Response-Conflict Moderates the Cognitive Control of Episodic and Contextual Load in Older Adults.

Objectives: Decline in cognitive control is one of the primary cognitive changes in normal aging. Reaching a consensus regarding the nature of these age-related changes, however, is complicated by the complexity of cognitive control as a construct.

Methods: Healthy older and younger adults participated in a multifactorial test of cognitive control.

Variability in interval production is due to timing-dependent deficits in Huntington's disease.

In Huntington's disease (HD), increased variability is seen in performance of motor tasks that require implicit control of timing. We examined whether timing variability was also evident in an explicit interval-timing task. Sixty subjects (21 controls, 19 manifest HD, and 20 pre-manifest HD) performed a single-interval production task with three target intervals (1.

The influence of cognitive reserve on strategy selection in normal aging.

Cognitive reserve (CR) has been proposed as a latent variable that can account for the frequent discrepancy between an individual's underlying level of brain pathology and their observed clinical outcome. A possible behavioral manifestation of CR is best strategy choice. Older adults have been shown to choose sub-optimal strategies for performing various tasks.

Age differences of multivariate network expressions during task-switching and their associations with behavior.

The effect of aging on functional network activation associated with task-switching was examined in 24 young (age=25.2±2.73 years) and 23 older adults (age=65.

Dual-tasking alleviated sleep deprivation disruption in visuomotor tracking: an fMRI study.

Effects of dual-responding on tracking performance after 49-h of sleep deprivation (SD) were evaluated behaviorally and with functional magnetic resonance imaging (fMRI). Continuous visuomotor tracking was performed simultaneously with an intermittent color-matching visual detection task in which a pair of color-matched stimuli constituted a target and non-matches were non-targets. Tracking error means were binned time-locked to stimulus onset of the detection task in order to observe changes associated with dual-responding by comparing the error during targets and non-targets.

The effects of stimulus degradation after 48 hours of total sleep deprivation.

Study Objectives: To test the hypothesis that total sleep deprivation (TSD) slows stimulus detection and evaluation processes. Towards that end we manipulate degradation of the imperative stimulus, a manipulation well established to affect the processes of interest, in a delayed letter recognition (DLR) task and the psychomotor vigilance task (PVT), and predicted that after TSD the ordinary reaction time (RT) slowing effect of stimulus degradation would be increased. These hypotheses were only partially confirmed (see below).

Task difficulty modulates young-old differences in network expression.

The extent of task-related fMRI activation can vary as a function of task difficulty. Also the efficiency or capacity of the brain networks underlying task performance can change with aging. We asked whether the expression of a network underlying task performance would differ as a function of task demand in old and young individuals.

The prefrontal model revisited: double dissociations between young sleep deprived and elderly subjects on cognitive components of performance.

Study Objectives: The prefrontal model suggests that total sleep deprivation (TSD) and healthy aging produce parallel cognitive deficits. Here we decompose global performance on two common tasks into component measures of specific cognitive processes to pinpoint the source of impairments in elderly and young TSD participants relative to young controls and to each other.

Setting: The delayed letter recognition task (DLR) was performed in 3 studies.

Oxycodone lengthens reproductions of suprasecond time intervals in human research volunteers.

Oxycodone, a popularly used opioid for treating pain, is widely abused. Other drugs of abuse have been shown to affect time perception, which, in turn, may affect sensitivity to future consequences. This may contribute to continued use.

Neural networks associated with the speed-accuracy tradeoff: evidence from the response signal method.

This functional neuroimaging (fMRI) study examined the neural networks (spatial patterns of covarying neural activity) associated with the speed-accuracy tradeoff (SAT) in younger adults. The response signal method was used to systematically increase probe duration (125, 250, 500, 1000 and 2000 ms) in a nonverbal delayed-item recognition task. A covariance-based multivariate approach identified three networks that varied with probe duration--indicating that the SAT is driven by three distributed neural networks.

Supporting performance in the face of age-related neural changes: testing mechanistic roles of cognitive reserve.

Age impacts multiple neural measures and these changes do not always directly translate into alterations in clinical and cognitive measures. This partial protection from the deleterious effects of age in some individuals is referred to as cognitive reserve (CR) and although linked to variations in intelligence and life experiences, its mechanism is still unclear. Within the framework of a theoretical model we tested two potential mechanistic roles of CR to maintain task performance, neural reserve and neural compensation, in young and older adults using functional and structural MRI.

fMRI activation during failures to respond key to understanding performance changes with sleep deprivation.

Study Objectives: During sleep deprivation (SD), failures to respond (FR) increase across a variety of tasks. This is the first systematic investigation of neural correlates of FR during SD. We use multivariate analysis to model neural activation separately for FR and responses (R) at each trial phase.

Performance degradation and altered cerebral activation during dual performance: evidence for a bottom-up attentional system.

Subjects performed a continuous tracking concurrently with an intermittent visual detection task to investigate the existence of competition for a capacity-limited stage (a bottleneck stage). Both perceptual and response-related processes between the two tasks were examined behaviorally and the changes in brain activity during dual-tasking relative to single-task were also assessed. Tracking error and joystick speed were analyzed for changes that were time-locked to visual detection stimuli.

The variable response-stimulus interval effect and sleep deprivation: an unexplored aspect of psychomotor vigilance task performance.

Study Objectives: The Psychomotor Vigilance Task (PVT) contains variable response-stimulus intervals (RSI). Our goal is to investigate the effect of RSI on performance to determine whether sleep deprivation affects the ability to attend to events across seconds and whether this effect is independent of impairment in sustaining attention across minutes, as measured by time on task.

