Basal Ganglia & Cortico-striate Loops Flashcards
Are basal ganglia bundles of white or gray matter? What hemisphere are they in? What are they?
masses of gray matter in cerebral hemispheres that surround the thalamus include: caudate putamen nucleus accumbens globus pallidus subthalamic nucleus substantia nigra, ventra tegmentum
Corpus striatum= _________= ________
striatum= caudate plus putamen
Where does the caudate extend into? What nucleus does it include
Head, body & tail extend into temporal lobe
Nucleus accumbens= ventral & anterior portion of caudate
What is the putamen separated from and by what?
separated from caudate by internal capsule (passes through windows b/w cell bridges)
What are the two globus pallidi and where are they in relation to putamen?
internal & external; medial to putamen
What is the subthalamus?
midbrain nucleus that interconnects w/globus pallidus
What structure contain pigmented cells & project to striatum?
substantia nigra, pars compacta (SNpc)
Why is the substantia nigra pars reticulata similar to GPi?
they both receive striatal input & inhibit thalamus via GABA in pathway
The basal ganglia form a _____
FEEDBACK LOOP
Motor/cognitive cortical programs are funneled through what?
striatum & globus pallidus
Globus pallidus projects to _____ which in turn conveys info back to _____ motor & _______ programs
thalamus, frontal cortex, refine cognitive
What are the roles of the substantia nigra and subthalamus in this loop?
both modulate loop activity to select or reinforce certain motor/cognitive outputs
What is used to excite and thus balance the activity of direct & indirect pathways in relation to motor/cognitive outcomes? What about to inhibit it?
excitatory= gluatmate inhibitory= GABA
What structure inhibits motor/behavioral output of the thalamus & cortex?
internal globus pallidus
What structures modulate impact of GPi on thalamus via direct or indirect pathways?
cortex, striatum & subthalamus
In relation to the cortex, striatum & subthalamus modulating the impact of GPi on the thalamus, what is the direct vs indirect pathway?
both are from the striatum
direct pathway goes to internal GB & facilitates behavioral responses
indirect pathway goes through external GP & subthalamus then depresses behavioral responses
*they are antagonists to e/o
How does the direct pathway of motor/cognitive modulation work?
cortex activates striatal neurons–> inhibit GPi–> less inhibition of thalamus by GPi= more activity in cortex= more movement!
How does the indirect pathway of motor/cognitive modulation work?
cortex activates different set of striatal neurons–> inhibit GPe
STh activates GPi to inhibit thalamus but GPe inhibits STh
disinhibition of GPi= general inhibition of thalmo-cortical activity
To determine onset, offset & scaling movements the striatal output does what 2 things?
permits intended movements (inhibits parts of GPi via direct path)
inhibits unintended movements (increasing GPi activity via indirect path)
What neurotransmitter activates direct & indirect pathways?
DOPAMINE!
activates pathway via D1 type DA receptors and inhibits indirect pathway via D2 type DA receptors
Where does dopamine come from? Where does it this structure project axons to to regulate direct & indirect pathways?
substania nigra; it projects axons to striatum
Besides activating or inactivating pathways how else does DA regulate direct & indirect pathways?
increases signal-to-noise ratio in striatum= enhances strong inputs & suppresses weak ones
By balancing direct & indirect pathways, what does this lead to in relation to DA?
this organizes & builds internally generated behaviors= can be reinforced by DA= become stereotypic behaviors
The distinct loops formed by the cortex, basal ganglia & thalamus allow what? What 4 things are these reliant on?
parallel processing of affective, cognitive & motor components of behavior
vision, motivation, execution, motor/premotor
What makes up the motivational loop?
vmPFC, orbitofrontal & anterior cingulate cortex, amygdala, hippocampus & all of them projecting onto nucleus accumbens/ventral striatum
What does the motivational loop do?
regulates motivational-emotional aspects of behavior
translates motivation into action by transferring reinforcing signals to motor & executive cortico-striage loops= habits form
What makes up the executive loop?
dorsolateral PFC & association cortices which project to caudate
What form of memory is involved in the executive loop?
working memory
What is executive function?
selection of appropriate movements, allocation of attention, planning, organizing, regulating, monitoring of goal related behavior, switching behavior set
internally generated movements
What makes up the motor/premotor loop?
