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In contemporary reinforcement learning models, reward prediction error (RPE), the difference between the expected and actual reward, is thought to guide action value learning through the firing activity of dopaminergic neurons. Given the importance of dopamine in reward learning and the involvement of Akt1 in dopamine-dependent behaviors, the aim of this study was to investigate whether Akt1 deficiency modulates reward learning and the magnitude of RPE using Akt1 mutant mice as a model. In comparison to wild-type littermate controls, the expression of Akt1 proteins in mouse brains occurred in a gene-dosage-dependent manner and Akt1 heterozygous (HET) mice exhibited impaired striatal Akt1 activity under methamphetamine challenge. No genotypic difference was found in the basal levels of dopamine and its metabolites. In a series of reward-related learning tasks, HET mice displayed a relatively efficient method of updating reward information from the environment during the acquisition phase of the two natural reward tasks and in the reverse section of the dynamic foraging T-maze but not in methamphetamine-induced or aversive-related reward learning. The implementation of a standard reinforcement learning model and the Bayesian hierarchical parameter estimation show that HET mice have higher RPE magnitudes and that their action values are updated more rapidly among all three test sections in T-maze. These results indicate that Akt1 deficiency modulates natural reward learning and RPE. This study showed a promising avenue for investigating RPE in mutant mice and provided evidence for the potential link from genetic deficiency, to neurobiological abnormalities, to impairment in higher-order cognitive functioning.

In this paper, an effective algorithm for compressing simple images, such as cartoons and man-drawn images, is proposed. Compared to existing methods, the proposed algorithm applies several new techniques. First, we classify the regions of an image into 4 classes (uniform, semi-uniform, multiple DCs, and non-uniform). For different classes, different coding algorithms are applied. Second, instead of calculating the average, we apply majority voting to determine DC terms. Moreover, a dividing and 2nd order polynomial approximation scheme is applied for boundary encoding. Simulations show that, when compressing simple images, the proposed algorithm much outperforms other state-of-the-art algorithms, especially in perception.

A series of 2-hydroxyethyl methacrylate/1-vinyl-3-(3-sulfopropyl)imidazolium betaine (HEMA/VSIB) copolymeric gels were prepared from various molar ratios of HEMA and the zwitterionic monomer VSIB. The influence of the amount of VSIB in copolymeric gels on their swelling behavior in water and various saline solutions at different temperatures and the drug-release behavior, compression strength, and crosslinking density were investigated. Experimental results indicated that the PHEMA hydrogel and the lower VSIB content (3%) in the HEMA/VSIB gel exhibited an overshooting phenomenon in their dynamic swelling behavior, and the overshooting ratio decreased with increase of the temperature. In the equilibrium water content, the value increased with increase of the VSIB content in HEMA/VSIB hydrogels. In the saline solution, the water content for these gels was not affected by the ion concentration when the salt concentration was lower than the minimum salt concentration (MSC) of poly(VSIB). When the salt concentration was higher than the MSC of poly(VSIB), the deswelling behavior of the copolymeric gel was more effectively suppressed as more VSIB was added to the copolymeric gels. However, the swelling behavior of gels in KI, KBr, NaClO4, and NaNO3 solutions at a higher concentration would cause an antipolyelectrolyte phenomenon. Besides, the anion effects were larger than were the cation effects in the presence of a common anion (Cl−) with different cations and a common cation (K+) with different anions for the hydrogel. In drug-release behavior, the addition of VSIB increased the drug-release ratio and the release rate. Finally, the addition of VSIB in the hydrogel improved the gel strength and crosslinking density of the gel. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2888–2900, 2001

Semi-interpenetrating network (semi-IPN) polymer gels and interpenetrating network (IPN) polymer gels with thermosensitivity were prepared by introducing a biodegradable polymer, chitosan, into the N-isopropyacrylamide (PNIPAAm) gel system. The swelling behavior, temperature sensitivity, pH sensitivity, gel strength, and drug-release behavior of PNIPAAm/chitosan semi-IPN and IPN hydrogels were investigated. The results indicated that the NIPAAm/chitosan semi-IPN and IPN hydrogels exhibited pH and temperature-sensitivity behavior and could slow drug release and diffusion from the gels. From the stress–strain curves of the hydrogels, the compression moduli of IPN gels containing crosslinked chitosan were higher than those of semi-IPN gels. This is because IPN gels have a more compact structure. The morphology of PNIPAAm/chitosan hydrogels was also investigated. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2487–2496, 2001

Graft polymerization of N-isopropylacrylamide (NIPAAm) onto styrene-butadiene-styrene (SBS) block copolymer using benzoyl peroxide was studied to improve the water absorptivity and thermosensitivity of SBS. The influence of various grafting reaction factors on the conversion of NIPAAm and the grafting percentage of SBS-g-NIPAAm were also investigated in the study. The experimental results showed that the conversion of SBS-g-NIPAAm was enhanced as the monomers of NIPAAm were increased. The maximum conversion of SBS-g-NIPAAm was observed when the molar ratio of NIPAAm to butadiene was 1.25. In addition, increasing the reaction time enhanced the conversion of SBS-g-NIPAAm; the maximum grafting percentage was obtained with a 4-h reaction. The optimal concentration of the initiator was 3 × 10−4 mol/20 mL of toluene, and the grafting reaction occurred at over 65°C. The test results of the hydrophilicity of the grafted membranes showed that the hydrophilicity and thermosensitivity were significantly enhanced by grafting NIPAAm onto SBS. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2641–2650, 2001

The electrocardiogram (ECG) signal is important for diagnosing cardiovascular diseases. However, in realistic scenario, the measured ECG signal is prone to be interfered by the artifacts caused from the respiration and the movement of patients. This artifact is called baseline wandering or baseline drifting and will lead to misdiagnosis if it is severe. Thus, pre-processing the measured ECG signal is necessary to make correct diagnosis. In this paper, we proposed a robust pre-processing method for extracting the baseline of ECG signals by the gradient varying weighting function. Our approach is adaptive to the input signal and is able to preserve the features of the ECG signal precisely. Simulation results show that our method outperforms other frequently used baseline extraction methods and has a good performance even if the input ECG signal is severely interfered by baseline drifting.