Deep brain stimulation (DBS) is a surgical procedure involving the insertion of a small electrode into the brain to modulate electrical activity. Over 40.000 patients worldwide have undergone placement of Medtronic Activa, the most popular DBS system (Schwalb & Hamani, 2008).
The connectivity of cortical and subcortical brain tissue is often too intricate to parse information from a single DBS electrode. Generation of meaningful visual perception by stimulation of the visual cortex for example requires a large number of much smaller electrodes (Schmidt et al, 1996). DBS is therefore used merely to suppress or normalise electrical activity in dysfunctional brain regions (hence the nickname 'brain pacemaker').
However, many monoaminergic neurons in the midbrain and brainstem fire in unison and project widely throughout the brain: by stimulating neurons that produce dopamine for instance, researchers can directly modulate dopamine concentrations in diverse cortical and subcortical regions (Hernandez et al, 2006; Garris et al, 1997; Fiorino et al, 1993; Bean & Roth, 1991). Stimulation of dopaminergic neurons, serotonergic neurons or the nerve bundles that carry their axons to cortical and subcortical targets is highly rewarding and is referred to as brain stimulation reward (BSR) in the literature.
BSR motivates animals to perform behaviors with which it is repeatedly associated and has been used to drive behaviors such as heavy physical exercise and learning (Burgess et al, 1991; Garner et al, 1991; Hermer-Vazquez et al, 2005). It seems likely that DBS of monoaminergic regions would support BSR also in humans and that it could be used to motivate behaviors such as physical exercise and learning.
There are two reasons to develop monoamine modulation by DBS (MMDBS) for human use:
- First, MMDBS could have a devastating impact on humanity if developed under autocratic regimes without public oversight and vigorous debate. It could for instance be used to create large factories of workers addicted to manual labour. Even if developed in a democracy there are numerous human rights concerns associated with MMDBS, including access control by the manufacturer, the potential for over-use, and aggravation of societal inequalities. These are very difficult problems whose solution will require the concerted effort of democratic societies.
- Second, MMDBS could be enormously beneficial if developed responsibly. It could help people exercise, thus attenuating the healthcare crisis in general and the obesity epidemic in particular. It could be combined with learning tutorials to aid people with learning difficulties. It could be used to motivate people to complete scientific research protocols, thus accelerating research in critical fields such as renewable energy and biomedicine. Moreover, it might offer a more dynamic alternative to pharmacological modulators of monoamines such as stimulants and antidepressants.