Pupillary dilations in a Target/Distractor visual task paradigm and attention deficit hyperactivity disorder (ADHD)

ADHD is a neurocognitive disorder characterized by attention difficulties, hyperactivity, and impulsivity, often persisting into adulthood with substantial personal and societal consequences. Despite the importance of neurophysiological assessment and treatment monitoring tests, their availability outside of research settings remains limited. Cognitive neuroscience investigations have identified distinct components associated with ADHD, including deficits in sustained attention, inefficient enhancement of attended Targets, and altered suppression of ignored Distractors. In this study, we examined pupil activity in control and ADHD subjects during a sustained visual attention task specifically designed to evaluate the mechanisms underlying Target enhancement and Distractor suppression. Our findings revealed some distinguishing factors between the two groups which we discuss in light of their neurobiological implications.

Time Courses of Attended and Ignored Object Representations

Selective attention prioritizes information that is relevant to behavioral goals. Previous studies have shown that attended visual information is processed and represented more efficiently, but distracting visual information is not fully suppressed, and may also continue to be represented in the brain. In natural vision, to-be-attended and to-be-ignored objects may be present simultaneously in the scene. Understanding precisely how each is represented in the visual system, and how these neural representations evolve over time, remains a key goal in cognitive neuroscience. In this study, we recorded EEG while participants performed a cued object-based attention task that involved attending to target objects and ignoring simultaneously presented and spatially overlapping distractor objects. We performed support vector machine classification on the stimulus-evoked EEG data to separately track the temporal dynamics of target and distractor representations. We found that (1) both target and distractor objects were decodable during the early phase of object processing (∼100 msec to ∼200 msec after target onset), and (2) the representations of both objects were sustained over time, remaining decodable above chance until ∼1000-msec latency. However, (3) the distractor object information faded significantly beginning after about 300-msec latency. These findings provide information about the fate of attended and ignored visual information in complex scene perception.

Anticipatory attention is a stable state induced by transient control mechanisms

Anticipatory attention is a neurocognitive state in which attention control regions bias neural activity in sensory cortical areas to facilitate the selective processing of incoming targets. Previous electroencephalographic (EEG) studies have identified event-related potential (ERP) signatures of anticipatory attention, and implicated alpha band (8–12 Hz) EEG oscillatory activity in the selective control of neural excitability in visual cortex. However, the degree to which ERP and alpha band measures reflect related or distinct underlying neural processes remains to be further understood. To investigate this question, we analyzed EEG data from 20 human participants performing a cued object-based attention task. We used support vector machine (SVM) decoding analysis to compare the attentional time courses of ERP signals and alpha band power. We found that ERP signals encoding attentional instructions are dynamic and precede stable attention-related changes in alpha power, suggesting that ERP and alpha power reflect distinct neural processes. We proposed that the ERP patterns reflect transient attentional orienting signals originating in higher order control areas, whereas the patterns of synchronized oscillatory neural activity in the alpha band reflect a sustained attentional state. These findings support the hypothesis that anticipatory attention involves transient top-down control signals that establish more stable neural states in visual cortex, enabling selective sensory processing.

Comparison of Multivendor Single-Voxel MR Spectroscopy Data Acquired in Healthy Brain at 26 Sites

Background The hardware and software differences between MR vendors and individual sites influence the quantification of MR spectroscopy data. An analysis of a large data set may help to better understand sources of the total variance in quantified metabolite levels. Purpose To compare multisite quantitative brain MR spectroscopy data acquired in healthy participants at 26 sites by using the vendor-supplied single-voxel point-resolved spectroscopy (PRESS) sequence. Materials and Methods An MR spectroscopy protocol to acquire short-echo-time PRESS data from the midparietal region of the brain was disseminated to 26 research sites operating 3.0-T MR scanners from three different vendors. In this prospective study, healthy participants were scanned between July 2016 and December 2017. Data were analyzed by using software with simulated basis sets customized for each vendor implementation. The proportion of total variance attributed to vendor-, site-, and participant-related effects was estimated by using a linear mixed-effects model. P values were derived through parametric bootstrapping of the linear mixed-effects models (denoted Pboot). Results In total, 296 participants (mean age, 26 years ± 4.6; 155 women and 141 men) were scanned. Good-quality data were recorded from all sites, as evidenced by a consistent linewidth of N-acetylaspartate (range, 4.4-5.0 Hz), signal-to-noise ratio (range, 174-289), and low Cramér-Rao lower bounds (≤5%) for all of the major metabolites. Among the major metabolites, no vendor effects were found for levels of myo-inositol (Pboot > .90), N-acetylaspartate and N-acetylaspartylglutamate (Pboot = .13), or glutamate and glutamine (Pboot = .11). Among the smaller resonances, no vendor effects were found for ascorbate (Pboot = .08), aspartate (Pboot > .90), glutathione (Pboot > .90), or lactate (Pboot = .28). Conclusion Multisite multivendor single-voxel MR spectroscopy studies performed at 3.0 T can yield results that are coherent across vendors, provided that vendor differences in pulse sequence implementation are accounted for in data analysis. However, the site-related effects on variability were more profound and suggest the need for further standardization of spectroscopic protocols. © RSNA, 2020 Online supplemental material is available for this article.

