A simple ERP method for quantitative analysis of cognitive workload in myoelectric prosthesis control and human-machine interaction.

Common goals in the development of human-machine interface (HMI) technology are to reduce cognitive workload and increase function. However, objective and quantitative outcome measures assessing cognitive workload have not been standardized for HMI research. The present study examines the efficacy of a simple event-related potential (ERP) measure of cortical effort during myoelectric control of a virtual limb for use as an outcome tool. Participants trained and tested on two methods of control, direct control (DC) and pattern recognition control (PRC), while electroencephalographic (EEG) activity was recorded. Eighteen healthy participants with intact limbs were tested using DC and PRC under three conditions: passive viewing, easy, and hard. Novel auditory probes were presented at random intervals during testing, and significant task-difficulty effects were observed in the P200, P300, and a late positive potential (LPP), supporting the efficacy of ERPs as a cognitive workload measure in HMI tasks. LPP amplitude distinguished DC from PRC in the hard condition with higher amplitude in PRC, consistent with lower cognitive workload in PRC relative to DC for complex movements. Participants completed trials faster in the easy condition using DC relative to PRC, but completed trials more slowly using DC relative to PRC in the hard condition. The results provide promising support for ERPs as an outcome measure for cognitive workload in HMI research such as prosthetics, exoskeletons, and other assistive devices, and can be used to evaluate and guide new technologies for more intuitive HMI control.

Monitoring daily function in persons with transfemoral amputations using a commercial activity monitor: a feasibility study.

OBJECTIVE: To assess in a feasibility study the mobility of persons with transfemoral amputations using data collected from a popular, consumer-oriented activity monitor (Fitbit). DESIGN: Observational cohort study. SETTING: Research hospital outpatient evaluation. PARTICIPANTS: Nine subjects with transfemoral amputations (4 women and 5 men, ages 21-64 years) and Medicare functional assessments (K level) of K3 (n = 7), K2 (n = 1), and K4 (n = 1). METHODS: One-week monitoring of physical activity using the Fitbit One activity monitor. MAIN OUTCOME MEASURES: Daily estimates of step counts, distance walked, floors/stairs climbed, calories burned, and proprietary Fitbit activity scores. For each day, the amount of time in each of the following levels of activity was also reported: sedentary, lightly active, fairly active, and highly active. RESULTS: The percentage of movement time above the fairly active level had a predictable relationship to the designated K level. The average activity measures show decreased levels of activity for obese subjects (body mass index >30). Estimated step counts were highly predictive/redundant with estimated miles walked without setting individual stride lengths. Using linear regression prediction models, calorie estimates were found to be highly dependent on subject age, height, and weight, whereas the proprietary activity score was independent of all 3 demographic factors. CONCLUSIONS: This feasibility study demonstrates that the Fitbit activity monitor estimates the activity of subjects with transfemoral amputations, producing results that correlate with their K-level functional activity classifications. The Fitbit activity score is independent of individual variations in age, weight, and height compared with estimated calories for this small sample size. These tools may provide useful insights into prosthetic use in an at-home environment.

Global position sensing and step activity as outcome measures of community mobility and social interaction for an individual with a transfemoral amputation due to dysvascular disease.

BACKGROUND AND PURPOSE: Community mobility of individuals following lower limb amputation is highly variable and has a great impact on their quality of life. Currently, clinical assessments of ambulatory ability and motivation influence prosthetic prescription. However, these outcome measures do not effectively quantify community mobility (ie, mobility outside of the clinic) of individuals with an amputation. Advances in global positioning systems (GPSs) and other wearable step-monitoring devices allow for objective, quantifiable measurement of community mobility. This case report will examine the combined use of a GPS unit and a step activity monitor to quantify community mobility and social interaction of an individual with transfemoral amputation due to dysvascular disease. CASE DESCRIPTION: A 76-year-old woman with a unilateral transfemoral amputation due to vascular disease carried a commercial GPS unit and step activity monitor to quantify her community mobility and social interaction every day over a period of 1 month. The step activity monitor was affixed to her prosthesis. The patient used a wheelchair as well as her prosthesis for everyday mobility. OUTCOME: Information from the GPS unit and step activity monitor provided quantitative details on the patient's steps taken in and out of the home, wheelchair use, prosthesis use, driving trips, and time spent on social and community trips. DISCUSSION: This case report describes a potential clinical measurement procedure for quantifying community mobility and social interaction of an individual with lower limb amputation. Future efforts are needed to validate this measurement tool on large sample sizes and in individuals with different mobility levels. Additionally, automatization of data analysis and technological approaches to reduce compromised GPS signals may eventually lead to a practical, clinically useful tool.

Cardiovascular fitness is associated with altered cortical glucose metabolism during working memory in ɛ4 carriers.

