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In psychology and neuroscience, motor planning is a set of processes related to the preparation of a movement that occurs during the reaction time (the time between the presentation of a stimulus to a person and that person's initiation of a motor response). Colloquially, the term applies to any process involved in the preparation of a movement during the reaction time, including perception-related and action-related processes. For example, the identification of a task-relevant stimulus is captured by the usual meaning of the term, “motor planning”, but this identification process is not strictly motor-related. Wong and colleagues (2015) have proposed a narrower definition to include only movement-related processes: "Specification of the movement trajectory for the desired action, a description of how the end-effector will produce such an action, and finally a description of the full set of the joint trajectories or muscle activations required to execute the movement."

The computation of the procedure occurs in the pre-motor region of the brain, which is supplemented by the somatosensory cortices (which provide input) and the primary motor cortex and supplementary motor cortex (which provide the means for output). Together, these regions allow for both simple and complex procedures to be perceived, planned, and executed.

History

In 1905, while studying the cells within the brain, Alfred Campbell discovered that the cells within neighbouring regions of the motor cortex differed in size from those found in what is now known as the primary motor cortex, as well in the supplementary motor cortex. Four years on from this, Korbinian Brodmann, while mapping the brain, came to the same conclusion along similar hypothesis, and highlighted the different regions as areas 4 and 6 respectively. John Fulton also contributed to this research in 1935, by carrying out lesion studies in the brains of monkeys. From this, he also concluded that the pre-motor cortex is a separate region of the motor cortex, with its own functions.

However, in 1937 Wilder Penfield suggested that there was no difference between the different areas of the motor cortex. Additionally, Clinton Woolsey reinforced this idea in 1956, after a study which physically analysed the motor map in monkeys. The conclusion drawn from the study was that there was no distinction to be made between different regions of the motor cortex.

The conclusions drawn by Penfield and Woolsey became the presiding theories over the anatomy of the motor cortex for 20 years, until Roland et al. discovered that blood flows to different regions of the motor cortex, depending on the complexity of the task. Additionally, Wise et al. discovered that the neurons in the brains of monkeys activated within specific regions, during the reaction time of complex procedures. From this, the pre-motor cortex was again recognised as a distinct region.

Neuroanatomy

Pre-motor cortex (highlighted in green)

The pre-motor cortex can be found in Brodmann area 6, neighbouring the primary motor cortex anteriorly when viewed laterally from the left hemisphere, and ventral to the supplementary motor cortex, again from the same viewpoint. The pre-motor cortex is connected to the primary motor cortex, in order to convey the plan that is to be carried out, and the parietal cortex, for the reception of sensory information.

Procedure

Motor planning process, as detailed by Wong et al.

The procedure performed during the motor planning stage can be broken down into five steps, however it is necessary to begin by stipulating that the importance of attention in this procedure is critical, as a lack of attention can lead to the reaction not being initiated. Therefore, if attention is not directed towards the stimulus, the process is not initiated, and consequently not carried out. The first of which being the acknowledgement of a stimulus. This is done from the reception of input from the senses within the body. From this, the stimulus is interpreted based on the emotional response of the individual (i.e., what some find pleasant others may find repulsive). This relates to the response, as a more dangerous stimulus requires a more urgent response. Additionally, the body then goes on to identify where the stimulus originated from and what its cause was (i.e., if it was a burn to the skin or an auditory warning to avoid something). Once the stimulus has been recognised and interpreted, a plan is generated. This can be based on previous knowledge and comprise of learned behaviour, or it could be compiled based purely on the environment as the best procedure possible at the time. The final step is to physically carry out the action, and therefore the desired movement is directed to the primary motor cortex for implementation.

Learning & Reinforcement

After a procedure is carried out, it is remembered for future replication. This is the life cycle of learned behaviour. Consequently, the reaction to an event, and perception of the event, can influence how one may react if a similar situation were to arise again. What is interesting (as a hypothesis) is how an individual’s perception of a task affects their feelings towards that task, if it is possible that the stimulus may occur again in the future. This may influence how disorders like anxiety disorder and PTSD arise, because of the response to an event which is interpreted to be severely dangerous, when that response (in reality, and entirely based on the situation) is not appropriate. Hypothetically, there may be a correlation between reinforcement (via motor planning) and mental health conditions (e.g., anxiety, PTSD), and although some research has been carried out in this fieldnone have looked specifically at this correlation.

Disorders

Two disorders predominately arise due to the inability to plan out motor movements. These disorders are categorised as dyspraxia, which relates to difficulty in performing actions that require planned movements, and dysmetria, which is difficulty performing actions that require movement in general.

Developmental coordination disorder is a form of dyspraxia found in adolescents, which makes it difficult for those with the condition to learn basic movement patterns, balance, and be spatially aware. Treatment of the condition can either be process-oriented, which equates to performing activities that improve a patient’s motor skills, and task-oriented, which focuses on practising the skills that a patient finds difficult.

Friedrich’s Ataxia is a form of dysmetria, which makes it difficult for sufferers to perform motor-related activities, partially due to an inability to plan their movements. Symptoms of this condition include a lack of coordination, relating to an inability to move limbs in the desired patterns, sporadic reflexes, which can either be spontaneous, prolonged, or lacking, and speech issues, due to the inability to move the facial appropriately. Treatment of this condition is broadly the same as it is for dyspraxia (i.e. reinforcement of behaviour), however muscle strengthening exercises are also utilised.

References

Category:Neuroanatomy Category:Aging-associated diseases Category:Ailments of unknown cause Category:Geriatrics Category:Cytoskeletal defects Category:Psychiatric diagnosis