Week 6 Motor Control (Dr Roger Newport) Corticospinal Damage Hemiparesis Cerebellar Damage

1. Week 6 Motor Control • (Dr Roger Newport) • Corticospinal Damage Hemiparesis • Cerebellar Damage Ataxia Timing Issues Motor Learning • Basal Ganglia Damage Parkinson’s Disease Huntingdon’s Chorea • Cortical Damage Apraxia

2. Corticospinal Damage Hemiparesis and Hemiplegia Definitions Hemiplegia: Paralysis Hemiparesis: Weakness The most common and obvious sign of stroke, but can be caused by a variety of reasons including: tumours Infection (e.g. meningitis / encephalitis) Metabolic imbalance congenital disorders Always as a result of damage to the corticospinal tract

3. Corticospinal Tract Originates in Primary Motor Cortex and neighboring regions Passes through Corona Radiata Internal Capsule Cerebral Peduncles Pons Pyramids Crosses in the Pyramidal Decussation Forms Anterior and Lateral Corticospinal tracts

4. Doctor, I’ve had a stroke but you can’t afford to give me a scan Yes, if we follow a few basic rules How can we tell where in the tract the damage is? Can we tell where my lesion is?

5. RULE NUMBER 1 There are 4 major sites causing hemiparesis: (1) Cortex (2) Internal Capsule (3) Corona Radiata (4) Brainstem RULE NUMBER 2 There is usually only one lesion. Bilateral lesions do occur, but then there are bilateral signs RULE NUMBER 3 If it is below the neck there will be no facial weakness.

6. Doctor, my lesion is in my spinal cord How do I know? From Left Cortex From Right Cortex Midbrain X Pons Facial nuclei Medulla Decussation SC To left limbs To right limbs Doctor, my lesion is in my spinal cord How do I know? Because I have no facial weakness

7. Crossed corticobulbar fibre L Cortex R Cortex To Upper Facial Muscles X &UnX input To Lower Facial Muscles UnX input only Facialnerve fibres Left-sided upper motor neurone facial weakness. Cortical damage does not affect the entire side of the face. Because of the bilateral innervation of the upper third of the face, only the lower two-thirds of the face would be affected by cortical damage Uncrossed Corticobulbar fibre

8. RULE NUMBER 4 The face is always weak on the same side as the arm and leg if it is an upper motor neurone facial weakness - except when the lesion is in the pons A lesion in the pons can result in crossed hemiparesis, i.e. contralateral limb weakness and ipsilateral facial weakness

9. Doctor, my lesion is in my spinal cord How do I know? From Left Cortex From Right Cortex Midbrain X To the R face Pons Facial nuclei Medulla Decussation SC To left limbs To right limbs Doctor, my lesion is in my pons How do I know? Because I have have crossed hemiparesis

10. RULE NUMBER 4 The face is always weak on the same side as the arm and leg if it is an upper motor neurone facial weakness - except when the lesion is in the pons RULE NUMBER 5 If the lesion is above the neck then it is on the opposite side to the hemiparesis.EVERYTHING, absolutely everything crosses if it’s going to the hemispheres. Your left brain receives sensation and visual input from the right side and sends out its motor output to the right side.

11. RULE NUMBER 7: THE LAW OF EXPECTATIONS If there is a left sided hemiparesis, which is an easy thing to observe: it follows that you can expect to find (if there is not a brainstem lesion): Left-sided upper motor neurone facial weakness. Left-sided sensory loss Left homonymous hemianopia (can be cortical or subcortical) If the lesion is in the cortex you expect cortical signs

12. Look at the eyes! Eyes look at involved hemisphere Eyes look away from the Hemiparesis • Left Hemisphere • Aphasia • Right hemiparesis • Right-sided sensory loss • Right visual field defect • Apraxia • Dysarthria (speech) • 3Rs Difficulty • Right Hemisphere • Extinction of left-sided stimuli • Left hemiparesis • Left-sided sensory loss • Left visual field defect • Poor left conjugate gaze • Spatial disorientation

13. Doctor, my lesion is in my cortex How do I know? Doctor, my lesion is in my cortex How do I know? X Because I have uneven arm and leg weakness and show cortical signs Internal capsule Corona Radiata But what if the brainstem and pons have been ruled out and there are no cortical signs? Remaining Candidates: Internal capsule Corona radiata

14. cortex C.R. I.C. Reticular formation Brainstem To LMN Fibres descending from the cortex are called the ‘corona radiata’ These fibres funnel through the internal capsule which lies between the thalamus and basal ganglia on their way to the brainstem. The reticulospinal tracts are two long descending pathways associated with the control of movements and posture. The lateral reticulospinal tract inhibit extensors.

