Stable Reference Frame Research Articles

Systematic distortions of perceptual stability investigated using immersive virtual reality

Using an immersive virtual reality system, we measured the ability of observers to detect the rotation of an object when its movement was yoked to the observer’s own translation. Most subjects had a large bias such that a static object appeared to rotate away from them as they moved. Thresholds for detecting target rotation were similar to those for an equivalent speed discrimination task carried out by static observers, suggesting that visual discrimination is the predominant limiting factor in detecting target rotation. Adding a stable visual reference frame almost eliminated the bias. Varying the viewing distance of the target had little effect, consistent with observers underestimating distance walked. However, accuracy of walking to a briefly presented visual target was high and not consistent with an underestimation of distance walked. We discuss implications for theories of a task-independent representation of visual space.

Geodetic Measurements of Crustal Deformation in the Western Mediterranean and Europe

Geodetic measurements of crustal deformation over large areas deforming at slow rates (< 5 mm/yr over more than 1000 km), such as the Western Mediterranean and Western Europe, are still a challenge because (1) these rates are close to the current resolution of the geodetic techniques, (2) inaccuracies in the reference frame implementation may be on the same order as the tectonic velocities. We present a new velocity field for Western Europe and the Western Mediterranean derived from a rigorous combination of (1) a selection of sites from the ITRF2000 solution, (2) a subset of sites from the European Permanent GPS Network solution, (3) a solution of the French national geodetic permanent GPS network (RGP), and (4) a solution of a permanent GPS network in the western Alps (REGAL). The resulting velocity field describes horizontal crustal motion at 64 sites in Western Europe with an accuracy on the order of 1 mm/yr or better. Its analysis shows that Central Europe behaves rigidly at a 0.4 mm/yr level and can therefore be used to define a stable Europe reference frame. In that reference frame, we find that most of Europe, including areas west of the Rhine graben, the Iberian peninsula, the Ligurian basin and the Corsica-Sardinian block behaves rigidly at a 0.5 mm/yr level. In a second step, we map recently published geodetic results in the reference frame previously defined. Geodetic data confirm a counterclockwise rotation of the Adriatic microplate with respect to stable Europe, that appears to control the strain pattern along its boundaries. Active deformation in the Alps, Apennines, and Dinarides is probably driven by the independent motion of the Adriatic plate rather than by the Africa-Eurasia convergence. The analysis of a global GPS solution and recently published new estimates for the African plate kinematics indicate that the Africa-Eurasia plate motion may be significantly different from the NUVEL1A values. In particular, geodetic solutions show that the convergence rate between Africa and stable Europe may be 30-60% slower than the NUVELIA prediction and rotated 10-30° counterclockwise in the Mediterranean.

Crustal velocity field of western Europe from permanent GPS array solutions, 1996-2001

We derive a new geodetic velocity field for western Europe and the Western Mediterranean by rigorously combining (1) a selection of 36 ITRF2000 sites, (2) a solution from a subset of sites of the European Permanent GPS Network (EUREF-EPN), (3) a solution of the French national geodetic permanent GPS network (RGP) and (4) a solution of a permanent GPS network in the western Alps (REGAL). The resulting velocity field describes horizontal crustal motion at 64 sites in Western Europe with an accuracy of the order of I mm yr - 1 or better. Its analysis shows that Central Europe (defined as east of the Rhine Graben and north of the Alps and the Carpathians) behaves rigidly at a 0.4 mm yr - 1 level and defines a stable Europe reference frame. In that reference frame, we find no significant motion at sites located west of the Rhine graben and on the Iberian peninsula, which sets an upper bound of 0.6 mm yr - 1 on horizontal motion across the Rhine graben and the Pyrenees. We find that the current strain pattern in the western Alps combines E-W extension and right-lateral shear. We confirm a counterclockwise rotation of the Adriatic microplate, which appears to control the strain pattern along its boundaries in the Friuli area, the Alps and the Apennines. Our results also suggest that the Africa-Eurasia plate motion in the Western Mediterranean may be 40-50 per cent slower that the NUVEL1A plate motion model and rotated 20°-30° counterclockwise.

