61 research outputs found
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A problem of overlap
Here we propose that earlier-demonstrated details in the primate visual cortical map may account for an otherwise puzzling (and problematic) finding in the current human fMRI literature. Specifically, the well-known regions LO and MT(+) reportedly overlap in the human cortical visual map, when those two regions are localized using standard stimulus comparisons in conventional fMRI experiments. Here we describe evidence supporting the idea that the apparent functional overlap between LO and MT arises from a third area (the MT crescent: “MTc”), which is well known to surround posterior MT based on earlier histological, neuroanatomical, and electrophysiological studies in nonhuman primates. If we assume that MTc also exists in human visual cortex, and that it has a location and functional properties intermediate to those in LO and MT, simplistic modeling confirmed that this arrangement could produce apparent overlap between localizers for LO and MT in conventional fMRI maps in human visual cortex
Increased Visual Stimulation Systematically Decreases Activity in Lateral Intermediate Cortex
Previous studies have attributed multiple diverse roles to the posterior superior temporal cortex (STC), both visually driven and cognitive, including part of the default mode network (DMN). Here, we demonstrate a unifying property across this multimodal region. Specifically, the lateral intermediate (LIM) portion of STC showed an unexpected feature: a progressively decreasing fMRI response to increases in visual stimulus size (or number). Such responses are reversed in sign, relative to well-known responses in classic occipital temporal visual cortex. In LIM, this “reversed” size function was present across multiple object categories and retinotopic eccentricities. Moreover, we found a significant interaction between the LIM size function and the distribution of subjects' attention. These findings suggest that LIM serves as a part of the DMN. Further analysis of functional connectivity, plus a meta-analysis of previous fMRI results, suggests that LIM is a heterogeneous area including different subdivisions. Surprisingly, analogous fMRI tests in macaque monkeys did not reveal a clear homolog of LIM. This interspecies discrepancy supports the idea that self-referential thinking and theory of mind are more prominent in humans, compared with monkeys
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A parametric study of fear generalization to faces and non-face objects: relationship to discrimination thresholds
Fear generalization is the production of fear responses to a stimulus that is similar—but not identical—to a threatening stimulus. Although prior studies have found that fear generalization magnitudes are qualitatively related to the degree of perceptual similarity to the threatening stimulus, the precise relationship between these two functions has not been measured systematically. Also, it remains unknown whether fear generalization mechanisms differ for social and non-social information. To examine these questions, we measured perceptual discrimination and fear generalization in the same subjects, using images of human faces and non-face control stimuli (“blobs”) that were perceptually matched to the faces. First, each subject’s ability to discriminate between pairs of faces or blobs was measured. Each subject then underwent a Pavlovian fear conditioning procedure, in which each of the paired conditioned stimuli (CS) were either followed (CS+) or not followed (CS−) by a shock. Skin conductance responses (SCRs) were also measured. Subjects were then presented with the CS+, CS− and five levels of a CS+-to-CS− morph continuum between the paired stimuli, which were identified based on individual discrimination thresholds. Finally, subjects rated the likelihood that each stimulus had been followed by a shock. Subjects showed both autonomic (SCR-based) and conscious (ratings-based) fear responses to morphs that they could not discriminate from the CS+ (generalization). For both faces and non-face objects, fear generalization was not found above discrimination thresholds. However, subjects exhibited greater fear generalization in the shock likelihood ratings compared to the SCRs, particularly for faces. These findings reveal that autonomic threat detection mechanisms in humans are highly sensitive to small perceptual differences between stimuli. Also, the conscious evaluation of threat shows broader generalization than autonomic responses, biased towards labeling a stimulus as threatening
Ultra-high spatial resolution BOLD fMRI in humans using combined segmented-accelerated VFA-FLEET with a recursive RF pulse design
Purpose
To alleviate the spatial encoding limitations of single-shot EPI by
developing multi-shot segmented EPI for ultra-high-resolution fMRI with reduced
ghosting artifacts from subject motion and respiration.
Methods
Segmented EPI can reduce readout duration and reduce acceleration factors,
however, the time elapsed between segment acquisitions (on the order of
seconds) can result in intermittent ghosting, limiting its use for fMRI. Here,
"FLEET" segment ordering--where segments are looped over before slices--was
combined with a variable flip angle progression (VFA-FLEET) to improve
inter-segment fidelity and maximize signal for fMRI. Scaling a sinc pulse's
flip angle for each segment (VFA-FLEET-Sinc) produced inconsistent slice
profiles and ghosting, therefore, a recursive Shinnar-Le Roux (SLR) RF pulse
design was developed (VFA-FLEET-SLR) to generate unique pulses for every
segment that together produce consistent slice profiles and signals.
Results
The temporal stability of VFA-FLEET-SLR was compared against
conventional-segmented EPI and VFA-FLEET-Sinc at 3 T and 7 T. VFA-FLEET-SLR
showed reductions in both intermittent and stable ghosting compared to
conventional-segmented and VFA-FLEET-Sinc, resulting in improved image quality
with a minor trade-off in temporal SNR. Combining VFA-FLEET-SLR with
acceleration, we achieved a 0.6-mm isotropic acquisition at 7 T--without zoomed
imaging or partial Fourier--demonstrating reliable detection of BOLD responses
to a visual stimulus. To counteract the increased repetition time from
segmentation, simultaneous multi-slice VFA-FLEET-SLR was demonstrated using
RF-encoded controlled aliasing.
