prefrontal cortex II Flashcards
what is BA10
frontopolar cortex
what is the gateway hypothesis of BA10
- Key distinction between stimulus-oriented (SO) and stimulus-independent (SI) attending
- Stimulus oriented – behaviour required to focus on current sensory input
- Stimulus independent – mental processing that accompanies self-generated thought
what is • Stimulus oriented
• Stimulus oriented – behaviour required to focus on current sensory input
what is • Stimulus independent
• Stimulus independent – mental processing that accompanies self-generated thought
• Patients with lesions to BA10 have deficits in …
• Patients with lesions to BA10 have deficits in multitasking on the 6 elements task (Burgess et al., 2000)
what is prospective memory
difficulty disengaging from externally driven behaviour to switch to an internal, goal-driven mode.
what did Burgess and colleagues do
Burgess and colleagues gave patients with different frontal lesions a multitasking task and found that patients with lesions in BA10 had problems with multitasking.
what did Gilbert and colleagues do
Gilbert and colleagues also presented neuroimaging evidence for gateway hypothesis of BA10. They gave subjects 3 tasks, all of which required switching between SO (stimulus oriented – attention to external stimuli) and SI (stimulus independent – attention to internal representations) processing modes.
what did Gilbert and colleagues find
- Double dissociation between lateral and medial parts of BA10
- Across all three tasks, medial BA10 showed stronger activation for external than internal processing.
- Lateral BA 10 shows greater activation when subjects switched between internal and external types of processing.
- Interpretation is that BA10 acts as a switch between internal and external (SI and SO) modes of processing.
what mental illness does BA10 have abnormal activation
schizophrenia
that patients with schizophrenia have abnormal activation in BA 10 during performance of a simple contextual processing task requiring subjects to identify targets (A followed by an X) amongst nontargets (AY, BX, BY).
could be argued that the hallucinations and delusions experienced by patients with schizophrenia are due to…
could be argued that the hallucinations and delusions experienced by patients with schizophrenia are due to a difficulty distinguishing whether perceptions are ‘real’ (in the sense of arising from the external world) or imaginary (in the sense of being internally generated – e.g. voices in the head). A deficient ‘gateway’ between SO and SI processing would explain the source of this problem.
Originally the evidence regarding the role of the OFC came from human neuropsychological studies using …
Originally the evidence regarding the role of the OFC came from human neuropsychological studies using the IOWA gambling task.
what was found in the Role of the orbitofrontal cortex in value-based decision making (iowa gambling task)
Bechara et al 1996
normal controls generally learned to avoid the risky decks and choose the decks that would give them an overall profit.
Patients with lesions to occipital, temporal and even dorsolateral prefrontal cortical regions showed equivalent performance, generally preferring the advantageous decks.
patients with OFC lesions showed an overall preference for the risky decks, resulting in an overall loss of money – they were unable to learn about the response-reward contingencies.
what did Bechara find in OFC lesion patients with skin conductance response?
What they found was that SCRs during reward and punishment were roughly equivalent in patients and controls. However, anticipatory SCRs (measured between the choice of deck and the receipt of the reward/punishment) were greatly reduced in patients with OFC lesions.
what are Somatic markers
- Somatic markers are the bodily reactions to emotional stimuli
- OFC supports learning of associations between …
- OFC supports learning of associations between somatic markers and complex situations
In a reversal learning task subjects have to…
In a reversal learning task subjects have to learn which card predicts a reward and then the contingencies are shifted.
Fellowers and Farah’s (2003) study included patients with DLPFC and ventromedial (OFC) lesions.
they found what?
Fellowers and Farah’s (2003) study included patients with DLPFC and ventromedial (OFC) lesions.
DLPFC were unimpaired. OFC had specific deficit at the reversal stage. They could learn the initial response contingencies but had problems learning about the new contingency.
The researchers argued that OFC is necessary not so much for learning about stimulus-reward contingencies but for unlearning of established associations.
Fellowers adn Farah said the OFC represents what
specialized neural cicuitry for rapidly unlearning o suppressing the influence of an established stimulus-reinforcement association
what did O’Doherty 2001 do
In this fMRI study, subjects performed a probabilistic reversal learning task in which they were rewarded for choosing one reward and punished for choosing the other one.
Once they learned which one was associated with reward, the contingencies changed and they had to learn to respond to the other stimulus.
what did O’Doherty 2001 find
They found that dissociable regions of the OFC responded preferentially to rewards and punishments – medial OFC showed a stronger response to reward. Lateral OFC showed a stronger response during the punishment phase just before a reversal. This suggests that different regions in the OFC respond to different types of outcome – medial OFC = reward. Lateral OFC = punishment.
what did Camille et al 2004 do
In Camille’s task subjects chose one of two wheels with different chances of winning.
