PubMed · 8628515
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A L Foundas, K Hong, C M Leonard, K M Heilman. 1996. The human primary motor cortex.. https://doi.org/10.1212/wnl.46.5.1491
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We investigated perceptual interactions between orientation selective cortical filters using a task in which the observer was to detect mirror symmetry in briefly flashed visual patterns composed of oriented Gabor elements. On each trial, the Gabor patches were randomly placed in one half of the stimulus region, and symmetry was generated by reflecting the positions of the patch centers across the vertical axis. A prespecified proportion of patches were in mirror symmetrical positions with the remaining patches placed at random positions. The perception of mirror symmetry was measured for three stimulus conditions: (1) same orientation (i.e. all the local Gabor elements were either vertical or horizontal), (2) mixed matching (i.e. the orientations could be randomly both vertical and horizontal with the constraint that the orientations in a mirror symmetrical pair were matching), and (3) mixed opposing (i.e. the orientations were both vertical and horizontal, but in a mirror symmetrical pair they were always orthogonal). We found that the perception of global symmetry was poorer (thresholds were elevated) when the local orientations of feature pairs were orthogonal than when they were matched. This result is consistent with the properties of the neurons in the corpus callosum, which selectively interconnect cortical filters with identical orientation specificity.
OBJECTIVE: Previous case reports supported the presence of the uncrossed pyramidal tract in exceptional patients. However, most of these case reports have not fully discussed involvement of the motor cortex controlling the ipsilateral limbs. DESIGN AND METHOD: The authors investigated a 62-year-old man who developed right hemiparesis after right putaminal hemorrhage by using MRI, transcranial magnetic stimulation, functional MRI (fMRI), and sensory evoked potentials. He had moderate weakness including the face, spasticity with brisk deep tendon reflexes and Babinski sign, and impaired vibration and position sense, all on the right side. RESULT: A MRI study showed hemorrhage in the right putamen and the wedge-shaped medulla. A fMRI study during a sequential finger opposition task showed activation in the motor cortex ipsilateral to the finger movements, but not on the contralateral side. Sensory evoked potentials showed cortical response ipsilateral to the side of stimulation. CONCLUSION: The pyramidal tract and the dorsal column-medial lemniscus pathway did not cross in the medulla in this patient. In view of the presence of the abnormal shape in the medulla and congenital scoliosis, a congenital factor might be responsible for the uncrossed pyramidal tract and dorsal column-medial lemniscus in this patient.
The studies described here use functional magnetic resonance imaging to test whether common or distinct cognitive and/or neural mechanisms are involved in extracting object structure from the different image cues defining an object's shape, such as contours, shading, and monocular depth cues. We found overlapping activations in the lateral and ventral occipital cortex [known as the lateral occipital complex (LOC)] for objects defined by different visual cues (e.g., grayscale photographs and line drawings) when each was compared with its own scrambled-object control. In a second experiment we found a reduced response when objects were repeated, independent of whether they appeared in the same or a different format (i.e., grayscale images vs line drawings). A third experiment showed that activation in the LOC was no stronger for three-dimensional shapes defined by contours or monocular depth cues, such as occlusion, than for two-dimensional shapes, suggesting that these regions are not selectively involved in processing three-dimensional shape information. These results suggest that common regions in the LOC are involved in extracting and/or representing information about object structure from different image cues.