Audio-Visual Perception of Self-Induced Apparent Motion

Apparent motion is the perception of the realistic smooth motion of an object which flashes or sounds first at one place and then at another. In a whole-head magnetoencephalography study, we assessed neural correlates of multisensory perception of apparent motion in 12 healthy volunteers. Two successive disks (1 diameter, 100 cm distance, ±6 eccentricity, 67 ms duration, 67 ms ISI) were displayed simultaneously with auditory white noise signals (simulated by means of auditory virtual reality at the same locations). Conditions with self-induced and random direction were compared. During the first condition, the direction of apparent motion stimuli was determined by the button press of the subject and during the second, the stimulus direction was selected randomly. The time of stimulus onset was self-induced in both conditions. Subjects were instructed to determine direction of motion after every sweep. We recorded 4 sessions with 260 sweeps in each subject. Similar evoked response fields were observed for self-induced and randomized sequences up to 140 ms after stimulus onset. The pattern accorded to distributed neuromagnetic activity. Peaking at about 160 ms, the difference field between the predictable and un-predictable condition exhibited a bilateral dipolar field structure with a higher negativity for the unpredictable stimulus directions. This pattern accords to the N1 component of auditory evoked fields. Globally, apparent motion seems to engage areas related to auditory, visual, and motor processing and posterior parietal regions. As the main contrast of interest of our study, predictable versus un-predictable, i.e., self-induced vs. random, directions affected in first place auditory areas. In a similar vein, stimulus adaptation in the auditory domain has been observed during the perception of one’s own speech. This specific mechanism seems to be of high neurobiological importance as impairments of these—mainly auditory—anticipatory projections have been suggested to be influential for hallucinations in schizophrenia

Convexity, Duality, and Effects

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Multi-target drug repositioning by bipartite block-wise sparse multi-task learning

Abstract Background Finding potential drug targets is a crucial step in drug discovery and development. Recently, resources such as the Library of Integrated Network-Based Cellular Signatures (LINCS) L1000 database provide gene expression profiles induced by various chemical and genetic perturbations and thereby make it possible to analyze the relationship between compounds and gene targets at a genome-wide scale. Current approaches for comparing the expression profiles are based on pairwise connectivity mapping analysis. However, this method makes the simple assumption that the effect of a drug treatment is similar to knocking down its single target gene. Since many compounds can bind multiple targets, the pairwise mapping ignores the combined effects of multiple targets, and therefore fails to detect many potential targets of the compounds. Results We propose an algorithm to find sets of gene knock-downs that induce gene expression changes similar to a drug treatment. Assuming that the effects of gene knock-downs are additive, we propose a novel bipartite block-wise sparse multi-task learning model with super-graph structure (BBSS-MTL) for multi-target drug repositioning that overcomes the restrictive assumptions of connectivity mapping analysis. Conclusions The proposed method BBSS-MTL is more accurate for predicting potential drug targets than the simple pairwise connectivity mapping analysis on five datasets generated from different cancer cell lines. Availability The code can be obtained at http://gr.xjtu.edu.cn/web/liminli/codes

Volumetric two-photon imaging of neurons using stereoscopy (vTwINS)

Two-photon laser scanning microscopy of calcium dynamics using fluorescent indicators is a widely used imaging method for large scale recording of neural activity in vivo. Here we introduce volumetric Two-photon Imaging of Neurons using Stereoscopy (vTwINS), a volumetric calcium imaging method that employs an elongated, V-shaped point spread function to image a 3D brain volume. Single neurons project to spatially displaced “image pairs” in the resulting 2D image, and the separation distance between images is proportional to depth in the volume. To demix the fluorescence time series of individual neurons, we introduce a novel orthogonal matching pursuit algorithm that also infers source locations within the 3D volume. We illustrate vTwINS by imaging neural population activity in mouse primary visual cortex and hippocampus. Our results demonstrate that vTwINS provides an effective method for volumetric two-photon calcium imaging that increases the number of neurons recorded while maintaining a high frame-rate