Neglect assessment as an application of virtual reality.

OBJECTIVE: In this study a cancellation task in a virtual environment was applied to describe the pattern of search and the kinematics of hand movements in eight patients with right hemisphere stroke. METHODS: Four of these patients had visual neglect and four had recovered clinically from initial symptoms of neglect. The performance of the patients was compared with that of a control group consisting of eight subjects with no history of neurological deficits. RESULTS: Patients with neglect as well as patients clinically recovered from neglect showed aberrant search performance in the virtual reality (VR) task, such as mixed search pattern, repeated target pressures and deviating hand movements. The results indicate that in patients with a right hemispheric stroke, this VR application can provide an additional tool for assessment that can identify small variations otherwise not detectable with standard paper-and-pencil tests. CONCLUSION: VR technology seems to be well suited for the assessment of visually guided manual exploration in space.

Use of a virtual human performance laboratory to improve integration of mathematics and biology in sports science curricula in Sweden and the United States.

New fields such as bioengineering are exploring the role of the physical sciences in traditional biological approaches to problems, with exciting results in device innovation, medicine, and research biology. The integration of mathematics, biomechanics, and material sciences into the undergraduate biology curriculum will better prepare students for these opportunities and enhance cooperation among faculty and students at the university level. We propose the study of sports science as the basis for introduction of this interdisciplinary program. This novel integrated approach will require a virtual human performance laboratory dual-hosted in Sweden and the United States. We have designed a course model that involves cooperative learning between students at Göteborg University and Stanford University, utilizes new technologies, encourages development of original research and will rely on frequent self-assessment and reflective learning. We will compare outcomes between this course and a more traditional didactic format as well as assess the effectiveness of multiple web-hosted virtual environments. We anticipate the grant will result in a network of original faculty and student research in exercise science and pedagogy as well as provide the opportunity for implementation of the model in more advance training levels and K-12 programs.

3D visualization and stereographic techniques for medical research and education.

While computers have been able to work with true 3D models for a long time, the same does not apply to the users in common. Over the years, a number of 3D visualization techniques have been developed to enable a scientist or a student, to see not only a flat representation of an object, but also an approximation of its Z-axis. In addition to the traditional flat image representation of a 3D object, at least four established methodologies exist: Stereo pairs. Using image analysis tools or 3D software, a set of images can be made, each representing the left and the right eye view of an object. Placed next to each other and viewed through a separator, the three dimensionality of an object can be perceived. While this is usually done on still images, tests at Mednet have shown this to work with interactively animated models as well. However, this technique requires some training and experience. Pseudo3D, such as VRML or QuickTime VR, where the interactive manipulation of a 3D model lets the user achieve a sense of the model's true proportions. While this technique works reasonably well, it is not a "true" stereographic visualization technique. Red/Green separation, i.e. "the traditional 3D image" where a red and a green representation of a model is superimposed at an angle corresponding to the viewing angle of the eyes and by using a similar set of eyeglasses, a person can create a mental 3D image. The end result does produce a sense of 3D but the effect is difficult to maintain. Alternating left/right eye systems. These systems (typified by the StereoGraphics CrystalEyes system) let the computer display a "left eye" image followed by a "right eye" image while simultaneously triggering the eyepiece to alternatively make one eye "blind". When run at 60 Hz or higher, the brain will fuse the left/right images together and the user will effectively see a 3D object. Depending on configurations, the alternating systems run at between 50 and 60 Hz, thereby creating a flickering effect, which is strenuous for prolonged use. However, all of the above have one or more drawbacks such as high costs, poor quality and localized use. A fifth system, recently released by Barco Systems, modifies the CrystalEyes system by projecting two superimposed images, using polarized light, with the wave plane of the left image at right angle to that of the right image. By using polarized glasses, each eye will see the appropriate image and true stereographic vision is achieved. While the system requires very expensive hardware, it solves some of the more important problems mentioned above, such as the capacity to use higher frame rates and the ability to display images to a large audience. Mednet has instigated a research project which uses reconstructed models from the central nervous system (human brain and basal ganglia, cortex, dendrites and dendritic spines) and peripheral nervous system (nodes of Ranvier and axoplasmic areas). The aim is to modify the models to fit the different visualization techniques mentioned above and compare a group of users perceived degree of 3D for each technique.

Haptic palpation of head and neck cancer patients--implication for education and telemedicine.

