Learning and decision-making change considerably from adolescence into adulthood. Adolescents undergo developmental changes in specific choice behaviors, such as goal-directed behaviors and motivational influences over choice. They also consistently show high levels of decision noise, i.e., choosing suboptimal options. However, it remains unknown whether these observations — the development of specific and more sophisticated choice processes and higher decision noise — are independent or related. It is possible that the development of specific choice processes might be impacted by age-dependent changes in decision noise.

To test this idea, Scholz, Deserno, and colleagues analyzed data from 93 participants between 12 and 42 years of age. The participants completed three reinforcement learning tasks: a task assessing motivational influences over choices, a learning task capturing adaptive decision-making in response to environmental changes, and a task measuring goal-directed behavior.

The results revealed that noise levels were strongly correlated across reinforcement learning tasks. Critically, noise levels mediated age-dependent increases in more sophisticated choice behaviors and performance gains. The findings suggest that unspecific noise mediates the development of highly specific functions or strategies.

One reason for these mediation effects could be a limited availability of cognitive resources in adolescents due to the ongoing development of brain areas related to cognitive control. Having fewer cognitive resources might make adolescents more prone to rely on computationally cheaper decision strategies, rendering them more susceptible to emotional, motivational and social influences.

Overall, the study provides novel insights into the computational processes underlying developmental changes in decision-making. According to the authors, future work may unravel the neural basis as well as the developmental and clinical real-life relevance of decision noise for neurodevelopmental disorders.

The authors add, “Teenagers make less optimal, so-called ‘noisy’ decisions. While these noisy decisions decrease when growing older, this decrease is also linked to the development of improved complex decision-making skills, such as planning and flexibility.”

There is an urgent need for faster and more cost-effective diagnostic tools to curb the spread of mpox and to prepare for the possibility of a future global pandemic. Researchers from University of California School of Medicine, Boston University, and their colleagues have now developed an optical biosensor that can rapidly detect monkeypox, the virus that causes mpox. The technology could allow clinicians to diagnose the disease at the point of care rather than wait for lab results. The study was published on November 14, 2024 in Biosensors and Bioelectronics.

In the clinic, mpox symptoms such as fever, pain, rashes and lesions resemble those of many other viral infections, says Partha Ray, an associate project scientist at UC San Diego School of Medicine and co-principal investigator on the study. “So just by looking at the patient, it is not easy for clinicians to distinguish monkeypox from these other diseases.”

What’s more, polymerase chain reaction (PCR) is currently the only approved method of diagnosing mpox. It is expensive, requires a laboratory, and can take days or weeks to get results. “A deadly combination when there is a fast-spreading epidemic or pandemic,” said Ray.

The search for a better molecular diagnostic for mpox draws on more than 10 years of research in the lab of Selim Ünlü, a distinguished professor of engineering at Boston University (BU) and co-principal investigator on the study. The lab has developed optical biosensors for detecting the viruses that cause Ebola hemorrhagic fever and COVID-19, among others. Ray’s team at UC San Diego collaborated with Ünlü’s lab, providing biological expertise and authenticated samples to Ünlü’s engineering team.

The study, led by first author Mete Aslan, a Ph.D. student in electrical and electronics engineering at BU, used a digital detection platform called Pixel-Diversity interferometric reflectance imaging sensor, or PD-IRIS, to detect the virus.

The researchers used samples collected from the lesions of a patient at UC San Diego Health with laboratory-confirmed mpox. They briefly incubated the samples with monoclonal monkeypox antibodies provided by Ray’s lab that bind to proteins on the surface of the virus. The virus-antibody complex was then transferred into tiny chambers on the surface of silicon chips on the sensor that were treated to fix these nanoparticles.

Shining precise wavelengths of red and blue light simultaneously on the chips caused interference, which resulted in slightly different responses when the virus-antibody nanoparticles were present. A color camera was used to detect this small signal and count individual particles with high sensitivity.

“You’re not trying to see the scattered light from the virus particle itself, but you’re looking at the interferometric signature of the field of scattered light mixed with the field that is reflected from the surface of the chip,” said Ünlü. He likens the process to FM radio, which mixes a weak signal containing information with a more powerful carrier signal at the same frequency, which, in turn, amplifies the weak signal.

The scientists also analyzed herpes simplex virus and cowpox virus samples, which have similar clinical presentations to mpox. The biosensor assay easily discriminated mpox samples from these other viruses, demonstrating that the specificity of the assay is essential for distinguishing mpox from these common viral diseases.

