likely to survive.
This seems a plausible (but by no means concrete) account of why older individuals who take regular exercise appear to have more grey matter and superior cognitive function than those who do not. Whatever the true explanation, it seems clear if you want to hang onto your marbles in the long term then it’s probably a good idea to take a regular stroll for the rest of your life.
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Dr Jack Lewis feels that all the scary terminology in brain anatomy does not have to seem intimidating:
A pair of cartoon rodents give a quick guided tour to the different parts of the human brain.
It’s a shame they don’t really mention the role of each area they name.
I guess that would have made making the lyrics rhyme even more complicated!
I have endeavoured to give a quick overview of which bit does what in the order that they are covered in the cartoon:
1) Neocortex – the whole large sheet of brain cells on the brain’s outer surface, folded up into the skull giving it the appearance of a walnut.
2) Frontal lobe – the region of the neocortex at the front of the brain, behind the forehead, which is much larger in humans than our monkey cousins and enables us to do all those complex functions that other primates cannot.
3) Brainstem – the part of the brain that ninja assasins aim for with their deadly chop where neck meets skull, it is involved in coordinating all the vital bodily functions that keep us alive e.g. breathing and heart rates.
4) Hippocampus – key brain area at the core of the temporal lobes (which run horizontally down the sides of the head from the temple to behind the ears) which is heavily involved in not just creating, but also retrieving memories. It also creates new brain cells in response to exercise!
5) Neural node – erm, I think they just needed something sciency sounding to rhyme with the other lines. The image THE BRAIN enlarges with the magnifying glass is a single brain cell complete with nucleus (which contains all the DNA) at it’s centre, the dendrites (receiving information from other brain cells) plus a single axon (along which electrical messages are sent to other brain cells).
6) Right hemisphere – the left and right sides of the neocortex are separated by a fluid filled gap yet are connected by a massive bundle of neuronal connections called the corpus callosum that bridge the gap enabling left and right sides to send and receive information between them.
7) Pons – All of the commands travelling from parts of the neocortex involved in motor control (i.e. body movements) pass through the pons which sits on top of the brainstem which is at the very top of the spinal cord through which the brain controls all the muscles of the body.
8) Cortex visual, usually referred to as the visual cortex, sits right at the back of the brain. So the eyes quite literally detect light striking the retina, at the back of the eyeball, and send this information all the way to the back of the brain before we can see anything!
9) Pineal, usually referred to as the pineal gland, is about the size of a grain of rice and produces melatonin which regulates the sleep/wake cycle. Daylight in the morning switches off melatonin production to make us feel awake, switching production back on in the evening so we can sleep.
10) Cerebellum left and right, critical for balance and co-ordinated muscle contractions important for effective speech, walking, running, swimming and all sporting activities etc.
11) Synapse – the gap between one neuron and the next. Electrical signals arriving at the end of one neuron releases tiny packets of brain chemicals that travel across the synapse, bind with special receptors on the other neuron to trigger or inhibit electrical signals its own electrical messages.
12) Hypothalamus – the most important site of hormone production and release that powerfully regulates innumerable body and brain functions.
13) Striate, a. k. a. striatum – enormously important subcortical brain area (deep in the brain not on the surface of the neocortex) involved in reward and motivation, planning and modulation of movements, named thus due to its stripy appearance.
14) Axon fibres – as mentioned before this is the part of the brain cell that sends electrical messages to other brain cells.
15) Matter grey, usually know as the famous Grey Matter. This is darker than the white matter as this is where all the synapses and cell bodies are. So it is in the grey matter that all the computational power of the brain is unleashed.
16) Central tegmental pathway: the tegmentum is a part of the midbrain – which lies between the striatum and the brain stem. Activation of the ventral tegmental area, i.e. the “belly” of the tegmentum, causes the feelings of intense pleasure when people eat, drink, have sex or take drugs.
17) Temporal lobe – the upper surface of the temporal lobes is the part of the brain we hear with.
18) White core matter, usually referred to as White Matter, consists of millions and millions of axonal fibres that ferrying electrical signals from one brain area to the next.
19) Forebrain – we’ve done that already
20) Skull – the bone in which our brain is cradled
21) Central fissure – the name for the fluid filled gap described earlier which separates the left and right hemispheres
22) Cord spinal, usually known as the spinal cord, through which axons pass sending messages from brain to body and body to brain.
23) Parietal – one of the lobes of the neocortex – involved in spatial awareness, focusing attention and mathematical calculations.
24) Pia mater – is the innermost of the three brain sacks (or meninges) which cushion and protect the brain.
25) Meningeal vein – blood vessels taking waste materials away from the outer parts of the neocortex.
26) Medulla oblongata – lower part of the brain stem, also involved in triggering reflexes like vomiting, sneezing, coughing etc.
27) Lobe limbic – usually known as limbic system, deep inside brain beneath the temporal lobes, involved in generating emotions.
28) Microelectrodes – there is not a microelectrode in sight so just ignore that lyric!
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