Spatial Stimuli Research Articles

Investigation of interocular blur suppression using luminance-modulated and contrast-modulated noise stimuli.

Presenting two sufficiently dissimilar images, one to each eye, may result in interocular suppression. The present study measured interocular suppression depth and extent in binocularly normal participants when blurring one eye only with varying dioptric lens powers (+0.5, +1, +2, and +4 D). Visual stimuli consisted of eight concentric rings of alternate polarity, divisible into eight sectors, within the central circular 24° visual field. Binocular "ring" stimuli therefore consisted of 64 individually testable dichoptic sectors. Using a two-alternative forced choice paradigm with a staircase procedure, signal strength of each dichoptic sector in the blurred eye was adjusted to perceptually match that of the surrounding ring from the nonblurred eye, determining the point of subjective equality. Rings were defined by differences in luminance (L), luminance-modulated noise (LM), or contrast-modulated noise (CM). Suppression depth was similar irrespective of sector location within the visual field and increased with increasing difference in interocular blur. Adding dynamic noise (LM vs. L stimuli) reduced the effect of blur on measured suppression depth. Significantly deeper suppression was measured for CM than for LM stimuli, both created using dynamic noise, the difference increasing at higher levels of interocular blur. As binocularity is disrupted with interocular blur, this result suggests that CM envelope combination may be processed by later mechanisms receiving binocular input than those required for the processing of LM stimuli. Differences in suppression depth between LM and CM stimuli could not be attributed to differences in spatial summation properties, stimulus visibility, noise modulation, or differential effects on blur discriminability.

The spatial properties of L- and M-cone inputs to electroretinograms that reflect different types of post-receptoral processing.

We studied the spatial arrangement of L- and M-cone driven electroretinograms (ERGs) reflecting the activity of magno- and parvocellular pathways. L- and M-cone isolating sine wave stimuli were created with a four primary LED stimulator using triple silent substitution paradigms. Temporal frequencies were 8 and 12 Hz, to reflect cone opponent activity, and 30, 36 and 48 Hz to reflect luminance activity. The responses were measured for full-field stimuli and for different circular and annular stimuli. The ERG data confirm the presence of two different mechanisms at intermediate and high temporal frequencies. The responses measured at high temporal frequencies strongly depended upon spatial stimulus configuration. In the full-field conditions, the L-cone driven responses were substantially larger than the full-field M-cone driven responses and also than the L-cone driven responses with smaller stimuli. The M-cone driven responses at full-field and with 70° diameter stimuli displayed similar amplitudes. The L- and M-cone driven responses measured at 8 and 12 Hz were of similar amplitude and approximately in counter-phase. The amplitudes were constant for most stimulus configurations. The results indicate that, when the ERG reflects luminance activity, it is positively correlated with stimulus size. Beyond 35° retinal eccentricity, the retina mainly contains L-cones. Small stimuli are sufficient to obtain maximal ERGs at low temporal frequencies where the ERGs are also sensitive to cone-opponent processing.

A morphological adaptation approach to path planning inspired by slime mould

Path planning is a classic problem in computer science and robotics which has recently been implemented in unconventional computing substrates such as chemical reaction–diffusion computers. These novel computing schemes utilise the parallel spatial propagation of information and often use a two-stage method involving diffusive propagation to discover all paths and a second stage to highlight or visualise the path between two particular points in the arena. The true slime mould Physarum polycephalum is known to construct efficient transport networks between nutrients in its environment. These networks are continuously remodelled as the organism adapts its body plan to changing spatial stimuli. It can be guided towards attractant stimuli (nutrients, warm regions) and it avoids locations containing hazardous stimuli (light irradiation, repellents, or regions occupied by predatory threats). Using a particle model of slime mould we demonstrate scoping experiments which explore how path planning may be performed by morphological adaptation. We initially demonstrate simple path planning by a shrinking blob of virtual plasmodium between two attractant sources within a polygonal arena. We examine the case where multiple paths are required and the subsequent selection of a single path from multiple options. Collision-free paths are implemented via repulsion from the borders of the arena. Finally, obstacle avoidance is implemented by repulsion from obstacles as they are uncovered by the shrinking blob. These examples show proof-of-concept results of path planning by morphological adaptation which complement existing research on path planning in novel computing substrates.

