Lecture 11: functional brain changes in sz – Part II Flashcards
In terms of executive function, people with SZ have problems with _____________________
working memory, planning, selective attention
People with SZ show activity in relevant regions, what are they?
- Dorsolateral and ventrolateral prefrontal cortex (DLPFC and VLPFC),
- anterior cingulate
- and parietal cortex
[But, sometimes show hypo-activation (too little) or hyper-activation (too much) especially in DLPFC]
Why do we sometimes see increases and sometimes decreases?
- There is an impairment in the function of the frontal lobe.
- You can think about blood flow and task difficulty
everyone has the same baseline, and as it gets harder you increase activity - but for SZ, they cannot have that same increase (cannot recruit additional ressources) in activity, therefore in comparison, it seems reduced.
- So in easier task, SZ recruit great ressources but cannot continue to do so when the task gets harder.
In other words what are the two theories as to Why do we sometimes see increases and sometimes decreases?
Theory #1:
1) Low working memory (task)
- Both groups recruit similar frontal resources
2) High working memory (task)
- SZ cannot recruit additional resources
Theory #2:
1) Low working memory (task)
- SZ recruit greater frontal lobe resources to do the same task
2) High working memory (task)
- SZ cannot recruit additional resources
What were the results of the Working memory and DLPFC function (Callicott, 2003) study.
Methodology:
- N- back task (DLPC)
- 14 patients/14 controls
- They see a series of letters and they are asked either to (0-back) repeat current letter.
- Or say the letter that was one back, so they hear the letter A and they have to say H (because that was the letter before the A)
- Or say 2-back (2 letters before the letter they see now).
- Patients and controls performed equally on 0-back
- SZ performed less well on 2-back (classic finding)
- SZ are using additional ressources.
- They have limited ressources in frontal lobes but for SZ they need to recruit these for lower-memory load task. however, when task becomes more difficult, they cannot push those ressources, therefore you see a decrease.
- **For SZ, we see a decrease in activity in DPLFC because they cannot push for additional ressources.
- You see this phenomenon in relatives of SZ
Unaffected siblings of SZ on the 2-back cognitive task (Callicott, 2003) main findings were:
- No differences in working memory performance (they were able to perform equally well to the controls)
- But, greater activity in frontal cortex in unaffected siblings
- Suggests low-level frontal lobe dysfunction even in unaffected siblings [which means they:]
- Must engage additional frontal resources to achieve the same level of performance
Discuss episodic memory in SZ
1) People with SZ do not have severe hippocampal memory deficits
- Recall is reduced compared to controls, but not as severe as patients with hippocampal lesions, or Alzheimers’s
- Recognition is relatively okay
2) But impairments in encoding and/or retrieval
- No effect of delay on memory deficits
- No benefit of semantic relatedness when learning words
3) Their deficits more linked to the frontal lobe
- For example, prefrontal cortex interactions with hippocampus for episodic memory retrieval.
People with SZ do not have severe hippocampal memory deficits, however their deficits more linked to the __________
frontal lobe
What were the 2 main conclusions from the encoding and retrieval task (Ragland, 2009) for SZ?
Encoding:
1) Frontal resources not adequate to assist encoding
2) Recruit additional regions (dPMC and cingulate)
Retrieval:
1) Frontal resources not adequate to contribute to retrieval
2) Recruit additional frontal polar regions
Explain the findings or the At risk groups (Crossley, 2009) N-Back tasks study.
- They tested 3 groups: people who do not have yet SZ (1st episode) , people who are at high risk and controls.
- Results showed equal performance across groups.
- All groups = greater frontal and parietal activity for 1- and 2-back
The only difference that they saw amongst groups is that 1st episode also had greater activity in auditory regions
So then they focused on why that is, and they saw that 1st episode have greater correlated activity in auditory and frontal, which could be because of one or two things:
- Greater reliance on auditory rehearsal
- Reduced inhibition of inner speech
How did Honey, et al., (1999) looked at the effect of medication on frontal lobe function based off the knowledge that reduced activity in frontal lobe is related to poorer executive function, episodic memory and decision making. They specifically looked that the right DLPC when patients were performing the N-Back task on an old medication than a new one.
What were the results and implication of the study?
1) DLPFC activity greater for 2-back compared to 0-back
2) ↑ DLPFC activity after 6 weeks treatment with 2nd generation antipsychotic (reduced effect on frontal dopamine)
This suggest that the new meds might be more beneficial and this is further evidence that dopamine is involved in the 2-back tasks.
What have we learned in terms of Emotion processing for SZ from Gur, (2007) and lePage (2011)
- There’s an over-activation of the emotion system (amygdala) which results in a reduction of emotional expression (flat affect).
Gur (2007)
- People with SZ show greater activity in the amygdala
- Greater amygdala activity related to greater flatness of affect (SANS scale)
LePage (2011)
- People with SZ still show greater activity in the amygdala for fearful faces
- Amygdala activity is related to severity of flat affect
In conclusion, what can we take from all these studies on brain functioning in SZ?
- Hallucinations related to abnormal activity in STG (Superior temporal gyrus) auditory regions
- Abnormal activity in prefrontal cortex during memory and executive function tasks
- Increased amygdala activity to fearful faces - related to flat affect
What are the three things we can speculate about the abnormal activity in prefrontal cortex during memory and executive function tasks?
- It may be lower than controls for harder tasks and higher than control for easier tasks.
- May improve with medication
- Abnormal interactions with other brain regions (hippocampus) [the additional ressources in other brain regions]
