Biomedical subjects

V Andrew Stenger

Publications and source records attributed to V Andrew Stenger.

At least 19 recordsLinked to original sources

PubMed2004

Behavioral equivalence, but not neural equivalence--neural evidence of alternative strategies in mathematical thinking.

In a functional magnetic resonance imaging study, we investigated how people solve mathematically equivalent problems presented in two alternative formats: verbal, story format or symbolic, equation format. Although representation format had no effect on behavior, anterior prefrontal activation was greater in the story condition and posterior parietal activation was greater in the equation condition. These results show that there exist alternative neural pathways that implement different and yet equally efficient problem-solving strategies.

Behavior↗

PubMed2004

Prefrontal cortex guides context-appropriate responding during language production.

Although language processing is thought to frequently require cognitive control, little is known about the cognitive and neural basis of the control of language. Here, we demonstrate that processing of context by the PFC plays an important role in the control of language comprehension and production. Using a missing letter paradigm and fMRI, we found that increased activation in the PFC (but not in posterior regions), while encoding and maintaining context information, predicted context-appropriate responses. Furthermore, greater selection demands increased activity during responding in the same regions engaged during the encoding and maintenance of context. Overall, as in other cognitive task domains, these results suggest that PFC context processing plays an important role in the control of language.

Adult↗

PubMed2004

The change of the brain activation patterns as children learn algebra equation solving.

In a brain imaging study of children learning algebra, it is shown that the same regions are active in children solving equations as are active in experienced adults solving equations. As with adults, practice in symbol manipulation produces a reduced activation in prefrontal cortex area. However, unlike adults, practice seems also to produce a decrease in a parietal area that is holding an image of the equation. This finding suggests that adolescents' brain responses are more plastic and change more with practice. These results are integrated in a cognitive model that predicts both the behavioral and brain imaging results.

Adolescent↗

PubMed2004

Opiate addicts lack error-dependent activation of rostral anterior cingulate.

BACKGROUND: Healthy individuals performing response suppression tasks activate anterior cingulate cortex with occurrence of false alarm error responses to nontargets. Fundamental questions include whether this error-related activation provides a signal contributing to behavioral control and, given generally poorer performance on such tasks by addicts, whether this signal is disrupted in addiction. METHODS: We used rapid, event-related functional magnetic resonance imaging to study 13 individuals with opiate dependence and 26 healthy control individuals performing a Go/NoGo task. RESULTS: Compared with controls, opiate addicts exhibited an attenuated anterior cingulate cortex error signal and significantly poorer task performance. In controls, the individual level of event-related anterior cingulate cortex activation accompanying false alarm error positively predicted task performance, particularly sensitivity in discriminating targets from nontargets. CONCLUSIONS: The attenuation of this error signal in anterior cingulate cortex may play a role in loss of control in addiction and other forms of impulsive behavior.

Adult↗

PubMed2004

Event-related functional magnetic resonance imaging of reward-related brain circuitry in children and adolescents.

BACKGROUND: Functional disturbances in reward-related brain systems are thought to play a role in the development of mood, impulse, and substance-abuse disorders. Studies in nonhuman primates have identified brain regions, including the dorsal/ventral striatum and orbital-frontal cortex, in which neural activity is modulated by reward. Recent studies in adults have concurred with these findings by observing reward-contingent blood oxygen level-dependent (BOLD) responses in these regions during functional magnetic resonance imaging (fMRI) paradigms; however, no previous studies indicate whether comparable modulations of neural activity exist in the brain reward systems of children and adolescents. METHODS: We used event-related fMRI and a behavioral paradigm modeled on previous work in adults to study brain responses to monetary gains and losses in psychiatrically healthy children and adolescents as part of a program examining the neural substrates of anxiety and depression in youth. RESULTS: Regions and time-courses of reward-related activity were similar to those observed in adults with condition-dependent BOLD changes in the ventral striatum and lateral and medial orbital-frontal cortex; specifically, these regions showed larger responses to positive than to negative feedback. CONCLUSIONS: These results provide further evidence for the value of event-related fMRI in examining reward systems of the brain, demonstrate the feasibility of this approach in children and adolescents, and establish a baseline from which to understand the pathophysiology of reward-related psychiatric disorders in youth.

Adolescent↗

PubMed2004

Anterior cingulate conflict monitoring and adjustments in control.

