Search

Acute mountain sickness (AMS), characterized by headache, nausea, fatigue, and dizziness when unacclimatized individuals rapidly ascend to high altitude, is exacerbated by exercise and can be disabling. Although AMS is observed in both normobaric (NH) and hypobaric hypoxia (HH), recent evidence suggests that NH and HH produce different physiological responses. We evaluated whether AMS symptoms were different in NH and HH during the initial stages of exposure and if the assessment tool mattered. Seventy-two 8 h exposures to normobaric normoxia (NN), NH, or HH were experienced by 36 subjects. The Environmental Symptoms Questionnaire (ESQ) and Lake Louise Self-report (LLS) were administered, resulting in a total of 360 assessments, with each subject answering the questionnaire 5 times during each of their 2 exposure days. Classification tree analysis indicated that symptoms contributing most to AMS were different in NH (namely, feeling sick and shortness of breath) compared to HH (characterized most by feeling faint, appetite loss, light headedness, and dim vision). However, the differences were not detected using the LLS. These results suggest that during the initial hours of exposure (1) AMS in HH may be a qualitatively different experience than in NH and (2) NH and HH may not be interchangeable environments. [ABSTRACT FROM AUTHOR]

Abstract: Near-infrared neuromonitoring (NIN) is based on near-infrared spectroscopy (NIRS) measurements performed through the intact scalp and skull. Despite the important effects of overlying tissue layers on the measurement of brain hemodynamics, the influence of scalp and skull on NIN sensitivity are not well characterized. Using 3555 Monte Carlo simulations, we estimated the sensitivity of individual continuous-wave NIRS measurements to brain activity over the entire adult human head by introducing a small absorption perturbation to brain gray matter and quantifying the influence of scalp and skull thickness on this sensitivity. After segmenting the Colin27 template into five tissue types (scalp, skull, cerebrospinal fluid, gray matter and white matter), the average scalp thickness was 6.9±3.6mm (range: 3.6–11.2mm), while the average skull thickness was 6.0±1.9mm (range: 2.5–10.5mm). Mean NIN sensitivity – defined as the partial path length through gray matter divided by the total photon path length – ranged from 0.06 (i.e., 6% of total path length) at a 20mm source–detector separation, to over 0.19 at 50mm separations. NIN sensitivity varied substantially around the head, with occipital pole exhibiting the highest NIRS sensitivity to gray matter, whereas inferior frontal regions had the lowest sensitivity. Increased scalp and skull thickness were strongly associated with decreased sensitivity to brain tissue. Scalp thickness always exhibited a slightly larger effect on sensitivity than skull thickness, but the effect of both varied with SD separation. We quantitatively characterize sensitivity around the head as well as the effects of scalp and skull, which can be used to interpret NIN brain activation studies as well as guide the design, development and optimization of NIRS devices and sensors. [Copyright &y& Elsevier]

Understanding the spatial and depth sensitivity of non-invasive near-infrared spectroscopy (NIRS) measurements to brain tissue–i.e., near-infrared neuromonitoring (NIN) – is essential for designing experiments as well as interpreting research findings. However, a thorough characterization of such sensitivity in realistic head models has remained unavailable. In this study, we conducted 3,555 Monte Carlo (MC) simulations to densely cover the scalp of a well-characterized, adult male template brain (Colin27). We sought to evaluate: (i) the spatial sensitivity profile of NIRS to brain tissue as a function of source-detector separation, (ii) the NIRS sensitivity to brain tissue as a function of depth in this realistic and complex head model, and (iii) the effect of NIRS instrument sensitivity on detecting brain activation. We found that increasing the source-detector (SD) separation from 20 to 65 mm provides monotonic increases in sensitivity to brain tissue. For every 10 mm increase in SD separation (up to ∼45 mm), sensitivity to gray matter increased an additional 4%. Our analyses also demonstrate that sensitivity in depth (S) decreases exponentially, with a “rule-of-thumb” formula S = 0.75*0.85depth. Thus, while the depth sensitivity of NIRS is not strictly limited, NIN signals in adult humans are strongly biased towards the outermost 10–15 mm of intracranial space. These general results, along with the detailed quantitation of sensitivity estimates around the head, can provide detailed guidance for interpreting the likely sources of NIRS signals, as well as help NIRS investigators design and plan better NIRS experiments, head probes and instruments. [ABSTRACT FROM AUTHOR]

