, 2011) To specifically manipulate L4 function, we replaced the

, 2011). To specifically manipulate L4 function, we replaced the Gal4 drivers with either half of the split-Gal4 system ( Luan et al., 2006) and obtained a splitL4-Gal4 line (L40980-VP16AD, L40987-Gal4DBD) that was expressed only in L4 and in no other neurons ( Figures 2J–2L).

To generate tools that would allow independent manipulations of L4 and other cell types using different binary expression systems, Crizotinib order we also replaced the Gal4 in the L4 drivers with two other transcription factors, LexA and QF ( Lai and Lee, 2006 and Potter et al., 2010). The L40987-LexA, L40987-QF, and L40980-QF lines recapitulated the expression pattern of their Gal4 progenitors ( Figures 2M–2O). L40987-QF was additionally expressed in trachea, which, however, did not interfere with our experiments. We first sought to determine the visual response properties of L4 (Figures 3A and 3B). We measured in vivo calcium signals from L4 terminals in medulla layers M2 and M4 (Figures 3B and 3C) using two-photon imaging of the genetically encoded calcium indicator TN-XXL ( Figures 3D–3G) ( Mank et al., 2008 and Reiff et al., 2010). When presented

with alternating increases and decreases in light intensity, the average ratiometric calcium signal of all cells decreased when the light was on and increased when the light was off, in both layers M2 OSI-906 mw and M4 ( Figure 3D and data not shown). This is consistent with L4 hyperpolarizing to brightening and depolarizing to darkening ( Douglass and Strausfeld, 1995). Very similar calcium signals were seen when either Gal4 or QF transcription factors were used to drive TN-XXL expression ( Figure 3D; see Experimental Procedures). Next we tested whether

L4 displays direction-selective responses to motion. In response to a narrow bright bar, moving on a dark background at 10°/s, L4 terminals responded with an initial decrease in calcium signal associated with the light increment when the bar reached their receptive field, followed by an increase in calcium signal Tolmetin as the bar left the receptive field (Figure 3E). Using bars that moved either horizontally or vertically, we found no signs of direction selectivity (Figure 3E). Similar results were obtained for bars moving at 20°/s and 50°/s (data not shown). To characterize the response properties of L4 under continuous, dynamic stimulation, we used a rapidly flickering, uniform-field stimulus with Gaussian distributed intensity changes. Using linear-filter estimation procedures, we extracted the temporal linear filter that best captured the calcium response as a function of time (Chichilnisky, 2001 and Sakai et al., 1988). This linear filter had a large negative lobe consistent with a sign inversion of the input contrast (Figure S3), results that are similar to those previously described for L2 (Clark et al., 2011).

Although speculative, given the likelihood that γ-8 inhibits the

Although speculative, given the likelihood that γ-8 inhibits the interaction of CNIH on GluA2 subunits, we believe that γ-8 may similarly inhibit CNIH interaction with GluA3. Previous studies, including our own, report little effect of CNIH overexpression on endogenous AMPARs. However, CNIHs clearly interact with AMPARs in heterologous cells and in neurons (Harmel et al., 2012; Shi et al., 2009; Schwenk et al., Idelalisib in vitro 2009; Kato et al., 2010a; Gill et al.,

2011, 2012). To test whether CNIHs have an important role in neurons but are expressed at saturating levels, we performed extensive analyses using genetic deletion and KD of CNIHs. Indeed, we found that deletion of CNIH-2/-3 causes a profound and selective reduction in AMPAR-eEPSC amplitude. selleck This is accompanied by faster decay of mEPSCs, faster deactivation and desensitization of glutamate-evoked currents from somatic patches, and compromised LTP induction. These results demonstrate a critical role for CNIHs in neuronal AMPAR regulation and are particularly fascinating given that the profound synaptic changes seen with the deletion of CNIH-2/-3 match those seen with the selective deletion of GluA1