Conflict monitoring by the anterior cingulate cortex (ACC) has been posited to signal a need for greater cognitive control, producing neural and behavioral adjustments. However, the very occurrence of behavioral adjustments after conflict has been questioned, along with suggestions that there is no direct evidence of ACC conflict-related activity predicting subsequent neural or behavioral adjustments in control. Using the Stroop color-naming task and controlling for repetition effects, we demonstrate that ACC conflict-related activity predicts both greater prefrontal cortex activity and adjustments in behavior, supporting a role of ACC conflict monitoring in the engagement of cognitive control.

Adult↗

PubMed2004

High temporal and spatial resolution 4D MRA using spiral data sampling and sliding window reconstruction.

Contrast-enhanced magnetic resonance angiography (CE-MRA) requires high spatial resolution to demonstrate detailed vasculature and high temporal resolution to capture the contrast bolus. Sparse bright voxels in MRA permit substantial undersampling in MRI data acquisition, allowing simultaneous high temporal and spatial resolution. We developed a time-resolved 3D MRA technique using the efficient spiral sampling trajectory, and performed off-resonance corrections using inhomogeneity field maps. View sharing and sliding window reconstruction were utilized to generate high temporal resolution. High-resolution 3D angiograms were generated at 1-2 s per frame, with a 5-8 ml gadolinium dose, in patients with vascular disease.

Arteriosclerosis↗

PubMed2004

Self-calibrated spiral SENSE.

Current standard sensitivity-encoded parallel imaging (SENSE) utilizes a fully sampled low-resolution reference scan to estimate the coil sensitivities. This reference scan adds scan time and may introduce misregistration artifacts. The purpose of this study was to investigate the feasibility of estimating the coil sensitivities for spiral SENSE directly from an undersampled k-space center. The limited spatial frequencies of the coil sensitivities, and the undersampling beyond the Nyquist radius cause image artifacts. A point spread function (PSF) analysis and experiments on both phantoms and humans identified an optimal radius for the k-space center by minimizing these image artifacts. The preliminary data indicate that self-calibrated SENSE is as accurate as standard SENSE, which uses a fully sampled reference scan.

Algorithms↗

PubMed2004

Errors without conflict: implications for performance monitoring theories of anterior cingulate cortex.

Recent theories of the neural basis of performance monitoring have emphasized a central role for the anterior cingulate cortex (ACC). Replicating an earlier event-related potential (ERP) study, which showed an error feedback negativity that was modeled as having an ACC generator, we used event-related fMRI to investigate whether the ACC would differentiate between correct and incorrect feedback stimuli in a time estimation task. The design controlled for response conflict and frequency and expectancy effects. Although participants in the current study adjusted their performance following error feedback, we did not observe error feedback-evoked ACC activity. In contrast, we did observe ACC activity while the same subjects performed the Stroop task, in which an area of the ACC activated during both conflict and error trials. These findings are inconsistent with previous dipole models of the error feedback negativity, and suggest the ACC may not be involved in the generation of this ERP component. These results question involvement of the ACC in the detection of errors per se when controlling for conflict.

Adult↗

PubMed2004

Cerebral activation during hypnotically induced and imagined pain.

The continuing absence of an identifiable physical cause for disorders such as chronic low back pain, atypical facial pain, or fibromyalgia, is a source of ongoing controversy and frustration among pain physicians and researchers. Aberrant cerebral activity is widely believed to be involved in such disorders, but formal demonstration of the brain independently generating painful experiences is lacking. Here we identify brain areas directly involved in the generation of pain using hypnotic suggestion to create an experience of pain in the absence of any noxious stimulus. In contrast with imagined pain, functional magnetic resonance imaging (fMRI) revealed significant changes during this hypnotically induced (HI) pain experience within the thalamus and anterior cingulate (ACC), insula, prefrontal, and parietal cortices. These findings compare well with the activation patterns during pain from nociceptive sources and provide the first direct experimental evidence in humans linking specific neural activity with the immediate generation of a pain experience.

Adult↗

PubMed2004

Skeletal muscle lipid concentration quantified by magnetic resonance imaging.

