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Cell types: encoding the brain’s BIOS

Excellent Substack writeup by Patrick Mineault on how cell types may specify innate behaviors and why mapping regions of the brain specialized to steer innate behaviors (via lots of distinct cell types) could lead us to more aligned AI systems. Highly convincing and elegant arguments made here! [ https://substack.com/home/post/p-189321289](https://substack.com/home/post/p-189321289)

Dwarkesh seemed very confused by this, asking a few different times: “Why would each reward function need a different cell type?” I empathize with Dwarkesh here! It is mysterious that a cell type could represent something as abstract as a reward. As a computational neuroscientist who mostly worked at the representation level during my PhD, I’ve leaned historically towards thinking of cell types as a mere “implementation detail”. But over conversations with Adam, Steve Byrnes, Paul Cisek, Tony Zador, and a few others, I’ve started to become convinced that cell types are a really useful lens to think about innate behaviors and rewards.

In this essay, I’ll unpack the conversation and answer the question: what do cell types have to do with reward functions? To answer it, we’ll need to understand what kind of information can be encoded in the genome, and how that information ultimately relates to connectomes and to cell types. I’ll connect the answer to the central claim of Adam: that these connections matter for AI, and AI safety in particular.

Andrew Barto and colleagues make the point that all primary rewards are internal, and must be genetically encoded. In reinforcement learning, which Barto co-developed along with Rich Sutton, an agent learns by receiving reward signals that indicate what is good and bad. The critical insight is that for biological organisms, all of these reward signals are internal —they are generated by the organism’s own nervous system. It is not a chunk of steak that gives reward: it is circuitry inside the brain that assigns positive valence to fat, salt, umami, heat, and texture. Things like money—secondary rewards—must be bootstrapped off of the pre-existing primary rewards.

Debugging a quantum processor: New method pinpoints qubit errors during logical operations

Researchers at the University of Innsbruck, together with partners from Sydney and Waterloo, have presented a new diagnostic method for quantum computers. It makes errors in individual quantum bits visible during logical calculation and evaluates them. The new method was demonstrated on an ion trap quantum processor in Innsbruck. It can be used to identify critical error sources—a key to developing more robust, fault-tolerant quantum processors.

In Physical Review X, the researchers present a scalable method that can be used to reliably characterize logical quantum operations at the level of the underlying quantum bits. Cycle error reconstruction identifies which physical errors influence the performance of logically encoded gates.

“With cycle error reconstruction, we can quantitatively capture the error structure and clearly distinguish between correctable and uncorrectable contributions,” says first author Robert Freund from the Department of Experimental Physics.

Unbalanced chromatin binding of Polycomb complexes drives neurodevelopmental disorders

Neurodevelopmental disorders from Polycomb complex missense mutations.

The causes of many neurodevelopmental disorders (NDDs) is yet to be determined.

The researchers report new missense mutations in the Polycomb repressive complex 1 (PRC1) E3 ligases RNF2 and RING1 in individuals with neurodevelopmental disorders.

Functional dissection of a deleterious variant reveals that balanced co-recruitment of Polycomb complexes to chromatin is essential for proper neurogenesis and for normal brain function and behavior. sciencenewshighlights ScienceMission https://sciencemission.com/Polycomb-complexes-drives-NDDs

Borges, González-Blanco, Arigela, et al. report new missense mutations in the PRC1 genes RNF2 and RING1 in individuals with neurodevelopmental disorders. Functional dissection of a deleterious variant reveals that balanced co-recruitment of Polycomb complexes to chromatin is essential for proper neurogenesis and for normal brain function and behavior.

Unveiling hidden variables in stressed bacteria

Noise in bacterial stress responses is often dismissed as mere randomness. While true stochasticity exists, much variation reflects hidden variables—cell state, history, and microenvironment—that are only now becoming measurable. Choudhary and Vincent review emerging tools that disentangle chance from determinism, moving microbiology toward more mechanistic and predictive frameworks.

Life-changing drug identified for children with rare epilepsy

A new experimental treatment for children with a hard-to-treat form of epilepsy is safe and can reduce seizures dramatically, helping them lead much healthier and happier lives, according to the findings of a UCL (University College London) and Great Ormond Street Hospital-led international clinical trial. In a paper published in The New England Journal of Medicine, researchers found that children with Dravet syndrome had up to 91% fewer seizures while being regularly administered a new medication called zorevunersen.

The results also show, for the first time, the potential to reduce the impact of the condition on a child’s mental processes and behavior. The children’s quality of life improved over a three-year period and most of the treatment’s side effects were mild.

Dravet syndrome is a devastating genetic condition that causes frequent, hard-to-control seizures and long-term neurodevelopmental impairment. The condition also causes feeding difficulties, movement problems and has a high risk of premature death. Current treatments fail to control seizures in most patients and there are no approved medicines that address the condition’s devastating cognitive and behavioral impacts.

How the brain suppresses itch during stress

The researchers then tested whether these stress-activated neurons directly influence itch. “We ran some pilot experiments, and we saw that surprisingly, acute stress was able to suppress acute itching,” says the first author of the study.

When the team artificially activated the stress neurons, scratching behaviour decreased in both short-term chemically induced itch and a psoriasis-like chronic itch model. Conversely, when these neurons were silenced, stress no longer reduced scratching. These results showed that these neurons are both necessary and sufficient for stress-induced suppression of itch.

“We show that a specific circuit in the lateral hypothalamus can suppress itch during acute stress, revealing how the brain directly links emotional states to sensory perception,” says the corresponding author. “By identifying the specific neural circuit that links stress to itch, we are opening the possibility of targeting these brain mechanisms to better manage chronic stress-induced worsening of itch.” ScienceMission sciencenewshighlights.

Researchers have mapped a neural circuit in the brain involved in the complex relationship between itch and stress. Their findings, published in Cell Reports, reveal how specific neurons activated during stress can directly regulate itch.

Itch and pain are both unpleasant sensations triggered by harmful or irritating stimuli, but they lead to different behavioural responses. While pain typically causes us to withdraw (such as pulling our hand away from a fire), itch drives scratching. Scientists have long known that emotional states such as stress and anxiety can influence the intensity of these sensations. While the neural mechanisms linking stress and pain have been studied extensively, the effect of stress on itch has remained poorly understood.

In the new study, the team focused on the lateral hypothalamic area (LHA), a brain region known to regulate stress, motivation, and emotional states. Using genetically engineered mouse models, the researchers identified a specific population of neurons in the LHA that become active during acute stress.

Continue reading “How the brain suppresses itch during stress” | >

Abstract: This study is directly relevant to the clinical care of patients with the most common malignant tumor of the peripheral nervous system

While providing fundamental biological insight👇

Harish N. Vasudevan & team reveal transcriptional, functional genetic, and cellular mechanisms of interferon signaling that underlie radiotherapy response in people with MPNST.

Address correspondence to: Harish N. Vasudevan, Helen Diller Cancer Research Building, 1,450 3rd Street, Mail Box 520, San Francisco, California 94,158, USA. Phone: 415.502.4107; Email: [email protected].

Restoring circadian rhythms in the hypothalamic paraventricular nucleus reverses aging biomarkers and extends lifespan in male mice

Now online! Enhancing circadian amplitude in mouse hypothalamic paraventricular nucleus neurons by 3′-deoxyadenosine treatment alleviates age-related pathologies and extends lifespan.

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