No abstract

Diverse artificial synapse structures and materials are widely proposed for neuromorphic hardware systems beyond von Neumann architecture owing to their capability to mimic complex information processing tasks such as image recognition, natural language processing, and learning. Nevertheless, temporal and spatial randomness in the movement of ion and electron particles that exist in materials usually prevents the solid‐state‐based synaptic devices from enabling the reliable modulation of synaptic plasticity. An aluminum nanoparticle (Al NP)‐embedded indium gallium zinc oxide (IGZO) synaptic transistor whose spike peak level and conductance change can be precisely modulated by the density of Al NPs within the IGZO channel is demonstrated. Essential synaptic functions including excitatory or inhibitory postsynaptic current, paired pulse facilitation, and short‐term potentiation or depression are also thoroughly emulated in the synaptic transistor device with the most optimized Al NP density: IGZO:Al NPs (6 nm). Moreover, controllable switching from short‐term to long‐term memory regimes essential for a learning task is demonstrated. Simulation results prove that this transistor can provide a decent recognition accuracy for neuromorphic computing. Indeed, the integrated IGZO:Al NP synaptic circuit with the effective synaptic plasticity will facilitate the implementation of a reconfigurable neuromorphic computing system.

Adolescence is associated with continued maturation of the cerebral cortex, particularly the medial prefrontal cortex (mPFC). We have previously documented pruning in the number of neurons, dendrites and synapses in the rat mPFC from preadolescence to adulthood, with the period of pubertal onset being particularly important. We hypothesized that dopaminergic innervation of this region, critical for executive functions, would also be influenced by pubertal onset. Here, we measured changes in the volume of tyrosine hydroxylase (TH) immunoreactive axons in all layers of the male and female mPFC from preadolescence to adulthood (postnatal day (P) 25, 35, 45, 60 and 90) as a marker of dopaminergic innervation. Assessing both total fiber volume and length, TH fibers were quantified by multiplying the mPFC volume by fiber density. While there were subtle layer-specific changes, TH fiber volume and length increased between P25 and P90 in both males and females. Contrary to our hypothesis, a role for pubertal onset in TH innervation of this region was not discernable. In summary, axons immunoreactive for TH increase with similar trajectories in the mPFC of male and female rats from pre-puberty to young adulthood.

Bisphenol A (BPA), an endocrine disruptor used in a variety of consumer products, has been found to alter the number of neurons in multiple brain areas in rats following exposure in perinatal development. Both the number of neurons and glia also change in the medial prefrontal cortex (mPFC) during adolescence, and this process is known to be influenced by gonadal hormones which could be altered by BPA. In the current study, we examined Long-Evans male and female rats that were administered BPA (0, 4, 40, or 400 µg/kg/day) during adolescent development (postnatal days 27–46). In adulthood (postnatal day 150), the number of neurons and glia in the mPFC were stereologically assessed in methylene blue/azure II stained sections. There were no changes in the number of neurons, but there was a significant dose by sex interaction in number of glia in the mPFC. Pairwise comparisons between controls and each dose showed a significant increase in the number of glia between 0 and 40 µg/kg/day in females, and a significant decrease in the number of glia between 0 and 4 µg/kg/day in males. In order to determine the type of glial cells that were changing in these groups in response to adolescent BPA administration, adjacent sections were labelled with S100β (astrocytes) and IBA-1 (microglia) in the mPFC of the groups that differed. The number of microglia was significantly higher in females exposed to 40 µg/kg/day than controls and lower in males exposed to 4 µg/kg/day than controls. There were no significant effects of adolescent exposure to BPA on the number of astrocytes in male or females. Thus, adolescent exposure to BPA produced long-term alterations in the number of microglia in the mPFC of rats, the functional implications of which need to be explored.

Recently, convolutional neural network (CNN) compression via low-rank decomposition has achieved remarkable performance. Finding the optimal rank is a crucial problem because rank is the only hyperparameter for controlling computational complexity and accuracy in compressed CNNs. In this paper, we propose a global optimal rank selection method based on Bayesian optimization (BayesOpt), which is a machine learning based global optimization technique. By utilizing both a simple objective function and a proper optimization scheme, the proposed method produces a global optimal rank that provides a good trade-off between computational complexity and accuracy degradation. In addition, our method also reflects the correlation of each rank in multi-rank selection, and is able to flexibly yield an optimal rank with a given fixed compression ratio. Experimental results indicate that the proposed algorithm can identify the global optimal rank regardless of the huge size of dataset or the various structural features of CNNs. In all experiments on multi-rank selection, the proposed method produces the rank with higher accuracy and lower computational complexity than the state-of-the-art rank selection method, variational Bayesian matrix factorization (VBMF).