Semiglobalization and international business strategy

If markets were either completely isolated by or integrated across borders, there would be little room for international business strategy to have content distinctive from ‘mainstream’ strategy. But a review of the economic evidence about the international integration of markets indicates that we fall in between these extremes, into a state of incomplete cross-border integration that I refer to as semiglobalization. More specifically, most measures of market integration have scaled new heights in the last few decades, but still fall far short of economic theory's ideal of perfect integration. The diagnosis of semiglobalization does more than just supply a relatively stable frame of reference for thinking about the environment of cross-border operations. It also calls attention to the critical role of location-specificity in the prospects of distinctive content for international business strategy relative to mainstream business and corporate strategy. In addition, it flags factors/products subject to location-specificity as being salient from the perspective of international business. Finally, it highlights the scope for strategies that strive to capitalize on the (large) residual barriers to cross-border integration, as well as those that simply try to cope with them.

Is there life beyond the principal states of polarization?

In this paper we show that it is possible to describe exactly the field intensity distorted by polarization mode dispersion (PMD) at the output of a single-mode fiber, without resorting to the principal states of polarization (PSPs). Such description is based on the eigenmodes of what we call the extracted matrices, for which we establish relationships with the PSPs, e.g., by showing their alignment with the PSPs when these are not depolarized over the signal bandwidth. We also show that the eigenmodes of the extracted matrices are less depolarized than the PSPs, and are thus the most convenient frame of reference to express the output field and intensity for high bit rate transmitted signals. We thoroughly investigate the properties of a recently introduced fiber model, which we refer to as the rotation model, based on the rotation of the extracted eigenmodes, which extends the intuition of Bruyère's PSPs rotation model (1996) to the most stable frame of reference, and hence is expected to give the most accurate description of the PMD fiber for large bandwidth signals. We finally provide a novel eye closure penalty (ECP) formula based on the extracted eigenmodes, and show its relation with the currently available ECP formulas. The accuracy of the novel ECP formula is tested against simulation results of transmission through a fiber synthesized by the rotation model.

Effects of head immobilization on the coordination and control of head and body reorientation and translation during steering.

Changing the direction of locomotion involves lateral translation of the body in addition to body reorientation to align with the new travel direction. We designed this study to investigate the CNS control of these postural adjustments. The specific aims of the study were: first, to test the hypothesis that anticipatory head movements towards the new travel path are proactively controlled by the CNS to provide a stable frame of reference for body reorientation and, second, to investigate the relative contribution of foot placement and other mechanisms to the control of lateral body translation during steering. We achieved these aims by carrying out a comprehensive biomechanical analysis of participants performing a steering paradigm and observing the effects of immobilizing the head (by fixing it to the trunk) on postural control and the sequencing of body segment reorientation. Participants performed a task whereby they were visually cued to change their direction of walking by 30 degrees or 60 degrees, left or right, at the midpoint of a 9-m path. The temporal sequence of body reorientation was consistent with previous findings that the head starts to turn in the direction of travel before the rest of the body. Translation of the centre of mass (COM) in the new travel direction was achieved both through alternate placement of the contralateral foot prior to the turn step and use of a hip strategy to control the body pendulum during swing. Immobilizing the head resulted in the following significant changes: earlier onset of trunk yaw with respect to cue delivery, later trunk roll onset and a reduction in trunk roll amplitude. These results provide valuable information regarding the biomechanics of steering and support the hypothesis that aligning the head with motor or locomotor goals using vision provides the CNS with a stable frame of reference, independent of gaze, that can be used to control the repositioning of the body in space.

