Biomedical subjects

Thomas J Ross

Publications and source records attributed to Thomas J Ross.

8 recordsLinked to original sources

PubMed2006

Cingulate activation increases dynamically with response speed under stimulus unpredictability.

Functional magnetic resonance imaging studies of cognition require repeated and consistent engagement of the cognitive process under investigation. Activation is generally averaged across trials that are assumed to tax a specific mental operation or state, whereas intraindividual variability in performance between trials is usually considered error variance. A more recent analysis approach postulates that these fluctuations can reflect variation in the very process taxed by the particular trial type. In the present study, participants responded to targets presented randomly in 1 of 4 peripheral locations. By employing a function of reaction time (RT) of individual trials as a linear regressor, brain regions were identified whose activation varied with RT on a trial-by-trial basis. Whole-brain analysis revealed that the anterior cingulate, posterior cingulate, and left angular/superior temporal gyri were more active in trials with faster RT but only when the target location was unpredictable. No such association was seen in trials where the target location was predicted by a central cue. These results suggest a role for the cingulate and angular gyri in the dynamic regulation of attention to unpredictable events. This is in accordance with the function of a default network that is active in the absence of top-down-focused attention and is thought to continuously provide resources for broad and spontaneous information gathering. Exploiting intertrial performance variability may be particularly suitable for capturing such spontaneous and elusive phenomena as stimulus-driven processes of attention.

Adaptation, Physiological↗

PubMed2006

Neuroanatomical dissociation between bottom-up and top-down processes of visuospatial selective attention.

Allocation of attentional resources to portions of the available sensory input can be regulated by bottom-up processes, i.e., spontaneous orientation towards an oncoming stimulus (stimulus-driven attention), and by top-down processes, i.e., intentionally and driven by knowledge, expectation and goals. The present study aimed at advancing the understanding of brain networks mediating bottom-up and top-down control of visuospatial attention by employing a paradigm that parametrically varied demands on these two processes. Spatial predictability of peripheral targets was parametrically varied by centrally cueing one, two, three or four of four possible locations. Reaction time decreased linearly with more precise valid cueing of the target location and increased with more precise invalid cueing. Event-related functional magnetic resonance imaging (fMRI) enabled measurement of blood oxygenation level-dependent (BOLD) responses to cues and to targets. A mostly left-hemispheric network consisting of left intraparietal sulcus, inferior and superior parietal lobule, bilateral precuneus, middle frontal gyri including superior frontal sulci, and middle occipital gyri displayed BOLD responses to cues that increased linearly with more precise spatial cueing, indicating engagement by top-down spatial selective attention. In contrast, bilateral temporoparietal junction, cingulate gyrus, right precentral gyrus and anterior and posterior insula, bilateral fusiform gyri, lingual gyri and cuneus displayed BOLD responses to targets that increased with their spatial unpredictability, indicating engagement by stimulus-driven orienting. The results suggest two largely dissociated neural networks mediating top-down and bottom-up control of visuospatial selective attention.

Adult↗

PubMed2005

Neural correlates of high and craving during cocaine self-administration using BOLD fMRI.

Modern theories of drug dependence hold the hedonic effects of drug-taking central to understanding the motivation for compulsive drug use. Previous neuroimaging studies have begun to identify brain regions associated with acute drug effects after passive delivery. In this study, a more naturalistic model of cocaine self-administration (SA) was employed in order to identify those sites associated with drug-induced high and craving as measures of reward and motivation. Non-treatment seeking cocaine-dependent subjects chose both when and how often i.v. cocaine administration occurred within a medically supervised SA procedure. Both functional magnetic resonance imaging (fMRI) data and real-time behavioral ratings were acquired during the 1-h SA period. Drug-induced HIGH was found to correlate negatively with activity in limbic, paralimbic, and mesocortical regions including the nucleus accumbens (NAc), inferior frontal/orbitofrontal gyrus (OFC), and anterior cingulate (AC), while CRAVING correlated positively with activity in these regions. This study provides the first evidence in humans that changes in subjective state surrounding cocaine self-administration reflect neural activity of the endogenous reward system.

Adult↗

PubMed2005

Head motion suppression using real-time feedback of motion information and its effects on task performance in fMRI.

