Showing papers by "University of Fribourg published in 1998"
TL;DR: Dopamine systems may have two functions, the phasic transmission of reward information and the tonic enabling of postsynaptic neurons.
Abstract: Schultz, Wolfram. Predictive reward signal of dopamine neurons. J. Neurophysiol. 80: 1–27, 1998. The effects of lesions, receptor blocking, electrical self-stimulation, and drugs of abuse suggest t...
3,962 citations
TL;DR: Dopamine neuron responses reflected the changes in reward prediction during individual learning episodes; dopamine neurons were activated by rewards during early trials, but activation was progressively reduced as performance was consolidated and rewards became more predictable.
Abstract: Many behaviors are affected by rewards, undergoing long-term changes when rewards are different than predicted but remaining unchanged when rewards occur exactly as predicted. The discrepancy between reward occurrence and reward prediction is termed an 'error in reward prediction'. Dopamine neurons in the substantia nigra and the ventral tegmental area are believed to be involved in reward-dependent behaviors. Consistent with this role, they are activated by rewards, and because they are activated more strongly by unpredicted than by predicted rewards they may play a role in learning. The present study investigated whether monkey dopamine neurons code an error in reward prediction during the course of learning. Dopamine neuron responses reflected the changes in reward prediction during individual learning episodes; dopamine neurons were activated by rewards during early trials, when errors were frequent and rewards unpredictable, but activation was progressively reduced as performance was consolidated and rewards became more predictable. These neurons were also activated when rewards occurred at unpredicted times and were depressed when rewards were omitted at the predicted times. Thus, dopamine neurons code errors in the prediction of both the occurrence and the time of rewards. In this respect, their responses resemble the teaching signals that have been employed in particularly efficient computational learning models.
1,083 citations
TL;DR: It is concluded that both the ethylene and jasmonate signaling pathways need to be triggered concomitantly, and not sequentially, to activate PDF1.2 upon pathogen infection.
Abstract: Activation of the plant defensin gene PDF1.2 in Arabidopsis by pathogens has been shown previously to be blocked in the ethylene response mutant ein2-1 and the jasmonate response mutant coi1-1. In this work, we have further investigated the interactions between the ethylene and jasmonate signal pathways for the induction of this defense response. Inoculation of wild-type Arabidopsis plants with the fungus Alternaria brassicicola led to a marked increase in production of jasmonic acid, and this response was not blocked in the ein2-1 mutant. Likewise, A. brassicicola infection caused stimulated emission of ethylene both in wild-type plants and in coi1-1 mutants. However, treatment of either ein2-1 or coi1-1 mutants with methyl jasmonate or ethylene did not induce PDF1.2, as it did in wild-type plants. We conclude from these experiments that both the ethylene and jasmonate signaling pathways need to be triggered concomitantly, and not sequentially, to activate PDF1.2 upon pathogen infection. In support of this idea, we observed a marked synergy between ethylene and methyl jasmonate for the induction of PDF1.2 in plants grown under sterile conditions. In contrast to the clear interdependence of the ethylene and jasmonate pathways for pathogen-induced activation of PDF1.2, functional ethylene and jasmonate signaling pathways are not required for growth responses induced by jasmonate and ethylene, respectively.
1,031 citations
TL;DR: It is shown that in cells transiently transfected with bax, Bax localizes to mitochondria and induces the release of cytochrome c, activation of caspase-3, membrane blebbing, nuclear fragmentation, and cell death, indicating that Bcl-2 can interfere with Bax killing downstream of and independently of cy tochrome c release.
Abstract: Following exposure of cells to stimuli that trigger programmed cell death (apoptosis), cytochrome c is rapidly released from mitochondria into the cytoplasm where it activates proteolytic molecules known as caspases that specifically cleave the amino-acid sequence DEVD and are crucial for the execution of apoptosis1,2,3,4 The protein Bcl-2 interferes with this activation of caspases by preventing the release of cytochrome c2,3,4 Here we study these molecular interactions during apoptosis induced by the protein Bax, a pro-apoptotic homologue of Bcl-2 (refs 5, 6) We show that in cells transiently transfected with bax, Bax localizes to mitochondria and induces the release of cytochrome c, activation of caspase-3, membrane blebbing, nuclear fragmentation, and cell death Caspase inibitors do not affect Bax-induced cytochrome c release but block caspase-3 activation and nuclear fragmentation Unexpectedly, Bcl-2 also fails to prevent Bax-induced cytochrome c release, although it co-localizes with Bax to mitochondria Cells overexpressing both Bcl-2 and Bax show no signs of caspase activation and survive with significant amounts of cytochrome c in the cytoplasm These findings indicate that Bcl-2 can interfere with Bax killing downstream of and independently of cytochrome c release
884 citations
TL;DR: The structure-function relationships delineating the activation process of class I PI3Ks involving various domains of adapter subunits, Ras, and interacting proteins are summarized and the role ofPI3K signaling in multicellular organisms is elucidated.
