Frontal Lobes Flashcards
Frontal lobe
• Precentral gyrus -> agranular (no layer IV)
• Prefrontal cortex -> granular (anterior to
precentral gyrus)
Precentral gyrus
• Motor cortex -> cytoarchitectonic area 4
- Fine motor movements
• Premotor cortex -> cytoarchitectonic area 6
- Planning sequences of movements
Posterior inferior frontal gyrus
Broca’s area -> cytoarchitectonic areas 45 and 44
- Area 44 -> articulation
- Area 45 -> cognitive; active retrieval of information from memory
Prefrontal cortex (PFC)
• Dorsolateral PFC (superior and middle frontal gyri)
- Mid-dorsolateral PFC (areas 9, 46, and 9/46)
- Posterior dorsolateral PFC (area 8 and rostral
area 6)
• Ventrolateral PFC (ventral frontal gyrus)
- Pars opercularis (area 44)
- Pars triangularis (area 45)
- Pars orbitalis and adjacent cortex (area 47/12)
- Mid-ventrolateral PFC = area 45 + area 47/12
• Fronto-polar region (area 10)
Testing of Frontal Patients
- Tests of divergent thinking
- Fluency tasks
- Temporal ordering tasks/ Recency discrimination tasks
- Self-ordered pointing task
Tests of convergent thinking
- One correct answer for each question (e.g. the sun is a star)
- Not sensitive to frontal lobe damage
Tests of divergent thinking
- Many different responses can be produced to the same question
- -> E.g. find as many uses to a single object as possible in a limited amount of time
- Sensitive to frontal lobe damage
Fluency tasks:
Verbal (word) fluency -> dominant left hemisphere
- Produce as many 4-letter words as possible in a limited amount of time
- Write down as many words as possible beginning with a specific letter in a limited amount of time
- > Very little spontaneous speech
Non-verbal fluency -> nondominant right hemisphere
- Draw as many different abstract designs as possible in a limited amount of time
Recency discrimination tasks
- Use verbal and non-verbal testing material
- Discriminate between the items shown most recently vs. the items shown a longer time ago
- Patients with frontal lobe lesions are impaired
- Patients with medial temporal lesions are not impaired
Self-ordered pointing task
Critical region is the middorsolateral prefrontal cortex (for both verbal and nonverbal stimuli) Verbal and nonverbal material: • Concrete words • Abstract words • Representational drawings • Abstract designs
Maze learning task
Stylus maze task = trial-and-error task Patients with frontal lobe lesions: - Failure to use feedback - Rule breaking behaviour - Loss of inhibition
Wisconsin card sorting test
- Important diagnostic tool for frontal lobe dysfunction
- Depends on dorsolateral prefrontal cortex
- Patients persevere with their responses
Jacobsen Lesion in Monkeys Experiment
Bilateral frontal lesions - Impaired on delayed-response task - Successful on visual discrimination task Bilateral parietal lesions - Unimpaired on both tasks
Delayed-response task
Keep track of the reward location in the current trial and inhibit the interference (memory of very similar responses) from the previous trials
Visual discrimination task
which one is bigger
Working Memory
brain system that provides temporary storage and
manipulation of the information necessary for such complex cognitive tasks as language comprehension, learning, and reasoning
Impairments on working memory tasks after prefrontal cortical lesions:
- Due to deficits in executive processing
- Loss of inhibitory control
- Failure to allocate attention to different types of information and monitor the contents of working memory in the posterior cortical regions
Mid-dorsolateral prefrontal cortex:
• Areas 9, 46 and 9/46 are involved in monitoring
or keeping track of information within working
memory
• Both spatial and non-spatial information
Patients with lesions in the mid-dorsolateral
prefrontal cortex
No difficulty with short-term memory tasks
(can reproduce fixed digit sequences normally e.g.
