@article{2732, abstract = {We consider a quantum particle moving in a harmonic exterior potential and linearly coupled to a heat bath of quantum oscillators. Caldeira and Leggett derived the Fokker Planck equation with friction for the Wigner distribution of the particle in the large-temperature limit: however, their (nonrigorous) derivation was not free of criticism, especially since the limiting equation is not of Lindblad form. In this paper we recover the correct form of their result in a rigorous way. We also point out that the source of the diffusion is physically restrictive under this scaling. We investigate the model at a fixed temperature and in the large-time limit, where the origin of the diffusion is a cumulative effect of many resonant collisions. We obtain a heat equation with a friction term for the radial process in phase space and we prove the Einstein relation in this case.}, author = {Castella, François and Erdös, László and Frommlet, Florian and Markowich, Peter}, issn = {0022-4715}, journal = {Journal of Statistical Physics}, number = {3-4}, pages = {543 -- 601}, publisher = {Springer}, title = {{Fokker-Planck equations as scaling limits of reversible quantum systems}}, doi = {10.1023/A:1018667323830}, volume = {100}, year = {2000}, } @article{2733, abstract = {The Li-Yau semiclassical lower bound for the sum of the first N eigenvalues of the Dirichlet–Laplacian is extended to Dirichlet–Laplacians with constant magnetic fields. Our method involves a new diamagnetic inequality for constant magnetic fields.}, author = {Erdös, László and Loss, Michael and Vougalter, Vitali}, issn = {0373-0956}, journal = {Annales de l'Institut Fourier}, number = {3}, pages = {891 -- 907}, publisher = {Association des Annales de l'Institut Fourier}, title = {{Diamagnetic behavior of sums Dirichlet eigenvalues}}, doi = {10.5802/aif.1777}, volume = {50}, year = {2000}, } @article{3149, abstract = {The prohormone convertases (PCs) are an evolutionarily ancient group of proteases required for the maturation of neuropeptide and peptide hormone precursors. In Drosophila melanogaster, the homolog of prohormone convertase 2, dPC2 (amontillado), is required for normal hatching behavior, and immunoblotting data indicate that flies express 80- and 75-kDa forms of this protein. Because mouse PC2 (mPC2) requires 7B2, a helper protein for productive maturation, we searched the fly data base for the 7B2 signature motif PPNPCP and identified an expressed sequence tag clone encoding the entire open reading frame for this protein. dPC2 and d7B2 cDNAs were subcloned into expression vectors for transfection into HEK-293 cells; mPC2 and rat 7B2 were used as controls. Although active mPC2 was detected in medium in the presence of either d7B2 or r7B2, dPC2 showed no proteolytic activity upon coexpression of either d7B2 or r7B2. Labeling experiments showed that dPC2 was synthesized but not secreted from HEK-293 cells. However, when dPC2 and either d7B2 or r7B2 were coexpressed in Drosophila S2 cells, abundant immunoreactive dPC2 was secreted into the medium, coincident with the appearance of PC2 activity. Expression and secretion of dPC2 enzyme activity thus appears to require insect cell-specific posttranslational processing events. The significant differences in the cell biology of the insect and mammalian enzymes, with 7B2 absolutely required for secretion of dPC2 and zymogen conversion occurring intracellularly in the case of dPC2 but not mPC2, support the idea that the Drosophila enzyme has specific requirements for maturation and secretion that can be met only in insect cells.