1. NATURE REVIEWS | NEUROSCIENCE SEP 01
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)
Food is placed on a tray
Experimenter grasping movements
Monkey grasping movements b)
Food is placed on a tray (with tool)
Experimenter grasping movements (with tool)
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
STS (superior temporal sulcus)
F5 (ventral premotor cortex)
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 is related 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