Adolescent cannabis use and brain systems supporting adult working memory encoding, maintenance, and retrieval.

Given prior reports of adverse effects of cannabis use on working memory, an executive function with a protracted developmental course during adolescence, we examined associations between developmental patterns of cannabis use and adult working memory (WM) processes. Seventy-five adults with longitudinal assessments of cannabis use (60 with reported use, 15 with no reported use) and prenatal drug exposure assessment completed a spatial WM task during fMRI at age 28. All subjects passed a multi-drug urine screen on the day of testing and denied recreational drug use in the past week.

Differentiating between clinical and behavioral phenotypes in first-episode psychosis during maintenance of visuospatial working memory.

Introduction: We probed the neural basis of working memory in individuals with first episode of psychosis (FEP) and assessed how these neural abnormalities are associated with behavioral performance and/or core to psychosis pathophysiology.

Methods: FEP (N=35) and matched controls (N=25) performed a visuospatial working memory task during fMRI acquisition. We isolated neural activity during the maintenance period and examined neural activity within regions typically engaged during a working memory task.

Protracted development of executive and mnemonic brain systems underlying working memory in adolescence: A longitudinal fMRI study.

Working memory (WM), the ability to hold information on-line to guide planned behavior, improves through adolescence in parallel with continued maturation of critical brain systems supporting cognitive control. Initial developmental neuroimaging studies with one or two timepoints have provided important though varied results limiting our understanding of which and how neural systems change during this transition into mature WM. In this study, we leverage functional magnetic resonance imaging (fMRI) longitudinal data spanning up to 9 years in 129 normally developing individuals to identify which systems demonstrate growth changes that accompany improvements in WM performance.

Functional connectivity differences in autism during face and car recognition: underconnectivity and atypical age-related changes.

Face recognition abilities improve between adolescence and adulthood over typical development (TD), but plateau in autism, leading to increasing face recognition deficits in autism later in life. Developmental differences between autism and TD may reflect changes between neural systems involved in the development of face encoding and recognition. Here, we focused on whole-brain connectivity with the fusiform face area (FFA), a well-established face-preferential brain region.

Developmental stages and sex differences of white matter and behavioral development through adolescence: a longitudinal diffusion tensor imaging (DTI) study.

White matter (WM) continues to mature through adolescence in parallel with gains in cognitive ability. To date, developmental changes in human WM microstructure have been inferred using analyses of cross-sectional or two time-point follow-up studies, limiting our understanding of individual developmental trajectories. The aims of the present longitudinal study were to characterize the timing of WM growth and investigate how sex and behavior are associated with different developmental trajectories.

Increased intra-individual reaction time variability in attention-deficit/hyperactivity disorder across response inhibition tasks with different cognitive demands.

One of the most consistent findings in children with ADHD is increased moment-to-moment variability in reaction time (RT). The source of increased RT variability can be examined using ex-Gaussian analyses that divide variability into normal and exponential components and Fast Fourier transform (FFT) that allow for detailed examination of the frequency of responses in the exponential distribution. Prior studies of ADHD using these methods have produced variable results, potentially related to differences in task demand.

Decreased connectivity and cerebellar activity in autism during motor task performance.

Although motor deficits are common in autism, the neural correlates underlying the disruption of even basic motor execution are unknown. Motor deficits may be some of the earliest identifiable signs of abnormal development and increased understanding of their neural underpinnings may provide insight into autism-associated differences in parallel systems critical for control of more complex behaviour necessary for social and communicative development. Functional magnetic resonance imaging was used to examine neural activation and connectivity during sequential, appositional finger tapping in 13 children, ages 8-12 years, with high-functioning autism (HFA) and 13 typically developing (TD), age- and sex-matched peers.

fMRI evidence for multisensory recruitment associated with rapid eye movements during sleep.

We studied the neural correlates of rapid eye movement during sleep (REM) by timing REMs from video recording and using rapid event-related functional MRI. Consistent with the hypothesis that REMs share the brain systems and mechanisms with waking eye movements and are visually-targeted saccades, we found REM-locked activation in the primary visual cortex, thalamic reticular nucleus (TRN), 'visual claustrum', retrosplenial cortex (RSC, only on the right hemisphere), fusiform gyrus, anterior cingulate cortex, and the oculomotor circuit that controls awake saccadic eye movements (and subserves awake visuospatial attention). Unexpectedly, robust activation also occurred in non-visual sensory cortices, motor cortex, language areas, and the ascending reticular activating system, including basal forebrain, the major source of cholinergic input to the entire cortex.

fMRI of intrasubject variability in ADHD: anomalous premotor activity with prefrontal compensation.

Objective: Children with attention-deficit/hyperactivity disorder (ADHD) consistently display increased intrasubject variability (ISV) in response time across varying tasks, signifying inefficiency of response preparation compared to typically developing (TD) children. Children with ADHD also demonstrate impaired response inhibition; inhibitory deficits correlate with ISV, suggesting that similar brain circuits may underlie both processes. To better understand the neural mechanisms underlying increased ISV and inhibitory deficits in children with ADHD, functional magnetic resonance imaging was used to examine the neural correlates of ISV during Go/No-go task performance.

Moderate variability in stimulus presentation improves motor response control.

To examine the impact of interstimulus "jitter" (i.e., randomization of the interval between successive stimulus events) on response control during continuous task performance, 41 healthy adults completed four go/no-go tasks that were identical except for interstimulus interval (ISI) jitter: a 0% jitter task with a fixed (1,000-ms) ISI, a 10% jitter task with an ISI range of 900-1,100 ms, a 30% jitter task with an ISI range of 700-1,300 ms, and a 50% jitter task with an ISI range of 500-1,500 ms.

Response inhibition and response selection: two sides of the same coin.

Response inhibition refers to the suppression of actions that are inappropriate in a given context and that interfere with goal-driven behavior. Studies using a range of methodological approaches have implicated executive control processes mediated by frontal-subcortical circuits as being critical to response inhibition; however, localization within the frontal lobe has been inconsistent. In this review, we present evidence from behavioral, lesion, neuroimaging, electrophysiology, and neurological population studies.

Functional magnetic resonance imaging evidence for abnormalities in response selection in attention deficit hyperactivity disorder: differences in activation associated with response inhibition but not habitual motor response.

Impaired response inhibition is thought to be a core deficit in attention deficit hyperactivity disorder (ADHD). Prior imaging studies investigating response inhibition in children with ADHD have used tasks involving different cognitive resources, thereby complicating the interpretation of their findings. In this study, a classical go/no-go task with a well-ingrained stimulus-response association (green = go; red = no-go) was used in order to minimize extraneous cognitive demands.

Meta-analysis of Go/No-go tasks demonstrating that fMRI activation associated with response inhibition is task-dependent.

FMRI studies of response inhibition consistently reveal frontal lobe activation. Localization within the frontal cortex, however, varies across studies and appears dependent on the nature of the task. Activation likelihood estimate (ALE) meta-analysis is a powerful quantitative method of establishing concurrence of activation across functional neuroimaging studies.

Functional brain correlates of response time variability in children.

During tasks requiring response inhibition, intra-individual response time variability, a measure of motor response preparation, has been found to correlate with errors of commission, such that individuals with higher variability show increased commission errors. This study used fMRI to examine the neural correlates of response variability in 30 typically developing children, ages 8-12, using a simplified Go/No-go task with minimal cognitive demands. Lower variability was associated with Go activation in the anterior cerebellum (culmen) and with No-go activation in the rostral supplementary motor area (pre-SMA), the postcentral gyrus, the anterior cerebellum (culmen) and the inferior parietal lobule.