How Are Cognitive And Physical Endurance Linked?

Post by Amanda Engstrom 

The takeaway

Engaging in cognitive tasks during physical activity makes exercise feel harder. Individuals with stronger cognitive abilities are less affected by this mental “cost,” suggesting that cognition and endurance capacity are closely linked. 

What's the science?

The combination of physical activity and cognitive tasks (such as navigation and working memory), known as cognitive-motor dual tasks, may play a critical role in the evolution of human foraging strategies and sustaining goal-oriented physical effort. In ancestral environments, humans had to perform dual functions for hunting and foraging, which likely shaped the evolution of human cognition. Prior work has shown that cognitive demands during short-duration movement can compete with locomotor resources and reduce physical endurance. This negative association has been attributed to the increased perception of physical effort and mental fatigue; however, this has not been directly tested. This week in PNAS, Aslan and colleagues conduct a randomized trial to elucidate how cognitive demands influence long-term endurance and fatigability.

How did they do it?

The experiment included thirty healthy individuals ages 18-53 (17 females, 13 males). Participants completed two endurance walking sessions at roughly 65% of their estimated maximum heart rate. One exercise session was done while simultaneously performing various executive function tasks (Exercise + Cognition; E+C), and the other was walking alone (Exercise alone; EA). During each session, the authors measured the participants' perceived effort using the Borg Rating of Perceived Exertion (RPE) scale and their perception of fatigability, which is the change in the participants' perception of effort. The authors also tracked the participants' oxygen consumption and carbon dioxide production to estimate the energetic cost of exercise and their respiratory exchange rate. Finally, to test whether higher cognitive function might buffer the negative effects of dual tasking on endurance, the authors evaluated participants’ cognitive performance before any physical activity, focusing on skills relevant to foraging success, like executive function, visuospatial abilities, and memory. 

What did they find?

Perceived effort was significantly greater during the E+C condition compared to EA. Six participants chose to stop early from exercise in the E+C condition, compared with only one participant stopping early in both conditions. 

This supports the idea that cognitive-motor dual tasks increase perceived effort during endurance activities. However, perceived fatigability—the rate of change in perceived effort—did not differ between conditions. The physical expenditure of participants, measured by net metabolic power and overall respiratory exchange rate, was significantly lower during the E+C condition compared to EA. Interestingly, participants had a greater respiratory exchange rate initially in the E+C condition compared to EA, but the values converged as the trial went on. This indicates that early in the E+C condition, participants utilized a greater proportion of carbohydrates as fuel than in the EA condition, but this proportion declined at a slightly more rapid rate over the duration of the E+C condition. In both the E+C and EA conditions, participants with better delayed memory had lower perceived effort. Additionally, participants with lower visuospatial ability and figure recall scores had a larger increase in perceived effort from the E+C to EA conditions compared to participants with higher scores on these tests.

What's the impact?

This study demonstrates a bidirectional relationship between aerobic endurance and cognitive function. Dual tasking appears to reduce endurance by increasing the overall perception of effort. The findings also show that the subjective feeling of effort does not necessarily track actual physiological cost. Overall, this study provides a framework for understanding how cognition can both constrain and support goal-oriented physical activity from an evolutionary standpoint as well as for modern training practices.


Access the original scientific publication here.

How Speech Relates to Brain Structural Changes in Psychiatric Illnesses

Post by Lila Metko 

The takeaway

Deficits in the ability to produce coherent, organized language are a common feature across many psychiatric disorders. The authors found that regardless of which specific psychiatric diagnosis an individual has, different types of deficits in their language correlate with specific changes in the brain structure. 

What's the science?

Language deficits are a feature of many psychiatric illnesses, and they span across several illness types, including both mood disorders and psychotic disorders. Formal thought disorder (FTD) is a disorder of deficits in the organization of thinking, writing, and verbal communication. Formal thought disorder and language deficits in general are associated with a poorer quality of life for individuals with psychiatric illnesses like schizophrenia spectrum disorder (SSD) or bipolar disorder. In a transdiagnostic sample - a sample containing individuals with multiple diagnoses - it was found that higher FTD disorganization is associated with lower grey matter in some regions of the brain. There have been few transdiagnostic studies that formally investigate the relationship between spoken language, the multiple dimensions of formal thought disorder, and neuroimaging analysis. This week in Molecular Psychiatry, Seuffert and colleagues used computer processing of human language to help map different features of speech onto brain structure. 

