Sensorimotor systems Learning, memory & amnesia

1. Sensorimotor systemsLearning, memory & amnesia Chapters 8 and 11

3. Three principles of sensorimotor function • hierarchical organization • Two other organizing characteristics? • motor output is guided by sensory input • The case of G.O. – darts champion • The exception? • learning changes the nature and locus of sensorimotor control

4. Posterior Parietal Association Cortex Function: Integrates information on the position of parts of the body and external objects to direct voluntary movement and attention. Sensory system inputs: visual, auditory and somatosensory. Outputs: dorsolateral PFC, secondary motor cortex and frontal eye fields.

5. Dorsolateral PFC Frontal eye field Auditory cortex Visual cortex Inputs to Posterior Parietal Association Cortex

6. Dorsolateral PFC Frontal eye field Auditory cortex Visual cortex Outputs to Posterior Parietal Association Cortex

7. Damage to the Posterior Parietal Association Cortex Can produce a variety of deficits • Perception and memory of spatial relationships • Reaching and grasping • Control of eye movements • Attention

8. Damage to the Posterior Parietal Association Cortex Apraxia – a disorder of voluntary movement not attributable to a simple motor deficit (weakness or paralysis) or to a deficit in comprehension or motivation. Results from unilateral damage to the left posterior parietal cortex.

9. Damage to the Posterior Parietal Association Cortex Contralateral neglect – a disturbance in a patient’s ability to respond to stimuli on the side of the body contralateral to a brain lesion (not a simple sensory or motor deficit). Often associated with large lesions of the right posterior parietal lobe.

10. Dorsolateral Prefrontal Cortex Function: plays a role in the evaluation of external stimuli and initiation of voluntary responses to those stimuli. Main input: posterior parietal cortex Outputs: secondary motor cortex primary motor cortex frontal eye fields

11. Dorsolateral Prefrontal connectivity

12. Dorsolateral Prefrontal cortex Neurons in this area respond to the characteristics of objects (e.g., color/shape), the location of objects or to both. The activity of other neurons is related to the response itself.

13. Secondary motor cortex Input: most from association cortex Output: primary motor cortex Two classic areas: • SMA • Premotor cortex

14. Secondary Motor Cortex Current classifications suggest • At least 7 different areas • 2 supplementary motor areas • SMA and preSMA • 2 premotor areas • PMd and PMv • 3 cingulate motor areas • CMAr, CMAv and CMAd

15. Secondary Motor Cortex • Subject of ongoing research • May be involved in programming movements in response to input from dorsolateral prefrontal cortex • Many premotor neurons are bimodal – responding to 2 different types of stimuli (most common - somatosensory and visual)

16. Primary Motor Cortex • Precentral gyrus of the frontal lobe • Major point of convergence of cortical sensorimotor signals • Major point of departure of signals from cortex • Somatotopic – more cortex devoted to body parts which make many movements

17. Motor homunculus

18. Primary Motor Cortex • Monkeys have two hand areas in each hemisphere, one receives feedback from receptors in skin. • Stereognosis – recognizing by touch – requires interplay of sensory and motor systems • Damage to primary motor cortex • Movement of independent body parts (e.g., 1 finger) • Astereognosia • Speed. accuracy and force of movement

19. Other sensorimotor structures outside of the hierarchy (sometimes called extrapyramidal systems) • Cerebellum • Basal ganglia both modulate and coordinate the activity of the pyramidal systems by interacting with different levels of the hierarchy.

20. Cerebellum • 10% of brain mass, > 50% of its neurons • Converging signals from • primary and secondary motor cortex • brain stem motor nuclei (descending motor signals) • Somatosensory and vestibular systems (motor feedback) • Involved in motor learning, particularly sequences of movement • Damage to cerebellum – disrupts direction, force, velocity and amplitude of movements; causes tremor and disturbances of balance, gait, speech, eye movement and motor sequence learning .

