1 NATURE REVIEWS | NEUROSCIENCE SEP 01 Neurophysiological mechanisms underlying the understanding and imitation of actionNATURE REVIEWS | NEUROSCIENCE SEP 01
2 ConceptsAction:Goal-directed behaviors that produces reward for the individualAction understandingThe capacity to achieve the internal description of an action and use it to organize appropriate future behaviourAction imitationTo imitate an observed action What are the neuronal mechanisms that underlie action understanding and imitation?
3 2 hypothesis for “action understanding“ Visual hypothesisAction 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 1996They can be specific to certain actionsThey don‘t respond to fake actions
5 Visual and motor responses of a mirror neuron in area F5 (monkey) Food is placed on a trayExperimenter grasping movementsMonkey grasping movementsb)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 gripWH .. whole hand
7 Mirror system in monkeys II AmygdalaPF (inferior parietal lobule)2/3STS (superior temporal sulcus)F5 (ventral premotor cortex)almost allnoneVisual systemMotor systemIn 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 conditionsFull vision, graspingHidden conditions, graspingFull vision mimicking graspingHidden conditions mimicking grasping
9 Mirror system in humans There are several experiments indicating that an mirror system also exists in humansEEG and MEG studies show that typical signals that are suppressed by motor neuron activity are also suppressed by action observationTMS (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“ ProThe visual properties of some STS neuronsContraNot clear how validation of the meaning of the observed object is achievedNot obvious how the complex properties could emerge
12 Action understanding: “direct matching hypothesis“ ProExistence of mirror neuronsEmerge of cells with complex properties with motorsystem as teacherNot just visual stimuli are involved for action understanding (Experiment)ContraActivation in motor areas might be due to motor preparation for imitation.
13 Imitation response facilitation motor actionsdissecting the observed actionmotor act_1 .. motor act_nobservation & understandingmirror neurons (coding for motor acts)imitationExecution of motor actions
14 ConclusionsThere is strong evidence for the important role of the “mirror system“ inAction understandingAction imitation