Biomedical subjects

James N Lee

Publications and source records attributed to James N Lee.

4 recordsLinked to original sources

PubMed2004

Neural representations of graspable objects: are tools special?

Recent cognitive and neuroimaging studies have examined the relationship between perception and action in the context of tools. These studies suggest that tools "potentiate" actions even when overt actions are not required in a task. Tools are unique objects because they have a visual structure that affords action and also a specific functional identity. The present studies investigated the extent to which a tool's representation for action is tied to its graspability or its functional use. Functional magnetic resonance imaging (fMRI) was used to examine the motor representations associated with different classes of graspable objects. Participants viewed and imagined grasping images of 3D tools with handles or neutral graspable shapes. During the viewing task, motor-related regions of cortex (posterior middle temporal gyrus, ventral premotor, and posterior parietal) were associated with tools compared to shapes. During the imagined grasping task, a frontal-parietal-temporal network of activation was seen with both types of objects. However, differences were found in the extent and location of premotor and parietal activation, and additional activation in the middle temporal gyrus and fusiform gyrus for tools compared to shapes. We suggest that the functional identity of graspable objects influences the extent of motor representations associated with them. These results have implications for understanding the interactions between "what" and "how" visual processing systems.

Adult↗

PubMed2004

MRI diffusion tensor reconstruction with PROPELLER data acquisition.

MRI diffusion imaging is effective in measuring the diffusion tensor in brain, cardiac, liver, and spinal tissue. Diffusion tensor tomography MRI (DTT MRI) method is based on reconstructing the diffusion tensor field from measurements of projections of the tensor field. Projections are obtained by appropriate application of rotated diffusion gradients. In the present paper, the potential of a novel data acquisition scheme, PROPELLER (Periodically Rotated Overlapping ParallEL Lines with Enhanced Reconstruction), is examined in combination with DTT MRI for its capability and sufficiency for diffusion imaging. An iterative reconstruction algorithm is used to reconstruct the diffusion tensor field from rotated diffusion weighted blades by appropriate rotated diffusion gradients. DTT MRI with PROPELLER data acquisition shows significant potential to reduce the number of weighted measurements, avoid ambiguity in reconstructing diffusion tensor parameters, increase signal-to-noise ratio, and decrease the influence of signal distortion.

Algorithms↗

PubMed2003

Preliminary results of a functional MRI study of brain activation patterns in stuttering and nonstuttering speakers during a lexical access task.

UNLABELLED: An fMRI study examining lexical access and lexical generation in nine non-stuttering and seven stuttering speakers is presented. Lexical access was examined during a word description task that was presented auditorily while subjects "silently" thought of the target words. Participants alternated between four 30-s rest blocks and four 30-s "active" blocks. Activation patterns were assessed utilizing a standard subtraction paradigm, where the activation during the rest blocks was subtracted from the activation during the active blocks. High levels of variability characterized activation patterns within both speaker groups. Group comparisons using random effects statistical analyses did not identify significant differences between the groups when corrected for multiple comparisons. Analyses were subsequently conducted by comparing the trends in the group activation patterns between the speaker groups using fixed (corrected) and random effects (uncorrected) analyses. Non-stuttering control speakers activated primarily left hemisphere cortical speech and language areas while the stuttering speakers appeared to produce more bilateral activation. Discussion of these results focuses on the specific within- and between-hemispheric activation patterns and possible interpretations of these patterns. EDUCATIONAL OBJECTIVES: The reader will learn about: (1) issues related to interpreting brain activation findings in stuttering speakers; (2) the role and neurological substrates of lexical access during speech production in non-stuttering and stuttering speakers; (3) the basics of functional MRI; and (4) the brain activation areas involved during a silent lexical retrieval task in non-stuttering and stuttering speakers.

Adult↗

PubMed2002

Measuring magnetic fields generated by DC currents in receive-only coils.

DC decoupling currents applied to receive-only coils during radiofrequency transmission can create stray magnetic fields capable of changing the resonant frequency of nearby nuclei. It is difficult to measure these fields with conventional field-mapping techniques because the fields are not present when the signal is acquired. The stray fields can be measured empirically with cardiac tags.

Magnetic Resonance Imaging↗