The importance of gray matter
Our brain and spinal cord contain gray matter (GM) which is responsible for the motor control and sensory perception in our body. GM contains motor neurons which send action potentials down the axon and into our muscle cells, which results in movement . There tends to be a stronger signal and more refined neural pathway when there is high GM density in the brain . Studies indicate that humans tend to increase GM density during childhood, followed by a loss of GM density after puberty [3, 4]. It is suggested that as we mature, the volume of synaptic connections decreases and our ultimate GM density is determined .
An interesting study by Gogtay et al.  reports that following brain maturation an adolescent’s GM density diminishes until young adulthood. However, this does not mean that we are unable to learn new motor patterns after puberty. Instead, it simply implies that the greatest “window of opportunity” for learning motor skills is before puberty, and that afterwards, motor skill pattern potential is limited due to the motor synapses closing.
Fast- and slow-stage learning
Changes in motor skill neuroplasticity are often divided into a “fast-stage” (short-term) and “slow-stage” (long-term). During fast-stage learning, it is believed that the primary motor cortex in our brain recruits substantially more neurons for new motor tasks . This increase in brain activity can result in vast improvements being seen within a single training session. After improving at a motor skill, we transition to the slow-stage of learning where multiple training sessions and repetitive practice is needed to retain or improve that skill.
Unlike the fast-stage, the slow-stage of learning results in small improvements at a much slower pace . This is due to neuroplasticity’s “use it or lose it” principle when it comes to motor skills . The brain’s plasticity will either slowly strengthen or reduce a motor pathway based on repetitive action, or the lack-of. However, past repetitive practice of motor tasks could lead to a quicker re-adaptation if there was stoppage of that skill . This term is called “savings” and is why many athletes can still perform a skill such as shooting a basketball, even after years of not practicing.
One important thing to consider with fast-stage and slow-stage learning is that the acquisition of a skill is highly task-specific and relevant to the person. Generally, the learning curve of a motor skill will look the same when considering the specificity and difficulty of certain skills (Figure 2).