These pathways regulate aru, directly or indirectly, in opposite

These pathways regulate aru, directly or indirectly, in opposite ways: the Egfr/Erk pathway activates, whereas the PI3K/Akt pathway inhibits aru function. The Egfr/Erk, PI3K/Akt pathways, and aru all function during nervous system development to establish normal ethanol sensitivity. Like the PI3K/Akt pathway

( Martín-Peña et al., 2006, Knox et al., 2007 and Howlett et al., 2008), aru also regulates synapse number, a morphological phenotype that correlates with ethanol sensitivity. aru is required in the PDF-expressing circadian pacemaker neurons to reduce ethanol sensitivity. Social isolation, which reduces synapse number in PDF neurons Cell Cycle inhibitor ( Donlea et al., 2009), restores normal synapse number and ethanol sensitivity to aru mutants. Thus, subjecting an adult mutant fly to a simple environmental manipulation counteracts a developmental abnormality and restores normal behavior. To identify genes that regulate ethanol-induced sedation, we conducted an unbiased screen of approximately 1000 random P element insertion lines. The screen was conducted in the inebriometer, which measures ethanol-induced loss of postural control (Weber, 1988 and Moore et al., 1998). Line 8.128 displayed a robust increase in ethanol sensitivity, revealed by a decrease in mean elution time (MET) Tenofovir molecular weight ( Figure 1A). 8.128 flies were healthy, fertile,

and the gross morphology of their brains appeared normal ( Figure S1A, available online). Importantly, 8.128 flies had a normal rate of ethanol absorption indicating that their increased sensitivity was not due to altered ethanol pharmacokinetics ( Figure S1B). We used the loss-of-righting reflex (LORR) assay (Rothenfluh et al., 2006) to further characterize the

ethanol sensitivity phenotype of 8.128 flies. In this assay, the LORR is measured by direct observation of flies after intermittent disruption of their balance during exposure to a continuous stream of ethanol vapor; flies that fail to right themselves are scored as sedated. In this assay, like the inebriometer, the time for 50% of 8.128 flies to reach sedation (ST50) was significantly decreased Methisazone compared to wild-type control (w Berlin) ( Figures 1B and 1C). Thus, 8.128 flies showed increased ethanol sensitivity in two independent behavioral assays. Importantly, 8.128 flies have a normal righting reflex in the in the absence of ethanol and show normal baseline locomotor activity and startle-induced climbing ( Figure S1C, data not shown). A precise excision of the P element in 8.128 flies restored normal ethanol sensitivity ( Figure 1D), demonstrating that the P element insertion is responsible for the increased ethanol sensitivity of 8.128 flies. Inverse PCR, DNA sequencing, and database searches ( revealed that the P element in 8.128 flies is inserted in the 5′ region of the arouser gene (aru, CG4276; Figure 2A), which encodes a predicted adaptor protein containing PTB and SH3 domains ( Tocchetti et al., 2003).

In the first scenario, the efficacy to elicit a response pattern

In the first scenario, the efficacy to elicit a response pattern would be independent of the presence of the second component, whereas in the second scenario the switch would

be defined by the specific ratio of the two components making up the mixture. To test this hypothesis, we again identified local populations generating two response modes (n = 5, in 2 mice) and selected two basis sounds exciting each of the modes. We synthesized mixtures of the two basis sounds with seven equally spaced mixture ratios and the individual mixture components in isolation (i.e., one of the basis sounds faded to silence). We compared the patterns of response to the isolated components and to the mixtures and computed the corresponding clustered similarity matrices (Figures 5H and S5). The sound level at which the transition

occurred depended on the specific sound and the local population. Importantly, Everolimus in all cases we found sound levels where both components of the mixture in isolation elicited a reliable response. However, when both components are presented at the same time one of the two response modes appeared to be dominant and only one of the patterns was excited (Figure 5H). Hence, instead of an additive response, the local network falls in a highly Selleckchem mTOR inhibitor nonlinear manner in either one of the two response modes. This indicates that the choice of one mode or the other is a winner-take-all decision, which may result from competitive interactions between neuronal populations. Our observations show that local populations of the auditory cortex are constrained to few response modes which encode a small number of sound categories enclosing several sounds. This implies that local populations are highly limited in their capacity to discriminate a large number

