To understand a sentence, the brain has to keep earlier words in mind as new ones arrive. Working memory makes that possible, holding information for a few seconds so we can compare it with new information, manipulate it, and use it to guide our behavior. We rely on it to follow conversations, solve problems, and decide what to do next. Yet sensory information fades within moments once a stimulus ends, leaving the brain with the demanding task of maintaining a usable representation of something that is no longer there. According to the team of researchers from UNIGE, in their findings published in Nature Communications, in mice, this ability relies partly on the claustrum, a thin structure deep within the brain between the insular cortex and the striatum. The claustrum supports working memory.
The scientists tested mice on tasks that required them to remember either a smell or a touch. Each animal received an initial stimulus, waited several seconds, and then received a second stimulus. The mouse had to determine whether the two were identical or different. By the time the second stimulus arrived, the first was gone, so success depended on retaining information about it during the wait. Temporarily reducing the activity of claustrum neurons cut the mice’s working memory performance in half. To control these neurons at precise moments during the task, the researchers used techniques including optogenetics. This method uses specific proteins to make selected neurons sensitive to light, allowing scientists to alter their activity through an optical fiber.
The intervention helped establish that the claustrum contributes to working memory rather than simply becoming active while another brain region does the necessary work. “The result was similar regardless of the type of stimulus, olfactory or tactile, and regardless of when the disruption occurred during the waiting period between the two stimuli. “Moreover, disrupting the claustrum specifically impairs the ability to use temporarily held information to guide behavior, without affecting perception itself,” said the study’s co-leader, Alan Carleton, full professor in the Department of Basic Neurosciences at UNIGE’s Faculty of Medicine. Working memory depends on interactions across a broad network that includes the prefrontal cortex, sensory regions, the parietal cortex, the thalamus, and other structures beneath the cortex.
These networks must preserve information while allowing the brain to continue perceiving, thinking, and acting, but how they maintain a representation over time remains largely unknown. The claustrum’s anatomy offers a reason to examine its contribution. “Its neurons are connected to almost all regions of the cortex, which puts it in a good position to receive and influence information from very different networks,” explains Carleton. Recordings from the mice allowed the researchers to examine how information was represented in claustrum activity during the gap between stimuli. “Our live recordings of claustrum neuron activity showed that a trace of the initial information persisted throughout the entire waiting period.