Malignancy in the head and neck area is a disease that often gives high morbidity in functions like speech, eating, breathing and cosmetics. To ensure a treatment of high clinical standard these patients are presented for a multidisciplinary tumor-team at Sahlgren University hospital. The team usually involves ENT-surgeons (Ear, Nose and Throat), oncologists, radiologists, pathologists, plastic surgeon, general surgeon and oral surgeons. The aim of the presentation is to classificate the tumor and suggests a treatment. The patients presented are from the whole western region of Sweden, and therefore some patients have to travel long distances. To minimize travel telemedicine was introduced 1998 with success [1]. One concern, when presenting a patient with telemedicine, has been the lack of possibility to palpate the tumor and the tissue surrounding it. To address this problem a 3D model of the tumor visualizes the region and possibly allows haptic palpation. Based on a series of high resolution CT/MR scans, a model of the region around the patients tumor is created. Haptic properties are added to the skin and subcutaneous structures (including the tumor) of the model. Initially, the haptic tuning is done by an examining physician, but in the final telemedical application, the aim is to develop a sensory device for this purpose (e.g. a position sensitive glove, such as Virtual Technologies, Inc. CyberGlove [2] and a graded system for setting firmness of the tissue). The model with its haptic properties can then be examined visually and haptically, the latter using a haptic device such as the SensAble PHANToM [3]. The present system uses a 3D model in VRML format based on reconstructed structures in the ROI (which includes the jawbones, the vertebra, the throat, major muscles and the skin) from high resolution CT. Haptic properties are added using MAGMA 2.5 (ReachIn Technologies AB, Sweden) [4]. Haptic force feedback is provided using a PHANToM Desktop (SensAble Technologies Inc) [3]. Visual feedback can be either monoscopic or stereoscopic (StereoGraphic CrystalEyes) [5]. The system will be used for concept testing and for evaluating possible limitations and/or the need for a modified examination protocol. Once a reliable set of parameters has been generated (using both professionals and medical students at various levels), the remote components will be added.

Modeling and modification of medical 3D objects. The benefit of using a haptic modeling tool.

The Computer Laboratory of the medical faculty in Goteborg (Mednet) has since the end of 1998 been one of a limited numbers of participants in the development of a new modeling tool together with SensAble Technologies Inc [http:¿www.sensable.com/]. The software called SensAble FreeForm was officially released at Siggraph September 1999. Briefly, the software mimics the modeling techniques traditionally used by clay artists. An imported model or a user defined block of "clay" can be modified using different tools such as a ball, square block, scrape etc via the use of a SensAble Technologies PHANToM haptic arm. The model will deform in 3D as a result of touching the "clay" with any selected tool and the amount of deformation is linear to the force applied. By getting instantaneous haptic as well as visual feedback, precise and intuitive changes are easily made. While SensAble FreeForm lacks several of the features normally associated with a 3D modeling program (such as text handling, application of surface and bumpmaps, high-end rendering engines, etc) it's strength lies in the ability to rapidly create non-geometric 3D models. For medical use, very few anatomically correct models are created from scratch. However, FreeForm features tools enable advanced modification of reconstructed or 3D scanned models. One of the main problems with 3D laserscanning of medical specimens is that the technique usually leaves holes or gaps in the dataset corresponding to areas in shadows such as orifices, deep grooves etc. By using FreeForms different tools, these defects are easily corrected and gaps are filled out. Similarly, traditional 3D reconstruction (based on serial sections etc) often shows artifacts as a result of the triangulation and/or tessellation processes. These artifacts usually manifest as unnatural ridges or uneven areas ("the accordion effect"). FreeForm contains a smoothing algorithm that enables the user to select an area to be modified and subsequently apply any given amount of smoothing to the object. While the final objects need to be exported for further 3D graphic manipulation, FreeForm addresses one of the most time consuming problems of 3D modeling: modification and creation of non-geometric 3D objects.

Virtual reality on the web: the potentials of different methodologies and visualization techniques for scientific research and medical education.

