Abstract
Introduction: Damage of the medial prefrontal lobe result in disinhibition of emotional and also aggressive
behavior. Recent observations demonstrated a predominant role for the medial prefrontal lobe in emotional
modulation (see Eippert et al. at this meeting). Although it has been demonstrated how humans react on
aggressive facial expression (Blair et al, 1999) no functional data about aggressive emotions evoked during
scanning have been reported yet. Here we demonstrate in a competitive reaction time paradigm (see Anderson
Dill, 2000) that aggressiveness or expecting punishment from an aggressor, results in differential representation
sides in the prefrontal lobe and the limbic system.
Method: 16 male subjects (mean age: 28.6 years) were examined in a competitive reaction time task. They were
told that if they react faster than another person (both met immediately before the test) they were allowed to
punish the opponent with a shot of a projectile on the finger and if they loose the opponent will do the same to
them. The intensity of the pain was individually adapted to ensure a painful punishment. In fact the opponent was
an associate of the lab and the amount of winning (36) and loosing (44) incidents was kept constant during the
experiment. Furthermore, the intensity of the punishment was linearly increased during the experiment (50
minutes) and subjects were presented a 3 second view of the opponent during the shot. 12 subjects believed to
play against a real opponent and reacted with an increasing amount of punishment and an increase of
self-attribution of aggression. All subjects were investigated during the task with a 3T Siemens Trio fMRI scanner
using EPI (TE: 30ms; TR: 1.5 sec, 1212 scans with 22 slices of 3+1 mm thickness) and a T1 3D investigation.
Heart rate, skin conductance and reaction time was documented during the scanning. fMRI data evaluation was
performed with SPM2 in a random effects design. Significant activation (p<0.05) was corrected for false positive
responses (AAL) within the voxel volume of medial prefrontal, lateral orbitofrontal lobe, bilateral insula, anterior
cingulate gyrus and bilateral amygdala.
Results: During the time course of the experiment subjects showed an increase of self-attribution of aggression
against the opponent (last versus first session: t(10)=3,31; p<0.01) and reacted more aggressive (t(10)=3.41;
p<0.01). Heart rate showed a characteristic increase before punishing and decrease before punishment.
BOLD-effect was increased during anticipation of the punishment (victim) in the dorsomedial prefrontal lobe
(PFC; BA 9; pc<0.05; coord.: 12; 57; 21) and during aggressive punishment (offender) in the bilateral
orbitofrontal lobe and insula (BA 47; pc<0.001; le: -45, 21, -15; ri: 45, 27, -18). Observation of the punishment of
the opponent resulted in activation of both the dorsomedial prefrontal (BA 9; pc<0.01; 12, 63, 15) and the right
orbitofrontal lobe (BA47; pc<0.05; 54, 33, -6). Additionally, the left amygdala (pc<0.01; -18, -3, -12) and insula
(pc<0.01; -33, 15, 6) was activated.
Discussion: This study is the first which succeeded to establish a behavioral task with increasing aggression
induction in a brain mapping environment. Furthermore it combines evaluation of psychological,
psychophysiological and fMRI-data evaluation. Whereas the dorsomedial PFC is active during confrontation of
aggression of others the bilateral orbitofrontal lobe and insula is active during offending aggressive acts.
