The capacity to reflect on one's sense of self is an important component of self-awareness. In this paper, we investigate some of the neurocognitive processes underlying reflection on the self using functional MRI. Eleven healthy volunteers were scanned with echoplanar imaging using the blood oxygen level-dependent contrast method. The task consisted of aurally delivered statements requiring a yes-no decision. In the experimental condition, participants responded to a variety of statements requiring knowledge of and reflection on their own abilities, traits and attitudes (e.g. 'I forget important things', 'I'm a good friend', 'I have a quick temper'). In the control condition, participants responded to statements requiring a basic level of semantic knowledge (e.g. 'Ten seconds is more than a minute', 'You need water to live'). The latter condition was intended to control for auditory comprehension, attentional demands, decision-making, the motoric response, and any common retrieval processes. Individual analyses revealed consistent anterior medial prefrontal and posterior cingulate activation for all participants. The overall activity for the group, using a random-effects model, occurred in anterior medial prefrontal cortex (t = 13.0, corrected P = 0.05; x, y, z, 0, 54, 8, respectively) and the posterior cingulate (t = 14.7, P = 0.02; x, y, z, -2, -62, 32, respectively; 967 voxel extent). These data are consistent with lesion studies of impaired awareness, and suggest that the medial prefrontal and posterior cingulate cortex are part of a neural system subserving self-reflective thought.

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Over the last 20 years, numerous papers that are relevant to understanding the problem of impaired self-awareness after moderately severe to severe traumatic brain injury have appeared. This article reviews many of these papers and summarizes salient findings relevant to rehabilitation and future research.

Anosognosia is the lack of awareness or the underestimation of a specific deficit in sensory, perceptual, motor, affective or cognitive functioning due to a brain lesion. This self-awareness deficit has been studied mainly in stroke hemiplegic patients, who may report no deficit, overestimate their abilities or deny that they are unable to move a paretic limb. In this review, a detailed search of the literature was conducted to illustrate clinical manifestations, pathogenetic models, diagnostic procedures and unresolved issues in anosognosia for motor impairment after stroke. English and French language papers spanning the period January 1990-January 2007 were selected using PubMed Services and utilizing research words stroke, anosognosia, awareness, denial, unawareness, hemiplegia. Papers reporting sign-based definitions, neurological and neuropsychological data and the results of clinical trials or historical trends in diagnosis were chosen. As a result, a very complex and multifaceted phenomenon emerges, whose variable behavioural manifestations often produce uncertainties in conceptual definitions and diagnostic procedures. Although a number of questionnaires and diagnostic methods have been developed to assess anosognosia following stroke in the last 30 years, they are often limited by insufficient discriminative power or a narrow focus on specific deficits. As a consequence, epidemiological estimates are variable and incidence rates have ranged from 7 to 77% in stroke. In addition, the pathogenesis of anosognosia is widely debated. The most recent neuropsychological models have suggested a defect in the feedforward system, while neuro-anatomical studies have consistently reported on the involvement of the right cerebral hemisphere, particularly the prefrontal and parieto-temporal cortex, as well as insula and thalamus. We highlight the need for a multidimensional assessment procedure and suggest some potentially productive directions for future research about unawareness of illness.

Personality disturbances associated with traumatic brain injury are reviewed. The varied structural pathology of the brain in this patient group makes it difficult to specify how different brain lesions may result in specific emotional and motivational disturbances. However, an attempt to clarify terms and review empirical findings is made. Longitudinal prospective studies that utilize appropriate control groups are needed. Future research may especially benefit by considering the long-term effects of early agitation following traumatic brain injury as well as the problem of aspontaneity and impairment of self-awareness.

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