Lecture 9 - Frontal and Parietal Lobes Flashcards
1
Q
Key terminology
A
- Gyrus = top of fold
- Sulcus = bottom of fold
- Fissure = deep grooves/sulci
2
Q
What is the boundary between the parietal and frontal lobes called?
A
Central sulcus (Rolandic fissure)
3
Q
What is the boundary between the parietal lobe and occipital lobe called?
A
Parietal-occipital fissure
4
Q
What is the boundary between the parietal lobe and temporal lobe called?
A
Lateral sulcus (Sylvian fissure)
5
Q
What sulci and gyri make up the postcentral gyrus?
A
Central sulcus, postcentral sulcus and postcentral gyrus
6
Q
What structures make up the posterior parietal lobe?
A
Superior parietal lobule (SPL), intraparietal sulcus (IPS) and inferior parietal lobule (IPL)
7
Q
What are the major anatomical subdivisions of the parietal lobe?
A
- Postcentral gyrus
- Posterior parietal lobe:
- Superior parietal lobule
- Intraparietal sulcus
- Inferior parietal lobule
8
Q
What are the major functional subdivisions of the parietal lobe?
A
- Primary somatosensory cortex (often called S1)
- Posterior parietal cortex:
- Intraparietal sulcus and superior parietal lobule
- Right inferior parietal lobule
- Left anterior parietal lobule
- Left posterior inferior parietal lobule
9
Q
What is the function of the primary somatosensory cortex (S1)?
A
- Feel
- Soma = body
- Main role = processing information about body sensations e.g. touch, pain, proprioception (map of various body part locations)
- Can be divided into at least 4 subdivisions (areas 1, 2, 3a and 3b).
- Input mainly from the thalamus and motor cortex
- Output mainly to motor cortex and posterior parietal cortex
10
Q
How did Penfield and Boldrey (1937) develop the somatotopic map?
A
- Penfield and Boldrey (1937) inserted electrodes in the somatosensory cortex of epileptic patients just before operating on them (patients were under local anaesthesia i.e. still awake)
- He stimulated different parts of the somatosensory cortex and recorded the sensations reported by the patients
- Led to the creation of a simplified (and partially incorrect) somatotopic map
11
Q
What is the Wilder Penfield’s Somatotopic Map?
A
- Note that some body parts have a larger dedicated area than others
- Also known as the somatosensory homunculus (man diagram - hands and face represent larger areas)
- While there is clear somatotopy, it is not as simple as depicted by Penfield (Seelke et al., 2012) – much more detailed e.g. individual digits
12
Q
Why should we be interested in the somatosensory cortex?
A
- Learn about brain organisation in general
- Even more important = learn about brain reorganisation
- After injuries
- Phantom limbs and phantom pain after amputations
- Reintegration of body parts after transplants
- Through learning (e.g. to play an instrument)
13
Q
Describe functional reorganisation in the somatosensory cortex
A
- Our brain is much more dynamic than we assume
- Functional reorganisation of S1 can occur within just 24 hours – very quick
- Kolasinski et al. (2016) showed this by an experiment where the little finger and ring finger were glued together
- Wanted to see how quickly the body would accept four fingers instead of five
- Two fingers glued together start behaving like one
14
Q
What is the function of the intraparietal sulcus and superior parietal lobule?
A
- Vision for action
- Overarching concept = vision for action -> dorsal (‘what’) visual stream (Goodale, 2011; Ganel & Goodale, 2018)
- Is there an object with which I can interact? What is its size and orientation? -> Objects in space, object relevance/attention
- Where is my body (arms, hands, eyes, finger) relative to the object? -> Reaching/grasping objects.
- More anterior areas – coding in hand-centred coordinate system (closer to motor cortex)
- More posterior areas – coding in vision-centred coordinate system (retinotopy) (closer to occipital lobe)
15
Q
What classic neuropsychological syndrome is caused by bilateral lesions to the intraparietal sulcus and superior parietal lobule?
A
- Balint syndrome (Jackson et al., 2009)
- Dorsal stream = ‘where/how’ pathway
- Ventral stream = ‘what’ pathway
- Optic ataxia: deficit in visually guided reaching movements e.g. can see pen but not reach to grasp it (Anderson et al., 2014)
- Oculomotor apraxia: inappropriate fixation of gaze and difficulties in voluntarily shifting fixation to other objects e.g. can’t change gaze from red square to purple
- Simultanagnosia: impaired ability to perceive multiple items in a visual display e.g. can see each ‘7’ but not the overall 7 figure
16
Q
How may involvement in cognitive functions derive from these rudimentary mechanisms?
A
- Higher functions may link to dysfunction in this area (wrong information sent forward to higher order learning)
- Visuospatial working memory -> link to representing the location of objects, coding what is relevant
- Mental rotation/imagery -> link to manipulating objects.
- Arithmetics -> link to moving eyes / hands to count, spatial layout (“mental number line”)?
17
Q
What is the function of the right inferior parietal lobe?
A
- Detect salient events in the environment, shift attention
- Singh-Curry & Husain (2009)
- Detection and encoding of salient or novel events (bottom-up attention, i.e., ‘up’ from stimuli via senses – brain interprets)
- Also involved with sustaining attention on current task goals
- Key role in maintaining attention on current task goal as well as encoding of salient events so that task-sets can be speedily reconfigured to deal with new challenges
- Lesion in this area = hemispatial neglect (Corbetta & Shulman, 2002)
18
Q
What is the function of the left anterior inferior parietal lobule?