15. cortex C.R. X I.C. Reticular formation Reticular formation Brainstem Brainstem Up } Fanning toes To LMN Normal plantar reflex Babinski extensor reflex So if input to the reticular nuclei is interrupted (as happens with a lesion of the internal capsule) extensor reflexes are no longer inhibited - result: the Babinski sign.

16. Doctor, my lesion is in my internal capsule How do I know? cortex C.R. X X I.C. Because I have equal arm and leg weakness and show the Babinski sign Reticular formation Brainstem To LMN X Doctor, my lesion is in my internal capsule How do I know?

17. No Ipsilateral damage Spinal cord Yes No FW same side as limb W? Pons Yes Yes Contralateral damage Internal Capsule Leg and arm equal? No Yes Cortical signs? Cortex No Corona Radiata Where is my lesion: summary? Facial Weakness?

18. Much more. If you want to speak to the cortex, you’ll have to go through the thalamus Thalamus Major components of the motor system But there is more to motor control than the corticospinal tract. Transforming sensory input into plans for voluntary movement Initiating and directing voluntary movement Movement learning, motivation and initiation Motor learning, timing and coordination

19. The Cerebellum: where is it and what does it do? Thought to be involved in: Balance Coordinating movement Timing of movements Timing of discontinuous movements Motor learning - acquiring and maintaining Sources of cerebellar injuries Toxins (ethanol, chemotherapy, anticonvulsants, ethanol). Autoantibodies (paraneoplastic cerebellar degeneration ) Structural lesions (strokes, MS, tumors, etc) Inherited cerebellar degenerations ( e.g. Freidreich's ataxia) Diagnosis usually by MRI

20. Vermis Paravermis Lateral Hemispheres Anterior Lobe Posterior Lobe Flocculus The cerebellum - basic divisions

21. Cerebellar Ataxia Midline effects } Postural instability e.g. fall to ipsilesional side Truncal ataxia Postural control and adjustment e.g. Romberg sign Gait ataxia Extensor rigidity Nystagmus Eye deviation if unilateral

22. Cerebellar Ataxia Hemispheric effects Asynergia Decomposition of movement Dysarthia Jerky speech pattern Dysmetria inability to stop a movement at desired point Dysdiadochokinesia inability to perform rapidly alternating movements Hypotonia decreased muscle tone, pendular knee jerk Intention Tremor usually evident during powerful movements, but absent or diminished with rest (contrast basal ganglia disorders) Remember : Lesions to the cerebellum do not destroy movement, they disrupt it. Ataxia = disordered movement

23. 10 pulses = 250 ms Pacemaker 20 pulses = 500 ms 40 Hz 25 ms 30 pulses = 750 ms Two basic models: Clock counter model Pacemaker produces output to counter Longer intervals represented by more pacemaker outputs in counter Interval model Different intervals represented by distinct elements Each corresponds to a specific duration 250 ms 500 ms 750 ms The Cerebellum and Timing Cerebellum is thought be involved in the timing of movements because cerebellum lights up in PET study of complex/novel timing tasks (Penhune et al. 1998) cerebellar patients are imparied at tasks like tapping along to a metronome beat

24. Multiple timer model Must be independent (interval) timers for each effector (finger/hand/limb etc.) as unilateral cerebellar damage gives rise to unimanual timing deficit, but bimanual tapping improves performance. Ivry, R.B. & Richardson, T. (2002).

25. Continuous movements Discontinuous movements have a specific temporal goal can be set going and left This is what is controlled by the cerebellum. Spencer et al (2003): Cerebellum is only responsible for stop-start movements, not continuous motion.