Recent evidence that attention is necessary, but not sufficient, for conscious perception

Early descriptions of attention in the psychological literature highlighted its interdependence with conscious awareness. As the study of attention developed, consciousness and attention began to be considered separable phenomena, experimentally and theoretically. In recent years, an energetic debate has developed concerning the extent to which the two phenomena are related. One school of thought considers the two to be doubly dissociable, whereas the other considers them to be necessarily linked. In this review, we highlight experimental findings from the last 5 years that contribute to the leading consensus view: attention is necessary, but not sufficient, for conscious perception. We review studies that show attention operating in conjunction with unconscious information, and other evidence linking attention necessarily to conscious perception. By drawing upon evidence that attention comprises many cognitive and neural processes, we argue that by studying how different forms of attention are related to conscious perception, it is possible to gain new insights about the neural states or processes that are necessary for conscious perception to occur.

Big GABA II: Water-referenced edited MR spectroscopy at 25 research sites

Accurate and reliable quantification of brain metabolites measured in vivo using ¹H magnetic resonance spectroscopy (MRS) is a topic of continued interest. Aside from differences in the basic approach to quantification, the quantification of metabolite data acquired at different sites and on different platforms poses an additional methodological challenge. In this study, spectrally edited γ-aminobutyric acid (GABA) MRS data were analyzed and GABA levels were quantified relative to an internal tissue water reference. Data from 284 volunteers scanned across 25 research sites were collected using GABA+ (GABA + co-edited macromolecules (MM)) and MM-suppressed GABA editing. The unsuppressed water signal from the volume of interest was acquired for concentration referencing. Whole-brain T₁-weighted structural images were acquired and segmented to determine gray matter, white matter and cerebrospinal fluid voxel tissue fractions. Water-referenced GABA measurements were fully corrected for tissue-dependent signal relaxation and water visibility effects. The cohort-wide coefficient of variation was 17% for the GABA + data and 29% for the MM-suppressed GABA data. The mean within-site coefficient of variation was 10% for the GABA + data and 19% for the MM-suppressed GABA data. Vendor differences contributed 53% to the total variance in the GABA + data, while the remaining variance was attributed to site- (11%) and participant-level (36%) effects. For the MM-suppressed data, 54% of the variance was attributed to site differences, while the remaining 46% was attributed to participant differences. Results from an exploratory analysis suggested that the vendor differences were related to the unsuppressed water signal acquisition. Discounting the observed vendor-specific effects, water-referenced GABA measurements exhibit similar levels of variance to creatine-referenced GABA measurements. It is concluded that quantification using internal tissue water referencing is a viable and reliable method for the quantification of in vivo GABA levels.

Four Months of Wearing a Balance Orthotic Improves Measures of Balance and Mobility Among a Cohort of Community-Living Older Adults

BACKGROUND AND PURPOSE

The Centers for Disease Control and Prevention estimated that there were 29 million falls and 7 million injuries in 2014 in the United States. Falls, decreased balance, and mobility disability are common in older adults and often result in loss of independence. Finding interventions to address these issues is important, as this age group is growing exponentially. Prior studies indicate balance and mobility can be improved by the balance-based torso-weighting (BBTW) assessment implemented through wear of a balance orthotic (BO). This study sought to determine the impact of wearing a BO on balance, mobility, and fall risk over time.

METHODS

This quasiexperimental, 1-group pre-/posttest study investigated the effect of 4 months of daily wear (4 hours per day) of a BO on mobility, balance, and falls efficacy in 30 older adults living in a retirement community with limited mobility defined by a Short Physical Performance Battery (SPPB) score range between 4 and 9 out of a maximum of 12 points. Pre- and posttreatment tests included the Timed Up and Go (TUG), Functional Gait Assessment (FGA), Falls Efficacy Scale (FES), and SPPB. Participants received the BBTW assessment, consisting of individualized assessment of 3-dimensional balance loss, and treatment with a strategically weighted and fitted BO to control balance loss. The BO was worn twice a day for 2 hours (4 hours per day) for 4 months. Participants continued regular activity and no other interventions were provided. All posttests were conducted after 4 months and at least 8 hours after removal of the BO. Subitems from the SPPB (gait speed [GS], 5-time sit-to-stand [FTSST], and tandem stance time [TST]) were analyzed as separate outcome measures. Data were analyzed with paired t tests with a Bonferroni correction (SPPB, GS, FGA, and FES) when statistical assumptions were met. Data that did not meet the statistical assumptions of the paired t test (FTSST, TST, and TUG) were analyzed with Wilcoxon signed rank tests with a Bonferroni correction.

