Neural basis of planning and action Flashcards
What are apraxias?
Inability to make skilled, voluntary movements accurately.
What are the types of apraxias?
- Ideomotor: Patients are unable to (or struggle to) carry out actions because they are unable to ‘imagine’ the types of movements needed in order to do so, despite knowing what types of movements are needed.
- Ideational: Inability to perform tasks related to objects as a result of losing the ability to conceptualise the purpose of an object.
- Constructional: Patients are unable to copy out images, both visually and to some extent mentally (they cannot draw).
- Speech: Difficulty in planning and executing the muscle movements of the mouth and tongue required for speech.
What areas of the brain are important in the planning and execution of actions?
- Posterior parietal cortex
- Secondary motor areas (lateral premotor area, supplementary motor area)
What is the location of the posterior parietal cortex (PPC)?
- Brodmann’s areas 5 & 7
- Posterior to the somatosensory cortex in the parietal lobe
What are the functions of the posterior parietal cortex?
- Anterior part: Concerned with integration of somatosensory information and proprioceptive information in order to judge position of the body.
- Posterior part: Concerned with integration of visual information.
What is the function of the posterior parietal cortex with respect to planning and executing actions?
- Posterior parietal cortex is mainly responsible for guidance of actions in the appropriate direction with respect to relevant stimuli in the external environment.
- “Where” aspect of “What, where, how” model of movement.
What deficits occur when there is damage to the posterior parietal cortex?
- Ideomotor apraxia: Dominant hemisphere PPC damage
- Constructional apraxia: Right PPC damage
What series of momements are made during the Kimura box test?
- Push top button with index finger
- Pull handle
- Press down bar with thumb
(movements are made in sequence specified)
What is the location of the secondary motor areas?
- Brodmann’s area 6.
- Frontal lobe anterior to the primary motor cortex
What is the nature of connectivity of the secondary motor areas?
- Both components make connection with M1 and PPC
- Both components output into cortico-spinal tract via M1
- SMA makes connection with the basal ganglia
- PM makes connections with cerebellum
What is the overall function of the secondary motor areas in planning and execution of actions?
- Programming of actions
- Selection of appropriate movements and ordering them in succinct sequence appropriate for required action
- Optimising conditions for performance of movements:
- Adjusting posture to maintain balance
- Inhibiting irrelevant movements
What are the specialised functions of individual components of the secondary motor area?
- SMA:
1. Bimanual coordination (use of both hands)
2. Planning of actions in absence of external cues (e.g. actions from memory) - PM: Planning of actions under guidance of external cues (e.g. imitating actions)
What evidence is there for function of the SMA?
- Lesion of SMA in monkeys result in:
- Deficits in bimanual coordination
- Failure of hand/finger orientation when food is approached
- Inability to raise hands without any purpose - Patients with lesions in SMA show “Alien hand syndrome”, whereby patients claim to experience movement of hands in absence of conscious control.
- PET studies have shown that SMA more active when patients perform sequence of finger movements from memory compared to imitation.
What is there for function of the PM?
- Lesion of PM in monkeys result in deficits in performing actions under guidance of external cues (e.g. copying movements).
- PET studies have shown that PM more active when patients perform sequence of finger movements by imitating external cue compared to from memory.
What are the main functions of the prefrontal cortex?
- Behavioural inhibition
- Attention
- Working memory
- Emotions
What systems are the prefrontal cortex connected to?
- Attention (posterior parietal cortex)
- Explicit memory (rhinal cortex & hippocampus)
- Emotional processing (amygdala + hypothalamus)
- Language processing (Broca’s area & Wernicke’s area)
- Control of actions (Basal ganglia)
What type of behaviour with regards to behavioural inhibition are displayed by patients with prefrontal cortex damage?
- “Perseverative behaviour”
- Patients find it very difficult to suppress already learned behaviour in favour of a new behaviour
What is the Wisconsin card sort test?
- Patients are shown pack of cards each with specific dimensions associated with them:
- Type of shape
- Number of shapes
- Colour of shapes - The patients are then asked to sort the pack of cards according to certain dimensions (patient needs to figure out dimensions for themselves while an experimenter tells patient if they are sorting the cards correctly or not).
- The dimensions of sorting are changed half way through experiment, forcing patients to change their sorting method.
What are the results of the Wisconsin card sort test when performed on patients with pfc damage?
- Patients with prefrontal cortex damage are unable to change their sorting behaviour once it has been set initially, so that despite experimenter telling them they are sorting the cards wrong when sorting rules are changed half-way throughout experiment, they continue to sort cards in the way they initially did.
- Many patients are aware of the fact that they are sorting the cards wrong, but are unable to control their behaviour.
What experiment was performed to test the role of pfc in attention?
- Different stimuli are presented in sequence.
- The stimuli can be different in 3 dimensions:
- Colour
- Form
- Movement
3, The subjects asked to judge whether current stimulus is same or different compared to previous stimulus in either:
- One specific dimension (selective attention)
- All 3 three dimensions (divided attention)
4. Activity in various parts of the brain is monitored as these tasks were performed by the subject using PET.
Which areas of the brain were most active for the selective attention task?
- Ventrolateral prefrontal cortex
- Infero-temporal cortex
Which areas of the brain were most active for the divided attention task?
- Dorsolateral prefrontal cortex
- Posterior parietal cortex
How was the role of pfc in working memory tested?
Monkeys need to be able to remember specific task over a brief delay of a few seconds after they have been trained to perform the task (delayed response tasks). There are several versions:
- Spatial version: Monkeys need to remember whether the food is placed in dish on the right or left.
- Object version: Monkeys need to remember which object to choose.
- Proprioceptive version: Monkeys need to remember whether to press a lever once or 5 times
What were the results of the delayed response task?
- Monkeys with pfc lesions were unable to perform tasks after a delay but were able to when delay was absent, suggesting that their working memory has been impaired.
- Controversial evidence suggests that lesions in different parts of the pfc leads to selective deficits in certain versions:
1. Dorsolateral pfc = Spatial version
2. Ventrolateral pfc = Object version
3. Dorsal pfc = Proprioceptive
