I’ve always wondered how the brain processes all the information that comes through the visual cortex each and every moment of our lives. Surely, the brain needs to strike a balance between working hard (high-resolution neural response to stimuli) and avoiding burnout (by opting for lower-resolution responses). The high-resolution way requires the brain to treat each stimulus as unique and responding to them as such while the low-resolution way uses a “standard” set of response to not-to-different stimuli to economize on effort. If this is how the brain works, I am curious to know how. After all, somewhere in our brain lies our consciousness, or as Descartes puts it succinctly, “I think, therefore I am.”
So, how does the brain perform its balancing act? Answers are suggested by a recent study just published in the prestigious scientific journal, Nature [1] led to Dr Carsen Stringer.
Stringer and her collaborators imonitored the neural response patterns of mice using a new technique developed by them (for ethical reasons, such studies can’t be performed on live human brains). They used this technique to record the response patterns of tens of thousands of neurons in the visual cortex of lab mice after flashing as many as 3,000 stimuli (images of natural scenes) to the animals.
Watch this Video:
What you are about to see is a field of cells in the visual cortex of a laboratory mouse examined in real time. We will see neurons light up as they fire in response to images presented by members of research team. The patterns of firing indicate that a Power Law is at work in the brain’s representation of the oncoming images: This means that majority of the neurons respond to more or less same stimuli, and that exponentially fewer neurons are tasked to respond to more unusual stimuli. See note 2 for details.
Another way to visualize what is happening is the following diagram which charts the number of neuron cells engaged in various types of stimuli. The % of stimuli-related variance on the horizontal axis measures how similar or different a bunch of stimuli are. The lower the number (i.e., low readings), the more similar they are, while higher numbers to the right indicates more unusual stimuli. You see that the the bulk of the response curve clusters around low readings. It then tails off to fewer and fewer neurons for more unusual stimuli. This nuanced response pattern of mice neurons is what enables the brain to be alert, yet not “get fried”.
Taken together, the research indicates that the sensory machinery of mice visual cortex is indeed a smart piece of work. If what holds for mice holds for humans (not as crazy as it sounds since mice and humans share virtually the same set of genes [3]), then this answers the question I posed at the beginning: how our brains can be so alert, yet remain literally so cool. It is highly possible that evolution has shaped our brain to figure a way to work really hard without getting fried.
Notes:
[1] Carsen Stringer et al. “High-dimensional geometry of population responses in visual cortex”, Nature, 571, 2019, 361-65.
[2] “A few dimensions account for most of the neural response” can be mathematically represented by a curve known as the Power-law curve. Power laws are ubiquitous in nature as well as man-made settings. Examples of the latter are the overwhelming dominance of a few key cities in accounting for the lion’s share of a country’s urban population, and the highly skewed distribution of wealth among just a small percentage of individuals. Evidently, the sensory machinery of mice brains (and likely ours) follow power law patterns.
[3] Overall, mice and humans share virtually the same set of genes. Almost every gene found in one species so far has been found in a closely related form in the other. Of the approximately 4,000 genes that have been studied, less than 10 are found in one species but not in the other. Check this link:
https://www.genome.gov/10001345/importance-of-mouse-genome