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

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.