WEEK 2 Flashcards
dopamine hypothesis
- psychosis is characterized by aberrant DA activity
- amphetamines and cocaine induce hallucinations and delusions in people via DA release. if given to a schizophrenic patient, their sxs would get worse.
- there is a higher D2 receptor density in schizophrenia, suggesting higher levels of DA.
- l-dopa is taken up quicker in patients with schizophrenia
- the degree of sensitisation of the mesostriatal DA system is linked to the severity of psychotic sxs.
DA pathways
- higher DA in the mesolimbic pathway gives rise to positive symptoms, and lower DA in the mesocortical pathway gives rise to negative symptoms
prediction errors and DA release
= dopamine-dependent signals that play a role in learning. the mesolimbic dopaminergic regions are important here.
- the nicer the reward, the higher the DA signal. the DA signal eventually shifts in time from reward to prediction signal. there’s a peak of DA release once the predictor stimulus appears, but once the reward is given as expected, there’s no increase. when a reward is predicted but not given, DA release decreases to below normal levels.
Miller’s hypothesis
= the process of acquiring the associations necessary for learning a conditioned response in an experimental animal depends on the presence of DA. in schiz patients, the excessive supply of cerebral DA may facilitate associations to the point where unrelated features are associated and treated as if they were meaningful combinations.
aberrant salience
in schiz patients, a stimulus that may not be meaningful evokes DA firing. when something is salient, inference is required to account for odd experiences so they can be interpreted in a meaningful way. so dysfunctional inferences start occuring. when beliefs become strong, individuals overlook evidence that could lead to disconfirmation.
antipsychotics and aberrant salience
when aberrant salience becomes distressful, tx is needed. antipsychotics block salience and subsequently support extinction and unlearning. side effects include loss of motivational salience of normal events.
reinforcement-related speeding
if something is reinforcing and there’s a potential reward following it, people will respond a lot faster to it.
- in patients with FEP, this is aberrant. they tend to respond to neutral stimuli faster than controls because of inappropriate motivation
unovershadowing
increasing expectancy associated with an absent stimulus
brain function and learning: caveats with studies
1) it’s possible that standard brain activation patterns may be present in psychosis but partially obscured by greater noise
2) brain signals may be more sensitive to real group differences than behavioral measures
3) patients may achieve comparable levels of performance to control subjects by performing alternative or compensatory neural strategies outside of areas of interest
4) could be due to the nature of the task - differences may become visible once task demands increase
hedonic experience and schizophrenia
- study found that schizophrenic patients report liking or enjoying positive things just as much as controls. it seems like they have consummatory pleasure (in the moment) but have difficulty anticipating pleasure in the future, which explains their anhedonia. they may like the taste of chocolate, but may not have the drive to go to a candy store to buy some.
anticipatory pleasure
= the act of predicting pleasure or enjoyment in the future, or “wanting”
- individuals with schiz struggle with this. they show lower activation in the ventral striatum when presented with reward-indicating cues. decreased activation is inversely related to the severity of negative symptoms. typical antipsychotics also decrease that activation.
how to measure reward anticipation:
1) learning task (murray)
2) monetary incentive delay task (MID)
value-effort computation
= the value of a reward or desirable outcome. this includes the positive or rewarding properties of an outcome as well as the internal stage of the organism. for example, the value of chocolate when someone’s on a diet may be different. there’s also the question of how much work it will take to get that outcome - is it worth it?
- individuals with schizophrenia struggle with generating, maintaining, and updating mental representations of value. there are issues with reversal learning of learned rules, and tasks that require rapid integration of info about rewards and punishment across trials in order to update value representation.
- study found that people with schizophrenia with severe negative symptoms were less likely than controls to do more effort when the outcome of a reward was certain: they may have computed the effort was not worth it, when, in fact, it actually was the most salient.
auditory hallucinations
= perceptions in the absence of external stimuli
- 60-70% of patients with schizophrenia experience them
- derogatory voices: up to 25% have attempted in response to them
- 25-30% of patients are refractory to treatment
2 hypotheses of auditory hallucinations
1) like epilepsy, the brain fires spontaneously in the auditory cortex. so the hearing parts are firing spontaneously, and as a result you start hearing voices
2) a lot of the time, we think in words. most of the time, we’re aware of it. in schizophrenia, there’s a lack of awareness of our own thinking, so the brain interprets it as an external voice.
capturing auditory hallucinations in an MRI scan
- have a patient who is hallucinating placed in the machine with the scanner off so there’s no noise.
- they then hear a noise that lasts 2-3 seconds. during this we acquire a brain image.
- we then ask: what were you thinking when the noise started?
- let them rest for 20-30 seconds (adjustable since we want to avoid anticipation). here we can get the experience of them lying in silence, at a relaxed state.
- the noise starts again for 2-3 seconds, and another image is captured.
- we then ask: what were you doing right before the noise started?
- we repeat this multiple times (60-100) so we can pick out times when the patient is experiencing hallucinations vs. when they are not.
- this works because there’s a delay in the brain when looking at imaging signals related to a particular stimulus. if i flash a light in your eyes, the increase in your visual cortex will occur 2-6 seconds after the light is flashed. so we can use the delay to capture their experience in silence.
MRI scan results: auditory hallucinations
- both the auditory cortex and the inferior frontal gyrus, Broca’s area, which is responsible for generating speech were active during hallucinations. so both the hearing and speaking parts of the brain are engaged.
- when hearing someone talk, both healthy controls and people have activation in the auditory cortex. there are no differences there. however, when asked to generate inner speech, healthy controls deactivate the auditory cortex. in patients with hallucinations though, this deactivation is weaker. so they switch it off a little bit, but nowhere near the same extent as healthy people. so monitoring your own thinking isn’t as efficient in patients with schizophrenia prone to auditory hallucinations.
structural connectivity: white matter and hallucinations
- wherever two parts of the brain are working together regularly, you get an increase in white matter connections.
- the superior longitudinal fasciculus links the frontal to the temporal cortex.
- patients who are currently hallucinating tend to have a higher integrity in the superior longitudinal fasciculus compared to patients who have hallucinated in the past and patients who do not hallucinate.
predictive and forward models
= when you plan to do something, your brain makes a prediction of the sensory consequences of it and feeds it into the appropriate sensory cortex
- impaired in patients with schizophrenia
examples of predictive or forward models
1) when you move your eyes from left to right, the world remains stable. this is because the brain predicts when we’re making an eye movement. however, if you suddenly poke yourself in the eye, the world shifts a bit.
2) you can’t tickle yourself because your brain is anticipating it. your brain will send a signal from the motor cortex to the sensory cortex of the foot and say: hey! that’s just me!. when someone else does it, it’s unpredictable, so you get the full effect.
HOT vs COLD neurocognition
COLD:
- perception
- memory
- reasoning
- attention
- visual processing
- problem solving
HOT:
- information processing within the social and emotional world
4 key social cognitive functions
1) theory of mind
2) emotion perception
3) social perception
4) attribution style
social perception vs. social knowledge
- social perception is the ability to use social cues to infer the situational events that generated the social cues. identifying interpersonal features in a social situation, like intimacy, status, mood, relationships between people.
- social knowledge is the awareness of the roles, rules, and goals that characterise social situations and guide social interactions
- both are closely associated, because the identification of social cues requires knowledge of what is typical in a given situation.
Michael Green’s social cognitive subdomains
1) experience sharing: mirror processing that takes place while watching another person
2) emotion experience: the response you have when seeing an unpleasant or pleasant image.
3) emotion regulation: self-reflective strategies such as reappraisal
