Transmission of blue (S) cone signals through the primate lateral geniculate nucleus

This study concerns the transmission of short-wavelength-sensitive (S) cone signals through the primate dorsal lateral geniculate nucleus. The principal cell classes, magnocellular (MC) and parvocellular (PC), are traditionally segregated into on- and off-subtypes on the basis of the sign of their response to luminance variation. Cells dominated by input from S-cones ('blue-on and blue-off') are less frequently encountered and their properties are less well understood. Here we characterize the spatial and chromatic properties of a large sample of blue-on and blue-off neurons and contrast them with those of PC and MC neurons. The results confirm that blue-on and blue-off cells have larger receptive fields than PC and MC neurons at equivalent eccentricities. Relative to blue-on cells, blue-off cells are less sensitive to S-cone contrast, have larger receptive fields, and show more low-pass spatial frequency tuning. Thus, blue-on and blue-off neurons lack the functional symmetry characteristic of on- and off-subtypes in the MC and PC pathways. The majority of MC and PC cells received no detectible input from S-cones. Where present, input from S-cones tended to provide weak inhibition to PC cells. All cell types showed evidence of a suppressive extra-classical receptive field driven largely or exclusively by ML-cones. These data indicate that S-cone signals are isolated to supply the classical receptive field mechanisms of blue-on and blue-off cells in the LGN, and that the low spatial precision of S-cone vision has origins in both classical and extraclassical receptive field properties of subcortical pathways.

Color signals in the primary visual cortex of marmosets

This study concerns the input from short-wavelength sensitive (S) cone photoreceptors to the primary visual cortex (striate cortex, Brodmann area 17, area V1) in marmosets. Signals from S-cones are thought to reach V1 by way of the koniocellular layers of the dorsal lateral geniculate nucleus. However, it is not known whether the S-cone afferent signals cause selective activation of cytochrome oxidase-rich cortical "blob" domains. To address this question, intrinsic optical signals and extracellular responses of V1 neurons were recorded. Stimuli consisted of drifting achromatic gratings and gratings that stimulated selectively either the S-cones or the medium-long wavelength sensitive (ML) cones. All stimuli produced contrast-dependent activation throughout the imaged regions of V1. The S- and ML-cone-selective stimuli produced activation levels of respectively 30% and 80% of that to achromatic gratings. No spatial variation in the strength of S-cone activation was apparent, and the ratio of S to ML activation was constant across all imaged regions. Consistently, in all of the single neurons recorded from V1, the functional input from S-cones was weaker than the input from ML-cones. We conclude that in the primary visual cortex of marmosets, S-cone signals are uniformly distributed.

Screening participation in individuals with a family history of colorectal cancer: a review

Literature regarding screening behaviour in individuals with a family history of colorectal cancer was reviewed, in order to determine the prevalence of screening in this population and identify factors associated with screening participation. Four electronic databases were searched from 1994. Thirty papers met the inclusion criteria, including 3 community surveys, 13 studies on first-degree relatives of colorectal cancer patients, and 14 studies on genetic services for colorectal cancer risk assessment. Individuals with a family history of colorectal cancer, who have not received risk assessment, frequently have never had any form of screening for colorectal cancer. Uptake of endoscopic screening when offered to individuals identified as being at increased risk was generally high (often >60% participation). Having a medical recommendation to screen, a stronger family history and perceiving fewer barriers to screening were identified as predictors of screening behaviour. Existing data suggest that use of screening tests in individuals with a family history of colorectal cancer is variable, and our understanding of factors associated with screening behaviour is limited. A number of methodological problems in research to date were identified, and further research is needed in order to inform interventions to support sustained screening participation in this population.

Urban birds have broader environmental tolerance

Urbanization dramatically changes the composition and diversity of biotic communities. The characteristics distinguishing species that persist in urban environments, however, are poorly understood. Here we test the hypothesis that broadly adapted organisms are better able to tolerate urbanization, using a phylogenetically controlled, global comparison of birds. We compared elevational and latitudinal distributions of 217 urban birds found in 73 of the world's largest cities with distributions of 247 rural congeners to test the hypothesis that urban birds possess broader environmental tolerance. Urban birds had markedly broader environmental tolerance than rural congeners, as estimated by elevational and latitudinal distributions. Our results suggest that broad environmental tolerance may predispose some birds to thrive in urban habitats. The mechanisms mediating such environmental tolerance warrant further investigation, but probably include greater behavioural, physiological and ecological flexibility.

Pre-migratory life history stages of juvenile Arctic birds: costs, constraints, and trade-offs

Many young birds on the Arctic tundra are confronted by a challenging task: they must molt their feathers and accumulate fat stores for the autumn migration before climatic conditions deteriorate. Our understanding of the costs and constraints associated with these stages is extremely limited. We investigated post-juvenal molt and premigratory fattening in free-ranging juvenile White-crowned Sparrows (Zonotrichia leucophrys gambelii) on the Arctic tundra. We found evidence for trade-offs between premigratory fat accumulation and molt: heavily molting birds had significantly less fat. Birds increased the rate of fat accumulation as the season progressed, but we found no evidence of a similar increase in rate of molt. Using a controlled captive study to isolate the energetic costs of body feather replacement, we found no difference in fat or size-corrected mass of birds actively growing body feathers as compared to controls. Molting birds, however, consumed 17% more food than controls, suggesting a significant cost of body feather growth. Our results provide evidence of significant costs, constraints, and trade-offs associated with post-juvenal molt and premigratory fat accumulation in young Arctic birds.