How did they do it?

The authors used natural language processing (NLP), a form of artificial intelligence to analyze and interpret language. They asked the participants, 194 with a mood disorder or psychotic disorder, and 178 healthy controls, to speak naturally to describe a set of four pictures. The total time they collected speech for each participant was 12 minutes, 3 minutes per picture. NLP was used to extract a broad set of linguistic features from each participant’s speed, which were entered into an exploratory factor analysis to identify the underlying dimensions that best explained variance across speakers. The factors were syntax complexity, richness and diversity in vocabulary, and breadth of focus in the narrative. Each participant underwent MRI imaging, and after excluding poor-quality images and artifacts, the researchers ended up with 303 participants with grey matter volume data and 247 participants with diffusion tensor imaging data. Diffusion tensor imaging is a specialized MRI technique that visualizes the diffusion of water molecules through tissue and is a particularly useful technique for visualizing the structure of white matter. 

What did they find?

The authors analyzed the relationship between the explorative analysis factors and dimensions of FTD. Syntax complexity correlated negatively with FTD Disorganization, Emptiness, and Incoherence, while vocabulary richness and diversity correlated negatively with only FTD Emptiness. This means that as these aforementioned FTD dimensions increased, the respective factors decreased. Narrow Thematic Focus (a narrow theme/narrative) was not associated with clinician-rated FTD, but showed a distinct neuroanatomical signature: a significant negative association with grey matter volume in a right-hemispheric cluster centered in the posterior insula and extending into the planum polare and putamen. No grey matter correlates were observed for the other two linguistic factors after stringent correction. In white matter analysis, each explorative analysis factor was negatively associated with functional anisotropy, a measure of white matter health, of at least one white matter tract. Vocabulary richness and diversity were associated with seven different white matter tracts, particularly within the frontotemporal regions. 

What's the impact?

This is the largest transdiagnostic study to date to map specific features of human speech onto structural brain changes in psychiatric illness. Since the quality of language is highly predictive of outcomes and quality of life in individuals with psychiatric disorders, this knowledge is especially important in the detection and treatment of these disorders. In understanding which regions of the brain are responsible for different aspects of spontaneous speech pathology, scientists are better equipped to discover treatments for them. 

How Diet Can Impact Memory Function

Post by Rebecca Glisson

The takeaway

Diets that include excessive amounts of fat or sugar can impair our memory. Receptors in the hippocampus, an area of the brain that plays a key role in memory, can become overactive with a high-fat and sugar diet, and blocking these receptors can improve memory.

What's the science?

More and more often, scientists are uncovering how our diet is linked to brain function. For example, the endocannabinoid system of the brain, which includes type-1 cannabinoid receptors (CB1Rs), is known to be overactive in people with too much fat or sugar in their diets. This week in Current Biology, Ducourneau and colleagues investigated how a poor diet can lead to memory dysfunction via the endocannabinoid system.

How did they do it?

The authors wanted to study how diet impacts memory, particularly in adolescents, a critical period for the development of memory function. They gave juvenile male mice either a diet with high-fat and high-sugar or a normal diet, then had them perform an object recognition test to evaluate their memory. The test consisted of presenting a mouse with an object, then a delay of either 3 hours to test short-term memory or 24 hours to test long-term memory, then presenting the mouse with the same object and a new object. If the mouse remembered the original object, then they spent more time exploring the new object. Mice were then injected with a CB1R receptor antagonist, which blocks the activity of this receptor, and then tested again for their memory performance.

What did they find?

Mice with high-fat and sugar diets did worse on the 24-hour long-term object recognition test than control mice. Short-term memory performance, however, was not affected by diet, as measured via a test administered only 3 hours post-exposure. This suggests that poor diets have more of an impact on long-term memory function than short-term memory. When mice on the high-sugar, high-fat diet were injected with the CB1R activity blocker, they performed better on their memory test. This suggests that CB1R is responsible for memory issues when impacted by poor diets.

What's the impact?

This study is the first to show that diets high in sugar and fat lead to long-term memory impairment via the endocannabinoid system. Further, this memory impairment can be reversed by blocking cannabinoid receptors. A poor diet is especially harmful for memory development in adolescence.

Access the original scientific publication here.