Academic and medical imaging are increasingly using computer based 3D reconstruction and/or visualization. Three-dimensional interactive models play a major role in areas such as preclinical medical education, clinical visualization and medical research. While 3D is comparably easy to do on a high end workstations, distribution and use of interactive 3D graphics necessitate the use of personal computers and the web. Several new techniques have been demonstrated providing interactive 3D via a web browser thereby allowing a limited version of VR to be experienced by a larger majority of students, medical practitioners and researchers. These techniques include QuickTimeVR2 (QTVR), VRML2, QuickDraw3D, OpenGL and Java3D. In order to test the usability of the different techniques, Mednet have initiated a number of projects designed to evaluate the potentials of 3D techniques for scientific reporting, clinical visualization and medical education. These include datasets created by manual tracing followed by triangulation, smoothing and 3D visualization, MRI or high-resolution laserscanning. Preliminary results indicate that both VRML and QTVR fulfills most of the requirements of web based, interactive 3D visualization, whereas QuickDraw3D is too limited. Presently, the JAVA 3D has not yet reached a level where in depth testing is possible. The use of high-resolution laserscanning is an important addition to 3D digitization.

Laser 3-D scanning for surface rendering in biomedical research and education.

A technique based on laser scanning is applied to body parts and organs. Laser light is projected onto the surface of objects and recorded by CCD sensors. This is a fast and flexible method for accurately scanning surface geometry. It also allows conversion to NURBS patches. We have, so far, made 'point-cloud' surface renderings from a head model, a plastic brain model, a human brain, moulds of bites and a cranium. The limits, quality, efforts and costs of employing the laser 3-D scanning technique are evaluated. The experiments are currently in progress and results give interesting 3D renderings and attempts to triangulated solid-models.

Production of CAL-programs in medicine, odontology and veterinary medicine in Sweden.

At the recommendation of the Swedish Government, the Council for the Renewal of Undergraduate Education was established in 1990. In 1993 the Council was declared a permanent National Agency by Swedish Parliament and became part of the newly established National Agency for Higher Education in 1995. The purpose of the Council for Renewal of Undergraduate Education is to promote and support endeavors to develop quality and renewal of undergraduate education. In particular the council awards grants to development activities. Once a year, teachers at Swedish universities, university colleges and professional schools can apply for funding. Applications are accepted for projects directed towards undergraduate education in all disciplines. The Council selects 15-20 projects and each project is funded for 1-3 years. An advisory group--MEDCAL (Computer Assisted Learning (CAL) in MEDicine, Odontology and Veterinary Medicine)--consisting of representatives from all universities supports the Council with registration and evaluation of programs, offers their opinions on the production of CAL and collaborates with similar organizations in other countries, e.g. Australia, Denmark, Germany, Great Britain and USA. In all, 12 projects within the frame of MEDCAL will be reported.

Paranodal Schwann cell mitochondria in spinal roots of the cat. An ultrastructural morphometric analysis.

We have calculated the number of paranodal Schwann cell mitochondria in adult feline ventral and dorsal lumbar spinal roots using ultrastructural serial section analysis. Distinct accumulations of paranodal mitochondria were noted in nerve fibres more than 4-5 microm in diameter. The calculated number of paranodal mitochondria increased linearly with fibre diameter from a few hundred up to 20,000-30,000 per node. A linear increase in the number of paranodal mitochondria per node also appeared as a function of nodal variables such as 'nodal axon membrane area', 'nodal Schwann cell membrane area', and 'node gap extracellular volume'. In large fibres (D = 15-18 microm), a calculated number of about 20,000 paranodal Schwann cell mitochondria were accumulated at each node of Ranvier and related to nodal axon membrane area of about 20 microm2. Our calculations indicate that, on the average, 1000 paranodal Schwann cell mitochondria with a total volume of 6.7 microm3, a total outer membrane area of 250 microm2 and a total inner membrane area of 580 microm2 projected to each microm2 of the nodal axon membrane via the nodal Schwann cell brush border.

3D-brain 2.0--narrowing the gap between personal computers and high end workstations.

