Recognition of the Intentionality of Actions in the Mirror Neuron System: An EEG Study

1
Recognition of the Intentionality of Actions in
the Mirror Neuron System An EEG Study Alexander
J. Bressler1, Lindsay M. Oberman1,2, Vilayanur
Ramachandran 1,2 Jaime A. Pineda3 1 Department
of Psychology, 2 Center for Brain and Cognition,
3 Department of Cognitive Science, UC San Diego,
La Jolla, California 92093
Task
Results
Introduction
It is important for humans to understand and
communicate well with one other, especially in
situations where one person must understand and
interpret the actions of others. This may be a
factor in developing a theory of mind and may
represent the basis for social learning and
interaction. The mirror neuron system (MNS) of
the mammalian brain is thought to be involved in
action recognition, and is one system that has
provided strong support for the direct-matching
hypothesis of action understanding1. Mirror
neurons were originally found in area F5 of the
ventral premotor cortex of the Macaque monkey.
Growing evidence now suggests that there is a
homologous system in Brocas area of the human
brain. These mirror neurons become activated
both when a particular action is performed and
when the same action is observed2. Previous
studies show that a decrease in EEG power in the
mu frequency band (8-13 Hz), or mu suppression,
reflects MNS activity during execution and
observation of motor actions3.The present study
investigated whether the MNS responds
differentially depending on the actors
intentions. If the MNS is involved in
understanding the deeper meaning behind an
action, mu wave suppression will vary between
conditions. In particular, if the participant is
involved solely in understanding the absolute
meaning of the action (without emotional content
or underlying intentions) then there should be no
difference in mu suppression between conditions.

• EEG data were collected during four observation
  conditions and one action condition
• Baseline Visual white noise.
• Non-goal Directed Action A hammer swinging up
  and down in space.
• Goal-Directed Action (no emotional intention)
  Hammering a nail into a board.
• Goal-Directed Action (emotional intention)
  Hammering a nail into what appears to be a human
  hand.
• Performed Action Subjects performed the same
  action as 2, the non-goal-directed action.
• To ensure subjects attended to the stimuli
  during conditions 2, 3, and 4, they were asked to
  perform a continuous performance task. The videos
  contained random 1 sec pauses in the repetitious
  motion. The condition 3 and 4 videos were looped
  so that approximately every 40 sec the video
  repeated. Participants were asked to count the
  number of times the video paused/repeated and to
  report the number at the end of the block.

Conclusions
The results were consistent with past findings in
that a person performing an action shows more mu
suppression than when only observing an action.
High mu (10-13 Hz) was most sensitive to this
effect. That is, the Performed Action condition
was more suppressed than the other experimental
conditions when compared to baseline. In the low
mu condition (8-10 Hz), there were no differences
among the experimental conditions, but all showed
mu suppression relative to baseline. The
non-goal-directed action video of the hammer did
not produce less suppression than the other
conditions. This is inconsistent with past
findings in which non-goal-directed actions
produce less mu suppression than goal-directed
actions. There was insufficient evidence to
conclude that the MNS responds differentially to
stimuli that differ only in intention since there
was no significant difference in mu suppression
between the board and hand conditions. However,
recent findings in a similar study using fMRI
have led to the conclusion that the MNS does play
a role in understanding the intentions behind
others actions5. This suggests that mu rhythms
may not be sensitive enough to distinguish these
differences in activity.
Background
At rest, the human sensorimotor cortex over scalp
locations C3, Cz and C4 spontaneously generates
oscillations in the 8-13 Hz frequency band (mu
rhythm) with large amplitudes due to the
synchronous firing of sensorimotor neurons.
During the observation of hand actions,
desynchronization occurs and mu rhythm amplitudes
decrease (mu wave suppression)4. When an action
is initiated, greater desynchronization occurs,
resulting in even smaller amplitudes of the mu
rhythm.
Analyses
? Power in the mu frequency at scalp locations
corresponding to primary motor cortex (C3, Cz,
and C4) were compared during the experimental
conditions relative to the baseline (visual white
noise). ? The ratio of the power during the
experimental conditions to the power during the
baseline condition was used as a measure of mu
wave suppression. ?A log transform of this ratio
was used for analysis to control for the
non-normality of ratio data due to lower
bounding. ?A log ratio of less than zero would
indicate suppression whereas a value of zero
would indicate no suppression and a value greater
than zero would indicate enhancement.
1.0 0 0.8 0 0.6 0
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