Not surprisingly, most research on the neurobiology of language focuses on language alone. However, new biological functions commonly make use of previously-existing mechanisms. Following this principle of 'co-optation', language is likely to rely on prior neurobiological substrates, whether or not these have become further specialized for language. The declarative/procedural (DP) model simply posits that language learning, storage, and use depend heavily on declarative and procedural memory. After all, most if not all of language must be learned, and these are arguably the two most important learning and memory circuits (or systems) in the brain. Crucially, both circuits are well-studied at many levels in both humans and animals, including their computational, developmental, anatomical, cellular, genetic, and evolutionary bases, leading to numerous specific and often novel predictions about language.  Thus, this is a powerful theoretical approach.

Our work on the DP model is strongly theoretical as well as empirical. The initial proposal of the theory in 1997 has been refined in subsequent theory papers, including extensions to second language, individual and group differences, and both neurodevelopmental disorders and adult-onset disorders. Much of our work on neurodevelopmental disorders is related to the Procedural circuit Deficit Hypothesis, as well as the Declarative Memory Compensation Hypothesis and the Compensation Underdiagnosis Hypothesis, which are based on the DP model. We have also extended the model to music, math, and reading.

INITIAL PROPOSAL OF THE THEORY

Initial paper, which proposed the declarative/procedural model, with supporting empirical evidence:

Ullman, M. T., Corkin, S., Coppola, M., Hickok, G., Growdon, J. H., Koroshetz, W. J., & Pinker, S. (1997). A Neural Dissociation within Language: Evidence that the mental dictionary is part of declarative memory, and that grammatical rules are processed by the procedural system. Journal of Cognitive Neuroscience, 9(2), 266-276.

SUBSEQUENT THEORY AND REVIEW PAPERS

Ullman, M. T. (2001). A neurocognitive perspective on language: The declarative/procedural model. Nature Reviews Neuroscience, 2, 717-726.

Ullman, M. T. (2001). The declarative/procedural model of lexicon and grammar. Journal of Psycholinguistic Research, 30(1), 37-69.

Ullman, M. T. (2001). The neural basis of lexicon and grammar in first and second language: The declarative/procedural model. Bilingualism: Language and Cognition, 4(1), 105-122.

Pinker, S., & Ullman, M. T. (2002). The past and future of the past tense. Trends in Cognitive Sciences, 6(11), 456-463.

Ullman, M. T. (2004).Contributions of neural memory circuits to language: The declarative/procedural model. Cognition, 92(1-2), 231-270.

Ullman, M. T., & Pierpont, E. I. (2005). Specific language impairment is not specific to language: The procedural deficit hypothesis. Cortex, 41(3), 399-433. (special issue on "The neurobiology of developmental disorders", edited by D. Bishop, M. Eckert and C. Leonard)

Ullman, M. T. (2005). More is sometimes more: Redundant mechanisms in the mind and brain. Observer, 18(12), 7, 46. (invited Presidential Column)

Ullman, M. T. (2006). Is Broca's area part of a basal ganglia thalamocortical circuit? Cortex, 42, 480-485. (special issue on "Integrative models of Broca's and the ventral premotor cortex", edited by R. Schubotz and C. Fiebach)

Ullman, M. T. (2008). The role of memory systems in disorders of language. In B. Stemmer & H. A. Whitaker (Eds.), Handbook of the Neuroscience of Language (pp. 189-198). Elsevier Ltd.

Ullman, M. T. (2013). The declarative/procedural model of language. In H. Pashler (Ed.),Encyclopedia of the Mind (pp. 224-226). Sage Publications.

Ullman, M. T. (2013). The declarative/procedural model. In P. Robinson (Ed.), Routledge Encyclopedia of Second Language Acquisition (pp. 160-164). Routledge.

Ullman, M. T. (2013). The role of declarative and procedural memory in disorders of language. Linguistic Variation, 13(2), 133-154. [This paper is an updated version of Ullman, 2008, in Handbook of the Neuroscience of Language.]

Ullman, M. T., Lum, J. A. G., & Conti-Ramsden, G. M. (2014). Domain specificity in language development. In P. Brooks & V. Kempe (Eds.), Encyclopedia of Language Development (pp. 163-166). Sage Publications.

Ullman, M. T. (2015). The declarative/procedural model: A neurobiologically motivated theory of first and second language. In B. VanPatten & J. Williams (Eds.), Theories in second language acquisition: An introduction (2nd ed., pp. 135-158). Routledge.

Ullman, M. T., & Pullman, M. Y. (2015). A compensatory role for declarative memory in neurodevelopmental disorders.  Neuroscience and Biobehavioral Reviews, 51, 205-222.

Ullman, M. T., & Pullman, M. Y. (2015). Adapt and overcome: Can a single brain system compensate for autism, dyslexia and OCD? Scientific American Mind, 24-25.

Ullman, M. T. (2016). The declarative/procedural model: A neurobiological model of language learning, knowledge and use. In G. Hickok & S. A. Small (Eds.), The Neurobiology of Language (pp. 953-68). Elsevier.

Evans, T. M., & Ullman, M. T. (2016). An extension of the procedural deficit hypothesis from developmental language disorders to mathematical disability. Frontiers in Psychology, 7, 1318.

Hamrick, P., Lum, J. A., & Ullman, M. T. (2018). Child first language and adult second language are both tied to general-purpose learning systems. Proceedings of the National Academy of Sciences, 115(7), 1487-1492. (Supporting Information)

Ullman, M. T., Earle, F. S., Walenski, M., & Janacsek, K. (2020). The neurocognition of developmental disorders of language. Annual Review of Psychology, 71, 389–417.

Ullman, M. T. (2020). The Declarative/Procedural Model: A Neurobiologically-Motivated Theory of First and Second Language. In B. VanPatten, G. D. Keating, & S. Wulff (Eds.), Theories in Second Language Acquisition (3rd ed., pp. 128-161). Routledge.

Morgan-Short, K., Hamrick, P., & Ullman, M. T. (2022). Declarative and Procedural Memory as Predictors of Second Language Development. In S. Li, P. Hiver, M. Papi (Eds.) The Routledge Handbook of Second Language Acquisition and Individual Differences (pp. 67-81). (Supporting Table 1). For link to Supporting Table in Open Science Framework click HERE. 

Morgan-Short, K., and Ullman, M.T. (2022). Declarative and procedural memory in second language learning: Psycholinguistic considerations. In A. Godfroid & H. Hopp (Eds.), The Routledge Handbook of Second Language Acquisition and Psycholinguistics. (pp. 322-334) Routledge. 

Ullman, M. T., & Morgan-Short, K. (2023). How the declarative and procedural memory brain circuits support second language: Electrophysiological, neuroimaging, and neurological evidence. In The Routledge Handbook of Second Language Acquisition and Neurolinguistics (pp. 165-176). Routledge.

Ullman, M. T. (in press, 2025). The Declarative/Procedural Model: A Neurobiologically-Motivated Theory of First and Second Language. In B. VanPatten, G. D. Keating, & S. Wulff (Eds.), Theories in Second Language Acquisition (4th ed.). Routledge.