Results from a study by researchers at Howard Hughes Medical Institute’s Janelia Research Campus reveals that "distant parts of the brain are called into action to store a single memory." The scientists observed mice, and their study has determined that the brain's cortex (or the outer layer of tissue that is supposed to generate the bulk of human thoughts and actions) depends on networks within the thalamus.
Karel Svoboda, the Janelia group leader who spearheaded the study, says that the discovery that the thalamus is necessary to temporarily store information so animals can "act on a past experience" implies that the region greatly affects the function of the cortex. Svoboda adds that this implies that the cortex is unable to preserve these memories by itself, highlighting the importance of the thalamus.
To illustrate, when a memory takes shape in the brain, "activity in the cells that store the information changes for the duration of the memory." Individual neurons are unable to stay active by themselves any longer than several milliseconds and groups of cells must cooperate to store the information. When neurons send signals back and forth, this can sustain their activity in the brief time "that it takes to store a short-term memory." (Related: Improve memory and increase vitality with Pennywort.)
Svoboda wants to learn how these memories are "formed and maintained, including where in the brain they are stored." In a previous study, Svoboda et al. observed that a region of the cortex in mice, referred to as the anterior lateral motor cortex (ALM), is responsible for short-term memory. A correlated activity in the ALM enables the mice to accomplish a memory-related task which involves experiencing a sensory cue, which must be remembered for a couple of seconds before they can react to the cue. If done correctly, the mice are given a reward.
Svoboda worked with his team to find out if the ALM can store these memories on its own or if it must work together with other regions of the brain. Since the ALM is linked to other parts of the brain through long-range connections, the logical conclusion would be to look into possible links between the region's long-range communications and memory storage.
Two postdoctoral researchers in Svoboda’s lab, Zengcai Guo and Hidehiko Inagaki, verified the connections individually. Through tests, they evaluated if switching off neurons in different parts of the brain hindered activity in the ALM associated with memory and if it affected the mice's ability to learn cues.
The results revealed that the thalamus had a significant effect on memory. Once the thalamic neurons were switched off, the cortex showed no signs of activity and short-term memories. Svoboda noted that the "cortex effectively becomes comatose."
Svoboda commented that these results also point out the "functional importance of connections between distant parts of the brain," which are usually overlooked since neuroscientists concentrate on other activity in specific regions. He concluded, "It was unexpected that these short-term memories are maintained in a thalamocortical loop… This tells us that these memories are widely distributed across the brain."
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