Motivation and decision-making: a new role for the vestibular system
Attentional capture (AC) in humans involves the involuntary direction of attention towards a target stimulus. This phenomenon is particularly strong with rewarding stimuli and in a number of addiction disorders. Accumulating evidence based on neuroimaging data point to a role of the Anterior Cingulate Cortex (ACC) in attention engagement to rewarding stimuli. The ACC is located deep beneath the brain’s surface, and therefore it cannot be reached easily with common neurostimulation devices.
A non-invasive method to study AC
Undertaken with the support of the Marie Skłodowska-Curie programme, the BRAVEST initiative used galvanic vestibular stimulation (GVS), a non-invasive method known to activate several areas in the central nervous system located deep beneath the surface of the brain. GVS stimulates the vestibular system – situated in the inner ear – by means of weak electric currents applied on the skin behind the ears. “GVS is suitable for investigating brain regions that support emotional and motivational processes while their dysfunction has been linked to a range of psychiatric disorders including anxiety and depression,” explains the research fellow Elvio Blini. BRAVEST research involved the participation of healthy subjects who received GVS or control stimulation. Simultaneously, they performed a motivational task for a monetary reward, granted to participants as a result of their performance. “Motivation is a powerful determinant of human performance and therefore, when responses were rewarded, we observed, unsurprisingly, stark performance boost,” emphasises Blini. Interestingly, these motivational benefits were reduced in participants receiving GVS, suggesting a link between the vestibular system and motivation.
BRAVEST significance
BRAVEST results confirm the long-held notion that our physiological states, conscious or not, are important determinants of decision-making and behaviour. “Think how desirable one’s preferred food would be when hungry versus when experiencing mild nausea,” outlines Blini. Results also challenge existing concepts on the role of the vestibular system only in balance, unveiling its implication in motivation with intriguing theoretical and practical projections. The collection of inner signals that describe the physiological state of the body and our ability to discern them is known as interoception. Interoception is increasingly studied because it may represent an important entry point for physical and mental well-being. Much emphasis has been so far given to cardiac, respiratory, or gastric signals. However, BRAVEST results show that vestibular information is equally important for interoception. Research into modern treatments for a range of psychiatric disorders involve the understanding of interoceptive processes and meta-cognition to maximise their efficacy. GVS has proved a valid method to study these processes and may also be beneficial as adjuvant in the treatment of clinical populations characterised by dysfunctional sensitivity to rewards such as addiction disorders. Further investigation into the interaction between the vestibular and motivational systems through neuroimaging is necessary to shed light on the neural mechanism of this interplay. Blini’s plans for the future include research into the use of GVS on smokers to reduce the excessive saliency of nicotine-related stimuli. Combined with further insight into the association between interoception and motivation, these efforts will provide a first proof of principle for the use of GVS in clinical practice.
Keywords
BRAVEST, attentional capture, reward, vestibular system, Galvanic vestibular stimulation, anterior cingulate cortex, addiction