UNLABELLED: Recent advances in personal computer hardware and software have pushed the graphic capacity of these easier to use and, more importantly, cheaper computers to a level approximating the current standard of high end workstations. The interactivity and graphic complexity of a modern PC is rapidly approaching the current standard on Silicon Graphics (although with respect to texture mapping, the SGI is still ahead of the PCs). The modern medical student laboring under increasingly higher demands with respect to versatility, not only in basic science and traditional medical knowledge, is also faced with the requirement to learn and understand modern scientific visualization and analytical instruments. Furthermore, basic knowledge of information technology and computer literacy is expected of the next generation medical professionals. These demands forces medical schools to increasingly invest in computers and information technology for educational purposes. Due to common class sizes, these computers are most commonly Windows PCs or Apple Macintoshes. For distance education, telematics or studies at home, personal computer versions of the workstation graphics are a necessity. 3D-Brain 2.0 is an educational software package intended to run on basic personal computers and utilizing modern software technologies such as QuickTime VR 2.0 and VRML 2.0, to provide the students with insight into modern clinical and scientific visualization, focusing on the anatomy and functionality of the human brain. The aim of this paper to test the validity and usefulness of these new visualization techniques. METHODS: 3D-Brain is based on human brains sliced in 1 mm sections (NB. NOT based on NLMs Visual Human). Each slice was photographed, digitized, optimized and aligned using proprietary software. The datasets were then created by manual tracing followed by triangulation, smoothing and 3D visualization using Silicon Graphics computers. For the QuickTime VR project, 684 images with a 10 degrees angle were generated for each scene and ported to an Apple Macintosh computer for further manipulation. VRML code was generated directly from the original dataset. All interactivity was programmed on a Macintosh and subsequently ported to the Windows95 PC platform. The minimum requirements to run the software are either a PowerPC based Macintosh computer or a Pentium based Windows 95 computer with 16 Mb, 16 bit display and a 4 speed CD-ROM. RESULTS AND DISCUSSION: 3D-Brain 2.0 provides medical students at Goteborg University the means to complement traditional teaching using visualization techniques and three-dimensional models. These techniques also serve as an insight into the different clinical means of visualization the student will encounter throughout his/her continued education and professional career. For educational purposes, it has been established that among the tested new visualization techniques, CD-ROM based software utilizing QTVR is still the best methodology to use for pedagogical software. VRML shows promise in porting these software packages to the Web while Open Inventor is the preferred format for research purposes.

The BRAIN project: an interactive learning tool using desktop virtual reality on personal computers.

The BRAIN-project is an endeavor in using computer aided learning to improve the understanding of the human brain anatomy. The project consists of four parts, each based on modular packages: BRAINIMAGES: Brain atlas consisting of horizontal and frontal brain slices spaced I mm apart enabling the identification of structures and areas of the brain. The software also contains views of the brain's outer surface with all pertinent structures marked. BRAINRADIOLOGY: Visualisation of the brain using CT, MRI and angiography. The different imaging techniques enable the user to explore the brain from several angles and also view the major blood vessels of the brain. NEUROHISTOLOGY: Cells of the brain using histologically stained sections. The program emphasizes the organization of cells in layers and the interaction of different cell types. 3D-BRAIN: Three dimensional reconstructions based on physical slices of a human brain. The reconstructed brain views are made interactive using a simple form of desktop virtual reality: QuickTime VR technology. The user can rotate the different views in all directions producing a 3D effect. The different views are designed to highlight important structures and their organization within the outlined (and semi transparent) brain surface. Contrary to similar applications, the actual three dimensional objects are not based on MRI or CT scans (with comparatively poor resolution), but on tracings made on high resolution images of photographs of actual sections of a postmortem brain. N.B., this approach produces 3D renderings in a more detailed and reliable way. The BRAIN project is designed as a support package for students in preclinical education by supplying additional means for gathering information pertinent to the curriculum. By cross linking, the students can switch from a three dimensional object to a corresponding slice, and then to the relevant histological sample and son on. The software components are based on a modular design enabling easy modification of the various parts and the entire project is designed to run on both Apple Macintosh and MS Windows based PCs.

Axonal constriction at Ranvier's node increases during development.

We have studied the ratio between the nodal and the internodal diameter (the dn/d(in) ratio) of large myelinated axons in the L7 ventral spinal root of the cat during pre- and postnatal development using light and electron microscopy. A substantial nodal constriction, dn/d(in) = 0.6, was found at the beginning of myelination, about 2 weeks before birth. The ratio decreased during the subsequent 10 weeks and approached the adult value of 0.47 (SE 0.01, N = 45) in the 8 weeks old kitten. The observations are discussed with respect to the maturation of the nodal region and to our earlier idea that the constricted nodal axon segments of large peripheral myelinated nerve fibres of adult cats and kittens 2 months and more of age are sites capable of interacting with and perhaps even controlling the passage of axonally transported materials.

Automated correction of linear deformation due to sectioning in serial micrographs.

