Sectional anatomy of the olfactory pathways

AIM

The purpose of this study was to provide practical anatomic data for imaging diagnosis of olfactory pathways and operation of nasal cavity and anterior cranial fossae.

METHODS

Sectional anatomy of olfactory pathways were investigated specially on 17 sets of Chinese adult cadavers and 9 sets of serial magnetic resonance (MR) imaging of normal adult on serial transverse, sagittal and coronal sections respectively.

RESULTS

We recognized olfactory bulb, olfactory tract, medial and lateral olfactory striae, olfactory trigone, anterior perforated substance and piriform lobe on transverse, sagittal and coronal sections respectively. On the 5-7 serial coronal sections from crista galli of ethmoid bone to the optic chiasm, the cusp ellipse olfactory bulb and the triangular tract were situated in the shallow part of the olfactory sulcus.

CONCLUSION

The olfactory bulb and olfactory tract lay tightly on the ethmoidal cribriform plate and jugum sphenoidale, in the olfactory cistern of the shallow part of the olfactory sulcus, the ethmoid sinus and sphenoid sinus inferiorly.

Comparison of photodegradative efficiencies and mechanisms of Victoria Blue R assisted by Nafion-coated and fluorinated TiO2 photocatalysts

The purposes of this research were to study the effects of two modified photocatalysts, Nafion-coated TiO(2) and fluorinated TiO(2), and photocatalytic degradation of Victoria Blue R in aqueous solution. Photocatalytic degradation of Victoria Blue R was accelerated by the modified photocatalysts. Bulk and surface characterizations of the resulting powders were carried out. Attachment of the anions to the TiO(2) surface using the Nafion-coated-TiO(2) possibly results in increased adsorption of the cationic dye, and the degradation rate is larger for the cationic dye. It was found that Victoria Blue R on the two illuminated TiO(2) surfaces underwent very different changes. To obtain a better understanding on the mechanistic details of this modified-TiO(2)-assisted photodegradation of the Victoria Blue R dye with UV irradiation, a large number of intermediates of the process were separated, identified, and characterized by a high-performance liquid chromatography-mass spectrometry technique. Several probable photodegradation pathways were proposed and discussed.

First Report of Capsicum chlorosis virus Infecting Amaryllis and Blood Lily in Taiwan

Capsicum chlorosis virus (CaCV), a thrips-transmitted, tentative species in the genus Tospovirus, family Bunyaviridae, was first identified in solanaceous crops, but also infects several ornamental crops such as orchid (4), gloxinia (3), and calla lily (1). From 2005 to 2007, virus-like yellow ringspots were observed on the leaves of amaryllis (Hippeastrum hybridum Hort.) and blood lily (Haemanthus multiflorus Martyn.) plants cultured in screenhouses and a private garden, respectively. Three of several hundred amaryllis plants in screenhouses from two places were observed as showing yellow ringspot symptoms and one of six blood lily plants was observed as showing similar yellow ringspot symptoms. Sap extracts from symptomatic leaves were inoculated to Chenopodium quinoa Willd. and the resulting local lesions were passaged three successive times to C. quinoa for virus isolation. Using the tospovirus genus-specific primers gL3637 and gL4435c designed from the conserved region in the L RNA (2), DNA fragments of the expected size of 800 bp were amplified by reverse transcription (RT)-PCR from field samples and local lesions from C. quinoa. Extracts from the diseased plants and local lesions of C. quinoa reacted strongly with antiserum against the nucleocapsid (N) protein of CaCV in ELISA and western blotting. To confirm the identity of this virus, we amplified the N gene from three amaryllis and one blood lily source using primer pair WN2328 and WN3534 designed from the S RNA of Watermelon silver mottle virus (1), and these products were cloned and sequenced. The sequence from each virus isolate was determined from three independent clones. The nucleotide and deduced amino acid sequences of N genes for the blood lily isolate (GenBank Accession No. EF101344) and three amaryllis isolates (GenBank Accession Nos. EF101343, EF137177, and FJ185170) had identities greater than 97% with that of a CaCV isolate infecting Capsicum spp. found in Australia (GenBank Accession No. AY036057). Phylogenetic analysis using maximum parsimony showed that these sequences clustered with CaCV. These results show that the virus identified from amaryllis and blood lily that were expressing yellow ringspot symptoms are isolates of CaCV. To our knowledge, this is the first report of CaCV naturally infecting amaryllis and blood lily and it could become an important threat to ornamental production in Taiwan. References: (1) C. C. Chen et al. Plant Dis. 91:1201, 2007. (2) F. H. Chu et al. Phytopathology 91:361, 2001. (3) H. T. Hsu et al. J. Gen. Plant Pathol. 66:167, 2000. (4) Y. X. Zheng et al. Eur. J. Plant Pathol. 120:199, 2008.

