Recurrent thalamo-cortical resonance

Recurrent thalamo-cortical resonance is an observed phenomenon of oscillatory neural activity between the thalamus and various cortical regions of the brain. It is proposed by Rodolfo Llinas and others as a theory for the integration of sensory information into the whole of perception in the brain. Thalamocortical oscillation is proposed to be a mechanism of synchronization between different cortical regions of the brain, a process known as temporal binding. This is possible through the existence of thalamocortical networks, groupings of thalamic and cortical cells that exhibit oscillatory properties.

Thalamocortical oscillation involves the synchronous firing of thalamic and cortical neurons at specific frequencies; in the thalamocortical system, the exact frequencies depend on current brain state and mental activity. Fast frequencies in the gamma range are associated with much of conscious thought and active cognition. The thalamus in this system acts as both the gate for sensory input to the cortex as well as the site for feedback from cortical pyramidal cells, implying a processing role in sensory perception in addition to its function in directing information flow. The state of the brain, whether it be conscious, in REM sleep, or non-rapid eye movement sleep, changes how sensory information is gated through the thalamus.

Thalamocortical networks consist of neurons in both the thalamus and cortex. The thalamic neurons are typically one of three types: thalamocortical, with axons extending into the cortex, reticular, and thalamic interneurons.Thalamocortical neurons (TC) vary significantly in size, which is correlated with the depth to which they project into the cortex. These cells are limited in their outputs and seem to only connect to the cortical layers and reticular thalamic neurons. Reticular neurons (RE), on the other hand, are highly interconnected and have their own intrinsic oscillatory properties. These neurons are capable of inhibiting thalamocortical activity via their direct connections to TCs. Corticothalamic neurons are the cortical neurons that TC neurons synapse on. These cells are glutaminergic excitatory cells that exhibit increasing activity as they become more depolarized. This activity is described as "bursting", firing in the gamma range at rates between 20 and 50 Hz.

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