of sounds. Yet at the level of the organism, sound discrimination does not show such constraints. How this apparent paradox could be resolved became evident when we probed various local populations within and across mice in several primary auditory fields (Figure 6A). In each case, the different local populations categorized different sets of sounds, suggesting that different local populations provide complementary information the to unambiguously encode a large number of sounds. To quantitatively assess this observation, we plotted response similarity matrices for a selection of 15 clearly distinct sounds (excluding mixtures and different sound levels; Figure 6B), in which the sound order is fixed (i.e., no clustering was performed; Figure 6C, top). In these plots, the sounds giving rise to a reliable response or being grouped in different modes differ from one population to the next. Thus, different populations are discriminating different sets of sounds.

Thus, this system will be generally applicable to analysis of mut

Thus, this system will be generally applicable to analysis of mutations in genes with a general neuronal action, for example FMRP, neuroligins, and MECP2. However, even for analysis of diseases that manifest in specific types of neurons, such as Parkinson’s disease, Ngn2 iN cells may be useful because in many neurological diseases the pathological processes are not restricted to the specfiic types of neurons in which the disease becomes manifest. Specifically, even if disease

such Ponatinib concentration as Parkinson’s or Huntington’s disease manifest in a dysfunction of dopaminergic or striatal neurons, respectively, this manifestation probably represents a particular vulnerability of specific types of neurons to a general disease process, and not a disease

process that is restricted to these types of neurons. Thus, even for such diseases it may not only be feasible, but actually be productive to examine Ngn2-generated iN cells as a homogeneous population of glutamatergic neurons, especially in coculture with mouse neurons or after transplantation into the mouse brain. H1 ESCs were obtained from WiCell Research Resources (Wicell, WI); the iPS#1 line was derived SCR7 in vitro from dermal fibroblasts of a Dystrophic epidermolysis bullosa patient carrying homozygous mutations in COL7A1, while the iPS#2 line was derived from dermal fibroblast of a sickle cell anemia patient and genetically corrected by homologous recombination ( Sebastiano et al., 2011). The type VII collagen gene is not expressed in neurons, patients with mutations have no brain phenotypes, and our study demonstrates that the mutation of this gene does not affect the molecular and functional properties of Ngn2-mediated iN cells. Both iPSC lines were generated from by infecting with a floxed polycistronic lentiviral reprogramming vector followed by Cre-mediated loop-out of the reprogramming factors ( Sommer et al., 2010). ESCs and iPSCs were maintained as feeder-free cells in mTeSR1 medium

(Stem Cell Technologies; Xu et al., 2010). Mouse glial cells were cultured from the forebrain of newborn wild-type CD1 mice ( Franke et al., 1998). Briefly, newborn mouse forebrain homogenates were digested with papain and EDTA for 30 min, cells were dissociated by harsh trituration to avoid growing of neurons, and plated onto T75 flasks in DMEM supplemented with 10% FBS. Upon reaching confluence, glial cells were trypsinized and replated at lower density a total of three times to remove potential trace amounts of mouse neurons before the glia cell cultures were used for coculture experiment with iN cells. Mouse cortical neurons were cultured as described ( Pang et al., 2011), added to iN cells 4–5 days after infection, and cocultured for an additional 2 weeks. Lentiviruses were produced as described (Pang et al.

405, p < 0 00001) This correlation remained significant even whe

405, p < 0.00001). This correlation remained significant even when the ongoing spike density was controlled by the mean interneuron firing rate (Figure 8C; r = 0.375, p < 0.00001). Moreover, the contribution of the coincident interneuron depolarization state to the change in the transmission probability was still significant when controlled for the total number of pyramidal

cell-interneuron 20ms pairing events (r = 0.268, p = 0.0008, partial correlation) and for running speed at times of the spike coincident events (r = 0.280, p = 0.0022, partial correlation). These results showed that temporal coincidence between the pre-synaptic pyramidal cell spikes and the postsynaptic interneuron excitation state further contributed to the direction and the magnitude of the synaptic changes. In this study, we have shown Ibrutinib that spatial learning on the cheeseboard maze was associated with the HSP assay dynamic reconfiguration of interneuron circuits in the CA1 pyramidal cell layer of the hippocampus. The strength of the local input that interneurons received from pyramidal cells was altered during learning,

