Phylogenetic versus ontogenetic fear-relevant pictures: EEG-source localisation by means of LORETA

Pripfl, J., Fischmeister, F. P. S., Gerstmayer, A., Leodolter, U., and Bauer, H.
Biological Psychology Unit, Department of Psychology, University of Vienna, Austria

Purpose Evolution has made some objects innate sources of fear (Russell, 1979) and has shaped some relatively hardwired and reflexive escape responses; however, mammals are also able of learning to fear initially neutral objects that have signalled danger through Pavlovian conditioning. This study addressed the question whether phylogenetic fear-relevant stimuli (e.g., spiders) are processed by different brain-structures than onotgenetic fear-relevant stimuli (e.g., pointed guns).

Methods 4 categories of pictures (neutral, ontogenetic fear-relevant, phylogenetic fear-relevant ‘snakes’ and ‘spiders’) were randomly presented to female subjects. Multi-channel evoked slow cortical potentials (SCPs; Bauer, 1998) were recorded during picture viewing. Low resolution electromagnetic tomography (LORETA; Pascual-Marqui, 1995) was used for quantitative localization of neural activity within the gray mater of the cortex. Inference-statistical analysis of the LORETA-values was done by means of 'statistical non-parametric mapping’ (SnPM; Holmes et al., 1996).

Results LORETA localized the sources of the EEG-data for all categories in the same brain regions (highest values were found in the ventral visual pathway) and SnPM indicated stronger activation in these regions for phylogenetic than for ontogenetic fear-relevant stimuli. Neutral stimuli elicited the lowest activation. Results are valid for N2, P3 and SCPs up to 3ooo ms post-stimulus.

Conclusion Our results show that phylogenetic as well as ontogenetic fear-relevant pictures are processed through the same cortical regions. However, the activity differences may reflect that more resources are assigned to phylogenetic than to onotgenetic fear-relevant cues, perhaps due to the influence of the amygdala.