A possible neurocognitive explanation for DLD

Ullman, M. T., Earle, F. S., Walenski, M., & Janacsek, K. (2020). The Neurocognition of Developmental Disorders of Language. Annual Review of Psychology, Vol 71, 71, 389-417.

Aim of the paper:

This paper reviews research in relation to a specific idea of what might be the brain and cognitive differences that cause DLD (as well as dyslexia and speech-sound disorders, such as stuttering). The paper looks at what is called the “Procedural circuit Deficit Hypothesis”. This hypothesis states that the language learning difficulties in individuals with DLD are due to differences in the brain circuitry that supports procedural memory. However, a different memory system (declarative memory) is not affected in individuals with DLD. This paper reviews evidence that supports this idea.

  • Procedural memory is behind how we learn to do things automatically, such as typing on a keyboard or riding a bicycle. It also helps us learn patterns on an implicit level, or without knowing we are learning things.

  • Declarative memory is most easily understood as things we know, such as facts about the world or our autobiographical memories. For instance, your address and your memories of your last birthday were learned in your declarative memory system.

  • Both memory systems are important for learning new things, such as language in early childhood. Memory and learning seem like separate things, but they are linked together in our minds!

What was found:

Procedural memory is more developed in younger children. Declarative memory needs more time and develops across childhood. If language learning is initially reliant on procedural memory, difficulties in this system in children with DLD may cause early delays in language development.

Procedural memory has been shown to be important for grammar learning. For instance, the better a person’s procedural memory, the better they use and understand grammar. However, grammar can be learned in both the procedural and declarative memory systems. As the declarative system needs time to develop in early childhood, this may be why there are delays in learning grammar in children with DLD.

Individuals with DLD have been shown to have structural differences in parts of the brain associated with procedural memory. However, researchers have not found consistent differences in the brains systems associated with declarative memory and learning. Overall, there is good evidence that problems with procedural learning may be the key problem in language learning in children with DLD.

What does this mean?

These ideas do not mean that children with DLD can’t learn from their procedural memory systems. But the ideas do indicate that their procedural learning is not as efficient as in children without DLD. Children with DLD are likely relying on the declarative learning and memory system, which tend to be used later in development. This may be why children with DLD learn language a bit later and with more effort than those without DLD.

Understanding the underlying reasons why children with DLD struggle to learn language is key for suitable therapy and treatment of DLD. Indeed, the authors suggest that there are “pharmacological, behavioural and other interventions” that can help enhance procedural and declarative memory ability. These interventions could be useful in children with DLD.

Where can I read this paper?

This paper is not open access, but can be accessed here.