What's the buzz

Carob leaves can fight food-poisoning

Leaves of the plant that yields carob — the substitute for chocolate that some consider healthier than chocolate — are a rich source of antibacterial substances ideal for fighting the microbe responsible for listeriosis, a serious form of food poisoning, according to a new study.

Nadhem Aissani and colleagues explain that the increase in antibiotic-resistant bacteria has fostered a search for new natural substances to preserve food and control disease-causing microbes.

They cite a need for new substances to combat Listeria monocytogenes, bacteria that caused food poisoning outbreaks in a dozen states with three deaths so far this year.
Carob has attracted attention as a potential antibacterial substance, but until now, scientists had not tested it against Listeria. Carob may be best-known as a substitute for chocolate that does not contain caffeine or theobromine, which makes chocolate toxic to dogs.

Tests have shown that extracts of carob leaves proved effective in inhibiting the growth of Listeria bacteria growing in laboratory cultures.

The results were promising enough for the scientists to plan further tests of carob extracts on Listeria growing in meat and fish samples.

The finding was reported in ACS’ Journal of Agricultural and Food Chemistry.

How to erase unwanted memories

Scientists have discovered not one, but two ways in which the brain allows us to voluntarily forget unwanted memories.

The findings may explain how individuals can cope with undesirable experiences and could lead to the development of treatments to improve disorders of memory control.
"This study is the first demonstration of two distinct mechanisms that cause such forgetting: one by shutting down the remembering system, and the other by facilitating the remembering system to occupy awareness with a substitute memory," says lead study author Roland Benoit of the MRC Cognition and Brain Sciences Unit at the University of Cambridge.

Two possible ways to forget unwanted memories are to suppress them or to substitute them with more desirable memories, and these tactics could engage distinct neural pathways.

To test this possibility, Benoit and Michael Anderson of the MRC Cognition and Brain Sciences Unit used functional magnetic resonance imaging to examine the brain activity of volunteers who had learned associations between pairs of words and subsequently attempted to forget these memories by either blocking them out or recalling substitute memories.

Although the strategies were equally effective, they activated distinct neural circuits. During memory suppression, a brain structure called dorsolateral prefrontal cortex inhibited activity in the hippocampus, a region critical for recalling past events. On the other hand, memory substitution was supported by caudal prefrontal cortex and midventrolateral prefrontal cortex—two regions involved in bringing specific memories into awareness in the presence of distracting memories.

"A better understanding of these mechanisms and how they break down may ultimately help understanding disorders that are characterized by a deficient regulation of memories, such as posttraumatic stress disorder," Benoit said.

"Knowing that distinct processes contribute to forgetting may be helpful, because people may naturally be better at one approach or the other,” he added.

Poorly ventilated rooms impair decision-making

Researchers at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) have found that even moderately elevated levels of indoor carbon dioxide (CO2) can significantly impair people’s decision-making performance.

On nine scales of decision-making performance, test subjects showed significant reductions on six of the scales at CO2 levels of 1,000 parts per million (ppm) and large reductions on seven of the scales at 2,500 ppm.

The most dramatic declines in performance, in which subjects were rated as “dysfunctional,” were for taking initiative and thinking strategically. The results were unexpected and may have particular implications for schools and other spaces with high occupant density.

“In our field we have always had a dogma that CO2 itself, at the levels we find in buildings, is just not important and doesn’t have any direct impacts on people. So these results, which were quite unambiguous, were surprising,” said Berkeley Lab scientist William Fisk, a co-author of the study.

The study was conducted with researchers from State University of New York (SUNY) Upstate Medical University.

The primary source of indoor CO2 is humans. While typical outdoor concentrations are around 380 ppm, indoor concentrations can go up to several thousand ppm.

Higher indoor CO2 concentrations relative to outdoors are due to low rates of ventilation, which are often driven by the need to reduce energy consumption.