26. No Prisms Prisms Off Prisms On The Cerebellum and Motor Learning The Cerebellum is thought to be involved in motor learning and the maintenance of movement accuracy because patients with cerebellar lesions are impaired at learning novel motor tasks. Evidence from prism adaptation ( e.g. Thach et al., 1992) Example data

27. CORTEX Error Correction Corticospinal Tract Cerebellum Inferior Olive Spino- cerebellar Tract Feedback from actual movement Spinal Cord The Feedback Circuit: One theory of how the cerebellum might correct movement

28. The basal ganglia a collection of nuclei deep in the white matter of the cerebral cortex. They include: Caudate Putamen globus pallidus substantia nigra subthalamic nucleus (the caudate nucleus and the putamen taken together all known as the striatum)

29.  The main input to the Basal Ganglia is exitatory from the frontal cortex (especially from the supplementary motor area SMA)  The striatum (C+P) inhibit the Globus Pallidus whose output to the thalamus is also inhibitory  The thalamic output to the cortex is exitatory.  Striatum activity is modulated by the Substantia Nigra There’s more: Direct and indirect loops. Direct Route Striatum - GPi - Th - cortex Indirect Route detours via GPe and SN. The release of dopamine stimulates D and inhibits InD routes +ve +ve -ve -ve -ve +ve Mod -ve)

30.  Gate Keeper or Brake Regulator? What is the function of the Basal Ganglia? Slow postural adjustments? - BG damage can cause postural disturbances Initiating movements? - BG patients can struggle to start movements Gate Keeper / Brake Regulator (e.g. Gazzaniga et al.)? BG acts in a regulatory way to facilitate desired voluntary movements and inhibit unwanted, often reflexive, movements The direct route enables the preferred action The indirect route suppresses unwanted movements Activity in the BG increases in anticipation of an intended movement

31. Lesions in specific nuclei tend to produce characteristic deficits. the slow and steady loss of dopaminergic neurons in SNpc leads to: Parkinson's disease, 3 symptoms usually associated with Parkinson's are: Tremor (+ve) most apparent at rest Rigidity (+ve) due to simultaneous contraction of flexors an extensors Bradykinesia (ive) difficulty initiating voluntary movement Akinesia illustrates intentional aspect of BG function +ve -ve -ve -ve +ve X -ve Fixed by removal of STN Remember the role of the GPi is inhibitory

32. Whereas degeneration of the caudate and putamen (inhibitory) leads to: Huntington's disease, or chorea, a hereditary disease of unwanted movements. produces continuous dance-like movements of the face and limbs A related disorder is hemiballismus, flailing movements of one arm and leg, which is caused by damage (i.e., stroke) to the subthalamic nucleus. +ve -ve X -ve +ve -ve Remember the role of the GPi is inhibitory

33. Apraxia What is apraxia? Apraxia has an exclusionary definition: It is a disorder of skilled movement that cannot be attributed to basic level sensory, motor or cognitive disturbances It is therefore a disorder of high-level perceptual, cognitive and/or motor systems Action system  Three component approach • 1. Perceptual processes  vision, proprioception, haptics, vestibular, auditory • 2. Cognitive processes  attention, semantic memory, decision-making, response selection, motor representations • 3. Motor processes  convert movement plan into motor response, control muscle activation

34. Some basic tests for apraxia

35. But watch out for confounds

36. Brain areas involved (Arcuate Fasciculus) Primary Motor cortex SMA (Broca’s area) Primary auditory ortex Primary Visual cortex Angular gyrus (Wernicke’s area)

37. Main types of Apraxia Ideational apraxia inability to produce a coherent action sequence - Kimura Box Impairment in the concept of an action ability to imitate gestures / produce movements on command spared Thought to occur when the motor programming area is destroyed by damage to the supramarginal gyrus, impairing the conceptual representation of an action and leading to deficits in using tools or performing an action to verbal command while imitation is spared (Koski (on web))

38. Ideomotor apraxia Impairment in the performance of skilled pantomime movements on verbal command or in imitation most commonly caused by parietal damage in the dominant hemisphere (LH). In this case bilateral apraxia results. (In rare cases a lesion to the right-hemisphere SMA or to the corpus callosum may also produce ideomotor apraxia. In this case the apraxia is restricted to the left limb.) Ideomotor apraxia occurs when the motor programming area is disconnected from the premotor and motor regions, so that the patient can conceptualize but not actually execute the action, demonstrating spared recognition of tools but deficient ability to use them appropriately or to imitate actions.

