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Biomedical subjects

Ryota Kanai

Publications and source records attributed to Ryota Kanai.

12 recordsLinked to original sources
PubMed2006

Single case of renal cell carcinoma and endocrine pancreatic head cancer occurring with von Hippel-Lindau disease.

Von Hippel-Lindau (VHL) disease is an autosomal dominant genetic disease in which various neoplastic lesions occur in multiple organs. Reported here is a case of VHL disease with concurrent renal cell carcinoma and endocrine pancreatic cancer. The patient was a 43-year old woman. On this occasion, the patient had sought treatment from her local physician, complaining chiefly of yellowing of the skin and bulbar conjunctiva. Abdominal ultrasound and computed tomography scans revealed a mass in the right kidney and a mass in the pancreatic head. Peripheral blood genetic analysis revealed an Arg/stop heteroconjugative mutation in codon 113 in exon 1 of the VHL gene on the short arm of chromosome 3 (p25-26). After various tests were performed, the patient was diagnosed with right renal cell carcinoma, malignant tumor of the pancreatic head, and multiple pancreatic cysts accompanying von Hippel-Lindau disease. Right nephrectomy and pancreatoduodenectomy were performed. Based on the histopathological results, the patient was diagnosed with right renal cell carcinoma and highly differentiated endocrine pancreatic cancer. Immunohistologically, a large number of atypical cells were found to be positive for both anti-chromogranin and anti-synaptophysin antibodies in the endocrine tumor. Immunostaining for each type of gut hormone was also performed, but all results were negative. Based on the above findings, nonfunctioning, highly differentiating endocrine cancer was diagnosed. This is the first confirmed case of renal cell carcinoma and endocrine pancreatic cancer occurring concurrently with VHL. This is an important case, so it is presented here along with a short discussion of the literature.

Adult↗
PubMed2005

Perceptual manifestations of fast neural plasticity: motion priming, rapid motion aftereffect and perceptual sensitization.

Visual neurons show fast adaptive behavior in response to brief visual input. However, the perceptual consequences of this rapid neural adaptation are less known. Here, we show that brief exposure to a moving adaptation stimulus-ranging from tens to hundreds of milliseconds-influences the perception of a subsequently presented ambiguous motion test stimulus. Whether the ambiguous motion is perceived to move in the same direction (priming), or in the opposite direction (rapid motion aftereffect) varies systematically with the duration of the adaptation stimulus and the adaptation-test blank interval. These biases appear and decay rapidly. Moreover, when the adapting stimulus is itself ambiguous, these effects are not produced. Instead, the percept for the subsequent test stimulus is biased to the perceived direction of the adaptation stimulus. This effect (perceptual sensitization) builds gradually over the time between the adaptation and test stimuli. Our results indicate that rapid adaptation plays a role mainly within early motion processing, whereas a slow potentiation controls the sensitivity at a later stage.

Adaptation, Physiological↗
PubMed2005

Perceptual alternation induced by visual transients.

When our visual system is confronted with ambiguous stimuli, the perceptual interpretation spontaneously alternates between the competing incompatible interpretations. The timing of such perceptual alternations is highly stochastic and the underlying neural mechanisms are poorly understood. We show that perceptual alternations can be triggered by a transient stimulus presented nearby. The induction was tested for four types of bistable stimuli: structure-from-motion, binocular rivalry, Necker cube, and ambiguous apparent motion. While underlying mechanisms may vary among them, a transient flash induced time-locked perceptual alternations in all cases. The effect showed a dependence on the adaptation to the dominant percept prior to the presentation of a flash. These perceptual alternations show many similarities to perceptual disappearances induced by transient stimuli (Kanai and Kamitani, 2003 Journal of Cognitive Neuroscience 15 664-672; Moradi and Shimojo, 2004 Vision Research 44 449-460). Mechanisms linking these two transient-induced phenomena are discussed.

Adaptation, Psychological↗
PubMed2005

[A case of resectable solitary liver metastasis from breast cancer].

We report a case of resectable solitary liver metastasis from breast cancer. A 53-year-old woman underwent a pectoral muscle-preserving mastectomy for T1 N0M0 (Stage I) left breast cancer in May 2000. Histopathologic diagnosis was medullary carcinoma. Thereafter, the patient was followed up with adjuvant chemotherapy. A solitary tumor in the right lobe of the liver at S6 was found 10 months after mastectomy by ultrasonography. With a diagnosis of liver metastasis from breast cancer, right hepatectomy was performed in May 2001. At present, she remains disease free for 4 years after hepatectomy. We think that a surgical procedure for liver metastasis from breast cancer, if possible, is beneficial in prolonged survival.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed2004

Vision: steady-state misbinding of colour and motion.

When you see a red ball rolling across the floor, the ball's redness, roundness and motion appear to be unified and inseparably bound together as features of the ball. But neurophysiological evidence indicates that visual features such as colour, shape and motion are processed in separate regions of the brain. Here we describe an illusion that exploits this separation, causing colour and motion to be recombined incorrectly while a stable stimulus is being viewed continuously.

