MIT's Nedivi: 'How the thalamus communicates with the cortex is a fundamental feature of how the brain interprets the world'

Researchers from the Massachusetts Institute of Technology (MIT) have made significant progress in understanding how the brain communicates using neural pathways, shedding new light on the brain's interpretation of the world.

The study focused on the thalamic inputs into the superficial layers of the cortex, a February news release from the institute said. Scientists have struggled to understand how it works so well given the scarcity of observed connections, or synapses, between the thalamus and cortex. 

“How the thalamus communicates with the cortex is a fundamental feature of how the brain interprets the world,” Elly Nedivi, William R. and Linda R. Young Professor of Neuroscience in The Picower Institute for Learning and Memory at MIT, said in the release.

In the study, which was published in Nature Neuroscience, researchers noted that thalamic inputs into superficial layers of the cortex are both rare and surprisingly weak, and they are diverse in their distribution patterns. In spite of these factors, they are both reliable and efficient representatives of information.

Researchers mapped thalamic synapses on 15 neurons in the visual cortex of mice. By modeling the effect of the inputs on each neuron's processing of visual information, scientists found that variations in the number and arrangement of thalamic synapses made them sensitive to visual stimuli. Although singular neurons could not interpret all aspects of the stimulus reliably, a small population of them working together could assemble the overall picture.

Nedivi explained that this feature confers a cost benefit and allows for reliable transfer of information. In addition, scientists developed techniques to track the individual inputs a cell receives in real-time, describing those inputs and their information to a given brain cell. The researchers used advanced mapping to investigate the thalamic inputs onto cortical neurons. The team collaborated with Idan Segev, a computational neuroscientist, who created a model of the cortical neurons based on the detailed measurements obtained by Nedivi's lab.

While no single cell provided comprehensive information about the visual input, approximately 20 cells together could decode all the visual information, which demonstrates a "wisdom of the crowd" phenomenon, the report stated.

A small, weak and diverse group of cells actually outperformed cells that acted like the best single cell when it came to representing the total visual input with at least 90% accuracy. Scientists said that suggests heterogeneity in thalamic inputs reduces the number of synapses required for accurate interpretation.

The study has important implications for understanding thalamic input into the cortex, but further studies must be conducted to explore them.

The research was funded by the National Eye Institute of the National Institutes of Health, the Office of Naval Research and the JPB Foundation, the release said. Along with Nedivi, the team involved in the study included Aygul Balcioglu, Kendyll Burnell, Alev Erisir, Rebecca Gillani, Taeyun Ku, Idan Segev and Michael Doron.