Blissfully unaware: Anosognosia and anosodiaphoria after acquired brain injury

Historically, anosognosia referred to under-report of striking symptoms of acquired brain injury (e.g., hemiplegia) with debilitating functional consequences and was linked with anosodiaphoria, an emotional reaction of indifference. It was later extended to include under-report of all manner of symptoms of acquired brain injury by the patient compared to clinicians, family members, or functional performance. Anosognosia is related to time since onset of brain injury but not consistently to demographic variables, lesion location (except that it is more common after unilateral right than left hemispheric injury), or specific neuropsychological test scores. This review considers all manifestations of anosognosia as a unitary phenomenon with differing clinical characteristics dictated by variability in linked cognitive impairments. It is concluded that anosognosia has three chief contributing factors: (1) procedural: measurement differences across studies in terms of symptom selection and the designation of a gold standard of patient symptomatology; (2) psychological: a tendency towards positive self-evaluation and the avoidance of adverse information, that also occurs in neurologically intact individuals; and (3) neuropathological: an increased likelihood of error recognition failure from disconnections that disrupt feedback between injured brain regions governing specific behaviours (symptoms) and anterior cingulate/insular cortex. Anosodiaphoria is considered as an associated symptom, resulting from the same psychological and neuropathological factors.