Bias↗
PubMed2004

Stopping the motion and sleuthing the flash-lag effect: spatial uncertainty is the key to perceptual mislocalization.

A moving object is perceived to lie beyond a static object presented at the same time at the same retinal location (flash-lag effect or FLE). Some studies report that if the moving stimulus stops moving (flash-terminated condition or FTC) the instant the flash occurs, a FLE does not occur. Other studies, using different stimuli, report that the FLE does, in fact, occur in the FTC. The FTC is thus a crucial turning point in theories of flash-lag. Unraveling the mystery of the FLE in the FTC will help unravel the mechanisms underpinning flash-lag and perhaps even perceptual localization in general. Our experiments show that eccentricity of the moving stimulus was a contributing factor, as were eccentricity of the flashed stimulus and spatial separation between the two stimuli. Other factors, such as contrast and offset of moving stimulus, also modulate the magnitude of the FLE in the FTC. We surmise that uncertainty in determining the position in space of a moving stimulus is a key requirement for the lag-effect. A lag-effect in the FTC challenges influential models, such as differential latency, motion extrapolation, and postdiction. Based partly on the notion of an asymmetric spread of activity that arises because of the sheer nature of motion and from a combination of established physiological mechanisms, we propose a schematic account of the present findings that subsumes previous psychological models and scaffolds past experimental findings.

Contrast Sensitivity↗
PubMed2004

Center-surround interactions in visual motion processing during binocular rivalry.

When each eye is confronted with a dissimilar stimulus, the percept will generally alternate between the two. This phenomenon is known as binocular rivalry. Although binocular rivalry occurs at locations where targets overlap spatially, the area surrounding rivalrous targets can modulate their dominance. Here we show that during binocular rivalry of oppositely moving gratings, a surrounding grating moving in the same direction as one of the two leads to increased dominance of the opposite direction of motion in the center. This increased dominance of the opposite direction in the center was observed irrespective of the eye to which the surround was presented. Inspection of the results for different conditions reveals that the preference for the opposite direction of motion cannot be explained by a single mechanism operating beyond binocular fusion. We therefore suggest that this phenomenon is the outcome of center-surround interactions at multiple levels along the pathway of visual motion processing.

Contrast Sensitivity↗
PubMed2004

Visual transients without feature changes are sufficient for the percept of a change.

A visual transient due to a sudden visual change is generally considered to draw our attention to a location of interest. In a series of experiments we investigated how visual transients facilitate change detection in a scene. In line with earlier reports, we found that a transient sensation has its roots in a temporal interaction at a monocular processing level. Interestingly, we also show that visual transients make it possible to detect a change in the eye of origin, despite the fact that observers have no clue as to which eye is stimulated. That is, visual transients are detected even when there is no perceptual change in the visual content after binocular fusion. More importantly, we show that observers cannot distinguish the transient due to a change in eye of origin from a feature change (the orientation of a Gabor). Both are perceived as actual changes. We conclude that a transient signal is sufficient for the visual system to judge whether something has changed over time.

Humans↗
PubMed2004

Blindness to inconsistent local signals in motion transparency from oscillating dots.

Visual processing involves hierarchical stages in which local features are initially analyzed and subsequently grouped into objects and surfaces. In the domain of motion perception, transparent motion has been used as a powerful tool to investigate the mechanisms underlying the grouping of local features. Here, we report a novel way of creating motion transparency from oscillating dots (MTOD). In this stimulus, individual dots move back and forth over a small distance. When the dots are oscillating in synchrony, global surfaces are also perceived as moving back and forth. However, when the oscillation desynchronizes, the percept turns into two moving surfaces that are sliding over each other continuously (streaming motion). The percept of MTOD is similar to conventional transparent motion, where individual dots move only in one direction. Also, when streaming motion is perceived, the detection of oscillation is impaired. This blindness to the oscillation becomes stronger, as the signal strength for the streaming motion is increased. These findings suggest that when global visual representations are constructed, weak and inconsistent local signals are discarded.

Humans↗
PubMed2003

Time-locked perceptual fading induced by visual transients.

After prolonged fixation, a stationary object placed in the peripheral visual field fades and disappears from our visual awareness, especially at low luminance contrast (the Troxler effect). Here, we report that similar fading can be triggered by visual transients, such as additional visual stimuli flashed near the object, apparent motion, or a brief removal of the object itself (blinking). The fading occurs even without prolonged adaptation and is time-locked to the presentation of the visual transients. Experiments show that the effect of a flashed object decreased monotonically as a function of the distance from the target object. Consistent with this result, when apparent motion, consisting of a sequence of flashes was presented between stationary disks, these target disks perceptually disappeared as if erased by the moving object. Blinking the target disk, instead of flashing an additional visual object, turned out to be sufficient to induce the fading. The effect of blinking peaked around a blink duration of 80 msec. Our findings reveal a unique mechanism that controls the visibility of visual objects in a spatially selective and time-locked manner in response to transient visual inputs. Possible mechanisms underlying this phenomenon will be discussed.

Blinking↗