(Lu et al., 2009). Because neurons lacking CNIH proteins look physiologically similar to neurons lacking GluA1, we hypothesized that removal of CNIH-2/-3 might have different effects in various AMPAR KO mice and therefore used these tools to probe CNIH-2 function. Knocking down CNIH-2 in hippocampal slices from GluA2 KO mice causes a profound reduction of AMPAR-eEPSCs, whereas knocking down CNIH-2 in slices from GluA1 KO mice has no effect, either on the amplitude or kinetics of AMPAR EPSCs. These physiological results support a selective action of CNIH-2/-3

on GluA1-containing receptors. We also found that CNIH-2 and GluA1 coimmunoprecipitate with GluA2 when using wild-type hippocampal no homogenates. However, in striking contrast, when using homogenates from GluA1 KO mice, CNIH-2 does not coimmunoprecipitate with GluA2. Furthermore, GluA2A3/γ-8 receptors, the most likely composition of the receptors remaining in neurons lacking GluA1 or CNIH-2/-3, are twice as fast as GluA1A2/γ-8 receptors. Thus, the 50% reduction in mEPSC decay observed in neurons lacking GluA1 and CNIH-2/-3 can be explained by the selective loss of synaptic GluA1-containing AMPARs. Why is the action of CNIH-2/-3 confined to the GluA1 subunit? Previous studies in heterologous systems have shown that CNIH-2 has significant effects on AMPARs containing and lacking GluA1 subunits (Schwenk et al., 2009). To address this seeming contradiction, we examined the interactions between CNIH-2 and γ-8, the most prevalent TARP in the hippocampus (Rouach et al., 2005), on the kinetics of AMPARs of defined subunit composition.

In this sentence the positions of “D1” and “D2” are reversed, an

In this sentence the positions of “D1” and “D2” are reversed, an error that has now been corrected in the article online. “
“An animal’s position in the local environment is monitored by a spectrum of functionally

specific cell types in the hippocampus and the adjacent parahippocampal areas, particularly the MEC. In the hippocampus, place cells fire selectively when the animal visits one or a few specific locations of the local environment (O’Keefe and Dostrovsky, 1971). In the MEC, grid cells fire at multiple locations that, for each cell, define a hexagonal grid that tessellates the entire space available to the animal (Hafting et al., 2005). Although the majority of cells in superficial MEC layers are grid cells (Sargolini et al., 2006), selleck products these cells intermingle with border cells, which fire whenever the animal comes close to one or several local geometric boundaries, such as the walls of the recording enclosure (Savelli et al., 2008 and Solstad et al., 2008). In layer III and deeper MEC layers, grid cells (Sargolini et al., 2006) also

mix with head direction cells, which fire only when the animal faces a given direction (Ranck, 1985 and Taube et al., 1990). The presence of multiple spatial cell types within the same brain system raises questions about their interrelationships. Place cells are probably generated from spatial inputs from the entorhinal cortex, the main cortical source of input to the hippocampus. The abundance of grid cells in the superficial layers Venetoclax research buy of MEC points to grid cells as a likely source for the place cell signal.

In several early models, place cell formation was explained by a Fourier mechanism in which periodic firing fields from grid cells with different grid spacing were linearly combined to generate single fields in hippocampal target neurons (O’Keefe and Burgess, 2005, Fuhs and Touretzky, 2006, McNaughton et al., 2006 and Solstad et al., 2006). This possibility has been challenged, however, by the observation that place cells mature faster than grid cells in young animals (Langston et al., 2010 and Wills et al., 2010). When rat pups until leave the nest for the first time at postnatal day 16 or 17 (P16–P17), many place cells already have sharply confined firing fields similar to those of adult animals. In contrast, grid cells are far from fully developed. Firing fields are irregular and variable in size and shape and although some spatial periodicity can be observed in some neurons, adult-like patterns do not appear until approximately 1.5 weeks later, near the age of 4 weeks. The lack of sharply confined grid outputs in the 2.5- to 4-week-old nervous system has raised the possibility that juvenile place cells receive spatial information from other functional cell populations, such as the border cells of the MEC.

, 2012 and Hille, 2001) Ion channel proteins form holes in membr

, 2012 and Hille, 2001). Ion channel proteins form holes in membranes that open and close in response to various chemical and electrical stimuli. These structures allow cells to tap into the energy stored selleck chemicals llc in transmembrane ionic gradients to generate the electrical signals that race through our nerves and muscles. In 1988, when Neuron launched, it published 21 papers devoted to some aspect of ion channel research in its first year. These covered topics spanning from basic channel biophysics to the behavior of channels in complex systems. In reflecting on the questions that motivated ion channel research 25 years ago, it is striking that the

