Have you ever rearranged your errands due to traffic or timing? How does your brain reprogram your mental map on the fly?

Imagine planning your errands, and mentally organizing your tasks, and suddenly, due to a shift in pick-up time or an unexpected delay, you need to change the entire sequence. How does your brain adjust and reprogram the order of tasks to accomplish everything efficiently?

Neuronal networks on a Brain

John von Neumann doubted that the brain's logical processes were comparable to those of computers, while Alan Turing envisioned computers as imitations of the brain. Decades of research later, the core challenge remains: How does the brain break down complex programs into distinct neural steps or building blocks in working memory? Is this process similar to computation, or does it transcend that framework?

Researchers designed a simple game for two macaque monkeys to understand how the brain works. The monkeys watched three dots appear one after the other on a screen arranged in a hexagon. They memorized the order for about half a second before a signal told them to either keep the same order or reverse it. Finally, a cue prompted them to touch the dots in the new sequence, while scientists recorded activity from thousands of brain cells in the frontal area.

This task allowed researchers to examine how frontal cortex neurons contribute to two types of working memory: passive (holding the original sequence) and active (manipulating the sequence). The findings revealed key insights into the neural mechanisms underlying spatial sequence processing.

Using a computational model, researchers discovered that the frontal neuron population encoded both the position and the order of the objects in the sequence. Neural activity even formed a hexagonal pattern, reflecting the spatial layout presented to the monkeys. When the animals had to decide whether to maintain or reverse the sequence, two distinct neural representations of the spatial sequence were prepared for mental sorting. But how exactly does the brain perform the "swapping" of sequences?

Think of it like swapping the contents of two cups—one filled with milk and the other with water. To switch them, you first need to pour each liquid into a temporary container before transferring them to the opposite cup. This operation, although simple, requires parallel processing—just like the neurons in the frontal cortex during mental sorting.

Researchers found that specific subpopulations of neurons were briefly activated after the rule cue to swap the sequence order, similar to how the liquids temporarily reside in containers. Interestingly, even during erroneous trials, these transient neural states appeared, demonstrating the frontal cortex’s critical role in mental programming.

Moreover, the study revealed that the temporary subspaces for mental swapping and those for working memory involved distinct subpopulations of neurons, each performing specialized functions. These findings suggest that different neuronal circuits are responsible for storing and manipulating information, providing a single-neuron basis for separating these cognitive tasks.

Researchers conclude that the brain’s ability to manage abstract associations between different cues and mental sorting processes can be broken down into key components: rule cues, temporary memory for swapping, and rank-based working memory subspaces. This system of mental organization shows how the frontal cortex orchestrates complex cognitive tasks by coordinating multiple neural processes.

The study’s findings offer a potential explanation for how the brain transfers information across neural spaces, answering John von Neumann's skepticism by illustrating how the brain handles parallel computations that feed into serial processes, creating an efficient system for mental programming.

References:

Sprevak, Mark, 'Turing’s model of the mind', The Turing Guide (Oxford, 2017; online edn, Oxford Academic, 12 Nov. 2020)

J. von Neumann, R. Kurzweil, The Computer and the Brain

(Yale Univ. Press, 2012).

Tian, Z., Chen, J., Zhang, C., Min, B., Xu, B., & Wang, L. (2024). Mental programming of spatial sequences in working memory in the macaque frontal cortex. Science (New York, N.Y.), 385(6716), eadp6091. https://doi.org/10.1126/science.adp6091

1. Frontal cortex – A part of the brain behind your forehead involved in decision-making, memory, and planning actions.

2. Neurons – Brain cells that send and receive signals.

3. Working memory – The brain’s short-term memory system used to hold and manipulate information temporarily.

4. Computational model – A computer-based simulation used to understand brain functions.

5. Neuronal activity – Electrical signals sent by neurons when they’re active.

6. Spatial sequence – A specific order of things based on where they are located.

7. Parallel processing – The ability to do multiple mental tasks at the same time.

8. Subpopulations of neurons – Small groups of neurons that work together for specific tasks.

9. Neural mechanisms – The processes and structures in the brain that make thoughts and actions happen.

10. Transient neural states – Short-lived changes in brain activity.

11. Neural spaces/subspaces – Areas or patterns of brain activity where information is temporarily stored or processed.

Serial processes – Actions or thoughts that happen one step at a time, in sequence.