“Within two minutes, we can tell whether someone has monkeypox or not,” said Ray. “From collecting the virus samples to getting the real-time data takes around 20 minutes.”

In the clinic, the rapidity of the test would allow healthcare providers to diagnose mpox cases much more quickly than sending samples out to a lab. This is especially important for slowing community spread in countries where healthcare resources are sparse. Clinicians could also start treatment, if available, more quickly.

Ray envisions the tests being mass-produced as kits and sold to clinics, further reducing costs. A single boxed kit could be used to test for a variety of viruses, such as syphilis or HIV.

“The chip would be the same,” said Ray. “The only thing that would be different here is the binding antibody that would be specific for a particular virus.”

Ray and Ünlü are working together toward the goal of commercialization, not only to address the urgent need for rapid mpox tests in the Democratic Republic of the Congo but also to keep outbreaks from turning into pandemics. However, the researchers say this effort will require government support because there is little market for diagnostics addressing future threats.

“If we don’t take care of this particular epidemic right now, it is not going to be limited within Africa,” said Ray.

Additional co-authors on the study include: Howard Brickner, Alex E. Clark, Aaron F. Carlin, UC San Diego; Elif Seymour, iRiS Kinetics, Boston University Business Incubation Center; Michael B. Townsend, Panayampalli S. Satheshkumar, Centers for Disease Control and Prevention; Iris Celebi, Boston University; Megan Riley, axiVEND.

The study was funded, in part, by the National Institute of Allergy and Infectious Diseases at the National Institutes of Health (P30 AI036214), and the National Science Foundation (NSF-TT PFI 2329817).

“Laser light casting a shadow was previously thought impossible since light usually passes through other light without interacting,” said research team leader Raphael A. Abrahao from Brookhaven National Laboratory, previously at the University of Ottawa. “Our demonstration of a very counter-intuitive optical effect invites us to reconsider our notion of shadow.”

In Optica, Optica Publishing Group’s journal for high-impact research, the researchers describe how they used a ruby crystal and specific laser wavelengths to show that a laser beam could block light and create a visible shadow due to a nonlinear optical process. This effect occurs when light interacts with a material in an intensity-dependent way and can influence another optical field.

“Our understanding of shadows has developed hand-in-hand with our understanding of light and optics,” said Abrahao. “This new finding could prove useful in various applications such as optical switching, devices in which light controls the presence of another light, or technologies that require precise control of light transmission, like high-power lasers.”

Lunch talk sparks idea

The new research is part of a larger exploration into how a light beam interacts with another light beam under special conditions and nonlinear optical processes. The idea started over a lunch conversation when it was pointed out that some experimental schematics made with 3D visualization software depict the shadow of a laser beam because they treat it as a cylinder without accounting for the physics of a laser beam. Some of the scientists wondered: Could this be done in a lab?

“What started as a funny discussion over lunch led to a conversation on the physics of lasers and the nonlinear optical response of materials,” said Abrahao. “From there, we decided to conduct an experiment to demonstrate the shadow of a laser beam.”

To do this, the researchers directed a high-power green laser through a cube made of standard ruby crystal and illuminated it with a blue laser from the side. When the green laser enters the ruby, it locally changes the material response to the blue wavelength. The green laser acts like an ordinary object while the blue laser acts like illumination.

The interaction between the two light sources created a shadow on a screen that was visible as a dark area where the green laser blocked the blue light. It met all the criteria for a shadow because it was visible to the naked eye, followed the contours of the surface it fell on and followed the position and shape of the laser beam, which acted as an object.

The laser shadow effect is a consequence of optical nonlinear absorption in the ruby. The effect occurs because the green laser increases the optical absorption of the blue illuminating laser beam, creating a matching region in the illuminating light with lower optical intensity. The result is a darker area that appears as a shadow of the green laser beam.

Shadow measurements

“This discovery expands our understanding of light-matter interactions and opens up new possibilities for utilizing light in ways we hadn’t considered before,” said Abrahao.

The researchers experimentally measured the dependence of the shadow’s contrast on the laser beam’s power, finding a maximum contrast of approximately 22%, similar to the contrast of a tree’s shadow on a sunny day. They also developed a theoretical model and showed that it could accurately predict the shadow contrast.

The researchers say that from a technological perspective, the effect they demonstrated shows that the intensity of a transmitted laser beam can be controlled by applying another laser. Next, they plan to investigate other materials and other laser wavelengths that can produce similar effects.