Transcript Slide 1
WELLCOME DEPARTMENT OF IMAGING NEUROSCIENCE Functional Imaging Laboratory Mirror Neurons 1996-2005 “Thus I regard Rizzolati's discovery [of mirror neurons] — and my purely speculative conjectures on their key role in our evolution — as the most important unreported story of the last decade.” Ramachandran, V.S. 2000, MIRROR NEURONS and imitation learning as the driving force behind "the great leap forward" in human evolution Mirror Neurons in Premotor Area • Neurons in monkey cortex have been found that respond not only to seeing the monkey’s hand grasp an item, but when other hands grasp it as well, including the homologous human hand. • The neuron does not respond to a pliers picking up the item. • Most mirror neurons respond best to one type of action, like picking up. • Mirror neurons may help us to understand what others are doing, how to react to their actions, but also how to imitate them Mirror neurons and action representation Brain, 1996; Exp Brain Res, 1996. • 92 of 532 premotor F5 neurons (15-20%) “discharge when the monkey makes active movements and when he observes specific meaningful actions performed by the experimenter.” • Specific to one or a few hand actions such as ‘Grasping’,’Holding’, ‘Manipulating’, and some to specific grasp (e.g. precision grip, finger prehension…). ---activated by view of grasping with hand, but not when grasping is done with a tool Possible role: discharge of neurons in mirror system generates an internal representation of the movement which is involved in the ‘understanding’ of motor events”. • • Mirror neurons infer hidden goals • … activity ‘represent’ observed goal-directed action. Neuron, 2001 • Activity of F5 Mirror Neurons was recorded in a 2x2 factorial design: – Full vision and Hidden condition – Object-directed and mimed action – 3 types of actions (Grasping, Holding, Placing) • 19 out of 37 recorded F5 Mirror Neurons (50%) were active during: • – Object-directed • action, visible or hidden – But not in the absence of object 19 out of 37 recorded F5 Mirror Neurons (50%) were active during: – Object-directed action, visible or hidden – Not in the absence of object “Half of the F5 Mirror Neurons recorded respond selectively to the observation of specific hand actions even when the final part of the action, i.e., the most crucial in triggering the response in full vision, is hidden from the monkey’s vision.” Mirror neurons with auditory properties • … activity ‘represent’ observed goal-directed action; • … can fire in response to actions even when goals are inferred. Science, 2002; Exp Brain Res, 2003. • Activity of F5 Mirror Neurons was recorded in response to action-related sound: – Perceive action (visual) and sound (auditory): V+S; – Visual only: V; Sound only: S; – Motor execution of the action: M; • 63 out of 497 neurons discharged during M and S: peanut breaking, paper ripping, dropping stick • 22 out of the 63 neurons showed the same action selectivity in V and S: audiovisual Mirror Neurons, and the amplitude of response to V, S and V+S was the same for 16 neurons; • Receiver Operator Characteristics (ROC) analysis using spike-count distribution yielded a 97% accuracy with V+S in predicting the action the monkey is observing (and only 81% for the action he is performing). Broca’s and Wernicke’s Areas “Perception” “Production” Broca’s Area (Negative Image) The two classic loci where brain damage impairs language performance. Warning: Localization of Aphasias is HIGHLY Variable Claim: The function of these areas reflects genetically-grounded language readiness and experience-based language adaptations. Wernicke’s Area MRI-scans from Keith A. Johnson, M.D. and J. Alex Becker The Whole Brain Atlas http://www.med.harvard.edu./AANLIB/home.html F5 is Homologous to Area 45 of Broca’s Area Monkey Massimo Matelli (in Rizzolatti and Arbib 1998) provides the key to relating F5 in the Monkey to Area 45 in the Human. Human Broca's Area: Areas 44 + 45