686 citations
TL;DR: This review traces the history of this enigmatic structure from its conception to the present time, brings to light the keen observational powers of morphologists at the turn of the century and reveals how their sagacious forethought anticipated current thinking on the role of perineuronal nets.
453 citations
TL;DR: Many of the behavior-related neurons investigated in the anterior striatum were influenced by an upcoming primary liquid reward and did not appear to code behavioral acts in a motivationally neutral manner.
Abstract: Hollerman, Jeffrey R., Leon Tremblay, and Wolfram Schultz. Influence of reward expectation on behavior-related neuronal activity in primate striatum. J. Neurophysiol. 80: 947–963, 1998. Rewards con...
395 citations
TL;DR: In this article, the authors investigated several properties of the minority game and gave an analytical expression of σ 2/N in the N ⪡ 2 M region. But they did not consider the influence of identical players on their gain and on the systems performance.
Abstract: We investigate further several properties of the minority game we have recently introduced. We explain the origin of the phase transition and give an analytical expression of σ2/N in the N ⪡ 2 M region. The ability of the players to learn a given payoff is also analyzed, and we show that the Darwinian evolution process tends to a self-organized state, in particular, the lifetime distribution is a power-law with exponent −2. Furthermore, we study the influence of identical players on their gain and on the systems performance. Finally, we show that large brains always take advantage of small brains.
383 citations
TL;DR: Two major signals emerge from PI3Kgamma: phosphoinositides that target PKB and protein phosphorylation that activates MAPK.
Abstract: Phosphoinositide 3-kinases (PI3Ks) activate protein kinase PKB (also termed Akt), and PI3Kgamma activated by heterotrimeric guanosine triphosphate-binding protein can stimulate mitogen-activated protein kinase (MAPK). Exchange of a putative lipid substrate-binding site generated PI3Kgamma proteins with altered or aborted lipid but retained protein kinase activity. Transiently expressed, PI3Kgamma hybrids exhibited wortmannin-sensitive activation of MAPK, whereas a catalytically inactive PI3Kgamma did not. Membrane-targeted PI3Kgamma constitutively produced phosphatidylinositol 3,4, 3,4,5-trisphosphate and activated PKB but not MAPK. Moreover, stimulation of MAPK in response to lysophosphatidic acid was blocked by catalytically inactive PI3Kgamma but not by hybrid PI3Kgammas. Thus, two major signals emerge from PI3Kgamma: phosphoinositides that target PKB and protein phosphorylation that activates MAPK.
332 citations
TL;DR: Different structures process reward information processed in different ways, whereas dopamine neurons emit a reward teaching signal without indicating the specific reward, striatal neurons adapt expectation activity to new reward situations, and orbitofrontal neurons process the specific nature of rewards.
322 citations
TL;DR: In this paper, the role played by various factors, such as distance, geometry, electronic nature of the bridging ligand, which control the occurrence of intercomponent electronic energy and electron transfer in dinuclear systems are discussed.
TL;DR: Investigating neuronal activity in the anterior striatum while monkeys repeatedly learned to associate new instruction stimuli with known behavioral reactions and reinforcers showed changes related to adaptations or reductions of expectations in new task situations and displayed activations that might serve to induce structural changes during learning.
Abstract: Tremblay, Leon, Jeffrey R. Hollerman, and Wolfram Schultz. Modifications of reward expectation-related neuronal activity during learning in primate striatum. J. Neurophysiol. 80: 964–977, 1998. Thi...
TL;DR: The neglect of free radicals over the past few years has been overcome, and they are no longer only considered as interesting reactive intermediates with limited synthetic potential, but also as opportunities for applications in catalysis.
