Activation maps for 24-pulse optogenetic stimulations at different frequencies. Image: Wu et al, Nature Communications

Breaking down complex brain functions

19 July 2023

A team of researchers from the University of Hong Kong uncovered how special brain activities, known as thalamic spindle activities, play a crucial role in memory consolidation. Their findings show potential new targets for treating memory deficits associated with aging.

One of the key functions of the brain is memory consolidation, which is the process by which memories are stored and retrieved. Thalamic spindle activities are a type of oscillatory activity in the brain that has long been believed to support memory consolidation. However, until now, the exact mechanisms by which this occurs have remained unclear.

Professor Ed X. Wu (Croucher Senior Research Fellow 2012) and his colleagues set out to tackle this complex question. The team used functional MRI and electrophysiology recordings in male rats to observe the brain’s response to optogenetically-evoked somatosensory thalamic spindle-like activities. They discovered that these activities targeted numerous sensorimotor and non-sensorimotor limbic regions in the brain, depending on the frequency and length of the stimulation. They found that stimulation at slow spindle frequency (8 Hz) and long spindle length (3 seconds) evoked the most robust brain-wide cross-modal activities.

“Stimulating the thalamus at these specific parameters significantly improved the rats’ performance in visual-somatosensory associative memory tasks,” said Professor Wu, emphasizing the importance of this discovery in understanding how memory works in the brain.

The researchers also found that these thalamic spindle activities propagate in a spatiotemporally specific manner. This means that they spread across the brain in a very specific pattern, both in terms of time and space. This propagation is thought to strengthen multi-target memory representation, thereby enhancing the memory consolidation process.

In addition to illuminating the mechanism of memory consolidation, the findings also have potential implications for the treatment of aging-related memory deficits. As people age, the decrease in spindle activities is considered one of the key factors contributing to memory consolidation deficits. The discovery of how thalamic spindle activities support memory consolidation could provide a new direction for potential therapeutic interventions.

The team also carried out parallel visual fMRI experiments which revealed response potentiation in several brain regions, especially superior colliculus, periaqueductal gray, and insular, retrosplenial and frontal cortices. This suggests that these regions play a significant role in the process of memory consolidation.

“We have been able to observe how thalamic spindle activities initiated at a specific thalamic nucleus propagate and target various downstream structures across the brain. This is a significant step forward in our understanding of memory consolidation at a systems level,” added Professor Wu.

The research team’s findings are expected to pave the way for future studies on memory consolidation and the development of potential treatments for memory deficits. The findings were published in Nature CommunicationsProfessor Wu's Croucher profile is here.