SLEEP AND AROUSAL: Thalamocortical Mechanisms

Abstract

Thalamocortical activity exhibits two distinct states: (a) synchronized rhythmic activity in the form of delta, spindle, and other slow waves during EEG-synchronized sleep and (b) tonic activity during waking and rapid-eye-movement sleep. Spindle waves are generated largely through a cyclical interaction between thalamocortical and thalamic reticular neurons involving both the intrinsic membrane properties of these cells and their anatomical interconnections. Specific alterations in the interactions between these cells can result in the generation of paroxysmal events resembling absence seizures in children. The release of several different neurotransmitters from the brain stem, hypothalamus, basal forebrain, and cerebral cortex results in a depolarization of thalamocortical and thalamic reticular neurons and an enhanced excitability in many cortical pyramidal cells, thereby suppressing the generation of sleep rhythms and promoting a state that is conducive to sensory processing and cognition.

Characterization of Rebound Depolarization in Neurons of the Rat Medial Geniculate Body In Vitro

“…induced by T-Ca 2? channels can increase the level of the cyclic adenosine monophosphate to upregulate the activation of HCN channels [44,45]. This interaction plays a physiological role in the generation of burst firing in single thalamocortical neurons and the oscillatory activity of neuronal networks in the thalamus [45][46][47][48][49][50].…”

Vigilance, alertness, or sustained attention: physiological basis and measurement

“…The burst state results from relative hyperpolarization and the tonic state from relative depolarization of the resting membrane potential (McCormick and Bal, 1997;Steriade et al, 1993). During EEG synchronized sleep when the thalamic neurons are hyperpolarized and in burst mode, there is a diminished responsiveness of thalamic sensory neurons to stimuli within their receptive fields with lowered signal-to-noise ratio (Livingstone and Hubel, 1981;McCormick and Feeser, 1990).…”

Interaction between neocortical and hippocampal networks via slow oscillations

“…Many reviews have discussed the mechanisms and functional significance of sleep spindles (McCormick and Bal, 1997;Destexhe and Sejnowski, 2001;Steriade et al, 2001). Briefly, the key EEG pattern of superficial sleep is a waxing-waning oscillatory pattern in the 12-18 Hz frequency range, known as the sleep spindle (Bremer, 1935;Steriade et al, 1993d).…”

“…The thalamus is organized locally and does not have the means to produce global synchrony (McCormick and Bal, 1997). The emerging thalamic spindles are transferred to the neocortex via topographic thalamo-cortical projections, and the spatially contiguous or distinct thalamic oscillations are synchronized by cortico-thalamic feedback (Kim et al, 1995;.…”