The mean and standard deviation of the distribution of group assembly sums

An interesting problem in linear programming is the group assembly problem which is mathematically equivalent to the general transportation problem of economics. Computer programs designed for the determination of exact and approximate optimal group assemblies have been available for some time. This paper presents formulas for the mean and squared standard deviation of the distribution of all possible group assembly sums. Computational techniques are presented and the results are related to those of the analysis of variance of a k -factor problem with n levels of each factor.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45717/1/11336_2005_Article_BF02289606.pd

Effect of the menstrual cycle on resting brain glucose metabolism in female rhesus monkeys

Little is known about the effects of the menstrual cycle on brain activity in primates. Here, we use 18F-fluorodeoxyglucose positron emission tomography to monitor changes in resting brain glucose metabolism across the menstrual cycle in female rhesus monkeys. Results showed greater activity in right lateral orbitofrontal cortex, a region involved in processing negatively valenced emotional stimuli, in the follicular compared with luteal phase. Estradiol levels were negatively correlated with activity in cortical and brainstem regions involved in emotional processing, and positively correlated with activity in areas involved in cognitive control and emotion regulation. In summary, the data suggest that in primates, fluctuations of ovarian hormones across the menstrual cycle influence activity in brain areas involved in emotion and its regulation

A Comparison of Resting State Brain Activity in Humans and Chimpanzees

In humans, the wakeful resting condition is characterized by a default mode of brain function involving high levels of activity within a functionally connected network of brain regions. This network has recently been implicated in mental self-projection into the past, the future, or another individual's perspective. Here we use [(18)F]-fluorodeoxyglucose positron emission tomography imaging to assess resting-state brain activity in our closest living relative, the chimpanzee, as a potential window onto their mental world and compare these results with those of a human sample. We find that, like humans, chimpanzees show high levels of activity within default mode areas, including medial prefrontal and medial parietal cortex. Chimpanzees differ from our human sample in showing higher levels of activity in ventromedial prefrontal cortex and lower levels of activity in left-sided cortical areas involved in language and conceptual processing in humans. Our results raise the possibility that the resting state of chimpanzees involves emotionally laden episodic memory retrieval and some level of mental self-projection, albeit in the absence of language and conceptual processing