7.5 Belt, parabelt, and dual streams

Beyond A1, auditory cortex divides into multiple anatomically and functionally distinct fields:

• Core (A1 and the adjacent rostral field R): primary auditory cortex; tonotopic; receives the dense lemniscal thalamic projection.
• Belt: a ring of fields around the core, including caudo-medial and rostro-medial belt, integrating across frequencies and processing more complex spectral combinations.
• Parabelt: a more lateral and rostral region, processing more complex stimuli still; receives most of its input from belt.

Beyond auditory cortex proper, processing diverges into two streams reminiscent of the visual system’s “what” and “where” pathways:

• A ventral / anterior stream, running forward into the superior temporal gyrus and temporal pole, specializing in what the sound is — speech identification, music recognition, voice recognition.
• A dorsal / posterior stream, running back and up into parietal cortex, specializing in where the sound is and how to act on it — spatial localization, audiomotor mapping (e.g., for vocalization, for playing a musical instrument).

The two streams are not completely separable, and a great deal of recent work has complicated the simple what/where dichotomy. But the basic distinction is real, and it parallels what we know about the visual system’s ventral and dorsal pathways.