Cognitive-behavioral therapy versus temporal pulse amplitude biofeedback training for recurrent headache

Sixty-four headache sufferers were allocated randomly to cognitive-behavioral therapy (CBT), temporal pulse amplitude (TPA) biofeedback training, or waiting-list control. Fifty-one participants (14M/37F) completed the study, 30 with migraine and 21 with tension-type headache. Treatment consisted of 8, 1-hour sessions. CBT was highly effective, with an average reduction in headaches from pre- to posttreatment of 68%, compared with 56% for biofeedback, and 20% for the control condition. Headaches continued to decrease to 12 month follow-up for CBT. Improvement with CBT was associated with baseline coping skills, social support, and physiological measures at rest and in response to stress, particularly TPA. Changes on some of these measures were correlated with changes in headaches. No significant predictors of response to biofeedback emerged.

The unsolved mystery of vision

Vision looms large in neuroscience--it is the subject of a gigantic literature and four Nobel prizes--but there is a growing realization that there are problems with the textbook explanation of how mammalian vision works. Here we will summarize the evidence behind this disquiet. In effect, we shall present a portrait of a field that is 'stuck'. Our initial focus, because it is our area of expertise, is on evidence that the early steps of mammalian vision are more diverse and more interesting than is usually imagined, so that our understanding of the later stages is in trouble right from the start. But we will also summarize problems, raised by others, with the later stages themselves.

Health beliefs and behaviors of women who have received genetic counseling for breast cancer

There are both genetic and behavioral risk factors for breast cancer, but the interaction between these factors is not clear. Little is known about the impact of receiving genetic risk information for breast cancer on behaviors such as diet and physical activity. Seven focus groups were conducted with 23 women who had recently received genetic counseling for breast cancer, in order to explore health beliefs and behaviors following genetic counseling. Findings revealed that there was much confusion and uncertainty about the associations between health behaviors and breast cancer risk, and participants reported that receiving genetic counseling had little impact on health protective behaviors. Further research is required to understand variation in response to genetic risk information, and to assess the impact of providing additional information regarding lifestyle factors.

Sample Tracking in an Automated Cytogenetic Biodosimetry Laboratory for Radiation Mass Casualties

Chromosome aberration-based dicentric assay is expected to be used after mass casualty life-threatening radiation exposures to assess radiation dose to individuals. This will require processing of a large number of samples for individual dose assessment and clinical triage to aid treatment decisions. We have established an automated, high-throughput, cytogenetic biodosimetry laboratory to process a large number of samples for conducting the dicentric assay using peripheral blood from exposed individuals according to internationally accepted laboratory protocols (i.e., within days following radiation exposures). The components of an automated cytogenetic biodosimetry laboratory include blood collection kits for sample shipment, a cell viability analyzer, a robotic liquid handler, an automated metaphase harvester, a metaphase spreader, high-throughput slide stainer and coverslipper, a high-throughput metaphase finder, multiple satellite chromosome-aberration analysis systems, and a computerized sample tracking system. Laboratory automation using commercially available, off-the-shelf technologies, customized technology integration, and implementation of a laboratory information management system (LIMS) for cytogenetic analysis will significantly increase throughput.This paper focuses on our efforts to eliminate data transcription errors, increase efficiency, and maintain samples' positive chain-of-custody by sample tracking during sample processing and data analysis. This sample tracking system represents a "beta" version, which can be modeled elsewhere in a cytogenetic biodosimetry laboratory, and includes a customized LIMS with a central server, personal computer workstations, barcode printers, fixed station and wireless hand-held devices to scan barcodes at various critical steps, and data transmission over a private intra-laboratory computer network. Our studies will improve diagnostic biodosimetry response, aid confirmation of clinical triage, and medical management of radiation exposed individuals.

Revisiting Jablonski (1993): cladogenesis and range expansion explain latitudinal variation in taxonomic richness

The increase in diversity towards the equator arises from latitudinal variation in rates of cladogenesis, extinction, immigration and/or emigration of taxa. We tested the relative contribution of all four processes to the latitudinal gradient in 26 marine invertebrate orders with extensive fossil records, examined previously by David Jablonski. Coupling Jablonski's estimates of latitudinal variation in cladogenesis with new data on patterns of extinction and current distributions, we show that the present-day gradient in diversity is caused by higher rates of cladogenesis and subsequent range expansion (immigration) at lower latitudes. In contrast, extinction and emigration were not important in the creation of the latitudinal gradient in ordinal richness. This work represents one of the first simultaneous tests of the role of all four processes in the creation of the latitudinal gradient in taxonomic richness, and suggests that low tropical extinction rates are not essential to the creation of latitudinal diversity gradients.