The terrestrial reference frame and the dynamic Earth

As early as the 15th century Swedes noticed that rocks in their harbors were slowly rising out of the sea [Ekman, 1991]. These local observations were not sufficient to distinguish whether the rocks were rising or the sea level falling. Later, it was realized that Fennoscandia was still rebounding from the last Ice Age. This historical observation is still relevant today. How can you know whether a point on the Earth's surface is slowly moving up, down, or horizontally? One must relate local measurements to a stable and accurate reference frame, one whose scale is much larger than the problem at hand. We remain concerned with sea‐level variations, but present‐day studies recognize that change must be measured from a global point of view and with respect to a globally well‐defined reference frame. Thus, the regional and national geodetic datums developed over the past 200 years are inappropriate for studying global‐level problems.

Intraplate deformation in western Europe deduced from an analysis of the International Terrestrial Reference Frame 1997 (ITRF97) velocity field

Although tectonic deformation in western Europe is essentially concentrated in the Appenines and Alpine (Alps, Pyrenees) mountain ranges, several large historical and instrumentally recorded earthquakes (M&gt;6) are known in the supposedly “stable” part of Europe. Because of its accuracy and internal consistency at a global scale, the International Terrestrial Reference Frame 1997 (ITRF97) velocity field allows testing of intraplate rigidity in western Europe at a millimeter per year level. Using the full statistical information available on the ITRF97 velocities, we identify a subset of sites located in central Europe that satisfies a rigid cap rotation with residual velocities &lt;1 mm/yr and therefore provide a stable Europe reference frame (SERF). In this reference frame we find residual velocities at European ITRF sites that are consistent with known active tectonic features. We identify a northward motion at sites located in Italy, with internal deformation of the Adriatic block rather than rigid plate motion and a westward motion of the westernmost part of Europe of the order of 1–2 mm/yr relative to central Europe. The relative motion of the Adriatic block and western Europe agrees with the current extension known in the Tyrrhenian sea and the Apennines. In central Europe, we find active deformation &lt;1 mm/yr in the eastern Alps and western Carpathians. In the Alpine range our results indicate E‐W extension across the western Alps and N‐S compression across the central and eastern Alps, in agreement with the strain regime deduced from seismotectonic observations. In Belgium and the Netherlands we find residual velocities of 1–1.5 mm/yr to the northwest at all the sites, most likely accommodated along the Upper and Lower Rhine Graben structures. An important outcome of this study is the identification of internal deformation of the order of 1–2 mm/yr in an area usually interpreted as “stable” Europe. This result should be further checked as new, denser, and more accurate space geodetic data sets with longer observation time spans, become available for Europe.

Crustal motion results derived from observations in the European geodetic VLBI network

Geodetic VLBI observations have been performed with the European geodetic VLBI network since early 1990 on a regular basis. The purpose of these observations is to determine crustal motion in Europe and to establish a stable reference frame for other space geodetic techniques. Over the years the size of the network and the number of participating stations has steadily increased. Today, the network extends from the island of Sicily in the south to the island of Spitsbergen/Svalbard in the north and from the Iberian peninsula in the west to the Crimean peninsula in the east. The area covered by the network is affected by two main geodynamic processes which are post-glacial rebound effects in the northern part, and the evolution of the Alps-Apennines orogenic systems in the southern part. With nearly 10 years of VLBI observations the determination of crustal motion in Europe is carried out with high accuracy. Baseline measurements are achieved with an accuracy of a few parts per billion. We compare the evolution of baseline lengths and topocentric station displacements with geophysical models. Strain rates in Europe on a large scale are determined from the results of the VLBI analysis.

Further study of the control of place cell firing by intra-apparatus objects.

