C C A M Gielen

Radboud University Nijmegen, Nijmegen, Provincie Gelderland, Netherlands

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Publications (48)187.21 Total impact

  • Julian J Tramper, C C A M Gielen
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    ABSTRACT: In most visuomotor tasks in which subjects have to reach to visual targets or move the hand along a particular trajectory, eye movements have been shown to lead hand movements. Because the dynamics of vergence eye movements is different from that of smooth pursuit and saccades, we have investigated the lead time of gaze relative to the hand for the depth component (vergence) and in the frontal plane (smooth pursuit and saccades) in a tracking task and in a tracing task in which human subjects were instructed to move the finger along a 3D path. For tracking, gaze leads finger position on average by 28 ± 6 ms (mean ± SE) for the components in the frontal plane but lags finger position by 95 ± 39 ms for the depth dimension. For tracing, gaze leads finger position by 151 ± 36 ms for the depth dimension. For the frontal plane, the mean lead time of gaze relative to the hand is 287 ± 13 ms. However, we found that the lead time in the frontal plane was inversely related to the tangential velocity of finger. This inverse relation for movements in the frontal plane could be explained by assuming that gaze leads the finger by a constant distance of ∼ 2.6 cm (range of 1.5-3.6 cm across subjects).
    Journal of Neuroscience 05/2011; 31(21):7857-66. · 6.91 Impact Factor
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    ABSTRACT: Subjective accenting is a cognitive process in which identical auditory pulses at an isochronous rate turn into the percept of an accenting pattern. This process can be voluntarily controlled, making it a candidate for communication from human user to machine in a brain-computer interface (BCI) system. In this study we investigated whether subjective accenting is a feasible paradigm for BCI and how its time-structured nature can be exploited for optimal decoding from non-invasive EEG data. Ten subjects perceived and imagined different metric patterns (two-, three- and four-beat) superimposed on a steady metronome. With an offline classification paradigm, we classified imagined accented from non-accented beats on a single trial (0.5 s) level with an average accuracy of 60.4% over all subjects. We show that decoding of imagined accents is also possible with a classifier trained on perception data. Cyclic patterns of accents and non-accents were successfully decoded with a sequence classification algorithm. Classification performances were compared by means of bit rate. Performance in the best scenario translates into an average bit rate of 4.4 bits min(-1) over subjects, which makes subjective accenting a promising paradigm for an online auditory BCI.
    Journal of Neural Engineering 04/2011; 8(3):036002. · 3.28 Impact Factor
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    ABSTRACT: An auditory rhythm can be perceived as a sequence of accented (loud) and non-accented (soft) beats or it can be imagined. Subjective rhythmization refers to the induction of accenting patterns during the presentation of identical auditory pulses at an isochronous rate. It can be an automatic process, but it can also be voluntarily controlled. We investigated whether imagined accents can be decoded from brain signals on a single-trial basis, and if there is information shared between perception and imagery in the contrast of accents and non-accents. Ten subjects perceived and imagined three different metric patterns (two-, three-, and four-beat) superimposed on a steady metronome while electroencephalography (EEG) measurements were made. Shared information between perception and imagery EEG is investigated by means of principal component analysis and by means of single-trial classification. Classification of accented from non-accented beats was possible with an average accuracy of 70% for perception and 61% for imagery data. Cross-condition classification yielded significant performance above chance level for a classifier trained on perception and tested on imagery data (up to 66%), and vice versa (up to 60%). Results show that detection of imagined accents is possible and reveal similarity in brain signatures relevant to distinction of accents from non-accents in perception and imagery. Our results support the idea of shared mechanisms in perception and imagery for auditory processing. This is relevant for a number of clinical settings, most notably by elucidating the basic mechanisms of rhythmic auditory cuing paradigms, e.g. as used in motor rehabilitation or therapy for Parkinson's disease. As a novel Brain-Computer Interface (BCI) paradigm, our results imply a reduction of the necessary BCI training in healthy subjects and in patients.