Traumatic brain injury (TBI) commonly results in residual memory difficulties. Such deficits are amenable to cognitive rehabilitation, but optimal selection of rehabilitation interventions remains a challenge. We hypothesized that diffusion tensor imaging (DTI) could be used to predict which individuals were likely to benefit from a specific memory rehabilitation intervention. Thirty-seven individuals with TBI, of all severities, first underwent DTI scanning, along with 18 matched controls. Participants with TBI then attended a 12-session memory intervention emphasizing internal memory strategies (I-MEMS). Primary outcome measures (HVLT, RBMT) were collected at the time of DTI scanning, and both immediately and one month post-therapy. In contrast to typical neuroimaging analysis, fractional anisotropy (FA) was used to predict long-term outcome scores, adjusting for typical predictors (injury severity, age, education, time since injury, pretest score). FA of the parahippocampal white matter was a significant negative predictor of HVLT, while the anterior corpus callosum, left anterior internal capsule, and right anterior corona radiata were negative predictors of RBMT outcome. The importance of these predictors rivaled those of pretest scores. Thus, FA measures may provide substantial predictive value for other cognitive interventions as well. The reason why higher FA was associated with less successful response to cognitive intervention remains unclear and will require further study. [ABSTRACT FROM AUTHOR]

Abstract: In previous work we introduced a novel method for reducing global interference, based on adaptive filtering, to improve the contrast to noise ratio (CNR) of evoked hemodynamic responses measured non-invasively with near infrared spectroscopy (NIRS). Here, we address the issue of how to generally apply the proposed adaptive filtering method. A total of 156 evoked visual response measurements, collected from 15 individuals, were analyzed. The similarity (correlation) between measurements with far and near source–detector separations collected during the rest period before visual stimulation was used as indicator of global interference dominance. A detailed analysis of CNR improvement in oxy-hemoglobin (O2Hb) and deoxy-hemoglobin (HHb), as a function of the rest period correlation coefficient, is presented. Results show that for O2Hb measurements, 66% exhibited substantial global interference. For this dataset, dominated by global interference, 71% of the measurements revealed CNR improvements after adaptive filtering, with a mean CNR improvement of 60%. No CNR improvement was observed for HHb. This study corroborates our previous finding that adaptive filtering provides an effective method to increase CNR when there is strong global interference, and also provides a practical way for determining when and where to apply this technique. [Copyright &y& Elsevier]

Primary objective: To determine test-re-test reliability of the Hopkins Verbal Learning Test-Revised (HVLT-R) in a group of individuals with traumatic brain injury (TBI). Research design: Single-group repeated measures design. Methods and procedures: Seventy-five individuals with TBI were administered the HVLT-R twice, with 6-8 weeks between the two test sessions. Main outcomes and results: Test-re-test reliability on HVLT-R scoring parameters ranged from 0.537-0.818, with seven of the eight scoring parameters exhibiting r > 0.6. At re-test, scores did not significantly change on any of the eight HVLT-R scoring parameters. Conclusions: HVLT-R use with individuals with TBI is supported. Test-re-test reliability of total recall and delayed recall sub-scores was particularly high. [ABSTRACT FROM AUTHOR]

Primary objective: To determine test–re-test reliability of the VIrtual Planning Test (VIP) in a group of individuals with traumatic brain injury (TBI). Research design: Single-group repeated measures design. Methods and procedures: Seventy-five individuals with TBI were administered the VIP, with 6–8 weeks between the two test sessions. Main outcomes and results: Test–re-test reliability on VIP scoring parameters—as measured by Pearson correlation coefficients—ranged from 0.341–0.855, with five of the seven scoring parameters exhibiting r > 0.6. Conclusions: Based on the findings of the current study, the VIP has overall moderate test–re-test reliability when administered to individuals with TBI. Some VIP scoring parameters, i.e. Total correct/accuracy and Total absence, demonstrated high test–re-test reliability. Others, i.e. Planning time and Total wrong order, demonstrated low test–re-test reliability. [ABSTRACT FROM AUTHOR]

Ambulatory diffuse optical tomography (aDOT) is based on near-infrared spectroscopy (NIRS) and enables three-dimensional imaging of regional hemodynamics and oxygen consumption during a person’s normal activities. Although NIRS has been previously used for muscle assessment, it has been notably limited in terms of the number of channels measured, the extent to which subjects can be ambulatory, and/or the ability to simultaneously acquire synchronized auxiliary data such as electromyography (EMG) or electrocardiography (ECG). We describe the development of a prototype aDOT system, called NINscan-M, capable of ambulatory tomographic imaging as well as simultaneous auxiliary multimodal physiological monitoring. Powered by four AA size batteries and weighing 577 g, the NINscan-M prototype can synchronously record 64-channel NIRS imaging data, eight channels of EMG, ECG, or other analog signals, plus force, acceleration, rotation, and temperature for 24+ h at up to 250 Hz. We describe the system’s design, characterization, and performance characteristics. We also describe examples of isometric, cycle ergometer, and free-running ambulatory exercise to demonstrate tomographic imaging at 25 Hz. NINscan-M represents a multiuse tool for muscle physiology studies as well as clinical muscle assessment. [ABSTRACT FROM AUTHOR]

