Monday, May 14, 2018

An Integrated Brain-Behaviour Model for Working Memory

Moser, D.A., Doucet, G.E., Ing, A., Schumann, G., Bilder, R.M., Frangou, S. (2017). An integrated brain-behaviour model for working memory. Molecular Psychiatry (00), 1-7.

This paper examines function of the brain’s working memory (WM) network and how it relates to behavioural and health factors. Working memory refers to the ability to hold task-relevant information in mind. Previous studies have shown that WM depends on activity coordinated across multiple regions of the brain, including the dorsolateral prefrontal cortex, the parietal cortex, and the dorsal anterior cingulate cortex. Function of this WM network can be characterized using functional magnetic resonance imaging (fMRI), an imaging technique that measures brain activity by detecting changes associated with blood flow. Three fMRI methods were examined in this study: (1) Regional activation, which involves looking at functional activation in specific areas of the brain during a task. (2) Functional connectivity, which examines correlations in activity between different brain regions to infer how these areas are functionally connected. And (3) Effective connectivity, which studies systematic changes in activity over time to assess causal interactions between brain regions. Using these, the aim of the study was to examine the relationship between function of the brain’s WM network and behavioural and health factors.

Participants were 828 healthy adults, between 22 and 37 years old. They underwent an fMRI scan while performing a 2-back WM task, in which they were asked to indicate whether a visual stimulus matched the stimulus from two trials before. They also completed a number of measures of sensorimotor processing, cognition, mental health, personality, physical health, and lifestyle factors.

Using a statistical technique called sparse canonical correlations to examine relationships between the neuroimaging and behavioural-health datasets, results indicated a significant association between WM function and all behavioural variables. Positive correlations were observed for cognitive and physical attributes, and negative correlations observed for suboptimal health indicators and negative lifestyle choices. Results across the fMRI measures underscored a relationship between working memory and non-affective cognition for both activation of the regions within the network and connections between the network. Correlations with physical health variables were observed for other areas of the brain, suggesting that this relationship was not specific to the WM network.

Overall, these findings suggest that function of the WM network is optimal in individuals with better cognitive abilities and physical well-being, while functional connectivity across the whole brain is reduced in individuals with suboptimal health and substance abuse. This study highlights the usefulness of measuring connectivity across the brain when studying cognitive processes, rather than examining brain areas in isolation. Applied to clinical practice, this highlights the importance of making connections. Drawing links between information and integrating multiple modalities into therapy sessions may help to engage more brain areas and strengthen connections between these brain areas.

Blogger: Alex Cross is an M.Cl.Sc. and Ph.D. Candidate in Speech-Language Pathology, supervised by Dr. Lisa Archibald and Dr. Marc Joanisse.

Tuesday, May 8, 2018

Critical Periods in Speech Perception: New Directions

Werker, J. F., & Hensch, T. K. (2015). Critical periods in speech perception: new directions. Annual review of psychology66.

This comprehensive review paper discusses the steps that support language development within the context of critical or sensitive periods. Critical or sensitive periods are windows, typically early in development, during which a sensory system is open to restructuring or learning based on input from the environment.

Original views on a critical period for language acquisition proposed that this window closed at the onset of puberty (e.g.: Lennenberg, 1967). However, this view has become much more nuanced, with language acquisition being characterized by multiple critical and sensitive periods throughout early development. The research reviewed in this paper demonstrates that infants become attuned to the properties of language gradually throughout development. This process of development starts with a sensitivity to global properties of language, such as being able to distinguish speech versus non-speech sounds. As infants develop, they become more sensitive to the fine-grained details in their native language. These processes are defined by critical periods, and development within these critical periods relies on both biological and environmental factors.

Some of the strongest evidence for critical periods in language acquisition comes from work examining phoneme discrimination in young infants. Phonemes are the units of sound in a language, such as the sounds /k/, /æ/, and /t/ in the word “cat”. Young infants are capable of discriminating phonemes from across the world’s languages. However, there is a process of perceptual narrowing around 8 to 10 months of age, which sharpens their perception to only those phoneme distinctions that are used in their native language. For example, an infant reared in an Japanese-speaking environment could discriminate between the phonemes /r/ and /l/ at 6 but not 10 months of age. This is because the phonetic distinction between these phonemes is not present in the Japanese language. However, an infant reared in an English-speaking environment can continue to discriminate between these phonemes after 10 months of age because the phonetic distinction between /r/ and /l/ is present in the English language. Once phoneme categories are in place at around 10 months of age, infants begin to show sensitivity to more complex aspects of language, such as recognizing familiar words in their native language. This example highlights how native language experience shapes perception, and the gradual and sequential native of language development.

Critical periods can be impacted by both biological and environmental factors. For instance, exposure to pharmacological agents during pregnancy can affect language critical periods. Additionally, factors such as being raised in a bilingual environment or receiving a cochlear implant can alter critical periods. Critical periods are important to understand because they demonstrate how early language exposure shapes later language skills. Overall, by examining language critical periods, clinicians and researchers can broaden their understanding of how language development unfolds.

Blogger: Nicolette Noonan is a PhD Candidate in Psychology, supervised by Dr. Lisa Archibald and Dr. Marc Joanisse