The Brain Becomes Strongest with "Seven Senses"? — The Mystery of the "Critical Dimension" Revealed by Recent Research: Maximizing Memory Capacity Occurs in Seven Dimensions

"The Five Senses" May Not Be the Optimal Solution?—What "Critical Dimension 7" Means

A paper published in Scientific Reports on August 15, 2025, tracked how the "swarms" of engrams, considered the carriers of memory, increase and decrease over the long term and how diverse concepts they can retain, using a new kinetic model that includes interactions with learning, forgetting, and stimuli. The authors report, based on both analysis and Monte Carlo calculations, that the number of distinguishable engrams reaches its maximum when the dimension of the conceptual space is 7—in other words, a critical dimension emerges. If each "feature" is mapped to one sense, this translates to "the optimal number of senses is 7."Nature

Why "7"? The Key to the Model

The paper adopts an intuitive yet universal rule: when a stimulus "hits" an engram, its sensitivity increases and its shape (spread) becomes sharper, whereas too much input from the environment causes its contours to diffuse. Analyzing the steady state where many engrams coexist, if the dimension is too low, concepts overlap and the number of distinguishable ones does not grow; if too high, the space becomes "sparse," reducing hit frequency, and consequently, the total number of concepts that can be retained decreases. The essence is that the peak balance is around 7. The authors also provide a theoretical explanation for this phenomenon.Nature

Trade-off Between Receptivity and "Sharpness of Concepts"

The model also demonstrated a tension where high receptivity makes it less likely to miss novel stimuli, but at the same time, the sharpness of concepts is compromised. In real neural circuit research, it has been reported that the structure and selectivity of engrams change in response to learning and inhibitory plasticity, which aligns with the theoretical suggestions.Nature

Reactions from SNS and Media: Enthusiasm and Caution

As of October 12, 2025 (JST), less than two months after its release, Altmetric has aggregated reactions from 21 X users, 8 Bluesky users, 11 news outlets, and 2 blogs. The overall score ranks in the **top 5%**, indicating a high level of interest. While the core of the dissemination is the general public, shares from researcher accounts are also observed, with geographical distribution spreading to the US, France, Germany, and more.Nature

In the media, Popular Mechanics introduced the topic with an easy-to-understand headline, "The Possibility of Humans Having Seven Senses," followed by SciTechDaily, TechXplore, and scientific media in Russian and German-speaking regions. The Debrief and news portals also covered the story, with the intuitive appeal of the number "7" making for eye-catching headlines.ct.moreover.com　SciTechDaily

On the other hand, on SNS,

• Supporters: Opinions such as "This could guide sensor design in AI and robotics" and "Adding new channels like magnetic sense and radiation sense to vision, hearing, touch, smell, and taste makes sense for improving learning efficiency."ct.moreover.com

• Cautious voices: "The correspondence of dimension = sense is an assumption and does not directly predict human physiological evolution," and "Experimental neuroscience backing is needed." The press release also clarifies that it is a "hypothetical interpretation."skoltech.ru

Will We Acquire "Seven Senses"?

The authors themselves do not claim that humans will immediately acquire two new senses. Rather, the more realistic application lies in the world of AI/neuromorphic systems. By designing systems that perform sensor fusion with diverse sensors such as magnetic, radiation, and chemical sensors in addition to vision and acoustics, targeting "around 7 channels" could potentially maximize the diversity of concepts.ct.moreover.com

Points to Note: Easily Misunderstood Aspects

1. "7 = Correct" is not a fixed conclusion. It may depend on the assumptions of the model and the statistics of the environment, and biological neural development and metabolic costs impose different constraints.Nature

2. Biological verification is yet to come. While engram research is advancing rapidly, the current claims are theoretical, and experimental verification across the entire brain is needed.Nature

3. The definition of "sense" is fluid. The debate changes depending on how pain, temperature, balance, and proprioception are counted. The paper treats them as **"feature dimensions"** and conveniently maps them to senses.Nature

The Value of the Research: A "Good Theory" That Drives Discussion

Theories simplify reality in exchange for providing intuition. The significance of this achievement lies in presenting the utility of a design theory, such as the trade-off between receptivity and sharpness of contours and the existence of an optimal dimension. Particularly, it provides a quantitative guideline for "how to increase channels" in the design of multi-sensor AI. While it is understandable that the media is abuzz with the catchy phrase "seven senses," the research community will likely refine this idea through the cycle of hypothesis and verification.Nature

Reference Links (Sources)

• Original Paper: Scientific Reports (Published August 15, 2025)Nature

• Altmetric Metrics (Updated October 12, 2025 / 21 X, 8 Bluesky, etc.)Nature

• Media Commentary: Popular Mechanics / SciTechDaily / TechXplore / The Debrief / The News (Pakistan)ct.moreover.com　SciTechDaily

• Related Reviews and Experimental Studies: Tomé et al., 2024 (Nat. Neurosci.), etc.Nature