Neuroscientists have long sought to identify the mechanisms required for conscious experience. In their new paper, Redinbaugh et al. show that, in macaques, the central lateral thalamus (CL) has a key role in the control of consciousness, through the modulation of specific corticocortical pathways.

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Consciousness is thought to involve feedforward and feedback interactions between cortical layers and areas. As the CL is connected to both superficial and deep cortical layers, it is well-positioned to modulate consciousness. Here, electrical stimulation of the CL in two anaesthetized macaques generated temporary behavioural indications of arousal, including face and body movements typical of wakefulness.

To further examine the CL’s role in consciousness, the authors simultaneously recorded neural activity in the CL and in two reciprocally connected cortical areas — the lateral intraparietal area (LIP) and the frontal eye field (FEF) — in response to an auditory stimulus. Sleep and anaesthesia were associated with less activity in the CL and in deep layers of the LIP and FEF than wakefulness, whereas CL stimulation reversed these changes.

Next, the authors considered how changes in consciousness state relate to interactions between and within these brain areas. Both anaesthesia and sleep were associated with a decreased coherence of alpha and gamma band oscillations in activity between deep and superficial layers within each cortical area, in comparison with wakefulness or CL stimulation. Similarly, there was a decrease in alpha and gamma coherence between the LIP and FEF and between the CL and the cortex under anaesthesia and during sleep. CL stimulation restored alpha and gamma coherence in a feedforward pathway between superficial layers of the LIP and superficial and middle layers of the FEF, and restored alpha coherence in feedback pathways projecting from the deep layers of the FEF to the LIP.

electrical stimulation of the CL in two anaesthetized macaques generated temporary behavioural indications of arousal

This study provides evidence for the involvement of intracolumnar and long-range corticocortical pathways in conscious experience and suggests that the CL has an essential role in driving these interactions. These findings could eventually contribute to the treatment of disorders of consciousness.