Retinotopic Mapping of Categorical and Coordinate Spatial Relation Processing in Early Visual Cortex

Spatial relations are commonly divided in two global classes. Categorical relations concern abstract relations which define areas of spatial equivalence, whereas coordinate relations are metric and concern exact distances. Categorical and coordinate relation processing are thought to rely on at least partially separate neurocognitive mechanisms, as reflected by differential lateralization patterns, in particular in the parietal cortex. In this study we address this textbook principle from a new angle. We studied retinotopic activation in early visual cortex, as a reflection of attentional distribution, in a spatial working memory task with either a categorical or a coordinate instruction. Participants were asked to memorize a dot position, with regard to a central cross, and to indicate whether a subsequent dot position matched the first dot position, either categorically (opposite quadrant of the cross) or coordinately (same distance to the centre of the cross). BOLD responses across the retinotopic maps of V1, V2, and V3 indicate that the spatial distribution of cortical activity was different for categorical and coordinate instructions throughout the retention interval; a more local focus was found during categorical processing, whereas focus was more global for coordinate processing. This effect was strongest for V3, approached significance in V2 and was absent in V1. Furthermore, during stimulus presentation the two instructions led to different levels of activation in V3 during stimulus encoding; a stronger increase in activity was found for categorical processing. Together this is the first demonstration that instructions for specific types of spatial relations may yield distinct attentional patterns which are already reflected in activity early in the visual cortex

Intrinsic activity in the fly brain gates visual information during behavioral choices

The small insect brain is often described as an input/output system that executes reflex-like behaviors. It can also initiate neural activity and behaviors intrinsically, seen as spontaneous behaviors, different arousal states and sleep. However, less is known about how intrinsic activity in neural circuits affects sensory information processing in the insect brain and variability in behavior. Here, by simultaneously monitoring Drosophila's behavioral choices and brain activity in a flight simulator system, we identify intrinsic activity that is associated with the act of selecting between visual stimuli. We recorded neural output (multiunit action potentials and local field potentials) in the left and right optic lobes of a tethered flying Drosophila, while its attempts to follow visual motion (yaw torque) were measured by a torque meter. We show that when facing competing motion stimuli on its left and right, Drosophila typically generate large torque responses that flip from side to side. The delayed onset (0.1-1 s) and spontaneous switch-like dynamics of these responses, and the fact that the flies sometimes oppose the stimuli by flying straight, make this behavior different from the classic steering reflexes. Drosophila, thus, seem to choose one stimulus at a time and attempt to rotate toward its direction. With this behavior, the neural output of the optic lobes alternates; being augmented on the side chosen for body rotation and suppressed on the opposite side, even though the visual input to the fly eyes stays the same. Thus, the flow of information from the fly eyes is gated intrinsically. Such modulation can be noise-induced or intentional; with one possibility being that the fly brain highlights chosen information while ignoring the irrelevant, similar to what we know to occur in higher animals

Sour Taste Responses in Mice Lacking PKD Channels

The polycystic kidney disease-like ion channel PKD2L1 and its associated partner PKD1L3 are potential candidates for sour taste receptors. PKD2L1 is expressed in type III taste cells that respond to sour stimuli and genetic elimination of cells expressing PKD2L1 substantially reduces chorda tympani nerve responses to sour taste stimuli. However, the contribution of PKD2L1 and PKD1L3 to sour taste responses remains unclear.We made mice lacking PKD2L1 and/or PKD1L3 gene and investigated whole nerve responses to taste stimuli in the chorda tympani or the glossopharyngeal nerve and taste responses in type III taste cells. In mice lacking PKD2L1 gene, chorda tympani nerve responses to sour, but not sweet, salty, bitter, and umami tastants were reduced by 25–45% compared with those in wild type mice. In contrast, chorda tympani nerve responses in PKD1L3 knock-out mice and glossopharyngeal nerve responses in single- and double-knock-out mice were similar to those in wild type mice. Sour taste responses of type III fungiform taste cells (GAD67-expressing taste cells) were also reduced by 25–45% by elimination of PKD2L1.These findings suggest that PKD2L1 partly contributes to sour taste responses in mice and that receptors other than PKDs would be involved in sour detection

The Relationship between Amygdala Activation and Passive Exposure Time to an Aversive Cue during a Continuous Performance Task