Olfactory Neuromodulation of Motion Vision Circuitry in Drosophila

SummaryIt is well established that perception is largely multisensory [1]; often served by modalities such as touch, vision, and hearing that detect stimuli emanating from a common point in space [2, 3]; and processed by brain tissue maps that are spatially aligned [4]. However, the neural interactions among modalities that share no spatial stimulus domain yet are essential for robust perception within noisy environments remain uncharacterized. Drosophila melanogaster makes its living navigating food odor plumes. Odor acts to increase the strength of gaze-stabilizing optomotor reflexes [5] to keep the animal aligned within an invisible plume, facilitating odor localization in free flight [6–8]. Here, we investigate the cellular mechanism for cross-modal behavioral interactions. We characterize a wide-field motion-selective interneuron of the lobula plate that shares anatomical and physiological similarities with the “Hx” neuron identified in larger flies [9, 10]. Drosophila Hx exhibits cross-modal enhancement of visual responses by paired odor, and presynaptic inputs to the lobula plate are required for behavioral odor tracking but are not themselves the target of odor modulation, nor is the neighboring wide-field “HSE” neuron [11]. Octopaminergic neurons mediating increased visual responses upon flight initiation [12] also show odor-evoked calcium modulations and form connections with Hx dendrites. Finally, restoring synaptic vesicle trafficking within the octopaminergic neurons of animals carrying a null mutation for all aminergic signaling [13] is sufficient to restore odor-tracking behavior. These results are the first to demonstrate cellular mechanisms underlying visual-olfactory integration required for odor localization in fruit flies, which may be representative of adaptive multisensory interactions across taxa.

Application of physics in the study of cell polarity during tumor cell migration

Investigation of tumors from a physics perspective has attracted more and more attention since the initiation, development, and metastasis of tumors are strongly influenced by the physical interactions between the tumor cells and their microenvironments. Since tumor metastasis accounts for more than 90% of cancer-associated death, one of the focuses is to understand its underlying mechanism, especially how tumor cells polarize during their migration. Cell polarization directs tumor-cell migration in response to a spatial stimulus, e.g., the gradient of chemokine or oxygen molecules. It forms the front and back edges of cells by estiblishing asymmetric distributions of cell polarity proteins such as the Rho family GTPases and organelles such as Golgi. This paper reviews how the experimental and theoretical studies combining physics with biology reveal the underlying mechanisms of cell migration and cell polarity. Experimental results demonstrate that the physics clues including extracellular matrix's mechanical properties, dimensionality, and topography are strongly coupled with the biochemical reactions to establish and maintain the cell polarity and direct cell migration. The cell migration mode in a more physiological three-dimensional (3D) matrix is different from that in a two-dimensional(2D) system. Moreover, the membrane tension is suggested to maitain cell polarity by inhibiting polarization processes outside the front edge. On the other hand, a series of reaction diffusion models have been developed to characterize cell polarity. Representative examples inculding Turing-type model, local-excitation and global-inhibition (LEGI) model, and wave-pinning model can capture certain features of cell polarization, however none of them takes the physical factors, such as the membrane tension, into account hence fails to explain previous published experimental results about the membrane tension with cell polarization. To further improve our understanding of the mechanism of cell polarity, in the future study it is experimentally important to estiblish 3D tumor systems and study the gene regulation network that can control cell polariztion by advanced microscope; theroetically it is of importance to build mathematical models for the chemical reaction diffusion systems coupled with the mechanical factors such as membarne tension. These studies will reveal the molecular mechanism of cell polarization and cell migration under a more physiological relevant condition. They may also help us understand how the higher deformation ability of cancer stem cells provides the higher migration capability compared with the normal cancer cells. Ultimately, they will facilitate developing new therapeutic strategy against tumor metastasis by targeting the signaling of tumor cells in response of physical stimuli.

