A simplified neuroscientific overview of why we need to fail in order to achieve motor skill success.
A team effort
Movement starts with the intention to move. This initial step involves the prefrontal cortex and the limbic system which assesses what movement is necessary to accomplish a goal.
I want to get over the hurdle. I need to jump over it.
Here, the supplementary motor area and the premotor area then collaborate to develop a detailed plan for the movement. The supplementary motor area focuses on refining the specific order, sequence, and timing of the movement. Meanwhile, the premotor cortex carefully selects the most appropriate motor plan to initiate the movement by integrating incoming sensory information [1].
I will need to run 5 steps towards the hurdle. I need to extend my right leg as straight as I can. The wind is coming against me, so my last step will need to be shorter and more powerful.
Figure 1. The main brain regions involved in motor planning and execution. The limbic system lies deep within the brain [2]. Adapted from Injurymap.
Little brain has a big role
The cerebellum, Latin for ‘little brain’, can be thought of an athlete’s (head) coach. Before the motor cortex can communicate commands to move via motor neurons in the spinal cord it must first pass through the cerebellum. This is a critical step where the motor plan undergoes modulation and refinement. Prior to carrying out a movement, the cerebellum receives information about the execution of the movement from the motor cortex and fine tunes this information to produce precise and well-timed movements [1]. Yet, the role of the cerebellum doesn't end there.
During the execution of the movement, the cerebellum continues to receive information from sensory receptors distributed throughout the body. This incoming sensory feedback provides the cerebellum with crucial information regarding the body's position. For example, proprioceptive receptors found within tendons may emit a signal to the cerebellum through the spinal cord to let it know that the right quadricep is extended at an angle of 75 degrees when clearing the hurdle. [3]
Error-driven learning
By integrating these two sets of information, the cerebellum can determine the difference between the intended movement (according to the motor plan), and the actual movement that is performed. With this information, movement is learnt and re-learnt, and movements are adjusted based on mistakes. This is called motor adaptation [4].
Because my last step was too short, I jumped onto the hurdle rather than over the hurdle. Time to reassess.
Motor adaptation is controlled by a specialised type of cell within the cerebellum called Purkinje cells. These cells are responsible for inhibiting the excitatory signals of the spinal cord which facilitate movement, through the release of the neurotransmitter GABA [5]. During motor adaptation, Purkinje cells send their inhibitory output signals to the deep cerebellar nuclei which have direct projections to the spinal cord. Decreasing the excitability of the spinal cord, allows for more precisely controlled motor movements, as it is believed to reduce signalling errors relating to incorrect or excessive firing [6].
Figure 2. The error driven learning cycle. The Purkinje cells receive vast input from other specialised cerebellar cells and inhibits output signalling of the DCN, decreasing the excitability of the spinal cord and leading to more controlled movements [7]. Adapted from The Neuroscientist.
With repeated practice and ongoing motor skill learning, Purkinje cells become more easily excited. Enhanced excitability increases the cells' capacity to generate and send the correct signals to the spinal cord in order to produce coordinated and controlled movement [8].
Feeling it
The cerebellum needs to know what the correct movement feels like before it can correct and fine tune movement. When the cerebellum is unsure what the correct movement is, it will make a guess. This guess, can result in the wrong movement being practised and learnt [4].
With repeated practice and cerebellar learning, movements that were once conscious and effortful are transformed into automatic actions. So rather than consciously attending to the specific mechanics and posture when executing a skill, attention can now be directed towards game strategies and more complex movements [9]. The cerebellum helps you to make it look easy.
References:
[1] Virameteekul S, Bhidayasiri R. We Move or Are We Moved? Unpicking the Origins of Voluntary Movements to Better Understand Semivoluntary Movements [Internet]. Frontiers in Neurology. 2022 Feb 21 [cited 2023, July, 10]. Available from: https://www.frontiersin.org/articles/10.3389/fneur.2022.834217/full
[2] File:Human Brain.png - Wikimedia Commons [Internet]. Wikimedia.org. 2019 [cited 2023, July 15]. Available from: https://commons.wikimedia.org/wiki/File:Human_Brain.png
[3] Physiopedia. Cerebellum [Internet].[place unknown: publisher unknown] [cited 20, July, 2023]. Available from: https://www.physio-pedia.com/Cerebellum
[4] Seidler RD, Kwak Y, Fling BW, Bernard JA. Neurocognitive Mechanisms of Error-Based Motor Learning. Advances in experimental medicine and biology [Internet]. 2013 Jan 1 [cited 2023, July, 9];782:10.1007/978-14614–54656_3. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3817858/
[5] Rogers kara. Purkinje cell | anatomy | Britannica. In: Encyclopædia Britannica [Internet]. 2019 [cited 2023, July, 20]. Available from: https://www.britannica.com/science/Purkinje-cell
[6] Heckman CJ, Mottram C, Quinlan K, Theiss R, Schuster J. Motoneuron excitability: The importance of neuromodulatory inputs. Clinical Neurophysiology [Internet]. 2009 Dec [cited 2023, July 9];120(12):2040–54. Available from:
[7] Popa LS, Streng ML, Ebner TJ. Purkinje Cell Representations of Behavior: Diary of a Busy Neuron. The Neuroscientist. 2018 Jul [cited 2023, July 15] 9;25(3):241–57.
Available from: https://pubmed.ncbi.nlm.nih.gov/29985093/
[8] Titley HK, Watkins GV, Lin C, Weiss C, McCarthy M, Disterhoft JF, et al. Intrinsic Excitability Increase in Cerebellar Purkinje Cells after Delay Eye-Blink Conditioning in Mice. The Journal of Neuroscience [Internet]. 2020 Feb 3 [cited 2023, July 17];40(10):2038–46. Available from: https://pubmed.ncbi.nlm.nih.gov/32015022/
[9] Muller-Townsend K. Transfer of automatic skills: the role of automaticity in skill Transfer of automatic skills: the role of automaticity in skill acquisition and transfer acquisition and transfer [Internet]. 2017[cited 2023 July 18]. Available from: https://ro.ecu.edu.au/cgi/viewcontent.cgi?referer=&httpsredir=1&article=2956&context=these