This paper describes an objective and automatic method for detection and correction of sectioning deformations in digitized micrographs, as well as an evaluation of the method applied to light and electron microscopic images of semi-thin and ultra-thin serial sections from brain cortex. The detection is based on matching of image subregions and the deformation model is bi-linear, i.e. two first-order polynomials are used for modelling compression/expansion in perpendicular directions. The procedure is applicable to prealigned serial two-dimensional sections and is primarily aimed at three-dimensional reconstruction of tissue samples consisting of a large number of cells with random distribution and morphology.

Dimensions of individual alpha and gamma motor fibres in the ventral funiculus of the cat spinal cord.

Using light and electron microscopy, axon diameter, myelin sheath thickness (measured as number of myelin lamellae) and internodal length of alpha and gamma motor axons of the L7 ventral root and spinal cord segment were investigated in serial cross-sections. The CNS internodes of the alpha motor fibres had, on average, an axon diameter of 8.6 microns, 105 myelin lamellae and a length of about 560 microns. The CNS internodes of the gamma motor fibres had, on average, an axon diameter of 3.4 microns, 66 myelin lamellae and a length of about 440 microns. Axon diameter at the nodes of Ranvier was 30-40% of the internodal axon diameter. Axon diameter, number of myelin lamellae and internodal length varied considerably between consecutive internodes. Statistical analysis showed no systematic increases or decreases. Regression analyses of the scatter plots of the number of myelin lamellae and internodal length against axon diameter showed large variations and correlation coefficients of r < 0.50. In conformity with ventral root (PNS) internodes (Nilsson & Berthold, 1988) the plotting of intrafunicular (CNS) internodal myelin volume against internodal axon mantle area showed linear correlations with correlation coefficients of r > 0.90. The mean axon diameter of the investigated CNS internodes was similar to, the mean number of myelin lamellae somewhat lower than, and the mean internodal length considerably shorter than that of internodes of axons of the L7 ventral root (Nilsson & Berthold, 1988). In contrast to the ventral root, the intrafunicular alpha motor fibres had higher g values (axon diameter/fibre diameter value) and lower il/d ratios (internodal length/axon diameter ratio) than is considered optimal for conduction. We consider that these deviations from the theoretical optimum are not large enough to impair the conduction properties of the CNS parts of the motor axons in a significant way.

Axoplasmic organelles at nodes of Ranvier. I. Occurrence and distribution in large myelinated spinal root axons of the adult cat.

Using light microscopy (LM) and electron microscopy (EM) we have examined the occurrence and distribution of axoplasmic organelles in large myelinated nerve fibres of the L7 ventral and dorsal spinal roots of the cat with special reference to the paranode-node-paranode (pnp)-regions. Ninety-eight percent of the 550 Toluidine Blue-stained paranode-node-paranode-regions examined in the light microscope contained dark-blue bodies accumulated distal to the midlevel of the paranode-node-paranode-region. Further, a veil of Toluidine Blue positive material was observed in about 50% of the paranode-node paranode-regions. In about 25% of these paranode-node-paranode-regions the veil lay distal to the midlevel of the paranode-node-paranode-region and in the remainder it lay proximally. Electron microscopy suggested that the ultrastructural equivalents of the dark-blue bodies and of the veil were dense lamellar bodies and a diffuse granular material, respectively. Our calculations indicate that from 70% to more than 90% of some organelles (dense lamellar bodies, multivesicular bodies and vesiculo-tubular membranous organelles) present in an axon are accumulated in the paranode-node-paranode-regions. The occurrence of these organelles in the individual paranode-node-paranode-regions varied within wide limits also in adjacent fibres. The dense lamellar and multivesicular bodies dominated the distal part of the paranode-node-paranode-regions while the vesiculo-tubular membranous organelles dominated the proximal part, i.e. the organelles showed a mutual proximo-distal segregation with reference to the midlevel of the paranode-node-paranode-region. Of seventeen paranode-node-paranode-regions analyzed ultrastructurally, seven were classified as 'fully segregated', that is 67% or more of the lamellar and multivescular bodies, present in the whole paranode-node-paranode-region, lay distal to the mid-level, and 67% or more of the vesiculo-tubular membranous organelles lay proximal to it.

Axoplasmic organelles at nodes of Ranvier. II. Occurrence and distribution in large myelinated spinal cord axons of the adult cat.

