Effect of artificial gravity on neurocognitive performance during head-down tilt bedrest.

This study evaluated the acute and chronic effects of intermittent and continuous Artificial Gravity (AG) on cognitive performance during 60 days of Head-down tilt bedrest (HDTBR), a well-established ground-based spaceflight analogue method. Participants were randomly assigned to three groups: intermittent AG, continuous AG, and HDTBR control group without AG exposure. Task performance and electrophysiological measures of attention and working memory were investigated during Simple and Complex tasks in the Visual and the Auditory modality. Compared to baseline, faster reaction time and better accuracy was present during HDTBR regarding the Complex tasks, however, the practice effect was diminished in the three HDTBR groups compared to an ambulatory control group. Brain potentials showed a modality-specific decrease, as P3a was decreased only in the Auditory, while P3b decreased in the Visual modality. No evidence for acute or chronic AG-related cognitive impairments during HDTBR was found.

Are head-down tilt bedrest studies capturing the true nature of spaceflight-induced cognitive changes? A review.

Although a number of studies have examined cognitive functions in space, the reasons behind the observed changes described by space research and anecdotal reports have not yet been elucidated. A potential source of cognitive changes is the cephalad fluid shift in the body caused by the lack of hydrostatic pressure under microgravity. These alterations can be modeled under terrestrial conditions using ground-based studies, such as head-down tilt bedrest (HDBR). In this review, we compare the results of the space and HDBR cognitive research. Results for baseline and in-flight/in-HDBR comparisons, and for baseline and post-flight/post-HDBR comparisons are detailed regarding sensorimotor skills, time estimation, attention, psychomotor speed, memory, executive functions, reasoning, mathematical processing, and cognitive processing of emotional stimuli. Beyond behavioral performance, results regarding brain electrical activity during simulated and real microgravity environments are also discussed. Finally, we highlight the research gaps and suggest future directions.

Persistent deterioration of visuospatial performance in spaceflight.

Although human adaptation to spaceflight has been studied for decades, little is known about its long-term effects on brain and behavior. The present study investigated visuospatial performance and associated electrophysiological responses in astronauts before, during, and after an approximately half-year long mission to the International Space Station. Here we report findings demonstrating that cognitive performance can suffer marked decrements during spaceflight. Astronauts were slower and more error-prone on orbit than on Earth, while event-related brain potentials reflected diminished attentional resources. Our study is the first to provide evidence for impaired performance during both the initial (~ 8 days) and later (~ 50 days) stages of spaceflight, without any signs of adaptation. Results indicate restricted adaptability to spaceflight conditions and calls for new research prior to deep space explorations.

Differential impact of acute hypoxia on event related potentials: impaired task-irrelevant, but preserved task-relevant processing and response inhibition.

The current study investigated how experimentally induced acute normobaric hypoxia affects attentional control functions during easy, monotonous visual sustained attention and response inhibition (modified Continuous Performance Task) and executive control tasks (number-size Stroop task). Along with behavioral efficiency, task-relevant and task-irrelevant information processing were investigated by measuring event related brain potentials (ERP) evoked by target stimuli (Target P3), task-relevant stimuli with no response needed (NoGo P3), and task-irrelevant novel stimuli (Novelty P3) during acute hypoxia exposure. Normobaric hypoxia was induced by adjusting the O2 content of the breathing mixture to obtain 80% peripheral oxygen saturation, equivalent of 5500 m above sea level. Here we report decreased Novelty P3 during acute normobaric hypoxia exposure, while Target P3 and NoGo P3, as well as behavioral efficiency remained intact. Our paper is the first to provide evidence for impaired novelty processing along with intact task-relevant information processing and response inhibition during normobaric hypoxic exposure.

Cognitive resilience after prolonged task performance: an ERP investigation.

Deleterious consequences of cognitive fatigue might be avoided if people respond with increased effort to increased demands. In this study, we hypothesized that the effects of fatigue would be more pronounced in cognitive functions reflecting compensatory effort. Given that the P3a event-related potential is sensitive to the direction and amount of attention allocated to a stimulus array, we reasoned that compensatory effort would manifest in increased P3a amplitudes. Therefore, we compared P3a before (pre-test) and after (post-test) a 2 h long cognitively demanding (fatigue group, n = 18) or undemanding task (control group, n = 18). Two auditory tasks, a three-stimulus novelty oddball and a duration discrimination two-choice response task were presented to elicit P3a. In the fatigue group, we used the multi-attribute task battery as a fatigue-inducing task. This task draws on a broad array of attentional functions and imposed considerable workload. The control group watched mood-neutral documentary films. The fatigue manipulation was effective as subjective fatigue increased significantly in the fatigue group compared to controls. Contrary to expectations, however, fatigue failed to affect P3a in the post-test phase. Similar null effects were obtained for other neurobehavioral measures (P3b and behavioral performance). Results indicate that a moderate increase in subjective fatigue does not hinder cognitive functions profoundly. The lack of objective performance loss in the present study suggests that the cognitive system can be resilient against challenges instigated by demanding task performance.

