Research Byte: Executive functions involve more than just the prefrontal structures--White matter matters

Neuroanatomical Substrates of Executive Functions: Beyond Prefrontal Structures

• Brianne M. Bettcher^{a, b, ,} ,
• Dan Mungas^c,
• Nihar Patel^a,
• Jonathan Elofson^a,
• Shubir Dutt^a,
• Matthew Wynn^a,
• Christa L. Watson^a,
• Melanie Stephens^a,
• Christine M. Walsh^a,
• Joel H. Kramer^a

• ^a University of California, San Francisco; Department of Neurology, Memory and Aging Center; San Francisco, CA
• ^b University of Colorado, Denver Anschutz School of Medicine; Departments of Neurosurgery and Neurology; Rocky Mountain Alzheimer’s Disease Center; Aurora, CO
• ^c University of California, Davis; Department of Neurology; Davis, CA

Received 6 August 2015, Revised 29 February 2016, Accepted 3 March 2016, Available online 3 March 2016

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Highlights

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Executive functions (EF) are not synonymous with ‘frontal’ tasks.

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Global atrophy was the only independent predictor of EF.

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Frontal volumes do not predict EF when statistically isolated from global atrophy.

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White matter metrics remain predictors of EF, independent of global atrophy.

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Abstract

Executive functions are often considered lynchpin “frontal lobe tasks”, despite accumulating evidence that a broad network of anterior and posterior brain structures supports them. Using a latent variable modeling approach, we assessed whether prefrontal grey matter volumes independently predict executive function performance when statistically differentiated from global atrophy and individual non-frontal lobar volume contributions. We further examined whether fronto-parietal white matter microstructure underlies and independently contributes to executive functions. We developed a latent variable model to decompose lobar grey matter volumes into a global grey matter factor and specific lobar volumes (i.e. prefrontal, parietal, temporal, occipital) that were independent of global grey matter. We then added mean fractional anisotropy (FA) for the superior longitudinal fasciculus (dorsal portion), corpus callosum, and cingulum bundle (dorsal portion) to models that included grey matter volumes related to cognitive variables in previous analyses. Results suggested that the 2-factor model (shifting/inhibition, updating/working memory) plus an information processing speed factor best explained our executive function data in a sample of 202 community dwelling older adults, and was selected as the base measurement model for further analyses. Global grey matter was related to the executive function and speed variables in all four lobar models, but independent contributions of the frontal lobes were not significant. In contrast, when assessing the effect of white matter microstructure, cingulum FA made significant independent contributions to all three executive function and speed variables and corpus callosum FA was independently related to shifting/inhibition and speed. Findings from the current study indicate that while prefrontal grey matter volumes are significantly associated with cognitive neuroscience measures of shifting/inhibition and working memory in healthy older adults, they do not independently predict executive function when statistically isolated from global atrophy and individual non-frontal lobar volume contributions. In contrast, better microstructure of fronto-parietal white matter, namely the corpus callosum and cingulum, continued to predict executive functions after accounting for global grey matter atrophy. These findings contribute to a growing literature suggesting that prefrontal contributions to executive functions cannot be viewed in isolation from more distributed grey and white matter effects in a healthy older adult cohort.

Working memory and IQ brain clock training and mechanisms linked?

It is no secret that I believe that there is a significant link between contemporary working memory (and training related studies) and mental timing mechanisms (and training to improve) that can not be ignored.  I keep running across the common neurological mechanisms of the frontal (esp. the dorsolateral PFC) and parietal cortex's, the frontal-parietal loop, the basal ganglia and dopamine.  I have hypothesized about this in a variety of posts (esp. the possibility of a temporal g domain-general mechanism) and have made this link in a couple on-line PPT slide shows.  Klingberg's article below is entirely consistent with these hypotheses (click here for more info on Klingberg's strong program of working memory research).

Klingberg, T. (2010).  Training and plasticity of working memory.  Trends in Cognitive Sciences, 14 (7), 317-324. (click here to view)

Working memory (WM) capacity predicts performance in a wide range of cognitive tasks. Although WM capacity has been viewed as a constant trait, recent studies suggest that it can be improved by adaptive and extended training. This training is associated with changes in brain activity in frontal and parietal cortex and basal ganglia, as well as changes in dopamine receptor density. Transfer of the training effects to non-trained WM tasks is consistent with the notion of training-induced plasticity in a common neural network for WM. The observed training effects suggest that WM training could be used as a remediating intervention for individuals for whom low WM capacity is a limiting factor for academic performance or in everyday life.

Technorati Tags: Psychology, school psychology, educational psychology, cognitive psychology, neuropsychology, neurosciences, neurotechnology, neurology, brain, brain function, cognitive abilities, intelligence, IQ brain clock, brain timing, mental timekeeping, brain rhythms, rhythm perception, brain synchrony, brain synchronization, neural synchrony, neural synchronization, brain clock, dyslexia, temporal processing, temporal g, working memory, brain fitness, brain training

Metronome training improves reading achievement

I previously blogged (a self-serving plug) about an "in press" research article that demonstrated that a mental-timing based intervention (Interactive Metronome; IM) improved reading achievement in elementary school children. The research summarized in this article suggests that a brain-based intervention may improve the resolution of a school child's internal brain clock and, in turn, produce positive reading achievement outcomes. [Check out my prior post for a necessary conflict of interest disclosure.] Also...click here for additional IM-related posts (@ the IQ Brain Clock) and mental time-keeping posts at my sister blog (IQ's Corner).

