Figure 3.

Hypothetical scenarios for learning syllable transitions. (A) A hypothetical scenario in which ChIs pauses are coincident with activation of ensembles “a” and “c” (green circle) and phasic increases in dopamine (DA, gray rectangle) occurs at T1. (A1) LTP (red rectangle) and LTD (blue rectangle) result at corticostriatal synapses on ensembles “a” and “c”, respectively. There is no change (black square) in the ensemble “b” when MSNs depolarization is not coincident with a pause in ChIs and/or phasic increases in DA. (A2) LTP (red arrow) results at “t1→a” synapses and LTD (blue dashed arrow) results at “t2/3→a” and “t2/3→c” synapses. Syllable “A” and “C” are omitted frequently at T2 and T3, resulting in reinforcement (learning) of the syllable sequence “A→B”. (B) Same as (A) but DA is active at T1 and T2 (B1). (B2) Syllable “A” and “C” are omitted frequently at T3 due to the LTD at “t3→a/c” synapses. Consequently, the production of syllable sequences “A→A”, “A→C” or “A→B” is reinforced. (C) Same as (A) but DA is active at T3 (C1). (C2) Syllable “A” is omitted frequently at T1 due to the LTD induced at “t1→a” synapses. Consequently, the production of syllable sequences “B→A” or “B→C” are reinforced.