}, author = {Hwang, Jae and Siekhaus, Daria E and Fuller, Robert and Taghert, Paul and Lindberg, Iris}, issn = {0021-9258}, journal = {Journal of Biological Chemistry}, number = {23}, pages = {17886 -- 17893}, publisher = {American Society for Biochemistry and Molecular Biology}, title = {{Interaction of Drosophila melanogaster prohormone convertase 2 and 7B2: Insect cell specific processing and secretion}}, doi = {10.1074/jbc.M000032200 }, volume = {275}, year = {2000}, } @article{11126, abstract = {Nuclear import of the two uracil-rich small nuclear ribonucleoprotein (U snRNP) components U1A and U2B′′ is mediated by unusually long and complex nuclear localization signals (NLSs). Here we investigate nuclear import of U1A and U2B′′ in vitro and demonstrate that it occurs by an active, saturable process. Several lines of evidence suggest that import of the two proteins occurs by an import mechanism different to those characterized previously. No cross competition is seen with a variety of previously studied NLSs. In contrast to import mediated by members of the importin-β family of nucleocytoplasmic transport receptors, U1A/U2B′′ import is not inhibited by either nonhydrolyzable guanosine triphosphate (GTP) analogues or by a mutant of the GTPase Ran that is incapable of GTP hydrolysis. Adenosine triphosphate is capable of supporting U1A and U2B′′ import, whereas neither nonhydrolyzable adenosine triphosphate analogues nor GTP can do so. U1A and U2B′′ import in vitro does not require the addition of soluble cytosolic proteins, but a factor or factors required for U1A and U2B′′ import remains tightly associated with the nuclear fraction of conventionally permeabilized cells. This activity can be solubilized in the presence of elevated MgCl2. These data suggest that U1A and U2B′′ import into the nucleus occurs by a hitherto uncharacterized mechanism.}, author = {HETZER, Martin W and Mattaj, Iain W.}, issn = {1540-8140}, journal = {Journal of Cell Biology}, keywords = {Cell Biology}, number = {2}, pages = {293--304}, publisher = {Rockefeller University Press}, title = {{An Atp-dependent, Ran-independent mechanism for nuclear import of the U1a and U2b′′ spliceosome proteins}}, doi = {10.1083/jcb.148.2.293}, volume = {148}, year = {2000}, } @article{11127, abstract = {Nuclear formation in Xenopus egg extracts requires cytosol and is inhibited by GTPγS, indicating a requirement for GTPase activity. Nuclear envelope (NE) vesicle fusion is extensively inhibited by GTPγS and two mutant forms of the Ran GTPase, Q69L and T24N. Depletion of either Ran or RCC1, the exchange factor for Ran, from the assembly reaction also inhibits this step of NE formation. Ran depletion can be complemented by the addition of Ran loaded with either GTP or GDP but not with GTPγS. RCC1 depletion is only complemented by RCC1 itself or by RanGTP. Thus, generation of RanGTP by RCC1 and GTP hydrolysis by Ran are both required for the extensive membrane fusion events that lead to NE formation.}, author = {HETZER, Martin W and Bilbao-Cortés, Daniel and Walther, Tobias C and Gruss, Oliver J and Mattaj, Iain W}, issn = {1097-2765}, journal = {Molecular Cell}, keywords = {Cell Biology, Molecular Biology}, number = {6}, pages = {1013--1024}, publisher = {Elsevier}, title = {{GTP hydrolysis by Ran is required for nuclear envelope assembly}}, doi = {10.1016/s1097-2765(00)80266-x}, volume = {5}, year = {2000}, } @article{11683, abstract = {The vertex connectivity κ of a graph is the smallest number of vertices whose deletion separates the graph or makes it trivial. We present the fastest known deterministic algorithm for finding the vertex connectivity and a corresponding separator. The time for a digraph having n vertices and m edges is O(min{κ3 + n, κn}m); for an undirected graph the term m can be replaced by κn. A randomized algorithm finds κ with error probability 1/2 in time O(nm). If the vertices have nonnegative weights the weighted vertex connectivity is found in time O(κ1nmlog(n2/m)) where κ1 ≤ m/n is the unweighted vertex connectivity or in expected time O(nmlog(n2/m)) with error probability 1/2. The main algorithm combines two previous vertex connectivity algorithms and a generalization of the preflow-push algorithm of Hao and Orlin (1994, J. Algorithms17, 424–446) that computes edge connectivity.}, author = {Henzinger, Monika H and Rao, Satish and Gabow, Harold N.