The role of white matter disconnections in Anosognosia for Hemiplegia

Anosognosia for Hemiplegia (AHP) is a disturbance in motor awareness, secondary to right brain hemisphere damage, in which patients are unaware of their limb paralysis (Babinski 1914). Decades of neuropsychological and neuroimaging studies revealed that AHP is unrelated to other co-occurring symptoms, such as neglect and memory impairments (Fotopoulou, 2014). Rather, some experimental evidences address AHP to the disruption of action monitoring (Berti et al., 2005) or error recognition processes (Moro et al., 2015). Others hypothesized an impairment in updating one’s beliefs about the self (Fotopoulou, 2008) that involves the failure of motivational/emotional (Vuilleumiere, 2004) and mnemonic (Mograbi & Morris, 2013) processes. Findings from lesion-based symptom-mapping studies revealed the multifaceted nature of the disease, by linking AHP to contradictory patterns of cortical areas. These inconsistencies are due to small sample sizes in most of these studies and to the lack of consideration of lesions remote effects that impact structurally connected circuits. We explored the probability of white matter disconnections in 174 patients (95 AHP patients), through an advanced lesion analysis software (Foulon et al.,2017), excluding clinical variables (motor impairment, lesion size, interval from lesion onset) and associated neuropsychological deficits of AHP (extra-personal and personal neglect, memory impairment). Our results indicated that AHP symptoms may be attributable to the disconnection of indirectly impaired areas. The involvement of three neural systems emerged: the limbic system, the pre-motor loop, and the ventral non spatial-attention network. The disconnection of the limbic system probably plays a role in the failure of updating the autobiographical representations of the self; the disconnection of some pre-motor loop structures contributes to the deficit in monitoring and error processing, and the ventral non-motor attention network disconnection is involved in the attention shifting from the self to the third person perspective. Together, these three systems contribute to the awareness of motor deficits.