BACKGROUND: Skeletal muscle lipid is associated with obesity and type 2 diabetes and may be altered by diet, physical activity, and weight loss. OBJECTIVE: We explored the utility of magnetic resonance imaging (MRI) for quantifying the lipid concentration of muscle tissue in vivo. DESIGN: Fat-selective MR images of the lower leg were taken in 8 normal-weight [body mass index (in kg/m(2)) < or = 24.9] and 8 obese (body mass index > 29.9) subjects to obtain spatial maps of lipid signal intensity within muscle tissue. Fast-spiral-sequence (echo time = 5.6-13.8 ms, repetition time = 1 s, 8 interleaves) MRI scans were conducted at 3.0 T by using an extremity transmit-receive coil. Lipid concentrations within muscle were determined from manually drawn regions of interest in the tibialis anterior (TA), soleus, and medial head of the gastrocnemius (MHG) muscle groups. RESULTS: There was extremely good agreement (mean R(2) = 0.985) between the fat signal intensity and the actual lipid concentration of standards containing 2.5, 5.0, and 10.0 g lipid/dL, which were placed on the subject's leg during each scan. The lipid content of both the soleus (2.99 +/- 0.37 g/dL) and the MHG (3.80 +/- 0.68 g/dL) was higher (P < 0.05) than that of the TA (1.83 +/- 0.28 g/dL). Lipid content was more than two-fold higher (P < 0.05) in the MHG of obese subjects (5.48 +/- 1.18 g/dL) than in the MHG of normal-weight subjects (2.54 +/- 0.47 g/dL), but did not differ significantly in the TA or soleus. CONCLUSIONS: MRI can be used to quantify lipid within human muscle tissue. MRI can also be used to detect differences in muscle lipid content among various muscle groups and between normal-weight and obese subjects.

Adult↗

PubMed2004

Regional brain activation during concurrent implicit and explicit sequence learning.

We used event-related fMRI to identify the brain regions engaged during explicit and implicit sequence learning (ESL and ISL, respectively). Twenty-four subjects performed a concurrent ESL and ISL task. Behavior showed learning in both conditions. Prefrontal (PFC), striatal, anterior cingulate cortex (ACC) and visual regions (V1, V2 and V3) were engaged during both ESL and ISL. With ESL there was increased activity in the visual regions on the predictable (i.e. learned pattern) trials. With ISL, however, there was a relative decrease in activity in visual regions. The opposite patterns in the visual regions highlight the different effects of ESL and ISL. The learning process was distinguished from the result of learning, by fitting subjects' functional magnetic resonance imaging data to their learning curve. This analysis revealed more extensive PFC activity during ESL and caudal ACC activity specific for the result of learning analysis, when the expected response was violated. Our results suggest a relative dissociation of the brain regions engaged during ESL and ISL, whereby ESL and ISL can be viewed as partially distinct but overlapping parallel processes.

Adolescent↗

PubMed2004

The relationship of three cortical regions to an information-processing model.

This research tests a model of the computational role of three cortical regions in tasks like algebra equation solving. The model assumes that there is a left parietal region-of-interest (ROI) where the problem expression is represented and transformed, a left prefrontal ROI where information for solving the task is retrieved, and a motor ROI where hand movements to produce the answer are programmed. A functional magnetic resonance imaging (fMRI) study of an abstract symbol-manipulation task was performed to articulate the roles of these three regions. Participants learned to associate words with instructions for transforming strings of letters. The study manipulated the need to retrieve these instructions, the need to transform the strings, and whether there was a delay between calculation of the answer and the output of the answer. As predicted, the left parietal ROI mainly reflected the need for a transformation and the left prefrontal ROI the need for retrieval. Homologous right ROIs showed similar but weaker responses. Neither the prefrontal nor the parietal ROIs responded to delay, but the motor ROI did respond to delay, implying motor rehearsal over the delay. Except for the motor ROI, these patterns of activity did not vary with response hand. In an ACT-R model, it was shown that the activity of an imaginal buffer predicted the blood oxygen level-dependent (BOLD) response of the parietal ROI, the activity of a retrieval buffer predicted the response of the prefrontal ROI, and the activity of a manual buffer predicted the response of the motor ROI.

Adolescent↗

PubMed2004

The BOLD hemodynamic response in healthy aging.