Phase description of oscillatory convection with a spatially translational mode

We formulate a theory for the phase description of oscillatory convection in a cylindrical Hele–Shaw cell that is laterally periodic. This system possesses spatial translational symmetry in the lateral direction owing to the cylindrical shape as well as temporal translational symmetry. Oscillatory convection in this system is described by a limit-torus solution that possesses two phase modes; one is a spatial phase and the other is a temporal phase. The spatial and temporal phases indicate the “position” and “oscillation” of the convection, respectively. The theory developed in this paper can be considered as a phase reduction method for limit-torus solutions in infinite-dimensional dynamical systems, namely, limit-torus solutions to partial differential equations representing oscillatory convection with a spatially translational mode. We derive the phase sensitivity functions for spatial and temporal phases; these functions quantify the phase responses of the oscillatory convection to weak perturbations applied at each spatial point. Using the phase sensitivity functions, we characterize the spatiotemporal phase responses of oscillatory convection to weak spatial stimuli and analyze the spatiotemporal phase synchronization between weakly coupled systems of oscillatory convection.

Tactile priming modulates the activation of the fronto-parietal circuit during tactile angle match and non-match processing: an fMRI study

The repetition of a stimulus task reduces the neural activity within certain cortical regions responsible for working memory (WM) processing. Although previous evidence has shown that repeated vibrotactile stimuli reduce the activation in the ventrolateral prefrontal cortex, whether the repeated tactile spatial stimuli triggered the priming effect correlated with the same cortical region remains unclear. Therefore, we used event-related functional magnetic resonance imaging (fMRI) and a delayed match-to-sample task to investigate the contributions of the priming effect to tactile spatial WM processing. Fourteen healthy volunteers were asked to encode three tactile angle stimuli during the encoding phase and one tactile angle stimulus during the recognition phase. Then, they answered whether the last angle stimulus was presented during the encoding phase. As expected, both the Match and Non-Match tasks activated a similar cerebral network. The critical new finding was decreased brain activity in the left inferior frontal gyrus (IFG), the right posterior parietal cortex (PPC) and bilateral medial frontal gyri (mFG) for the match task compared to the Non-Match task. Therefore, we suggest that the tactile priming engaged repetition suppression mechanisms during tactile angle matching, and this process decreased the activation of the fronto-parietal circuit, including IFG, mFG and PPC.

Tracking and discrete dual task performance with different spatial stimulus–response mappings

The effect of spatial compatibility on dual-task performance for various display–control configurations was studied using a tracking task and a discrete four-choice response task. A total of 36 participants took part in this study, and they were asked to perform the primary tracking task while at the same time to respond to an occasional signal. Different levels of compatibility between the stimuli and responses of the discrete response task were found to lead to different degrees of influence on the tracking task. However, degradation of performance was observed for both tasks, which was probably due to resource competition for the visual and spatial resources required for simultaneous task operation and required for bimanual responses. No right–left prevalence effect for the spatial compatibility task was observed in this study, implying that the use of unimanual two-finger responses may not provide the right conditions for a significant effect in the horizontal right–left dimension.Practitioner Summary: The effect of spatial compatibility in multiple display–control configurations was examined in a dual-task paradigm. The analyses of keen competition for visual and spatial resources in processing the dual tasks under different degrees of stimulus–response compatibility provide useful ergonomics design implications and recommendations for visual interfaces requiring frequent visual scanning.