Introduction We hypothesized that cerebral alterations in edema, perfusion, and/or intracranial pressure ( ICP) are related to the development of acute mountain sickness ( AMS). Methods To vary AMS, we manipulated ambient oxygen, barometric pressure, and exercise duration. Thirty-six subjects were tested before, during and after 8 h exposures in (1) normobaric normoxia ( NN; 300 m elevation equivalent); (2) normobaric hypoxia ( NH; 4400 m equivalent); and (3) hypobaric hypoxia ( HH; 4400 m equivalent). After a passive 15 min ascent, each subject participated in either 10 or 60 min of cycling exercise at 50% of heart rate reserve. We measured tissue absorption and scattering via radio-frequency near-infrared spectroscopy ( NIRS), optic nerve sheath diameter ( ONSD) via ultrasound, and AMS symptoms before, during, and after environmental exposures. Results We observed significant increases in NIRS tissue scattering of 0.35 ± 0.11 cm−1 ( P = 0.001) in subjects with AMS (i.e., AMS+), consistent with mildly increased cerebral edema. We also noted a small, but significant increase in total hemoglobin concentrations with AMS+, 3.2 ± 0.8 μmolL−1 ( P < 0.0005), consistent with increased cerebral perfusion. No effect of exercise duration was found, nor did we detect differences between NH and HH. ONSD assays documented a small but significant increase in ONSD (0.11 ± 0.02 mm; P < 0.0005) with AMS+, suggesting mildly elevated ICP, as well as further increased ONSD with longer exercise duration ( P = 0.005). Conclusion In AMS+, we found evidence of cerebral edema, elevated cerebral perfusion, and elevated ICP. The observed changes were small but consistent with the reversible nature of AMS. [ABSTRACT FROM AUTHOR]

The feasibility and utility of wearable 24-h multimodality neuromonitoring during daily activities are demonstrated. We have developed a fourth-generation ambulatory near infrared spectroscopy device, namely NINscan 4. NINscan 4 enables recording of brain function (via cerebral hemodynamics), systemic hemodynamics, electrocardiography, and actigraphy simultaneously and continuously for up to 24 h at 250-Hz sampling rate, during (and with minor restriction to) daily activities. We present initial 24-h human subject test results, with example analysis including (1) comparison of cerebral perfusion and oxygenation changes during wakefulness and sleep over a 24-h period and (2) capturing of hemodynamic changes prior, during and after sudden waken up in the night during sleep. These results demonstrate the first ambulatory 24-h cerebral and systemic hemodynamics monitoring, and its unique advantages including long-term data collection and analysis capability, ability to catch unpredictable transient events during activities of daily living, as well as coregistered multimodality analysis capabilities. These results also demonstrate that NINscan 4's motion artifact at 1- head move- g ment is smaller than physiological hemodynamic fluctuations during motionless sleep. The broader potential of this technology is also discussed. [ABSTRACT FROM AUTHOR]

Recent behavioral investigations have revealed that autistics perform more proficiently on Raven's Standard Progressive Matrices (RSPM) than would be predicted by their Wechsler intelligence scores. A widely-used test of fluid reasoning and intelligence, the RSPM assays abilities to flexibly infer rules, manage goal hierarchies, and perform high-level abstractions. The neural substrates for these abilities are known to encompass a large frontoparietal network, with different processing models placing variable emphasis on the specific roles of the prefrontal or posterior regions. We used functional magnetic resonance imaging to explore the neural bases of autistics' RSPM problem solving. Fifteen autistic and eighteen non-autistic participants, matched on age, sex, manual preference and Wechsler IQ, completed 60 self-paced randomly-ordered RSPM items along with a visually similar 60-item pattern matching comparison task. Accuracy and response times did not differ between groups in the pattern matching task. In the RSPM task, autistics performed with similar accuracy, but with shorter response times, compared to their non-autistic controls. In both the entire sample and a subsample of participants additionally matched on RSPM performance to control for potential response time confounds, neural activity was similar in both groups for the pattern matching task. However, for the RSPM task, autistics displayed relatively increased task-related activity in extrastriate areas (BA18), and decreased activity in the lateral prefrontal cortex (BA9) and the medial posterior parietal cortex (BA7). Visual processing mechanisms may therefore play a more prominent role in reasoning in autistics. Hum Brain Mapp, 2009. © 2009 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]