The allocation of attention modulates negative emotional processing in the amygdala. However, the role of passive exposure time to emotional signals in the modulation of amygdala activity during active task performance has not been examined. In two functional Magnetic Resonance Imaging (fMRI) experiments conducted in two different groups of healthy human subjects, we examined activation in the amygdala due to cued anticipation of painful stimuli while subjects performed a simple continuous performance task (CPT) with either a fixed or a parametrically varied trial duration. In the first experiment (N = 16), engagement in the CPT during a task with fixed trial duration produced the expected attenuation of amygdala activation, but close analysis suggested that the attenuation occurred during the period of active engagement in CPT, and that amygdala activity increased proportionately during the remainder of each trial, when subjects were passively exposed to the pain cue. In the second experiment (N = 12), the duration of each trial was parametrically varied, and we found that amygdala activation was linearly related to the time of passive exposure to the anticipatory cue. We suggest that amygdala activation during negative anticipatory processing depends directly on the passive exposure time to the negative cue

Monounsaturated fatty acid, carbohydrate intake, and diabetes status are associated with arterial pulse pressure

<p>Abstract</p> <p>Background</p> <p>Diabetes is a global epidemic. Cardiovascular disease (CVD) is one of the most prevalent consequences of diabetes. Nutrition is considered a modifiable risk factor for CVD, particularly for individuals with diabetes; albeit, there is little consensus on the role of carbohydrates, proteins and fats for arterial health for persons with or without diabetes. In this study, we examined the association of macronutrients with arterial pulse pressure (APP), a surrogate measure of arterial health by diabetes status and race.</p> <p>Methods</p> <p>Participants were 892 Mexican Americans (MA), 1059 Black, non-Hispanics (BNH) and 2473 White, non-Hispanics (WNH) with and without diabetes of a weighted sample from the National Nutrition and Health Examination Survey (NHANES) 2007-2008. The cross-sectional analysis was performed with IBM-SPSS version 18 with the complex sample analysis module. The two-year sample weight for the sub-sample with laboratory values was applied to reduce bias and approximate a nationally, representative sample. Arterial stiffness was assessed by arterial pulse pressure (APP).</p> <p>Results</p> <p>APP was higher for MA [B = 0.063 (95% CI 0.015 to 0.111), p = 0.013] and BNH [B = 0.044 (95% CI 0.006 to 0.082), p = 0.018] than WNH, controlling for diabetes, age, gender, body mass index (BMI), fiber intake, energy intake (Kcal) and smoking. A two-way interaction of diabetes by carbohydrate intake (grams) was inversely associated with APP [B = -1.18 (95% CI -0.178 to -0.058), p = 0.001], controlling for race, age, gender, BMI, Kcal and smoking. BNH with diabetes who consumed more mono-unsaturated fatty acids (MUFA) than WNH with diabetes had lower APP [B = -0.112 (95%CI-0.179 to -0.045), p = 0.003] adjusting for saturated fatty acids, Kcal, age, gender, BMI and smoking.</p> <p>Conclusion</p> <p>Higher MUFA and carbohydrate intake for persons with diabetes reflecting lower APP may be due to replacement of saturated fats with CHO and MUFA. The associations of APP with diabetes, race and dietary intake need to be confirmed with intervention and prospective studies. Confirmation of these results would suggest that dietary interventions for minorities with diabetes may improve arterial health.</p

Individual Differences and Metacognitive Knowledge of Visual Search Strategy

A crucial ability for an organism is to orient toward important objects and to ignore temporarily irrelevant objects. Attention provides the perceptual selectivity necessary to filter an overwhelming input of sensory information to allow for efficient object detection. Although much research has examined visual search and the ‘template’ of attentional set that allows for target detection, the behavior of individual subjects often reveals the limits of experimental control of attention. Few studies have examined important aspects such as individual differences and metacognitive strategies. The present study analyzes the data from two visual search experiments for a conjunctively defined target (Proulx, 2007). The data revealed attentional capture blindness, individual differences in search strategies, and a significant rate of metacognitive errors for the assessment of the strategies employed. These results highlight a challenge for visual attention studies to account for individual differences in search behavior and distractibility, and participants that do not (or are unable to) follow instructions

S1P lyase regulates DNA damage responses through a novel sphingolipid feedback mechanism