and, as a result, many of them developed firing associations to newly formed pyramidal assemblies that were part of the spatial maps representing information about recently acquired spatial memories. While the firing of some interneurons was bound to the expression of new pyramidal assemblies, other interneurons dissociated their firing from the activity of the same assemblies. These firing associations, manifested by rapid fluctuations of the interneurons firing rate, were mirrored by changes of their monosynaptic connection weight. Interneurons that increased their firing associations to new pyramidal assemblies overall received strengthened inputs from pyramidal cells that were members of a new assembly. Moreover,

the opposite trend was observed for interneurons that decreased their associations to new assemblies, these received weaker local pyramidal inputs following learning. Importantly, this circuit reconfiguration took place during the learning session and it remained stable in subsequent sleep and memory probe sessions. In analyzing the temporal expression of pyramidal assemblies representing old and newly developed maps during STK38 learning, we found that the old assemblies were present even later during learning, with old and new cell assemblies alternating even within a single learning trial. In addition, assemblies of the new maps emerged rather abruptly, in parallel with the rapid improvement of the behavioral performance of the animal within the initial learning trials. As learning progressed the newly established maps were then refined, together with an increase of the frequency of the new assemblies, and thus dominated late learning periods.

Thalamocortical axons start to form during early embryogenesis an

Thalamocortical axons start to form during early embryogenesis and follow a complex Tyrosine Kinase Inhibitor Library order pathway: they run through the ventral thalamus, travel internally through the ventral telencephalon—through the medial ganglionic eminence (MGE) and the lateral ganglionic eminence (LGE)—and reach the neocortex (Auladell et al., 2000, Lopez-Bendito and Molnar, 2003, Metin and Godement, 1996 and Molnar et al., 1998). Several studies have revealed that the ventral telencephalon is a major intermediate target for these axons (Braisted

et al., 1999, Metin and Godement, 1996 and Molnar et al., 1998). For instance, guidepost neurons forming early projections to the dorsal thalamus have been proposed to promote the entrance of TAs into the ventral telencephalon (Metin and Godement, 1996, Mitrofanis and Baker, 1993 and Molnar et al., 1998), and the local expression of protocadherins controls the further progression of thalamocortical connections (Uemura et al., 2007 and Zhou et al., 2008). Finally, several classical guidance cues have been shown to control specific steps of TA navigation along their path toward Romidepsin the neocortex, including Netrin1, Neuregulin1 (Nrg1), and Slit2 (Bagri et al., 2002, Braisted et al., 2000,

Braisted et al., 2009, Garel and Rubenstein, 2004, Leighton et al., 2001, Lin et al., 2003 and Lopez-Bendito et al., 2006). The secreted Slit proteins control a large number of cellular processes, including cell migration and axon guidance, via their binding to Roundabout (Robo) receptors (Geisen et al., 2008, Nguyen-Ba-Charvet et al., 2004, Wu et al., 1999 and Zhu et al., 1999). In particular, Slits and Robos control evolutionarily conserved Mephenoxalone guidance decisions during ventral

midline crossing and positioning of longitudinal tracts, mainly via a repulsive activity (Brose et al., 1999, Farmer et al., 2008, Kidd et al., 1998, Long et al., 2004, Nguyen Ba-Charvet et al., 1999, Nguyen-Ba-Charvet et al., 2002, Plump et al., 2002, Rajagopalan et al., 2000, Shu et al., 2003b and Simpson et al., 2000). In the rodent forebrain, Slit2, Robo1, and Robo2 have been implicated in the guidance of several major axonal tracts, including TAs (Andrews et al., 2006, Bagri et al., 2002, Braisted et al., 2009 and Lopez-Bendito et al., 2007). For instance, Slit2, and to a lesser extent Slit1, mediates a repulsive activity that prevents axons from growing toward the ventral midline, by direct binding to Robo1 and Robo2 receptors (Bagri et al., 2002, Braisted et al., 2009 and Lopez-Bendito et al., 2007). In addition to the aforementioned guidance cues, we have shown in mice that a tangential neuronal cell migration from the LGE into the MGE is required to form a permissive corridor for pioneer TAs (Lopez-Bendito et al., 2006). These “corridor cells” follow an internal route within the nonpermissive MGE, and delineate the future path of growing TAs, by having a short-range activity via the expression of membrane-bound Nrg1 (Lopez-Bendito et al., 2006).