spirit, if not the details, of the studies exemplified

in Neuron’s inaugural year mark many of the same questions that occupy the field today. These include: what is the physical nature of a channel ( Auld et al., 1988, Ballivet et al., 1988, Deneris et al., 1988, Levitan et al., 1988, Lotan et al., 1988, Rudy et al., 1988 and Timpe http://www.selleckchem.com/GSK-3.html et al., 1988)? How do ions and pharmacological tools interact with channel pores ( MacKinnon et al., 1988, Miller, 1988 and Miller et al., 1988)? Where are particular channels expressed ( Harris et al., 1988, Siegel, 1988, Wang et al., 1988, Wisden et al., 1988 and Wollner et al., 1988) and how is this regulated by development or electrical activity ( Goldman et al., 1988 and Hendry and Jones, 1988)? much How do channels respond to manipulations in diverse types of excitable cells ( Doerner and Alger, 1988, Haydon and Man-Son-Hing, 1988, Lechleiter et al., 1988, Lipscombe et al., 1988, Maricq and Korenbrot, 1988, Pfaffinger et al., 1988 and Yakel and Jackson, 1988)? At the silver anniversary of the journal, we reflect on how much the field has changed, how certain classes of questions persist, and highlight some key open questions that rest upon the major achievements

of the past quarter century but that still represent areas of great opportunity for discovery. The ion channel field is vast and it would take a book to do it justice. Great progress has been made in understanding how channels “gate” their pores. To capture some of this excitement in a short space, we focus on three areas of phenomenal advancement that frame key unaddressed problems: (1) the transformation from cartoon to three dimensions of our understanding of the molecular nature of channels, (2) a tale of one mechanism that is central to understanding neural signaling, voltage sensing, and (3) how the complicated, multicomponent protein complexes of channels are assembled and delivered to the right place in the cell. These basic issues permeate the biological functions of all ion channels and understanding such facets of channel biology remains critical for unraveling how channels operate in normal and disease states.

The ΔTsat shift was +180 ms (upward) for Grk1+/− responses compar

The ΔTsat shift was +180 ms (upward) for Grk1+/− responses compared to wild-type, and −250 ms (downward) for Grk1S561 responses. Assuming downstream signaling is the same in WT, Grk1+/−, and Grk1S561L rods, the lifetimes of R∗(τReff) can be calculated from these ΔTsat values ( Gross and Burns, 2010): equation(1) τReff=[1τE+(1τReff,wt−1τE)e−ΔTsat/τE]−1. Assuming the lifetime of R∗ in normal rods (τReff,wt) is 40 ms (Gross and Burns, 2010), the values

of τReff for Grk1+/− and Grk1S561L rods calculated with Equation 1 are 76 ms and 15 ms, respectively. Thus, modifying the expression level or catalytic activity of rhodopsin kinase tunes the effective lifetime of R∗ and the vertical offset of the Tsat relation, while the slower, G∗-E∗ deactivation governs the

slope of the relation. To examine the consequences this website of shorter and longer R∗ effective lifetimes for the SPR, we recorded the responses of Grk1+/− and Grk1S561L rods to very dim flashes and found little change in the amplitude of the SPR ( Figure 1C; Table 1). Grk1+/− rods with ∼2-fold longer effective R∗ lifetime (τReff = 76 ms versus 40 ms for WT rods) had only a modest, 23% increase in SPR amplitude. Rods expressing transgenic Grk1S561L, with a more than 2-fold shorter effective R∗ lifetime (τReff = 15 ms), had only a 24% decrease in SPR amplitude. Overall, while the effective R∗ lifetimes of the three genetic lines span a 5-fold range with ratios of about 1:2.7:5, the normalized average SPR amplitudes span a much smaller ABT-263 see more range, with ratios of 1:1.3:1.6. These results establish that SPR amplitude does not vary in proportion to R∗ lifetime. In principle, R∗ molecules with longer lifetimes should activate more PDE molecules on the disc membrane and result in larger decreases in cGMP, locally closing a greater fraction of CNG channels. Because the density of PDE is only about 150 holoenzymes per disc face (1:300 ratio to rhodopsin, Pentia et al., 2006), it is conceivable that the rate of G∗-E∗ production may decrease as available PDE