Crossmodal attention switching: Auditory dominance in temporal discrimination tasks

Visual stimuli are often processed more efficiently than accompanying stimuli in another modality. In line with this “visual dominance”, earlier studies on attentional switching showed a clear benefit for visual stimuli in a bimodal visual–auditory modality-switch paradigm that required spatial stimulus localization in the relevant modality. The present study aimed to examine the generality of this visual dominance effect. The modality appropriateness hypothesis proposes that stimuli in different modalities are differentially effectively processed depending on the task dimension, so that processing of visual stimuli is favored in the dimension of space, whereas processing auditory stimuli is favored in the dimension of time. In the present study, we examined this proposition by using a temporal duration judgment in a bimodal visual–auditory switching paradigm. Two experiments demonstrated that crossmodal interference (i.e., temporal stimulus congruence) was larger for visual stimuli than for auditory stimuli, suggesting auditory dominance when performing temporal judgment tasks. However, attention switch costs were larger for the auditory modality than for visual modality, indicating a dissociation of the mechanisms underlying crossmodal competition in stimulus processing and modality-specific biasing of attentional set.

The Directional Response of Chemotactic Cells Depends on a Balance between Cytoskeletal Architecture and the External Gradient

Polarized migrating cells display signal transduction events, such as activation of phosphatidylinositol 3-kinase (PI3K) and Scar/Wave, and respond more readily to chemotactic stimuli at the leading edge. We sought to determine the basis of this polarized sensitivity. Inhibiting actin polymerization leads to uniform sensitivity. However, when human neutrophils were "stalled" by simultaneously blocking actin and myosin dynamics, they maintained the gradient of responsiveness to chemoattractant and also displayed noise-driven PIP3 flashes on the basal membrane, localized toward the front. Thus, polarized sensitivity does not require migration or cytoskeletal dynamics. The threshold for response is correlated with the static F-actin distribution, but not cell shape or volume changes, membrane fluidity, or the preexisting distribution of PI3K. The kinetics of responses to temporal and spatial stimuli were consistent with the local excitation global inhibition model, but the overall direction of the response was biased by the internal axis of polarity.

The Simon effect in action: planning and/or on-line control effects?

Choice reaction tasks are performed faster when stimulus location corresponds to response location (Simon effect). This spatial stimulus-response compatibility effect affects performance at the level of action planning and execution. However, when response selection is completed before movement initiation, the Simon effect arises only at the planning level. The aim of this study was to ascertain whether when a precocious response selection is requested, the Simon effect can be detected on the kinematics characterizing the online control phase of a non-ballistic movement. Participants were presented with red or green colored squares, which could appear on the right, left, above, or below a central cross. Depending on the square's color, participants had to release one of two buttons (right/left), then reach toward and press a corresponding lateral pad. We found evidence of the Simon effect on both action planning and on-line control. Moreover, the investigation of response conflict at the level of previous trials (i.e., n-1), a factor that might determine interference at the level of the current response, revealed a conflict adaptation process across trials. Results are discussed in terms of current theories concerned with the Simon effect and the distinction between action planning and control.

Better together? The cognitive advantages of synaesthesia for time, numbers, and space

Synaesthesia for time, numbers, and space (TNS synaesthesia) is thought to have costs and benefits for recalling and manipulating time and number. There are two competing theories about how TNS synaesthesia affects cognition. The “magnitude” account predicts that TNS synaesthesia may affect cardinal magnitude judgements, whereas the “sequence” account suggests that it may affect ordinal sequence judgements and could rely on visuospatial working memory. We aimed to comprehensively assess the cognitive consequences of TNS synaesthesia and distinguish between these two accounts. TNS synaesthetes, grapheme–colour synaesthetes, and nonsynaesthetes completed a behavioural task battery. Three tasks involved cardinal and ordinal comparisons of temporal, numerical, and spatial stimuli; we also examined visuospatial working memory. TNS synaesthetes were significantly more accurate than nonsynaesthetes in making ordinal judgements about space. This difference was explained by significantly higher visuospatial working memory accuracy. Our findings demonstrate an advantage of TNS synaesthesia that is more in line with the sequence account.

