Tag Archives: #suppress

Lower Current Leads to Highly Efficient Memory (Physics)

Researchers are a step closer to realizing a new kind of memory that works according to the principles of spintronics which is analogous to, but different from, electronics. Their unique gallium arsenide-based ferromagnetic semiconductor can act as memory by quickly switching its magnetic state in the presence of an induced current at low power. Previously, such current-induced magnetization switching was unstable and drew a lot of power, but this new material both suppresses the instability and lowers the power consumption too.

Field-like torque tries to align the magnetization with the plane of the material, but to work as a memory device the magnetization needs to be perpendicular to this. © 2020 Ohya et al.

The field of quantum computing often gets covered in the technical press; however, another emerging field along similar lines tends to get overlooked, and that is spintronics. In a nutshell, spintronic devices could replace some electronic devices and offer greater performance at far low power levels. Electronic devices use the motion of electrons for power and communication. Whereas spintronic devices use a transferable property of stationary electrons, their angular momentum, or spin. It’s a bit like having a line of people pass on a message from one to the other rather than have the person at one end run to the other. Spintronics reduces the effort needed to perform computational or memory functions.

Spintronic-based memory devices are likely to become common as they have a useful feature in that they are nonvolatile, meaning that once they are in a certain state, they maintain that state even without power. Conventional computer memory, such as DRAM and SRAM made of ordinary semiconductors, loses its state when it’s powered off. At the core of experimental spintronic memory devices are magnetic materials that can be magnetized in opposite directions to represent the familiar binary states of 1 or 0, and this switching of states can occur very, very quickly. However, there has been a long and arduous search for the best materials for this job, as magnetizing spintronic materials are no simple matter.

“Magnetizing a material is analogous to rotating a mechanical device,” said Associate Professor Shinobu Ohya from the Center for Spintronics Research Network at the University of Tokyo. “There are rotational forces at play in rotating systems called torques; similarly there are torques, called spin-orbit torques, in spintronic systems, albeit they are quantum-mechanical rather than classical. Among spin-orbit torques, ‘anti-damping torque’ assists the magnetization switching, whereas ‘field-like torque’ can resist it, raising the level of the current required to perform the switch. We wished to suppress this.”

Ohya and his team experimented with different materials and various forms of those materials. At small scales, anti-damping torque and field-like torque can act very differently depending on physical parameters such as current direction and thickness. The researchers found that with thin films of a gallium arsenide-based ferromagnetic semiconductor just 15 nanometers thick, about one-seven-thousandth the thickness of a dollar bill, the undesirable field-like torque became suppressed. This means the magnetization switching occurred with the lowest current ever recorded for this kind of process.

Reference: Miao Jiang, Hirokatsu Asahara, Shoichi Sato, Shinobu Ohya and Masaaki Tanaka. Suppression of the field-like torque and ultra-efficient magnetisation switching in a spin-orbit ferromagnet. Nature Electronics. DOI: 10.1038/s41928-020-00500-w. https://www.nature.com/articles/s41928-020-00500-w

Provided by University of Tokyo

Neuroscience Study Finds ‘Hidden’ Thoughts In Visual Part Of Brain (Neuroscience)

How much control do you have over your thoughts? What if you were specifically told not to think of something—like a pink elephant?

Participants used the left side of their brains to come up with the thought, and the right side to try and suppress it.

A recent study led by UNSW psychologists has mapped what happens in the brain when a person tries to suppress a thought. The neuroscientists managed to ‘decode’ the complex brain activity using functional brain imaging (called fMRI) and an imaging algorithm.

Their findings suggest that even when a person succeeds in ignoring a thought, like the pink elephant, it can still exist in another part of the brain—without them being aware of it.

In their study they tracked the brain activity in 15 participants as they completed several visualizations and thought suppression exercises. Participants were given a written prompt—either green broccoli or a red apple—and challenged not to think of it. To make this task even harder, they were asked to not replace the image with another thought.

After 12 seconds, participants confirmed whether they were able to successfully suppress the image or if the thought suppression failed. Eight people were confident they’d successfully suppressed the images—but their brain scans told a different story. They found that visual cortex—the part of the brain responsible for mental imagery—seemed to be producing thoughts without their awareness.

Brain neurons fired and then pulled oxygen into the blood each time a thought took place. This movement of oxygen, which was measured by the fMRI machine, created particular spatial patterns in the brain.

The researchers decoded these spatial patterns using an algorithm called multivoxel pattern analysis (MVPA). MVPA is a type of decoding algorithm based in machine learning that allows us to read thoughts. The algorithm could distinguish brain patterns caused by the vegetable/fruit prompts.

Eight study participants were confident they’d successfully suppressed the images of the red apple or green broccoli, but their brain scans suggested otherwise. Credit: Shutterstock

The scans showed that participants used the left side of their brains to come up with the thought, and the right side to try and suppress it. Prof. Pearson hopes this functional brain mapping will help future researchers know which areas of the brain to target for potential intrusive thought therapies. This study can help explain why forcefully trying not to think about something always fails. For example, for someone trying to quit smoking, trying not to think about having a cigarette is a very bad strategy.

These findings build on a behavioral study Prof. Pearson’s team at UNSW Science’s Future Minds Lab conducted last year, which tested how suppressed thoughts can influence perception.

They know that you can have conscious and unconscious perception in your visual cortex—for example, they can show someone an image of a spider, make the image invisible, but their brain will still process it. But until now, they didn’t know this also worked with thoughts.

Both studies point towards the elusive world of the “unconscious,” which Prof. Pearson plans to explore in his future work.

They’re interested in this idea that imagination can be unconscious—that these thoughts can appear and influence our behavior, without us even noticing. More evidence is starting to suggest unconscious thoughts do occur, and they can decode them.

References: Roger Koenig-Robert et al. Decoding Nonconscious Thought Representations during Successful Thought Suppression, Journal of Cognitive Neuroscience (2020). DOI: 10.1162/jocn_a_01617