Thalamocortical projection

Bayer, L., Eggermann, E., Saint-Mleux, B. et al. (2002). Selective action of orexin (hypocretin) on nonspecific thalamocortical projection neurons. J. Neurosci. 22, 7835-9. 

The excitatory neurotransmitter glutamate is released upon depolarization by the corticostratial, corticosub-thalamic, subthalamic, and thalamocortical projection neurons. As such, these excitatory neurons are key players in the functional anatomy of the basal ganglia and the CSTC loops. While the activity of these neurons is likely to be important in TS, only limited data are available to evaluate their role in this disease. 

Macchi G, Bentivoglio M, Molinari M, Minciacchi D (1984) The thalamo-caudate versus thalamocortical projections as studied in the cat with fluorescent retrograde double labeling. Exp Brain Res 54 225-239. 

Kosar E, Grill HJ, Norgren R. 1986. Gustatory cortex in the rat. II. Thalamocortical projections. Brain Res 379 342-352. 

Proposed model of vibrotactile representation in SI. (a) Thalamocortical arbors in SI have multiple clusters extending across millimeters of cortex (Garraghty et al., 1989). (b) Single SA, RA, or PC fibers terminate in layer IV with three arbors (colored disks). These arbors project in turn to superficial layers ll/lll. Thus, some cortical columns are dominated by a single SA, RA, or PC input, whereas others have mixed input (overlapping disks)... 

It must be borne in mind that physiological studies have shown (Goff, 1970) that it is possible to record late potentials where only the specific system is present after destruction of the non-specific pathways. From these studies it is suggested that late evoked potentials may not reflect activity mediated by an independent extralemniscal projection system but appears to be dependent on the integrity of the lemniscal system at the thalamocortical and cortical level. 

The MGB and AC form the auditory thalamocortical system. As with other sensory systems, extensive projections to and from the cortical region exist in this system. The MGB has three divisions, the ventral, dorsal, and medial. The ventral division is the largest and has the most precise tonotopic organization. Almost aU its input is from the ipsilateral ICC through the brachium of the 1C. Its large bushy cells have dendrites oriented so as to He in isofrequency layers, and the axons of these neurons project to the AC. 

Neiirons discharging at the tremor frequency are found in several brain areas [224, 225], but when afferent discharges were eliminated it was apparent that rhythmic discharges in the motor cortex and the ventrolateral thalamus were those involved [226-228]. It is probable that the cerebral rhythms are linked to those in the thalamus since studies of their disruption by experimental lesions demonstrate the importance of thalamocortical pathways [229-232], particularly monosynaptic projections from the ventrolateral thalamus to pyramidal tract neurons [233],... 

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