A three-stimulus midsession reversal task in pigeons with visual and spatial discriminative stimuli

In a two-stimulus visual discrimination task with a reversal in reward contingencies midway through each session, pigeons produce a surprising number of both anticipatory (i.e., before the reversal) and perseverative (i.e., after the reversal) errors. In the current work, we examined pigeons' (Columba livia) patterns of responding on a 90-trial, three-stimulus visual or spatial discrimination task with two changes in reward contingency (one after Trial 30 and one after Trial 60) during each session. On probe sessions where pecking the first-correct stimulus was rewarded for the first 60 rather than 30 trials, pigeons on a spatial discrimination pecked the first-correct stimulus until it was no longer rewarded, while visual discrimination birds ceased responding to the first-correct stimulus even while it was still being rewarded. On probe sessions where the onset of the first trial was delayed 7min, pigeons' performance on the visual discrimination was disrupted by the interval delay, but performance in the spatial condition was more similar to baseline. Pigeons use different strategies (temporal control vs. local reinforcement) on midsession reversal tasks with visual versus spatial stimuli, suggesting that they are selectively permeable to changes in information (global vs. local reinforcement rates).

Selective deficit of spatial short-term memory: Role of storage and rehearsal mechanisms

We report the neuropsychological and MRI investigation of a patient (GP) who developed a selective impairment of spatial short-term memory (STM) following damage to the dorso-mesial areas of the right frontal lobe. We assessed in this patient spatial STM with an experimental procedure that evaluated immediate and 5–20 s delayed recall of verbal, visual and spatial stimuli. The patient scored significantly worse than normal controls on tests that required delayed recall of spatial data. This could not be ascribed to a deficit of spatial episodic long-term memory because amnesic patients performed normally on these tests. Conversely, the patient scored in the normal range on tests of immediate recall of verbal, visual and spatial data and tests of delayed recall of verbal and visual data. Comparison with a previously described patient who had a selective deficit in immediate spatial recall and an ischemic lesion that affected frontal and parietal dorso-mesial areas in the right hemisphere (Carlesimo GA, Perri R, Turriziani P, Tomaiuolo F, Caltagirone C. Remembering what but not where: independence of spatial and visual working memory in the human brain. Cortex. 2001 Sep; 37(4):519–34) suggests that the right parietal areas are involved in the short-term storage of spatial information and that the dorso-mesial regions of the right frontal underlie mechanisms for the delayed maintenance of the same data.

Learning what from where: Effects of Spatial Regularity on Nonspatial Sequence Learning and Updating

The current study examined the influence of redundant stimulus features on our ability to build and update representations of our environment. We hypothesized that our ability to process redundant spatial features would speed our ability to adapt to changing nonspatial regularities. Using a computerized version of the children's game "rock-paper-scissors", undergraduates were instructed to win as often as possible against a computer opponent. The computer's plays were repeating sequences of five choices that were presented either with spatial regularity (i.e., "rock" would always appear on the left, "paper" in the middle, and "scissors" on the right) or without spatial regularity (i.e., the items were equally likely to appear in any of the three locations). Once participants learned a sequence, the computer switched to a different sequence without participants being informed that a switch had occurred. Redundant spatial regularity improved a participant's ability both to learn sequences of plays and to update their plays to reflect new computer sequences. Our results suggest that our perceptual system is sensitive to redundant spatial stimulus features and that this information can improve learning and updating.

Feedback, both fast and slow: how the retina deals with redundancy in space and time.

