Tag: brain

Shadows

Shadows are so visually telling that it takes little to move into emotionally tinged narratives. But it is the visual aspects that we primarily deal with here, with a special focus on several types of misrepresentations of shadows — shadows doing impossible things — that nevertheless reap a payoff for scene layout and do not look particularly shocking.

Painters have long struggled with the difficulties of depicting shadows, so much so that shadows — after a brief, spectacular showcase in ancient Roman paintings and mosaics — are almost absent from pictorial art up to the Renaissance and then are hardly present outside traditional Western art.
We have singled out some broad categories of solutions to pictorial problems: depicted shadows having trouble negotiating obstacles in their path; shadow shapes and colors that stretch credibility; inconsistent illumination in the scene; and shadow character getting lost.

Astrocytes

The star-shaped cells usually help clear away toxic particles that build up in the brain naturally or after head trauma, and are supposed to nourish neurons. But laboratory tests on mice show astrocytes also release toxic fatty acids to kill off damaged neurons, confirming a suspicion many neurologists have had for years. “Our findings show the toxic fatty acids produced by astrocytes play a critical role in brain cell death. The results provide a promising new target for treating, and perhaps even preventing, many neurodegenerative diseases”.

Astrocytes regulate the response of the central nervous system to disease and injury and have been hypothesized to actively kill neurons in neurodegenerative disease. Here we report an approach to isolate one component of the long-sought astrocyte-derived toxic factor. Notably, instead of a protein, saturated lipids contained in APOE and APOJ lipoparticles mediate astrocyte-induced toxicity. Eliminating the formation of long-chain saturated lipids by astrocyte-specific knockout of the saturated lipid synthesis enzyme ELOVL1 mitigates astrocyte-mediated toxicity in vitro as well as in a model of acute axonal injury in vivo. These results suggest a mechanism by which astrocytes kill cells in the central nervous system.

Animal Numerosity

Practically every animal that scientists have studied — insects and cephalopods, amphibians and reptiles, birds and mammals — can distinguish between different numbers of objects in a set or sounds in a sequence. They don’t just have a sense of “greater than” or “less than,” but an approximate sense of quantity: that 2 is distinct from 3, that 15 is distinct from 20. This mental representation of set size, called numerosity, seems to be “a general ability,” and an ancient one. Many species have displayed a capacity for abstraction that extends to performing simple arithmetic, while a select few have even demonstrated a grasp of the quantitative concept of 0 — an idea so paradoxical that very young children sometimes struggle with it. Both monkeys and honeybees know how to treat 0 as a numerosity, placing it on a mental number line much as they would numerosity 1 or 2. And crows can do it, too.

LSD lowers priors

An important aspect of predictive processing is that each hypothesis generated by a level in the hierarchy is associated with a notion of confidence in the hypothesis, which in turn is based on prior expectations. Could psychedelics be altering our perception of reality by messing with this process? Friston and Robin Carhart-Harris think so. If psychedelics mess with prior beliefs, that might also explain why they cause one to hallucinate a reality that’s untethered from real-world expectations.

Representational Drift

Neurons that represented the smell of an apple in May and those that represented the same smell in June were as different from each other as those that represent the smells of apples and grass at any one time. Representational drift occurs in a variety of brain regions besides the piriform cortex. Its existence is clear; everything else is a mystery. How can animals possibly make any lasting sense of the world if their neural responses to that world are constantly in flux? If such flux is common, “there must be mechanisms in the brain that are undiscovered and even unimagined that allow it to keep up.”

NeuroRights

Neuro rights advocates propose 5 additions to human rights: the rights to personal identity, free will, mental privacy, equal access to mental augmentation, and protection from algorithmic bias. Who owns the copyright to a recorded dream? What laws should exist to prevent one person from altering the memory of another through a neural implant? How do we maintain mental integrity separate from an implanted device? If someone can read our mind, how do we protect the read-out of our thoughts as our own?

Engram

Almost all neuroscientists base their search—for the physical basis of memory (the engram)—on the assumption that temporal-pairing causes learning. They are dedicated to this assumption—even though, as Rescorla pointed out 50 years ago, experimental attempts to define temporal-pairing have always failed. This failure is as striking now as it was 50 years ago. Anything that gets neuroscientists to abandon the idea that temporal-pairing is a useful scientific concept is a step toward discovering the physical basis of memory. Each neuron contains billions of (almost) incomprehensibly-tiny molecular machines. Molecular biologists have developed an astonishing array of techniques for visualizing/manipulating the actions of these little machines. These techniques will allow molecular biologists to follow the machines inside this huge neuron to the engram—to the tiny machine that encodes the experience-gleaned facts so that these learned/remembered facts can inform later behavior.

2021-11-19: This feels like a really big deal:

Biology feels different right now. New broadly enabling technologies and tools are driving forward progress in nearly every specific field at a rapid pace. The large scale adoption and application of a powerful set of common tools has created a virtuous cycle of further technology refinement and engineering. The rate of iteration is increasing, and previously intractable problems are now within reach. While RNA-seq and MPRAs are both valuable approaches, they come with some limitations. Fundamentally, each measurement represents a single static slice of a dynamic process which is only inferred by attempting to piece together the slices. The quality of the reconstruction is limited by sampling density. What if we could measure these systems continually as they occurred in a way that didn’t require destructive sampling? Here, the fundamental idea is that “DNA is the natural medium for biological information storage, and is easily ‘read’ through sequencing.” This forms the basis for this new technology: ENGRAM (ENhancer-driven Genomic Recording of transcriptional Activity in Multiplex). The workflow of this technique is very similar to that of the MPRA introduced above, but with an important twist. Instead of destroying the cell and sequencing a ratio of barcodes, the transcription event is recorded by the insertion of a barcode into a locus of DNA in the cell via prime editing. They went further and showed that they could effectively multiplex this technique by reading out all 3 signals in response to stimulants in a single population of cells. Even more, they showed a proof-of-concept for reading out the order in which events occurred.

Attention & memory

attention and working memory share the same neural mechanisms. Importantly, their work also reveals how neural representations of memories are transformed as they direct behavior.

“When we act on sensory inputs we call it ‘attention. But there’s a similar mechanism that can act on the thoughts we hold in mind.”