Chromate reduction by zero-valent Al metal as catalyzed by polyoxometalate

In spite of a high reduction potential of zero-valent Al (ZVAl), its ability to reduce Cr(VI), a widespread pollutant, to less toxic Cr(III) remains to be uncovered. In the present study, Cr(VI) reduction by ZVAl was conducted to evaluate the potential application of Al as a reductant for Cr(VI). Polyoxometalate (POM, HNa(2)PW(12)O(40)), a catalyst, was used to accelerate Cr(VI) reduction by Al. The reaction of 0.192mM Cr(VI) on ZVAl was investigated in the presence of N(2) or O(2) at pH 1. A slight decrease in Cr(VI) concentration was observed on as-received (uncleaned) ZVAl due to the presence of oxide layer with a low surface area (ca. 3.4x10(-3)m(2)/g) of ZVAl. On addition of 0.1mM POM, Cr(VI) reduction on uncleaned ZVAl increased significantly. This is attributed to the unique properties of POM, which has a Brphinsted acidity higher than usual inorganic acids such as H(2)SO(4) and HCl. Thus, POM could remove rapidly the oxidize layer on ZVAl, followed by acting as a shuttle for electron transfer from ZVAl to Cr(VI). Under a N(2) atmosphere, one- or two-electron reduction of POM by ZVAl was responsible for Cr(VI) reduction in the early stage of the reaction. However, during reaction with ZVAl over 120min, three-electron reduction of POM predominated over Cr(VI) reduction. On interaction of O(2) with reduced POM, the formation of H(2)O(2) was responsible for subsequent Cr(VI) reduction. The results suggest that POM is an efficient catalyst for Cr(VI) reduction by Al due to the extremely rapid consumption of reduced POM or H(2)O(2) by Cr(VI).

Abstract B42: Methotrexate inhibits histone deacetylase activity and exhibits anti-tumor activity via acetylation and stabilization of p53

Methotrexate (MTX) is a dihydrofolate reductase (DHFR) inhibit or that has been widely used as an anti-cancer drug in different kinds of human cancers. Histone deacetylase (HDAC) overexpression is usually found in tumors, which inhibits the expression of tumor suppressor genes. HDAC inhibitors (HDACi) reactivate these tumor suppressor genes and serve as potential anticancer drugs. In the present study, we found that MTX shared structural similarity with HDACi. Molecular modeling analysis provided an evidence for the interaction of MTX with HDAC. In vitro HDAC activity assay demonstrated its inhibition on HDAC activity in various human cancer cells. The global acetylation of histone-H3 was also induced by MTX. Post-translational modification of p53 plays a critical role in regulating its activity and stability. MTX promoted p53 acetylaion at Lys 373/382 and phosphorylation at Ser15 and Ser392, then increasing its stability and transcriptional activity. Stabilized p53 further induced the expression of its downstream gene, p21. MTX induced apoptosis and inhibited cell viability, which was dependent on p53 expression. This study provides the first time that MTX acts as a HDACi. In addition, MTX induces p53 acetylation and stabilization, and mediates p53-dependent apoptosis and growth inhibition in human cancer cells.

