Prostheses for the will

INTRODUCTION: THE NEUROBIOLOGY OF THE WILL The will is a complex set of cognitive (including affective and motivational) and motor capacities that enable us to initiate and complete action plans. Neurological and psychiatric disorders impair these capacities because of dysfunction in neural circuits mediating them. Parkinson’s disease (PD), major depressive disorder (MDD), obsessive-compulsive disorder (OCD), and other conditions can be understood as disorders of the will involving overactive, underactive or inactive critical nodes of these circuits (Lozano and Lipsman, 2013). Neural prostheses such as brain-computer interfaces (BCIs), hippocampal prostheses (HPs), and deep-brain stimulation (DBS) can bypass, replace, or modulate damaged or dysfunctional circuits and thereby restore or enhance the capacities necessary to translate intentions into actions. In this respect, they can be described as prostheses for the will. Philosophers claim that for the will to be free, actions must not be generated by causal routes that bypass and undermine agent’s control of the mental states that issue in them (Mele, 1995). Presumably, this would include manipulation of the brain by an artificial implanted device. Yet neural prostheses that bypass, replace, or modulate dysfunctional circuits do not undermine but instead restore this control when it has been lost and can enhance it when it is impaired by brain injury or neurodegeneration. They restore control of thought and behavior by restoring the relevant motor and mental functions. I will describe the different respects in which the three neural prostheses in question can achieve this goal.