Zona incerta

The zona incerta is a horizontally elongated region of gray matter in the subthalamus below the thalamus. Its connections project extensively over the brain from the cerebral cortex down into the spinal cord. As a result, posterior medial thalamus neurons fail to respond to ascending sensory inputs, and function primarily in 'higher-order' mode, concerned with relaying trans-cortical information. By contrast, increased cholinergic activity during wakefulness and enhanced vigilance suppresses zona incerta -mediated inhibition, thereby ungating posterior thalamus responses to ascending inputs.The zona incerta is in a position to form a primal synaptic interface of the diencephalon, linking diverse sensory channels to appropriate visceral, arousal, attention and posture-locomotion responses. The different sensory inputs, whether exteroreceptive (somatic) or interoreceptive (visceral), influence these activities by driving zona incerta cells with different projection patterns and functions; each of these cells may be located in different sectors of the zone… In essence, it is suggested that the zona incerta has the pathways to integrate both exteroreceptive (e.g. somatosensory) and interoreceptive (e.g. thirst) sensory challenges, so that visceral activity, arousal, attention and/or posture locomotion are altered and/or generated. The zona incerta could form a neural niche in the thalamus from where these responses are 'recruited' immediately, as to give an instant response. a significant suppression of both spontaneous and evoked activity in inhibitory neurons in zona incerta and abnormally high spontaneous and evoked activity of neurons in posterior thalamus in animals with central pain syndrome. The positive association between behavioral and neurophysiological thresholds in rats with central pain syndrome is consistent with a causal role for suppressed incerto-thalamic inputs in central pain syndrome. The zona incerta is a horizontally elongated region of gray matter in the subthalamus below the thalamus. Its connections project extensively over the brain from the cerebral cortex down into the spinal cord. Its function is unknown, though several potential functions related to 'limbic–motor integration' have been proposed, such as controlling visceral activity and pain; gating sensory input and synchronizing cortical and subcortical brain rhythms. Its dysfunction may play a role in central pain syndrome. It has also been identified as a promising deep brain stimulation therapy target for treating Parkinson's disease. Its existence was first described by Auguste Forel in 1877 as a 'region of which nothing certain can be said'. A hundred and thirty years later in 2007, Nadia Urbain and Martin Deschênes of Université Laval noted that the 'zona incerta is among the least studied regions of the brain; its name does not even appear in the index of many textbooks.' This nucleus is located medially to the internal capsule, ventral to the thalamus, and is contiguous with the thalamic reticular nucleus. The nucleus separates the lenticular fasciculus from the thalamic fasciculus (also known as the 'field H1 of Forel') .Its cells are very heterogeneous differing widely in their shape and size. Its chemoarchitecture is also diverse containing up to 20 different types of neurochemically defined cells. It has been noted that 'There are few diencephalic regions that have as much cellular and neurochemical diversity'. In the rat four areas are usually identified. These areas lack clear cell-free borders and merge into each other. Zona incerta neurons have dendrites with a wide span 0.8 mm and their axons give off collaterals that arborized locally within the zona incerta providing a means for lateral inhibition. The ventral area of the zona incerta has been described as having 'a network of GABAergic cells with widespread interconnections, so that cells in one subsector may influence the activity of cells in a different subsector'. The zona incerta together with the hypothalamus is one of the two areas of the brain that produces the neuropeptide melanin concentrating hormone. Dopaminergic ones are also more prevalent. There are in addition populations of cells producing somatostatin, angiotensin II and melanocyte stimulating hormone. The zona incerta has connections to the cerebral cortex, diencephalon, basal ganglia, brainstem and spinal cord.