39. Ideomotor apraxia (cont.) Can be ok with ipsilesional limb Have greatest difficulty when imitating transitive movements (tool use) Several types of errors Use body parts instead of imagined tool (e.g. scissors) Perseverative errors (do previous pantomime) Sequencing (e.g open door twist before reach or pull before twist) Most characteristic are spatial errors Postural (e.g. wrong grip) Spatial orientation (e.g. not cutting in one plane) Spatial movement (e.g screwdriver shoulder not wrist) Impairment in knowing how, rather than what to do

40. SMA AG 2 forms of ideomotor apraxia (Heilman and Rothi, 1993) Loss of praxicons in supramarginal or angular gyrus Perform poorly to command, cannot comprehend gestures 2. Disconnection of praxicons from premotor and motor areas (caused by lesions anterior to SMG/AG. Praxicon = stored spatiomotor gesture representations which provide the ‘‘time-space-form picture of the movement’’ (Liepmann & Maas, 1907) a ‘movement formula’ if you like But, Ochipa et al (1990) Patient could comprehend Panto and panto to command, but not imitate transitive gestures Praxicons stored in dominant inferior parietal lobe

41. Auditory/verbal input (command) Visual input (gesture or object) 2 route model lexical route Auditory Analysis Visual Analysis Input praxicon } Semantics (learnt actions) SMG/AG Output praxicon Output praxicon can recognise/comprehend, but can’t produce Between input and output praxicon able to recognise, but not produce object gestures, but can do so to verbal command Input praxicon unable to recognise/comprehend gestures, but can do so to verbal command Direct route can do meaningful gestures only Any of above can still imitate meaningful and meaningless gestures Innervatory patterns (motor plan) (SMA) Direct Non-lexical Motor sytems

42. Quick review Damage to: Input praxicon unable to recognise/comprehend gestures, but can do so to verbal command Between input and able to recognise, but not produce object output praxicon gestures, but can do so to verbal command Output praxicon can recognise/comprehend, but can’t produce Any of above can still imitate meaningful and meaningless gestures Direct route can do meaningful gestures only

43. Auditory/verbal input (command) Visual input (gesture or object) 2 route model lexical route Auditory Analysis Visual Analysis Input praxicon } Semantics (learnt actions) SMG/AG Output praxicon Innervatory patterns (motor plan) (SMA) Direct Non-lexical Motor sytems Problem is when a patient can do meaningless imitation, but not meaningful imitation (MF (Bartolo, 2001)) Another patient that causes problems for this model is BG (Buxbaum, 2000) who can do tool-use gestures, but not other gestures, but whose meaningless imitation is worse than meaningful imitation

44. Lexical route Direct route In PPC Buxbaum 2000 Dynamic interplay between knowledge of tool use and stored learnt gestures and body-centred representations of how to do actions (the body schema). The boxes on the left can supplement or boost the damaged processes of the right hand box.

45. A closer look at Patient BG: • gestures nearly normally with tool in hand • And recognises gestures quite well • gesture representations can be accessed by visual input • more deficient in imitating meaningless gesture-like movements • than spatially matched meaningful gesture analogues • direct route damaged? • But, unable to gesture to command , to sight of object or imitation • output praxicon damaged? • difficulty in matching gestures (but not objects), • especially when a spatial transformation is required • deficient processes not conceptual or visual,but spatiomotor

46. 1. What is the basis for the relative integrity of BG’s tool use? 2. Why does she fail to use the direct route upon provision of a model to be imitated? One possibility is dual lesions to both lexical and direct route more parsimonious explanation: BG’s pattern reflects damage to a unitary set of procedures or representations common to both lexical and direct routes (Buxbaum, 2000).

47. Apraxia summary 2 main types of apraxia 2-route model explains most functional characteristics of ideomotor apraxia are covered by the 2-route model, but Cannot account for dissociation between being able to perform meaningless, but not meaningful gestures (patient MF (Bartolo)) Cannot account for preserved tool-use gesture with impaired other geture and impaired meaningless imitation (patient BG (Buxbaum)