Transcript ExamplePoster

EEG study of the mirror neuron system
in children with HFA
Ruth Raymaekers, Jan Roelf Wiersema & Herbert Roeyers
Introduction
diPelligrino (1992), Rizzolatti and colleagues (2001) discovered a unique set of premotor neurons in macaque monkeys called mirror neurons. These
neurons appear to respond both when a primate performs an action and when it sits motionless observing another individual performing the same
action. There is indirect evidence that a comparable neuronal system is present in humans, most likely also situated in the premotor cortex . Thus, the
mirror neuron system (MNS) is a type of observation/execution matching system that is primarily thought to be involved in perception and
comprehension of motor acts. In addition, the human MNS has been implicated in a variety of higher order cognitive processes: imitation, TOM
abilities, empathy, social cognition and language. Autism Spectrum Disorders (ASD) are characterized by deficits in these skills.
MNS as neural substrate for deficits in social interaction and communication in ASD?
Several studies have investigated the MNS in ASD leading to the finding that this system is dysfunctional in ASD. Unfortunately, the number of
participants was mostly small and the age range large. Furthermore different neurophysiological methodologies have been used: fMRI (Williams et al.,
2006; Dapretto et al., 2005) or EEG (Oberman et al., 2005, 2006; Bernier et al., 2007). The MNS can be examined with the aid of EEG measurements,
by monitoring the so-called mu frequency band oscillations. At rest, motor neurons spontaneously fire in synchrony leading to large amplitude EEG
oscillations in the 8 through 13 Hertz frequency band (mu band). When subjects perform an action, these neurons fire asynchronously, thereby
decreasing the power of this mu band. During observed motor actions, the MNS is the only network that has been identified to be active in the area of
the premotor and sensorimotor cortices, suggesting that mu wave suppression to observed actions could be used as a selective measure of the
functioning of the MNS.
Method
In the current study, children between 8 and 13 years participated. The HFA
group contained 20 children and was matched on age and IQ to a group of
typically developing children. All children were asked to participate in a task
that consisted of 4 conditions. In three of them, a video had to be watched:
(1) a video of a hand movement, (2) two balls that moved to and fro each
other, and (3) a video of white noise or static. In the other condition (4), the
children had to imitate the hand movement. All conditions were
counterbalanced with the restriction that the self movement condition
always came after the video of the moving hand. Throughout the
experiment, children were asked to sit as quietly as possible and watch the
videos carefully.
Mu suppression was calculated as the natural log of the ratio of the power
in the experimental conditions relative to the power during the baseline
condition (white noise). The ratios were measured by three electrodes close
to the sensorimotor cortex: C3, Cz and C4.
HFA
N = 20
Control
N = 15
CA(years)
M
sd
IQ
M
sd
11.2
1.5
10.7
1.3
105
14.6
111
20.9
Gender
M:F
18:2
12:3
Selection Procedure
Clinical diagnosis
Questionnaires for parents and teacher:
Disruptive Behavior Disorder rating scale
Child Behavior Checklist / Teacher Report Form
Social Communication Questionnaire
Diagnostic interview parents
Autism Diagnostic Interview – Revised
Diagnostic Interview Schedule for Children-IV
WISC-III: Total IQ > 85 (Vocabulary, Similarities,
Block Design, Picture Arrangement)
Results
Controls
Hand / Noise
HFA
VideoHand / Noise
Balls / Noise
0,00
0,00
-0,05
-0,05
Ln (Condition/Baseline)
Ln (Condition/Baseline)
VideoHand / Noise
Video hand
-0,10
-0,15
-0,20
-0,25
-0,30
-0,35
Hand / Noise
Balls / Noise
Control
HFA
-0,10
C3
Cz
C4
C3
3,0
-0,15
Cz
C4
2,5
-0,20
2,0
-0,25
1,5
-0,30
1,0
-0,35
0,5
0,0
7
-0,45
-0,45
Hand
3,5
-0,40
-0,40
White noise
C3
Cz
8
9
10
11
12
13
13
14
14 7
8
9
11
12
13
14 7
7
8
8
9
9
10
10
11
11
12
12
13
13
14
14
Frequency (Hz)
C4
Self-condition: mu suppression is significant in this condition as
compared to the white noise baseline. There is no significant group
difference. Video displaying a moving hand: relative to the baseline,
the mu frequency is again suppressed. But suppression is not that strong
as compared to the self condition. For the ASD group, the MNS is
apparently also working. All but for electrode C4, there is a clear mu
suppression with respect to the baseline. Furthermore, the differences
between the groups are not significant for electrodes Cz and C4. For
electrode C3, at best a trend is observed.
10
0.4
0.4
Control group
ASD group
0.2
0.2
0.0
0.0
-0.2
-0.2
-0.4
-0.4
-0.6
-0.6
-0.8
-0.8
60
70
Cz
80
90
C3
C4
100
110
Linear (Cz)
120
130
Linear (C3)
140
150
Linear (C4)
160
60
70
Cz
80
90
C3
C4
100
110
Linear (Cz)
120
130
Linear (C3)
140
150
160
Linear (C4)
Discussion
The manipulation was successful, the adopted methodology therefore proved suitable to probe the functioning of the MNS. However, we have not
found a confirmation of the results of other MNS studies in ASD. Our results indicate that the MNS is functioning in the control group as well as in
children with HFA. A quick check of correlations with other variables showed that the observed effects might depend on these variables. Inverse
correlations were identified between mu suppression and IQ for HFA and control groups. So, it appears that these correlates have to be taken actively
into account when setting up a paradigm and definitely call for further research.
Corresponding author: Ruth Raymaekers, Ghent University, Department of
Experimental-Clinical and Health Psychology, Research Group Developmental Disorders;
Henri Dunantlaan 2, 9000 Gent; [email protected]