Abstract: The neglect of free radicals over the past few years has been overcome, and they are no longer only considered as interesting reactive intermediates with limited synthetic potential. New opportunities are opened up by performing radical reactions in the presence of Lewis acids. Rate enhancement of radical addition to olefins as well as stereochemical control of such reactions can be achieved in a unique manner. Recent examples of enantioselective radical reactions and perspectives for applications in catalysis are discussed.
TL;DR: This study explored a neural network model that used a reward-prediction error signal strongly resembling dopamine responses for learning movement sequences and efficiently allowed the model to learn long sequences.
Abstract: Dopamine neurons appear to code an error in the prediction of reward. They are activated by unpredicted rewards, are not influenced by predicted rewards, and are depressed when a predicted reward is omitted. After conditioning, they respond to reward-predicting stimuli in a similar manner. With these characteristics, the dopamine response strongly resembles the predictive reinforcement teaching signal of neural network models implementing the temporal difference learning algorithm. This study explored a neural network model that used a reward-prediction error signal strongly resembling dopamine responses for learning movement sequences. A different stimulus was presented in each step of the sequence and required a different movement reaction, and reward occurred at the end of the correctly performed sequence. The dopamine-like predictive reinforcement signal efficiently allowed the model to learn long sequences. By contrast, learning with an unconditional reinforcement signal required synaptic eligibility traces of longer and biologically less-plausible durations for obtaining satisfactory performance. Thus, dopamine-like neuronal signals constitute excellent teaching signals for learning sequential behavior.
TL;DR: The results suggest that at least two dimensions of facial information contribute to a face's apparent distinctiveness, but that these sources of information are differentially affected by turning the face upside-down.
Abstract: Distinctiveness contributes strongly to the recognition and rejection of faces in memory tasks. In four experiments we examine the role played by local and relational information in the distinctiveness of upright and inverted faces. In all experiments subjects saw one of three versions of a face: original faces, which had been rated as average in distinctiveness in a previous study (Hancock, Burton, & Bruce, 1996), a more distinctive version in which local features had been changed (D-local), and a more distinctive version in which relational features had been changed (D-rel). An increase in distinctiveness was found for D-local and D-rel faces in Experiment 1 (complete faces) and 3 and 4 (face internals only) when the faces had to be rated in upright presentation, but the distinctiveness of the D-rel faces was reduced much more than that of the D-local versions when the ratings were given to the faces presented upside-down (Experiments 1 and 3). Recognition performance showed a similar pattern: presented...
TL;DR: In this article, the authors investigate band bending, electron affinity and work function of differently terminated, doped and oriented diamond surfaces by X-ray and ultraviolet photoelectron spectroscopy.
TL;DR: In this review the latest developments implicating salicylic acid as a signal molecule in systemic resistance are discussed and contrasted with new signalling pathways which, seemingly, are based on alternative mechanisms.
TL;DR: In this paper, a general approach to explain the Zipf's law of city distribution is presented, where the simplest interaction (pairwise) is assumed, individuals tend to form cities in agreement with the well-known statistics.
Abstract: We present a general approach to explain the Zipf's law of city distribution. If the simplest interaction (pairwise) is assumed, individuals tend to form cities in agreement with the well-known statistics.
TL;DR: It is shown that three cell types highly overexpressing functional Bcl‐2 displayed caspase‐3 activation and underwent apoptosis in response to infection with alphaviruses Semliki Forest and Sindbis as efficiently as vector control counterparts.
Abstract: Bcl-2 oncogene expression plays a role in the establishment of persistent viral infection by blocking virus-induced apoptosis. This might be achieved by preventing virus-induced activation of caspase-3, an IL-1beta-converting enzyme (ICE)-like cysteine protease that has been implicated in the death effector phase of apoptosis. Contrary to this model, we show that three cell types highly overexpressing functional Bcl-2 displayed caspase-3 activation and underwent apoptosis in response to infection with alphaviruses Semliki Forest and Sindbis as efficiently as vector control counterparts. In all three cell types, overexpressed 26 kDa Bcl-2 was cleaved into a 23 kDa protein. Antibody epitope mapping revealed that cleavage occurred at one or two target sites for caspases within the amino acid region YEWD31 (downward arrow) AGD34 (downward arrow) A, removing the N-terminal BH4 region known to be essential for the death-protective activity of Bcl-2. Preincubation of cells with the caspase inhibitor Z-VAD prevented Bcl-2 cleavage and partially restored the protective activity of Bcl-2 against virus-induced apoptosis. Moreover, a murine Bcl-2 mutant having Asp31, Asp34 and Asp36 substituted by Glu was resistant to proteolytic cleavage and abrogated apoptosis following virus infection. These findings indicate that alphaviruses can trigger a caspase-mediated inactivation of Bcl-2 in order to evade the death protection imposed by this survival factor.
