Neurophysiological mechanisms underlying the understanding and imitation of action

1. Neurophysiological mechanisms underlying the understanding and imitation of action NATURE REVIEWS | NEUROSCIENCE SEP 01

2. Concepts • Action: • Goal-directed behaviors that produces reward for the individual • Action understanding • The capacity to achieve the internal description of an action and use it to organize appropriate future behaviour • Action imitation • To imitate an observed action  What are the neuronal mechanisms that underlie action understanding and imitation?

3. 2 hypothesis for“action understanding“ • Visual hypothesis Action understanding is based on visual analysis of the different elements that form the action. • Direct matching hypothesis (“mirror system“) While understanding an action the visual input is directly mapped on the motorsystem that would be responsible to do the task by oneself.  The aim of this paper is to give evidence to the “direct matching hypothesis“

4. Mirror system in monkeys I • Mirror neurons are a particular class of visuomotor neurons. • They where discovered in F5 (ventral premotor cortex, neurons code for goal related motor acts) in 1996 • They can be specific to certain actions • They don‘t respond to fake actions

5. Visual and motor responses of a mirror neuron in area F5 (monkey) • b) • Food is placed on a tray (with tool) • Experimenter grasping movements (with tool) • Monkey grasping movements • a) • Food is placed on a tray • Experimenter grasping movements • Monkey grasping movements

6. Visual and motor responses of a mirror neuron in area PF (Recordet in the right hemisphere) PG .. precision grip WH .. whole hand

7. Mirror system in monkeys II Amygdala PF (inferior parietal lobule) 2/3 F5 (ventral premotor cortex) STS (superior temporal sulcus) almost all none Visual system Motor system In these connected areas neurons can be found that are responsive to biological movements

8. Activity of a mirror neuron in F5 in response to action observation in full vision and in hidden conditions • Full vision, grasping • Hidden conditions, grasping • Full vision mimicking grasping • Hidden conditions mimicking grasping

9. Mirror system in humans • There are several experiments indicating that an mirror system also exists in humans • EEG and MEG studies show that typical signals that are suppressed by motor neuron activity are also suppressed by action observation • TMS (transcranial magnetic stimulation) • Excitability of the spinal cord during action observation  Experiments show that action observation isrelated to activation of cortical areas that are involved in motor control

10. Localization of the human mirror system (by brain imaging) • Brain imaging experiments provide evidence for the following homologues areas in monkey and human: • Broca‘s area BA44 (considered to be devoted to speech production)  F5 (ventral premotor cortex) • STS and PF seem to have similar jobs in human and monkey brain

11. Action understanding: “visual hypothesis“ • Pro • The visual properties of some STS neurons • Contra • Not clear how validation of the meaning of the observed object is achieved • Not obvious how the complex properties could emerge

12. Action understanding: “direct matching hypothesis“ • Pro • Existence of mirror neurons • Emerge of cells with complex properties with motorsystem as teacher • Not just visual stimuli are involved for action understanding (Experiment) • Contra • Activation in motor areas might be due to motor preparation for imitation.

13. Imitation  response facilitation motor actions dissecting the observed action motor act_1 .. motor act_n observation & understanding mirror neurons (coding for motor acts) imitation Execution of motor actions

14. Conclusions • There is strong evidence for the important role of the “mirror system“ in • Action understanding • Action imitation