The angular positions of hippocampal place cell firing fields are accurately controlled by the position of a single salient cue card attached to the wall of a recording cylinder; when the card is rotated, fields rotate equally. In contrast, the control exerted by 3-dimensional objects placed directly in the recording arena depends on their arrangement. When three objects lie on the vertices of an isosceles triangle near the center of the cylinder they rarely exert any control over the angular positions of firing fields. However, if the isosceles triangle is dilated so that its vertices are against the apparatus wall, the objects exert virtually ideal control over angular field position. Why do the objects gain control when they are against the cylinder wall? One possibility is that the asymmetry in the object set is more easily detected when the objects are far apart so that they provide a better polarizing cue. This hypothesis assumes that the identity of individual landmarks is not recognized by the place cell system whereas their geometric arrangement provides crucial information for controlling place field positions. If this is true, putting the 3 objects against the cylinder wall on the vertices of an equilateral triangle should cause a loss of stimulus control over the angular positions of firing fields. To the contrary, we found that the firing fields of most place cells (23/29) were accurately controlled by the equilateral object arrangement. Moreover, 5/6 of the uncontrolled cells were in a single animal. These results bolster our previous suggestion that the centrally placed objects fail to control place field positions because the computations necessary to form a stable reference frame are very difficult when the animal can go between stimuli.

Eye-head coordination for the steering of locomotion in humans: an anticipatory synergy

We investigated head and gaze orientation in six healthy volunteers walking along 90° corner trajectories, both at light and with eyes closed. We found that head and eyes systematically deviated toward the future direction of the curved trajectory. Anticipation lead was about 1 s. Strikingly, the same behaviour was observed in darkness. In backward (BW) locomotion along the trajectory (from end- to start-point), gaze deviated toward the opposite direction, such that the forward locomotor pattern did not appear time-reversed. Orienting movements displayed higher amplitude, reproducibility and time lead in the forward (FW) direction at light. We suggest that anticipatory orienting synergies belong to the behavioural repertoire of human navigation and may reflect the need to prepare a stable reference frame for intended action.

The role of GPs in the WEGENER project

In recent years, the Global Positioning System (GPS) has become a major tool for high precision geodesy. The precision is now better than 1 ppb. In this paper, the importance of GPS for the WEGENER project is highlighted. First, an overview of the GPS system is presented including a description of the development of its capabilities. One of the most significant developments of the past few years has been the establishment of the International GPS Service for Geodynamics (IGS). Thanks to its standards and products, the state-of-the-art in high precision GPS has been advanced considerably. Therefore, a summary of the goals and principles of IGS is presented next. This is followed by a compilation of the major GPS projects in Europe and its surrounding areas, since 1988. Most of these are not related to the WEGENER project, but it shows how much work has already been done. It also indicates the possible future role of GPS in WEGENER. Since all these projects are usually quite independent, they might benefit from the existence of a consistent, dense, accurate regional reference frame. This is exemplified by the success of IGS, which is based on an expanding global network of continuously operating permanent GPS stations. It provides a stable global reference frame, which makes it feasible to combine the results from independent field campaigns. In certain regions of the world the coverage is not yet optimal, however, and it is planned to further densify the IGS network. Therefore, it might be interesting to establish a dense regional GPS network in the general research area of WEGENER, which extends from Greenland to mid-Asia. This idea is promoted in Section 5 of the paper, where it is proposed to create such a network under the name of WEGNET, for WEGENER GPS Network. It would seek to establish new sites where none exist yet and to include existing stations that may already have been established for other purposes. Apart from providing a regional densification of IGS and a reference frame for WEGENER, the network may also yield valuable contributions to the monitoring of tectonic motions in the area and for studies concerning ocean and atmospheric loading.

Development of Locomotor Balance Control in Healthy Children

ASSAIANTE, C. Development of locomotor balance control in healthy children. NEUROSCI BIOBEHAV REV 22(4) 527–532, 1998.—A set of experimental studies showing how inter-segmental coordination develops during childhood in various locomotor tasks is reviewed. On the basis of these results and two functional principles (stable reference frame and control of the degrees of freedom of the body joints), we recently proposed an ontogenetic model for the sensorimotor organization of balance control in humans [5]. In this model, the hypothesis was put forward that the two main modes of equilibrium control (ascending vs descending temporal organization) operate alternatively and are associated with either of two modes of head–trunk linkage (` en bloc' vs articulated) during four successive periods in the course of ontogenesis. The advantage of this model is that it is heuristic and therefore open to further improvements, including the generalization of these balance strategies to most of the posturo-kinetic activities, the comparison between unperturbed natural balance and reactions to postural disturbances. Some improvements are suggested, and are illustrated by the studies of inter-segmental coordination in new experimental tasks such as hops using one foot or two feet and the initiation of gait. These new results are consistent with the idea that mastery of the degrees of freedom to be controlled simultaneously during the movement improves gradually with age. Moreover, they support the concept of multiple reference frames which operate in a complementary manner or in concert to permit the most appropriate organization of balance control, depending on the environmental requirements.