Iron Concentration in Deep Gray Matter Structures is Associated with Worse Visual Memory Performance in Healthy Young Adults.

Abnormally high deposition of iron can contribute to neurodegenerative disorders with cognitive impairment. Since previous studies investigating cognition-brain iron accumulation relationships focused on elderly people, our aim was to explore the association between iron concentration in subcortical nuclei and two types of memory performances in a healthy young population. Gender difference was found only in the globus pallidus. Our results showed that iron load characterized by R2* value on the MRI in the caudate and putamen was related to visual memory, while verbal memory was unrelated to iron concentration.

THE RELATIONSHIP BETWEEN SERUM CHOLESTEROL AND VERBAL MEMORY MAY BE INFLUENCED BY BODY MASS INDEX (BMI) IN YOUNG HEALTHY WOMEN.

The objective of this study was to examine the relationship between verbal memory and total cholesterol (TC) levels related to body mass index (BMI) in healthy young women. Verbal memory was assessed using the Rey Auditory-Verbal Learning Test (RAVLT) while total serum cholesterol was measured by enzymatic colorimetric test. In order to analyze the potential significance of BMI subjects were divided into three groups according to their calculated BMI percentile values. No significant correlation was found when assessing the group as a whole. However a remarkable pattern of correlation emerged when assessing the BMI groups separately: a close-to-significant positive correlation was found for total learning score and TC in the low BMI group, no correlation emerged in the medium BMI group while a strong inverse correlation was found in the high BMI group. These findings indicate that the relationship between verbal memory and serum TC level is also influenced by BMI.

2D:4D finger ratio positively correlates with total cerebral cortex in males.

Although there is evidence that the ratio of 2nd-4th digit length (2D:4D) correlates with prenatal testosterone level, psychological and health traits only two studies have assessed the relationship with brain morphological features. Here we investigated the association between the 2D:4D ratio and several brain subvolumes. Seventy-five subjects between the ages of 18 and 30 were included in the study. The length of the 2nd and 4th digits were measured with an electronic vernier caliper while MRI measurements were performed on a Siemens Magnetom Trio Tim (3T) system. Freesurfer software suite was used for volumetric segmentation. Finger ratio significantly positively correlated with total cerebral cortex, total cerebellar white matter and total cerebellar cortex in males but not in females. Our results indicate that prenatal testosterone, as estimated by the 2D:4D ratio has an effect on adult brain morphology in males.

Problematic internet use is associated with structural alterations in the brain reward system in females.

Neuroimaging findings suggest that excessive Internet use shows functional and structural brain changes similar to substance addiction. Even though it is still under debate whether there are gender differences in case of problematic use, previous studies by-passed this question by focusing on males only or by using gender matched approach without controlling for potential gender effects. We designed our study to find out whether there are structural correlates in the brain reward system of problematic Internet use in habitual Internet user females. T1-weighted Magnetic Resonance (MR) images were collected in 82 healthy habitual Internet user females. Structural brain measures were investigated using both automated MR volumetry and voxel based morphometry (VBM). Self-reported measures of problematic Internet use and hours spent online were also assessed. According to MR volumetry, problematic Internet use was associated with increased grey matter volume of bilateral putamen and right nucleus accumbens while decreased grey matter volume of orbitofrontal cortex (OFC). Similarly, VBM analysis revealed a significant negative association between the absolute amount of grey matter OFC and problematic Internet use. Our findings suggest structural brain alterations in the reward system usually related to addictions are present in problematic Internet use.

Milk and dairy consumption correlates with cerebral cortical as well as cerebral white matter volume in healthy young adults.

The objective of this study was to investigate the relation between habitual milk and dairy consumption and brain morphology as assessed by magnetic resonance imaging (MRI) investigations in 119 young healthy university students. MRI measurements were performed on a Siemens Magnetom Trio Tim (3T) system while FreeSurfer software suite was used for volumetric segmentation. Dietary habits related to milk and dairy consumption were assessed by a structured questionnaire. Total cerebral cortex, total cerebral white matter, and total cerebral parenchyma were significantly related with cottage cheese and total protein intake from milk and dairy also when controlled for age and gender in the multivariate model. Our results indicate that dietary habits related with milk and dairy are proportionally associated with volumes of both cerebral cortex and cerebral white matter.

Intracranial volume inversely correlates with serum 25(OH)D level in healthy young women.