RESULTS AND DISCUSSION

Twenty-four participants, average age 87 (5.7) years, completed the study. Paired t tests indicated that mean group scores on the SPPB, GS, and FGA significantly improved from pre- to posttests. The SPPB improved by 1.3 points (P = .001). GS improved by 0.09 m/s (P = .004) and both mean values improved beyond fall risk cutoffs. The FGA also improved by 2.6 points (P = .001). There were no significant changes in FES scores (P = .110). Wilcoxon signed rank tests indicated median group scores of the FTSST significantly improved from pre- to posttests by 7.4 seconds (P = .002) and median TUG times improved by 3.5 seconds (P = .004). There were no changes in TST (P = .117).

CONCLUSIONS

This study suggests that wearing a BO for 4 hours per day for 4 months results in improvements in functional assessments related to fall risk (SPPB, GS, FGA, TUG, and FTSST) in a group of older adult participants with limited mobility.

Big GABA: Edited MR spectroscopy at 24 research sites

Magnetic resonance spectroscopy (MRS) is the only biomedical imaging method that can noninvasively detect endogenous signals from the neurotransmitter γ-aminobutyric acid (GABA) in the human brain. Its increasing popularity has been aided by improvements in scanner hardware and acquisition methodology, as well as by broader access to pulse sequences that can selectively detect GABA, in particular J-difference spectral editing sequences. Nevertheless, implementations of GABA-edited MRS remain diverse across research sites, making comparisons between studies challenging. This large-scale multi-vendor, multi-site study seeks to better understand the factors that impact measurement outcomes of GABA-edited MRS. An international consortium of 24 research sites was formed. Data from 272 healthy adults were acquired on scanners from the three major MRI vendors and analyzed using the Gannet processing pipeline. MRS data were acquired in the medial parietal lobe with standard GABA+ and macromolecule- (MM-) suppressed GABA editing. The coefficient of variation across the entire cohort was 12% for GABA+ measurements and 28% for MM-suppressed GABA measurements. A multilevel analysis revealed that most of the variance (72%) in the GABA+ data was accounted for by differences between participants within-site, while site-level differences accounted for comparatively more variance (20%) than vendor-level differences (8%). For MM-suppressed GABA data, the variance was distributed equally between site- (50%) and participant-level (50%) differences. The findings show that GABA+ measurements exhibit strong agreement when implemented with a standard protocol. There is, however, increased variability for MM-suppressed GABA measurements that is attributed in part to differences in site-to-site data acquisition. This study's protocol establishes a framework for future methodological standardization of GABA-edited MRS, while the results provide valuable benchmarks for the MRS community.

Individual differences in GABA content are reliable but are not uniform across the human cortex

¹H magnetic resonance spectroscopy (MRS) provides a powerful tool to measure gamma-aminobutyric acid (GABA), the principle inhibitory neurotransmitter in the human brain. We asked whether individual differences in MRS estimates of GABA are uniform across the cortex or vary between regions. In two sessions, resting GABA concentrations in the lateral prefrontal, sensorimotor, dorsal premotor, and occipital cortices were measured in twenty-eight healthy individuals. GABA estimates within each region were stable across weeks, with low coefficients of variation. Despite this stability, the GABA estimates were not correlated between regions. In contrast, the percentage of brain tissue per volume, a control measure, was correlated between the three anterior regions. These results provide an interesting dissociation between an anatomical measure of individual differences and a neurochemical measure. The different patterns of anatomy and GABA concentrations have implications for understanding regional variation in the molecular topography of the brain in health and disease.

Pattern of clefts of the lip and palate managed over a three year period at a Nairobi hospital in Kenya

BACKGROUND

The pattern of cleft lip and palate in the African population remains uncertain. The few studies of clefts in African populations have suggested that the pattern of these defects may be significantly different from those reported in other population groups. However, most of these studies have been based on very small sample sizes bringing into question the validity of those findings.

OBJECTIVE

To analyse the pattern of cleft lip and palate cases managed at a Nairobi hospital.

DESIGN

A retrospective descriptive study.

SETTING

Gertrude's Garden Children's Hospital, a private exclusive children's hospital in Nairobi, where cleft lip and palate treatment was being offered at subsidised rates to needy children under the sponsorship of an international organization.

SUBJECTS

Three hundred and nine cases were seen during the study period.

RESULTS

Age at presentation ranged between 1 week and 45 years, with 75% presenting between 0-5 years. The average age was 10 months. Gestation histories were missing for most cases but for those with gestation histories none were significant. Most children ranked between first to third birth orders, suggesting birth to young mothers. Six cases of associated deformities were identified among the cases. No syndromic clefts were seen. The most common cleft deformity was the cleft lip and palate (CL+P) followed by isolated cleft lip (CL). Isolated cleft palate was least common. There was a male preponderance in all cleft types and most of the clefts occurred on the left side.

CONCLUSION

The pattern of clefts in this study does not differ significantly from those reported in the literature for the non-African populations.

Interpersonal trust and delinquency: a reply to Rotter

Rotter's comments on the validity of his Interpersonal Trust Scale are discussed in terms of: the validity of the scale with incarcerated delinquents, alternative hypotheses of social class and situational factors to explain our negative results, and the need for further studies before the Interpersonal Trust Scale can be accepted as a measure of interpersonal trust.