Head-Trunk Coordination During Hops Using One or Two Feet in Children and Adults

The main purpose of this study was to investigate the development of head-trunk coordination during single hops using one foot or two feet in children of two ages (5.5 to 6 and 7 to 7.5) and adults (n = 6/group). The kinematics of the subjects' hops were analyzed by means of an automatic optical TV-image processor called the ELITE system. The absolute angular dispersion of the head, trunk, and leg about the pitch and the roll axis were measured. Head and trunk pitch and roll anchoring indexes were calculated in order to compare the stabilization of a given segment with respect both to external space and to the underlying anatomical segment. Results were analyzed separately for 3 phases: take-off, flight, and landing. Only the last two phases, flight and landing, are presented in this paper, and the following was found: 1) During flight, under both unipedal and bipedal conditions, head and trunk stabilization in space about the pitch axis occurred in children as well as in adults, suggesting an articulated operation of the head-trunk unit. In contrast, during landing, in children and adults, head stabilization in space tended to disappear while trunk stabilization in space was still present, suggesting an en bloc operation of the head-trunk unit. Similarly, pelvis stabilization in space about the roll axis occurred in all subjects during both flight and landing under unipedal conditions, where lateral balance control is of primary importance. Taken together, these results suggest that head stabilization in space is phase dependent, while trunk stabilization is phase independent. The trunk, including the pelvis, may thus constitute a stable reference frame from which anteroposterior and lateral balance control is organized during hops. 2) For head-trunk coordination, whatever the component of rotation, the two groups of children differed from adults, but did not differ from each other, suggesting that, while jumping, the transition between 6 and 7 years of age in the organization of balance control takes place in the coordination of the lower limbs during the preparatory phase of the take-off.

Eustatic Curve for the Middle Jurassic--Cretaceous Based on Russian Platform and Siberian Stratigraphy: Zonal Resolution

We have used the stratigraphy of the central part of the Russian platform and surrounding regions to construct a calibrated eustatic curve for the Bajocian through the Santonian. The study area is centrally located in the large Eurasian continental craton, and was covered by shallow seas during much of the Jurassic and Cretaceous. The geographic setting was a very low-gradient ramp that was repeatedly flooded and exposed. Analysis of stratal geometry of the region suggests tectonic stability throughout most of Mesozoic marine deposition. The paleogeography of the region led to extremely low rates of sediment influx. As a result, accommodation potential was limited and is interpreted to have been determined primarily by eustatic variations. The central part of the Russian latform thus provides a useful frame of reference for the quantification of eustatic variations throughout the Jurassic and Cretaceous. The biostratigraphy of the Russian platform provides the basis for reliably determining age and eustatic events. The Mesozoic section of the central part of the Russian platform is characterized by numerous hiatuses. In this study, we filled the sediment gaps left by unconformities in the central part of the Russian platform with data from stratigraphic information from the more continuous stratigraphy of the neighboring subsiding regions, such as northern Siberia. Although these sections reflect subsidence, the time scale of variations in subsidence rate is probably long relative to the duration of the stratigraphic gaps to be filled, so the subsidence rate can be calculated and filtered from the stratigraphic data. We thus have compiled a more complete eustatic curve than would be p ssible on the basis of Russian platform stratigraphy alone. Relative sea level curves were generated by backstripping stratigraphic data from well and outcrop sections distributed throughout the central part of the Russian platform. For determining paleowater depth, we developed a model specifically designed for this region based on paleoecology, sedimentology, geochemistry, and paleogeography. The curve describes a series of high-frequency eustatic events superimposed on longer term trends. Many of the events identified from our study can be correlated to those found by Haq et al. (1988) and other sea level studies from other parts of the world, but there are significant differences in the relative magnitudes of events. Because the eustatic curve resulting from this study is based on a stable reference frame, the curve can be used in sedimentary basin modeling and as a tool for quantifying subsidence history from the stratigraphy of passive margins, basins, and other active regions.