    Clinical neurophysiology: official journal of the International Federation of Clinical Neurophysiology 02/2011; 122(8):1526-32. · 3.12 Impact Factor
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    ABSTRACT: Simultaneous tactile finger stimulation evokes transient ERP responses that are smaller than the linear summation of ERP responses to individual stimulation. Occlusion and lateral inhibition are two possible mechanisms responsible for this effect. The present study disentangles these two effects using steady-state somatosensory evoked potentials (SSSEP). Simultaneous stimulation on adjacent and distant finger pairs with the same and different stimulation frequencies are compared. The index finger (IF), middle finger (MF) and little finger (LF) were mechanically stimulated with a frequency of 18, 22 or 26Hz, respectively. Stimulation was applied for each finger separately, and for the IF (18Hz) in combination with either the MF or LF for 22 and 26Hz, respectively. A measure for interaction (IR) was calculated for the P60 component and the SSSEP amplitude. Significant interactions were found in both the P60 response and in the SSSEP response. Stimulation of adjacent finger combinations caused more interaction than distant finger combinations. No difference was found between stimulation of two fingers with the same or a different frequency. Our results indicate that lateral inhibition is mainly responsible for the interaction effect. These observations provide further insight in the mechanisms behind interaction between somatosensory inputs.
    Clinical neurophysiology: official journal of the International Federation of Clinical Neurophysiology 12/2010; 121(12):2090-6. · 3.12 Impact Factor
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    ABSTRACT: Normal rat kidney (NRK) fibroblasts have electrophysiological properties and intracellular calcium dynamics that are dependent upon their growth stage. In the present study we show that this differential behavior coincides with a differential calcium entry that can be either capacitative or non-capacitative. Confluent cells made quiescent by serum deprivation, which have a stable membrane potential near -70 mV and do not show spontaneous intracellular calcium oscillations, primarily exhibit the capacitative mechanism for calcium entry, also called store-operated calcium entry (SOCE). When the quiescent cells are grown to density-arrest in the presence of EGF as the sole polypeptide growth factor, these cells characteristically fire spontaneously repetitive calcium action potentials, which propagate throughout the whole monolayer and are accompanied by intracellular calcium transients. These density-arrested cells appear to exhibit in addition to SOCE also receptor-operated calcium entry (ROCE) as a mechanism for calcium entry. Furthermore we show that, in contrast to earlier studies, the employed SOCs and ROCs are permeable for both calcium and strontium ions. We examined the expression of the canonical transient receptor potential channels (Trpcs) that may be involved in SOCE and ROCE. We show that NRK fibroblasts express the genes encoding Trpc1, Trpc5 and Trpc6, and that the levels of their expression are dependent upon the growth stage of the cells. In addition we examined the growth stage dependent expression of the genes encoding Orai1 and Stim1, two proteins that have recently been shown to be involved in SOCE. Our results suggest that the differential expression of Trpc5, Trpc6, Orai1 and Stim1 in quiescent and density-arrested NRK fibroblasts is responsible for the difference in regulation of calcium entry between these cells. Finally, we show that inhibition or potentiation of SOCE and ROCE by pharmacological agents has profound effects on calcium dynamics in NRK fibroblasts.
    Cellular signalling 02/2010; 22(7):1044-53. · 4.09 Impact Factor
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    M Zeitler, A Daffertshofer, C C A M Gielen
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    ABSTRACT: We studied the dynamics of synchronization in asymmetrically coupled neural oscillators with time delay. Stability analysis revealed that symmetric excitatory coupling results in synchrony at multiple phase relations. Asymmetry yields two saddle-node bifurcations of the stable states when coupling is asymmetric. By contrast, with inhibitory coupling only in phase or antiphase is stable as long as coupling is symmetric. Otherwise, these stable states shift or even vanish. The reduced bistability range suggests the beneficial role of asymmetric coupling for reliable neural information transfer.
    Physical Review E 07/2009; 79(6 Pt 2):065203. · 2.31 Impact Factor
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    Constantinus C A M Gielen, Tjeerd M H Dijkstra, Irene J Roozen, Joke Welten
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    ABSTRACT: In this study we have investigated movements in three-dimensional space. Since most studies have investigated planar movements (like ellipses, cloverleaf shapes and "figure eights") we have compared two generalizations of the two-thirds power law to three dimensions. In particular we have tested whether the two-thirds power law could be best described by tangential velocity and curvature in a plane (compatible with the idea of planar segmentation) or whether tangential velocity and curvature should be calculated in three dimensions. We defined total curvature in three dimensions as the square root of the sum of curvature squared and torsion squared. The results demonstrate that most of the variance is explained by tangential velocity and total curvature. This indicates that all three orthogonal components of movements in 3D are equally important and that movements are truly 3D and do not reflect a concatenation of 2D planar movement segments. In addition, we have studied the coordination of eye and hand movements in 3D by measuring binocular eye movements while subjects move the finger along a curved path. The results show that the directional component and finger position almost superimpose when subjects track a target moving in 3D. However, the vergence component of gaze leads finger position by about 250msec. For drawing (tracing) the path of a visible 3D shape, the directional component of gaze leads finger position by about 225msec, and the vergence component leads finger position by about 400msec. These results are compatible with the idea that gaze leads hand position during drawing movement to assist prediction and planning of hand position in 3D space.
