volitie 2 Flashcards
what happens if there is damage to the pathways to the M1
both pathways contribute to voluntary action
damage to these pathways can impact the capacity to exercise volition
What is optic ataxia
ataxia - lack of coordination
optic - visual
problems using visual information to coordinate movement
which pathway is optic ataxia associated with
optic ataxia is associated with damage to the parietal pathway - involved in sensory guided actions
damage through stroke - disrupts the flow of info in this pathway
parkinson’s disease
difficulty performing voluntary actions
tremor
stooped posture
difficulty getting movements up and running
which pathway is parkinson’s associated with
damage to subcortical pathway
how does parkinson’s affect the brain
loss of dopamine producing cells in substantia nigra - these cells project up to the striatum
striatum represents the input to the basal ganglia
if there is less dopamine producing cells, basal ganglia is not able to do its job - so signals are not being sent up to the cortex
disorders in the experience of voluntary action
unusual experiences of control where the experience of movements seems to be dissociated from what they are able to do
there are patients with disorders in which they experience of action seems to be abnormal
patients experience a persistent dissociation between the ability to act and the experience of action
anosognosia
lack of awareness of disease
different types of anosognosia:
- anosognosia for hemianaesthesia - sensory loss - no longer able to experience sensation in certain parts of the body but patient seems to be unaware of that
- anosognosia for cerebral achromatopsia - loss of colour vision - feels they still have colour vision
anosognosia for hemiplegia AHP
patient unable to move a particular body part bc it’s paralysed
but patients is unaware of this deficit
where is AHP located in the brain
lesions to right perisylvian regions
paralysis on opposite side
if right side is damage, left side of body is paralysed
AHP example
presented patients who had anosognosia and without with a screen
asked to place paralysed hand behind screen
on screen is live video footage of hand that is told is their paralysed hand - but it’s just a rubber hand
patients instructed to move the hand, let experimenter move their hand, remain stationary
so for each of these 3 instructions the rubber hand would either move or not move
patient had to say whether or not they moved after each trial
RESULTS
when the patient is being asked to make movement and rubber hand on screen doesn’t move - they still report they have moved
conclusions
patients rely on their intentions to move
intending to perform movements is sufficient to generate a feeling of having actually moved
schizophrenia
positive symptoms - presence of something that shouldn’t be there
delusions
hallucinations
passivity symptoms - delusions of control
they can move but they feel like something else is controlling them
not a problem with a control of action - problem with experience of action
study on passive symptoms
tested healthy controls
patients with delusions
patients without delusions
they made hand movements that they could not see - they saw visual feedback abt the movements presented onto a screen
movements they saw on the screen were either own movements shown in real time, movements of experimenter performing similar movement to ppt or movement of experimenter performing different movement
was the movement on the screen your own or the experimenter’s
when the experimenter was doing the same movements, all groups errors shoot up but especially in delusional patients - difficult to judge whether movement is their own
experiment of delusions of control in schizophrenia
3 groups
patients with delusions
patients without delusions
healthy controls
made movements and saw feedback of movements
1 condition: feedback was presented on a different level of spatial distortion - saw movement in perfect alignment or feedback was rotated to an increasing degree
2 condition:
introduced a time delay between the movement that was made and movement shown on screen - time delayed increased as condition progressed
do the hand movements on screen match your own movements
patients with delusions in both conditions take much longer to recognise discrepancies between what they are doing and what they are shown on the screen
so if feedback is rotated, they take longer to detect
if there is delay, patient with delusions take longer to detect delays
why do distortions in the experience of action happen in Sz patients with delusions
inability to predict consequences of their own movements
what cognitive processes give rise to the normal experience of voluntary control
the comparator model - how one controls movements and if we are in control of our actions or not
prediction gives us a sense of voluntary control over our actions
the experience of voluntary control is based on our ability to predict sensory consequences of movements
when we make a movement we start with a goal and we are in a desired state
controllers can issue a motor command - to achieve a desired state
motor command gets sent from motor cortex to spinal cord and to muscles
that produces movement
that is producing sensory feedback
person is able to estimate the state of the system - where their body is
when motor command issue is sent, a copy of motor command is read by predictors and they use this command to predict that the state of the system is going to be
if predicted state doesn’t match the desired state then system needs to put breaks on and update motor command
if we were able to predict accurately what happens, this tells the system we were in control
prediction is crucial for giving us a sense of control
whats the comparator model like in SZ
in sz there is problem with predicting future states
what evidence is there that patients can’t predict the future sensory consequence of their movements
when we can predict the consequences of our actions accurately, our brains don’t care about the sensory information - they ignore it
if we can’t predict, our brain processes that info - Sz patients can tickle themselves
tickle in Sz patients
sz patients with and without delusion symptoms and healthy controls
apply a tactile stimulus to hand or experimenter do it for them
rate how tickly it was
control experienced self applied tactile stimulation as less tickly than when it was applied by experimenter
same with non-delusional patients
those with symptoms don’t report any difference in the tickle sensation
