Research report
Towards a functional neuroanatomy of self processing: effects of faces and words

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Abstract

We studied the neural correlates of self vs. non-self judgements using functional magnetic resonance imaging (fMRI). Individually tailored faces and personality trait words were used as stimuli in three experiments (exp.). In the first two experiments, brain activation was measured while subjects viewed morphed versions of either their own (self face exp.) or their partner’s face (partner’s face exp.), alternating in blocks with presentation of an unknown face. In the self face exp. right limbic areas (hippocampal formation, insula, anterior cingulate), the right middle temporal lobe, left inferior parietal and left prefrontal regions showed signal changes. In the partner’s face exp., only the right insula was activated. In the third exp., subjects made decisions about psychological trait adjectives previously categorized as describing their own attributes. Activation was present in the precuneus, the left parietal lobe, left insula/inferior frontal gyrus and the left anterior cingulate. A reaction time advantage was present when subjects responded to self-relevant words. The main area with signal changes during self-reference processing, regardless of the type of stimulus, was the left fusiform gyrus. The self-relevant stimuli engaged to a differential extent long term and working memory, semantic and emotional processes. We suggest that regions activated by these stimuli are engaged in self-processing.

Introduction

Processing of self relevant information and self knowledge is regarded as distinct from processing ‘objective’ information [30], [56]. Self knowledge is stored in two main memory systems, semantic and episodic memory. Episodic memory [61], [68] deals with individual (‘narrative’) episodes that are definable with respect to time and place, whereas semantic memory contains abstracted facts about the world and who we are, which we need for interaction with our environment. It is assumed that different brain regions contribute to these various forms of memory processing [41], [62]. In experiments on memory encoding and retrieval it has been shown that relating information to oneself (self-referent effect) enhances recall [5], [33], [35], [54], [63]. This phenomenon is largely independent of access to autobiographical narrative memory [34], [37]. There is evidence for the relative independence of semantic and episodic autobiographical memory systems, which can each be accessed independently [13], [42], [70]. The neural systems involved in modality independent self-knowledge are unknown.

A powerful cue for investigating self-information processing is our own face, which we see regularly in the mirror and in photographs. Mirror recognition does not occur in humans before 18 months [1] or in other primates, except adult great apes [21], [48]. Self recognition can therefore be considered a complex neurocognititive function. Several recent studies [29], [31], [65], [66] could demonstrate a unique behavioral response towards the subjects’ own face, compared to familiar control faces. It is not known, whether there is a distinct anatomical basis of facial self recognition, although severe deficits in this ability have been found in Alzheimer’s Disease [7], [49] and a larger P300 response to the subjects’ own face compared to familiar faces has been reported [46].

In this study, we wished to shed light on the functional anatomy of processing of self relevant information. We wanted to address whether there are distinct cerebral regions underlying the ability to distinguish between self and non-self, a fundamental capacity of biological systems, and whether such a system is engaged regardless of stimulus material (faces or visually presented words).

We used functional magnetic resonance imaging (fMRI) to delineate significant changes in blood oxygenation level dependent contrast as an index of changes in local neuronal activity in the brains of human volunteers. In 2 experiments, we measured localized MRI signal changes while subjects were presented with photos of their own face, their partner’s face and unknown faces. In a further fMRI experiment, we investigated semantic self knowledge by visual presentation of personality trait words.

Based on previous PET studies [14], [17] and clinical data [32], [36], [67], we hypothesized that early sensory input regions are activated by self-referring stimuli irrespective of stimulus modality. We predicted that differential effects would be seen for higher order processing, namely greater right hemispheric activation for one’s own face [51] (vs. other face) and greater left sided activation for self-descriptive words (vs. non-self descriptive).

Section snippets

Subjects

Six male, right handed [4] volunteers in stable heterosexual relationships were recruited. All participants were healthy, native English speakers, on no medication and with no history of neurological or psychiatric illness. Only subjects with a generally positive attitude towards themselves and their partner were selected. The mean estimated IQ [45] was 115 (S.D. 5). Neither the subjects nor their partners wore spectacles and none had facial hair. Subjects knew their partners between 1 and 16

Behavioral data

The behavioral data obtained during scanning are shown in Table 1. Accuracy judgements for both of the face experiments was 99.2%. Reaction time showed delayed response for the known (self, partner) vs. the unknown faces. There was no significant reaction time difference when judgement for the self face was compared with judgement for partner faces or the reaction times for the unknown faces between both experiments.

In exp. 3, the self descriptive traits were judged significantly faster than

Discussion

In the present study, we attempted to map out the neural system involved in self-information processing. In two separate, individually tailored experiments, the subjects’ own face and self describing personality trait adjectives were used as stimuli. Irrespective of modality, (face or words) the left fusiform gyrus was activated. Differential signal changes for the own face experiment involved the right limbic system and left prefrontal areas. The regions specialized for analysis of verbal self

Acknowledgements

T.K. was supported by the German Research Foundation (DFG); C.S. by the Pilkington Family Trusts, E.T.B and M.L.P. by the Wellcome Trust. We thank P.K. McGuire, P. Fletcher and J.A. Gray for advice on earlier versions of the manuscript, and C. Andrew for technical support

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