    Cortex 08/2008; 45(3):340-55. · 6.16 Impact Factor
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    ABSTRACT: We have investigated synchronization and propagation of calcium oscillations, mediated by gap junctional excitation transmission. For that purpose we used an experimentally based model of normal rat kidney (NRK) cells, electrically coupled in a one-dimensional configuration (linear strand). Fibroblasts such as NRK cells can form an excitable syncytium and generate spontaneous inositol 1,4,5-trisphosphate (IP(3))-mediated intracellular calcium waves, which may spread over a monolayer culture in a coordinated fashion. An intracellular calcium oscillation in a pacemaker cell causes a membrane depolarization from within that cell via calcium-activated chloride channels, leading to an L-type calcium channel-based action potential (AP) in that cell. This AP is then transmitted to the electrically connected neighbor cell, and the calcium inflow during that transmitted AP triggers a calcium wave in that neighbor cell by opening of IP(3) receptor channels, causing calcium-induced calcium release (CICR). In this way the calcium wave of the pacemaker cell is rapidly propagated by the electrically transmitted AP. Propagation of APs in a strand of cells depends on the number of terminal pacemaker cells, the L-type calcium conductance of the cells, and the electrical coupling between the cells. Our results show that the coupling between IP(3)-mediated calcium oscillations and AP firing provides a robust mechanism for fast propagation of activity across a network of cells, which is representative for many other cell types such as gastrointestinal cells, urethral cells, and pacemaker cells in the heart.
    AJP Cell Physiology 05/2008; 294(4):C917-30. · 3.71 Impact Factor
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    ABSTRACT: Cultures of normal rat kidney (NRK) fibroblasts may display spontaneous calcium action potentials which propagate throughout the cellular monolayer. Pacemaking activity of NRK cells was studied by patch clamp electrophysiology and vital calcium imaging, using a new experimental approach in which a ring was placed on the monolayer in order to physically separate pacemakers within or under the ring and follower cells outside the ring. Stimulation of cells inside the ring with IP(3)-generating hormones such as prostaglandin F(2alpha) (PGF(2alpha)) resulted in the induction of periodic action potentials outside the ring, which were abolished when the L-type calcium channel blocker nifedipine was added outside the ring, but not inside the ring. PGF(2alpha)-treated cells displayed asynchronous IP(3)-mediated calcium oscillations of variable frequency, while follower cells outside the ring showed synchronous calcium transients which coincided with the propagating action potential. Mathematical modelling indicated that addition of PGF(2alpha) inside the ring induced both a membrane potential gradient and an intracellular IP(3) gradient, both of which are essential for the induction of pacemaking activity under the ring. These data show that intercellular coupling between PGF(2alpha)-treated and non-treated cells is essential for the generation of a functional pacemaker area whereby synchronization of calcium oscillations occurs by activation of L-type calcium channels.
    Cell Calcium 04/2008; 44(5):429-40. · 4.33 Impact Factor
  • A. C. C. Coolen, C. C. A. M. Gielen
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    ABSTRACT: In this letter we consider the effect of random transmission delays on the dynamics of a fully connected neural network. We show that, if these delays are also present during a learning stage in which patterns are presented in succession, the network will be capable of regenerating this sequence of patterns. This capability does not depend on the actual distribution of the delays. For the condition where the pattern sequence has a nonzero correlation time we present an equation with which to compute the time-dependent overlap of the system state with the sequence.
    EPL (Europhysics Letters) 07/2007; 7(3):281. · 2.26 Impact Factor
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    ABSTRACT: Many cells reveal oscillatory behavior. Some cells reveal action-potential firing resulting from Hodgkin-Huxley (HH) type dynamics of ion channels in the cell membrane. Another type of oscillation relates to periodic inositol triphospate (IP3)-mediated calcium transients in the cytosol. In this study we present a bifurcation analysis of a cell with an excitable membrane and an IP3-mediated intracellular calcium oscillator. With IP3 concentration as a control parameter the model reveals a complex, rich spectrum of both stable and unstable solutions with hysteresis corresponding to experimental data. Our results reveal the emergence of complex behavior due to interactions between subcomponents with a relatively simple dynamical behavior.