21. Basal Ganglia • A collection of nuclei • Part of neural loops that receive cortical input and send output back via the thalamus (cortical-basal ganglia-thalamo-cortical loops) • Modulate motor output and cognitive functions • Cognitive functions of the basal ganglia

22. Descending Motor Pathways • Two dorsolateral • Corticospinal • Corticorubrospinal • Two ventromedial • Corticospinal • Cortico-brainstem-spinal tract • The corticospinal tracts are direct pathways

25. Ventromedial one direct tract, one that synapses in the brain stem More diffuse Bilateral innervation Proximal muscles Posture and whole body movement Dorsolateral Vs Ventromedial Motor Pathways Dorsolateral • one direct tract, one that synapses in the brain stem • Terminate in one contralateral spinal segment • Distal muscles • Limb movements

26. Experiments by Lawrence and Kuypers (1968) • Experiment 1: bilateral transection of the • Dorsolateral (DL) corticospinal tract • Results: • monkeys could stand, walk and climb • difficulty reaching improved over time • could not move fingers independently of each other or release objects from their grasp.

27. Experiments by Lawrence and Kuypers (1968) • Experiment 2: • The same monkeys with DL corticospinal tract lesions received 1 of 2 additional lesions: • The other indirect DL tract was transected • Both ventromedial (VM) tracts were transected

28. Experiments by Lawrence and Kuypers (1968) • Experiment 2 Results: • The DL group could stand, walk and climb but limbs could only be used to ‘rake’ small objects of interest along the floor • VM group had severe postural abnormalities: great difficulty walking or sitting. Although they had some use of the arms they could not control their shoulders.

29. Experiments by Lawrence and Kuypers (1968) • Conclusions: • the VM tracts are involved in the control of posture and whole-body movements • the DL tracts control limb movements (only the direct tract controls independent movements of the digits.

30. The case of H.M. • Intractable epilepsy • one generalized convulsion each week • Several partial convulsions each day • 1953 surgery: Bilateral medial temporal lobectomy • temporal pole • amygdala • entorhinal cortex • hippocampus

31. Corkin et al. (1997)

32. Corkin et al. (1997)

33. Effects of Bilateral Medial Temporal Lobectomy • Convulsions were dramatically reduced • IQ increased from 104 to 118 • Short-term memory (STM) intact • Temporally-graded retrograde amnesia • Severe anterograde amnesia

34. Amnesia • Retrograde (backward-acting) – unable to remember the past • Anterograde(forward-acting) – unable to form new memories • While H.M. was unable to form most types of new long-term memories, his STM was intact

35. Mirror-drawing task H.M.’s performance improved over 3 days (10 trials/day) despite the fact that he could not consciously remember the task on days 2 and 3.

36. Rotary-Pursuit Test H.M.’s performance improved over 9 daily practice sessions; again, with no recognition of the experience

37. Explicit vs Implicit Memories • Explicit memories – conscious memories • Implicit memories – unconscious memories Repetition priming tests were developed to assess implicit memory performance;

38. Incomplete pictures test

39. Implications of H.M.’s amnesia • Medial temporal lobes are involved in memory formation. • STM and LTM are dissociable – H.M. is unable to consolidate certain kinds of explicit memory. • the fact that he could form some memories suggests that there are multiple memory systems in the brain.

40. Medial Temporal Lobe Amnesia • Not all patients with this form of amnesia are unable form new explicit long-term memories, as was the case with H.M. Two kinds of explicit memory: Semantic memory (general information) may function normally while episodic memory (events that one has experienced) does not – they are able to learn facts, but do not remember doing so (the episode when it occurred)

41. Vargha-Khadem et al., (1997) • Studied three children that had bilateral temporal lobe damage early in life. • Like H.M., the children could not form episodic memory, however they did acquire reasonable levels of factual knowledge and language ability in mainstream school.

42. Effects of Cerebral Ischemia on the Hippocampus and Memory • R.B. suffered damage to just one part of the hippocampus (CA1 pyramidal cell layer) and developed amnesia • R.B.’s case suggests that hippocampal damage alone can produce amnesia • H.M.’s damage and amnesia was more severe than R.B.’s

44. Object-Recognition Memory • Early animal models of amnesia involved implicit memory and assumed the hippocampus was key • 1970’s – monkeys with bilateral medial temporal lobectomies showed LTM deficits in the delayed nonmatching-to-sample test • Like H.M., performance was normal when memory needed to be held for only a few seconds (within the duration of STM)

45. Delayed nonmatching-to-sample task pretend you’re the monkey Sample stimulus touch it and get a yummy treat

46. 10 min delay during which other sample stimuli are presented

47. Choice phase: pick the image that is new Another yummy treat Darn, no food

48. Testing object-recognition memory

49. Medial temporal lobe (MTL)

50. Delayed non-match to sample results