The role of declarative and procedural memory in disorders of language

Language is often assumed to rely on domain-specific neurocognitive substrates. However, this human capacity in fact seems to crucially depend on general-purpose memory systems in the brain. Evidence suggests that lexical memory relies heavily on declarative memory, which is specialized for arbitrary associations and is rooted in temporal lobe structures. The mental grammar instead relies largely on procedural memory, a system that underlies rules and sequences, and is rooted in frontal/basal-ganglia structures. Developmental and adult-onset disorders such as Specific Language Impairment, autism, Tourette syndrome, Parkinson’s disease, Huntington’s disease, and non-fluent aphasia each seem to involve particular grammatical deficits and analogous non-linguistic procedural memory impairments, as well as abnormalities of procedural memory brain structures. Lexical and declarative memory remain relatively intact in these disorders, and may play compensatory roles. In contrast, Alzheimer’s disease, semantic dementia, fluent aphasia and amnesia each affect lexical and declarative memory, and involve abnormalities of declarative memory brain structures, while leaving grammar and procedural memory largely intact. Overall, the evidence suggests that declarative and procedural memory play critical roles in language disorders, as well as in language more generally.