The sitting tasks included sitting on an Automatic Abs air-cushio

The sitting tasks included sitting on an Automatic Abs air-cushion (Licensing Services International Inc.,

Philadelphia, PA, USA), a stability ball (Cando®; Fabrication Enterprises Inc., White Plains, NY, USA), or an immobile surface (chair) for a duration of 30 min each while kinematic and ground reaction force data were collected. A 5-min break was offered between each sitting condition. The immobile surface condition required participants to sit on a wooden box 40 cm in height without a backrest. In the air-cushion condition, the participants sat on the same wooden box with an Automatic Abs air-cushion placed on top. The Automatic Abs air-cushion was an air-filled cushion 30.5 cm in diameter

and 5 cm thick. During ERK inhibitor the stability ball condition, the participant sat on a stability ball 177 cm in circumference. The sitting posture was standardized for all participants. For each condition, participants XAV-939 nmr were instructed to place each foot on a separate force plate. Participants remained seated with an upright trunk, their hands resting on their thighs, and their knees flexed at 90° during data collection. For the duration of each trial, the participants viewed a 52-inch flat screen television 20 feet away which displayed a television show at approximately eye level. All participants wore compression shirts and shorts and were barefoot during testing. Anthropometric measurements were taken of each participant, including height, weight, leg length, anterior superior iliac spine and posterior superior iliac spine distances, ankle, knee and wrist width, shoulder offset, and hand thickness. Thirty-two retro-reflective markers (diameter = 14 mm) were placed on the participant using a modified Plug-in-Gait model with additional makers placed over the fifth metatarsal head, the sacrum, and the superior rim of the side of the iliac crest. Past research had examined and verified the validity of the Plug-in-Gait protocol in a gait laboratory much setting.12 and 13 To ensure reliability of the experiment, an experienced researcher (KW) was designated

to perform subject measurements and marker placements for all the participants. Posture was monitored by 12 Vicon MX-40 infrared cameras sampling at 60 Hz (Vicon; Oxford Metrics, Oxford, UK). The Vicon system tracked the position of the reflective markers in space for the duration of each trial. Ground reaction forces at the feet were collected using two AMTI OR6-7 force plates (Advanced Mechanical Technology Inc., Watertown, MA, USA) sampling at 600 Hz by placing one foot on each force plate. Data were processed using Vicon Nexus v.1.7 and the biomechanical variables were calculated using Visual 3D v.4.9 (C-motion Inc., Germantown, MD, USA). Trunk angle, trunk center of mass, and center of pressure were measured for each sitting trial.

This latter finding is consistent with the developmental time cou

This latter finding is consistent with the developmental time course, from which it has

been argued that place cell firing could not be driven by grid cell firing, because stable place cell firing precedes stable grid cell firing (Wills et al., 2010), although stable boundary-related firing is seen at this early developmental stage (Bjerknes et al., 2014). However, from the “charts” point of view, grid cell-mediated path integration could determine the initial place cell representation in a new environment; environmental sensory associations then stabilize place cell firing as the environment becomes familiar and could replace the original grid cell input. To test the charts hypothesis, Brandon et al. (2014) recorded selleck chemicals place cell firing

in novel and familiar environments while disrupting hippocampal theta by inactivating the septum. They found, as before, a severe reduction in theta power in the LFP in hippocampus PLX-4720 nmr and mEC and in the theta rhythmicity of place cell firing. This level of reduction corresponded to complete disruption of grid cell firing patterns in a previous paper using muscimol inactivation (Brandon et al., 2011) and in two grid cells recorded in the current study. There was also little effect of the septal inactivation on place cell firing in the familiar environment (apart from a slight reduction in the size of firing fields). When the rats were put into a novel environment, normal levels of place cell “remapping” were seen (i.e., generation of new, orthogonal, firing patterns in the new environment compared to the familiar one). The new firing patterns were unchanged

by recovery from the inactivation 24 hr later. Thus, the formation of new place of cell representations in a novel environment appears not to require theta rhythmicity or grid cell firing patterns. This contradicts suggestions that the spatial modulation of place cell firing reflects mechanisms dependent on theta oscillations (see Burgess and O’Keefe, 2011 for a review). If it is true that grid cells implement a preconfigured metric based on path integration or “chart” (McNaughton et al., 2006), then this result also suggests that new place cell representations are not built on such charts. Nonetheless, a slight reduction in place cell firing rates was observed in the inactivation group, and the characteristic increase in stability during the 30 min trial in control animals was reduced in the inactivation group. This suggests that grid cells do have a functional input to place cell firing and that this input strengthens with experience of a new environment and improves the spatial stability of place cell firing, even if it does not determine their firing fields. This study raises several interesting questions, aside from the debate about the primacy of sensory input versus path integration.