Citation Information: Cancer Res 2009;69(23 Suppl):B42.

Patient-driven loop control for ambulation function restoration in a non-invasive functional electrical stimulation system

PURPOSE

In this study, a patient-driven loop control in a non-invasive functional electrical stimulation (FES) system was designed to restore ambulation function of patients with stroke with their residual capabilities.

METHOD

With this patient-driven loop control, patients use the electromyographic (EMG) signals from their voluntary controlled muscles in affected extremity to adjust stimulus parameters of the system. A special designed FES system generated electrical stimuli to excite the paralysed muscles through surface electrodes on the basis of the control command from the residual myoelectric signals. The EMG signals were also served as the trigger and the adjustment of stimulus parameters and thereby adding versatility of the FES system. One patient with hemiplegia was recruited to conduct clinical evaluation and treated by using the new closed-loop FES system.

RESULTS

The experimental results showed that hemiplegic could successfully control the system to restore their lost ambulation functions with the strategy of patient-driven loop control. It is revealed that the mean velocity, cadence, stride length, active ankle motion range and functional ambulation category have improved significantly from 0.22 + or - 0.17 m/s, 37.3 + or - 15.5 steps/min, 0.32 + or - 0.11 m, 10 degrees , level 2 to 0.46 + or - 0.23 m/s, 58.2 + or - 19.1 steps/min, 0.73 + or - 0.22 m, 35 degrees , level 4 respectively for the patient. A paired t-test indicated that differences in the EMG of the tibialis anterior and the gastrocnemius muscles between patient's disabled (affected-side) foot and normal (unaffected-side) foot are not significant (p > 0.05) after 12 weeks of training.

CONCLUSIONS

According to the experiment results, this patient-driven loop control can be beneficial for patient with hemiplegia to restore their ambulation functions such as dorsi-flexion and plantar-flexion. The control strategy of this study has the potential to be employed not only in the FES system but also in other assistive devices.

Nanocontact resistance and structural disorder induced resistivity variation in metallic metal-oxide nanowires

Several systems of metallic metal-oxide nanowires (NWs), including pure RuO2 and as-implanted and annealed Ru(0.98)Cu(0.02)O2 and Ru(0.93)Cu(0.07)O2 NWs, have been employed in two-probe electrical characterizations by using a transmission electron microscope-scanning tunneling microscope technique with a gold tip. Thermal, mechanical, and electron beam exposing treatments are consecutively applied to reduce the electrical contact resistance, generated from the interface between the NW and the gold tip, so as to evaluate the intrinsic NW resistance. It is found that the residual contact resistance cannot be entirely removed. For each system of metallic metal-oxide NWs, several tens of NWs are applied to electrical characterizations and the total resistances unveil a linear dependence on the ratio of the length to the area of the NWs. As a result, the average resistivity and the contact resistance of the metallic metal-oxide NWs could be evaluated at room temperatures. The average resistivities of pure RuO2 NWs agree well with the results obtained from standard two- and four-probe electrical-transport measurements. In addition, the as-implanted Cu-RuO2 NWs reveal disordered crystalline structures in high-resolution TEM images and give higher resistivities in comparison with that of pure RuO2 NWs. The residual contact resistances of all kinds of metallic metal-oxide NWs unveil, more surprisingly, an approximation value of several kilohms, even though the average resistivities of these NWs change by more than one order of magnitude. It is argued that the ductile gold tip makes one or more soft contacts on the stiff metal-oxide NWs with nanometer roughness and the nanocontacts on the NWs contribute to the electrical contact resistance.

