I have long thought of the thalamus as the ‘grand central station’ of the brain. An extension of the spinal cord (the reticular formation) comes through the lower brain and ends in the thalamus. It is the ascending reticular formation that controls consciousness – when it is active, we are aware and when it is quiet, we are not aware. The signals that keep us awake come from the brain stem up the reticular formation into the thalamus, at the thalamic reticular nucleus. The parts of the thalamus seems to be connected to everything else too. It sends signals and receives signals from every part of the cortex and these signals are essential for consciousness. It has input from all the senses which it feeds on to the cortex (bar smell which mostly goes straight to the cortex and reaches the thalamus via the cortex). The thalamus communicates with the basal gangia and receives information on motor commands through them. And on it goes; there seems to be little that does not involve the thalamus directly or indirectly.
Basilis Zikopoulos and Helen Barbas have a series of papers on attention that put the gate to attention in the thalamic reticular nucleus. We have attention that is top-down and centered on the current task, bottom-up and centered on novel sensory input. They imply that there is also attention centered on strong emotional inputs. The thalamic reticular nucleus inhibits contributions to attention. It receives input from the amygdala (the emotional center) and if this is intense, other potential objects of attention are inhibited. The frontal cortex gives input to the same area and may trigger the inhibition of other potential objects of attention to give top-down attention. Input in the same area from the thalamic mediodorsal nucleus may serve the same purpose for bottom-up attention. The strength and priority of these signals would be used by the thalamic reticular nucleus to drive the spotlight of attention.
Here is the abstract from Zikopoulos and Barbas’ recent paper, Pathways for Emotions and Attention Converge on the Thalamic Reticular Nucleus in Primates, in the Journal of Neuroscience:
How do emotional events readily capture our attention? To address this question we used neural tracers to label pathways linking areas involved in emotional and attentional processes in the primate brain (Macaca mulatta). We report that a novel pathway from the amygdala, the brain’s emotional center, targets the inhibitory thalamic reticular nucleus (TRN), a key node in the brain’s attentional network. The amygdalar pathway formed unusual synapses close to cell bodies of TRN neurons and had more large and efficient terminals than pathways from the orbitofrontal cortex and the thalamic mediodorsal nucleus, which similarly innervated extensive TRN sites. The robust amygdalar pathway provides a mechanism for rapid shifting of attention to emotional stimuli. Acting synergistically, pathways from the amygdala and orbitofrontal cortex provide a circuit for purposeful assessment of emotional stimuli. The different pathways to TRN suggest distinct mechanisms of attention to external and internal stimuli that may be differentially disrupted in anxiety and mood disorders and may be selectively targeted for therapeutic interventions.