week 8 Flashcards
(28 cards)
What is the basal ganglia?
The basal ganglia are an old set of subcortical nuclei that modulate motor control, decision-making, and limbic processes via loops with the cortex and thalamus.
Which nuclei are part of the basal ganglia?
They include the striatum (caudate, putamen, nucleus accumbens), globus pallidus (internal [GPi] and external [GPe]), subthalamic nucleus (STN), and substantia nigra (particularly the pars compacta [SNc]).
How does the basal ganglia influence motor control?
It influences motor output by modulating thalamic activity and, in turn, motor areas of the cortex, essentially acting as an action selector.
What role does the basal ganglia play in relation to the prefrontal and limbic circuits?
It exerts influence on both motor as well as prefrontal and limbic regions, integrating motivational and cognitive signals into movement and decision-making.
What are the direct and indirect pathways in the basal ganglia?
The direct pathway facilitates movement by disinhibiting thalamic signals, while the indirect pathway suppresses unwanted movements by increasing thalamic inhibition.
How does dopamine affect the direct and indirect pathways?
Dopamine enhances the direct (D1 receptor-mediated) pathway to promote movement and suppresses the indirect (D2 receptor-mediated) pathway to avoid excessive inhibition.
What happens with neuronal loss in the substantia nigra pars compacta (SNc)?
The loss of dopamine-producing neurons in the SNc disrupts the balance of direct and indirect pathways, leading to movement disorders, notably Parkinson’s disease.
What are the cardinal motor symptoms of Parkinson’s disease?
The three main symptoms are akinesia/bradykinesia (slowed or absent movement), rigidity, and resting tremor.
How is L-DOPA used to treat Parkinson’s disease?
L-DOPA is a dopamine precursor that replenishes dopamine levels, helping to restore the balance between the basal ganglia pathways and improve motor function.
What effects can long-term L-DOPA therapy have on the basal ganglia circuits?
Chronic L-DOPA treatment may shift the balance back toward the direct pathway, but it can also result in complications such as dyskinesias due to overcompensation.
Besides Parkinson’s disease, what other basal ganglia pathologies are mentioned?
Other conditions include Huntington’s disease, hemiballism, and Tourette’s syndrome, often involving loss of striatal neurons or abnormal STN activity.
What loops do the basal ganglia form with other brain regions?
They form multiple loops connecting the cortex, striatum, pallidum, and thalamus, each loop participating in different functions such as motor control, cognition, and emotion.
How is reinforcement learning linked to the basal ganglia?
The basal ganglia use dopamine signals to reinforce behaviors based on reward or punishment, adjusting future actions to maximize positive outcomes.
How does reinforcement learning in the basal ganglia differ from learning in the cerebellum?
While the basal ganglia depend on reward-based reinforcement learning, the cerebellum uses error correction signals to fine-tune movements.
What does intracortical electric stimulation (ICS) demonstrate in relation to dopamine?
ICS in dopamine-releasing areas, like the nucleus accumbens, is reinforcing and shows that direct stimulation of dopamine pathways produces rewarding effects.
What is the affordance competition model?
It proposes that multiple potential actions are specified in parallel and then compete through biased selection rather than a strict serial “decide then act” process.
How does the affordance competition model differ from the classical view of motor planning?
Unlike the classical model where decisions are made before planning, the affordance model suggests that action selection and specification occur simultaneously in a dynamic competition.
What role does the dorsolateral prefrontal cortex (dlPFC) play in action selection?
The dlPFC is involved in evaluating costs and benefits, integrating cognitive control with motivational signals during the selection of actions.
What does “cognition leaking into the motor system” imply about free will?
It suggests that the conscious self may not be the initiator of actions but is instead informed about decisions that the motor system has already begun to plan.
What did Libet’s experiment reveal about the timing of conscious intention to move?
Libet’s findings showed that the brain’s readiness potential precedes the conscious awareness of the intention to move, challenging traditional notions of free will.
How have modern fMRI studies contributed to our understanding of decision-making pre-movement?
fMRI studies using pattern classification have decoded decision signals up to 10 seconds before subjects become aware of their intention to move, further questioning the role of conscious will.
How is mental imagery of movement related to actual motor execution?
Brain regions such as the premotor cortex and SMA are activated during both mental imagery and physical execution, indicating that similar neural pathways are involved in planning and imagining actions.
What are Brain Machine Interfaces (BMIs) and their potential application?
BMIs interpret brain signals—often those related to motor imagery—to control external devices, offering significant potential for rehabilitation and assistive technologies.
How do dopamine signals reinforce behavior?
Dopamine release during rewarding events strengthens glutamate transmission and facilitates long-term potentiation, which reinforces the neural circuits underlying the rewarded behavior.
