When I returned to Sports Science following my accident my body was weak and uncoordinated and it felt like I was injected with lead. I needed a lot of motivation just to get through the day.
During my Postdoc research I thus set out to study the brain areas responsible for moving the body.
Turns out that this is not very clear at all.
Part of the problem is that researchers have traditionally focused their efforts on only one side of the movement coin. Either on the sensory-motor side or on the internal drivers of movement, but hardly ever on the two together.
A simple way to relate to how the brain moves the body is studying eating behavior. A simple scientific experiment involving a single celled organisms like a protozoan can be used to study sensory motor processes. Chances are you remember from high school biology how a protozoan literally ‘swarms’ around a food particle to engulf it within a vacuole inside itself. On the other hand, if an acid droplet is added to the medium the protozoan moves sharply away from it.
A step up in complexity in sensory motor experiments is using the lamprey eel that has a primitive brain and a spinal cord, which can be studied in minute detail during eating behaviour.
A further jump in complexity would be measuring a single brain cell in a primate during the reaching out, gripping and drinking of a juice reward after being prompted by a flashing light.
Conversely scientist can choose to study a simple stimulus in a very complex organism, like the effect of a finger prick on the human brain.
The above are examples of stimulus-response type experiments that examines the sensory motor system in response to an outside stimulus.
Turning now to the other side of the movement equation, the internal drivers, it goes without saying that the hungrier the primate the more vigorous would be its movement. And herein lies the problem – in order to measure the brain activity associated with hunger, or any other internal drive for that matter, the head of the lab animal, or human participant, would have to be fixed firmly in place.
It’s not easy to move vigorously when your head is fixed firmly in place.
The question I kept asking myself was how does the brain move the body if there is only an 'internal drive', without any direct outside stimuli, to set off the movement?
The locomotor system in the lamprey eel, a primitive vertebrate, helps us to better understand motivated movement. Turns out that all vertebrates from fish to amphibians thru to reptiles, mammals, primates and humans have remarkably similar locomotor circuitries in the brain, so we can learn a lot from the primitive motivated behaviour of the lamprey eel following the sensing of food in the water.
In this regard, the sense of smell is of extreme importance to the majority of vertebrates. Think of a shark moving reflexively towards blood in the water or a lion picking up the scent of an antelope.
Only advanced mammals are able to override the powerful effect that smell has on all motivated behaviours.
How complex must the brain be to override the powerful effects of smell? New world monkeys classified as ‘platyrrhines’ (flat noses) are still at the mercy of airborne chemicals. A flat nose means the monkeys have nostrils pointing directly forward to best pick up airborne chemicals.
Only ‘catarrhines’ (down noses) like orang-utans, gorillas, chimps and humans have prefrontal cortices (PFC - brain tissue just above and behind the eyes) developed enough to be able to override the potent effect the olfactory cortex has on movement.
A sizable olfactory cortex has massive survival potential given that it receives signals directly from the environment via the so-called vomero-nasal organ (VMO). The VMO is situated in the nose and senses pheromone and allomone chemicals.
Pheromones are airborne chemicals produced in a species different to itself. A good example of this is mice detecting the pheromones of its natural predators, eg. ferrets and cats in double quick time via the VMO.
Sight and hearing, the other early warning senses, signals the cortex via a relay through the thalamus resulting in split second delays, which may well prove to be fatal.
On the other hand, pheromones and allomones (chemicals from the same species) that float in the air are shuttles to the reptilian brain (R-brain) in double quick time, completely bypassing the thinking brain. A very effective early warning system.
Even though the VMO is inactive in humans, ordinary human smell also short circuits the thinking brain and activates dopaminergic nuclei in the R-brain that releases the neurotransmitter dopamine, which then up-regulates the recruitment of the skeletal muscles to help us 'forage' for the food we can smell.
In fact, the R-brain dopaminergic nuclei also releases dopamine into the thinking brain and ‘recruits’ the thinking brain to work with the R-brain, rather than the other way around. This is the hallmark of all 3 motivated behaviours – defensive, ingestive and reproductive behaviours, whereby the R-brain 'recruits' the thinking brain into doing its bidding.
Returning to our simplified model of ingestive behaviour in the lamprey eel, research shows that the smell (airborne chemicals) of the food particle activates the olfactory cortex of the eel that then directly stimulates the dopaminergic nuclei in the midbrain to up-regulate the swimming muscles via the reticulo-spinal nerves.
The greater the number of these dopaminergic nuclei that are stimulated the more vigourous the movement.
In the human brain there are about half a million of these midbrain dopaminergic nuclei, which are normally inhibited to enable us to sit still, but if required to achieve a sought after goal they are activated in direct proportion to how much we value attainment of said goal.
Activating all 500 000 of our dopaminergic nuclei at the same time will make us as powerful as Spiderman on speed. Not a good thing as it will result in us ripping up our muscles unused to this kind of effort. A more sustainable effort is thus needed that necessitates a more precise release of dopamine.
Voluntary behaviours, on the other hand, works the other way around - the thinking brain recruits the R-brain, also know as top-down control. Though it is nowhere near as powerful as our motivated behaviours, we nevertheless persist in our top down control of movement as we falsely believe we have greater control over the outcome that way.
As it is , our willy-nilly top-down control over our defensive behavioural programme in the R-brain plays havoc with the hormones and neurotransmitter chemicals released into our thinking brains and blood circulation, which eventually gives rise to a host of non-communicable diseases, weight gain, fatigue, infertility, and the like.
There is a way, though, to give regulatory control back to our R-brains to allow it to keep our body in tip top condition, at a healthy weight, fertile and full of energy.
The heart (or more correctly the cardiovascular (CV) system since the heart and blood circulation works as a system) must be continuously monitored in order to regulate our defensive behaviours.
If you have too much nervous energy in your heart (edginess) you have to engage in posturally correct movement to neutralise the destructive effects that excessive adrenaline has on the heart and to enable you to operate with heightened awareness.
Always keeping in mind that the CV system is under dominant Sympathetic Nervous System (Fight & Flight) control and is extremely well adapted to keeping us alive in life or death situations, but it is also extremely wasteful of bodily resources and will destroy all our bodily organs if misused on a daily basis.
So it is imperative not to use the heart to regulate what must be left to the viscera and ingestive behaviour. I.e. it is futile to try and manage your weight via cardiovascular exercise – you are merely wasting valuable energy and end up leaving your energy out on the road instead of making productive use of it.
Your visceral feedback will always tell you whether the food you ate agrees with you or not, but only if you are fully 'in your body'. Appetite and ingestive behaviour, as regulated by the R-brain, will always trump calorie counting and diet prescriptions when it comes to keeping our weight where we want it. Not that calorie counting and diet prescriptions won't work, rather that it is far simpler and more sustainable to allow the R-brain to regulate ingestive behaviours.