New study identifies gateway to conscious perception

We all have an innate sense of what it feels like to be conscious. Explaining exactly what consciousness is or being able to point to the mechanics that underpin it, however, is a totally different ball game. In part because of this ineffability, it's proven extremely difficult to study.

A recent paper, however, offers some rare progress. Looking beyond the cerebral cortex, which has been the focus of the lion's share of consciousness research in cognitive disciplines to date, a new study in Science reveals that specific regions of the deep-lying thalamus have a crucial role to play, in gating what rises to conscious perception.

In this study, Zepeng Fang at the National Natural Science Foundation of China and colleagues studied five people who had all had electrodes implanted in their brains (not for the purposes of this experiment, but for the treatment of persistent headaches). By collaborating with these participants, the team were able to capture high resolution temporal and spatial data from deeper areas of the brain, which are much more difficult to characterise with typical non-invasive methods.

These participants were given a visual task: they had to watch a screen, and the moment they saw a circle made up of vertical lines appear, they had to shift their gaze in one direction. The researchers varied the contrast between the lines of the circle and the background, so that sometimes it was easily perceptible, whilst at other times, they knew it would be hit or miss as to whether it would actually be perceived.

Data from the electrodes showed that in instances when the circle was consciously perceived, two specific regions of the thalamus — the intralaminar and medial thalamic nuclei — become active first, followed by the lateral prefrontal cortex. When activity in all of these regions became synchronised, that's when the participants experienced the conscious perception. "Importantly, the thalamocortical interactions were shown to originate from the intralaminar and medial thalamic nuclei, but not from the prefrontal cortex," the researchers stress.  

The thalamus has long been known to receive incoming sensory signals and to relay them on to other parts of the brain for processing. But this work demonstrates a "decisive" role for these two regions of the thalamus in the generation of conscious visual experience, the researchers write.

"This conclusion is a significant advance in our understanding of the network basis of visual awareness in humans," wrote Peter Stern, who edited the paper for Science, in a summary that accompanied it.

The new findings appear to gel well with the 'thalamic dynamic core theory', which proposes that the cortex has a higher-level role in our conscious perceptions, and that the thalamus plays a central role in conscious experiences.

Interestingly, other recent work on consciousness in non-human animals has found that crows — which lack a layered cerebral cortex, but do have the evolutionarily more ancient thalamus — have conscious sensory perceptions. The team thinks that, in humans, input from the cortex makes for a much more complex experience, enabling "the richness of conscious experience, like emotion consciousness, self-consciousness and so on, through sophisticated computation," they write. But in pinning down a fundamental role for regions of the thalamus, this new research will inform efforts to investigate just what other animals may be conscious of, too.

Read the paper in full:
Fang, Z., Dang, Y., Ping, A., Wang, C., Zhao, Q., Zhao, H., Li, X., & Zhang, M. (2025). Human high-order thalamic nuclei gate conscious perception through the thalamofrontal loop. Science, 388(6742). https://doi.org/10.1126/science.adr3675

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