A study published in the journal Science in April 2025 by Mingsha Zhang of Beijing Normal University identified for the first time how deep brain structures, specifically the thalamus, are activated when the brain becomes aware of its own thoughts (conscious awareness).
Neuroscientists have long known that the cerebral cortex (the outer layer of the brain) is involved in the awareness of specific thoughts. However, the role of deeper structures has been difficult to investigate due to the need for invasive surgeries in humans and challenges in animal experiments.
In this study, researchers monitored the brain activity of patients who had electrodes implanted in their brains to treat severe headaches. Participants performed a simple visual task (moving their eyes as they noticed a briefly displayed icon), with the icon designed to be consciously perceived only half of the time.
Simultaneous recordings of neural activity in the thalamus and cortex revealed significant differences when participants were aware of the icon compared with when they were not. Activity in the thalamus, in certain areas, was stronger and occurred earlier than in the cortex during conscious perception, suggesting that the thalamus acts as a filter, controlling which sensory information reaches consciousness.
This finding is supported by previous studies in animals. Researchers at the University of Sydney described the work as “remarkable” because it allowed them to observe the temporal coordination of neural activity between different brain regions.
While the study is considered an elaborate investigation into the role of the thalamus in consciousness, some question whether the task actually captured neural activity specific to conscious experience or simply attention to a stimulus.
The researchers plan to conduct further experiments in humans and monkeys to further investigate brain activity related to consciousness.
