Where in the brain is the Basal Ganglia located?
It is subcortical (under to cortex) in the middle of the brain
What pathways are there through the basal ganglia?
Direct and indirect pathway
What is the input and output to the basal ganglia?
- The medial globus pallidus (GPm) projects to the motor cortex via the thalamus
- the putamen received input from the cortical areas (striatum - motor cortex)
What is the basal ganglia important for?
Releasing the movements at the right time
How does the direct excitatory pathway of the basal ganglia work?
- the putamen received an excitatory signal from the cortex
- This leads to putamen to give out an increased inhibitory signal to the medial globus pallidus (GPm) through the lateral globus pallidus (GPI)
- the GPm then sends a reduced inhibitory signal to the thalamus
- The thalamus then sends an increased excitatory signal to the motor cortex
- this pathway allows movement to happen
How does the indirect pathway of the basal ganglia work?
- There is an increased inhibitory signal from the putamen to the lateral globus pallidus (GPI)
- There is a reduced inhibitory signal from the GPI to the STN (subthalamic nucleus) (STN become more active)
- There is increased excitatory output from the STN to the GPm
- There is increased inhibitory output from the GPm to the thalamus
- There is then reduced excitatory output from the thalamus to the cortex
- this prevents undesired movement occurring
How does the Basal ganglia act as ‘gain control’
- Direct pathway: allows desired movements to occur
- Indirect pathway: prevents undesired movements occurding
What happens with Parkinson’s and the basal ganglia?
The lack of dopamine has opposing effects on the two pathways.
- The direct pathway is underactive due to increased GPm activity
- The indirect pathway is overactive leading to increased GPm activity
What does increased GPm activity in Parkinson’s lead to?
Increased inhibition of the thalamus and reduced excitation of the cortex
What can you see in people who have taken anti-psychotic medicine sometimes?
Parkinson’s symptoms
Why do Parkinson’s patients sometimes have blank looks?
Because the muscles of the face can be affected
Why do people with parkinson’s exhibit dyskinesia?
It is induced by the drugs which are used to treat Parkinson’s
is the Basal ganglia only involved in motor control?
No. Different BG loops project to different cortical areas - cognitive as well as motor functions. BG may play an analogous role for attention and could be involved in vision and emotion
How can Parkinson’s be treated?
- administering L-DOPA (precursor to dopamine) - causes dsykinesia
- newer dopaminergic drugs
- surgery - lesions and deep brain stimulation
How does deep brain stimulation work with Parkinson’s?
- battery operated stimulator delivers electrical stimulation to target areas (thalamus, subthalamic nucleus and globus pallidus)
- Sort of switches of subthalamic nucleus (meaning that there will be less excitatory input to GPm leading to reduced inhibition of the thalamus and greater excitation of the motor cortex)
Is Huntington’s genetic and if so how?
yes it is an inherited autosomal dominant condition
What symptoms does Huntington’s produce?
- Chorea
- memory loss
What is Huntington’s caused by?
Degeneration of putamen and caudate
Can you die from Huntington’s?
Yes
How is Huntington’s caused in the basal ganglia?
- Underactivity of the indirect pathway
- reduced inhibition of the lateral globus pallidus (GPI)
- Increased inhibition of the STN
- reduced activity of GPm
- leads to too much movement
What are the cognitive impairments of people with Huntington’s?
- attention
- executive functioning
- speed of processing
- prospective memory (remembering to do things at some point in the future)
- emotion recognition
What are the symptoms of Tourette syndrome?
Simple tics e.g. eye blinking, nose twitching
- complex tics e.g. scratching, gestures, utterances
When may Tourette’s syndromes increase and decrease?
May increase during times of stress and decrease when concentrating
Is Tourettes hereditary?
Yes