    Physical Review Letters 04/2007; 98(9):098107. · 7.73 Impact Factor
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    ABSTRACT: Oscillatory activity of cells has been the topic of many studies. Oscillatory activity can be due to action potential firing corresponding to the well-known Hodgkin-Huxley (HH) type dynamics of ion-channels in the cell membrane or due to IP3-mediated calcium oscillations in the endoplasmic reticulum (ER) causing periodic oscillations of calcium transients in the cytosol. In this study we show that coupling of these two oscillatory mechanisms may reveal a complex, rich spectrum of both stable and unstable states of cells with hysteresis. The predicted bi-stability corresponds to experimentally observed states. This illustrates that the different behavior of cells is not the consequence of differentiation in cells with different properties, but rather reflects different states of a single cell type.
    02/2007;
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    ABSTRACT: ABSTRACT Stimuli that are presented with a constant frequency elicit responses in the brain that oscillate at that same frequency, also known as steady-state responses (SSRs). SSRs promise to be useful brain patterns for brain computer interfaces (BCI), because their amplitudes can be modulated by attention. However, signal-to-noise ratios are relatively low, and stronger brain signals are needed to increase performances. Previous research on crossmodal amplification has demonstrated that stimulation in one modality can amplify brain signals elicited by stimulation in another modality, thereby yielding stronger signals. To investigate the possibilities of crossmodal amplification for use in BCI- systems, an offline EEG experiment based on a frequency-tagging paradigm was carried out, with stimuli presented in three modality condition: an auditory, tactile and audio- tactile condition. Frequency tags were 20 and 28 Hz. Stimuli were either presented to one side of the body (passive perception condition) or to both sides, and the participant had to focus attention on one side of his body,(selective attention condition). To ensure attention, small time interruptions (phase shifts) were added to the streams, and the participant was instructed to count the number of interruptions at the attended side. Evoked power at the tagging frequencies was then used to make a comparison between
    01/2007;
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    ABSTRACT: Many cell types exhibit oscillatory activity, such as repetitive action potential firing due to the Hodgkin-Huxley dynamics of ion channels in the cell membrane or reveal intracellular inositol triphosphate (IP$_3$) mediated calcium oscillations (CaOs) by calcium-induced calcium release channels (IP$_3$-receptor) in the membrane of the endoplasmic reticulum (ER). The dynamics of the excitable membrane and that of the IP$_3$-mediated CaOs have been the subject of many studies. However, the interaction between the excitable cell membrane and IP$_3$-mediated CaOs, which are coupled by cytosolic calcium which affects the dynamics of both, has not been studied. This study for the first time applied stability analysis to investigate the dynamic behavior of a model, which includes both an excitable membrane and an intracellular IP$_3$-mediated calcium oscillator. Taking the IP$_3$ concentration as a control parameter, the model exhibits a novel rich spectrum of stable and unstable states with hysteresis. The four stable states of the model correspond in detail to previously reported growth-state dependent states of the membrane potential of normal rat kidney fibroblasts in cell culture. The hysteresis is most pronounced for experimentally observed parameter values of the model, suggesting a functional importance of hysteresis. This study shows that the four growth-dependent cell states may not reflect the behavior of cells that have differentiated into different cell types with different properties, but simply reflect four different states of a single cell type, that is characterized by a single model.
