This article presents findings from a study on the single-neuronal elements of speech production in humans, using acute ultrahigh-density Neuropixels recordings in the language-dominant prefrontal cortex. The researchers discovered neurons that encode detailed information about the phonetic arrangement and composition of planned words during natural speech. These neurons represent the specific order and structure of articulatory events before utterance, reflect the segmentation of phonetic sequences into distinct syllables, and accurately predict the phonetic, syllabic, and morphological components of upcoming words. The findings reveal a remarkably structured organization and encoding cascade of phonetic representations by prefrontal neurons in humans, demonstrating a cellular process that can support the production of speech. The study used single-neuronal recordings from the language-dominant prefrontal cortex of participants undergoing planned intraoperative neurophysiology. The recordings were obtained from the posterior middle frontal gyrus, a region known to be involved in word planning and production. The participants performed a naturalistic speech production task, articulating a wide variety of words in a replicable manner. The researchers constructed a feature space based on the constituent phonemes of each word and used generalized linear models to quantify the degree to which variations in neuronal activity during planning could be explained by individual phonemes. The study found that the firing activities of many neurons were explained by the constituent phonemes of the word before utterance. These neurons were selectively tuned to the planned production of specific phonemes and reflected the spectral properties of the articulated words. The researchers also found that these neurons could be used to decode the phonetic composition of the upcoming words with significant accuracy. The study also examined the motoric and perceptual processes involved in speech production. Neurons that reflected the phonetic composition of words during planning were largely distinct from those that reflected their composition during perception. The findings suggest that speaking and listening engaged largely distinct but complementary sets of cells in the neural population. The study further examined the syllabic and morphological features of speech production. The researchers found that the activities of neurons reflected the presence of specific planned syllables and morphemes. These neurons encoded information about the syllables and morphemes, suggesting that they played a role in the segmentation and order of phonemes in individual words. The study also examined the spatial distribution of neurons in the prefrontal cortex. The findings suggest a gradation of cellular representations, with caudal areas showing progressively higher proportions of selective neurons. Finally, the study examined the temporal organization of representations during speech production. The researchers found that the activities of these neurons followed a consistent, temporally ordered morphological–phonetic–syllabic dynamic before utterance. The findings suggest that these neurons encoded information about the phonetic, syllabic, and morphological components of upcoming words in a structured and temporally ordered manner. Overall, the study provides evidence that prefrontal neurons in the language-dominant cortex play a crucial role in the planning and productionThis article presents findings from a study on the single-neuronal elements of speech production in humans, using acute ultrahigh-density Neuropixels recordings in the language-dominant prefrontal cortex. The researchers discovered neurons that encode detailed information about the phonetic arrangement and composition of planned words during natural speech. These neurons represent the specific order and structure of articulatory events before utterance, reflect the segmentation of phonetic sequences into distinct syllables, and accurately predict the phonetic, syllabic, and morphological components of upcoming words. The findings reveal a remarkably structured organization and encoding cascade of phonetic representations by prefrontal neurons in humans, demonstrating a cellular process that can support the production of speech. The study used single-neuronal recordings from the language-dominant prefrontal cortex of participants undergoing planned intraoperative neurophysiology. The recordings were obtained from the posterior middle frontal gyrus, a region known to be involved in word planning and production. The participants performed a naturalistic speech production task, articulating a wide variety of words in a replicable manner. The researchers constructed a feature space based on the constituent phonemes of each word and used generalized linear models to quantify the degree to which variations in neuronal activity during planning could be explained by individual phonemes. The study found that the firing activities of many neurons were explained by the constituent phonemes of the word before utterance. These neurons were selectively tuned to the planned production of specific phonemes and reflected the spectral properties of the articulated words. The researchers also found that these neurons could be used to decode the phonetic composition of the upcoming words with significant accuracy. The study also examined the motoric and perceptual processes involved in speech production. Neurons that reflected the phonetic composition of words during planning were largely distinct from those that reflected their composition during perception. The findings suggest that speaking and listening engaged largely distinct but complementary sets of cells in the neural population. The study further examined the syllabic and morphological features of speech production. The researchers found that the activities of neurons reflected the presence of specific planned syllables and morphemes. These neurons encoded information about the syllables and morphemes, suggesting that they played a role in the segmentation and order of phonemes in individual words. The study also examined the spatial distribution of neurons in the prefrontal cortex. The findings suggest a gradation of cellular representations, with caudal areas showing progressively higher proportions of selective neurons. Finally, the study examined the temporal organization of representations during speech production. The researchers found that the activities of these neurons followed a consistent, temporally ordered morphological–phonetic–syllabic dynamic before utterance. The findings suggest that these neurons encoded information about the phonetic, syllabic, and morphological components of upcoming words in a structured and temporally ordered manner. Overall, the study provides evidence that prefrontal neurons in the language-dominant cortex play a crucial role in the planning and production