Striatal GABAergic control of human reward anticipation

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The dopaminergic midbrain (substantia nigra and ventral tegmental area (SN/VTA)), is associated with computation of reward prediction signals. This reward prediction error is essential for learning. GABA also plays a crucial role in this process, GABAergic neurons in the VTA appear to encode the reward prediction independent of outcome. It is however still unclear what drives this GABA response, i.e. where information encoding this reward prediction originates. Potential candidates are the orbital frontal cortex and striatum. We test for a potential role for the striatum as input to form this reward prediction. We hypothesized that the influence of the striatum occurs indirectly through activation of the GABAergic interneurons in the SN/VTA. We measured GABA concentration bilaterally in the striatum and occipital cortex using MR spectroscopy. Reward anticipation was induced using a monetary incentive delay task. We found significant differential activity in the VTA upon presentation of reward prediction and neutral cues, which thus reflected a reward anticipation response. We report a trend level correlation between VTA reward response and striatal GABA levels, but nothing from the occipital cortex. This correlation was specific for BOLD activity during cue outcome presentation. We suggest that this timeframe corresponds with VTA GABAergic signaling of reward anticipation.
Faculteit der Sociale Wetenschappen