The thalamic reticular nucleus is part of the ventral thalamus that forms a capsule around the
thalamus
The thalamus (from Greek θάλαμος, "chamber") is a large mass of gray matter located in the dorsal part of the diencephalon (a division of the forebrain). Nerve fibers project out of the thalamus to the cerebral cortex in all direct ...
laterally. However, recent evidence from mice and fish question this statement and define it as a dorsal thalamic structure. It is separated from the thalamus by the
external medullary lamina
Medullary laminae of thalamus are layers of myelinated fibres that appear on cross sections of the thalamus. They also are commonly referred to as laminae medullares thalami or medullary layers of thalamus. The specific layers are:
*Lamina medull ...
. Reticular cells are
GABAergic
In molecular biology and physiology, something is GABAergic or GABAnergic if it pertains to or affects the neurotransmitter GABA. For example, a synapse is GABAergic if it uses GABA as its neurotransmitter, and a GABAergic neuron produces GABA. A ...
, and have discoid dendritic arbors in the plane of the nucleus.
Thalamic Reticular Nucleus is variously abbreviated TRN, RTN, NRT, and RT.
Input and output
The thalamic reticular nucleus receives input from the
cerebral cortex
The cerebral cortex, also known as the cerebral mantle, is the outer layer of neural tissue of the cerebrum of the brain in humans and other mammals. The cerebral cortex mostly consists of the six-layered neocortex, with just 10% consisting o ...
and dorsal thalamic nuclei. Most input comes from collaterals of fibers passing through the thalamic reticular nucleus. Primary thalamic reticular nucleus efferent fibers project to dorsal thalamic nuclei, but never to the cerebral cortex. This is the only thalamic nucleus that does not project to the cerebral cortex, instead it modulates the information from other nuclei in the thalamus. Its function is modulatory on signals going through thalamus (and the reticular nucleus).
The thalamic reticular nucleus receives massive projections from the external segment of the Globus Pallidus, thought to play a part in disinhibition of thalamic cells, which is essential for initiation of movement (Parent and Hazrati, 1995)
It has been suggested that the reticular nucleus receives afferent input from the
reticular formation
The reticular formation is a set of interconnected nuclei that are located throughout the brainstem. It is not anatomically well defined, because it includes neurons located in different parts of the brain. The neurons of the reticular formatio ...
and in turn projects to the other thalamic nuclei, regulating the flow of information through these to the cortex. There is debate over the presence of distinct sectors within the nucleus that each correspond to a different sensory or cognitive modality.
For original connectivity anatomy see Jones 1975.
For discussion of mapping and cross modality pathways see Crabtree 2002.
References
Further reading
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Thalamic nuclei