Transcript Neurophysiological mechanisms underlying the understanding

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
Visual and motor responses of a mirror
neuron in area F5 (monkey)
a)
b)
• Food is placed on a tray
• Food is placed on a tray (with tool)
• Experimenter grasping movements
• Experimenter grasping movements
(with tool)
• Monkey grasping movements
• Monkey grasping movements
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
Amygdala
PF (inferior parietal
lobule)
2/3
STS (superior
temporal sulcus)
F5 (ventral
premotor cortex)
none
almost all
Visual system
Motor system
In these connected areas neurons can be found that are
responsive to biological movements
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
dissecting the observed action
motor act_1 .. motor act_n
observation & understanding
mirror neurons (coding for motor acts)
imitation
Execution of motor actions
Conclusions
• There is strong evidence for the important
role of the “mirror system“ in
– Action understanding
– Action imitation