    08/2006;
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    ABSTRACT: This study tested the validity of the assumption that intrinsic kinematic constraints, such as Listing's law, can account for the geometric features of three-dimensional arm movements. In principle, if the arm joints follow a Listing's constraint, the hand paths may be predicted. Four individuals performed 'extended arm', 'radial', 'frontal plane', and 'random mixed' movements to visual targets to test Listing's law assumption. Three-dimensional rotation vectors of the upper arm and forearm were calculated from three-dimensional marker data. Data fitting techniques were used to test Donders' and Listing's laws. The coefficient values obtained from fitting rotation vectors to the surfaces described by a second-order equation were analyzed. The results showed that the coefficients that represent curvature and twist of the surfaces were often not significantly different from zero, particularly not during randomly mixed and extended arm movements. These coefficients for forearm rotations were larger compared to those for the upper arm segment rotations. The mean thickness of the rotation surfaces ranged between approximately 1.7 degrees and 4.7 degrees for the rotation vectors of the upper arm segment and approximately 2.6 degrees and 7.5 degrees for those of the forearm. During frontal plane movements, forearm rotations showed large twist scores while upper arm segment rotations showed large curvatures, although the thickness of the surfaces remained low. The curvatures, but not the thicknesses of the surfaces, were larger for large versus small amplitude radial movements. In conclusion, when examining the surfaces obtained for the different movement types, the rotation vectors may lie within manifolds that are anywhere between curved or twisted manifolds. However, a two-dimensional thick surface may roughly represent a global arm constraint. Our findings suggest that Listing's law is implemented for some types of arm movement, such as pointing to targets with the extended arm and during radial reaching movements.
    Experimental Brain Research 06/2006; 171(2):139-54. · 2.22 Impact Factor
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    Leigh A Mrotek, C C A M Gielen, Martha Flanders
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    ABSTRACT: Little is known about the manual tracking of targets that move in three dimensions. In the present study, human subjects followed, with the tip of a hand-held pen, a virtual target moving four times (period 5 s) around a novel, unseen path. Two basic types of target paths were used: a peanut-shaped Cassini ellipse and a quasi-spherical shape where four connected semicircles lay in orthogonal planes. The quasi-spherical shape was presented in three different sizes, and the Cassini shape was varied in spatial orientation and by folding it along one of the three bend axes. During the first cycle of Cassini shapes, the hand lagged behind the target by about 150 ms on average, which decreased to 100 ms during the last three cycles. Tracking performance gradually improved during the first 3 s of the first cycle and then stabilized. Tracking was especially good during the smooth, planar sections of the shapes, and time lag was significantly shorter when the tracking of a low-frequency component was compared to performance at a higher frequency (-88 ms at 0.2 Hz vs. -101 ms at 0.6 Hz). Even after the appropriate adjustment of the virtual target path to a virtual shape tracing condition, tracking in depth was poor compared to tracking in the frontal plane, resulting in a flattening of the hand path. In contrast to previous studies where target trajectories were linear or sinusoidal, these complex trajectories may have involved estimation of the overall shape, as well as prediction of target velocity.
    Experimental Brain Research 06/2006; 171(1):99-115. · 2.22 Impact Factor
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    D G Liebermann, A Biess, C C A M Gielen, T Flash
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    ABSTRACT: This study was aimed at examining the assumption that three-dimensional (3D) hand movements follow specific paths that are dictated by the operation of a Listing's law constraint at the intrinsic joint level of the arm. A kinematic model was used to simulate hand paths during 3D point-to-point movements. The model was based on the assumption that the shoulder obeys a 2D Listing's constraint and that rotations are about fixed single-axes. The elbow rotations were assumed to relate linearly to those of the shoulder. Both joints were assumed to rotate without reversals, and to start and end rotating simultaneously with zero initial and final velocities. Model predictions were compared to experimental observations made on four right-handed individuals that moved toward virtual objects in "extended arm", "radial", and "frontal plane" movement types. The results showed that the model was partially successful in accounting for the observed behavior. Best hand-path predictions were obtained for extended arm movements followed by radial ones. Frontal plane movements resulted in the largest discrepancies between the predicted and the observed paths. During such movements, the upper arm rotation vectors did not obey Listing's law and this may explain the observed discrepancies. For other movement types, small deviations from the predicted paths were observed which could be explained by the fact that single-axis rotations were not followed even though the rotation vectors remained within Listing's plane. Dynamic factors associated with movement execution, which were not taken into account in our purely kinematic approach, could also explain some of these small discrepancies. In conclusion, a kinematic model based on Listing's law can describe an intrinsic joint strategy for the control of arm orientation during pointing and reaching movements, but only in conditions in which the movements closely obey the Listing's plane assumption.