The injurious consequences of ionizing radiation (IR) to normal human cells and the acquired radioresistance of cancer cells represent limitations to cancer radiotherapy. IR induces DNA damage response pathways that orchestrate cell cycle arrest, DNA repair or apoptosis such that irradiated cells are either repaired or eliminated. Concomitantly and independent of DNA damage, IR activates acid sphingomyelinase (ASMase), which generates ceramide, thereby promoting radiation-induced apoptosis. However, ceramide can also be metabolized to sphingosine-1-phosphate (S1P), which acts paradoxically as a radioprotectant. Thus, sphingolipid metabolism represents a radiosensitivity pivot point, a notion supported by genetic evidence in IR-resistant cancer cells. S1P lyase (SPL) catalyzes the irreversible degradation of S1P in the final step of sphingolipid metabolism. We show that SPL modulates the kinetics of DNA repair, speed of recovery from G2 cell cycle arrest and the extent of apoptosis after IR. SPL acts through a novel feedback mechanism that amplifies stress-induced ceramide accumulation, and downregulation/inhibition of either SPL or ASMase prevents premature cell cycle progression and mitotic death. Further, oral administration of an SPL inhibitor to mice prolonged their survival after exposure to a lethal dose of total body IR. Our findings reveal SPL to be a regulator of ASMase, the G2 checkpoint and DNA repair and a novel target for radioprotection

Amiloride-sensitive channels in type I fungiform taste cells in mouse

<p>Abstract</p> <p>Background</p> <p>Taste buds are the sensory organs of taste perception. Three types of taste cells have been described. Type I cells have voltage-gated outward currents, but lack voltage-gated inward currents. These cells have been presumed to play only a support role in the taste bud. Type II cells have voltage-gated Na⁺and K⁺current, and the receptors and transduction machinery for bitter, sweet, and umami taste stimuli. Type III cells have voltage-gated Na⁺, K⁺, and Ca²⁺currents, and make prominent synapses with afferent nerve fibers. Na⁺salt transduction in part involves amiloride-sensitive epithelial sodium channels (ENaCs). In rodents, these channels are located in taste cells of fungiform papillae on the anterior part of the tongue innervated by the chorda tympani nerve. However, the taste cell type that expresses ENaCs is not known. This study used whole cell recordings of single fungiform taste cells of transgenic mice expressing GFP in Type II taste cells to identify the taste cells responding to amiloride. We also used immunocytochemistry to further define and compare cell types in fungiform and circumvallate taste buds of these mice.</p> <p>Results</p> <p>Taste cell types were identified by their response to depolarizing voltage steps and their presence or absence of GFP fluorescence. TRPM5-GFP taste cells expressed large voltage-gated Na⁺and K⁺currents, but lacked voltage-gated Ca²⁺currents, as expected from previous studies. Approximately half of the unlabeled cells had similar membrane properties, suggesting they comprise a separate population of Type II cells. The other half expressed voltage-gated outward currents only, typical of Type I cells. A single taste cell had voltage-gated Ca²⁺current characteristic of Type III cells. Responses to amiloride occurred only in cells that lacked voltage-gated inward currents. Immunocytochemistry showed that fungiform taste buds have significantly fewer Type II cells expressing PLC signalling components, and significantly fewer Type III cells than circumvallate taste buds.</p> <p>Conclusion</p> <p>The principal finding is that amiloride-sensitive Na⁺channels appear to be expressed in cells that lack voltage-gated inward currents, likely the Type I taste cells. These cells were previously assumed to provide only a support function in the taste bud.</p

Optic Flow Stimuli in and Near the Visual Field Centre: A Group fMRI Study of Motion Sensitive Regions

Motion stimuli in one visual hemifield activate human primary visual areas of the contralateral side, but suppress activity of the corresponding ipsilateral regions. While hemifield motion is rare in everyday life, motion in both hemifields occurs regularly whenever we move. Consequently, during motion primary visual regions should simultaneously receive excitatory and inhibitory inputs. A comparison of primary and higher visual cortex activations induced by bilateral and unilateral motion stimuli is missing up to now. Many motion studies focused on the MT+ complex in the parieto-occipito-temporal cortex. In single human subjects MT+ has been subdivided in area MT, which was activated by motion stimuli in the contralateral visual field, and area MST, which responded to motion in both the contra- and ipsilateral field. In this study we investigated the cortical activation when excitatory and inhibitory inputs interfere with each other in primary visual regions and we present for the first time group results of the MT+ subregions, allowing for comparisons with the group results of other motion processing studies. Using functional magnetic resonance imaging (fMRI), we investigated whole brain activations in a large group of healthy humans by applying optic flow stimuli in and near the visual field centre and performed a second level analysis. Primary visual areas were activated exclusively by motion in the contralateral field but to our surprise not by central flow fields. Inhibitory inputs to primary visual regions appear to cancel simultaneously occurring excitatory inputs during central flow field stimulation. Within MT+ we identified two subregions. Putative area MST (pMST) was activated by ipsi- and contralateral stimulation and located in the anterior part of MT+. The second subregion was located in the more posterior part of MT+ (putative area MT, pMT)