TL;DR: This article developed a scale of language proficiency in the form of a "descriptor bank" using an item-banking methodology to develop a flexible scale of stand-alone criterion statements with known difficulty values.
Abstract: This paper reports results from a Swiss National Science Research Council project which aimed to develop a scale of language proficiency in the form of a ‘descriptor bank’. Up until now, most scales of language proficiency have been produced by appeal to intuition and to those scales which already exist rather than to theories of linguistic description or of measurement. The intention in this project was to use an item-banking methodology to develop a flexible scale of stand-alone criterion statements with known difficulty values.The project took place in two rounds: the first for English (1994), the second for French, German and English (1995). In each year pools of descriptors were produced by analysing available proficiency scales. Through workshops with representative teachers, the descriptors were then refined into stand-alone criterion statements considered to be clear, useful and relevant to the sectors concerned. Selected descriptors presented on questionnaires were then used by participating teac...
TL;DR: Data suggest a general mechanism exists where acute activation of the MAP kinase cascade promotes G1 progression/S phase entry and that chronic activation ofThe MAP Kinase cascade inhibits this process, and demonstrate that NGF can cause either acute/phasic or sustained activation ofthe MAP kinases cascade in different cell types.
Abstract: Bailie et al. [In Vitro Cell Dev. Biol. (1992) 28A, 621-624] reported that primary cultures of rat hepatocytes possess low affinity binding sites for nerve growth factor (NGF). NGF treatment of primary cultures of rat hepatocytes with a maximally effective concentration of NGF (20 ng/ml, 0.8 nM) caused acute phasic activation of Raf-1 and p42(MAPkinase), and a smaller sustained activation of B-Raf. The transient increase in Raf-1 and p42(MAPkinase) activity returned to baseline within approximately 30 min. NGF treatment of hepatocytes did not induce expression of cyclin dependent kinase (cdk) inhibitor proteins, but instead stimulated cdk2 activity and increased [3H]thymidine incorporation into DNA. In contrast to hepatocytes, NGF treatment of PC12 pheochromocytoma cells caused large sustained activations of B-Raf and p42(MAPkinase), and a lower phasic activation of Raf-1. The sustained activations of B-Raf and p42(MAPkinase) were for more than 5 h. Treatment of PC12 cells with NGF increased p21(Cip1/WAF-1) expression, reduced cdk2 activity and inhibited DNA synthesis, the opposite to the effects of NGF treatment of hepatocytes. However when p42(MAPkinase) was chronically activated in hepatocytes, via infection with an inducible oestrogen receptor-Raf-1 fusion protein, expression of p21(Cip-1/WAF1) and p16(INK4a) cdk inhibitor proteins increased, cdk2 activity decreased, and DNA synthesis decreased. Equally, treatment of hepatocytes with 50 mM ethanol elevated the basal activity of p42(MAPkinase) and temporally extended the ability of NGF treatment to activate p42(MAPkinase). Ethanol and NGF co-treatment increased expression of p21(Cip-1/WAF1) and p16(INK4a) cdk inhibitor proteins and decreased hepatocyte DNA synthesis. These data demonstrate that NGF can cause either acute/phasic or sustained activation of the MAP kinase cascade in different cell types. Acute activation of the MAP kinase cascade correlated with increased DNA synthesis. In contrast, sustained activation of the MAP kinase cascade correlated with increased expression of cdk inhibitor proteins, a reduction in cdk activity, and an inhibition of DNA synthesis. These data suggest a general mechanism exists where acute activation of the MAP kinase cascade promotes G1 progression/S phase entry and that chronic activation of the MAP kinase cascade inhibits this process.
TL;DR: A new statistical approach based on global typographical features is proposed to the widely neglected problem of font recognition that aims at the identification of the typeface, weight, slope and size of the text from an image block without any knowledge of the content of that text.