molecules are depleted by longer-lived R∗ molecules. Thus, we calculated the average number of G∗-E∗ molecules active during the SPR and compared this to the total number of PDE molecules on the disc (see Experimental Procedures). Assuming a maximal rate of 300 s−1 for R∗ activation of the G protein (Leskov et al., 2000; Heck and Hofmann, 2001) and our measured R∗ and G∗-E∗ lifetimes, only ∼7 G∗-E∗ complexes are predicted at the peak of the SPR in normal rods (τReff = 40 ms). For Grk1+/− rods (τReff = 76 ms), the maximum number of G∗-E∗ units active during the SPR is only ∼10 (7% of the total number; Figure 2A, dashed line plotted against righthand ordinate). Thus, even if the maximal rate of G protein activation is 2-fold higher than current estimates, PDE depletion makes negligible contribution to the SPR amplitude stability over the range of R∗ lifetimes extending well beyond 76 ms.

sets a first milestone for future studies of the ontogeny of func

sets a first milestone for future studies of the ontogeny of functional connectivity and crosstalk between the HC and PFC. The fact that SB-type Screening Library manufacturer events are present in primary sensory areas as well as in the PFC suggests that the mechanisms underlying discontinuous

neonatal activity patterns are highly conserved among distinct cortical areas and in different species, including humans. In rats, the discontinuous events are seen during early postnatal development, whereas in humans they occur during the second and third trimesters of gestation, as indicated by work on preterm babies (Dreyfus-Brisac, 1962 and Vanhatalo et al., 2002). This fits well with what is known regarding cross-species calibration of developmental stage between the rodent and human cortex. Hence, information on the generation and properties of the

early events gained in animal experiments is likely to be useful in the interpretation and clinical assessment of the preterm EEG. Here, it is worth noting that oscillations within classical EEG frequency bands do not imply anything regarding their mechanisms of generation. Thus, it remains to be seen to what extent, for instance, early gamma-band activity bears similarities to gamma oscillations in the adult cortex. Brockmann et al. propose that the oscillatory drive from the HC to the PFC facilitates the morphological and functional development of the PFC and enables the refinement Capmatinib in vitro of the behaviorally relevant communication scaffold between the two areas. These speculations are consistent

with what is generally thought about activity-dependent plasticity in the developing cortex. However, direct experimental demonstration of an instructive role for early HC activity in the refinement of PFC connectivity will require further work with specific manipulations of spatiotemporal network patterns without gross alterations Metalloexopeptidase of firing at the single-neuron level (Xu et al., 2011). A point worth raising here is that the discontinuous activity patterns seen in the developing cortex may have multiple roles, in addition to their (as-yet to-be-proven) effects on neuronal wiring. Interestingly, recent work has suggested that in rats and preterm babies, the weak retinal output is amplified by SB-like network events in the visual cortex, enabling an early form of vision before eye opening in rats and before birth in humans (Colonnese et al., 2010). The HC-PFC circuitry is most likely not immediately involved in overt behavior or sensory processing in the neonate rat, as also concluded by Brockmann et al. However, the possibility remains that even during sleep, the HC-PFC activity has preadaptive, “anticipatory” functions—analogous to the one described above for the visual system—which serve to harmonize brain development with regard to future conditions (Hinde, 1970).

Within the context of a role for this region in model-based compu

Within the context of a role for this region in model-based computations, the findings by Nicolle et al. starkly demonstrate just how flexible the value computations in this region are: not only does vmPFC reflect valuation based on one’s own preferences when those are needed to guide choice, but the same region can also reflect the preferences of another person when those preferences

are relevant to the choice process. In addition to the valuation signals noted in vmPFC, Nicolle et al. also report a striking pattern of value-related BOLD activation in dmPFC. Specifically, on trials in which the subjects made choices on behalf of their partners, dmPFC responded to the difference in the self value for the two available prizes, while in trials in which subjects chose for themselves, dmPFC responded to the difference in their partner selleck products values. It is interesting to note that the self- versus other-oriented distinction was not reflected in the neural activations in either dmPFC or vmPFC. That is, although one value signal reflected the subjects’ own preferences for discounting and the other, arguably more social, value

