The influence of vagal nerve stimulation on reward-based selective attention

Vagal nerve stimulation is a relatively new medical therapy in which the
central nervous system is stimulated with electrical pulses in order to relieve
disease symptoms. In vagal nerve stimulation (VNS), electrical pulses are
directed to the left vagal nerve (10th cranial nerve) in the lateral part of
the neck via a system that includes neurosurgically implanted electrode leads
and a pulse generating pacemaker device. The VNS procedure is already an
approved treatment option for treatment resistant epilepsy and depression.
Several studies have also shown non-symptomatic beneficial effects of VNS.
These include neuromodulatory characteristics (Engineer et al. 2011) and
enhancing effects on cognition and memory (Clark et al. 1999). The precise
mechanisms underlying the beneficial effects of VNS are currently not well
understood. In order to understand these mechanisms it is important to have a
better idea of the non-symptomatic effects of stimulation. It is plausible that
the cognitive side effects of VNS are far more reaching including effects on
reward processing and visual attention but this has never been tested yet.

The objective of our study is to investigate the relationship between
electrical stimulation of the central nervous system (VNS) and reward-based
selective attention. In order to do so, we will ask subjects to complete a set
of tasks on a standard computer. These tasks, aimed at probing the
reward-driven distribution of selective attention are already used in other
reward studies (some of which in our own lab), where money is given as a
reward. In our study, we will both repeat these findings with a monetary reward
in the presence and absence of stimulation, and we will perform a version of
the task in which the monetary reward following a correct response is replaced
by acute vagal nerve or deep brain stimulation. With this approach we wish to
determine whether the direct stimulation of the reward center in the brain
interferes with the effects of a monetary reward and/or has by itself an effect
that is comparable to the delivery of monetary rewards. This research will
provide more insight into the effects of VNS on neuronal processes, which might
eventually extend the scope of this therapy.

Patients that will perform the experiments are all treated with VNS. We will
ask patients to perform the tasks at the AMC. We will conduct the experiments
in separate blocks, lasting in total approximately 2 hours. We aim to find an
effect of VNS on reward processing and selective visual attention. All tasks
that we intend to use in this patient study have already been conducted by
healthy observers, revealing clear effects of reward on the distribution of
visual attention. We will first repeat the basic experiment in the VNS patients
in the absence of stimulation to obtain a baseline measure of the effect shown
in the healthy observers. We well then move on to test the impact of
stimulation on the underlying reward-based attention mechanisms.

The burden for the patients will consist of visiting the AMC to conduct visual
search and simultaneity judgment tasks for 2 hours. To our knowledge, there
will be no additional risks associated with our experiments. Participating
patients will not benefit directly from the experiments. They will, however,
contribute to the extension of knowledge about vagal nerve stimulation in
future patients. In addition, they will help to improve understanding of reward
processing in the human brain.