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1 JHU BME 580.422 Biological Systems II Adaptation of Visuomotor Maps Disorders of parietal cortex Reza Shadmehr.

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Presentation on theme: "1 JHU BME 580.422 Biological Systems II Adaptation of Visuomotor Maps Disorders of parietal cortex Reza Shadmehr."— Presentation transcript:

1 1 JHU BME Biological Systems II Adaptation of Visuomotor Maps Disorders of parietal cortex Reza Shadmehr

2 2 xhxh Proprioceptive state of the body: arm, head, and eye positions xtxt xaxa qq f q hand location in fixation coordinates  Target location in fixation coordinates q Displacement vector in fixation coordinates Displacement vector in proprioceptive coordinates Force (motor output) Schematic of the computations involved in reaching

3 3

4 4 A C B 0.5 sec PPC cell Control Task Delay Task D F E 0.5 sec Somatosensory cortex cell Control Task Delay Task PPC neurons encode target of intended movement during the delay period Crammond and Kalaska 1989

5 5 PPC neurons encode target of intended movement even after it disappears Kalaska JF Can J Physiol Pharmacol 1996

6 6 …left of fixation Delayed pointing Delayed pointing with intervening saccade Activation area when the remembered target is to the right of fixation Human PPC neurons code for target location in fixation centered coordinates Medendorp et al Left cortex Right cortex

7 7 Deltoid muscle Primary motor cortex cell Posterior parietal cortex cell (area 5) Opposing loadNo loadAssisting load 500 ms 100 imp/s PPC neurons encode target location and not the forces necessary to reach that target Kalaska JF (1988) Kalaska et al. J Neurosci 1989

8 8 Experiment: rotate each eye by 180 o. After 4-5 months, no sign of adaptation. “When the piece of meat was moved back and forth in the water several centimeters above and a little to one side of the animals, they tilted their heads downward on that side and began to move toward the bottom of the aquarium. Even though the newts happened to be resting on the bottom when the lure was thus waved above them, they cocked their heads down under them and began pushing about among the pebbles of the bottom with the nose and forefeet. If the lure was placed below the animals, the head and forebody were tilted upward and the newts started toward the surface.” Newts show an inability to adapt to radical changes in the optics of vision

9 9 A B Day 3Day 34 Latency (s) Pre-Days of reversing Post- C Primates adapt to radical changes in optics of vision

10 10 x ee xtxt x dv 11 22 c1c1 c2c2 target camera

11 11 AB Wedge prisms: rapid adaptation and equally rapid de- adaptation indicates short-term changes in existing networks

12 12 With extensive training, throwing with wedge prisms can become a skill. This indicates formation of a new map for the prism and the ability to switch on context.

13 13 ModelCopy Patients with lesion in the right hemisphere may exhibit neglect of the left visual space Marshall JC & Halligan PW (1995) Nature 373:521

14 14 Committeri, G. et al. Brain : Neglect of the extra-personal and personal space Test for neglect of extra-personal space: Line bisection test, figure copying, reading a sentence. Test for neglect of personal space: use a comb, use a razor to shave the face, use a lipstick. Neglect of extra-personal space: lesion of the right frontal lobe, ventral premotor cortex Neglect of personal space: lesion of the right inferior parietal cortex STG: superior temporal gyrus MFG: medial frontal gyrus WM: white mater SMG: supramarginal gyrus

15 15 Prism glasses produce after affects that improves the sense of “straight ahead” in neglect patients Rossetti Y. et al. (1998) Nature 395:166

16 16 PrismsControls original pre- post- late Prism glasses produce after affects that reduce the neglect observed in PPC lesions Rossetti Y. et al. (1998) Nature 395:166

17 17 Apraxia Apraxia is an inability to perform skilled movements, particularly tool use, in the absence of elementary motor deficits (weakness, normal posture or tone). It is most commonly associated with damage to the parietal cortical areas of the left hemisphere. When the patient is asked to demonstrate use of a screwdriver, the patient may position his hand as if holding a pen. When given a partially driven nail into a piece of wood, and a collection of tools, they may select a scissor to drive the nail rather than a hammer. In performing a task that requires a sequence of actions, these patients may have difficulty in putting the acts in the proper order. For example, demonstrate how to prepare a letter and envelope for mailing.

18 18 Understanding actions of others: the mirror neuron system Social skills and theory of mind: the awareness that other people have beliefs and desires as we do, but different from our own, and that these beliefs and desires guides their actions. By observing their actions, we can guess their goals and intentions.

19 19 Fogassi et al. (2005) Science 308: D

20 20 Fogassi et al. (2005) Science 308:

21 21 Actions are planned in fixation centered coordinates: Position of the hand and the target are represented in terms of their location with respect to the fixation. Neurons combine proprioceptive information with visual information using a gain field. Movements are planned in terms of goals, not in terms of detailed forces. Lesion of the right parietal cortex can result in neglect. Lesion of the left parietal cortex can result in apraxia. Mirror neurons might provide a mechanism through which we understand the intention of others. Summary of the posterior parietal cortex


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