}, issn = {0196-6774}, journal = {Journal of Algorithms}, keywords = {Computational Theory and Mathematics, Computational Mathematics, Control and Optimization}, number = {2}, pages = {222--250}, publisher = {Elsevier}, title = {{Computing vertex connectivity: New bounds from old techniques}}, doi = {10.1006/jagm.1999.1055}, volume = {34}, year = {2000}, } @article{11685, abstract = {We consider the problem of sampling URLs uniformly at random from the Web. A tool for sampling URLs uniformly can be used to estimate various properties of Web pages, such as the fraction of pages in various Internet domains or written in various languages. Moreover, uniform URL sampling can be used to determine the sizes of various search engines relative to the entire Web. In this paper, we consider sampling approaches based on random walks of the Web graph. In particular, we suggest ways of improving sampling based on random walks to make the samples closer to uniform. We suggest a natural test bed based on random graphs for testing the effectiveness of our procedures. We then use our sampling approach to estimate the distribution of pages over various Internet domains and to estimate the coverage of various search engine indexes.}, author = {Henzinger, Monika H and Heydon, Allan and Mitzenmacher, Michael and Najork, Marc}, issn = {1389-1286}, journal = {Computer Networks}, keywords = {URL sampling, Random walks, Internet domain distribution, Search engine size}, number = {1-6}, pages = {295--308}, publisher = {Elsevier}, title = {{On near-uniform URL sampling}}, doi = {10.1016/s1389-1286(00)00055-4}, volume = {33}, year = {2000}, } @article{11694, abstract = {We consider exploration problems where a robot has to construct a complete map of an unknown environment. We assume that the environment is modeled by a directed, strongly connected graph. The robot's task is to visit all nodes and edges of the graph using the minimum number R of edge traversals. Deng and Papadimitriou [Proceedings of the 31st Symposium on the Foundations of Computer Science, 1990, pp. 356-361] showed an upper bound for R ofd O(d)m and Koutsoupias (reported by Deng and Papadimitriou) gave a lower bound of Ω≠(d2m), where m is the number of edges in the graph and d is the minimum number of edges that have to be added to make the graph Eulerian. We give the 1rst subexponential algorithm for this exploration problem, which achieves an upper bound of dO(logd)m. We also show a matching lower bound of d≠(logd)m for our algorithm. Additionally, we give lower bounds of 2≠(d)m, respectively, d≠(logd)m for various other natural exploration algorithms.}, author = {Albers, Susanne and Henzinger, Monika H}, issn = {1095-7111}, journal = {SIAM Journal on Computing}, keywords = {directed graph, exploration algorithm}, location = {El Paso, TX, United States}, number = {4}, pages = {1164--1188}, publisher = {Society for Industrial and Applied Mathematics}, title = {{Exploring unknown environments}}, doi = {10.1137/s009753979732428x}, volume = {29}, year = {2000}, } @article{11770, abstract = {We compare several algorithms for identifying mirrored hosts on the World Wide Web. The algorithms operate on the basis of URL strings and linkage data: the type of information about Web pages easily available from Web proxies and crawlers. Identification of mirrored hosts can improve Web-based information retrieval in several ways: first, by identifying mirrored hosts, search engines can avoid storing and returning duplicate documents. Second, several new information retrieval techniques for the Web make inferences based on the explicit links among hypertext documents—mirroring perturbs their graph model and degrades performance. Third, mirroring information can be used to redirect users to alternate mirror sites to compensate for various failures, and can thus improve the performance of Web browsers and proxies. We evaluated four classes of “top-down” algorithms for detecting mirrored host pairs (that is, algorithms that are based on page attributes such as URL, IP address, and hyperlinks between pages, and not on the page content) on a collection of 140 million URLs (on 230,000 hosts) and their associated connectivity information. Our best approach is one which combines five algorithms and achieved a precision of 0.57 for a recall of 0.86 considering 100,000 ranked host pairs.