Water-assisted CO(2) laser ablated glass and modified thermal bonding for capillary-driven bio-fluidic application

The glass-based microfluidic chip has widely been applied to the lab-on-a-chip for clotting tests. Here, we have demonstrated a capillary driven flow chip using the water-assisted CO(2) laser ablation for crackless fluidic channels and holes as well as the modified low-temperature glass bonding with assistance of adhesive polymer film at 300 degrees Celsius. Effect of water depth on the laser ablation of glass quality was investigated. The surface hydrophilic property of glass and polymer film was measured by static contact angle method for hydrophilicity examination in comparison with the conventional polydimethylsiloxane (PDMS) material. Both low-viscosity deionized water and high-viscosity whole blood were used for testing the capillary-driving flow behavior. The preliminary coagulation testing in the Y-channel chip was also performed using whole blood and CaCl(2) solution. The water-assisted CO(2) laser processing can cool down glass during ablation for less temperature gradient to eliminate the crack. The modified glass bonding can simplify the conventional complex fabrication procedure of glass chips, such as high-temperature bonding, long consuming time and high cost. Moreover, the developed fluidic glass chip has the merit of hydrophilic behavior conquering the problem of traditional hydrophobic recovery of polymer fluidic chips and shows the ability to drive high-viscosity bio-fluids.

Rapid diagnosis of tuberculosis directly from clinical specimens using a gene chip

The aim of this study was to explore a gene chip capable of detecting the presence of Mycobacterium tuberculosis isolates directly in clinical sputum specimens and to compare it with current molecular detection techniques. At first, we selected 13 M. tuberculosis-specific target genes to construct a gene chip for rapid diagnosis. Using the membrane array method, we diagnosed M. tuberculosis by gene chip directly from 246 sputum specimens from patients suspected of having tuberculosis. Among 80 M. tuberculosis complex (MTBC) culture-positive sputum specimens, the MTBC detection rate was 62.5% (50/80) by PCR-restriction fragment length polymorphism (RFLP), 70% (56/80) by acid-fast staining, and 85% (68/80) by the membrane array method. Furthermore, subspecies showed different gene expression patterns in the membrane array. In conclusion, MTBC could be detected directly in sputum by the membrane array method. The rapidity of detection and the capability of differentiating subspecies could make this method useful in the control and prevention of tuberculosis.

Exploring the origin of the directional emission from a microcavity with a large-aperture surface-emitting laser

The origin of the direction emission from a microcavity is investigated with a large-aperture surface-emitting laser with an equilateral-triangular shape. Experimental results reveal that a wide-spread eigenmode and a localized superscar mode can display quite similar far-field directional emissions. This experimental finding is theoretically confirmed with the quantum-billiard wave function and the approximation of the paraxial propagation.

Combined treatment with denbinobin and Fas ligand has a synergistic cytotoxic effect in human pancreatic adenocarcinoma BxPC-3 cells

BACKGROUND AND PURPOSE

Human pancreatic carcinoma is a highly malignant cancer. Previous studies have shown that the decoy receptor 3 (DcR3) for Fas ligand (FasL) plays significant roles in tumour progression and immune suppression. In the present study, we evaluated the anti-cancer activity of a natural compound, denbinobin (5-hydroxy-3,7-dimethoxy-1,4-phenanthraquinone), through decreasing DcR3 levels in human pancreatic adenocarcinoma cell lines.

EXPERIMENTAL APPROACH

We used immunoprecipitation and ELISA assays to examine DcR3 levels, and used FACS to determine the percentage of cells with a sub-G1 DNA content.

KEY RESULTS

AsPC-1 and BxPC-3 human pancreatic cancer cells express high levels of DcR3. Denbinobin concentration-dependently decreased DcR3 levels in BxPC-3 cells. MTT and flow cytometry assays indicated that BxPC-3 was FasL-resistant because high concentrations (100 ng.mL(-1)) of soluble FasL did not inhibit cell growth. However, combinations of denbinobin (3 micromol.L(-1)) with lower concentrations of soluble FasL (10, 30 and 50 ng.mL(-1)) or membrane-bound FasL, were synergistic on cell growth inhibition and apoptosis. Exogenous excess DcR3 reversed this synergistic effect. We observed no significant increase in the levels of surface Fas, cleaved forms of caspase-8, -3, -9, Bax, Bid, Bcl-xL, cytochrome c or mitochondrial membrane potentials following denbinobin treatment. However, denbinobin treatment increased the levels of apoptosis-inducing factor.

