- When trying to understand if oromotor and speech use the same system of motor planning, researchers have proposed a "task-dependent" model
- This model suggests that speech and oromotor activity have different systems for motor planning, which are controlled by different forms of neural circuitry
- Previous neuroimaging studies have supported this theory by observing differences in the activity at the level of the cerebellum and motor cortex when speech vs. tongue movements were produces
- This opposes the integrative model

Task-Dependent Model of Motor Planning

- Proposes that there is one broad motor system that is shared between speech and oromotor activities 
- Previous studies have looked at the differences in voluntary oral movements vs. chewing in primates, and found that the lateral prefrontal cortex used in both types of activities
- After damaging this area, researchers found they could not perform trained tasks, or move their jaw as well during chewing 
- It has ben hypothesized that this is because they utilize an "overlapping neural tissue"/ circuit system for both of these skills, supporting the integrative model 
- This opposes the task-dependent model 

Integrative Model of Motor Planning

- When investigating how motor planning may be shared (or different) between speech and oromotor activities, two models have been proposed: the task-dependent model and the integrative model 
- Both models are supported by existing research, signifying that elements of both models may be true (although further research must be done to support this claim)

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- Researchers have questioned whether the same type of  motor planning mechanisms are used in speech versus physical movement of the mouth (known as oromotor activity)
- Ultimately, they found both speech and oromotor activities use the same neural networks associated with a specific type of motor planning but both activities had different "dynamics" of motor planning (meaning different regions of the brain were involved at different "levels" when presented with a certain stimulus that activates either speech or oromotor movement)
- These findings support both the integrative and task-dependent model 

Motor Planning in Speech and Movement

Lancheros M, Jouen AL, Laganaro M. Neural dynamics of speech and non-speech motor planning. Brain Lang. 2020 Apr;203:104742. doi: 10.1016/j.bandl.2020.104742. Epub 2020 Jan 24. PMID: 31986473.

Neural dynamics of speech and non-speech motor planning

- In order to  study the neural circuitry associated with motor planning, it must be isolated from the process known as pre-motor planning, which is associated with "linguistic encoding" (putting a non-linguistic thought into words) rather than the process of speech itself (where words become "phonetically encoded")
- These two processes can be separated by creating a delay in completing a certain task, that will stimulate the participant to either speak, or perform oromotor activity 
- In this way, participants will only participate in motor planning after the delay, and thus give researchers a clear separation between the two processes

Differentiating between Pre-Motor vs. Motor Planning

- In order to clearly understand the different purposes of speech vs. the physical movements of the mouth associated with speech, different definitions have been given to each activity/ concept
- "Speech" is defined as the process of creating phonetic associations with words that have been chosen to represent an abstract idea
- Speech does utilize physical processes (including the respiratory/articulatory processes) in order to achieve its previously defined purpose 
- "Oromotor activity" is defined as the process of creating these words (syllables, phonemes, etc.), as well as non-verbal oral movements 

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