The thalamic intralaminar nuclei: A role in visual awareness.

We briefly review the anatomy and functional properties of the intralaminar nuclei (ILN) of the thalamus and the neurological disorders associated with their dysfunction. The ILN project over a wide range of cortical territories and are connected to several subcortical structures that place the ILN within the distributed networks underlying arousal, attention, working memory, and gaze control. The temporal structure of the spike discharges of ILN neurons can be controlled by levels of arousal and visuomotor behavior. Taken together, the anatomy, cellular physiology, and clinical data suggest that in the state of wakefulness, the ILN neurons promote the formation of an “event-holding” function in the cortex. In the prefrontal cortex, this function facilitates the storage of target location in working memory. In the frontal eye fields, the function produces sustained activation that anticipates the onset of intended eye movements. In the posterior parietal cortex, the sustained activation can be boosted at the start of the intersaccadic interval and can operate as an attentional gate regulating the flow of information back to the prefrontal cortex. The attentional gate is of limited capacity, as is working memory, and is best utilized during the intersaccadic interval. The ILN may help to synchronize the eye movement commands of the frontal eye fields with the episodic dynamics of the attentional gate and working memory.