Which three structures of the motor/premotor loop project updated info back to the same cortex?
primary, premotor, supplementary & somatosensory cortex which all project to putamen (putamen, GP & thalamus project updated programs back to same cortex)
What is the motor/premotor loop for?
programming & initiation of internally generated movements
controls movement direction & scaling (hammering a nail)
What makes up the visual loop?
extrastriate cortex (inferotemporal & fusiform gyrus) & projects to body & tail of caudate
In the visual loop, where does the caudate project back to?
through globus pallidus & thalamus to visual & prefrontal cortex (esp executive portion)
What does the visual loop form?
more elaborate visual categories (more elaborate than those of simple/complex cells in visual cortex)
What does the visual loop do?
integrates visual input into declarative & procedural learning of tasks
Visual info from visual association cortices is looped to where?
into body & tail of caudate & then back to cortex (reinforced by DA)
*pathways from visual to executive/motor loops is part of basis for learning to associate appropriate response w/each stimulus alternative
What are the three types of memory?
declarative, emotional, procedural (non-declarative) memory
Declarative memory: part of brain, what is it for?
hippocampus-limbic
episodic memories are stimulus-stimulus associations that are consolidated into semantic memory in cortex
Emotional memory: part of brain, what is it for?
amygdala
fear conditioning by association of stimulus & aversion
Procedural memory: parts of brain, what are the parts of the brain for procedural memory for?
cerebellum: combines learned movements to produce well-executed motor skill behavior
basal ganglia: habit formation= association of motor responses w/reinforcing stimuli to build repertoire of motor actions to be triggered by appropriate environmental stimuli
What are the 4 characteristics of procedural memory?
are implicit, rigid, procedural &suitable to guide cue-based & egocentric navigation
Parallel loops of procedural memory operate to facilitate what three things?
category representation
action selection
instrumental & reward learning
What is category representation associated with?
stimulus categories derived from association sensory cortex & then linked to appropriate behaviors
What is action selection?
loops select & group neuronal populations that focus on desired motor response
What is instrumental & reward learning?
conditioning behavior to novel cognitive or emotional cues; task switching to more appropriate behavior, DA reinforced
What is category representation crucial for?
SURVIVAL! essentially being able to tell not harmful from harmful; link determination to appropriate behavior
Declarative visual categories depend on ____ & _____ regions involved in working memory & executive attention
hippocampus & prefrontal regions
Declarative visual categorizing skills are usually attained within how many trials?
ONE
Procedural visual categories depend on _____ using ______
visual cortico-striate loop, tail of caudate
Visual cortico-striate loop of procedural visual categories branches to what two other loops and integrates w/what?
executive & premotor loops & integrates w/executive control
How does action selection work?
phasic DA activity to striatum selects responses from motivational, executive & sensorimotor loops & combines them to form goals, actions & movements
Instrumental learning involves ____ & action; ____
goal & action; stimulus reponses
How do habits develop in relation to instrumental learning?
w/a shift from goal-directed action to stimulus-response association & behavior becomes inflexible
What are the three DA pathways that project from midbrain (and where do they project to) and modulate behavior responses by associative learning & reinforcement?
nigrostriatal: SN projects to striatum
mesolimbic: ventral tegmentum projects to nucleus accumbens
mesocortical: ventral tegmentum projects to prefrontal cortex
DA alter both _____ & _____ cells to increase their _______ which ______ corticostriatal connections & = conditioning of a stimulus to a motor pathway
presynaptic & postsynaptic; excitability; strengthening
Before learning occurs, the mosaic of broken mirrors model allows for what?
association of any environmental cue w/any action!
Under incorrect learning, inappropriate plasticity in indirect pathway leads to what?
inappropriate inhibition & diminished facilitation= talk-related elements become increasingly noisy & less distinct against background compared even to naive processing
What is naive, pre-learned state?
processing through basal ganglia is undifferentiated
Reward learning is condition by _____ instead of _____.
stimulus w/a reward or outcome rather than w/motor response itself
Reward learning is mediated by what other loop?
motivational loop (vmPFC, orbitofrontal cortex & nucleus accumbens)
The vmPFC receives info about what from what other regions?
info about ‘value’ of response from OFC, amygdala & hippocampus
What is the OFC the majory sensory cortex for?
taste & small, affective aspects of touch & temp, & vision
What neurons located where respond to food, water & success?
mesolimbic dopamine neurons in ventral tegmentum
What interacts to provide top down reward & reinforcement along successive spiraling connections?
three frontal loops (motivational to executive to motor loops of basal ganglia)
In learning a task subjects use _____ & _____ loops to learn through following instructions
motivational & executive
New instructions initiate what?
prefrontal activity again
External stimuli stimulates what? What is it associated with?
stimulates mostly sensorimotor loop & are associated w/willful behavior
Internal triggers stimulate what? And are associated with what?
activity mostly in associative & limbic loops & associated w/motivationally derived behavior
Predominance of motivation-based, internally cued actions leads to what?
actions that are repetitive, internally guided, aimless, resistant to interferenceby external stimulus= stereotypic= TOURETTE’S SYNDROME