Abstract: A new statistical approach based on global typographical features is proposed to the widely neglected problem of font recognition. It aims at the identification of the typeface, weight, slope and size of the text from an image block without any knowledge of the content of that text. The recognition is based on a multivariate Bayesian classifier and operates on a given set of known fonts. The effectiveness of the adopted approach has been experimented on a set of 280 fonts. Font recognition accuracies of about 97 percent were reached on high-quality images. In addition, rates higher than 99.9 percent were obtained for weight and slope detection. Experiments have also shown the system robustness to document language and text content and its sensitivity to text length.
University of Fribourg1, CERN2, University of Ljubljana3, Boston University4, University of Liverpool5, University of the Mediterranean6, Delft University of Technology7, Royal Institute of Technology8, Paul Scherrer Institute9, University of Ioannina10, DSM11, Aristotle University of Thessaloniki12, University of Coimbra13, Centre national de la recherche scientifique14
TL;DR: The first observation of time-reversal symmetry violation through a comparison of the probabilities of K 0 transforming into K0 and K 0 into K 0 as a function of the neutral-kaon eigentime t was reported in this article.
TL;DR: In this paper, the authors discuss examples of transition metal complexes where MLCT, LMCT, MMCT, and exciton LCT transitions have been observed and discuss theoretical methods to assign configurations, i.e. comparison methods, exciton theory or quantum mechanical calculations, for selected examples.
TL;DR: Radiolabeling studies with untreated leaves showed that SA was synthesized from phenylalanine and that both cinnamic and benzoic acid were intermediates in the biosynthesis pathway, and the specific activity of SA was found to be lower when leaves were treated with AA than in control leaves.
Abstract: Spraying potato (Solanum tuberosum L.) leaves with arachidonic acid (AA) at 1500 μg mL−1 led to a rapid local synthesis of salicylic acid (SA) and accumulation of a SA conjugate, which was shown to be 2-O-β-glucopyranosylsalicylic acid. Radiolabeling studies with untreated leaves showed that SA was synthesized from phenylalanine and that both cinnamic and benzoic acid were intermediates in the biosynthesis pathway. Using radiolabeled phenylalanine as a precursor, the specific activity of SA was found to be lower when leaves were treated with AA than in control leaves. Similar results were obtained when leaves were fed with the labeled putative intermediates cinnamic acid and benzoic acid. Application of 2-aminoindan-2-phosphonic acid at 40 μm, an inhibitor of phenylalanine ammonia-lyase, prior to treatment with AA inhibited the local accumulation of SA. When the putative intermediates were applied to leaves in the presence of 2-aminoindan-2-phosphonic acid, about 40% of the expected accumulation of free SA was recovered, but the amount of the conjugate remained constant.
TL;DR: The data demonstrate that multiple agonists stimulate DNA synthesis in primary cultures of hepatocytes via a Ras/Rac1/Cdc42/SEK/JNK/c-Jun pathway and suggest that signaling by the JNK/stress-activated protein kinase cascade, rather than by the PI3 kinases cascade, plays the pivotal role in the ability of agonists to stimulateDNA synthesis inPrimary cultures of rat hepatocytes.
Abstract: The ability of signaling via the JNK (c-Jun NH2-terminal kinase)/stress-activated protein kinase cascade to stimulate or inhibit DNA synthesis in primary cultures of adult rat hepatocytes was exami...
TL;DR: It is concluded that the preserved functional capacity of manipulations with the hand opposite the early lesion can be essentially attributed to a cortical reorganization around the old lesion.
Abstract: Infant monkeys were subjected to unilateral lesions of the motor cortex (mainly its hand representation). After maturation, they showed normal use of the contralateral hand for global grip movements. However, as compared with the ipsilateral hand, precision grip tasks requiring relatively independent finger movements were performed with less dexterity, particularly if adjustments of the wrist position were necessary. The purpose of this study was to investigate mechanisms which may be responsible for the rather well, although not complete, preservation of manipulative behaviour of these adult monkeys. To this end, the hand representations were mapped bilaterally with intracortical microstimulation in the mature monkeys, and the dexterity of both hands assessed quantitatively in a precision grip task. The behavioural effects of reversible inactivations of the primary (M1) and supplementary (SMA) motor cortical areas were then tested. The following were found. (i) The hand contralateral to the lesion exhibited subtle but significant dexterity deficits, as compared with the ipsilateral hand; the deficit was essentially for complex movements requiring dissociation of the thumb-index finger pinch from the other digits, involving also an arm rotation. (ii) Reversible inactivation of the M1 hand representation in the intact hemisphere dramatically impaired dexterity of the opposite hand without affecting the ipsilateral hand (contralateral to the early lesion). (iii) A relatively complete hand representation was found to occupy a new territory, medial to the old lesion. (iv) The role of this new displaced representation was crucial for the preserved dexterity of the opposite hand, as evidenced by its functional inactivation. In contrast, inactivation of both SMA cortices did not interfere with the manipulative behaviour. It is thus concluded that the preserved functional capacity of manipulations with the hand opposite the early lesion can be essentially attributed to a cortical reorganization around the old lesion. Under the present experimental conditions, contributions from either the SMA or the intact M1 appear not to be crucial.