Design: A control group following their normal sleep routines and 3 groups exposed to 54 hours of total sleep deprivation performed a 10-minute PVT every 6 hours for 9 total test runs.

The impact of age-related changes on working memory functional activity.

This work investigated associations of age-related brain atrophy and functional neural networks identified using multivariate analyses of BOLD fMRI data in young and elder participants (young, N=37; mean age=25; elders, N=15; mean age=74). Two networks were involved in retaining increasing loads of verbal information in working memory. Network utilizations were used to test associations between function and indices of grey matter volume changes using voxel based morphometry.

Evidence for age-related changes to temporal attention and memory from the choice time production task.

The effect of aging on interval timing was examined using a choice time production task, which required participants to choose a key response based on the location of the stimulus, but to delay responding until after a learned time interval. Experiment 1 varied attentional demands of the response choice portion of the task by varying difficulty of stimulus-response mapping. Choice difficulty affected temporal accuracy equally in both age groups, but older participants' response latencies were more variable under more difficult response choice conditions.

Age effects on load-dependent brain activations in working memory for novel material.

Three competing models of cognitive aging (neural compensation, capacity limitations, neural inefficiency) were examined in relation to working memory for novel non-verbal material. To accomplish this goal young (n=25) and old (n=25) participants performed a delayed item recognition (DIR) task while being scanned with bold fMRI. The stimuli in the DIR task consisted of computer-generated closed-curve shapes with each shape presented only once in the testing conditions of each participant.

The response-signal method reveals age-related changes in object working memory.

Sixteen healthy young adults (ages 18-32) and 16 healthy older adults (ages 67-81) completed a delayed response task in which they saw the following visual sequence: memory stimuli (2 abstract shapes; 3,000 ms), a blank delay (5,000 ms), a probe stimulus of variable duration (one abstract shape; 125, 250, 500, 1,000, or 2,000 ms), and a mask (500 ms). Subjects decided whether the probe stimulus matched either of the memory stimuli; they were instructed to respond during the mask, placing greater emphasis on speed than accuracy. The authors used D.

Effects of feedback on time production errors in aging participants.

In two experiments, healthy participants ages 60 years and older provided peak-interval time production data for two target intervals (6 and 17s) over 2 days (baseline and retest sessions). In Experiment 1, three groups of participants were provided with two types of feedback during the baseline session that assisted either decision criteria setting or memory updating. During the retest session, run after a 24-h delay, each group received either one of the two types of feedback, or no feedback at all.

A common neural network for cognitive reserve in verbal and object working memory in young but not old.

Epidemiologic evidence suggests that cognitive reserve (CR) mitigates the effects of aging on cognitive function. The goal of this study was to see whether a common neural mechanism for CR could be demonstrated in brain imaging data acquired during the performance of 2 tasks with differing cognitive processing demands. Young and elder subjects were scanned with functional magnetic resonance imaging (fMRI) while performing a delayed item response task that used either letters (40 young, 18 old) or shapes (24 young, 21 old).

Distinct spatial patterns of brain activity associated with memory storage and search.

The time it takes for a human participant to decide whether a given stimulus is an element of a remembered set increases approximately linearly with the number of elements in the set. Here we tested for and detected a spatial pattern of brain activity whose magnitude of expression during this memory search process correlates with set size. We then tested the idea that memory search simply involves a re-activation of neurons involved in remembering the set by statistically comparing the patterns of brain activity corresponding to memory search and set size dependent working memory maintenance.

Single-dose levodopa administration and aging independently disrupt time production.

We tested the hypothesis that age-related time production deficits are dopamine-mediated. The experiment was conducted double-blind, and with random assignment of 32 healthy aged and 32 healthy young participants to either inert placebo or levodopa (200 mg) groups. The procedure included training participants to produce two target time intervals (6 and 17 sec) in separate blocks, drug/placebo administration, a 1-hr delay, and then delayed free-recall time production retesting without feedback.

A firing rate model of Parkinsonian deficits in interval timing.

To account for deficits in interval timing observed in Parkinson's Disease (PD) patients, we develop a model based on the accumulating firing rate of a neural population with recurrent excitation. This model naturally produces the curvilinear accumulation of neural activity introduced to timing psychophysics by Miall (Models of Neural Timing, Elsevier Science, 1996), and implicated in Parkinsonian timing by Malapani and Rakitin (Functional and Neural Mechanisms of Interval Timing, CRC Press, 2003). The parameters essential for our model are the strength of the net neural feedback and the mean rate of inputs to the population from external brain areas.

The effects of spatial stimulus-response compatibility on choice time production accuracy and variability.

Five experiments examined the relations between timing and attention using a choice time production task in which the latency of a spatial choice response is matched to a target interval (3 or 5 s). Experiments 1 and 2 indicated that spatial stimulus-response incompatibility increased nonscalar timing variability without affecting timing accuracy and that choice reaction time practice reduced choice time production variability. These data support a "temporal discounting" model in which response choice and timing occur in series, but the interval timed is shortened to account for nontemporal processing.

Age-related differences in executive control of working memory.

In two experiments, we used dual-task methodology to assess the effect of aging on executive control of working memory. We hypothesized that (1) age-related dual-task costs would be observed even when individual tasks represent different perceptual modalities; (2) age would modulate the effect of increased temporal overlap on dual-task performance; and (3) the vulnerability of specific memory mechanisms to interference would be age related. We found that aging was associated with disproportionate dual-task costs that increased when extending the overlap between individual tasks.