}, author = {Bharat, Krishna and Broder, Andrei and Dean, Jeffrey and Henzinger, Monika H}, issn = {0002-8231}, journal = {Journal of the American Society for Information Science}, number = {12}, pages = {1114--1122}, publisher = {Wiley}, title = {{A comparison of techniques to find mirrored hosts on the WWW}}, doi = {10.1002/1097-4571(2000)9999:9999<::aid-asi1025>3.0.co;2-0}, volume = {51}, year = {2000}, } @inproceedings{11802, abstract = {In this paper we survey algorithmic aspects of Web information retrieval. As an example, we discuss ranking of search engine results using connectivity analysis.}, author = {Henzinger, Monika H}, booktitle = {8th Annual European Symposium on Algorithms}, isbn = {9783540410041}, issn = {1611-3349}, location = {Saarbrücken, Germany}, pages = {1–8}, publisher = {Springer Nature}, title = {{Web information retrieval - an algorithmic perspective}}, doi = {10.1007/3-540-45253-2_1}, volume = {1879}, year = {2000}, } @article{11893, abstract = {We present fully dynamic algorithms for maintaining the biconnected components in general and plane graphs. A fully dynamic algorithm maintains a graph during a sequence of insertions and deletions of edges or isolated vertices. Let m be the number of edges and n be the number of vertices in a graph. The time per operation of the best deterministic algorithms is 𝑂(𝑛√) in general graphs and O(log n) in plane graphs for fully dynamic connectivity and O(min m2/3 ,n}) in general graphs and 𝑂(𝑛√) in plane graphs for fully dynamic biconnectivity. We improve the later running times to 𝑂(𝑚log𝑛‾‾‾‾‾‾‾√) in general graphs and O(log 2n ) in plane graphs. Our algorithm for general graphscan also find the biconnected components of all vertices in time O(n).}, author = {Henzinger, Monika H}, issn = {1095-7111}, journal = {SIAM Journal on Computing}, number = {6}, pages = {1761--1815}, publisher = {Society for Industrial & Applied Mathematics}, title = {{Improved data structures for fully dynamic biconnectivity}}, doi = {10.1137/s0097539794263907}, volume = {29}, year = {2000}, } @article{8526, author = {Kaloshin, Vadim}, issn = {0003-486X}, journal = {The Annals of Mathematics}, keywords = {Statistics, Probability and Uncertainty, Statistics and Probability}, number = {2}, pages = {729--741}, publisher = {JSTOR}, title = {{An extension of the Artin-Mazur theorem}}, doi = {10.2307/121093}, volume = {150}, year = {1999}, } @article{883, abstract = {Sympatric speciation, the origin of two or more species from a single local population, has almost certainly been involved in formation of several species flocks, and may be fairly common in nature. The most straightforward scenario for sympatric speciation requires disruptive selection favouring two substantially different phenotypes, and consists of the evolution of reproductive isolation between them followed by the elimination of all intermediate phenotypes. Here we use the hypergeometric phenotypic model to show that sympatric speciation is possible even when fitness and mate choice depend on different quantitative traits, so that speciation must involve formation of covariance between these traits. The increase in the number of variable loci affecting fitness facilitates sympatric speciation, whereas the increase in the number of variable loci affecting mate choice has the opposite effect. These predictions may enable more cases of sympatric speciation to be identified.