Biased competition in the absence of input bias: predictions from corticostriatal computation

Classical accounts of biased competition (BC) require an input bias to resolve the competition between neuronal ensembles driving downstream processing. However, flexible and reliable selection of behaviorally-relevant ensembles can occur with unbiased stimulation: striatal D1 and D2 medium spiny neurons (MSNs) receive balanced cortical input, yet their activity determines the choice between GO and NO-GO pathways in the basal ganglia. We present a corticostriatal model identifying three candidate mechanisms that rely on physiological asymmetries to effect rate- and time-coded BC in the presence of balanced inputs. First, tonic input strength determines which MSN phenotype exhibit higher mean firing rate (FR). Second, low strength oscillatory inputs induce higher FR in D2 MSNs but higher coherence between D1 MSNs. Third, high strength inputs oscillating at distinct frequencies preferentially activate D1 or D2 MSN populations. Of these candidate mechanisms, only the latter accommodates observed rhythmic activity supporting rule-based decision making in prefrontal cortex.