Beyond Separability: Closed-Loop Brain Stimulation and the Distribution of Moral Responsibility

Adaptive deep brain stimulation (aDBS) and other genuinely closed-loop brain–computer interfaces deliver stimulation according to a learned control policy that is continuously updated by the patient's own neural activity. This activity is itself being shaped by the stimulation. This paper argues that this architecture undermines the conceptual frameworks currently used to evaluate moral responsibility for actions performed by patients using such devices. Individualist, historicist, and relational accounts of agency each, in different ways, presuppose what I call a separability assumption: that the patient's contribution and the device's contribution to action can in principle be distinguished and weighted, even where doing so in practice is difficult. I argue that genuinely adaptive systems defeat this assumption, not because patient and device are merely causally entangled (ordinary biological coupling is too) but because three features of aDBS together produce a coupling of a different kind: the device's policy is externally authored, continuously modified by patient neural activity, and intervenes on the very tissue whose activity is shaping it. The contributions the separability picture asks us to apportion are each, individually, joint products of the other. I then propose that aDBS sits far enough toward the structurally entangled end of a spectrum of joint-agency cases that the practical default for responsibility-attribution flips: distribution becomes the default, and any specific localization requires affirmative justification. Four loci: patient, clinical team, manufacturer, and regulator, bear distinct, irreducible kinds of responsibility, picked out by a constitutive criterion. To address the dissolution worry, I distinguish the synchronic locus of action from the diachronic locus of moral standing, arguing that the patient retains the latter through capacities the synchronic distribution does not defeat. I close with implications for informed consent and neurorights, proposing in the latter case a category of "constitutive rights" alongside existing protective rights.