A comparative analysis of the morphology of corticothalamic projections in mammals

• Published in: Brain Research Bulletin Vol. 53; no. 6; pp. 727 - 741
• Main Authors: Rouiller, Eric M, Welker, Egbert
• Format: Book Review Journal Article
• Language: English
• Published: New York, NY Elsevier Inc 01-12-2000; Elsevier Science
• Subjects: Anatomy; Animals; Auditory cortex; Biological and medical sciences; Cat; Central nervous system; Cerebral Cortex - cytology; Cerebral Cortex - physiology; Fundamental and applied biological sciences. Psychology; Mammalia; Mammals - anatomy & histology; Mammals - physiology; Monkey; Motor cortex; Neural Pathways - cytology; Neural Pathways - physiology; Presynaptic Terminals - physiology; Presynaptic Terminals - ultrastructure; Rodent; Somatosensory cortex; Thalamus; Thalamus - cytology; Tracing; Vertebrates: nervous system and sense organs; Visual cortex; Somatosensory cortex; Visual cortex; Motor cortex; Cat; Monkey; Thalamus; Tracing; Rodent; Auditory cortex; Fissipedia; Carnivora; Cerebral cortex; Central nervous system; Rodentia; Projection; Review; Anatomy; Vertebrata; Mammalia; Primates; Comparative study; Brain (vertebrata)
• ISSN: 0361-9230; 1873-2747
• DOI: 10.1016/S0361-9230(00)00364-6

Recent anatomical tracing methods have revealed new principles underlying the organization of corticothalamic connections in the mammalian nervous system. These data demonstrated the distribution of two types of synaptic contacts in the corticothalamic projection: small (<1 μm) and giant (2–10 μm) axon terminals. We compare the organization of corticothalamic projections in the auditory, somatosensory, visual, and motor systems of a variety of mammalian species, including the monkey. In all these systems and species, both types of corticothalamic terminals have been observed. Small endings formed the major corticothalamic terminal field, whereas giant terminals were less numerous and formed additional terminal fields together with small terminals. After comparing their spatial distribution, as well as the degree of reciprocity between the corticothalamic and thalamocortical projections, different roles are proposed for small and giant endings. Small terminals are typically present in the projection serving the feed-back control of the cerebral cortex on the thalamic nucleus from which it receives its main projection. In contrast, giant terminals are involved in feed-forward projections by which activity from a cortical area is distributed, via the thalamus, to other parts of the cerebral cortex. The cross-species and cross-systems comparison reveals differences in the mode of feed-forward projection, which may be involved in the activation of other parts of the same cortical area or form part of a projection that activates
other cortical areas.