A new study published in Science has identified thalamus as a central actor in the way humans consciously aware of visual information. By recording electrical activity directly from the brain of five patients during a visual task, scientists discovered that specific thalamic regions are activated earlier and more strongly during moments of visual consciousness. These results suggest that medial intralamine and thalamic nuclei act as a bridge that initiates conscious perception by influencing the activity of the prefrontal cortex.
Thalamus is a small egg -shaped structure located in the center of the brain. It acts as a center to relay sensory information – such as sight, sound and touch – with the cerebral cortex, where perception and interpretation occur. In addition to this relay role, it also helps to regulate vigilance, sleep and attention.
Although thalamus has long understood as a relay station for sensory information, it has been largely considered as a support player – important to maintain awakening, but not as the real source of conscious experience. This study questions this idea, offering new evidence that thalamus is more than simplifying signals. It can actively shape what is entering our conscience.
To investigate, the research team took advantage of a unique opportunity to record a deep brain activity in humans. Five adult men undergoing treatment for severe and drug -resistant headaches had stereoéncephalographic electrodes (SEEG) located in their brain. These electrodes allowed researchers to monitor neural activity in real time in several brain regions, including various parts of the Thalamus and the prefrontal cortex.
The participants accomplished a task of visual consciousness which presented images on the verge of conscious visibility. With each test, a patterned stimulus appeared briefly on one side of a central fixing point. Some images were brilliant and clearly visible, while others were weak and difficult to detect. Sometimes no stimulus has been shown at all. After each test, the participants responded with an eye movement indicating if they had seen the stimulus and where it had appeared.
This configuration allowed researchers to compare the brain activity between the tests where participants consciously saw the stimulus and the tests where they did not do so, even if the visual entry was almost identical. This critical contrast helped isolate neural processes specifically linked to consciousness, rather than a simple sensory entry.
The results have shown that certain regions deeply in thalamus – in particular the central medial nucleus, the medial medial medial nucleus and the parafascicular nucleus – increased increased activity during trials when the participants said they saw the stimulus. These regions are known as intralamine and medial thalamic nuclei. Their responses occurred earlier and with greater intensity than activity in other Thalamic regions, such as ventral nuclei, and even earlier than the responses in the prefrontal cortex.
Using a range of analyzes, the researchers found that these high -level thalamic nuclei had higher electrical signals, an increase in low -frequency oscillations and more synchronized activity during moments of consciousness. It is important to note that the time of this activity – taking around 200 milliseconds after the presentation of the stimulus – was aligned with the first known brain signatures of conscious perception, such as the negativity signal of the visual consciousness recorded in previous studies based on the scalp.
To understand how these signals travel through the brain, the researchers examined how different regions of the brain communicated during conscious and unconscious tests. They measured the synchronization of neural oscillations, in particular in the Thêta frequency range (around 4 to 8 Hz), which was linked to cognitive control and awareness. They also analyzed the transverse coupling, which describes how slow brain rhythms can coordinate faster activity in other areas. The two measures revealed that the medial intralaminary and thalamic regions led to neural coordination with the prefrontal cortex during conscious perception.
In other words, when the participants were aware of the stimulus, the thalamus did not simply react to the sensory contribution – it actively shaped the brain’s response, sending signals to the prefrontal cortex and helped organize an activity on the scale of the brain in support of consciousness.
Additional analyzes have shown that the neural models of the Thalamus and the prefrontal cortex co -led information on the knowledge of the participants of the stimulus, rather than simply reflecting aspects of the task such as the contrast force, the motor response or the reaction time. This strengthens the case that these regions are directly involved in conscious perception, rather than reflections simply downstream from other cognitive processes.
Interestingly, researchers also found that activity in thalamus, especially in intralamine and medial nuclei, could start even before the stimulus appears. This pre-stimulus activity was more synchronized in the tests where participants would later report to be aware of the stimulus, which suggests that these regions could help prepare the ground for conscious perception by influencing brain preparation.
This study is the first to offer such detailed recordings from multiple thalamic nuclei in humans during a task designed to probe the border between conscious and unconscious visual perception. Previous studies using imaging methods such as functional MRI or Magnetotephalography have alluded to thalamic involvement in consciousness but lacked precision to determine when and where this activity occurred. The use of Seeg here has provided a rare opportunity to capture the dynamics of deep brain structures with a high temporal and spatial resolution.
The results provide strong support for the idea that consciousness is not only a cortical phenomenon. Instead, Thalamus – in particular its high order nuclei – appears to play an active and early role in the provision of our consciousness. This can reflect the unique position of the thalamus as a center, with widespread connections to the cortical and subcortical brain regions, which allows it to coordinate the complex models of neural activity required so that consciousness emerges.
However, the authors note certain limitations. The study was conducted in a small sample of five male patients, who all had electrodes located for clinical reasons related to the processing of headache. Although their cognitive capacities and their vision are intact, these participants do not represent the general population. In addition, the placement of the electrodes has been determined by medical needs, and not the research objectives, which means that certain regions of the brain may have been subchantned or completely missed.
In addition, although the study strongly suggests that medial intralamine and thalamic nuclei initiate the conscious perception process, it does not exclude important contributions from the cortex. The prefrontal cortex, in particular the lateral regions, has always shown significant activity and has participated in networks of synchronized neurons during awareness. Researchers suggest that thalamus can act as a door or initiator, while the Cortex develops the content of the experience.
The study, “High -level high -level thalamic nuclei conscious perception through the thalamofrtontal loop“, Was written by Zepeng Fang, Yuanyuan Dang, An’an Ping, Chenyu Wang, Qianchuan Zhao, Hulin Zhao, Xiaoli Li and Mingsha Zhang.
