In a bustling lab blending computational modeling with experimental precision, neuroscientist Julie Haas and her team delve into the mysteries of how our brains focus on specific stimuli amidst a sea of sensory information. Their work explores the functions of the thalamic reticular nucleus (TRN), a group of cells linking the thalamus to the cerebral cortex. The TRN receives input from both the cortex and most nuclei of the thalamus, with its neurons modulating the thalamus’ responses as it relays sensory input to the rest of the brain.

Francis Crick, the co-discoverer of DNA’s structure, first hypothesized that the TRN acts as a "neural searchlight" enabling us to prioritize sensory input. Haas’s work aims to uncover how this intricate process unfolds and what makes the TRN uniquely suited for its role in selective attention. Her lab focuses on electrical synapses, which allow neurons to communicate quickly and efficiently. She is particularly interested in how the strength of these synapses affects TRN circuits and their critical role in controlling attention.

The TRN functions as a sensory stop sign, regulating which signals from our environment reach the brain’s cortex for further processing. Sensory information enters through the brainstem and travels through the thalamus before reaching the cortex, where it is integrated into coherent thoughts and perceptions. The TRN ensures we pay attention to specific sensory cues while ignoring others.

“We think the TRN says, ‘Pay attention to this sound but not that sound,” says Haas, associate professor of neuroscience in the department of biological sciences. “Our major goal is to figure out how the TRN does that—how the connections within it contribute to that process, how those connections change as a function of what you experience, and how the TRN integrates neural signals from all across your brain into the process of attention.”

Using groundbreaking tools like optogenetics and advanced imaging, the lab maps the TRN’s neural network. Optogenetics allows researchers to stimulate individual neurons with light and observe their connections with remarkable spatial and temporal precision.

One exciting avenue of the lab’s research explores a potential link between the amygdala, known for its role in fear, and the TRN. Collaborating with neuroscientist Maria Geffen of the University of Pennsylvania, Haas’s lab investigates how fear signals from the amygdala might influence the TRN’s attention-regulating functions.

Haas’s team injected a virus expressing a green fluorescent protein into the TRN to trace its connections in the brain. This work confirmed the expected link between the TRN and the amygdala. Researchers are now recording TRN neurons receiving amygdalar input to characterize this synaptic connection, laying the groundwork for understanding how fear sharpens sensory focus.

As Haas and her team continue their work, they shed light not just on the TRN but also on the broader question of how we experience and navigate the world around us. Through their research, the mysteries of attention are becoming just a little clearer.