Although many studies have looked at the mechanisms of anosognosia relating to cognitive and memory difficulties, they remain obscure and poorly unerstood. Having barely been studied, the mechanisms of anosognosia relating to changes in personality traits are even less understood. Just as memory can be affected, so can the personality during the course of Alzheimer's. It is this last type of anosognosia which Jedidi focussed on in his doctoral thesis, entitled Mechanisms of anosognosia: semiology and functional imaging.

'A better understanding of the neuropsychological mechanisms and anatomical correlates (in terms of cerebral malfunctions) of different sub-types of anosognosia enable patients' treatment to be better targeted and better adapted', explains the neurologist.

A third-person perspective

An initial study was carried out at the Cyclotron Research Centre (CRC) using functional magnetic resonance imaging (fMRI). Principal authors: Haroun Jedidi and Arnaud D'Argembeau, neuropsychologist and F.R.S. - FNRS tenured Research Assistant. Twenty-three young subjects had to give an opinion about their own personality traits. 'We presented these volunteers with a series of descriptive adjectives' indicated Jedidi. 'During their time in the fMRI, the subjects had to judge to what extent these adjectives described them. Just after the functional acquisition, they carried out the same assessment, but this time also specifying how sure they were about whether they have this character trait and to what point it was important for them to have it.'

The results of this study tended to suggest that the activity of the dorsomedial prefontal cortex is related to a cognitive evaluation of personality traits, i.e. with the certainty of possessing or not possessing a specific personality trait, and that the ventromedial prefrontal cortex appears to be involved in a more emotional assessment- the importance of having a given personality trait.

Armed with these results, Jedidi then looked at anosognosia affecting changes in personality traits in Alzheimer's patients.

It is generally considered that this type of anosognosia is partly explained by a deficit in updating the view of the self (autobiographical information). As such, the subject is no longer aware of changes in their personality traits. It is known that the dorsomedial prefrontal cortex plays a role in terms of integrating many high-level cognitive processes, in particular those involved in self-awareness and facial recognition.

A group of 37 patients suffering from the early stages of Alzheimer's disease and another group of older, healthy patients had their resting cerebral activity recorded using positon emission tomography (TEP). They were then asked to answer a personality questionnaire consisting of 40 items. They had to evaluate each proposition on a scale from 1 to 4 (1: 'I am not at all distracted', 2: 'A little distracted'; 3: 'Very', 4: 'Extremely'). Moreover, the participants had to conduct this exercise twice, the first time referring to their current personality, and the second referring to their personality ten years ago. In addition, a friend or family member of each volunteer was asked to answer, under the same conditions, questions about the personality of the participant they were accompanying. A series of differential scores were thus established, using this information.