Biomedical subjects

Noriko Yamagishi

Publications and source records attributed to Noriko Yamagishi.

7 recordsLinked to original sources

PubMed2006

Biolistic inoculation of soybean plants with soybean dwarf virus.

Soybean dwarf virus (SbDV), a member of the genus Luteovirus, has been transmitted only by aphid vectors. The possibility of using a biolistic procedure of transmitting SbDV to soybean plants without relying on aphid vectors was investigated. Biolistic inoculation using the Helios Gene Gun System with RNA transcribed in vitro from a full-length cDNA clone of the DS strain of SbDV (pSV-DS) resulted in 1/12 to 3/13 soybean plants infected systemically. The infected soybean plants showed the characteristic symptoms of SbDV-DS within 6 weeks after inoculation and the accumulation of SbDV-specific RNA species such as genomic and subgenomic RNAs in the upper non-inoculated leaves. The progeny virus derived from RNA transcribed in vitro from pSV-DS could be transmitted by aphid vectors, as is the case with native SbDV-DS. This is the first report of direct inoculation of soybean plants with SbDV without using aphid vectors.

Biolistics↗

PubMed2006

Development of resistant transgenic soybeans with inverted repeat-coat protein genes of soybean dwarf virus.

In an attempt to generate soybean plants resistant to soybean dwarf virus (SbDV), we transformed a construct containing inverted repeat-SbDV coat protein (CP) genes spaced by beta-glucuronidase (GUS) sequences into soybean somatic embryos via microprojectile bombardment. Three T(0) plants with an introduced CP gene were obtained, and one generated T(1) seeds. The presence of the transgene in T(1) plants was confirmed by PCR and Southern blot hybridization analysis, but expression of CP was not detected by northern blot hybridization analysis. Two months after inoculation of SbDV by aphid, T(2) plants contained little SbDV-specific RNA and remained symptomless. These plants contained SbDV-CP-specific siRNA. These results suggest that the T(2) plants achieved resistance to SbDV by an RNA-silencing-mediated process.

Capsid Proteins↗

PubMed2005

Discrimination of four soybean dwarf virus strains by dot-blot hybridization with specific probes.

Soybean dwarf virus (SbDV) is divided into four strains (YS, YP, DS, and DP) on the basis of host symptoms in infected soybean plants and on aphid vector specificity. To detect and discriminate each strain of SbDV by dot-blot hybridization, probes Y, D, S, and P were prepared. Probes Y and D, covering most of the 3'-noncoding region of the viral genome containing the sequence of small subgenomic RNA, could discriminate strains in accord with the host symptoms. Probes S and P were derived from the 5'-half of open reading frame 5 encoding the N-terminal half of the readthrough domain which is closely related to the aphid vector specificity of each strain. Thus, the four SbDV strains could be discriminated by the combination of these probes. This method, based on a procedure specific to the SbDV sequence, is a good alternative for routine examination of infected plants in soybean breeding programs for evaluation of resistance to SbDV and for assessment of the distribution of each strain in epidemiological studies.

Luteovirus↗

PubMed2005

Attentional shifts towards an expected visual target alter the level of alpha-band oscillatory activity in the human calcarine cortex.

Neuronal operations associated with the top-down control process of shifting attention from one locus to another involve a network of cortical regions, and their influence is deemed fundamental to visual perception. However, the extent and nature of these operations within primary visual areas are unknown. In this paper, we used magnetoencephalography (MEG) in combination with magnetic resonance imaging (MRI) to determine whether, prior to the onset of a visual stimulus, neuronal activity within early visual cortex is affected by covert attentional shifts. Time/frequency analyses were used to identify the nature of this activity. Our results show that shifting attention towards an expected visual target results in a late-onset (600 ms postcue onset) depression of alpha activity which persists until the appearance of the target. Independent component analysis (ICA) and dipolar source modeling confirmed that the neuronal changes we observed originated from within the calcarine cortex. Our results further show that the amplitude changes in alpha activity were induced not evoked (i.e., not phase-locked to the cued attentional task). We argue that the decrease in alpha prior to the onset of the target may serve to prime the early visual cortex for incoming sensory information. We conclude that attentional shifts affect activity within the human calcarine cortex by altering the amplitude of spontaneous alpha rhythms and that subsequent modulation of visual input with attentional engagement follows as a consequence of these localized changes in oscillatory activity.

Adult↗

PubMed2005

Task-specific disruption of perceptual learning.

For more than a century, the process of stabilization has been a central issue in the research of learning and memory. Namely, after a skill or memory is acquired, it must be consolidated before it becomes resistant to disruption by subsequent learning. Although it is clear that there are many cases in which learning can be disrupted, it is unclear when learning something new disrupts what has already been learned. Herein, we provide two answers to this question with the demonstration that perceptual learning of a visual stimulus disrupts or interferes with the consolidation of a previously learned visual stimulus. In this study, we trained subjects on two different hyperacuity tasks and determined whether learning of the second task disrupted that of the first. We first show that disruption of learning occurs between visual stimuli presented at the same orientation in the same retinotopic location but not for the same stimuli presented at retinotopically disparate locations or different orientations at the same location. Second, we show that disruption from stimuli in the same retinotopic location is ameliorated if the subjects wait for 1 h before training on the second task. These results indicate that disruption, at least in visual learning, is specific to features of the tasks and that a temporal delay of 1 h can stabilize visual learning. This research shows that visual learning is susceptible to disruption and elucidates the processes by which the brain can consolidate learning and thus protect what is learned from being overwritten.

Adult↗

PubMed2003

Attentional modulation of oscillatory activity in human visual cortex.

The effects of attentional modulation on activity within the human visual cortex were investigated using magnetoencephalography. Chromatic sinusoidal stimuli were used to evoke activity from the occipital cortex, with attention directed either toward or away from the stimulus using a bar-orientation judgment task. For five observers, global magnetic field power was plotted as a function of time from stimulus onset. The major peak of each function occurred at about 120 ms latency and was well modeled by a current dipole near the calcarine sulcus. Independent component analysis (ICA) on the non-averaged data for each observer also revealed one component of calcarine origin, the location of which matched that of the dipolar source determined from the averaged data. For two observers, ICA revealed a second component near the parieto-occipital sulcus. Although no effects of attention were evident using standard averaging procedures, time-varying spectral analyses of single trials revealed that the main effect of attention was to alter the level of oscillatory activity. Most notably, a sustained increase in alpha-band (7-12 Hz) activity of both calcarine and parieto-occipital origin was evident. In addition, calcarine activity in the range of 13-21 Hz was enhanced, while calcarine activity in the range of 5-6 Hz was reduced. Our results are consistent with the hypothesis that attentional modulation affects neural processing within the calcarine and parieto-occipital cortex by altering the amplitude of alpha-band activity and other natural brain rhythms.

Adult↗

PubMed2002

Attentional processes link perception and action.

Behavioural studies on normal and brain-damaged individuals provide convincing evidence that the perception of objects results in the generation of both visual and motor signals in the brain, irrespective of whether or not there is an intention to act upon the object. In this paper we sought to determine the basis of the motor signals generated by visual objects. By examining how the properties of an object affect an observer's reaction time for judging its orientation, we provide evidence to indicate that directed visual attention is responsible for the automatic generation of motor signals associated with the spatial characteristics of perceived objects.

Attention↗