CONCLUSIONS AND IMPLICATIONS

Denbinobin and FasL trigger a synergistic cytotoxic effect in human pancreatic adenocarcinoma cells. Denbinobin mediated a decrease in levels of DcR3, which played a major role in this synergistic effect, and also increased caspase-independent apoptosis, via apoptosis-inducing factor.

Malignancies associated with dermatomyositis and polymyositis in Taiwan: a nationwide population-based study

BACKGROUND

Previous studies showed that idiopathic inflammatory myopathies (IIM) carried an increased risk of cancers. However, no large-scale study of IIM has been conducted in the Chinese population.

OBJECTIVES

We sought to delineate the association of IIM and various cancer types from a nationwide database in Taiwan.

METHODS

We analysed the published national data from records of National Health Insurance claims. Cases of dermatomyositis (DM) and polymyositis (PM) from 2000 to 2005 and cancers registered in the catastrophic illness profile from 1997 to 2006 were collected. A nationally representative cohort of 1,000,000 enrollees was included for comparison.

RESULTS

In total, 136 patients (12.8%) among 1059 cases of DM and 46 persons (7.0%) among 661 cases of PM carried internal malignancies. Patients with DM tended to have cancers of nasopharynx, lung and breast. On the other hand, patients with PM tended to have breast, uterine cervix and lung cancers. Compared with the general population, DM gave a 10-fold increased risk for cancers, in which a 66-fold increased risk for nasopharyngeal carcinoma and a 31-fold increased risk for lung cancer were the two most significant. For patients with PM, a 6-fold increased risk for cancer was observed. Juvenile DM had a 16-fold increased risk for haematopoietic or lymphoid malignancy. Two thirds of comorbid malignancies were detected shortly after the diagnoses of IIM, within a mean of 1-2 years. Overall, younger patients with IIM carried the highest risk for malignancies, especially those in their twenties and thirties.

CONCLUSIONS

This is the first large-scale study to report the associated malignancies and the cancer risk of IIM in Taiwan.

The synthesis and characterization of [(124)I]IMPY, a thioflavin-S derivative, in transgenic mouse models of Alzheimer's disease

6-[(124)I]iodo-2-(4'-N,N-dimethylamino)-phenylimidazo[1,2-a]pyridine ([(124)I]IMPY) was synthesized and characterized as a positron-emitting probe to identify Alzheimer's disease in transgenic mouse models. A significant reduction in radioactivity retention in the hippocampus and frontal cortex by co-incubation with nonradioactive IMPY was observed. Highly specific retention of radioactivity in beta-amyloid-rich regions of brain sections was also noted. This study demonstrated that [(124)I]IMPY was a promising probe for the mouse model and may be useful for positron emission tomography to image beta-amyloid plaques in the human brain.

Full-length sequence analysis of a distinct isolate of Bidens mottle virus infecting sunflower in Taiwan

The full-length genome of a potyvirus, previously known as sunflower chlorotic spot virus isolate SF-1 (SCSV-SF-1) which causes novel symptoms on sunflowers (Helianthus annuus), was sequenced and analyzed. The genome of SCSV-SF-1 is 9,741 nucleotides long, encoding a polyprotein of 3,071 amino acids containing the consensus motifs of potyviruses. Sequence comparison revealed that the 3'-terminus of SCSV-SF-1 shared over 96% similarities with isolates of Bidens mottle virus (BiMoV). However, SCSV-SF-1 has a very narrow host range, excluding the diagnostic host species for BiMoV, Bidens pilosa and Zinnia elegans. Therefore, SCSV-SF-1 is a distinct isolate of BiMoV. This is the first report of the full-length nucleotide sequence of BiMoV infecting sunflower in Taiwan.