}, author = {Kondrashov, Alexey and Kondrashov, Fyodor}, issn = {0028-0836}, journal = {Nature}, number = {6742}, pages = {351 -- 354}, publisher = {Nature Publishing Group}, title = {{Interactions among quantitative traits in the course of sympatric speciation}}, doi = {10.1038/22514}, volume = {400}, year = {1999}, } @article{3444, abstract = {This study examined intermittent, high-frequency (100-200 Hz) oscillatory patterns in the CA1 region of the hippocampus in the absence of theta activity, i.e., during and in between sharp wave (SPW) bursts. Pyramidal and interneuronal activity was phase-locked not only to large amplitude (>7 SD from baseline) oscillatory events, which are present mainly during SPWs, but to smaller amplitude (<4 SD) patterns, as well. Large-amplitude events were in the 140-200 Hz, "ripple" frequency range. Lower-amplitude events, however, contained slower, 100-130 Hz ("slow") oscillatory patterns. Fast ripple waves reversed just below the CA1 pyramidal layer, whereas slow oscillatory potentials reversed in the stratum radiatum and/or in the stratum oriens. Parallel CA1-CA3 recordings revealed correlated CA3 field and unit activity to the slow CA1 waves but not to fast ripple waves. These findings suggest that fast ripples emerge in the CA1 region, whereas slow (100-130 Hz) oscillatory patterns are generated in the CA3 region and transferred to the CA1 field.}, author = {Csicsvari, Jozsef L and Hirase, Hajima and Czurkó, András and Mamiya, Akira and Buzsáki, György}, issn = {0270-6474}, journal = {Journal of Neuroscience}, number = {16}, publisher = {Society for Neuroscience}, title = {{Fast network oscillations in the hippocampal CA1 region of the behaving rat}}, doi = {10.1523/JNEUROSCI.19-16-j0001.1999}, volume = {19}, year = {1999}, } @article{3445, abstract = {The medial septal region and the hippocampus are connected reciprocally via GABAergic neurons, but the physiological role of this loop is still not well understood. In an attempt to reveal the physiological effects of the hippocamposeptal GABAergic projection, we cross-correlated hippocampal sharp wave (SPW) ripples or theta activity and extracellular units recorded in the medial septum and diagonal band of Broca (MSDB) in freely moving rats. The majority of single MSDB cells (60%) were significantly suppressed during SPWs. Most cells inhibited during SPW (80%) fired rhythmically and phase-locked to the negative peak of the CA1 pyramidal layer theta waves. Because both SPW and the negative peak of local theta waves correspond to the maximum discharge probability of CA1 pyramidal cells and interneuron classes, the findings indicate that the activity of medial septal neurons can be negatively (during SPW) or positively (during theta waves) correlated with the activity of hippocampal interneurons. We hypothesize that the functional coupling between medial septal neurons and hippocampal interneurons varies in a state-dependent manner.}, author = {Dragoi, George and Carpi, Daniel and Recce, Michael and Csicsvari, Jozsef L and Buzsáki, György}, issn = {0270-6474}, journal = {Journal of Neuroscience}, number = {14}, pages = {6191 -- 6199}, publisher = {Society for Neuroscience}, title = {{Interactions between hippocampus and medial septum during sharp waves and theta oscillation in the behaving rat}}, doi = {10.1523/JNEUROSCI.19-14-06191.1999}, volume = {19}, year = {1999}, } @inbook{3456, abstract = {L-a-amino-3-hydroxy-5-methyl-4-isoxazolepropionate receptors (AMPARs) and N-methyl-D-aspartate receptors (NMDARs) are the two major types of postsynaptic glutamate receptors (GluRs) that mediate excitatory synaptic transmission in the mammalian central nervous system (CNS). Both AMPARs and NMDARs are multimeric proteins, probably tetramers, formed by a variety of molecularly distinct subunits. AMPARs can be assembled from four types of subunits, termed GIuR-A, -B, -C, and -D (or, in an alternative nomenclature, G1uR1, G1uR2, GluR3, and G1uR4). Additional molecular diversity of AMPARs is generated by alternative splicing of the flip-flop module and RNA editing at the Q/R and R/G site. NMDARs are heteromers primarily assembled from NR1 subunits and NR2A, B, C, or D subunits. Various splice variants have been identified for the NR1 subunit, and a new NR3 subunit has been discovered recently. Considering all combinatorial possibilities, the molecular diversity of glutamate-receptor channels is considerable (HOLLMANN, this volume).