Motor Control Circuits

Motor Control Circuits & function

• generally b.g. and cerebellar

• function: coordinate, integrate, and refine movements from direct/indirect activation pathways

B.G. Circuit function

• communicate very closely w/SMA (go signal & initiation map)

• b.g.- select/supress motor programs and send to SMA

• activate cells in initiation map

• structures: striatum, GPe, GPi, Substantia Nigra, Subthalamic Nucleus

Motor Control Circuit: 4 steps

1. cortical regions (PMC, pMC, SMA, PSC) provide input to striatum (mostly putamen) 

2. simultaneously, SNc provides dopamine to striatum

3. through b.g. circuit, we get output from GPi to thalamus to SMA so SMA can make decision on timing

4. UMN communicates w/contralateral LMN - b.g. primarily influences the contralateral periphery

B.G. Neural inputs

• SMA- medial BA 6 & superior BA 8 (initiation)

• PMC- BA 4 (detailed motor commands to periphery)

• PSC- BA 1, 2, 3, (provides copy of expected SS outcomes to b.g.)

• pMC- BA 6 (sequencing detailed motor commands)

• ** all enter b.g. via putamem then GPi

B.G. Neural outputs

• thalamus to cortex (SMA) - ipsilateral to where b.g. is

B.G. Lesion results in:

• reduced vocal intensity 

• sensory- motor vocal mismatch (other ppls perception doesnt match own)

• Parkinsonis

• Hypokinetic dysarthria 

Hypokinetic Dystarthria characteristics

• breathiness - decreased adduction

• fast AMRs & SMRs (b/c smaller movements)

• reduced loudness - shift in FF targets (cant detect errors so lack of air signal)

• short rushes of speech- increase in artic. rate at end of phrases especially 

• rapid/blurred phonemes- smaller artic. movements equals more over time- patient may not achieve full contact of bilabials or alveolars and may go to next target before full closure. 

Hypokinetic Dysarthria: patient reports

• sensory motor voice mismatch 

• may say they talk too fast or mumbled

• describe speech as stuttering 

• may not experience anxiety about issues and cannot predict when it will happen again 

• may report inconsistent rate of disfluencies

Hyperkinetic Dysarthria characteristics

• degeneration of neurons in indirect b.g. pathway, which suppresses unwanted movements

• distorted vowels- b/c jaw and tongue position move during middle of vowels 

• excess loudness variation- increased adduction = intermittent volume increase

• sudden or forced expiration

• voice stoppages/arrests

• innapropriate vocal noises - extra lip smacking, jaw, and tongue movement

• Huntingtons disease

Hyperkinetic Dysarthria: patient reports

• may deny or not be aware of extraneous movements

• report slower speech (possibly due to pausing speech in between extra movements and waiting to resume)

• may report using sensory tricks (chewing gum etc) to supress movement, but only works temporarily 

• may notice inability to hold steady postures

• can affect 1+ multiple motor systems, so many complain about abnormal movements at reast and when they try to start moving