Biomedical subjects

Lawrence R Frank

Publications and source records attributed to Lawrence R Frank.

7 recordsLinked to original sources

PubMed2003

Ventromedial prefrontal cortex activation is critical for preference judgments.

Preference judgment, the process of selecting a response from several alternatives based on which alternative the subject likes best, is an important aspect of daily life. The current study examined whether neural substrates that are thought to be critical for generating somatic markers are involved in preference judgments. Fifteen healthy, right-handed subjects performed a preference judgment task during functional magnetic resonance imaging. The medial frontal gyrus was significantly more activated during the preference judgment trials, relative to visual discrimination trials. Other areas that were also differentially activated included the posterior parietal cortex, the anterior cingulate and the left anterior insula. These findings are consistent with the role of the ventromedial prefrontal cortex in the representation of complex appetitive states.

Adult↗

PubMed2003

Neural response to alcohol stimuli in adolescents with alcohol use disorder.

BACKGROUND: Cue reactivity studies in alcohol-dependent adults have shown atypical physiological, cognitive, and neural responses to alcohol-related stimuli that differ from the responses of light drinkers. Cue reactivity and its neural substrates are unclear in youth. We hypothesized that teens with alcohol use disorder would show greater brain response than nonabusing teens to alcohol images relative to neutral beverage images in limbic and frontal brain regions. METHODS: We tested the hypotheses in a cross-sectional functional magnetic resonance imaging study. Adolescents aged 14 to 17 were recruited from local high schools. Teens with alcohol use disorders (n = 15) and demographically similar infrequent drinkers (n = 15) met strict exclusion criteria (no left-handedness or neurological, other psychiatric, or other substance use disorders). Diagnoses were determined by means of structured and semistructured clinical interviews. Subjects were shown pictures of alcoholic and nonalcoholic beverage advertisements during blood oxygen level-dependent functional magnetic resonance imaging. Self-reports of craving were obtained before and after cue exposure. RESULTS: Teens with alcohol use disorders showed substantially greater brain activation to alcoholic beverage pictures than control youths, predominantly in the left anterior, limbic, and visual system areas (P<.05; cluster threshold, 515 microL). The degree of brain response to the alcohol pictures was highest in youths who consumed more drinks per month and reported greater desires to drink. CONCLUSIONS: These results confirm previous studies by demonstrating an association between the urge to drink alcohol and blood oxygen use in areas of the brain previously linked to reward, desire, positive affect, and episodic recall. This study extends this relationship to adolescents with relatively brief drinking histories using visual alcohol stimuli, and suggests a neural basis for response to alcohol advertisements in youths with drinking problems.

Adolescent↗

PubMed2003

Increased diffusion sensitivity with hyperechos.

It is shown that the introduction of a 180 degrees refocusing pulse into a standard diffusion weighted stimulated echo sequence is equivalent to the simplest hyperecho sequence with identical diffusion weighting but equal or greater signal-to-noise (SNR) and thus equal or greater diffusion contrast. For high b-value imaging, the hyperecho sequence thus possesses the high diffusion contrast in the presence of small T(1)/T(2) ratios characteristic of stimulated echo sequences but with less than the 50% loss in SNR that is associated with the stimulated echo. For low b-value imaging, the hyperecho signal converges to that of the standard spin echo. The advantages of the two-pulse diffusion weighted hyperecho sequence are demonstrated theoretically. Experimental results are shown in the application to high angular resolution diffusion encoding (HARD) in normal human brain.

Anisotropy↗

PubMed2003

Alternative brain organization after prenatal cerebral injury: convergent fMRI and cognitive data.