​ByBy the time visual information leaves the retina for the brain, it has undergone several rounds of processing. Most prominently, that information has been filtered to amplify differences in contrast, between either two points in space or two points in time. The initial step in that amplification is carried out by horizontal cells, whose job is not only to receive signals from a group of adjacent photoreceptor cells (rods or cones) but also to send inhibitory feedback signals back to the photoreceptors, turning down the weakest outputs and allowing only the strongest to get through. Schematic drawing of the vertebrate retina combined with the immunolocalization of the ecto-ATPase NDTPdase1 (green). This much has been known for several decades, but the cell physiological details of the feedback mechanism have been controversial. Part of the puzzle has been the paradoxical requirement for both very fast feedback, needed to highlight spatial differences, and slower feedback, needed to process temporal ones. In this issue of PLOS Biology, Rozan Vroman, Maarten Kamermans, and colleagues resolve this apparent paradox: they show that horizontal cells in the goldfish retina employ two simultaneous feedback mechanisms, the slower of which relies on a newly described mechanism, creating an extracellular buffer by secreting and hydrolyzing ATP. Horizontal cells affect the activity of cone cells by changing the rate of flow of positively charged calcium ions from the extracellular space through calcium channels into the cone cell. The authors measured that current within individual cone–horizontal cell synapses, and found that the curve reflecting the current change was best described as the sum of two exponential functions, one representing an initial fast increase and the other a slower one. The fast component was very fast indeed, inconsistent with the inevitable delay imposed when cells are separated by a synaptic gap. Instead, the authors show that connexin hemichannels on the horizontal cell membrane were involved. These channels allowed current to flow into the horizontal cell, increasing the negative charge of the intercellular space and increasing the flow of calcium into the cone cell, locally depolarizing it. This direct (“ephaptic”) connection makes the synapse among the fastest of all known inhibitory synapses. But it was the slow component that held the most surprises. The authors noted that light-induced feedback responses of horizontal cells can be completely blocked by carbenoxolone, which antagonizes not only connexin but also another channel, called pannexin 1 (Panx1). Panx1 is also present in the synapse and is known to mediate release of ATP. The authors showed that depolarized horizontal cells released ATP, an effect that could be blocked by addition of a specific Panx1 antagonist, probenecid. When hydrolyzed, ATP produces phosphates and H+ ions (protons), which could acidify the intercellular space as well as buffer it against pH changes. The authors used immunolabeling to show that an ATP hydrolase was present on the exterior surface of the horizontal cell, and that blocking this enzyme reduced the slow component of the feedback response. Artificial alkalization of the synaptic space had the same effect. The ATP that is released via Panx1 is thus hydrolyzed and leads to slight acidification of the synaptic cleft, which inhibits presynaptic calcium channels and inhibits the neurotransmitter release of photoreceptors. The combination of two feedback components with different speeds allows the horizontal cell–cone system to respond to both spatial and temporal variation, the authors argue. Spatially, the role of the horizontal cell is, in effect, to subtract the average level of activity in multiple adjacent cones from the output of each, allowing only the most prominent signals through. That subtraction must happen very fast for a moving signal to be processed correctly—and the ephaptic component is about as fast as it gets. Temporally, the horizontal cell must subtract out long-lasting stimulation from the cone output, which by definition requires a slower mechanism, provided by the Panx1–ATPase system. Although these experiments were done in fish, mice also express Panx1 at their horizontal cell synapses, suggesting the mechanism likely operates in mammals as well. The authors speculate that variations in the relative activity of the fast and slow mechanisms may contribute to interspecies differences in responsiveness to spatial versus temporal stimuli. They also point out that Panx1 is widely distributed in the brain, suggesting that an ATP pH effect may contribute to feedback systems in other types of neurons as well. Vroman R, Klaassen LJ, Howlett MHC, Cenedese V, Klooster J, et al. (2014) Extracellular ATP Hydrolysis Inhibits Synaptic Transmission by Increasing pH Buffering in the Synaptic Cleft. doi:10.1371/journal.pbio.1001864

Objective and subjective indexes of auditory motion processing

The study focused at the objective and subjective indexes of human hearing system sensitivity towards different types of moving sound stimuli. The experiment employed two methods: electrophysiological (MMN recording) and psychophysical method (two-alternative forced choice). Two types of spatial sound stimuli simulated gradual and abrupt sound motion from the head midline. MMN as an objective index of spatial discrimination has been obtained in response to the subthreshold and the suprathreshold stimuli. An increase of trajectory length of the moving stimuli resulted in an increase of the MMN amplitude and of subjective discrimination as well, although their correlation remained below the significance level. The results obtained are discussed from the point of view of preconscious perception of auditory spatial information.

