Cortical image density determines the probability of target discovery during active search.

An analysis of target detection as a function of target eccentricity was made on eye movement data collected from three monkey subjects during active visual search. Target detection probability was invariant across array set size and eccentricity conditions when the cortical density of relevant stimuli surrounding the target was held constant. When target color was used to guide search, the effective cortical density was the density of stimuli that shared the target's color. Thus the passive constraint of cortical magnification in combination with an active selection for a stimulus attribute, in this case color, sets the spatial framework for detection of the target.

MR of post traumatic spinal cord lesions. Unexpected improvement of hemorrhagic lesions.

Fifteen patients who sustained spinal cord trauma were evaluated by MR within 72 hours of injury. Nine patients had hemorrhagic and six had nonhemorrhagic traumatic spinal cord lesions. Three patients with hemorrhagic and all six patients with nonhemorrhagic lesions showed some degree of neurological improvement on follow-up examinations. In two of the three patients with hemorrhagic lesions who improved, the hemorrhage was extensive. This supports the observation that hemorrhagic lesions are not always associated with a poor clinical outcome.

Cerebral venous thrombosis. Demonstration with magnetic resonance angiography.

Three patients with cerebral venous thrombosis (CVT) were imaged with magnetic resonance angiography (MRA). Initial spin-echo magnetic resonance (MR) demonstrated acute or subacute thrombosis in all patients. The presence of thrombosis was confirmed with MRA. Repeat MRA in the three patients revealed partial recanalization in one and almost complete recanalization in two patients. The etiology of CVT is reviewed, and the advantages of MRA are compared with conventional MR imaging and computed tomography in the evaluation of CVT.

The origin of thalamic inputs to the "hand" representation in the primary motor cortex.

We used retrograde transport of WGA-HRP to examine the origin of thalamic inputs to the "hand" representation in the primary motor cortex of macaques (Macaca nemestrina). Injections were placed in either the crest of the precentral gyrus or the rostral bank of the central sulcus. The sites for injection in the sulcus were determined by using intracortical stimulation to map the location of hand representation. We found that the precentral gyrus and central sulcus receive their predominant input from different subdivisions of the ventrolateral thalamus. Ventralis posterior lateralis pars oralis (VPLo) provides the most substantial input to a portion of the hand representation on the gyrus. In contrast, Ventralis lateralis pars oralis (VLo) provides the most substantial input to a portion of the hand representation in the sulcus. Prior studies have shown that VPLo is a major site of termination of cerebellar efferents and that VLo is a major site of termination of pallidal efferents. Thus, our results indicate that both the basal ganglia and the cerebellum "directly" influence the "hand" representation of the primary motor cortex.

Morphometric analysis of distinct microanatomy near the base of proximal tubule cells.

Models of cell shape in the rabbit S2 proximal renal tubule were derived from transmission electron micrographs and compared with scanning micrographs. Standard morphometric procedures were used to measure basolateral cell membrane surface density (SVt) relative to total epithelial volume in numerous zones of cell height. In the basal 20% region we also measured the volume fraction (F) of intercellular spaces and calculated new surface densities in reference only to the intercellular volume, SVi = SVt/F, or to the cellular volume, SVc = SVt/(1-F). Combined use of these surface densities then enabled us to calculate the diameter, length, and separation of effectively cylindrical microvilli at the cell base. Assuming that lateral cell membranes are radially oriented in the apical region but disposed on microvillus like structures of arbitrary orientation at the cell base, an improved cell model was developed that agreed with the scanning picture throughout the entire cell height. Basal microvillar elements contain approximately 60% of the total basolateral cell membrane surface area and possibly constitute a hydrostatic resistive region for absorbate flow. These features have interesting physiological implications.

Exencephaly: sonographic findings and radiologic-pathologic correlation.

Exencephaly is a rare precursor of anencephaly in which a large amount of brain tissue is present despite the absence of the calvaria. It was discovered together with hydramnios in a near-term fetus. Sonographic, angiographic, and pathologic findings are discussed.