OBJECTIVES: Vitamin D is important in normal brain development. In animals low vitamin D level is associated with brain morphological alterations including enlargement of the brain. Whether a similar association exists in humans is unknown. Here we investigated the relationship between vitamin D and total intracranial volume as well as total volume of the cortical grey and cerebral white matter and that of the ventricles in young healthy women. METHODS: To assess volumes we applied semi-automatic user-independent MR volumetry. For the vitamin D measurements automated electrochemiluminescence immunoassay was used. RESULTS: We found a significant negative correlation between vitamin D and total intracranial volume as well as total cortical grey and cerebral white matter volumes. DISCUSSION: This association may reflect a trait-like relationship between vitamin D and brain size possibly determined in early development.

Are there any gender differences in the hippocampus volume after head-size correction? A volumetric and voxel-based morphometric study.

Previous findings on normal sexual dimorphism in hippocampal volume have not always been consistent. This study investigated gender differences in hippocampal volume using different head-size correction strategies. T1-weighted MR images were collected in 99 healthy, Caucasian, university students (66 female subjects; mean age: 23.1 ± 2.3, range: 19-31 years). Sexual dimorphism in hippocampus was investigated by automated MRI volumetry and voxel-based morphometry (VBM) using both general linear model (GLM) and proportion head-size correction strategies. Absolute hippocampal volumes were larger in men than women. After adjusting for head-size, the proportion method indicated larger hippocampi in women than men, while no gender differences were found using the GLM approach. Investigating absolute hippocampal volumes in 15 head-size matched pairs of males and females indicated no gender differences. We suggest that there is no sexual dimorphism in hippocampal size and the apparent gender differences found by the proportion method may have more to do with head-size than with sex. The GLM and proportion head-size correction strategies are not interchangeable and may yield different results. The importance of the present findings is mostly related to scientific reproducibility across MRI volumetry or VBM studies.

Alexithymia is associated with low level of vitamin D in young healthy adults.

OBJECTIVE: Vitamin D plays an important role in brain development and functioning. Low levels of vitamin D have been described in several psychiatric and neurologic conditions including autism spectrum disorder. Alexithymia that shows high comorbidity with autism is also present in the general population as well as hypovitaminosis D. METHODS: Here we assessed the relation between alexithymia as measured by the Toronto Alexithymia Scale-20 and vitamin D level in healthy young adults. Results We found an inverse correlation between the levels of alexithymia and vitamin D. DISCUSSION: These data suggest the association between disturbed emotional processing and low levels of vitamin D to be present in young healthy subjects.

White-matter microstructure and language lateralization in left-handers: a whole-brain MRI analysis.

Most people are left-hemisphere dominant for language. However the neuroanatomy of language lateralization is not fully understood. By combining functional magnetic resonance imaging (fMRI) and diffusion tensor imaging (DTI), we studied whether language lateralization is associated with cerebral white-matter (WM) microstructure. Sixteen healthy, left-handed women aged 20-25 were included in the study. Left-handers were targeted in order to increase the chances of involving subjects with atypical language lateralization. Language lateralization was determined by fMRI using a verbal fluency paradigm. Tract-based spatial statistics analysis of DTI data was applied to test for WM microstructural correlates of language lateralization across the whole brain. Fractional anisotropy and mean diffusivity were used as indicators of WM microstructural organization. Right-hemispheric language dominance was associated with reduced microstructural integrity of the left superior longitudinal fasciculus and left-sided parietal lobe WM. In left-handed women, reduced integrity of the left-sided language related tracts may be closely linked to the development of right hemispheric language dominance. Our results may offer new insights into language lateralization and structure-function relationships in human language system.

Effects of spinal cord stimulation on heart rate variability in patients with chronic pain.

BACKGROUND: Spinal cord stimulation has become an established clinical option for treatment of refractory chronic pain and angina pectoris, but its precise mechanism of action is unclear. We investigated the effect of spinal cord stimulation (SCS) on heart rate variability (HRV) and evaluating its influence on the sympathetic/parasympathetic balance in chronic pain. MATERIALS AND PURPOSE: Seven patients (three men, four women) with SCS due to chronic pain were included. The SCS was programmed in three different ways: (i) to stimulate at an amplitude known to generate paresthesias (ON-state), (ii) at a subliminal level (SUB state), or (iii) switched off (OFF-state). HRV analysis was based on 5-min segments of the consecutive normal RR intervals and was performed with custom software (Kubios HRV Analysis). RESULTS: The mean heart rate was higher in ON state compared to SUB state (p = 0.018) and the high-frequency component of the HRV was lower in ON compared to OFF period (p = 0.043). Other HRV parameters values did not significantly differ during the three tested periods. CONCLUSION: Spinal cord stimulation in chronic pain seems to be accompanied by reduced parasympathetic tone, unlike SCS in angina pectoris where previous studies found a reduced cardiac sympathetic tone. Our study might lead to understand the mechanism of action of SCS We investigated a relatively small number of patients, which is the main limitation of our study. Thus, further studies with larger number of patients are required for validation of our results.