tVNS, Caffeine & Motor Learning - Pilot Results

Vagus nerve stimulation has been shown to increase global neural plasticity in the cortex (Engineer et al, 2011). This type of neural plasticity can be used to facilitate changes in the cortex to treat neurological and psychological disorders (Sclaepfer et al, 2007; George et al, 2008; Uthman et al, 2004 & Bodenlos et al, 2007), and has also been shown to increase consolidation effects when used in learning tasks. These experiments used VNS over a period of weeks and months.

These studies all used iVNS which is a form of VNS which relies upon an implanted electrode. Kraus et al (2004) has showed successfully that tVNS, a method of VNS which utilises nerve fibre connections in the auricular canal and is a reliable method of stimulating the vagus nerve.

Caffeine is a heavily used stimulant which acts on the central nervous system by blocking adenosine receptors. This kind of stimulation has been investigated for the possibility of it having beneficial cognitive effects, specifically on memory and learning. The current research landscape of caffeine and it's effect on cognition is quite noisy. Angelucci et al (1999) has shown that caffeine differentially affects the different stages of memory processing and that its effect depends on the particularities of the task itself. Mednick et al (2008) has shown that motor skill learning is significantly decremented by the use of caffeine compared to a control group, however showed that perceptual learning was significantly increased compared to a control group. Tieges et al (2006) has shown that anticipatory processes are benefited by a caffeine supplement, which aids task switching.

In amongst all of this research lies the question still, can caffeine aid learning when it comes to a task that relies on perception and action. More specifically, the task of producing a 90 degree movement.

Participants were recruited through the use of recruitment posters. 2 male participants were recruited to the tVNS group and female 1 participant was recruited to the caffeine group. Control data was acquired from a previous study with the same design.

Participants took part in an experiment which assessed baseline ability at creating a 90 degree movement on day 1, training with either the stimulation or supplement took place on day 2, a post training assessment took place on day 3 and a retention assessment took place on day 10.

Initial results (see figure above) show that control data outperforms both the vagus nerve stimulation and caffeine group. The control group ability on creating a 90 degree movement increased by 0.32 between baseline and post training whilst the caffeine group increased by only 0.12 and the tVNS group increased by only 0.06. The results of this study show that a short training session on one day may not be enough to create a global plastic effect needed to facilitate learning and may actually inhibit learning to an extent.

After a discussion with both Andrew Wilson and Jim Deuchars on the experiment design and pilot data a decision has been made to move forward with a longer training schedule expanded over various days. Retention will also be assessed 7 days after post training assessment and again 14 days after post training assessment to investigate the consolidating effects of tVNS.