Gameplay in "Escaping Titan" will feature several abilities to improve physical and mental abilities through the use of Synapse Stimulant Implants that provide these abilities specifically through stimulating particular areas of the brain. Last month we discussed means of stimulating the brain to tie in with the concepts of SSI's in the game. This month we're going to start in on the functions of dorsal premotor cortex (and primary motor cortex) to help us with understanding the "Self-Buff" ability.
"Self-Buff." Sounds pretty appealing. If you have a gamer's physique, you may envy the "Buff" nature of athletes and body builders. Or not - but as a adventurer, you might just need those abilities to survive the next challenge to come your way. So what would it take to enhance reflexes, strength and muscle control?
To start with, let's discuss the motor cortex and control of muscles, then we'll move on to functions of the premotor cortex. Primary motor cortex (red shading in the figure above) is the major control center for muscle movement. Neurons - the cells that form the brain - generate signals that project from motor cortex down to the spinal cord, out to various muscle and organs, and cause an action. The connections of the brain's motor cortex to muscle should be reasonably obvious by now. First we have the "Motor Homunculus" (below) with it's distorted map of the body to show how the motor cortex is organized with respect to outputs to the major muscle groups. In addition to the obvious muscle connections (which we will get back to in a minute), there are connections to the arteries, to regulate the diameter (and hence pressure) of the blood vessels. There are connections to the skin, to change the thickness, control sweat, control temperature and cause "piloerection" (goosebumps) which is a remnant of a reaction to raise hairs and increase the insulating properties of the fur which humans don't have! Less obvious are the connections to the organs to speed up or slow down activity, cause release of chemicals (hormones) and prepare the body for different conditions.
By the way - these latter functions all tie into the Self-Buff ability to control and enhance muscular abilities during gameplay!
To list off the types of outputs from brain: we have (1) visceral control, (2) neuroregulatory control, (3) hormonal release control, (4) involuntary motor control, and (5) voluntary motor control. By visceral control (1), I mean direct control of the primary organs - for example, the heart will beat even without direct input from the brain- however, that input will cause the heart to slow down or speed up its rate. Likewise, the muscles that line blood vessels and the stomach & intestines (what we call "smooth muscle") have local circuits that control them, but inputs from the brain will change the speed and amount of contraction of the muscle, thus changing pressures and rate of flow (of blood or intestinal contents). Neuroregulatory control (2) is the control of the neural signals to and from the body. We all know of the ability to control or ignore certain sensory signals: pain, hunger, full bladder, etc. This ability is actually due to neural commands from the brain to the nuclei that relay signals to the brain. A certain amount of control of inputs (just like the control of eardrum or iris to limit visual or auditory range) is built into the sensory system to allow the brain to override signals when necessary. Hormonal release control (4) relates to the various *glands* throughout the brain and body, most notably the pineal, pituitary, adrenals, sweat, salivary and genitalia. These glands all release (or change) their chemical contents when stimulated by neural commands. Involuntary motor control comprises all of the reflexes and automatic functions controlled by the brain that a person does not have to think about. The heart beats, the diaphragm and ribcage create the breathing cycle, the stomach and intestines squeeze and relax to promote digestion, and muscles in the pelvic region tighten to limit the flow of fluids and solids when not needed. Virtually all of the neurons that control the above four functions originate in the mesencephalon (e.g. medulla) or lower (spinal cord or ganglia near the appropriate organs).
Finally, voluntary motor control (5) consists of all of the muscles that we can move just by thinking about them: Arms, legs, tongue, fingers, with additional voluntary overrides of involuntary functions (eyeblink, deep breath, bladder retention) etc. These functions (and neurons) are the ones that arise from the motor cortex.
To further understand how all of this works together, there is one further key piece of information: Muscles can only pull. They cannot push.
So how does limb movement work? Clearly there is some sort of a push-pull system going on?
Well, there is an oppositional system, but it is more appropriately a "pull-pull" system. Consider Da Vinci's famous "Vitruvian Man" drawing (above). This illustrates the best coordinate system for talking about anatomical positioning. In the drawing, all limbs are extended, the joints are straight, and the opposing muscle groups are at equal lengths. To bend an arm from this position, the elbow must be bent, changing the angle between upper and lower arms to something less than 180 degrees. This is accomplished by muscles contracting on the *inside* of the arm (inside the elbow joint). To re-straighten the arm, muscles on the outside of the arm contract, pulling the elbow and bones back into alignment.
We call the first action "flexion" - i.e. any muscle that reduces joint angle to less than 180 degrees is a "flexor". The straightening action is "extension" and the muscles are termed "extensors." To complete the process, there is a reflex "wired" through the spinal cord to relax extensors when the flexors contract, and vice versa. For circular or circumferential muscles, such as the iris of the eye, or sphincters (ureter and anus), the arrangement is a bit more complicated - there are circular muscles that surround the opening, and radial muscles at right angles. As shown in the illustration below, contracting the circular muscle closes the opening, contraction of the radial muscle opens it. Coordination of the opposing muscle groups is regulated by cerebellum and brainstem/spinal cord- so even for *voluntary* muscle movement, there is a certain measure of involuntary control.
So now that we have the means of interacting with all of the muscles and controlling so many systems of the body - how does our brain decide *what* to do, and when to do it? In other words - is there a program for performing muscle and body movements?
In short, the answer is yeas, and that's where the dorsal premotor cortex comes in. With some assistance of the cerebellum (for coordination) and a few other motor control neurons around the body, the DPMC is the main locus of planning motor movements. This can have some startling applications to prosthetic limbs and brain interfaces as discussed last month! However, since it just would not be fair (hah!) to reveal all of our secrets at once - more discussion of DPMC location (for the "Operation"-style minigame) and function (for Self-Buff) will be continued next month!
Until then - Take Care of your Brain... and it will Take Care of You!