A voluntary head motion suppression method using feedback to subjects of their own head motion information is demonstrated. A real-time fMRI system was developed on standard MR imaging hardware for this purpose. The head motion information was simplified as a four-way arrow display that changed color from green to red when a composite head motion index went beyond a specified threshold. The arrow indicators were integrated into a version of the commonly used visual N-BACK task. Results suggest a significant suppression of head motion consistently in all subjects while the influence on task performance and brain activation was minimal. It is proposed that under certain experimental conditions, voluntary head motion suppression may feasibly be employed without significant compromise of fMRI data.

Adult↗

PubMed2004

Comparability of functional MRI response in young and old during inhibition.

When using fMRI to study age-related cognitive changes, it is important to establish the integrity of the hemodynamic response because, potentially, it can be affected by age and disease. However, there have been few attempts to document such integrity and no attempts using higher cognitive rather than perceptual or motor tasks. We used fMRI with 28 healthy young and older adults on an inhibitory control task. Although older and young adults differed in task performance and activation patterns, they had comparable hemodynamic responses. We conclude that activation during cognitive inhibition, which was predominantly increased in elders, was not due to vascular confounds or specific changes in hemodynamic coupling.

Adult↗

PubMed2003

Multiple neuronal networks mediate sustained attention.

Sustained attention deficits occur in several neuropsychiatric disorders. However, the underlying neurobiological mechanisms are still incompletely understood. To that end, functional MRI was used to investigate the neural substrates of sustained attention (vigilance) using the rapid visual information processing (RVIP) task in 25 healthy volunteers. In order to better understand the neural networks underlying attentional abilities, brain regions where task-induced activation correlated with task performance were identified. Performance of the RVIP task activated a network of frontal, parietal, occipital, thalamic, and cerebellar regions. Deactivation during task performance was seen in the anterior and posterior cingulate, insula, and the left temporal and parahippocampal gyrus. Good task performance, as defined by better detection of target stimuli, was correlated with enhanced activation in predominantly right fronto-parietal regions and with decreased activation in predominantly left temporo-limbic and cingulate areas. Factor analysis revealed that these performance-correlated regions were grouped into two separate networks comprised of positively activated and negatively activated intercorrelated regions. Poor performers failed to significantly activate or deactivate these networks, whereas good performers either activated the positive or deactivated the negative network, or did both. The fact that both increased activation of task-specific areas and increased deactivation of task-irrelevant areas mediate cognitive functions underlying good RVIP task performance suggests two independent circuits, presumably reflecting different cognitive strategies, can be recruited to perform this vigilance task.

Adolescent↗

PubMed2003

Cingulate hypoactivity in cocaine users during a GO-NOGO task as revealed by event-related functional magnetic resonance imaging.

Although extensive evidence exists for the reinforcing properties of drugs of abuse such as cocaine, relatively less research has addressed the functional neuroanatomical correlates of the cognitive sequelae of these drugs. We present a functional magnetic resonance imaging study of a GO-NOGO task in which successful performance required prepotent behaviors to be inhibited. Significant cingulate, pre-supplementary motor and insula hypoactivity was observed for both successful NOGOs and errors of commission in chronic cocaine users relative to cocaine-naive controls. This attenuated response, in the presence of comparable activation levels in other task-related cortical areas, suggests cortical and psychological specificity in the locus of drug abuse-related cognitive dysfunction. The results suggest that addiction may be accompanied by a disruption of brain structures critical for the higher-order, cognitive control of behavior.

Adult↗

PubMed2002

Cognitive mechanisms of nicotine on visual attention.

Understanding nicotine's neurobiological and cognitive mechanisms may help explain both its addictive properties and potential therapeutic applications. As such, functional MRI was used to determine the neural substrates of nicotine's effects on a sustained attention (rapid visual information-processing) task. Performance was associated with activation in a fronto-parietal-thalamic network in both smokers and nonsmokers. Along with subtle behavioral deficits, mildly abstinent smokers showed less task-induced brain activation in the parietal cortex and caudate than did nonsmokers. Transdermal nicotine replacement improved task performance in smokers and increased task-induced brain activation in the parietal cortex, thalamus, and caudate, while nicotine induced a generalized increase in occipital cortex activity. These data suggest that nicotine improves attention in smokers by enhancing activation in areas traditionally associated with visual attention, arousal, and motor activation.

Administration, Cutaneous↗