Conclusions
VFA-FLEET with a recursive RF pulse design supports acquisitions with low
levels of artifact and spatial blur, enabling fMRI at previously inaccessible
spatial resolutions with a "full-brain" field of view.Comment: 51 pages (including supplement), 8 main figures, 6 supporting
figures. For supporting videos (8), please visit
https://github.com/aveberman/vfa-fleet. Note: this work has been accepted for
publication at Magnetic Resonance in Medicin
Thermoresistant Newcastle disease vaccine effectivelyprotects SPF, native, and commercial chickens inchallenge with virulent virus
Background: Due to the more stability and a better homogenecity in immune response, the use of thermoresistant vaccines in different chicken types has been increased. Objective: This study aimed to evaluate the efficacy of a newly developed Newcastle disease vaccine (ND.TR.IR ) originating from 1-2 strain in specific pathogen-free (SPF) and native and broiler chickens. Methods: Following determination of pathogenicity indices on the candidate seed, three efficacy examinations were conducted. In the first experiment, 120 1-day-old SPF chickens were randomly allocated to six groups and either vaccinated with ND.TR.IR via eye drop at 1, 7, and 21 days of age (V-1, V-7, and V-21), or considered as non-vaccinated control groups (C-1, C-7, and C-21). At 20th post-vaccination day, sera hemag-glutination inhibition (HI) antibody titres against ND virus (NDV) were measured and then the chickens were challenged by virulent NDV (vNDV). In the second and third experiments, the efficacy of ND.TR.IR vaccine was compared to routine vaccination program (B1 and LaSota) in native and broiler chickens that were vaccinated at 10 and 20 days of age, respectively. The HI antibody titres were measured on 10, 20, 30, and 40 days of age, and also challenge efficacy test with vNDV was conducted on 30 days of age. Results: The studied virus, as a vaccinal seed, complied with the pathogenicity indices of avirulent NDV and molecular identity of 1-2 strain. In the efficacy evaluation trials, the vaccinated chickens had higher HI antibody titres against NDV compared with their corresponding control chickens (p < 0.05). Results of the challenge tests indicated 95% and 100% protection against vNDV in native, SPF, and broiler-vaccinated chickens, respectively. Conclusions: The present findings indicated that administration of ND.TR.IR induced appropriate HI antibody titres against NDV in SPF, native, and broiler chickens associated with good protection in efficacy test
Neural Correlate of Filtering of Irrelevant Information from Visual Working Memory
In a dynamic environment stimulus task relevancy could be altered through time and it is not always possible to dissociate relevant and irrelevant objects from the very first moment they come to our sight. In such conditions, subjects need to retain maximum possible information in their WM until it is clear which items should be eliminated from WM to free attention and memory resources. Here, we examined the neural basis of irrelevant information filtering from WM by recording human ERP during a visual change detection task in which the stimulus irrelevancy was revealed in a later stage of the task forcing the subjects to keep all of the information in WM until test object set was presented. Assessing subjects' behaviour we found that subjects' RT was highly correlated with the number of irrelevant objects and not the relevant one, pointing to the notion that filtering, and not selection, process was used to handle the distracting effect of irrelevant objects. In addition we found that frontal N150 and parietal N200 peak latencies increased systematically as the amount of irrelevancy load increased. Interestingly, the peak latency of parietal N200, and not frontal N150, better correlated with subjects' RT. The difference between frontal N150 and parietal N200 peak latencies varied with the amount of irrelevancy load suggesting that functional connectivity between modules underlying fronto-parietal potentials vary concomitant with the irrelevancy load. These findings suggest the existence of two neural modules, responsible for irrelevant objects elimination, whose activity latency and functional connectivity depend on the number of irrelevant object
Impact of opioid-free analgesia on pain severity and patient satisfaction after discharge from surgery: multispecialty, prospective cohort study in 25 countries
Background: Balancing opioid stewardship and the need for adequate analgesia following discharge after surgery is challenging. This study aimed to compare the outcomes for patients discharged with opioid versus opioid-free analgesia after common surgical procedures.Methods: This international, multicentre, prospective cohort study collected data from patients undergoing common acute and elective general surgical, urological, gynaecological, and orthopaedic procedures. The primary outcomes were patient-reported time in severe pain measured on a numerical analogue scale from 0 to 100% and patient-reported satisfaction with pain relief during the first week following discharge. Data were collected by in-hospital chart review and patient telephone interview 1 week after discharge.Results: The study recruited 4273 patients from 144 centres in 25 countries; 1311 patients (30.7%) were prescribed opioid analgesia at discharge. Patients reported being in severe pain for 10 (i.q.r. 1-30)% of the first week after discharge and rated satisfaction with analgesia as 90 (i.q.r. 80-100) of 100. After adjustment for confounders, opioid analgesia on discharge was independently associated with increased pain severity (risk ratio 1.52, 95% c.i. 1.31 to 1.76; P < 0.001) and re-presentation to healthcare providers owing to side-effects of medication (OR 2.38, 95% c.i. 1.36 to 4.17; P = 0.004), but not with satisfaction with analgesia (beta coefficient 0.92, 95% c.i. -1.52 to 3.36; P = 0.468) compared with opioid-free analgesia. Although opioid prescribing varied greatly between high-income and low- and middle-income countries, patient-reported outcomes did not.Conclusion: Opioid analgesia prescription on surgical discharge is associated with a higher risk of re-presentation owing to side-effects of medication and increased patient-reported pain, but not with changes in patient-reported satisfaction. Opioid-free discharge analgesia should be adopted routinely
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