The intralaminar thalamus: a review of its role as a target in functional neurosurgery

Abstract

The intralaminar thalamus, in particular the centromedian-parafascicular complex, forms a strategic node between ascending information from the spinal cord and brainstem and forebrain circuitry that involves the cerebral cortex and basal ganglia. A large body of evidence shows that this functionally heterogeneous region regulates information transmission in different cortical circuits, and is involved in a variety of functions, including cognition, arousal, consciousness, and processing of pain signals. Not surprisingly, the intralaminar thalamus has been a target area for (radio)surgical ablation and deep brain stimulation in different neurological and psychiatric disorders. Historically, ablation and stimulation of the intralaminar thalamus have been explored in patients with pain, epilepsy, and Tourette syndrome. Moreover, deep brain stimulation has been used as an experimental treatment for disorders of consciousness and a variety of movement disorders. In this review, we provide a comprehensive analysis of the underlying mechanisms of stimulation and ablation of the intralaminar nuclei, historical clinical evidence, and more recent (experimental) studies in animals and humans to define the present and future role of the intralaminar thalamus as a target in the treatment of neurological and psychiatric disorders.

Human intralaminar and medial thalamic nuclei transiently gate conscious perception through the thalamocortical loop

“…In the anatomical view, the medial group of thalamic nuclei, including MD, extensively connected with PFC 32,33 , which has been considered as a key node in consciousness perception 19,34 . Meanwhile, the intralaminar nucleus, including CM and Pf, were found to connect with more brain areas, including the cortical areas, such as frontal, parietal, cingulate cortex, medial temporal lobe and occipital lobe; and subcortical areas, such as striatum and cerebellum 13,14 . In contrast, anatomical connections of the ventral and ventrolateral thalamic nuclei are mainly confined to the motor network including basal ganglia, cerebellum and motor cortex 28 .…”

“…Intralaminar nuclei were well-known to maintain human wakefulness and conscious states. Impairment of intralaminar nuclei can cause a disorder of consciousness 14 , whereas stimulation of intralaminar nuclei improved the level of conscious states and even restored arousal and awareness 44,45 . Such effect of those thalamic nuclei indicated their ‘gate’ role in conscious states 14,15 .…”

“…Thalamus, as one of the most important subcortical structures, have long been known to be involved in regulating conscious states, especially for the high-order nuclei like intralaminar nuclei 14,15 . However, tough both being necessary aspects of consciousness, conscious states and conscious contents are very different 16,17 .…”

“…The neural mechanism underlying conscious states are explored by contrasting the neural activities in different conscious states, including awake, asleep, anesthetic states and so on. And the essential neural substrates supporting conscious states are mainly found in subcortical structures, like the brainstem and some high-order thalamic nuclei 14,15 . In contrast, the neural correlates of specific conscious content are studied in awake state, through comparing the neural activities when subjects reported aware or unaware of a stimulus, e.g., visual, auditory and somatosensory, etc.…”

“…As for the rare intracranial recording, capturing the neural activity in the thalamic nuclei during patients performing a consciousness task can be very hard due to several reasons. Firstly, the thalamic recording is usually conducted on the patients ongoing a deep brain stimulation (DBS) treatment 14,15 . These patients are conventionally suffering from severe neural disease, like disorders of consciousness (DoC) and Parkinson disease, which greatly prohibit them from conducting sophisticated consciousness tasks.…”