A
- Use objects in appropriate way; pantomime object use (acting out)
- Reynaud et al. (2016)
- Understanding tool-use actions
- Lesion in this area – apraxia (can’t perform particular actions as a result of brain damage) with possible impairments:
- Imitation of gestures
- Communicative gestures (pantomime thumbs up/object)
- Real tool use
19
Q
What is the function of the left posterior inferior parietal lobule?
A
- Detect salient events in one’s thoughts?
- Seghier (2012) – if we are detecting bottom-up information, it will go on to effect:
- Semantic processing
- Reading and comprehension
- Default mode processing (mind wandering)
- Number processing
- Memory retrieval
- Theory of mind
- (and others)
- Integrative account for more posterior areas (Cabeza et al., 2012)
- Bottom-up attention to internally generated stimuli (attention to internal thoughts)
- Contrasts from the right inferior parietal lobule which relies on bottom-up information from environmental stimuli
20
Q
Why might function be difficult to understand?
A
Animal models might not work for these areas (inferior parietal cortex and lateral prefrontal cortex) - Van Essen & Dierker, 2007
21
Q
What sulci and gyri are located in the frontal lobe?
A
Cingulate sulcus and cingulate gyrus
22
Q
What are the three main subdivisions of the frontal cortex?
A
- Primary motor cortex (M): giant Betz cells in layer V
- Premotor cortex (PM): no granular cells in layer IV
- Prefrontal cortex (PF): granular cells in layer IV
23
Q
What is Brodmann’s (1909) classic cytoarchitectonic map?
A
- Brodmann’s (1909) classic cytoarchitectonic map:
- Primary motor: Brodmann area (BA) 4
- Premotor: BA 6
- Transition (‘dysgranular’): BA44
- Prefrontal: BA’s 8, 9, 10, 11, 45, 46, 47
- Broca’s area: BAs 44 + 45 (sometimes only BA 44)
- MRI-based multimodal parcellation = strong evidence that there are more areas than identified by Brodmann
- MRI = detect things at voxel level (one millimetre cubed)
24
Q
What is the function of the motor cortex?
A
- Control of skeletal muscles together with other structures; most notable, basal ganglia, thalamus and cerebellum
- Roughly somatotopically organised (“motor homunculus”)
25
What is the function of the premotor cortex?
(High-order motor control)
- Movement planning
- Movement selection
- Movement sequencing
- Inhibitory control of motor cortex (supplementary motor area on medial side of hemisphere)
26
TMS
- Disrupt brain functions
- Deep brain stimulation to treat tremors in Parkinson’s (understanding brain and structures is so important)
27
What is the traditional approach to studying the neuropsychology of the prefrontal cortex?
- Neuropsychological tests conducted on patients with frontal lobe lesion deficits
- Verbal fluency (Milner, 1964) = e.g. ‘write down as many words beginning with F as possible.’ 1 minute, then A and S (frontal lobe patients struggle to come up with as many words and to switch letters)
- Wisconsin Card Sorting Test (WCST: Milner, 1964) = perseveration: continue to use ‘no longer correct rule’ (sort by colour not shape, then change midway through to sort by shape – frontal lobe deficits can’t shift new rule)
- Stroop task (Perret, 1974)
- Tower of London (Shallice, 1982) – people with frontal lobe deficits can’t move from start position to achieve goal position
28
How is poor sensitivity and specificity an issue with traditional approaches?
- Sensitivity = ability of test to identify those with prefrontal lesions (and are impaired)
- Specificity = ability of test to not identify those impaired by lesions in other areas
- Not all patients with frontal lesions have difficulties
- Some patients with non-lesions have difficulties
29
How is knowing which function is impaired an issue with the traditional approach?
- For example, perseveration in the WCST
- Working memory issue? [“What rule did I try already?”]
- Long-term memory issue? [“What are the rules?”]
- Difficulties suppressing old rule?
- Difficulties activation new rule?
- Sustained attention issue?
- Issue known as problem impurity of tasks
- Dangerous to conclude deficit lies in process required by task
30
What is Stuss and Alexander's (2007)/Stuss (2011) more recent approach?
- Basic approach:
- Devise simple tests -> single processes
- Manipulate difficulty and context -> more complex processes
- Based on Norman and Shallice’s Supervisory Attention System
- Lesion-symptom mapping – devised simple tasks for people with prefrontal lesions to map and correlate what would happen
- Example tasks: simple RT, choice RT, cued RT, tapping, go-no-go task
31
What are Stuss' conclusions?
- Lateral PFC = executive function
- Left: task setting
- Right: monitoring
- Dorsomedial PFC = energisation
- Process of initiating and sustaining any response
- Orbital PFC = behavioural and emotional self-regulation
- Polar PFC = metacognition
- ‘Thinking about thinking’
32
Evaluate Stuss et al.'s approach
- Lesion-symptom mapping is interesting – further refined with modern structural MRI -> voxel-based lesion-symptom mapping
- Exact processes are still unclear – are the tasks really process-pure? Are the labels chosen (i.e. energisation) appropriate? (cover all deficits)
- General problems with patient studies – small sample sizes, lesions restricted to grey/white but not both
33
What is the final evaluation for the function of LPFC?
- Adaptivity per se is plausible but it is restricted (i.e. not every area can represent everything
- Hierarchical organisation per se is plausible but exact processes associated with the different areas are still quite unclear
- Relationship to Stuss’ neuropsychological results not clear (e.g. suggested hemispheric specialisation) e.g. how do you know just left/right causing problem?
- What is needed? – computational models combined with experimental evidence (brain imaging, brain stimulation, lesion)
- Prefrontal still a problem we don’t fully understand
- No lobe is an island (Modha & Singh, 2000)
