PT  - JOURNAL ARTICLE
AU  - Diuk, Carlos
AU  - Tsai, Karin
AU  - Wallis, Jonathan
AU  - Botvinick, Matthew
AU  - Niv, Yael
TI  - Hierarchical Learning Induces Two Simultaneous, But Separable, Prediction Errors in Human Basal Ganglia
AID  - 10.1523/JNEUROSCI.5445-12.2013
DP  - 2013 Mar 27
TA  - The Journal of Neuroscience
PG  - 5797--5805
VI  - 33
IP  - 13
4099  - http://www.jneurosci.org/content/33/13/5797.short
4100  - http://www.jneurosci.org/content/33/13/5797.full
SO  - J. Neurosci.2013 Mar 27; 33
AB  - Studies suggest that dopaminergic neurons report a unitary, global reward prediction error signal. However, learning in complex real-life tasks, in particular tasks that show hierarchical structure, requires multiple prediction errors that may coincide in time. We used functional neuroimaging to measure prediction error signals in humans performing such a hierarchical task involving simultaneous, uncorrelated prediction errors. Analysis of signals in a priori anatomical regions of interest in the ventral striatum and the ventral tegmental area indeed evidenced two simultaneous, but separable, prediction error signals corresponding to the two levels of hierarchy in the task. This result suggests that suitably designed tasks may reveal a more intricate pattern of firing in dopaminergic neurons. Moreover, the need for downstream separation of these signals implies possible limitations on the number of different task levels that we can learn about simultaneously.