Retrospective interviews reveal unawareness of weakness following reversible hemispheric suppression: An exploratory study using selective anesthesia for functional evaluation

Abstract

Unawareness of weakness—defined as an explicit failure to recognize one’s own limb paresis after brain damage—has long been considered predominantly linked to right-hemisphere dysfunction, yet its laterality remains controversial. We retrospectively analyzed 86 sessions of Selective Anesthesia for Functional Evaluation (SAFE) conducted in 53 patients with surgical epilepsy. SAFE involves delivering a short-acting anesthetic into a single cortical artery branch, resulting in reversible cortical suppression. Contralateral weakness was defined as a positive Barré sign in the upper limb, corresponding to a Manual Muscle Test score of <3. Following the anesthetic effect, patients were asked whether they had experienced any motor impairment. Explicit unawareness was probed using two standardized questions, followed by a limb-specific inquiry. Interviews were conducted in real-time during 28 infusions and repeated within 30 sec of motor recovery in the remaining 58 sessions. Unawareness occurred in 41 of 52 left-hemisphere infusions (78.8%) and in 26 of 34 right-hemisphere infusions (76.5%). Real-time and immediate post hoc ratings were concordant in 26 of 28 paired assessments (93%). Infusions into the M2-superior division were associated with higher rates of unawareness than those into the M2-inferior division (odds ratio = 2.3, 95% confidence interval: 1.1–5.1). Within this reversible perfusion-suppression model, the frequency of unawareness of weakness was hemispherically balanced, promoting a cautious re-evaluation of the presumed right-hemisphere dominance. SAFE provides a practical tool for isolating transient awareness deficits without structural injury and may help bridge pharmacological and lesion-based approaches to brain–behavior mapping.