Below is the reference citation (with link to pdf copy of the article) and abstract.

This is exciting stuff. If the reader wants additional information regarding possible reasons for the success of this intervention, check out the Time Doc's recent IM Keynote PowerPoint presentation.

In addition, I've added this article to the "key research articles" section of this blog.

• Taub, G., McGrew, K. & Keith, T. (2007). Improvements in interval time tracking and effects on reading achievement, Psychology in the Schools, 44 (8), 849-863. (click here to view)

• This study examined the effect of improvements in timing/rhythmicity on students’ reading achievement. 86 participants completed pre- and post-test measures of reading achievement (i.e., Woodcock-Johnson III, Comprehensive Test of Phonological Processing, Test of Word Reading Efficiency, and Test of Silent Word Reading Fluency). Students in the experimental group completed a 4-week intervention designed to improve their timing/rhythmicity by reducing the latency in their response to a synchronized metronome beat, referred to as a synchronized metronome tapping (SMT) intervention. The results from this non-academic intervention indicate the experimental group’s post-test scores on select measures of reading were significantly higher than the non-treatment control group’s scores at the end of 4 weeks. This paper provides a brief overview of domain-general cognitive abilities believed effected by SMT interventions and provides a preliminary hypothesis to explain how this non-academic intervention can demonstrate a statistically significant effect on students’ reading achievement scores.

Technorati Tags: psychology, educational psychology, education, neuropsychology, IQ, intelligence, reading, reading achievement, dyslexia, mental time keeping, brain clock, temporal processing, Interactive Metronome

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The nature of mental time-keeping research

I've previously highlighted the important mental timing research of Dr. Penny Lewis at the IQ Brain clock (she is listed as one of the blogs "mental timing scholars" - see link section).

Although her important 2006 publication (Remembering the Time - see "key research articles" link section) suggests that contemporary research has started to zero in on the possible locations of the internal brain clock, I found what she wrote in 2005 (which was less specific about possible brain functions and locations) to be a very nice easy-to-read summary of the nature of the search for the mental/interval time clock. I have reproduced her words below...food for thought. Nicely written statement of the nature of mental timing research progress. I've also added this article to the "key research article" section for those who want to read the entire manuscript.

Lewis, P. & Walsh, V. (2005). Time Perception: Components of the Brain’s Clock. Current Biology, 15 (10), 389-391.

• Our brains measure time continuously. We are aware of how long we have been doing a particular thing, how long it has been since we last slept, and how long it will be until lunch or dinner. We are ready, at any moment, to make complex movements requiring muscle coordination with microsecond accuracy, or to decode temporally complex auditory signals in the form of speech or music. Our timing abilities are impressive, diverse and worthy of investigation. But they are not very well understood.
• Many models of time perception have been put forward...collectively postulating a wide variety of different mechanisms. Regardless of their diversity, the models all agree that temporal information is processed in many ways: it is remembered, compared to other temporal information, combined with sensory information, and used in the production of motor outputs.
• The holy grail of timing research is to understand the ‘time-dependent process’: a mechanism equivalent to a piezoelectric crystal in a man-made clock or the movement of a shadow on a sundial. This has proven an elusive goal, to the extent that ideas about how this mechanism might work remain near the level of conjecture. Researchers have had great difficulty in pinning timing-related activity in the brain to any specific type of function. This is largely because most time measurement tasks draw upon more than one process, making it difficult to tease the various components apart.

Technorati Tags: psychology, educational psychology, school psychology, neuropsychology, neuroscience, intelligence, working memroy, Gsm, executive function, executive attention, attention, mental time-keeping, interval timing, brain clock, internal master clock

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How the brain processes quantitative information-new studies

New research summarized at Science Daily that is providing new insights into how the brain processes quantiative/numerical (Gq/Gf-RQ) information. Below is the first paragraph of the article.

• Two studies in the January 18, 2007, issue of the journal Neuron, published by Cell Press, shed significant light on how the brain processes numerical information--both abstract quantities and their concrete representations as symbols. The researches said their findings will contribute to understanding how the brain processes quantitative information as well as lead to studies of how numerical representation in the brain develops in children. Such studies could aid in rehabilitating people who suffer from dyscalculia--an inability to understand, remember, and manipulate numbers. The researchers also said their findings offer insight into the mystery of how the brain learns to associate abstract symbols precisely with quantities.

Scientific American also provides coverage of these two studies

Technorati Tags: psychology, educational psychology, education, school psychology, special education, LD, learning disabilities, dyscalculia, Gq, Gf, quantitative, math, numerical, neuropsychology, information processing

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