For over 150 years, neuroscientists have known that a small region in the left frontal lobe—Broca’s area—plays a crucial role in speech production. Named after French physician Paul Broca, who identified it in the 1860s, this brain region has become synonymous with our ability to speak. But recent discoveries suggest that Broca’s area is just one player in a far more complex and fascinating neural orchestra than we ever imagined.

The Mystery of the Overlooked Region

Interestingly, Broca himself hinted at this complexity. In his original writings, he noted that not only the third frontal convolution (what we now call Broca’s area) but also “perhaps the second” frontal convolution—the middle frontal gyrus—seemed important for speech. For over a century, researchers largely ignored this observation. Yet modern brain imaging studies kept showing activation in this more dorsal (upper) region during speech tasks. Scientists saw it repeatedly but didn’t quite know what to make of it.

The breakthrough came from converging evidence across multiple research methods. Direct electrical stimulation of patients’ brains during neurosurgery revealed two distinct speech-related zones on the precentral gyrus (the motor strip of the brain). Functional brain imaging showed these same two areas lighting up during speech. And detailed brain mapping identified a previously obscure region called “area 55b” that seemed to bridge higher-level language planning and lower-level motor control.

Two Hierarchies, Not One

What emerged from this research is a revolutionary idea: We don’t have just one speech production system in the frontal lobe—we have two parallel hierarchies working in concert.

The ventral (lower) hierarchy is the familiar one, involving Broca’s area and the regions just behind it. This system handles what we might call the “phonetic” aspects of speech—the precise coordination of tongue, lips, and jaw movements needed to produce consonants and vowels in the right sequence. Think of it as the system that turns the word “cat” into the specific mouth movements needed to articulate those sounds.

The dorsal (upper) hierarchy is the newly recognized system. It involves the posterior middle frontal gyrus and dorsal precentral areas. This system specializes in controlling voice pitch and prosody—the melody and rhythm of speech. It coordinates the larynx (voice box) and breathing to produce the rising and falling intonations that distinguish a question from a statement, or that emphasize one word over another in a sentence.

Why Two Systems?

This dual architecture makes evolutionary and functional sense. The larynx—our voice box—is controlled by a unique region of motor cortex that appears to be distinctively human. Non-human primates have only one laryngeal motor area, but humans have two: a ventral one (shared with other primates) and a dorsal one (unique to humans). This dorsal laryngeal motor cortex may be the neural foundation for our uniquely human capacity for voluntary control of voice pitch.

The dorsal speech system doesn’t just control pitch mechanically. Brain recordings show it responds to pitch-related acoustic features in heard speech and becomes active during both speaking and singing. It appears to integrate information about loudness, rhythm, and pitch to produce the prosodic patterns that give speech its emotional color and grammatical structure.

When Things Go Wrong

Understanding these two systems helps explain different types of speech disorders. Damage to the ventral system can cause apraxia of speech—difficulty coordinating the precise articulatory movements needed for clear speech. Damage to the dorsal system may affect prosody, making speech sound flat or robotic, or disrupting the ability to use pitch to convey meaning.

Interestingly, people who stutter show relatively weak connectivity in the ventral speech network but normal connectivity in the dorsal network. This may explain why many people who stutter can sing fluently—singing relies more heavily on the preserved dorsal system.

The Bigger Picture

This discovery of parallel speech hierarchies represents more than just adding another region to the brain map. It reveals a fundamental principle: Complex human abilities like speech are built from multiple specialized subsystems, each with its own evolutionary history and computational logic.

The ventral system, handling rapid articulation of consonants and vowels, may represent a relatively recent evolutionary innovation. The dorsal system, controlling voice pitch and prosody, may have deeper evolutionary roots in primate vocalizations. Together, they create the rich, nuanced communication system that makes human language possible.

Looking Forward

As neuroscience continues to map the brain’s language networks with increasing precision, we’re moving beyond the simple notion of “Broca’s area for speech production.” We’re discovering that speech—something that feels so effortless and automatic—emerges from the coordinated activity of multiple hierarchical systems, each contributing its own essential component to the final product.

This research reminds us that even our most familiar abilities harbor hidden complexity. Every time we speak, two ancient neural hierarchies dance together, one shaping the articulation of sounds, the other painting those sounds with the melody and rhythm that convey meaning and emotion. It’s a duet that Broca himself might have appreciated, had he lived to see his initial hunch confirmed by modern neuroscience.

References

Hickok, Venezia, & Teghipco. (2023). Beyond Broca: neural architecture and evolution of a dual motor speech coordination system. Brain. 146:1775-1790