Neural Networks and Cognitive Control (3)

Question 1

What is schizophrenia?

Answer 1

• a chronic and severe mental disorder that affects how a person thinks, feels, and behaves
• people with schizophrenia may seem like they have lost touch with reality
• affects cognition, feelings and behaviour

Question 2

What are some schizophrenia facts?

Answer 2

• about 1% of Canadians
• more frequent in males
• late adolescence and early adulthood are peak onset periods (25 m and 27 f)

Question 3

What are positive symptoms?

Answer 3

• psychotic behaviours not generally seen in healthy people

- hallucinations, delusions, though disorders, movement disorders

Question 4

What are negative symptoms?

Answer 4

• disruptions to normal emotions and behaviours

- “flat affect”, reduced feelings of pleasure, difficulty beginning and sustaining activities, reduced speaking

Question 5

What are the cognitive deficits of schizophrenia?

Answer 5

• attention: impairments in endogenous selective attention
• working memory: especially with high load, distraction or manipulation
• episodic memory: impaired use of contextual cues to organize information at encoding or retrieval
• executive function: impairments in set switching, planning, and dual-task coordination

Question 6

What is Braver, Barch and Cohen (1999)’s hypothesis?

Answer 6

• perhaps many of the cognitive deficits in schizophrenia can be accounted for by a single underlying impairment of cognitive control: impaired dopamine fating of working memory

Question 7

What are the participants?

Answer 7

• 16 matched controls
• 16 participants with schizophrenia: neuroleptic-naive (experiencing first hospitalization for psychotic symptoms and not treated with medication yet)

Question 8

What is the cognitive control task?

Answer 8

• AX-CPT
• see a sequence of letters (cues and probes)
• target is an X that followed an A

Question 9

What is the model?

Answer 9

• cognitive control model with dopamine gating

- impairment: noisy dopamine gating unit

Question 10

What is the model fitting?

Answer 10

• account for performance of controls with intact model

- account for performance of participants with schizophrenia with impaired model

Question 11

What are the two conditions?

Answer 11

• short delay condition: cue, short delay, probe (or target if X)
• long delay condition: cue, long delay, probe (or target if x)

Question 12

What is context sensitivity?

Answer 12

• comparing correctly pushing X and incorrectly pushing X
• AX hits vs BX false alarms
• ability to use context (A or B) to guide correct response to X

Question 13

What is context cost?

Answer 13

• compare reaction time of AY and BY trials
• should be able to response fast on BY trials because B indicates that even with X, target response is not necessary
• cost of context (A or B) on speed of response to Y

Question 14

What does the gating model look like?

Answer 14

• cue: needs to be stored in prefrontal cortex/working memory
• gating unit (DA): decides if new information should be let into working memory or not
• context (PFC): working memory maintenance that applies top-down control to probe and output

Question 15

What is affected in an impaired gating model?

Answer 15

• the gating unit is noisy

- it can be modeled this way

Question 16

What does the behavioural data for context sensitivity look like?

Answer 16

• patients have a lower sensitivity to context
• fewer AX hits and more BX false alarms
• interaction with delay: even lower sensitivity at long delay

Question 17

What does the behavioural data for context cost look like?

Answer 17

• patients have a smaller context cost: meaning the difference in reaction time between AY and BY trials is smaller
• interaction with delay: even smaller context cost at long delay
• (more cost means you are keeping track of things well)

Question 18

What does the model data show?

Answer 18

• use of intact model and noisy gating model

- the main effect and interaction are similar compared to the human data

Question 19

What does normal function of the DA gating unit look like?

Answer 19

• low tonic (stable) activity: keeps gate closed and maintains WM contents
• high phasic (pulse) activity: opens gate, updates WM contents

Question 20

What does the impaired function of the DA gating unit look like?

Answer 20

• higher tonic activity: gate may open randomly, WM contents may be lost
• lower phasic activity: gate may fail to open, WM contents may not be updated

Question 21

How are the results explained by the impaired function?

Answer 21

• cost isn’t shown because patients fail to store for context (A or B)
• interaction effects result because information is more likely to leak out over a longer period of time after the probe

Question 22

How does this help us understand schizophrenia?

Answer 22

• a single unified explanation for a collection of seemingly disparate symptoms, including impairments of attention, working memory, episodic memory, executive function
• a proposed neural impairment that accounts for cognitive deficits

Question 23

Why is computational psychiatry important and useful?

Answer 23

• neural network models provide an explicit, mechanistic account of cognitive processes in terms of their neural implementation
• can explore hypotheses about the neural basis of mental illness by creating focal impairments in models and investigating consequences
• leads to improved diagnosis, treatment and management