Shaping Embodied Neural Networks for Adaptive Goal-directed Behavior

The acts of learning and memory are thought to emerge from the modifications of synaptic connections between neurons, as guided by sensory feedback during behavior. However, much is unknown about how such synaptic processes can sculpt and are sculpted by neuronal population dynamics and an interaction with the environment. Here, we embodied a simulated network, inspired by dissociated cortical neuronal cultures, with an artificial animal (an animat) through a sensory-motor loop consisting of structured stimuli, detailed activity metrics incorporating spatial information, and an adaptive training algorithm that takes advantage of spike timing dependent plasticity. By using our design, we demonstrated that the network was capable of learning associations between multiple sensory inputs and motor outputs, and the animat was able to adapt to a new sensory mapping to restore its goal behavior: move toward and stay within a user-defined area. We further showed that successful learning required proper selections of stimuli to encode sensory inputs and a variety of training stimuli with adaptive selection contingent on the animat's behavior. We also found that an individual network had the flexibility to achieve different multi-task goals, and the same goal behavior could be exhibited with different sets of network synaptic strengths. While lacking the characteristic layered structure of in vivo cortical tissue, the biologically inspired simulated networks could tune their activity in behaviorally relevant manners, demonstrating that leaky integrate-and-fire neural networks have an innate ability to process information. This closed-loop hybrid system is a useful tool to study the network properties intermediating synaptic plasticity and behavioral adaptation. The training algorithm provides a stepping stone towards designing future control systems, whether with artificial neural networks or biological animats themselves

Investigation and documentation of hybridization between Parkinsonia aculeata and Cercidium praecox (Leguminosae : Caesalpinioideae)

Morphometric, cytogenetic, geographical and ecological evidence for hybridization between Parkinsonia aculeata and Cercidium praecox is presented. Morphometric investigation using the character count procedure and cytogenetic observations confirm hybrid status. All diagnostic morphometric characters were intermediate in the hybrid. Both parents (2n = 28) show regular tetrad formation and pollen fertility greater than 94%. Hybrids have a chromosome number of 2n=28 or 2n=30, and display meiotic abnormalities including lagging chromosomes and micronucleus formation; less than 21% of hybrid pollen was fertile. Ecological and geographical information suggests that hybridization is occurring at increasing frequency due to the expanding range of P. aculeata associated with cultivation as an ornamental, coupled with ecological disturbance and weediness, and the cultivation of C. praecox and hybrids as fodder, ornamental and shade trees. Hybrid fertility and phenological observations, in conjunction with F-weighted principal component analysis, suggest that the progeny of F1 hybrids are established. The hybrid is formally described as P. x carterae