}, author = {Monyer, Hannah and Jonas, Peter M and Rossier, Jean}, booktitle = {Ionotropic Glutamate Receptors in the CNS}, editor = {Jonas, Peter M and Monyer, Hannah}, isbn = {9783642085390}, pages = {309 -- 339}, publisher = {Springer}, title = {{Molecular determinants controlling functional properties of AMPARs and NMDARs in the mammalian CNS}}, doi = {10.1007/978-3-662-08022-1_9}, volume = {141}, year = {1999}, } @inbook{3457, abstract = {Principal neurons and interneurons are the two main classes of cells in cortical neuronal networks. Principal neurons (granule cells or pyramidal neurons) have transregional axonal projections and release glutamate onto their postsynaptic target cells. In contrast, interneurons have local, but often extensive, axonal arborizations and use γ-aminobutyric acid (GABA) as a transmitter. Although interneurons represent only approximately 10% of the neuronal population, they control the electrical activity of the entire network (FREUND and BUZSÁKI 1996). Interneurons forming inhibitory synapses on the somata or axon initial segments of their postsynaptic target cells are thought to set the threshold of action potential initiation (MILES et al. 1996) and can synchronize the collective activities of large principal neuron ensembles (COBB et al. 1995). In contrast, interneurons establishing inhibitory synapses mainly on dendrites could suppress dendritic Na+ or Ca2+ spikes (BUZSÁKI et al. 1996; MILES et al. 1996) and, thus, regulate plasticity at glutamatergic synapses in the cortex (DAVIES et al.1991).}, author = {Geiger, Jörg and Roth, Arnd and Taskin, Birol and Jonas, Peter M}, booktitle = {Ionotropic Glutamate Receptors in the CNS}, editor = {Monyer, Hannah and Jonas, Peter M}, isbn = {9783642085390}, pages = {363 -- 398}, publisher = {Springer}, title = {{Glutamate-mediated synaptic excitation of cortical interneurons}}, doi = {10.1007/978-3-662-08022-1_11}, volume = {141}, year = {1999}, } @article{3515, abstract = {Oscillations in neuronal networks are assumed to serve various physiological functions, from coordination of motor patterns to perceptual binding of sensory information. Here, we describe an ultra-slow oscillation (0.025 Hz) in the hippocampus. Extracellular and intracellular activity was recorded from the CA1 and subicular regions in rats of the Wistar and Sprague-Dawley strains. anesthetized with urethane. in a subgroup of Wistar rats (23%), spontaneous afterdischarges (4.7 +/- 1.6 s) occurred regularly at 40.8 +/- 15.7 s. The afterdischarge was initiated by a fast increase of population synchrony (100-250 Hz oscillation; “tonic” phase), followed by large-amplitude rhythmic waves and associated action potentials at gamma and beta frequency (15-50 Hz; “clonic” phase). The afterdischarges were bilaterally synchronous and terminated relatively abruptly without post-ictal depression. Single-pulse stimulation of the commissural input could trigger afterdischarges, but only at times when they were about to occur. Commissural stimulation evoked inhibitory postsynaptic potentials in pyramidal cells. However, when the stimulus triggered an afterdischarge, the inhibitory postsynaptic potential was absent and the cells remained depolarized during most of the afterdischarge. Afterdischarges were not observed in the Sprague-Dawley rats. Long-term analysis of interneuronal activity in intact, drug-free rats also revealed periodic excitability changes in the hippocampal network at 0.025 Hz. These findings indicate the presence of an ultra-slow oscillation in the hippocampal formation. The ultra-slow clock induced afterdischarges in susceptible animals. We hypothesize that a transient failure of GABAergic inhibition in a subset of Wistar rats is responsible for the emergence of epileptiform patterns. (C) 1999 IBRO. Published by Elsevier Science Ltd.