Neural population representation hypothesis of visual flow and its illusory after effect in the brain: psychophysics, neurophysiology and computational approaches

The neural representation of motion aftereffects induced by various visual flows (translational, rotational, motion-in-depth, and translational transparent flows) was studied under the hypothesis that the imbalances in discharge activities would occur in favor in the direction opposite to the adapting stimulation in the monkey MST cells (cells in the medial superior temporal area) which can discriminate the mode (i.e., translational, rotational, or motion-in-depth) of the given flow. In single-unit recording experiments conducted on anaesthetized monkeys, we found that the rate of spontaneous discharge and the sensitivity to a test stimulus moving in the preferred direction decreased after receiving an adapting stimulation moving in the preferred direction, whereas they increased after receiving an adapting stimulation moving in the null direction. To consistently explain the bidirectional perception of a transparent visual flow and its unidirectional motion aftereffect by the same hypothesis, we need to assume the existence of two subtypes of MST D cells which show directionally selective responses to a translational flow: component cells and integration cells. Our physiological investigation revealed that the MST D cells could be divided into two types: one responded to a transparent flow by two peaks at the instances when the direction of one of the component flow matched the preferred direction of the cell, and the other responded by a single peak at the instance when the direction of the integrated motion matched the preferred direction. In psychophysical experiments on human subjects, we found evidence for the existence of component and integration representations in the human brain. To explain the different motion perceptions, i.e., two transparent flows during presentation of the flows and a single flow in the opposite direction to the integrated flows after stopping the flow stimuli, we suggest that the pattern-discrimination system can select the motion representation that is consistent with the perception of the pattern from two motion representations. We discuss the computational aspects related to the integration of component motion fields

MT neurons in the macaque exhibited two types of bimodal direction tuning as predicted by a model for visual motion detection

AbstractWe previously proposed a model for detecting local image velocity on the magnocellular visual pathway (Kawakami & Okamoto (1996) Vision Research, 36, 117–147). The model detects visual motion in two stages using the hierarchical network that includes component and pattern cells in area MT. To validate the model, we predicted two types of bimodal direction tuning for MT neurons. The first type is characteristic of component cells. The tuning is bimodal when stimulated with high-speed spots, but unimodal for low-speed spots or for bars. The interval between the two peaks widens as the spot’s speed increases. The second type is characteristic of pattern cells. The tuning is bimodal when stimulated with low-speed bars, but unimodal for high-speed bars or for spots. The interval widens as the bar’s speed decreases. To confirm this prediction, we studied the change of direction tuning curves for moving spots and bars in area MT of macaque monkeys. Out of 35 neurons measured at various speeds, six component cells and four pattern cells revealed the predicted bimodal tunings. This result provided neurophysiological support for the validity of the model. We believe ours is the first systematic study that records the two types of bimodality in MT neurons

Elevated serum CYFRA 21-1 level as a diagnostic marker for thymic carcinoma

Background No useful tumor markers have been identified for the diagnosis of thymic carcinomas. Serum cytokeratin 19 fragment, measured using the CYFRA 21-1 immunoassay, is used as a tumor marker for squamous cell carcinomas in various malignant tumors. Here, we evaluated the value of CYFRA 21-1 in diagnosing thymic carcinoma. Methods We retrospectively reviewed 94 patients with pathological diagnoses of thymic carcinoma or thymoma (32 and 62 patients, respectively) who were referred to our departments between January 2000 and March 2019. Primary outcomes included tumor marker levels and their diagnostic accuracy. Results Patients with thymic carcinoma were significantly more likely to be male (thymic carcinoma, 68.8%; thymoma, 40.3%; p = 0.02), have an advanced TNM stage (p < 0.01), and a significantly higher CYFRA 21-1 level than those with thymoma (thymic carcinoma: median = 4.2 ng/ml; interquartile range [IQR] = 2.1-6.1 ng/ml vs. thymoma: median = 1.2 ng/ml; IQR = 0.9-1.7 ng/ml; p < 0.01). Receiver operating characteristic curves demonstrated that the area under the curve for CYFRA 21-1 to distinguish thymic carcinoma from thymoma was 0.86 (95% confidence interval [CI]: 0.74-0.93; cutoff = 2.7 ng/ml; sensitivity = 68.8%; specificity = 95.2%). Multivariable analysis demonstrated that CYFRA 21-1 (odds ratio = 25.6; 95% CI: 4.6-141.6; p < 0.01) was an independent predictor for thymic carcinoma after adjusting for TNM stage. Conclusions Serum CYFRA 21-1 level may help in diagnosing thymic carcinoma