When we engage our working memory, we temporarily retain information in our brain. A team of researchers has now demonstrated that the key to understanding working memory relies not only on what one is storing in memory but also why – highlighting the “working” aspect of working memory, which underscores the purpose of storing information in the first place. Specifically, the study focuses on both how we store the visual properties of our memories in the occipital lobe, where our visual system resides, and on how the neural codes that store those memories change over time as people begin to prepare a response that depends on the memory.

In the study, the response simply required people to look where they remembered an object that disappeared several seconds ago. This sheds light on the intricate interplay between memory formation and the cognitive processes that guide our actions. As you read this sentence, for example, your working memory holds the words temporarily, and this could influence how you interpret the information and potentially respond to it. The importance of working memory to many of our cognitive abilities is well known, but less clear are the neurological machinations driving this process.

According to conventional textbook theories, the encoding patterns within our working memory remain constant over time. This signifies that the neural activity pattern responsible for storing a specific visual memory remains unchanged from its initial encoding, regardless of whether it’s been a mere second or a substantial 10 seconds. These intricate neural activity patterns serve as the repositories of visual memories, effectively forming a temporal bridge that connects a past stimulus with a forthcoming memory-guided response.

However, recent investigations involving animals have revealed that the neural patterns responsible for memory are notably more fluid. In fact, the stability of memory codes has been brought into question, as they seem to exhibit perplexing changes over time.

To delve into this phenomenon, researchers Li and Curtis, known for their prior breakthroughs in deciphering the organization of our working memory within the brain, developed innovative techniques. Their goal was to not only quantify the shifting neural dynamics but also to render these dynamics intelligible. To achieve this, they projected intricate neural measurements onto a simple 2D plane, akin to the screen of a laptop or smartphone.

The accompanying video vividly illustrates the progression of neural activity during a working memory trial. Initially, a cluster of activity emerges, encoding the briefly presented visual target (depicted as a pink circle), evident in both the primary visual cortex (V1) and a higher-level visual area (V3AB). In V3AB, this activity cluster remains fixed at the target location throughout the memory retention period. However, within V1, a line of activity evolves during the delay period between the individual’s current gaze direction (indicated by a pink cross) and the intended eye movement after the delay.

The researchers posit that this evolving line represents the projected path of the intended gaze shift that individuals are mentally rehearsing but have yet to execute.

While prior research had documented the dynamic nature of neural activity during working memory, the underlying cause for these dynamics had remained enigmatic. The latest findings help shed light on this puzzle. They suggest that these dynamic neural patterns are manifestations of the transformation of past sensory experiences—what has recently been perceived—into anticipated behaviors guided by memory—what actions might be taken based on that memory.

More information: Clayton E. Curtis, Neural population dynamics of human working memory, Current Biology (2023). DOI: 10.1016/j.cub.2023.07.067. www.cell.com/current-biology/f … 0960-9822(23)01039-4