Then they either got partial feedback or full feedback
They asked patients to rate their level of satisfaction with the outcome.
what did Camille et al 2004 find
What you find in normal healthy subjects is that they show higher ratings of satisfaction when they win compared to lose, but they also show much higher ratings of satisfaction when they find out they would have won less or lost more if they had chosen the alternative wheel. And they show much lower ratings when they find out they would have won more or lost less if they had chosen the other wheel.
OFC patients did not show this pattern of counterfactual thinking – they didn’t modulate their ratings according to whether the alternative wheel would have been a win or lose.
Suggests a key role for the OFC in being able to experience the consequences of winning and losing, but more importantly to integrate information from different sources of outcome
what did Coricelli et al. (2005) find
did the wheel task
- OFC activation greater when non-obtained outcome is a loss, only when complete feedback is given\
- Key role for OFC in representing the heightened emotional experience associated with avoiding a loss
- Physiological response associated with loss avoidance (‘somatic marker’) is interpreted by OFC and used to guide future responding.
neuroimaging study
Role of the Orbitofrontal Cortex in Cognitive Control
- Facilitating effective decision making based on knowledge of the value of different actions
- Retrieving the value of goals that are the outcome of the decision making process
- Establishing a relative preference ranking of goals
- Sending signals to other brain regions (parietal, motor cortex) to compute action values and guide responding
what are corticostriatal loops
These loops seem to occur in parallel, with different loops connecting different PFC regions and hypothesised to play different roles – for example, a reward processing loop that connects the ventral striatum to the OFC and an executive control loop that connects the DLPFC to the dorsal striatum.
Role for the basal ganglia in cognitive control: evidence from Parkinson’s Disease
- Gradual loss of dopamine neurons in the striatum (basal ganglia)
- Originally thought to be purely motor disorder
what did Cools et al do
Cools and colleagues gave PD patients a task set shifting task, in which they were required to either name the letter or the number on each trial depending on the colour of the background screen. In the crosstalk condition, both numbers and letters were presented together and the patient had to focus on the relevant stimulus and ignore the irrelevant. In the no-crosstalk condition the number or letter was presented on its own.
what did COols et al find
The results showed that PD patients were significantly impaired relative to healthy controls on switch trials (when required to switch between naming letters and naming numbers) but only in the crosstalk condition. The results show that PD patients have a deficit in task set shifting, especially under conditions of attentional distraction.
what did Brozoski (1979) find about dopamine
• Brozoski (1979) – dopamine depletion in the PFC of monkeys causes a deficit in spatial working memory nearly as severe as complete ablation (removal)
what did Dodds et al fo
examined the effects of methylphenidate (commonly used to treat ADHD) on brain activation during reversal learning. Methylphenidate is a dopamine reputake inhibitor, which means that after dopamine is released into the synapse, it prevents its re-absorption, leading to an overall increase in extra-cellular dopamine levels.
We gave healthy subjects a probabilistic reversal learning task in the MRI scanner.
On each trial, subjects are presented with two abstract visual patterns. Using trial-and-error feedback, subjects must discover which of the two patterns is correct (the subject’s choice is indicated here with a small, black arrowhead). Feedback (a green smiley face or red sad face) is presented as soon as the subject has chosen one of the patterns with a left or right button press. After several correct trials, the contingencies switch and the subject must switch to selecting the other pattern.
what did dodds et al find
The results showed a strikingly clear effect. We examined in which areas of the brain activation was modulated by methylphenidate when the subject switched their response from one pattern to another. The only region that showed such modulation was the putamen (part of the striatum). Thus, the results show a key role for striatal dopamine in mediating cognitive flexibility.
what did Stelzel et al (2013) do
Stelzel et al (2013)
Stelzel and colleagues followed this study up with a task switching paradigm in which subjects had to perform one of two tasks – either decide whether a number was odd or even, or decide whether a number was greater than or less than 5 – depending on the shape around the number.
what did Stelzel fin d
Looking at which brain regions were modulated by bromocriptine during switching, they found again that striatal activation during switching was affected by the drug (there was a smaller difference in activation between switch and nonswitch trials under drug than under placebo). However, they also found that the drug modulated fronto-striatal connectivity during switching. These results thus demonstrate that dopamine plays a key role in cognitive flexibility and it achieves this function by modulating the functional connections between the striatum and the PFC.
current goal states (or tasks or stimulus-response contingencies) are …
current goal states (or tasks or stimulus-response contingencies) are represented by coalitions of neurons in the PFC
