Summary: A recent investigation involving intracranial recordings from humans indicates that the thalamus, especially its higher-order areas, is crucial in initiating conscious perception. By observing brain activity during a visual task, researchers identified that the intralaminar and medial thalamic nuclei activated prior to the prefrontal cortex, implying that the thalamus is responsible for starting conscious awareness.
This synchronization of thalamus-to-cortex signals counters the conventional belief that only cortical areas are responsible for perception. These results enhance our comprehension of how neural circuits contribute to consciousness and underscore the significant function of subcortical structures.
Key Facts:
- Early Activator: Activations in intralaminar thalamic areas occur ahead of the prefrontal cortex during perception.
- Signal Sync: Conscious perception is aligned with synchronized activities between the thalamus and PFC.
- Thalamic Gateway: Findings advocate for a gating function of the thalamus in facilitating conscious awareness.
Source: AAAS
Using direct intracranial brain recordings from humans, a new investigation shows that the thalamus, a small deep-brain region, is critical for conscious perception.
The authors indicate that particular high-order thalamic areas serve as a portal to awareness by relaying signals to the prefrontal cortex.
These discoveries illuminate the complexities of human consciousness.
Deciphering the neural basis of human consciousness represents one of the most formidable challenges in neuroscience.
Earlier studies proposed that consciousness could be categorized into two elements: conscious state (for example, being awake or asleep) and conscious content (specific experiences or perceptions).
While subcortical structures mainly manage conscious states, numerous theories highlight the significance of subcortical-cortical loops in conscious perception.
Nevertheless, many investigations concerning conscious perception have predominantly centered on the cerebral cortex, with few addressing the role of subcortical regions, like the thalamus. Its involvement in conscious perception has frequently been considered limited to supporting sensory information.
To gain a better insight into the thalamus’s involvement in conscious perception, Zepeng Fang and colleagues conducted an innovative clinical experiment, simultaneously recording stereoelectroencephalography (sEEG) data from the intralaminar, medial, and ventral thalamic nuclei and prefrontal cortex (PFC). This was done while five chronic, drug-resistant headache patients with implanted intracranial electrodes engaged in a novel visual consciousness task.
Fang et al. uncovered that the intralaminar and medial thalamic nuclei demonstrated earlier and stronger consciousness-related neural activity than the ventral nuclei and PFC.
Interestingly, the authors noticed that the activity between the thalamus and PFC—particularly the intralaminar thalamus—was coordinated during the onset of conscious perception, suggesting that this thalamic area serves as a gatekeeper in promoting PFC activity during conscious awareness.
About this consciousness and neuroscience research news
Author: Science Press Package Team
Source: AAAS
Contact: Science Press Package Team – AAAS
Image: The image is attributed to Neuroscience News
Original Research: Closed access.
“Human high-order thalamic nuclei gate conscious perception through the thalamofrontal loop” by Hulin Zhao et al. Science
Abstract
Human high-order thalamic nuclei gate conscious perception through the thalamofrontal loop
INTRODUCTION
Investigating the neural substrates that underlie human consciousness ranks among the most captivating and daunting endeavors in contemporary science. There are at least two distinct forms of consciousness: the conscious state (such as awake, asleep, and coma) and the conscious content (specific conscious experience). The activity in human high-order thalamic nuclei is recognized to be closely related to conscious states.
Yet, it remains unclear how these thalamic nuclei and thalamocortical interactions contribute directly to the fleeting process (occurring within milliseconds) of human conscious perception.
While most research has concentrated on identifying the neural correlates of conscious perception in the cerebral cortex, far fewer studies have looked into the operational significance of subcortical structures, including high-order thalamic nuclei.
Recently, it has been hypothesized that high-order thalamic nuclei function as gates to modulate cortical activity during conscious perception. However, there exists a paucity of direct empirical evidence from human studies endorsing this claim.
RATIONALE
The thalamus has traditionally been regarded as merely a conduit for sensory data essential for conscious perception rather than as a direct contributor. However, this notion has been contested by novel theoretical hypotheses and empirical evidence, predominantly derived from anatomical and neuroimaging studies, which demonstrate the thalamus’s direct involvement in various cognitive functions.
Although several consciousness theories suggest that thalamocortical loops could play a pivotal role in human conscious perception, the specific processing and transfer of consciousness-related information within these loops remain largely unknown.
Moreover, given the functional heterogeneity among thalamic nuclei, it is crucial to delineate the distinct roles played by different thalamic nuclei in conscious perception.
However, precisely capturing neural activity with high spatial and temporal resolution within human thalamic nuclei and across thalamocortical loops presents significant challenges due to technical limitations.
Simultaneous intracranial recordings from human thalamic nuclei and thalamocortical loops present an exceptional opportunity to clarify the dynamic processes involved in thalamocortical integration during the onset of conscious perception.
RESULTS
We concurrently recorded sEEG data from multiple thalamic nuclei and the prefrontal cortex (PFC) while participants engaged in a novel visual consciousness task. In this task, the synchronized saccadic responses between conscious and unconscious conditions largely mitigated the potential for confusion between report-related activity and consciousness-related activity.
Comparatively, the intralaminar and medial nuclei exhibited earlier and more robust consciousness-linked activity than the ventral nuclei and PFC, encompassing both event-related potential (ERP) and event-related spectral perturbation (ERSP).
Transient thalamofrontal neural synchronization and cross-frequency coupling were both influenced by the θ phase (2 to 8 Hz) of activity within the intralaminar and medial nuclei during the emergence of conscious perception.
The coupling between these two thalamic regions and lateral PFC (LPFC) was found to be more pronounced than that observed between these regions and other PFC subdivisions during conscious perception.
Further decoding analysis of stimulus-evoked activity in the intralaminar and medial nuclei along with the LPFC indicated that the highest accuracy was achieved when decoding conscious perception (distinguishing conscious from unconscious) compared to differentiating other task-related events (such as stimulus intensity, rule cues, saccade direction, and saccade reaction time).
CONCLUSION
We furnish direct sEEG evidence from the human brain that substantiates the gating function of the intralaminar and medial nuclei in the rapid process of conscious perception. More precisely, the intralaminar and medial nuclei are more influential than the ventral nuclei during the emergence of conscious awareness.
The interactions between the LPFC and the intralaminar and medial nuclei, which stem from the intralaminar and medial nuclei, may play a critical role during conscious perception. Furthermore, the stimulus-evoked activity within the thalamofrontal loop primarily encodes consciousness-related information rather than other relevant task events.
These findings endorse the perspective that the intralaminar and medial thalamic nuclei serve as a gate to modulate PFC activity during the onset of conscious perception.