Loss of IKKbeta activity increases p53 stability and p21 expression leading to cell cycle arrest and apoptosis

Elevated levels of NF-kappaB are frequently detected in many inflammatory diseases and cancers. Blocking the IKK-NF-kappaB pathway has been seen as a promising approach for new therapies. By employing the dominant-negative mutant of IKKbeta, our data revealed that loss of IKKbeta activity reduces not only the proliferation and invasion of lung adenocarcinoma A549 cells in vitro but also the tumour formation, metastasis and angiogenesis in mouse xenograft model. Treatment of IKKbeta inhibitors (CYL-19s and CYL-26z) leads to the arrest of cell cycle progression at G1 and G2/M, followed by apoptosis. IKKbeta inhibitors can increase the protein stability, nuclear accumulation and promoter-binding activity of p53, leading to the p21 gene transcription. Furthermore, knockdown of IKKbeta by siRNA increased the stability and expression of p53 and p21 promoter activity. In addition, IKKbeta inhibitor-induced p53 and p21 expressions were augmented in the presence of IKKbeta siRNA. Correlation between p53 acetylation and its protein stabilization was also seen after treatment with IKKbeta inhibitors. These results suggest that loss of IKKbeta activation is important for the enhancement of p53 stability, leading to p21 expression and cell cycle arrest and apoptosis of tumour cells.

Correlated electric fluctuations in GaN nanowire devices

We report an experimental study on the correlation spectrums between different sections of a multi-contact GaN nanowire device. Our results indicate that there exists a negative correlation between the voltage fluctuations of adjacent sections of the nanowire separated by a metal contact in the transition region between the low-frequency 1/f noise and the high-frequency white thermal noise. We suggest that this correlation is caused by the voltage fluctuation under the contact area.

Transient dynamics of coherent waves released from quantum billiards and analogous observation from free-space propagation of laser modes

The transient dynamics of the eigenstates and coherent states released from a square quantum billiard is analytically and numerically investigated. It is experimentally verified that this transient dynamic can be analogously observed with the free-space propagation of the lasing modes emitted from the laterally confined, vertically emitted cavities. Furthermore, we exploit a chaotically shaped cavity to originally demonstrate the diffraction-in-time characteristics of the chaotic wave functions. It is found that the transient patterns of chaotic wave functions exhibit a striking feature of random branching behavior with the appearance of intricate interference fringes.

Gabapentin toxicity: an important cause of altered consciousness in patients with uraemia

Gabapentin toxicity should be considered one of the differential diagnoses of altered consciousness in patients with compromised renal function, even after a single dose. We report a 57-year-old woman with diabetes mellitus and uraemia on regular haemodialysis who developed severe dizziness and lethargy after a single recommended dose of gabapentin for bilateral leg dysthesia. Because of progressive drowsiness and decreasing level of consciousness, one session of haemodialysis was performed and clinical recovery was dramatic. The adverse effects of gabapentin seem to vary from person to person and should be viewed with a high degree of suspicion, especially in patients taking this drug at the beginning.