}, author = {Penttonen, Markku and Nurminen, Nina and Miettinen, Riitta and Sirviö, Jouni and Henze, Darrell and Csicsvari, Jozsef L and Buzsáki, György}, issn = {0306-4522}, journal = {Neuroscience}, number = {3}, pages = {735 -- 743}, publisher = {Elsevier}, title = {{Ultra-slow oscillation (0.025 Hz) triggers hippocampal afterdischarges in Wistar rats}}, doi = {10.1016/S0306-4522(99)00367-X}, volume = {94}, year = {1999}, } @article{3518, abstract = {Information in neuronal networks may be represented by the spatiotemporal patterns of spikes. Here we examined the temporal coordination of pyramidal cell spikes in the rat hippocampus during slow-wave sleep. In addition, rats were trained to run in a defined position in space (running wheel) to activate a selected group of pyramidal cells. A template-matching method and a joint probability map method were used for sequence search. Repeating spike sequences in excess of chance occurrence were examined by comparing the number of repeating sequences in the original spike trains and in surrogate trains after Monte Carlo shuffling of the spikes. Four different shuffling procedures were used to control for the population dynamics of hippocampal neurons. Repeating spike sequences in the recorded cell assemblies were present in both the awake and sleeping animal in excess of what might be predicted by random variations. Spike sequences observed during wheel running were “replayed” at a faster timescale during single sharp-wave bursts of slow-wave sleep. We hypothesize that the endogenously expressed spike sequences during sleep reflect reactivation of the circuitry modified by previous experience. Reactivation of acquired sequences may serve to consolidate information.}, author = {Nádasdy, Zoltán and Hirase, Hajima and Czurkó, András and Csicsvari, Jozsef L and Buzsáki, György}, issn = {0270-6474}, journal = {Journal of Neuroscience}, number = {21}, pages = {9497 -- 9507}, publisher = {Society for Neuroscience}, title = {{Replay and time compression of recurring spike sequences in the hippocampus}}, doi = {10.1523/JNEUROSCI.19-21-09497.1999}, volume = {19}, year = {1999}, } @article{3519, abstract = {In contrast to sensory cortical areas of the brain, the relevant physiological inputs to the hippocampus, leading to selective activation of pyramidal cells, are largely unknown. Pyramidal cells are thought to be phasically activated by spatial cues and a variety of sensory and motor stimuli. Here, we used a behavioural `space clamp' method, which involved the confinement of the actively running animal in a defined position in space (running wheel) and kept sensory inputs constant. Twelve percent of the recorded CA1 pyramidal cells were selectively active while the rat was running in the wheel. Cell firing was specific to the direction of running and disappeared after rotating the recording apparatus. The discharge frequency of pyramidal cells and interneurons was sustained as long as the rat ran continuously in the wheel. Furthermore, the discharge frequency of pyramidal cells and interneurons increased with increasing running velocity, even though the frequency of hippocampal theta waves remained constant. The discharge frequency of some `wheel-related' pyramidal cells could increase more than 10-fold between 10 and 100 cm/s, whereas the firing rate of `non-wheel' cells remained constantly low. We hypothesize that: (i) a necessary condition for place-specific discharge of hippocampal pyramidal cells is the presence of theta oscillation; and (ii) relevant stimuli can tonically and selectively activate hippocampal pyramidal cells as long as theta activity is present.}, author = {Czurkó, András and Hirase, Hajima and Csicsvari, Jozsef L and Buzsáki, György}, issn = {0953-816X}, journal = {European Journal of Neuroscience}, number = {1}, pages = {344 -- 352}, publisher = {Wiley-Blackwell}, title = {{Sustained activation of hippocampal pyramidal cells by ‘space clamping' in a running wheel}}, doi = {10.1046/j.1460-9568.1999.00446.x}, volume = {11}, year = {1999}, }