Identifying longitudinal trends within EEG experiments.

Differential brain response to sensory stimuli is very small (a few microvolts) compared to the overall magnitude of spontaneous electroencephalogram (EEG), yielding a low signal-to-noise ratio (SNR) in studies of event-related potentials (ERP). To cope with this phenomenon, stimuli are applied repeatedly and the ERP signals arising from the individual trials are averaged at the subject level. This results in loss of information about potentially important changes in the magnitude and form of ERP signals over the course of the experiment. In this article, we develop a meta-preprocessing step utilizing a moving average of ERP across sliding trial windows, to capture such longitudinal trends. We embed this procedure in a weighted linear mixed effects model to describe longitudinal trends in features such as ERP peak amplitude and latency across trials while adjusting for the inherent heteroskedasticity created at the meta-preprocessing step. The proposed unified framework, including the meta-processing and the weighted linear mixed effects modeling steps, is referred to as MAP-ERP (moving-averaged-processed ERP). We perform simulation studies to assess the performance of MAP-ERP in reconstructing existing longitudinal trends and apply MAP-ERP to data from young children with autism spectrum disorder (ASD) and their typically developing counterparts to examine differences in patterns of implicit learning, providing novel insights about the mechanisms underlying social and/or cognitive deficits in this disorder.

Kidney transplantation in the morbidly obese: complicated but still better than dialysis.

Obese patients are denied renal transplantation in many centers. We report results regarding obesity from a new transplant program (1999 through 2007). Six hundred and forty-two patients were transplanted: 439 patients with BMI < 30 (Group 1), 109 patients with BMI 30.1-34.9 (Group 2), and 89 patients with BMI > 35 (Group 3). Follow-up was at least one yr. Medical and surgical management was performed by the same team throughout the study period. There were no demographic differences between groups except for increased diabetes in Groups 2 and 3. Actuarial graft and patient survivals were not statistically different between groups. Group 3 patients had numerical trends toward more delayed graft function and lower graft survivals but these did not reach statistical significance. Biopsy-proven rejections did not differ between groups. Wound infections were statistically significant in Groups 2 and 3 compared to Group 1 (p < 0.01). Despite increased wound infection rates with increased BMI, transplanting patients with morbid obesity results in better survival for individual patients than dialysis. Thus, there is no a priori ethical reason for treating obese ESRD patients differently from those with other comorbidities.

Age-related top-down suppression deficit in the early stages of cortical visual memory processing.

In this study, electroencephalography (EEG) was used to examine the relationship between two leading hypotheses of cognitive aging, the inhibitory deficit and the processing speed hypothesis. We show that older adults exhibit a selective deficit in suppressing task-irrelevant information during visual working memory encoding, but only in the early stages of visual processing. Thus, the employment of suppressive mechanisms are not abolished with aging but rather delayed in time, revealing a decline in processing speed that is selective for the inhibition of irrelevant information. EEG spectral analysis of signals from frontal regions suggests that this results from excessive attention to distracting information early in the time course of viewing irrelevant stimuli. Subdividing the older population based on working memory performance revealed that impaired suppression of distracting information early in the visual processing stream is associated with poorer memory of task-relevant information. Thus, these data reconcile two cognitive aging hypotheses by revealing that an interaction of deficits in inhibition and processing speed contributes to age-related cognitive impairment.

Physiologic artifacts in resting state oscillations in young children: methodological considerations for noisy data.

We quantified the potential effects of physiologic artifact on the estimation of EEG band power in a cohort of typically developing children in order to guide artifact rejection methods in quantitative EEG data analysis in developmental populations. High density EEG was recorded for 2 min while children, ages 2-6, watched a video of bubbles. Segments of data were categorized as blinks, saccades, EMG or artifact-free, and both absolute and relative power in the theta (4-7 Hz), alpha (8-12 Hz), beta (13-30 Hz) and gamma (35-45 Hz) bands were calculated in 9 regions for each category. Using a linear mixed model approach with artifact type, region and their interaction as predictors, we compared mean band power between clean data and each type of artifact. We found significant differences in mean relative and absolute power between artifacts and artifact-free segments in all frequency bands. The magnitude and direction of the differences varied based on power type, region, and frequency band. The most significant differences in mean band power were found in the gamma band for EMG artifact and the theta band for ocular artifacts. Artifact detection strategies need to be sensitive to the oscillations of interest for a given analysis, with the most conservative approach being the removal of all EMG and ocular artifact from EEG data. Quantitative EEG holds considerable promise as a clinical biomarker of both typical and atypical development. However, there needs to be transparency in the choice of power type, regions of interest, and frequency band, as each of these variables are differentially vulnerable to noise, and therefore, their interpretation depends on the methods used to identify and remove artifacts.

Top-down enhancement and suppression of the magnitude and speed of neural activity.

Top-down modulation underlies our ability to selectively attend to relevant stimuli and to ignore irrelevant stimuli. Theories addressing neural mechanisms of top-down modulation are driven by studies that reveal increased magnitude of neural activity in response to directed attention, but are limited by a lack of data reporting modulation of neural processing speed, as well as comparisons with a perceptual (passive view) baseline necessary to evaluate the presence of enhancement and suppression. Utilizing functional MRI (fMRI) and event-related potential recordings (ERPs), we provide converging evidence that both the magnitude of neural activity and the speed of neural processing are modulated by top-down influences. Furthermore, both enhancement and suppression occur relative to a perceptual baseline depending on task instruction. These findings reveal the fine degree of influence that goal-directed attention exerts upon activity within the visual association cortex. We further document capacity limitations in top-down enhancement corresponding with working memory performance deficits.

Disseminated intravascular coagulation (DIC) in a kidney donor associated with transient recipient DIC.

It has been controversial whether or not to accept kidneys for transplantation from donors with disseminated intravascular coagulation (DIC). We report two recipients who received the kidneys from a donor with DIC following traumatic head injury. Despite evidence of donor kidney glomerular fibrin deposits and ongoing low-grade DIC in the recipients, which resolved after 5-7 days; both recipients did well suggesting that donors with DIC can be successfully used for renal transplantation.

Morbid obesity does not preclude successful renal transplantation.

Many renal transplantation centers arbitrarily deny transplantation to patients with morbid obesity usually defined as body mass index > 35. We present a series of 173 primary renal transplant patients in a new transplant program that accepted all recipients with 3 yrs or greater life expectancy and no active malignancy or infection. When the patient outcomes are divided into groups by body mass index, it can be seen as expected that patients with body mass index > 30 have an increased prevalence of wound infections (p < 0.05). However, aside from this complication there are no statistically significant outcome differences between the three groups realizing the possibility of type II statistical error because of small numbers. Graft survival, patient survival and other surgical complications are the same in all groups regardless of body mass index. At the end of the 3-yr interval with a minimum transplant follow-up of 3 months, 169 of 173 patients were alive and 163 of 173 transplants were functioning. Based on our experience, morbid obesity should not be used to exclude patients arbitrarily from transplantation anymore than advanced age or diabetes should.