Preferring alphabet–keyboard compatibility: Congruency between spatial codes shapes the affective connotation of letters

When letters are encountered, two spatial stimulus codes resulting from their positions within the alphabet and on the computer keyboard are activated mentally. If these two spatial codes match, letter processing is more efficient. The present study tested whether the processing fluency gain resulting from alphabet–keyboard compatibility also enhances affective evaluations of letters. In Experiment 1, participants preferred alphabet–keyboard compatible over incompatible letters in a forced-choice preference rating. Similarly, in Experiment 2, liking ratings for alphabet–keyboard compatible letters were higher compared to incompatible letters. Moreover, in Experiment 3, preference ratings of non-words were positively correlated with the relative number of alphabet–keyboard compatible letters within these letter strings. These findings suggest that alphabet–keyboard compatibility shapes the affective connotation of letters. Moreover, this processing fluency–valence association is activated at the level of letters as well as whole letter strings.

Hippocampal place cell responses to distal and proximal cue manipulations in dopamine D2 receptor-knockout mice

The human hippocampus is critical for learning and memory. In rodents, hippocampal pyramidal neurons fire in a location-specific manner and form relational representations of environmental cues. The important roles of dopaminergic D1 receptors in learning and in hippocampal neural synaptic plasticity in novel environments have been previously shown. However, the roles of D2 receptors in hippocampal neural plasticity in response to novel and familiar spatial stimuli remain unclear. In order to clarify this issue, we recorded from hippocampal neurons in dopamine D2 receptor-knockout (D2R-KO) mice and their wild-type (WT) littermates during manipulations of distinct spatial cues in familiar and novel environments. Here, we report that D2R-KO mice showed substantial deficits in place-cell properties (number of place cells, intra-field firing rates, spatial tuning, and spatial coherence). Furthermore, although place cells in D2R-KO mice responded to manipulations of distal and proximal cues in both familiar and novel environments in a manner that was similar to place cells in WT mice, place fields were less stable in the D . The axes represent the differences between the peak and the valley of each waveform of EL2 and EL3.2R-KO mice in the familiar environment, but not in the novel environment. The present results suggested that D2 receptors in the hippocampus are important for place response stability. The place-cell properties of D2R-KO mice were similar to aged animals, suggesting that the alterations of place-cell properties in aged animals might be ascribed partly to alterations in the D2R in the HF of aged animals.

The Rostro-Caudal Axis of Frontal Cortex Is Sensitive to the Domain of Stimulus Information

Evidence suggests that lateral frontal cortex implements cognitive control processing along its rostro-caudal axis, yet other evidence supports a dorsal-ventral functional organization for processes engaged by different stimulus domains (e.g., spatial vs. nonspatial). This functional magnetic resonance imaging study investigated whether separable dorsolateral and ventrolateral rostro-caudal gradients exist in humans, while participants performed tasks requiring cognitive control at 3 levels of abstraction with language or spatial stimuli. Abstraction was manipulated by using 3 different task sets that varied in relational complexity. Relational complexity refers to the process of manipulating the relationship between task components (e.g., to associate a particular cue with a task) and drawing inferences about that relationship. Tasks using different stimulus domains engaged distinct posterior regions, but within the lateral frontal cortex, we found evidence for a single rostro-caudal gradient that was organized according to the level of abstraction and was independent of processing of the stimulus domain. However, a pattern of dorsal/ventral segregation of processing engaged by domain-specific information was evident in each separable frontal region only within the most rostral region recruited by task demands. These results suggest that increasingly abstract information is represented in the frontal cortex along distinct rostro-caudal gradients that also segregate along a dorsal-ventral axis dependent on task demands.