An ontogenetic model for the sensorimotor organization of balance control in humans

On the basis of a review of the literature including the authors' own experimental studies, a model for the ontogenesis of balance control in children was developed. This qualitative ontogenetic model has to do with the equilibrium strategies built up by children in situations which are difficult but within the scope of their abilities. The model involves two functional principles. First: The stable reference frame on which the balance control is based can be either the support on which the subject is standing or the vertical gravity. When the frame of reference is the support surface, balance control is temporally organized either from the feet to the head (posture) or from the hip to the head (locomotion) (ascending organization). When the frame of reference is the vertical gravity, balance control is temporally organized from the head to the feet (descending organization). Secondly: Children gradually become able to master the various degrees of freedom which have to be controlled simultaneously during movement. For example, the head can be stabilized either on the trunk with the neck structures blocked (the en bloc mode of operation) or in space with the neck structures loose (the articulated mode). Four main periods can be said to occur during the human life span. The first extends from birth up to the acquisition of the upright stance. This period is characterized by the development of postural responses along a cephalocaudal gradient. This chronological cephalocaudal progression with age of the ability to control several body segments may correspond to a descending temporal organization of unperturbed postural control, associated with an articulated operation of the head-trunk unit. The second period takes place from the acquisition of the upright stance up to around the age of 6. During this period, our experimental results are consistent with an ascending organization of balance control, from the feet to the head in postural stance and from the hips to the head in locomotion. This ascending organization is associated with an en bloc mode of head-trunk operation, which serves to minimize the degrees of freedom. The third period begins at around the age of 7 and continues up to an upper age-limit which is as yet unknown. It is characterized by the return to an articulated mode of head—trunk operation, whereby the head stabilization necessary for the descending temporal organization of balance control is ensured. Lastly, the fourth period, which is reached during adulthood, combines the main features of the third period with a new skill involving the articulated operation of the head-trunk unit along with a selective control of the degrees of freedom at the neck level.

AN INDIRECT INTERFERENTIAL METHOD FOR MEASURING THE DEFORMATIONS OF STRUCTURES IN TEMPERATURE

The dimensional stability of a base of ceramic glass, designed to constitute a stable reference frame, has been determined with interferometric measurements in flowing air with variable temperature. An interferometric arrangement composed by one beam splitter and two mirrors was assembled directly on the base. The irradiance I(t) as a function of temperature at constant pressure was collected in the highest order of the interference pattern, I(t) shows a cyclic behavior, due to the superposition of the air refractivity variations and of the mechanical stretching of the frame. The component of the signal due to the air refractivity alone can be regarded as the reference signal, with a valuable periodicity in the inverse-temperature space, i.e. in the expansion coefficients space. The remaining component corresponding to the deformations of the supporting structure can be evaluated as a phase modulation of the reference signal. Preliminary results of measurements show that an equivalent thermal expansion coefficient of the order of magnitude of ±2·10–8 °C–1 can be probed. The theoretical and actual resolving power of the method, the unavoidable effects due to the presence of air, and some algorithms useful for noise reduction are discussed.

A neural network model of sensoritopic maps with predictive short-term memory properties.