Selleckchem ABT-263 signal reflected the preferences subjects attributed to their partners, each was encoded in vmPFC when relevant for choice and in dmPFC when it was not. The pattern of dmPFC activations is particularly surprising in this regard, given the role commonly attributed found to the region in supporting social cognition (Amodio and Frith, 2006). In particular, the ability to “mentalize,” or to attribute intentions, beliefs, and other mental states to other agents is consistently associated with activation of this region across fMRI and PET studies (Frith and Frith, 2003). However, the present results suggest that anterior dmPFC in the present task may not necessarily be “social” at all, but instead might facilitate the simulation of signals that are currently not relevant for choice, regardless of whether those signals correspond to representations about the

self or another person. Such an interpretation conforms to theories of dmPFC function that claim that its critical role lies in the creation of representations of the world that are decoupled from the sensory environment (Frith and Frith, 2003). Such a computational process could still underlie social inferences by allowing for the simulation of other agents, but importantly, its functional remit is not limited to social contexts, but rather to any situation in which simulation of events divorced from the sensory environment is required. The above-mentioned interpretation of the dmPFC findings raises an interesting question: Why are these value signals in dmPFC being computed in the first place? The presence of these activations is somewhat surprising in the task used by Nicolle et al., because the respective variables they represent are, at least superficially, irrelevant to the choice at hand.

For a given opsin gene, functional expression levels and the ligh

For a given opsin gene, functional expression levels and the light power density selleck chemicals llc reaching the expressing cells will together determine the efficacy of light-based control (Figure 3A). To estimate this density of light reaching the targeted cells one must consider the propagation of light in tissue. Light propagation in biological tissue can be modeled as a combination of absorption and scattering, with scattering playing an especially important role in mature

myelinated brain tissue (Vo-Dinh, 2003). The transmission properties of light through the brain also depend strongly on wavelength, with longer-wavelength light scattering less and therefore penetrating more deeply (Figure 3). We have taken several HKI-272 complementary approaches to measuring and estimating the depth of light propagation under typical experimental conditions, specifically for the illumination of deep brain structures using thin optical fibers. In one approach (Aravanis et al., 2007), an optical fiber emitting a known

light power was lowered into a block of unfixed brain tissue, and light power was measured on the underside of the block, giving a transmission fraction for the tissue sample (nontransmitted light was either absorbed by or reflected out of the sample). This measurement was repeated for a range of tissue thicknesses by stepping the fiber through the block. These data were fit with standard equations for the propagation of light in diffuse scattering media (Kubelka-Munk model; Vo-Dinh, 2003), in order to estimate parameters that could be used to predict depth of transmitted light power in other experimental configurations. To estimate the light power density at a given distance from the fiber tip, the beam was modeled as spreading conically within the tissue, with an angle determined by the optical properties of the fiber.

This model, while involving a number of unrealistic assumptions including that the sample is a homogeneous, ideal diffuser illuminated from one side with diffuse light, and that reflection PAK6 and absorption are constant over the thickness of the sample, nevertheless allowed a good fit to measured data (Figures 3B and 3C; Aravanis et al., 2007) when used to estimate light power density at progressively deeper sites. Next, to directly observe the lateral spatial extent of the illuminated region at various distances from the fiber, we repeated the experiments above with the block of brain tissue placed on a thin diffusing layer revealing the two-dimensional pattern of illumination at the bottom of the block; this screen was imaged from below as the fiber was lowered through either brain tissue, or saline solution, and the resulting images were stacked to create a three-dimensional volume (Figures 3D and 3E).

Local neurons, in contrast, fired low-amplitude Ca2+ spikes and d

Local neurons, in contrast, fired low-amplitude Ca2+ spikes and displayed spike frequency adaptation caused by Ca2+-dependent potassium currents. Fast GABA (LN-PN and LN-LN connections) and nicotinic cholinergic synaptic currents (PN-LN connections) were modeled by first order activation schemes. The equations for all intrinsic and synaptic currents are given in the Supplemental Information and are based on Bazhenov et al., 2001a and Bazhenov et al., 2001b. In Figure 1, Figure 2 and Figure 3 we simulated isolated networks of LNs. The population of LNs and the specific

connectivity are shown in the respective figures. In the following figures we this website simulated networks including both excitatory PNs and inhibitory LNs. Drawing from the basic anatomy of the insect AL, the PNs received inputs from LNs and projected random connections back to LNs.