The occurrence and distribution of axoplasmic organelles in large myelinated axons of the ventral, the lateral and the dorsal funiculi of L7 spinal cord segments of the cat have been studied using electron microscopy (EM). Most organelles were found to be concentrated to the paranode-node-paranode (pnp)-regions and they showed their highest relative concentration in the constricted part of these regions, i.e. at the nodes of Ranvier. In the paranode-node-paranode-regions of the lateral and dorsal funiculi, large dense bodies predominated distal to the nodal mid-level and vesiculo-tubular membranous organelles proximal to it. This pattern of organelle distribution, a proximo-distal (with reference to the neuron soma) segregation of the organelles, was only faintly indicated in the paranode-node-paranode-regions of the alpha motor axons of the ventral funiculus. These paranode-node-paranode-regions were, apart from a weak proximo-distal segregation of a few organelles, characterized by deposits of electron dense granules and clusters of large round mitochondria. We conclude that there are two types of organelle accumulation and distribution in the paranode-node-paranode-regions of large spinal cord nerve fibres of the cat. One type is found in the lateral and dorsal funiculi, i.e. in axons with terminal (synaptic) fields inside the blood-brain-barrier. The other type is found in the alpha motor axons of the ventral funiculus, i.e. in axons with their terminal field in the PNS and thus outside the blood-brain barrier. It should be noted that retrogradely transported material in the alpha motor axons has passed through a long sequence of paranode-node-paranode-regions equipped with Schwann cells before it reaches the CNS, while material transported retrogradely in the axons of the dorsal and lateral funiculi has not. The following discussion includes a comparison of the organelle accumulation and distribution in these two types of CNS paranode-node-paranode-regions with the organelle accumulation and distribution observed in the paranode-node-paranode-regions of PNS axons.

Computer-assisted 3D analysis of cell distributions in the normal and epileptic cerebral cortex: description of a methodology in progress.

This paper describes software routines that (a) visualizes a stack of several thousands of aligned sequential photographic two-dimensional (2D) images stored in an image processing system; (b) creates a data base containing information about objects identified sequentially from the 2D images; (c) transfers the data base to a graphical terminal; (d) reconstructs a three-dimensional (3D) object space; and (e) supports on-line interaction between the image processing system and the graphical terminal. As an application example, the cell content of a prism of motor cerebral cortex of the cat is reconstructed. Preliminary results from reconstructing human epileptic temporal cortex (cortical microdysgenesia) are also reported.

3D reconstruction of biological objects from sequential image planes--applied on cerebral cortex from cat.

A prism of cat cerebral cortex was reconstructed with a method for three-dimensional (3D) representation of biological objects. A series of 918 semithin sections were digitized into an image analysis system. The images were aligned and analyzed, and a data base with the coordinates and a classification of the cells was created. The data base (i.e., the cortical prism) was visualized in a 3D graphic terminal, and parameters such as columnar and lamellar organization, clustering, and cell density were analyzed. A neuronal perikaryon and its neurites was reconstructed and shown together with the cortical prism.

Metabolic relationships between proteins of myelin and paranodally shedded, partially degraded myelin fragments in the rabbit CNS.

The "close-to-node" regions of myelinated nerve fibres, i.e., the paranodal end segments, are generally thought to be sites of high metabolic activity and myelin sheath turnover. Data on turnover rates of individual myelin constituents are conflicting but there exists a common belief that myelin is metabolized as independent molecules rather than as a unit. The occurrence of paranodal Marchi-positive bodies, with morphological and biochemical properties consistent with partially degraded myelin, prompted us to examine the temporal dynamics of the incorporation of radioactive precursor label in the major proteins of myelin and the Marchi-positive bodies. 3H-leucine was administered intrathecally in adult rabbits. After various survival times, the spinal cord was subfractionated by ultracentrifugation in a discontinuous two-step 0.32 M/0.85 M sucrose gradient. Myelin was collected from the interface and a floating fraction, heavily enriched in Marchi-positive bodies, was recovered on top of the 0.32 M sucrose. By scintillation counting and by gel fluorography combined with immunoblotting, a gradual appearance with time of partially degraded peptides of myelin-associated protein and 2',3'-cyclic nucleotide 3'-phosphodiesterase was seen in the floating fraction but not in myelin. The temporal dynamics of the specific activities of these two proteins and myelin-basic protein and proteolipid protein were consistent with a typical source-product relationship between myelin and the material in the floating fraction. In conjunction with earlier morphological and biochemical findings, these data may suggest that Marchi-positive bodies appear as a consequence of myelin catabolism.