Coordinated orienting movements can be accurately performed without direct sensory control. Ocular saccades, for instance, have been shown to be reprogrammed after target disappearance when an intervening eye movement is electrically triggered before the saccade onset. Saccadic eye movements can also be executed toward memorized targets, even when the subject has been passively moved in darkness. Two hypotheses have been proposed to account for this goal-invariance property: either (i) the goal is reconstructed and memorized in the stable frame of reference linked to the environment ("allocentric, coordinates") or (ii) the goal is selected and memorized in the sensors-related maps ("egocentric coordinates") and is continuously updated by efferent copies of the motor commands. In this paper, we shall describe a formal neural network based on this second hypothesis. The results of the simulation show that target position can be memorized and accurately updated in a topologically ordered map, using a velocity-signal feedback. Moreover, this network has been submitted to a simple learning procedure by using the intermittent visual recurring afferent signal as the teaching signal. A similar mechanism could be involved in control of limb movement.

Eustatic sea-level curve based on a stable frame of reference: Preliminary results

Numerous errors have crept into previous ecstatic curves because they have relied on unstable reference frames such as passive margins. A stable frame of reference is found in the Russian platform and allows a eustatic curve to be constructed without the subsidence corrections needed for subsiding margins. The stability of the Russian platform is indicated by flat-lying Mesozoic-Cenozoic sedimentary strata that have remained undeformed and untilted since deposition. These strata are no thicker than 200 m throughout the Russian platform. Individual lithofacies are continuous over large distances, suggesting a very flat hypsometry in which facies types were particularly sensitive to changes in sea level. The tectonic stability of the Russian platform allows ecstatic curves to be constructed through two complementary methods. The first method, the results of which we present here, uses backstripping to calculate sea-level changes from stage to stage. The second method uses the elevation of former shoreline deposits to calculate the net sea-level change from a former sea level to present sea level. Preliminary results suggest an unsteady 110-m rise in sea level from Bajocian to Albian time.

The compartmentalization of the monkey and rat cerebellar cortex: zebrin I and cytochrome oxidase

The cerebellar cortex of mammals is composed of parasagittal zones that encompass the afferent inputs, the efferent corticonuclear and corticovestibular projections, and a number of intrinsic molecular markers. One such marker is the polypeptide antigen zebrin I that is recognized by monoclonal antibody (mab) Q113. In rodents, zebrin I immunocytochemistry reveals an array of parasagittal Purkinje cell compartments. In the present study, zebrin I has been used to reveal the molecular heterogeneity of the cerebellar cortex in the squirrel monkey ( Saimiri sciureus). As in rodents, zebrin I is Purkinje cell specific in the primate cerebellum and not all Purkinje cells are immunoreactive. Immunocytochemistry on frontal or horizontal sections reveals a system of bands of zebrin I + cells extending through the vermis of both anterior and posterior lobes. A midline (P1 +) band and two more lateral bands (P2 + and P3 +) are found in all lobules. The situation in the paravermis and hemispheres is similar, with alternating zebrin I + and zebrin I − compartments, but the complex lobulation obscures the precise band pattern: it seems probable that 4 additional bands are present in the hemispheres, as in rodents. Comparison of rat and monkey cerebellums suggests that the cortex has expanded in primates by the growth of the same individual bands found in rats rather than by the addition of supplementary compartments. The zebrin I compartmentalization revealed by using mab Q113 is reproducible from individual and thus provides a stable frame of reference that has been used to compare the different chemoarchitectonic patterns found in the cerebellar cortex. In the present study, the histochemical zonation of cytochrome oxidase (CO) is compared with the Purkinje cell compartmentalization revealed by zebrin I immunoreactivity in the rat and monkey cerebellar cortex. In the adult rat, the CO zonation is present in the molecular and granular layers and respects the same architectonic boundaries as zebrin I. The high CO-activity bands coincide with the zebrin I − and the CO-weak bands with the zebrin I + compartments. In contrast, in the cerebellar cortex of the squirrel monkey, the CO band pattern occurs predominantly in the granular layer. Nevertheless, there is still a precise correspondence to the zebrin I zonation. However, in the monkey the CO-rich bands coincide with the zebrin I + compartments and CO-weak bands with zebrin I − zones. The differential CO expression between Purkinje cell compartments is present in rat from birth, suggesting that it is a fundamental characteristic of the zebrin I phenotype and not a secondary response to patterns of use.