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

Understanding how the brain handles sequences of sounds has long been a challenge. Research now reveals that specific brain regions are crucial for encoding ordinal position within those sequences. Scientists recorded neuronal activity from two brain areas in macaque monkeys while they listened to structured auditory sequences.

In the auditory cortex, neural activity reset with each new sound, creating repetitive, stimulus-specific patterns. This means the auditory cortex primarily represents individual sounds, not their order. On the other hand, the frontal cortex exhibited a different pattern. Activity in this area evolved progressively across the sequence, occupying distinct areas of neural space for each position in the sequence.

This progressive activity in the frontal cortex allowed researchers to decode the ordinal position of sounds independently of their identity. In contrast, the auditory cortex showed limited ability to decode position despite robust identification of individual sounds. The frontal neurons also had longer timescales and were less synchronized with each sound's presentation, suggesting they integrate information across the sequence.

In summary, these findings highlight the frontal cortex as a critical area for encoding ordinal position during auditory sequence processing. While the auditory cortex excels at representing individual sounds, it relies more on auditory cues than positional information.