(2012) crossed a Gli1-CreERT2 mouse line with floxed Pten and GFP

(2012) crossed a Gli1-CreERT2 mouse line with floxed Pten and GFP recombination reporter mice. Because the hippocampal dentate gyrus is one of the few adult brain regions wherein neural progenitors persist postnatally, tamoxifen treatment of the mice beginning at postnatal day 14, along with inefficient Cre-mediated recombination, enabled relatively specific Pten knockout in a minority

of DGCs. They found that loss of PTEN and the subsequent increase in mTOR signaling induced profound abnormalities in DGC morphology that recapitulate those seen in TLE. Affected DGCs displayed neuronal hypertrophy, abnormal basal dendrites, dramatically increased dendritic spine density, and ectopic locations Galunisertib nmr ( Figure 1C). In 82% of animals, Pten deletion led to spontaneous seizures beginning as early as 4 weeks GSK2656157 after tamoxifen treatment and increasing in severity over time. By correlating the degree of recombination with the presence of an epilepsy phenotype, they observed that Pten deletion in as few as 9% of DGCs was sufficient to induce epilepsy. Because Gli1 is expressed in subgranular

and subventricular zone neural progenitors, as well as in subsets of glia, it was important to exclude these as a source of epileptogenic plasticity. No morphological changes were observed in the very small subset of glia (less than 3% in the densest region) that underwent recombination. In addition, alterations due to Pten deletion were much less robust in the olfactory bulb than the dentate gyrus. More importantly, Pun et al. (2012) recorded EEG simultaneously from the hippocampus and olfactory bulb and found that seizure onsets occurred in the hippocampus without any corresponding activity in the bulb. They also confirmed that the pathological effects of Pten deletion were mediated via mTOR activation by blocking GBA3 them with

rapamycin, an mTOR inhibitor. Rapamycin treatment prevented epilepsy development in three animals and decreased seizure frequency by more than ten-fold in two others. The treatment also abolished mossy fiber sprouting, but the importance of this effect for attenuating seizures is uncertain given that others have found rapamycin treatment produces transitory effects, and the degree of sprouting does not correlate well with seizure reduction ( Buckmaster and Lew, 2011). Interestingly, Pun et al. (2012) found that some DGCs that sprout do not show evidence of recombination, suggesting that mossy fiber sprouting may be a consequence of seizures, rather than a cause. The proximate cause of epilepsy in this model is, of course, the elimination of PTEN from a subset of postnatally generated neurons. Although this induces profound abnormalities in a minority of DGCs, it is not clear how these abnormalities specifically relate to epileptogenesis.

Therefore, the Lyapunov function always decreases if the system b

Therefore, the Lyapunov function always decreases if the system behaves according to (Equation 5), (Equation 6) and (Equation 7).

Since the function is limited from below, the stable states AG-014699 concentration of the system are described by the local minima of the Lyapunov function. The cost function for the threshold-linear neuronal activation function g(u) = [u – θ]+ shown in Figure 5A can be approximated by a linear function when the firing rates of the GC are not too large: equation(Equation 11) C(a)≈θa,a≥0. For negative values of firing rates a, the cost function is infinitely big, reflecting the fact that negative firing rates are not available. For our model to have a Lyapunov function, a more general condition than Wmi=εW˜im may hold. Indeed, the sufficient condition for the existence of the Lyapunov function is that the network weight matrix

