This week’s papers from Boston labs.

Mason Inman

Brain takes statistical approach to gauging glossiness

How do we tell whether a surface is glossy or matte, wet or dry? According to a paper published online in Nature this week, our brains likely use a simple rule, based on the balance of light and dark spots seen on the surface, to reliably detect differences in surface quality.

The researchers, including Lavanya Sharan and Edward Adelson of MIT, made images of stucco material painted with matte or glossy finishes, and digitally modified scans of Michelangelo sculptures to make them appear glossy or matte. They adjusted the images so that the total amount of light in each was the same.

Researchers showed subjects glossy and matte images to figure out how their brains can tell the difference. Credit: Digital Michelangelo Project

They asked research subjects to rate the glossiness in these images. And they plotted the number of light and dark pixels in the images to show their distribution.

For matte surfaces, the distribution of pixels was skewed towards the dark end of the spectrum, and for glossy surfaces, the distribution slanted towards the bright end. The shape of the distribution correlated strongly with the subjects’ glossiness ratings, the study showed, suggesting that the brain is sensitive to fine differences in the images’ lightness and darkness parameters.

The same results were seen when subjects were looking at bits of crumpled paper or cotton fabric, suggesting that a similar mechanism in the brain underlies how we perceive a wide variety of textures.

Mammalian hormones help bacteria spread Lyme disease

Some microbes are adept at making themselves at home in various host species—and spreading disease from one species to another—despite the hosts’ different physiological environments.

According to Tufts researchers, mammals harboring the Lyme disease-causing bacteria unwittingly provide hormone signals that tell the microbe when to prepare to transfer into another host.

The team, led by Linden Hu, studied the bacterium Borrelia burgdorferi, which resides in various mammals like mice and dogs and causes Lyme disease when transmitted to humans. The bacteria move from one animal to another by hitching a ride in the blood meal of a biting tick. They colonize the tick’s gut, producing high levels of a protein called OspA on their outer surface, which helps them attach to the gut lining.

The bacteria produce very little OspA when in mammals, so researchers wondered whether the microbes prepare for the transfer to ticks by ramping up the production of the protein and, if this is the case, what causes them to do so.

They found that the bacteria are able to sense and react when a tick bites their host. When bitten, mammals release hormones that trigger inflammation, such as epinephrine. The Tufts researchers showed that these hormones bind to the bacteria, increasing the production of OspA and effectively telling the microbe that it’s time to move into a tick.

In mouse studies, the team found that blocking these hormones reduced by half the chances of the bacteria moving from the mice to uninfected ticks. The research appeared online this week in the Proceedings of the National Academy of Sciences.