    Experimental Brain Research 06/2006; 171(2):155-73. · 2.22 Impact Factor
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    Martha Flanders, Leigh A Mrotek, C C A M Gielen
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    ABSTRACT: Arm and hand movements are generally controlled using a combination of sensory-based and memory-based guidance mechanisms. This study examined similarities and differences in visually-guided and memory-guided arm movements, and sought to determine as to what extent certain control principles apply to each type of movement. In particular, the 2/3 power law is a principle that appears to govern the formation of complex, curved hand trajectories; it specifies that the tangential velocity should be proportional to the radius of curvature raised to an exponent of 1/3. A virtual reality system was used to project complex target paths in three-dimensional (3D) space. Human subjects first tracked (with the tip of a handheld pen) a single target moving along an unseen path. The entire target path then became visible and the subject traced the shape. Finally, the target shape disappeared and the subject was to draw it, in the same 3D space, from memory. Most aspects of the movements (speed, path size, shape and arm postures) were very similar across the three conditions. However, subjects adhered to the 2/3 power law most closely in the tracing condition, when the entire target path was visible. Also, only within the tracing condition, there were significant differences in the value of the exponent depending on the size and the spatial orientation of the trajectory. In the tracking and drawing conditions, the exponent was greater than 1/3, indicating that subjects spent more time in areas of tight curvature. This may represent a strategy for learning and remembering the complex shape.
    Experimental Brain Research 06/2006; 171(1):116-28. · 2.22 Impact Factor
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    ABSTRACT: In many biological systems, cells display spontaneous calcium oscillations (CaOs) and repetitive action-potential firing. These phenomena have been described separately by models for intracellular inositol trisphosphate (IP3)-mediated CaOs and for plasma membrane excitability. In this study, we present an integrated model that combines an excitable membrane with an IP3-mediated intracellular calcium oscillator. The IP3 receptor is described as an endoplasmic reticulum (ER) calcium channel with open and close probabilities that depend on the cytoplasmic concentration of IP3 and Ca2+. We show that simply combining this ER model for intracellular CaOs with a model for membrane excitability of normal rat kidney (NRK) fibroblasts leads to instability of intracellular calcium dynamics. To ensure stable long-term periodic firing of action potentials and CaOs, it is essential to incorporate calcium transporters controlled by feedback of the ER store filling, for example, store-operated calcium channels in the plasma membrane. For low IP3 concentrations, our integrated NRK cell model is at rest at -70 mV. For higher IP3 concentrations, the CaOs become activated and trigger repetitive firing of action potentials. At high IP3 concentrations, the basal intracellular calcium concentration becomes elevated and the cell is depolarized near -20 mV. These predictions are in agreement with the different proliferative states of cultures of NRK fibroblasts. We postulate that the stabilizing role of calcium channels and/or other calcium transporters controlled by feedback from the ER store is essential for any cell in which calcium signaling by intracellular CaOs involves both ER and plasma membrane calcium fluxes.
    Biophysical Journal 01/2006; 89(6):3741-56. · 3.67 Impact Factor
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    ABSTRACT: Indirect evidence suggests that patients with Parkinson's disease (PD) have deficits not only in motor performance, but also in the processing of sensory information. We investigated the role of sensory information processing in PD patients with a broad range of disease severities and in a group of age-matched controls. Subjects were tested in two conditions: pointing to a remembered visual target in complete darkness (DARK) and in the presence of an illuminated frame with a light attached to the index finger (FRAME). Differences in pointing errors in these two conditions reflect the effect of visual feedback on pointing. PD patients showed significantly larger constant and variable errors than controls in the DARK and FRAME condition. The difference of the variable error in the FRAME and DARK condition decreased as a function of the severity of PD. This indicates that any deficits in the processing of proprioceptive information occur already at very mild symptoms of PD, and that deficits in the use of visual feedback develop progressively in later stages of the disease. These results provide a tool for early diagnosis of PD and shed new light on the functional role of the brain structures that are affected in PD.
    European Journal of Neuroscience 02/2005; 21(1):239-48. · 3.75 Impact Factor

Publication Stats

487 Citations
187.21 Total Impact Points

Institutions

  • 1994–2011
    • Radboud University Nijmegen
      • • Donders Institute for Brain, Cognition, and Behaviour
      • • Department of Biophysics
      Nijmegen, Provincie Gelderland, Netherlands
  • 2010
    • Sint Maartenskliniek
      Nymegen, Gelderland, Netherlands
  • 2007
    • Universiteit Utrecht
      • Division of Zoological Medicine
      Utrecht, Provincie Utrecht, Netherlands
  • 1996
    • Ruhr-Universität Bochum
      • Institut für Neuroinformatik
      Bochum, North Rhine-Westphalia, Germany