Presentation on theme: "Neurophysiological mechanisms underlying the understanding and imitation of action NATURE REVIEWS | NEUROSCIENCE SEP 01."— Presentation transcript:
Neurophysiological mechanisms underlying the understanding and imitation of action NATURE REVIEWS | NEUROSCIENCE SEP 01
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?
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“
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
a) 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 Visual and motor responses of a mirror neuron in area F5 (monkey)
Visual and motor responses of a mirror neuron in area PF (Recordet in the right hemisphere) PG.. precision grip WH.. whole hand
Mirror system in monkeys II STS (superior temporal sulcus) PF (inferior parietal lobule) F5 (ventral premotor cortex) In these connected areas neurons can be found that are responsive to biological movements almost all 2/3 none Visual systemMotor system Amygdala
Activity of a mirror neuron in F5 in response to action observation in full vision and in hidden conditions a)Full vision, grasping b)Hidden conditions, grasping c)Full vision mimicking grasping d)Hidden conditions mimicking grasping
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
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
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
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.
Imitation response facilitation motor actions motor act_1.. motor act_n mirror neurons (coding for motor acts) observation & understanding Execution of motor actions imitation dissecting the observed action
Conclusions There is strong evidence for the important role of the “mirror system“ in –Action understanding –Action imitation