Ordinal position in auditory sequences is encoded in population dynamics in macaque frontal cortex

Abstract

The ability to extract structure from sensory sequences requires tracking not only stimulus identity but also ordinal position within a sequence. How and where ordinal information is represented in the primate brain remains unclear. Here, we recorded activity in populations of single neurons simultaneously from auditory cortex and ventrolateral prefrontal cortex in macaques passively listening to structured auditory sequences. Population-level analyses revealed that frontal cortex activity evolved progressively across the sequence, occupying distinct regions of neural state space for successive ordinal positions. In contrast, auditory cortex population activity reset with each element, producing stereotyped, stimulus-locked trajectories. Consistent with this dissociation, frontal cortex populations robustly decoded ordinal position independently of stimulus identity, whereas auditory cortex showed weak positional decoding despite strong identity representations. Frontal neurons further exhibited longer intrinsic timescales and reduced synchronization to element presentation, supporting integration of information across multiple elements. Together, these findings identify frontal activity as a key substrate for ordinal position encoding during auditory sequence processing, while auditory cortex primarily supports element-specific sensory representations.