Functions
The function of the Zona incerta is unknown, "To this day, we are still not certain of the precise function of this 'zone of uncertainty'" However it is suggested to have possible roles in "limbic–motor integration".
- Visceral survival activities.
Zona incerta controls such activities as water and food intake, sexuality and cardiovascular activity. This control is related to its effects upon the nearby posterior hypothalamus with which it shares similar connections and neurochemically defined cell types.
The zona incerta receives pain input through the spinothalamic tract and this has been shown to control the activity of the pain transmission pathway in the posterior thalamus.
Electrical or chemical stimulation of the zona incerta creates limbic-related movements, such as those associated with defense orientation and copulation.
- Sensory-motor activities.
At rest sensory input to the higher sensory areas of the cerebral cortex is gated through the thalamus. It has moreover been proposed that the zona incerta provides a top-down disinhibitory mechanism of this gating when there is sensory-motor activity such as the tactile use of whiskers.
This has also been linked to sensory gating changes between sleep and waking. In this occurs a zona incerta mediated inhibition of thalamic nuclei such the somatosensory posterior medial thalamus. This is most strong when cholinergic input to the zona incerta is reduced as during slow-wave sleep and during anesthesia. The consequence of this has been explained upon information processing:
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 projects to the superior colliculus and these link to the initiation of orientating eye and head movements. In monkeys for example neuronal activity in the zona incerta "pauses" before the start of a saccade and resumes at the end of a saccade.
- Synchronizing cortical and subcortical brain rhythms and integration.
The GABAergic input received from the cerebral cortex has been suggested to synchronize thalamocortical and brainstem rhythms by providing a link between basal ganglia output and the cerebello-thalamo cortical loop. This allows it to synchronize oscillations generate by the basal ganglia during the preparation and execution of intended movements. One function of the loop is to carry movement instructions to the motor cortex through zona incerta output to the ventral lateral nucleus neurons in the cerebello-thalamocortical loop and to brainstem motor neurons in the medial reticular formation and midbrain extrapyramidal area. This acts to synchronize the basal ganglia areas involved in planning and execution of the movement with those in the brainstem controlling axial and proximal limb muscles with those areas in the motor cortex that control distal limb movements.
- Synthesis
John Mitrofanis at the University of Sydney has proposed a general theory that might underlie some of the above.
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.
Read more about this topic: Zona Incerta
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