The AL model simulated in Figure 5 included 20 LNs and 100 PNs. LN-PN connections were determined such that each PN occupied a position on the grid in Figure 5. We tested the network with a larger population of LNs and PNs with random connectivity to obtain the same result (propagating waves of activity in the 2D plane). With random connections the population of PNs simulated did not cover all points on the 2D grid. However, the waves of activity could be clearly seen despite gaps in the grid of PNs. We also simulated a network with chromatic number three and were able to generate 2D wave-fronts that propagated along orthogonal directions. Intracellular recordings (Figure 1 and Figure 7) Oxymatrine selleck chemicals were made from local neurons in adult locusts (Schistocerca americana) obtained from a crowded colony. Animals were immobilized and stabilized with wax with one antenna secured. The brain was exposed, desheathed, and superfused with locust saline as previously described ( Laurent and Davidowitz, 1994). Intracellular electrodes were sharp glass micropipettes (O.D = 1.0 mm, Warner Instruments, 80–230 MΩ, Sutter P97 horizontal puller,

Sutter Instruments) and were filled with 0.5 M potassium acetate and 5% neurobiotin (Vector Laboratories). Data were digitally acquired (5 kHz sampling rate, LabView software and PCI-6602 DAQ and PCI- MIO-16E-4 hardware, National Instruments), stored on a PC hard drive, and analyzed off-line using MATLAB (The MathWorks, Inc.). Odor puffs were dilute grass volatiles delivered as described in Brown et al. (2005). This work was supported by grants from the US National Institute of Deafness and other Communication Disorders (C.A. and M.B.), the US National Institute of Neurological Disorders and Stroke (M.B.) and a US National Institute of Child Health and Human Development intramural award (M.S.). The authors would like to thank Professor Gilles Laurent for many stimulating discussions and insightful suggestions and Stacey Brown Daffron for providing examples of recordings from LNs made in vivo. C.

Parametric statistics were performed using ANOVA with genotype as

Parametric statistics were performed using ANOVA with genotype as a factor and significance was accepted at a p value lower selleck chemical than 0.05. We thank Drs. J. Elmquist, L. Gan, and C. Birchmeier for the Phox2bCre and Atoh1Cre mice, and Lbx1 antibody, respectively. We also thank V. Brandt for editorial input. This work was supported by American Heart Association SouthWest affiliate Predoctoral Fellowship

to W.H.H. (11PRE6080004); National Research Service Award to C.S.W. (NS066601); the Gene Expression and Microscopy Cores of the Baylor College of Medicine-Intellectual and Developmental Disabilities Research Center (HD24064); Cancer Prevention Research Institute of Texas to T.J.K. (RP110390); National selleck chemicals llc Heart, Lung, and Blood Institute to S.T. and P.A.G. (R01HL089742); and Howard Hughes Medical Institute to H.Y.Z. “
“Neurons are anatomically and functionally polarized cells that conduct nerve impulses in a vectorial fashion. Impulses are received by dendrites, propagated through the soma, and eventually transmitted by axons. To accomplish these specialized functions, the plasma membrane of each of these domains possesses a distinct set of transmembrane proteins, including receptors, channels, transporters, and adhesion

molecules (Horton and Ehlers, 2003; Lasiecka and Winckler, 2011). Although much has been learned about the signaling and cytoskeletal processes that contribute to the establishment of neuronal polarity (Arimura and Kaibuchi,

2005), the molecular mechanisms that underlie the biosynthetic sorting of transmembrane proteins to the different neuronal domains remain poorly understood (Horton and Ehlers, 2003; Lasiecka and Winckler, 2011). Polarized sorting probably involves recognition of specific determinants within the transmembrane proteins by molecular machinery that directs transport to different plasma membrane domains. Because sorting to the dendrites and soma often share a common mechanism, these compartments are jointly referred to as the “somatodendritic” domain (Horton and ADAMTS5 Ehlers, 2003; Lasiecka and Winckler, 2011). Dotti and Simons (1990) first demonstrated a correlation between sorting of transmembrane proteins to the somatodendritic and axonal domains of neurons and the basolateral and apical domains of polarized epithelial cells, respectively, suggesting that polarized sorting in these cell types has a similar underlying mechanism (Dotti and Simons, 1990). This correlation has held for many transmembrane proteins (Horton and Ehlers, 2003; Lasiecka and Winckler, 2011), although exceptions have also been reported (e.g., Silverman et al., 2005; Jareb and Banker, 1998).