Several previous studies have compared the blood oxygen level-dependent (BOLD) hemodynamic response (HDR) in healthy elderly subjects to the HDR in young subjects. Some studies have found a relative decreased amplitude in the elderly in the visual cortex, whereas other studies have found the elderly HDR amplitude in the visual cortex to be nearly identical to that in young subjects. A possible explanation for the different findings is that the peak voxel HDR is similar between the groups, but that the HDR in the group-averaged region-of-interest (ROI) is "washed out" by the inclusion of less significant voxels (due to a smaller extent of activation in the elderly) or by the inclusion of negative-peaking voxels. We tested this hypothesis using event-related functional magnetic resonance imaging (fMRI ). While undergoing fMRI, subjects performed a simple visual and motor task, pressing with their index fingers in response to visual presentation of the word tap. Data from 18 subjects, 8 young and 10 elderly, were analyzed. For each subject, a visual and a motor ROI was selected by choosing the most significant positive voxels within the anatomically defined ROI. This individual subject approach excluded both low-significance and negative-peaking voxels. Similar peaks were found for the elderly and the young subjects in both motor and visual regions and a more sustained BOLD response was found for the elderly in both regions. Additionally, as predicted, a greater percentage of voxels with a negative HDR was found for the elderly in the visual region; this finding was also replicated in our reanalysis of an independent fMRI and aging study from the fMRI Data Center. Functional neuroimaging observations of negative HDRs in visual areas have been interpreted as the effect of unconstrained processing during rest. Our results suggest that the elderly may have more unconstrained visual processing during the rest condition in the scanner. The observation that the group differences in the BOLD response are sensitive to voxel selection (e.g., inclusion of low-significance and/or negative voxels) underscores the importance of ROI selection criteria in the interpretation of fMRI studies using elderly populations.

Adult↗

PubMed2003

The evaluation of brain activity in response to taste stimuli--a pilot study and method for central taste activation as assessed by event-related fMRI.

BACKGROUND: Brain pathways contribute to the regulation of appetite behaviors, and advancements in brain imaging offer new opportunities in determining whether disturbances of these pathways play a role in pathological feeding behaviors in humans. We developed a standardized method for the assessment of brain activation in response to taste stimuli. METHODS: Five healthy control women were positioned in a 1.5 T GE magnet resonance (MR) scanner for functional MR imaging (fMRI). They received 1.0 cm3 samples of 1 M glucose solution or artificial saliva (25 mM KCl, 2 mM NaHCO3). Fluid challenges were delivered by a programmable syringe pump (J-Kem Scientific, St. Louis, MO). E-Prime software (Psychology Software Tools Inc., Pittsburgh, PA) coordinated taste stimulation with MR scanning. Data were analyzed using NeuroImaging software (NIS). RESULTS: Healthy women showed increased orbitofrontal cortex activation when glucose was compared to artificial saliva. In addition, mesial and lateral temporal cortical regions contrasted glucose from artificial saliva. CONCLUSIONS: This study demonstrates a design for the systematic study of brain activation after taste stimulation using fMRI and computer controlled stimulus delivery. The results are consistent with previous studies, showing activation in higher order brain centers that are involved in emotional coding of taste experience.

Adult↗

PubMed2003

Competition and representation during memory retrieval: roles of the prefrontal cortex and the posterior parietal cortex.

In this functional-MRI study we examined the hypothesis that the prefrontal cortex responds differently to the extent of competition during retrieval, whereas the parietal cortex is responsible for problem representation that should not be directly related to the competition. Participants mastered arbitrary person-location pairs, and their recognition memory was tested in a functional-MRI session. The pairs were constructed such that a person was associated with one, two, or three different locations and vice versa. The recognition time increased with the number of associations, reflecting increased competition. A confirmatory analysis of imaging data with prespecified prefrontal and parietal regions showed that, although both regions were highly involved during memory retrieval, only the prefrontal region responded to the levels of competition. This result was consistent with predictions of an information-processing model as well as with an exploratory identification of regions of interest.

Adult↗

PubMed2003

Predicting the practice effects on the blood oxygenation level-dependent (BOLD) function of fMRI in a symbolic manipulation task.

Based on adaptive control of thought-rational (ACT-R), a cognitive architecture for cognitive modeling, researchers have developed an information-processing model to predict the blood oxygenation level-dependent (BOLD) response of functional MRI in symbol manipulation tasks. As an extension of this research, the current event-related functional MRI study investigates the effect of relatively extensive practice on the activation patterns of related brain regions. The task involved performing transformations on equations in an artificial algebra system. This paper shows that the base-level activation learning in the ACT-R theory can predict the change of the BOLD response in practice in a left prefrontal region reflecting retrieval of information. In contrast, practice has relatively little effect on the form of BOLD response in the parietal region reflecting imagined transformations to the equation or the motor region reflecting manual programming.

Adult↗

PubMed2003

Variable-density spiral 3D tailored RF pulses.

A variable-density spiral method is presented for reducing three-dimensional tailored radiofrequency pulse duration. Pulse length reductions of 21-32% are possible, with only a small error in the desired excitation profile. The method is demonstrated using simulations, phantom experiments, and T(2)*-weighted images of brain regions with susceptibility-induced intravoxel dephasing. Four 19.7-ms shots were needed to excite a 5-mm-thick slice with reduced susceptibility artifacts in the sinus region at 3T.

Artifacts↗