BACKGROUND: The possibility that ɛ4 may modulate the effects of fitness in the brain remains controversial. The present exploratory FDG-PET study aimed to better understand the relationship among ɛ4, fitness, and cerebral metabolism in 18 healthy aged women (nine carriers, nine noncarriers) during working memory. METHODS: Participants were evaluated using maximal level of oxygen consumption, California Verbal Learning Test, and FDG-PET, which were collected at rest and during completion of the Sternberg working memory task. RESULTS: Resting FDG-PET did not differ between carriers and noncarriers. Significant effects of fitness on FDG-PET during working memory were noted in the ɛ4 carriers only. High fit ɛ4 carriers had greater glucose uptake in the temporal lobe than the low fit ɛ4 carriers, but low fit ɛ4 carriers had greater glucose uptake in the frontal and parietal lobes. CONCLUSIONS: We demonstrate that fitness differentially affects cerebral metabolism in ɛ4 carriers only, consistent with previous findings that the effects of fitness may be more pronounced in populations genetically at risk for cognitive decline.

Exercise improves cognition and hippocampal plasticity in APOE epsilon4 mice.

BACKGROUND: Human studies on exercise, cognition, and apolipoprotein E (APOE) genotype show that epsilon4 carriers may benefit from regular physical activity. METHODS: We examined voluntary wheel-running, memory, and hippocampal plasticity in APOE epsilon3 and APOE epsilon4 transgenic mice at 10-12 months of age. RESULTS: Sedentary epsilon4 mice exhibited deficits in cognition on the radial-arm water maze (RAWM), a task dependent on the hippocampus. Six weeks of wheel-running in epsilon4 mice resulted in improvements on the RAWM to the level of epsilon3 mice. Hippocampal brain-derived neurotrophic factor (BDNF) levels were similar in epsilon3 and epsilon4 mice, and after exercise BDNF was similarly increased in both epsilon3 and epsilon4 mice. In sedentary epsilon4 mice, tyrosine kinase B (Trk B) receptors were reduced by 50%. Exercise restored Trk B in epsilon4 mice to the level of epsilon3 mice, and in epsilon4 mice, exercise dramatically increased synaptophysin, a marker of synaptic function. CONCLUSIONS: Our results support the hypothesis that exercise can improve cognitive function, particularly in epsilon4 carriers.

Electroencephalographic coherence during visuomotor performance: a comparison of cortico-cortical communication in experts and novices.

The authors assessed electroencephalographic coherence to determine the relation between cortico-cortical communication and visuomotor skill in 15 expert and 21 novice rifle shooters. They then calculated coherence and phase angles among the prefrontal (F3, F4) and ipsilateral cortical regions (central, temporal, parietal, occipital) during the aiming period for the theta (4-7 Hz), low-alpha (8-10 Hz), high-alpha (11-13 Hz), low-beta (14-22 Hz), high-beta (23-35 Hz), and gamma (36-44 Hz) bands. The authors subjected them separately to a series of analyses of variance (Group X Hemisphere X Region X Epoch). Experts generally exhibited lower coherence compared with novices, with the effect most prominent in the right hemisphere. The groups also exhibited differences in phase angle in a number of frequency bands. Coherence was positively related to aiming movement variability in experts. The results support refinement of cortical networks in experts and differences in strategic planning related to memory processes and executive influence over visual-spatial cues.

Exercise, APOE, and working memory: MEG and behavioral evidence for benefit of exercise in epsilon4 carriers.

Performance on the Sternberg working memory task, and MEG cortical response on a variation of the Sternberg task were examined in middle-aged carriers and non-carriers of the APOE epsilon4 allele. Physical activity was also assessed to examine whether exercise level modifies the relationship between APOE genotype and neurocognitive function. Regression revealed that high physical activity was associated with faster RT in the six- and eight-letter conditions of the Sternberg in epsilon4 carriers, but not in the non-carriers after controlling for age, gender, and education (N=54). Furthermore, the MEG analysis revealed that sedentary epsilon4 carriers exhibited lower right temporal lobe activation on matching probe trials relative to high-active epsilon4 carriers, while physical activity did not distinguish non-carriers (N=23). The M170 peak was identified as a potential marker for pre-clinical decline as epsilon4 carriers exhibited longer M170 latency, and highly physically active participants exhibited greater M170 amplitude to matching probe trials.

The unique relation of physical activity to executive function in older men and women.

PURPOSE: To determine whether physical activity participation was specifically and positively associated with executive function in older individuals after accounting for age, education, and IQ. METHODS: Participants were 120 healthy men (N = 38) and women (N = 82) aged 65-92 yr (mean = 78.9, SD = 5.8), who were free of depression and dementia (Beck Depression Inventory and Mini-Mental Status Exam, respectively), had above-average intelligence (mean = 118.1, SD = 9.4) as indexed by the Kaufman Brief Intelligence Test (K-BIT), and stable patterns of physical activity during a 3- to 5-yr period before the study. Participants completed the Yale Physical Activity Survey (YPAS) for older adults and the Stroop Color and Word Test to assess inhibitory executive function. RESULTS: Hierarchical regression analyses revealed that YPAS summary index scores explained a small, but significant amount of variance in Stroop color-word and interference scores (DeltaR2 = 2 and 4%, respectively) after accounting for intelligence and age. The YPAS index was unrelated to nonexecutive performance. CONCLUSIONS: The results support specificity of the physical activity/cognition relationship in older individuals. The results may be explained by additive benefit from participation in physical activity to the frontal lobe (i.e., beyond any benefits from cognitive stimulation), a region that mediates executive function and experiences accelerated age-related decline. In summary, habitual physical activity is positively related to executive performance in older men and women into the 10th decade.