First Report of Pepper veinal mottle virus in Tomato and Pepper in Taiwan

In May of 2006, samples from tomato plants (Solanum lycopersicum cv. Known-you 301) exhibiting necrotic symptoms on stems, petioles, and leaves were collected from Chiayi County, Taiwan. Double-antibody sandwich-ELISAs were performed using Cucumber mosaic virus, Tomato mosaic virus, Potato virus Y, Watermelon silver mottle virus, and Chilli veinal mottle virus (ChiVMV) polyclonal antibodies. Three of eight samples reacted with antibodies against ChiVMV but not with the others. Using the potyvirus degenerate primers (Hrp 5/Pot 1) (2), an expected 1.5-kb DNA fragment including the 3'-end of the NIb gene, the complete coat protein (CP) gene, and the 3'-nontranslatable region of the virus was amplified from total RNA isolated from these three samples by reverse transcription (RT)-PCR. A homology search in GenBank indicated that the new tomato-infecting virus in Taiwan belongs to Pepper veinal mottle virus (PVMV) since they shared >90% amino acid identity in the CP gene. A virus culture (Tom1) isolated from one of the diseased tomatoes was then established in Chenopodium quinoa and Nicotiana benthamiana and the CP gene was amplified and sequenced (GenBank Accession No. EU719647). Comparisons of the 807-nt CP gene with those of five PVMV isolates available in GenBank showed 81.5 to 93.1% nucleotide and 90.0 to 97.8% amino acid identity. Tom1 induced irregular necrotic lesions on stems, petioles, and leaves of tomato while inducing only mild mottle symptoms on pepper. Serological cross reaction between ChiVMV and PVMV has been observed previously (1,3) and also found in this study. To differentiate these two potyviruses by RT-PCR, primer pair CPVMVup/dw (5'-TATTC(T/C)TCAGTGTGG(A/T/C)T(T/C)CCACCAT and 5'-(T/C)C(A/T)C(A/T)(A/T/G)(A/T)AA(A/G)CCATAA(A/C)(A/C)ATA(A/G)T(T/C)T) was designed on the basis of the comparison of the CP gene and the 3'-nontranslatable region of the PVMV and ChiVMV. DNA fragments of 171 and 259 bp are expected to be amplified from ChiVMV and PVMV, respectively, by RT-PCR with primers CPVMVup/dw. In a field survey done in 2006, samples from diseased peppers (Capsicum annuum) that reacted with the polyclonal antibodies against ChiVMV were further identified by RT-PCR with primers CPVMVup/dw, indicating that both ChiVMV and PVMV infected pepper crops (Capsicum spp.) in Taiwan. A pepper isolate (Pep1) of PVMV was obtained from Nantou County through three times of single lesion passages on C. quinoa and then propagated on N. benthamiana. The CP gene of Pep1 was amplified and sequenced (GenBank Accession No. EU719646) and found to share 99.1% nucleotide and 100% amino acid identity with that of Tom1. Pep1 caused mild mottle symptoms on leaves of both tomato and pepper. To our knowledge, this is the first report of the presence of PVMV in Taiwan as well as in East Asia. References: (1) B. Moury et al. Phytopathology 95:227, 2005. (2) S. S. Pappu et al. Plant Dis. 82:1121, 1998. (3) W. S. Tsai et al. Plant Pathol. 58:408, 2008.

Forward and backward connections in the brain: a DCM study of functional asymmetries

In this paper, we provide evidence for functional asymmetries in forward and backward connections that define hierarchical architectures in the brain. We exploit the fact that modulatory or nonlinear influences of one neuronal system on another (i.e., effective connectivity) entail coupling between different frequencies. Functional asymmetry in forward and backward connections was addressed by comparing dynamic causal models of MEG responses induced by visual processing of normal and scrambled faces. We compared models with and without nonlinear (between-frequency) coupling in both forward and backward connections. Bayesian model comparison indicated that the best model had nonlinear forward and backward connections. Using the best model we then quantified frequency-specific causal influences mediating observed spectral responses. We found a striking asymmetry between forward and backward connections; in which high (gamma) frequencies in higher cortical areas suppressed low (alpha) frequencies in lower areas. This suppression was significantly greater than the homologous coupling in the forward connections. Furthermore, exactly the asymmetry was observed when we examined face-selective coupling (i.e., coupling under faces minus scrambled faces). These results highlight the importance of nonlinear coupling among brain regions and point to a functional asymmetry between forward and backward connections in the human brain that is consistent with anatomical and physiological evidence from animal studies. This asymmetry is also consistent with functional architectures implied by theories of perceptual inference in the brain, based on hierarchical generative models.