ABSTRACT
Animal studies have shown that the striatal cholinergic system plays a role in behavioural flexibility but, until recently, this system could not be studied in humans due to a lack of appropriate non-invasive techniques. Using proton magnetic resonance spectroscopy (1H-MRS) we recently showed that the concentration of dorsal striatal choline (an acetylcholine precursor) changes during reversal learning (a measure of behavioural flexibility) in humans. The aim of the present study was to examine whether regional average striatal choline was associated with reversal learning. We measured choline at rest in both the dorsal and ventral striatum using 1H-MRS and examined its relationship with performance on a probabilistic learning task with a reversal component. Task performance was described using a simple reinforcement learning model that dissociates the contributions of positive and negative prediction errors to learning. Average levels of choline in the dorsal striatum were associated with performance during reversal, but not during initial learning. Specifically, lower levels of choline in the dorsal striatum were associated with a lower number of perseverative trials. Moreover, choline levels explained inter-individual variance in perseveration over and above that explained by learning from negative prediction errors. These findings suggest that the dorsal striatal cholinergic system plays an important role in behavioural flexibility, in line with evidence from the animal literature and our previous work in humans. Additionally, this work provides further support for the idea of measuring choline with 1H-MRS as a non-invasive way of studying human cholinergic neurochemistry.
Acknowledgments
This study was supported by a Human Frontier Science Program (HFSP) grant (RGP0048/2012), and an Engineering and Physical Sciences Research Council (EPSRC) doctoral training grant (EP/L505043/1). The funders had no involvement in study design, in the collection, analysis, and interpretation of data, in writing the report, or in the decision to submit the paper for publication. The authors would like to thank Rosie Gillespie and Emma Davis for assistance with data collection.
Footnotes
Conflict of Interest: The authors declare no competing interests.