Flashcards in Basal Ganglia Deck (12)
What are the major constituents of the basal ganglia? What is meant by the term striatum? Where are the basal ganglia located?
Caudate + putamen = striatum
Caudate (follows lateral ventricle into temporal lobe)
Putamen (sort of inside caudate, lateral to thalamus)
Nucleus accumbens (ventral/anterior caudate)
Globus pallidus (medial to putamen)
Subthalamic nucleus (just inf to thalamus, in midbrain)
Substantia nigra & Ventral tegmentum (just inf to STh, in midbrain)
Describe the sources of dopamine neuromodulation for the striatum.
Substantia nigra, pars compacta, projects to striatum
What is a corticostriate (CS) loop?
Cortical programs for thought and behavior get fed through the striatum and globus pallidus for refinement. This allows you to first select the best pathway for a cortical activity, then reinforce it with input of dopamine. This allows you to learn patterns and also form habits.
The loop goes: Cortex to striatum, DA exchange with substantia nigra, then through globus pallidus via subthalamic nucleus, then up through the thalamus back to cortex.
What are the four known CS loops and what parts of the cortex do each of them involve? What are the general functions of each of the loops?
Motor: Motor system/Somatosensory to putamen, fine control of movements (like playing a piano)
Executive: dlPFC/posterior parietal to caudate head, rationalization, strategy selection
Motivational: vmPFC/ACC to nucleus accumbens, motivational-emotional aspects of behavior
Visual: temporal/vlPFC to caudate body/tail, helps you interpret visual stimuli
Distinguish procedural memory from declarative and emotional memories.
Declarative memories are events or facts that you can recall and talk about.
Emotional memories are emotional responses triggered unconsciously in response to stimuli.
Procedural memory is habit formation/skill learning, a set of motor actions triggered by stimulus that is (at least originally) goal-oriented: accomplish a task.
What are the three aspects of procedural memory?
1. Category representation: gives meaning to sensations
2. Action selection: what am I going to do?
3. Instrumental and reward learning: switching tasks to a more appropriate one, reinforced by dopamine. Reward is accomplishing the goal.
What impact does dopamine neuromodulation have in action selection and instrumental/reward learning?
A dopamine reward is provided for pathways that result in desired actions. This reinforces these pathways, so that you learn to use them for accomplishing your goal.
Distinguish between instrumental and reward learning. What is the difference in their outcomes?
Instrumental: From a naive undifferentiated state, neurons undergo corticostriatal learning. Task-related elements are facilitated while incorrect elements are inhibited.
Reward learning: Behavior is conditioned by association of stimulus with reward, rather than with motor response. This becomes habit, so you don't need motivation anymore, you just have it programmed in that this is good. Dopamine strengthens links between behavior and reward.
What are the general actions of addictive drugs on the motivational CS loop?
Drugs of addiction reinforce addictive behavior: transient enhancement of DA in accumbens highlights behaviors that led to it. Enhancement of DA may occur by inhibiting DA uptake or enhancing its release. The accumbens is part of the motivational loop.
What are the characteristics and causes of: chorea, athetosis, hemiballismus, Parkinson’s disease? How does pathology of dopamine neuromodulation fir in these conditions?
Chorea: (excess DA) involuntary jerky movements due to death of indirect striatal neurons. Can't inhibit undesired movements. All possible movements are executed.
Athetosis: (excess DA) snakelike writhing of limbs, loss of indirect striatal neurons, lose inhibition.
Hemiballismus: (excess DA) unilateral flailing of limbs due to lesion of subthalamus by a virus. Reduces inhibitory control over thalamus and cortical output.
Parkinson's disease: dopamine deficiency due to death of dopaminergic neurons in substantia nigra. Rigidity, tremor, inability to switch behaviors.
What are the general functions of the direct and indirect pathways of CS loops?
The interplay of the two pathways allows you to select a particular response from a variety of options.
Internal globus pallidus (the Great Inhibitor) inhibits output of motor programs from thalamus to cortex.
In the direct pathway, the striatum inhibits GPi, in turn reducing the inhibition of the thalamus. Less inhibition of the thalamus leads to greater activity in the cortex, therefore more movement. Direct: inhibit the inhibitor.
Subthalamus normally stimulates GPi to inhibit thalamus.
In the indirect pathway, the striatum inhibits GPe. GPe inhibits STh, which dis-inhibits GPi. This leaves it free to inhibit the thalamus, resulting in lower cortical activity and less movement. Indirect: dis-inhibit the inhibitor.