Gik=∑iW˜imWmk is symmetrical (Hertz et al., 1991). This is true if, for example, Wmi=W˜inEnm, where Enm   is an arbitrary symmetrical M  -by-M   matrix. Thus, condition Wmi=εW˜im is sufficient but not necessary for the network to have a Lyapunov function. However, we argue that this condition is necessary for the system to be described by the Lyapunov function in the form of Equation 2. We will distinguish two types of Lyapunov functions. First, we consider Selleckchem Dabrafenib the homogeneous case, when the Lyapunov function has the following form: equation(Equation 12) L0(a→)=12ε∑m=1M(xm−∑iWmiai)2. The homogeneous case corresponds to a vanishingly small threshold for the activation of the GCs. In this case, we still constrain the firing rates to be nonnegative. The inhomogeneous Lyapunov function is equation(Equation 13) L(a→)=L0(a→)+∑iθiai,with the same constraint

ai≥0ai≥0. We prove here the two theorems that limit the number of coactive GCs (i.e., the ones for which ai≠0ai≠0). The response of MCs is rm=xm−i∑Wmiairm=xm−∑iWmiai. Assume that the M  -dimensional receptive fields of the GCs W→i are the Bumetanide vectors of the general position; i.e., every subset of M   vectors W→i are linearly independent. Then, in the minimum of the homogeneous Lyapunov function ( Equation 12), either rm = 0 for all m (i.e., MCs do not respond, and GC representation is complete) or fewer than M GCs are active. In the former case (rm = 0), all of the GCs may be active. Proof:   Assume that M   or more GCs are simultaneously active. Let us vary slightly the activity of only one active GC: Δak=εΔak=ε. The corresponding variation in the Lyapunov function is ΔL0=(r→⋅W→k)ε+O(ε2). Because we are considering the minimum of the Lyapunov function, all of the scalar products (r→⋅W→k) must be zero, which is possible only if r→=0 or the number of vectors W→k is less than M. Consider the set of N   (M   + 1)-dimensional vectors Ω→i=(W→i,θi). Assume that these vectors are of the general position; i.e., any subset of M + 1 of these vectors is linearly independent.

, 2005, Ungerleider et al , 2008 and Pouget et al , 2009) In thi

, 2005, Ungerleider et al., 2008 and Pouget et al., 2009). In this sense, V4 is well positioned for integrating top-down influences with information about stimuli from the bottom-up direction. Causal Interactions between Frontal and Visual Cortical Areas? Although imaging and neuropsychological studies strongly suggested that feedback signals from fronto-parietal cortex interact with sensory signals in visual areas such as V4, it has been

difficult to prove a causal link between activity in frontal (or parietal) cortex and modulation of visually driven Pomalidomide order activity. One area in prefrontal cortex that has been proposed as a source of top-down influence is the frontal eye fields (FEF), a cortical area responsible for directing eye movements. During overt attention, FEF initiates circuits which direct the center of gaze toward salient objects. During covert attention, similar neuronal mechanisms may be at play (which has led to the “pre-motor theory of attention”) ( Corbetta et al., 1998, Corbetta, 1998, Hoffman and Subramaniam, 1995, Kustov and Robinson, 1996, Moore et al., 2003, Moore and

Armstrong, 2003, Moore and Fallah, 2001, Moore and Fallah, Screening Library purchase 2004, Nobre et al., 2000 and Rizzolatti et al., 1987). If so, then FEF should play a causal role in directing attention and in influencing V4 activity. Currently, the only evidence of causal influences from FEF comes from studies of spatial attention. Moore and colleagues mafosfamide provided the first elegant evidence showing such a causal link (Moore

and Fallah, 2004). By using microstimulation in FEF, they showed a causal relationship between altered activity in the FEF and spatially specific enhanced visual representations within V4. Second, they showed that microstimulation in FEF increased perceptual abilities at the stimulated visuotopic locations. More recently, using fMRI methods, Ekstrom and colleagues examined the effect of electrical microstimulation in FEF on visually driven responses in V4 and other extrastriate cortical areas of behaving monkeys (Ekstrom et al., 2008 and Ekstrom et al., 2009). They found that voxels in V4 which showed the strongest enhancement of fMRI activity caused by FEF microstimulation were not the voxels with the strongest visual responses, but rather adjacent voxels. In fact, strongly visually driven voxels themselves were unaffected or even suppressed by FEF microstimulation. These results led them to test whether effects of electrical stimulation on visually driven activity in V4 would be stronger in the presence of “distractor” stimuli. Without distractors, electrical stimulation increased fMRI activity in V4. With distractors (which normally cause a decrease in activity), the activity in V4 voxel increased substantially beyond the effect without distractors. These results are consistent with neurophysiological studies that show stronger enhancement in the presence of competitive distractors.