TL;DR: A nanoscale turbine wheel is an apt description of the structure of the enantiomerically pure helicate, which precipitates as PF6 salt on mixing dissolved AgPF6 with the ligand L2 (a bis-bidentate ligand comprising two condensed α-pinene/bipyridine units linked by a xylylene bridge).
Abstract: A nanoscale turbine wheel is an apt description of the structure of the enantiomerically pure helicate [Ag6 (L2)6 ]6+ (1), which precipitates as PF6 salt on mixing dissolved AgPF6 with the ligand L2 (a bis-bidentate ligand comprising two condensed α-pinene/bipyridine units linked by a xylylene bridge). The helicate has an outer diameter of about 3 nm and an inner diameter of 0.84 nm, and is a potential model for the study of stereospecific recognition processes.
TL;DR: The existence of short-lived proteins that may serve the role of caspase-independent effectors of apoptosis and attractive targets of the death-protective action of Bcl-2 are suggested.
TL;DR: In this paper, the authors characterized nine sections of the Lower Cretaceous of the French and Swiss Jura platform using eight universally applicable criteria (geometry, lateral extent, morphology, biological activity, mineralization, facies contrast, diagenetic contrast, and biostratigraphy).
Abstract: Discontinuities in sedimentation are commonly expressed as surfaces in outcrop sections and are due to rapid and substantial environmental changes. On shallow-marine carbonate platforms most such surfaces represent hiatuses below biostratigraphic resolution, and detailed analysis is necessary to identify and evaluate the environmental change involved. Surfaces in nine sections of the Lower Cretaceous of the French and Swiss Jura platform are characterized on the basis of eight universally applicable criteria (geometry, lateral extent, morphology, biological activity, mineralization, facies contrast, diagenetic contrast, and biostratigraphy). Nine different surface types are distinguished by their common features and environment of formation. All of them are related to environmental changes in the form of subaqueous erosion, subaerial exposure, subaqueous omission, or changes in texture and facies. The distribution of surface types in the studied sections shows that condensation and exposure-related surfaces tend to occur repetitively in certain intervals. Calibrated by biostratigraphy, these surface zones can be correlated across the platform from proximal to distal positions. In comparison with the global sequence-stratigraphic framework (Hardenbol et al. 1997) most exposure zones correlate with third-order sequence boundaries; condensation zones fall in between. In the studied sections, third-order eustatic sea-level drops appear to be represented rather by zones of small-scale discontinuities than by widespread and well-marked single sequence boundaries. This is explained by the superposition of high-frequency, low-amplitude sea-level fluctuations on a larger-scale sea-level trend under greenhouse conditions. The lateral extent of the surface zones varies through time and indicates important changes in platform morphology. Changes in local subsidence rate indicated by variable thicknesses of the deposits in comparison with second- and third-order sea-level trends suggest an evolution of the French Jura platform from a ramp-type morphology in the late Middle Berriasian to a flat-topped platform in the Late Berriasian. The Early Valanginian again is characterized by increased differential subsidence and well-marked platform morphology. This study demonstrates that: (1) small-scale and short-lived discontinuities can reflect large-scale variations of relative sea level; (2) on shallow platforms characterized by small topographic variations and lateral facies changes, third-order sequence-stratigraphic surfaces are not necessarily expressed by one widespread single surface, but by zones of surfaces indicating repeated environmental changes; surface zones can serve as an additional tool for correlation and interpretation of platform evolution; and (3) small-scale discontinuities form an integral part of the stratigraphic record and should receive the same attention as the sedimentary deposits they delimit.