A qualitative study of health professionals' views regarding provision of information about health-protective behaviors during genetic consultation for breast cancer

This study aimed to explore health professionals' views and practice regarding the provision of information about health-protective behaviors (e.g., exercise, alcohol consumption, diet) during genetic consultation for breast cancer. Ten genetic counselors participated in three focus groups, and seven medical specialists were interviewed in a focus group or individually. Data was analyzed using the constant comparative method. Findings suggested that health professionals held differing, often opposing, views about the value of health-protective behaviors for women at increased risk of breast cancer. The content and extent of information provided about health-protective behaviors varied widely, and participants expressed a need to form consensus regarding information provision both within and across clinics. The main barriers to providing information regarding health-protective behaviors included the lack of research evidence regarding the impact of these factors and higher priority of other information need to be provided in the limited consultation time. Participants generally did not consider it their role to promote health-protective behaviors, and were concerned about the psychological impact of providing information about behavioral risk factors during genetic consultations.

Geniculocortical relay of blue-off signals in the primate visual system

A fundamental dichotomy in the subcortical visual system exists between on- and off-type neurons, which respectively signal increases and decreases of light intensity in the visual environment. In primates, signals for red-green color vision are carried by both on- and off-type neurons in the parvocellular division of the subcortical pathway. It is thought that on-type signals for blue-yellow color vision are carried by cells in a distinct, diffusely projecting (koniocellular) pathway, but the pathway taken by blue-off signals is not known. Here, we measured blue-off responses in the subcortical visual pathway of marmoset monkeys. We found that the cells exhibiting blue-off responses are largely segregated to the koniocellular pathway. The blue-off cells show relatively large receptive fields, sluggish responses to maintained contrast, little sign of an inhibitory receptive-field surround mechanism, and negligible functional input from an intrinsic (melanopsin-based) phototransductive mechanism. These properties are consistent with input from koniocellular or "W-like" ganglion cells in the retina and suggest that blue-off cells, as previously shown for blue-on cells, could contribute to cortical mechanisms for visual perception via the koniocellular pathway.

Specificity of M and L cone inputs to receptive fields in the parvocellular pathway: random wiring with functional bias

Many of the parvocellular pathway (PC) cells in primates show red-green spectral selectivity (cone opponency), but PC ganglion cells in the retina show no anatomical signs of cone selectivity. Here we asked whether responses of PC cells are compatible with "random wiring" of cone inputs. We measured long-wavelength-sensitive (L) and medium-wavelength-sensitive (M) cone inputs to PC receptive fields in the dorsal lateral geniculate of marmosets, using discrete stimuli (apertures and annuli) to achieve functional segregation of center and surround. Receptive fields between the fovea and 30 degrees eccentricity were measured. We show that, in opponent PC cells, the center is dominated by one (L or M) cone type, with normally <20% contribution from the other cone type (high "cone purity"), whereas non-opponent cells have mixed L and M cone inputs to the receptive field center. Furthermore, opponent response strength depends on the overall segregation of L and M cone inputs to center and surround rather than exclusive input from one cone type to either region. These data are consistent with random wiring. The majority of PC cells in both foveal (<8 degrees) and peripheral retina nevertheless show opponent responses. This arises because cone purity in the receptive field surround is at least as high as in the center, and the surround in nearly all opponent PC cells is dominated by the opposite cone type to that which dominates the center. These functional biases increase the proportion of opponent PC cells, but their anatomical basis is unclear.

Response variability of marmoset parvocellular neurons

This study concerns the properties of neurons carrying signals for colour vision in primates. We investigated the variability of responses of individual parvocellular lateral geniculate neurons of dichromatic and trichromatic marmosets to drifting sinusoidal luminance and chromatic gratings. Response variability was quantified by the cycle-to-cycle variation in Fourier components of the response. Averaged across the population, the variability at low contrasts was greater than predicted by a Poisson process, and at high contrasts the responses were approximately 40% more variable than responses at low contrasts. The contrast-dependent increase in variability was nevertheless below that expected from the increase in firing rate. Variability falls below the Poisson prediction at high contrast, and intrinsic variability of the spike train decreases as contrast increases. Thus, while deeply modulated responses in parvocellular cells have a larger absolute variability than weakly modulated ones, they have a more favourable signal: noise ratio than predicted by a Poisson process. Similar results were obtained from a small sample of magnocellular and koniocellular ('blue-on') neurons. For parvocellular neurons with pronounced colour opponency, chromatic responses were, on average, less variable (10-15%, p<0.01) than luminance responses of equal magnitude. Conversely, non-opponent parvocellular neurons showed the opposite tendency. This is consistent with a supra-additive noise source prior to combination of cone signals. In summary, though variability of parvocellular neurons is largely independent of the way in which they combine cone signals, the noise characteristics of retinal circuitry may augment specialization of parvocellular neurons to signal luminance or chromatic contrast.