5 2 7 9 4 3 1)
BUT cannot give digits from a list at random
(cannot perform “mental checklist” e.g. 5 2 5 3 2 5 )
Mid-ventrolateral prefrontal cortex
• Areas 45 and 47/12 • Active retrieval from long-term memory (and NOT automatic (passive) retrieval from longterm memory)
Active retrieval of information from long-term memory
- Goes beyond simple recognition that some stimuli are familiar while others are not
- Initiated under conscious effort and guided by the subject’s goals/plans
- ~ Google: SEARCH within a specific CONTEXT for SPECIFIC INFORMATION
Automatic retrieval
- Triggered by sensory stimuli
- Requires connections between the posterior temporal and parietal association areas
- May involve the subcortical structures
Prefrontal cortex is involved in
- Monitoring of information within working memory (mid-dorsolateral prefrontal cortex)
- Active retrieval of information (mid-ventrolateral prefrontal cortex)
- Allocation of attention to competing stimuli in the environment on the basis of conditional rules (posterior dorsolateral prefrontal cortex)
Why is the case of Phineas Gage important for the history of neuroscience?
- Extraordinary physical recovery
* Dramatic change in personality due to frontal lobe damage
Damage to the ventromedial frontal cortex results from
- Rupture of aneurysms located in the anterior cerebral or anterior communicating arteries -> bilateral lesion
- Surgical removal of tumors (e.g. orbitofrontal meningiomas)
- Head injury -> bilateral damage
Patients with damage to the ventromedial frontal (= prefrontal) cortex
Emotional and behavioural changes/ maladaptive behaviour:
• Impaired ability to make rational decisions in personal and social domains
• Impaired processing of emotion
Few, if any, cognitive deficits:
• Normal ability to solve abstract problems and perform calculations
• Normal ability to recall appropriate knowledge and pay attention to it
• Normal performance on tests of executive (frontal lobe) function
Ventromedial frontal cortex
- Involved in emotional aspect of decision making, learning and social behavior
- Connections with limbic and subcortical structures
Patient C.D.
- Bilateral damage to the ventromedial frontal cortex
- Elevated error rate on the task that requires cognitive flexibility and assesses shifting skills
- Inability to slow down response rate in order to provide more accurate answers
- Inflexibility in behaviour -> inability to change behaviour to get different/more desirable results
- Impulsivity and disinhibition
Single neurons in the ventromedial prefrontal cortex
encoding the emotional value of visual stimuli
Ventromedial frontal cortex dysfunction
- Major depressive disorder (MDD) -> abnormally high activity in ventromedial frontal cortex
- Post-traumatic stress disorder (PTSD)
Two main hypotheses about the ventromedial frontal cortical contribution to specific mood and
anxiety disorders
- Failure of the ventromedial frontal cortex to downregulate the amygdala
- Enhanced activity of the ventromedial frontal cortex -> increased autonomic responses and negative affect
Posterior ventromedial frontal cortex is positively associated with
negative effect
Perigenual ventromedial frontal cortex is positively associated with
positive effect
Two extreme positions on human reasoning
• Rule-based -> content/context-insensitive
- Use formal logic to solve problems
• Associative -> familiarity and social context of a specific situation
- Compare to situations encountered in the past
- Look at each problem individually
- Solve problems on a case-per-case basis
Damage to the ventromedial frontal cortex results in
- Failure to guide choice by feeling
- Failure to use familiarity in decision making
- Fail to process emotional information of situations normally
- > Impairment in decision-making
Patients with ventromedial frontal cortical damage
Possess and can access the knowledge necessary to imagine different actions and scenarios of future outcomes
BUT
Fail to act on such knowledge when making a specific decision towards a future outcome
- Immediate consequences of an action and not the long-term consequences influence decision-making
Somatic Marker Hypothesis
Emotional (somatic) mechanism may indicate the potential consequences of an action and so help make an advantageous decision when selecting among different responses
Somatic Markers
somatic markers are changes in the body and mind
- Help our cognitive processes make decisions
- Help distinguish good (advantageous) choices from bad (disadvantageous) choices
- Acquired from our previous experiences with rewarding (pleasant) and punishing (unpleasant) stimuli/events
Iowa Gambling Task
Patient Group 1:
• Bilateral damage
• Lesion overlap in the ventral and medial frontal cortex (includes bilateral ventromedial frontal and orbitofrontal cortex)
continued to choose disadvantageous cards
Patient Group 2:
• Bilateral damage
• Lesion overlap in amygdala
Did not generate SCRs in reaction to reward and punishment
Electrodermal skin conductance response
was used to demonstrate (and indirectly measure) somatic state activation (arousal/depression of the nervous system) in the Iowa gambling task
- change in electrical resistance in skin
