pharm of parkinson's Flashcards
Feedback controller
system in which environment first change and then controller causes a change to compensate
slow and often overcompensate
example of feedback controller
thermostat that can turn on heater or cooler to keep room at steady temp
decr temp –> turn on heater
but time and sense delay causes overshoot and turns on cooler
feedforward controller
uses sensory data to calculate state coming at future time (predicted state)
cues to predict future system based on internal model
feedforward controller example
thermostat turn on heter or cooler to keep room at steady temp
can sense window open, outside temp to predict change in room temp and act pre-emptive to counteract temp drop
therefore, controller has model of system and calculates how changes in one variable will affect output and how controlled variable will affect same output in opposite direction
ddifference between feedback vs feedforward
feedback = react to a change
feed forward = plans ahead and make changes
if use feedback instead of feedforward –> you get oscillation or intention tremor
role of parietal cortex in matching joint position sense with visual coordinates for reaching motion
map from occipital to parietal
how does parietal association cortex guide you to reach target
- stream of info for “where” advances dorsally from occipital cortex to parietal lobe
parietal association cortex = btwn visual “where pathway and joint position”, it senses info from somatosensory cortex
then integrates info about target and somatosensory info about limb position
fed into motor cortex in frontal lobe to guide movement of libm to target
where are parietal association cortex located
located around intraparietal sulcus
can calculate difference btwn target and joint angles necessary and send to premotor cortex
describe brodmann area 6
calculates difference btwn current location and desired location so command for proper joint angle changes to reach desired location
sent info to primary motor cortex
what is meant by internal model of the system to match joint angles to visual coordinates
specifies predictions about what joint angles will achieve given location in visual coordinate
purpose of cerebellum adapting cortical networks to change relationship btwn joint position sense and visual coordinates
to fix mismatch btwn visual coord of target and joint angles to get to the target that was different than expected
how does cerebellum make corrections
connection btwn parietal and premotor cortices causes re-calibration so
if visual coord (like adding prism) and given set of joint angles differ, rain adapt (ADAPTATION DEPENDS ONLY ON CEREBELLUM)
cellular mechanism of cerebellar correction for adaptation
pathway from parietal cortex to premotor for adaptation
parietal cortex sends cortico-pontine fibers thru internal capsule and synapse on ponto-cerebellar neurons
reach contralateral pontine gray that send out cerebro-cerebellum’s mossy fibers
mossy fibers synapse on granule cells whose paralell fibers synapse on purkinje
purkinje send output to dentate –> thalamus –> motor and premotor cortex
what are mossy fiber input a reflection of ?
mossy fiber input = current state of parietal cortical mapping btwn visual and proprioceptive signals
what else sends fibers to purkinje cells besides mossy fibers
1) inferior olivary nucleus sends climbing fibers
2) simultaneous climbing fibers + parallel fibers causes synaptic strength changes of parallel-purkinje synapses
what drives inferior olivary activty
what is the purpose of this
1) GABA-ergic neurons from deep cerebellar nuclei
and
2) multiple sensory modalities (prop and visual feeback) which differ for subregions of ION and project to diff functional zones of cerebellum
therefore, also an additional reflection of parietal cortex mapping of visual and proprioceptive coordinates
what happens if proprioceptive and visual feedback exactly what current parietal network would predict,
parietal network convey to ION would cancel out visual feedback so NO CHANGE IN ION ACTIVITY
function of ION what drives expected vs observed state
compares expected state = deep cerebellar nuclei as reflection of parietal network with
observed state = visual and prop feedback
what happens if prop feedback and visual feedback different than what expect
describe LTD
signal generated by ION proportional to magnitude of difference
error signal carried by climbing fibers to cerebellar cortex to initatie complex spikes in purkinje cells
simult parallel + climbing fiber on purkinje undergo synaptic change (LTD) to decr efficacy of parallel fiber to fire Purkinje (deactivate error movement)
How does ION contribute to adaptation
inferior olive fires when there is error/mismatch btwn observed and intended state
describe VTA
where is it located
what is housed in it
important where
located in midline at floor of midbrain
contains DA cell bodies of mesocorticolimbic-DA system
important in cognition, motivation, drug addiction, emotion
role of DA neurons in VTA/SNc to convey reward prediction errors to striatum
describe what happens first
1) push button on vending machine
2) what you want comes out and spike in AP by DA neurons
3) after few trials, you learn to associate symbol on machine with reward so fire DA AP each time button (reward predicting cue) seen
4) over more trials, after relation btwn cue and reward established and expected, DA release stops
mechanism of how DA neurons in VTA/SNc to convey reward prediction errors to striatum
pathway of what happens
DA/basal ganglia function similar to ION
both convey predictions about rewards
1) DA neurons convey current predictions about rewards (present state of cortico-striatal network)
2) additional input to SNc/VTA convey info (efference copy directly to subst nigra) about actual reward experience
3) unexpected reward strongly activate DA neurons
4) DA releases into striatum to alter activity and plasticity of cortico-striatal network
5) networks that correctly predict error reinforced and those that don’t diminsihed
how is DA/basal ganglia similar to ION
formation of action sequences via recalibration of direct and indirect paths to correctly predict rewarding behaviors
also state of revised network conveyed via striosome to VTA/SNc to now predict reward and VTA/SNc won’t discharge in response to discrepancy btwn expected and observed rewards so corticostriatal network intact until next unexpected reward
compare ION in cerebellum vs VTA/SNc in corticostriatal
1) type of error signal
2) return projection
3) comparator?
4) what conveys prediction
5) critic of …
1) cerebellum = ION; basal ganglia = DA neurons
2) cerebellum = reach ION directly from deep cerebellar nuclei or indirect via red nucleus to find error btwn expect and actual
basal ganglia = reach DA from groups of stratal medium spiny neurons in striosomes to find error
3) both comparators
4) cerebellum = GABAergic inhib neurons via deep cerebellar nuclei to IO
basal ganglia = GABAergic inhib nurons via striosome to SNc
5) critic of parallel-purkinje vs critic of cortico-striatal