The current study presents both longitudinal behavioral data and functional activation data documenting the effects of early focal brain injury on the development of spatial analytic processing in two children, one with prenatal left hemisphere (LH) injury and one with right hemisphere (RH) injury. A substantial body of evidence has shown that adults and children with early, lateralized brain injury show evidence of spatial analytic deficits. LH injury compromises the ability to encode the parts of a spatial pattern, while RH injury impairs pattern integration. The two children described in this report show patterns of deficit consistent with the site of their injury. In the current study, their longitudinal behavioral data spanning the age range from preschool to adolescence are presented in conjunction with data from a functional magnetic resonance imaging (fMRI) study of spatial processing. The activation results provide evidence that alternative profiles of neural organization can arise following early focal brain injury, and document where in the brain spatial functions are carried out when regions that normally mediate them are damaged. In addition, the coupling of the activation with the behavioral data allows us to go beyond the simple mapping of functional sites, to ask questions about how those sites may have come to mediate the spatial functions.

Adolescent↗

PubMed2002

Characterization of anisotropy in high angular resolution diffusion-weighted MRI.

The methods of group theory are applied to the problem of characterizing the diffusion measured in high angular resolution MR experiments. This leads to a natural representation of the local diffusion in terms of spherical harmonics. In this representation, it is shown that isotropic diffusion, anisotropic diffusion from a single fiber, and anisotropic diffusion from multiple fiber directions fall into distinct and separable channels. This decomposition can be determined for any voxel without any prior information by a spherical harmonic transform, and for special cases the magnitude and orientation of the local diffusion may be determined. Moreover, non-diffusion-related asymmetries produced by experimental artifacts fall into channels distinct from the fiber channels, thereby allowing their separation and a subsequent reduction in noise from the reconstructed fibers. In the case of a single fiber, the method reduces identically to the standard diffusion tensor method. The method is applied to normal volunteer brain data collected with a stimulated echo spiral high angular resolution diffusion-weighted (HARD) acquisition.

Anisotropy↗

PubMed2002

Analysis and design of perfusion-based event-related fMRI experiments.

Perfusion-based functional magnetic resonance imaging (fMRI) using arterial spin labeling (ASL) methods has the potential to provide better localization of the functional signal to the sites of neural activity compared to blood oxygenation level-dependent (BOLD) contrast fMRI. At present, experiments using ASL have been limited to simple block and periodic single-trial designs. We present here an adaptation of the general linear model to perfusion-based fMRI that enables the design and analysis of more complicated designs, such as random and semirandom event-related designs. Formulas for the least-squares estimate of the perfusion response and the F statistic for the detection of a response are derived. Exact expressions and useful approximations for detection power and estimation efficiency are presented, and it is shown that the trade-off between power and efficiency for perfusion experiments is similar to that previously observed for BOLD experiments. The least-squares estimate is compared with an estimate formed from the running subtraction of tag and control images. The running subtraction estimate is shown to be approximately equal to a temporally low-pass-filtered version of the least-squares estimate. Numerical simulations and results from ASL experiments are used to support the theoretical findings.

Algorithms↗

PubMed2002

Functional MRI of global and local processing in children.

Functional magnetic resonance imaging was used to examine developmental change in hemispheric biases for globally and locally directed analysis of hierarchical forms. In a previous reaction time (RT) study, which presented hierarchical stimuli to the visual hemifields, children 7 to 14 years of age demonstrated an emerging pattern of hemispheric differences. Initially children analyzed local elements more slowly, without a strongly lateralized advantage for local or global level processing. With age, children's development was marked by a left hemisphere advantage for local level processing that resembled an adult's and a trend toward a right hemisphere advantage for global. In the current study, 20 children 12 to 14 years old were imaged during attend-global and attend-local conditions to determine whether the developmental change in cognitive measures corresponded to a change in distribution of functional activation. Children formed two groups based on their RT performance, immature-bilateral (IB) or mature-lateralized (ML). The volume of task-related activation within lateral temporo-occipital regions of interest was compared for global and local conditions between the two groups. The IB children showed greater activation overall for local level processing, comparable activation across the two hemispheres for the global condition, and a trend of right greater than left hemisphere activation for local. In contrast, the ML children displayed right greater than left hemisphere activation during global analysis and the opposite during local processing. Importantly these patterns of functional activation mirror the profiles of RT performance. Together they demonstrate a shift from undifferentiated, bilateral processing toward hemispheric lateralization.

Aging↗