Subcortical Neurons Reflect Conscious Tactile Perception in Humans

Concepts de base

Subcortical neurons in the subthalamic nucleus and thalamus modulate their firing rates in relation to the conscious detection of tactile stimuli, providing direct neurophysiological evidence for the involvement of subcortical structures in perceptual consciousness.

Résumé

The study investigated the role of subcortical structures, specifically the subthalamic nucleus (STN) and thalamus, in the neural correlates of conscious tactile perception in humans. The authors recorded single neuron activity from these regions in patients undergoing deep brain stimulation surgery while they performed a tactile detection task.
The key findings are:

A significant proportion of neurons in the STN and thalamus modulated their firing rate in relation to the task, either after the cue or during the stimulation window, suggesting their involvement in task-related processes.

A subset of neurons (23%) showed differential firing rates between detected and undetected tactile stimuli, indicating their role in conscious tactile perception. These perception-selective neurons were found in both the STN and thalamus.

The perception-selective neurons showed higher firing rates for missed trials compared to hit trials in 6 out of 8 cases, suggesting a potential role in elevating the decision threshold for conscious access.

Control analyses confirmed that these neuronal modulations were not simply due to differences in stimulus intensity or onset, but specifically related to the conscious detection of the stimuli.

The results provide the first direct neurophysiological evidence in humans that subcortical structures, in addition to the cortex, contribute to the neural correlates of conscious tactile perception. This challenges the cortico-centric view of consciousness and highlights the importance of considering subcortical contributions in understanding the neural basis of conscious experience.

Stats

The stimulus intensity was kept around the detection threshold using a staircase procedure, with the average absolute intensity being similar for hit and miss trials.
The hit rate was comparable between participants with Parkinson's disease (0.51) and essential tremor (0.52).
The false alarm rate was also similar between the two patient groups (0.24).

Citations

"Our results provide direct neurophysiological evidence of the involvement of subcortical structures in for the detection of vibrotactile stimuli, thereby calling for a less cortico-centric view of the neural correlates of consciousness."
"The present results, therefore, indicate that the contribution of subthalamic neurons to decisional processes is not limited to discrimination tasks or motor planning, but may also regulate the threshold at which accumulated evidence gives rise to a conscious percept."

Idées clés tirées de

Subcortical correlates of consciousness with human single neuron recordings

by Pereira,M., ... à www.biorxiv.org 01-30-2023

https://www.biorxiv.org/content/10.1101/2023.01.27.525684v3

Questions plus approfondies

How do the perception-selective subcortical neurons interact with and influence the activity of cortical neurons during conscious tactile perception?

Perception-selective subcortical neurons play a crucial role in shaping the conscious tactile perception experience by interacting with and influencing the activity of cortical neurons. These subcortical neurons are involved in detecting and processing sensory stimuli, particularly in the thalamus and subthalamic nucleus.
During conscious tactile perception, the activity of these perception-selective subcortical neurons can influence cortical neurons through various pathways. One key mechanism is through the thalamocortical loops, where the thalamus acts as a gateway for sensory information to reach the cortex. The thalamus relays sensory inputs to specific cortical areas, allowing for the integration and processing of tactile information. The activity of perception-selective subcortical neurons can modulate the flow of sensory information through these loops, influencing the firing patterns of cortical neurons involved in conscious perception.
Additionally, subcortical-cortical connections facilitate the communication between subcortical structures and cortical regions. The subthalamic nucleus, for example, has connections with the cortex and can regulate cortical activity through these connections. By modulating the firing rates of cortical neurons, perception-selective subcortical neurons can shape the conscious experience of tactile perception. This interaction between subcortical and cortical neurons is essential for the integration of sensory information and the generation of conscious awareness of tactile stimuli.

How do the subthalamic nucleus and thalamus modulate the threshold for conscious access to sensory stimuli?

The subthalamic nucleus and thalamus play a critical role in modulating the threshold for conscious access to sensory stimuli, particularly in the context of tactile perception. These subcortical structures are involved in regulating the flow of sensory information and determining whether sensory stimuli reach conscious awareness.
One potential mechanism by which the subthalamic nucleus and thalamus modulate the threshold for conscious access is through the regulation of decisional processes. The subthalamic nucleus, for example, has been implicated in elevating the decisional threshold on accumulated sensory evidence. By influencing decision-making processes, these subcortical structures can determine the level of evidence required for a sensory stimulus to reach conscious perception.
Additionally, the thalamus, as part of the thalamocortical loops, plays a crucial role in gating sensory information to the cortex. The thalamus filters and processes sensory inputs before relaying them to the cortex, influencing the likelihood of sensory stimuli reaching conscious awareness. The activity of the thalamus and subthalamic nucleus can adjust the threshold for conscious access by modulating the transmission of sensory signals and regulating the integration of sensory information in the cortex.
Overall, the subthalamic nucleus and thalamus contribute to setting the threshold for conscious access to sensory stimuli by regulating decisional processes, modulating sensory information flow, and influencing the integration of sensory inputs in the cortex.

Could similar subcortical contributions to conscious perception be observed in other sensory modalities, such as vision or audition?

Yes, similar subcortical contributions to conscious perception can be observed in other sensory modalities, such as vision or audition. Subcortical structures, including the thalamus and subthalamic nucleus, play a crucial role in processing sensory information and influencing conscious awareness across different sensory modalities.
In vision, for example, the thalamus relays visual information from the retina to the visual cortex, where conscious visual perception occurs. Subcortical neurons in the thalamus can modulate the transmission of visual signals and influence the threshold for conscious access to visual stimuli. Similarly, the subthalamic nucleus may play a role in regulating decisional processes and shaping the conscious experience of visual perception.
In the auditory domain, subcortical structures like the thalamus are involved in processing auditory information and transmitting it to the auditory cortex for conscious perception. Subcortical neurons in the thalamus and other subcortical regions can modulate the processing of auditory stimuli and impact the threshold for conscious access to auditory information.
Overall, subcortical contributions to conscious perception are not limited to tactile stimuli but extend to other sensory modalities like vision and audition. The interactions between subcortical and cortical structures in processing sensory information and determining conscious awareness are fundamental across various sensory domains.