Neurobiology of learning, memory and cognition: Neural basis of planning and action

Question 1

Apraxias
Ideomotor apraxias?
Associated with damage to?

Answer 1

Motor disorders in which there is a difficulty in performing purposeful or voluntary movements.

4 major types: limb, oral, agraphic, constructional

Many are ideomotor apraxias: inability to perform purposeful movement to command or on imitation, but usually preserved ability to perform these actions spontaneously.

Often impairments in learning new sequences of actions (Kimura box test)

Associated with damage to posterior parietal cortex, frontal premotor areas, and the connections between them.

Question 2

Limb apraxia

Associated with damage to?

Answer 2

Problems with arm, hand & finger movements

Associated with bilateral damage to parietal or premotor cortex.

Question 3

Oral apraxia

Answer 3

Problems with programming movements of the throat, lips & tongue to produce sequences of speech

Question 4

Agraphic apraxia

Answer 4

Particular type of writing deficit

Question 5

Constructional apraxia

Associated with damage to?

Answer 5

Inability to copy mental or visual pictures.

Associated with right parietal damage

Question 6

Difference between parietal & premotor damage

Answer 6

Parietal: associated with deficits in execution & recognition of movement
Premotor: associated with deficits in execution but NOT recognition

Question 7

Posterior parietal cortex
Functions

Connections?

Answer 7

Areas 5 & 7

Rostral part: integration of somatosensory & proprioceptive info relating the relative position of body segments to their movement
Posterior part: integration of visual info about events located in the external environment. Also control of reaching into extra-personal space: mediates between spatial perception & the direction of action (Mountcastle)

Spatial attention.

Reciprocally connected to the lateral & medial premotor areas of the frontal lobes.

Question 8

Mountcastle studies on posterior parietal function.

Answer 8

Lesions in monkeys impair sequential reaching movement e.g removing polo mints from a bent wire

Recordings from single units in monkeys demonstrate existence of neurones in area 7 which:
- arm projection neurones: fire when monkey detects a visual target, increase firing as arm is projected towards target, decrease when target reached.

• manipulation neurons: fire when target is manipulated.

Question 9

Lateral premotor cortex (PM)
Connections?

Functions?

Functional studies?

Answer 9

Connections with motor cortex, posterior parietal cortex
Also connected to cerebellum > basal ganglia
Outputs to subcortical motor systems & cortico-spinal tract via primary motor cortex (area 4)

Programming of actions: Movement using external cues to direct action

Ablation in monkeys-> deficits in performing hand actions based upon/ directed by external cues

PET studies reveal greater action in PM when relying on external cues to determine sequence of finger movements than when performing movements from memory.

Question 10

Supplementary motor area (SMA)
Connections?

Functions?

Functional studies?

Answer 10

Connections with motor cortex, posterior parietal cortex
Also connected to basal ganglia > cerebellum
Outputs to subcortical motor systems & cortico-spinal tract via primary motor cortex (area 4)

Programming of actions: Particularly important for bimanual coordination, contributes to movement with no external cues (internal generation of action)

Ablation in monkeys ->

• deficit in bimanual coordination
• failure to orient hands & fingers accurately as approach food
• failure to raise hand (in absence of external cues) to get peanut reward

Patients with pathology may show alien hand syndrome

Far more activated when performing a learned sequence of finger movements than when relying on external cues to signal a novel sequence.

Question 11

Alien hand syndrome

Answer 11

Actions of hand are divorced from conscious control.

Associated with pathology of SMA

Question 12

Release of reflexes

Answer 12

Integral part of premotor area functions (PM, SMA) = inhibiting inappropriate actions, esp inappropriate reflexes.

Many reflexes present at birth become inhibited during development, may re-appear following damage to premotor areas e.g sucking, rooting, grasping.

Denny-Brown: mechanisms reside in parietal lobe, inhibited by frontal lobes (premotor cortex)

Question 13

Planning of action- brain regions involved?

Answer 13

Prefrontal cortex

Question 14

Selection and programming of actions- Brain regions involved

Answer 14

Posterior parietal cortex
Lateral premotor cortex & supplementary motor area

BUT NB executive control arises from a distributed neural network. No single part of the brain is the ‘chief executive’

Question 15

Prefrontal cortex

Frontal subjects show:
Connections?
Homogenous area?

Answer 15

Evolved partly to enable higher order planning of actions & provide overall executive control of behaviour in social & non-social contexts.

Frontal subjects: lack of initiative, poor planning ability, inability to cope in novel situations, poor social skills.

Connections with: specialised processing modules in posterior cortex, declarative memory systems in temporal lobes, limbic structures involved in emotional processing, basal ganglia (higher-order control of action)

Not homogenous, different areas have different connectivity patterns, lesions of these different areas result in different behavioural deficits.

Question 16

Prefrontal cortex and behavioural inhibition.

Region implicated?

Answer 16

Damage to pfc- impairments in inhibition of complex behaviours.
e.g failure to inhibit previously relevant rules governing behaviour- the Wisconsin Card Sort Test.
Primarily associated with damage to lateral pfc

Monkeys with prefrontal damage also show ‘behavioural inflexibility/ perserverative behavoiur’. On discrimination reversal tests, having learned that one out of a pair of objects is associated with reward, find it difficult to switch responding to other object when that object becomes rewarded instead.

Question 17

Prefrontal cortex and attention

DL vs VL

Answer 17

PET studies have shown pfc to be part of a distributed neural network involved in spatial & feature attention.

Dorsolateral activated most when selectively attending to spatial features (NB also posterior parietal cortex)

Ventrolateral activated most when selectively attending to visual features (NB also infero-temporal cortex)

Question 18

Prefrontal cortex and working memory

Answer 18

Goldman-Rakic: Pfc appears to be necessary for attending selectively to stimuli in the external world, & maintaining attention to stimuli in the mind- ‘on-line’ - when they are no longer present in the outside world.

Damage in monkeys impair performance in delayed response tasks: Impaired at choosing correct response if delay between ‘sample’ and ‘choice’ stage, not impaired if there is no delay.
Some neurons in lateral pfc in monkeys shown to fire during delayed period of spatial & object versions of delayed response task.

Similar impairments in spatial delayed response seen in humans with dorsal pfc damage. (object & proprioceptive not looked at)

Question 19

Prefrontal cortex and emotion
Connections?
Patient EVR?

Answer 19

Orbital regions

• have large reciprocal connections with limbic system e.g amygdala, hypothalamus, cingulate cortex
• damage disrupts social & emotional behaviour. e.g in monkeys submissive & solicitation behaviour in intact females in response to the advances of a male replaced by indifference & aggression. Damaged females also show indifference to their own offspring.
• patient EVR (damage to orbital pfc): ‘incapable of either maintaining an enduring attachment to a sexual partner or functioning as a responsible parent;
• damage in humans is also accompanied by impaired autonomic activity to emotion provoking pictures e.g nudity & mutilation, but not to loud noises.

Question 20

Damasio- role of orbital pfc in emotion

Answer 20

Proposes that the orbital pfc is imp in enabling emotions to contribute to complex decision making.
May provide ‘gut feeling’