Dense Blobs Research Articles

The dorsomedial visual area of owl monkeys: connections, myeloarchitecture, and homologies in other primates.

Cortical connections of the dorsomedial visual area (DM) of owl monkeys were revealed with injections of the bidirectional tracer, wheatgerm agglutinin conjugated with horseradish peroxidase (WGA-HRP), or the retrograde fluorescent tracer, diamidino yellow. Microelectrode recordings in two cases identified DM as a systematic representation of the visual hemifield in a densely myelinated rectangle of cortex just rostral to the dorsomedial portion of the second visual area (V-II, or area 18). Cortex was flattened and cut parallel to the surface in all cases so that the myeloarchitectonic borders of DM and other areas such as the primary visual area (V-I or area 17), V-II or area 18, and the middle temporal visual area (MT) could be readily determined, and the surface view patterns of connections could be directly appreciated. The ipsilateral pattern of connections of DM were dense and visuotopically congruent with area 17, area 18, and MT, and moderate to dense connections were with the medial visual area (M), the rostral division of the dorsolateral visual area, the dorsointermediate area, the ventral posterior area, the caudal division of inferotemporal cortex (ITc), the ventral posterior parietal area, and visuomotor cortex of the frontal lobe. The connections of DM were concentrated in the cytochrome oxidase (CO)-dense blobs of area 17, the CO-dense bands of area 18, and the CO-dense regions of MT. Callosal connections of DM were with matched locations in DM in the opposite hemisphere, and with VPP. The ipsilateral connections of DM with area 17 were confirmed by injecting WGA-HRP into area 17 in one owl monkey. In addition to labelled cells and terminals in area 18 and MT, bidirectionally transported tracer was also apparent in DM. Evidence for the existence of DM in other primates was obtained by injecting area 17 and examining the areal patterns of connections and myeloarchitecture in three species of Old World monkeys, two additional species of New World monkeys, and prosimian galagos. In all of these primates, one of three major targets of area 17 was a densely myelinated zone of cortex just rostral to dorsomedial area 18, in the location of DM in owl monkeys. Thus, it seems likely that DM is a visual area common to all primates.

Dendritic sampling across processing streams in monkey striate cortex.

Cytochrome oxidase (CO) dense blobs in primate striate cortex provide a striking example of parallel processing of visual information. The level of isolation of the blobs from the surrounding interblob tissue was investigated in the present study by combining CO staining with Golgi impregnation of dendritic arbors in the same tissue sections. The data are based on material from two marmoset and three squirrel monkeys. The analysis was conducted on two types of Golgi preparations. In the first preparation, dense networks of overlapping dendrites were impregnated over blob margins. The results of analyzing these networks with transmission and confocal microscopy revealed that dendritic arbors penetrate freely through blob margins. Statistical analysis revealed that the density of dendritic crossings at blob margins was similar to that found at blob and interblob centers. In the second type of Golgi preparation, single, isolated neurons were impregnated. Studies of such neurons revealed occasional examples of dendritic arbors that appeared to reflect back from blob margins, but counter examples were equally abundant. Bias index analysis indicated that dendritic arbors were generally unaffected by the presence of a nearby blob margin. Scanning a large number of impregnated arbors indicated that at least half of the population of blob-related neurons had dendrites in both blob and interblob territory. Under the conditions of free dendritic penetration of blob margins, the sole factor that determines the level of blob/interblob mixing appears to be the relationship between blob size and the dendritic spread of blob neurons. Interestingly, in both the marmoset and squirrel monkeys this size ratio is similar despite a large difference in their cortical surface area. Thus, it is hypothesized that blob size is optimally matched to the dendritic span so as to create a smooth transition of dendritic sampling from blob to interblob-related processing streams.

APL and the search for the ultimate prime number program (part 1)

A new interpretation of the knots in the M87 jet is presented. It is proposed that they are the sites of dense blobs of gas lying within a directed supersonic jet. Jet kinetic energy is dissipated in each knot behind a strong bow shock, where particle acceleration and magnetic field amplification can occur. The momentum flux incident on these obstacles accelerates them in the direction of the jet, and they should cease to radiate efficiently when their velocity approaches that of the jet. The eight known optical knots may be interpreted as either supernova remnants or interstellar clouds. The five outermost knots could be fragments of one such object which became dynamically unstable.

Cortical integration of parallel pathways in the visual system of primates

Injections of wheatgerm agglutinin conjugated with horseradish peroxidase (WGA-HRP) were placed in the middle temporal visual area (MT) of squirrel monkeys to reveal the distributions of interconnections with functionally distinct modules in areas 17 and 18. In agreement with previous reports, brain sections cut parallel to the surfce of manually flattened cortex and reacted for cytochrome oxidase (CO) revealed CO dense blobs in area 17 and alternating CO dense thick and thin bands separated by CO light interbands in area 18. Alternate sections stained for myelin indicated that the CO light interblobs and interbands are more densely myelinated than the CO dense blobs and bands. Our major finding is that projections from MT to areas 17 and 18 are both to modules projecting to MT and modules projecting to other targets. In area 17, the cells in the middle layers projecting to injection sites in MT typically were distributed in several short merging and diverging rows, suggesting the convergence of projections from several matched orientation columns in area 17 to the restricted injection site in MT. Backward projections from MT to more superficial layers in area 17 were distributed more evenly across cortex and over a wider area of cortex. These terminations were dense throughout the interblob cortes which includes all orientation columns and neurons projecting to area 18, but were light over the blobs. As previously reported, neurons in area 18 projecting to MT were located in one set of the CO dense bands. However, these bands appeared to be thin rather than thick. More superficial label reflecting projections from MT to area 18 was distributed over both thin bands projecting to MT and the thick bands projecting elsewhere. The results suggest that an important function of backward connections is to integrate information across diverging processing streams.

Hot Stripes Rather than Hot Spots in Cataclysmic Binaries: 2 - D Hydrodynamic Models

AbstractTwo-dimensional hydrodynamic models of the collision region between the stream and the disk in a cataclysmic binary are presented. The adiabatic collision results in significant mass loss from the system and produces large turbulent regions in outer parts of the disk. Radiative cooling of the collision region leeds to a semi-continuous injection of mass into the disk in the form of dense blobs of gas. In both cases the hot regions obtained as a result of the collision are over 1/6 of the circumference of the disk long and almost 40% of its radius deep, deserving to be renamed ‘hot stripes’.

Supernova Remnants

AbstractThe present structure and recent changes in Cas A are discussed. On the deepest available exposures the optical remnant of this supernova is seen to consist of an almost complete shell. The southern part of this shell is outlined by knots that have developed during the last decade. It is pointed out that moving nebulosity in which [O III] radiation is particularly strong is distributed differently from nebulosity in which the [O III]/[S II] ratio is more nearly normal. Observation of the motions of individual knots suggests a model in which dense blobs of matter, which have a highly anomalies composition, become luminous as they plough through a stationary interstellar (or circumstellar) medium.