Dopamine D1-like receptors consist of D1 (D1A) and D5 (D1B) receptors and play a key role in working memory. However, their possibly differential contribution to working memory is unclear. In birds, the D1-like receptor family is extended and consists of the D1A, D1B, and D1D receptors. Their possibly differential contribution to cognitive training is mostly unclear. Biopsychologists from Bochum and Düsseldorf combined a working memory training protocol with a stepwise increase of cognitive subcomponents and real-time RT-PCR analysis of dopamine receptor expression in pigeons to identify molecular changes that accompany training of isolated cognitive subfunctions. They conducted a behavioral working memory paradigm that works like Russian Matryoshka dolls: The four tasks were designed with increasing cognitive demands such that task 2 had one cognitive component more than task 1, task 3 had more components than task 2 and so on. By subtraction of cognitive faculties between tasks, expression changes ofD1A, D1B, andD1D in striatum and avian "prefrontal cortex", could therefore be mapped to specific subcomponents of cognitive training. The data show that D1B receptor plasticity follows a training that includes active mental maintenance of information, whereas D1A and D1D receptor plasticity in addition accompanies learning of stimulus-response associations. Plasticity of D1-like receptors plays no role for processes like response selection and stimulus discrimination. None of the tasks altered D2 receptor expression. The present study shows for the first time that different cognitive components of working memory training have distinguishable effects on D1-like receptor expression.

Herold, C., Joshi, I., Hollmann, M., Güntürkün, O. (2012). Prolonged cognitive training increases D5 receptor expression in the avian prefrontal cortex. PLoS ONE, 7: e36484.