Motor Control, Lecture 11 Flashcards
Basal Ganglia Circuitry
Putamen receives inputs from cortical areas (striatum), while GPm projects back to the cortex.
Direct Pathway (Excitatory): Allows desired movements to occur.
Excitatory signal from the cortex.
Increased inhibitory signal from Putamen to GPm.
Reduced inhibitory signal from GPm to Thalamus.
Increased excitatory signal from thalamus to motor cortex.
Indirect Pathway (Inhibitory): Prevents undesired movements.
Increased inhibitory signal from Putamen to GPI.
Reduced inhibitory signal from GPI to STN.
Increased excitatory input to GPm.
Increased inhibitory output to thalamus.
Reduced excitatory output to cortex.
Parkinson’s Disease
Lack of dopamine has opposing effects on the two pathways.
Underactive direct pathway (increased GPm activity).
Overactive indirect pathway (increased GPm activity).
Both lead to increased inhibition of the thalamus and reduced excitation of the cortex.
Results in motor symptoms associated with Parkinson’s disease.
Basal Ganglia Loops and Other Symptoms
Different basal ganglia loops project to different cortical areas, impacting both motor and cognitive functions.
The basal ganglia’s dysfunction can lead to various symptoms beyond motor impairments.
Treatment Options for Movement Disorders
L-dopa: Converts to dopamine in the brain to compensate for dopamine deficiency in Parkinson’s disease. However, long-term use can cause dyskinesias.
Newer dopaminergic drugs: Aim to provide more targeted and controlled delivery of dopamine, minimizing side effects like dyskinesias.
Surgery - Lesions and Deep Brain Stimulation (DBS): Lesioning procedures disrupt specific neural circuits, while DBS involves implanting electrodes for electrical stimulation to modulate abnormal neural activity.
Deep Brain Stimulation (DBS)
Battery-operated stimulator delivers electrical stimulation to targeted areas in the brain.
Targets the thalamus, subthalamic nucleus (STN), and globus pallidus (GP).
Reduces the effects of the indirect pathway by modifying neural activity in the circuitry.
Results in reduced STN activity, reduced excitation of GPm, reduced inhibition of the thalamus, and increased excitation of the motor cortex.
Huntington’s Disease (HD)
Inherited autosomal dominant condition with onset in the 30s or 40s.
Characterized by chorea (uncontrolled movements) and degeneration of the putamen and caudate.
No cure or specific treatment available at present.
HD leads to underactivity of the indirect pathway, resulting in reduced inhibition of GPI, increased inhibition of STN, and reduced activity of GPm.
Cognitive Impairments in Huntington’s Disease (HD)
HD can be associated with various cognitive impairments, including:
Difficulties with attention.
Impaired executive function.
Slowed speed of processing.
Challenges with prospective memory.
Impaired emotion recognition.
These cognitive deficits are observed in addition to the motor symptoms associated with HD.
Comprehensive rehabilitation approaches may be needed to address cognitive challenges in HD.
Tourette Syndrome (TS)
TS is characterized by simple and complex tics, such as eye blinking, scratching, gestures, and utterances.
Tics may increase during times of stress and decrease when concentrating.
Prevalence: > 1000 per 100,000 children (greater than 1 in 1000).
TS has a hereditary component and is linked to obsessive-compulsive disorder (OCD).
Increased dopamine from the substantia nigra contributes to TS symptoms.
Overactivity of the direct pathway in the basal ganglia leads to disinhibition of unwanted movements, explaining aberrant movements and potential links to OCD symptoms.
Moving and the Environment in Parkinson’s Disease (PD)
Moving in the environment can have both detrimental and beneficial effects in PD.
Detrimental: “Freezing” of movement, commonly experienced near the edges of doorways.
Beneficial: Paradoxical movement, where external cues or specific environmental conditions facilitate movement in PD.
Internal vs. external movements and the therapeutic use of movement cueing are important considerations in PD management.
Action Observation in Parkinson’s Disease (PD)
Observing actions has shown potential benefits in driving movement in PD.
Studies have shown that viewing a reaching movement can facilitate one’s own reach.
Action observation combined with physiotherapy has been found helpful in managing freezing episodes in PD.
There is potential for using imitation and action observation techniques in treating PD, but further research is needed to better understand their effectiveness.
Action Observation Plus Motor Imagery (AO+MI)
Combining action observation with motor imagery has shown promising results.
In healthy young participants, motor imagery or attention instructions led to greater vertical amplitude in reaching movements.
This effect was also observed in people with Parkinson’s, where AO+MI boosted imitation of movement amplitude.
AO+MI has the potential to enhance motor function in individuals with PD.
Focus Group for Potential Intervention
In a focus group setting, potential intervention strategies using observation and imitation were discussed.
Examples of observation/imitation in daily life included activities in a gym, yoga or exercise class, and while walking.
Movement imagery examples involved daily activities such as getting out of bed.
A range of actions were suggested for training, such as using a computer mouse, brushing teeth, folding laundry, and turning pages.
Personalization and choice of actions were deemed important, along with maintaining motivation throughout the intervention process.
