Recent studies suggested involvement of the striatum in decision-making and action selection. Striatal projection neurons receive action-related inputs from the cerebral cortices, reward prediction error signal from dopamine neurons and signals from cholinergic interneurons in the striatum. To study the signals conveyed by the striatal cholinergic neurons, projection neurons and midbrain dopamine neurons during decision-making and action selection, we recorded 265 tonically active neurons (TANs; presumed cholinergic interneuron) and 239 phasically active neurons (PANs; presumed projection neuron) from 2 macaque monkeys. After depressing a start button, the monkeys chose 1 of 3 target buttons with correct rates at 1st, 2nd, 3rd and repetition trials of 33, 50, 85 and 95%, respectively. Correct choices were followed by beep sound and reward water. 175 TANs responded to the reinforcer beeps after 1st, 2nd, 3rd choices with similar magnitudes, but showed almost no responses at the repetition trial. 18 of 147 PANs responding to the beeps showed the discharges varied with the reward probability. Other 18 PANs discriminated trials during repetition epoch from those during trial and error epoch. The reinforcer beeps evoked reward prediction error signals in dopamine neurons in other 3 monkeys. Our results suggested unique participations of cholinergic and dopamine signals in the striatal mechanisms for decision and action selection. [J Physiol Sci. 2007;57 Suppl:S8]
