Evolution and ontogeny of neural circuits

Recent studies on neural pathways in a broad spectrum of vertebrates suggest that, in addition to migration and an increase in the number of certain select neurons, a significant aspect of neural evolution is a “parcellation” (segregation-isolation) process that involves the loss of selected connect...

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Bibliographic Details
Published in:The Behavioral and brain sciences 1984-09, Vol.7 (3), p.321-331
Main Author: Ebbesson, Sven O. E.
Format: Article
Language:English
Subjects:
Biological and medical sciences
commissures
development
Evolution
Fundamental and applied biological sciences. Psychology
Isolated neuron and nerve. Neuroglia
lateralization
learning
neocortex
neural circuits
Neural networks
olfactory system
Ontogeny
plasticity
somatosensory pathways
superior colliculus
Target Article
thalamus
Vertebrates: nervous system and sense organs
visual pathways
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Summary:Recent studies on neural pathways in a broad spectrum of vertebrates suggest that, in addition to migration and an increase in the number of certain select neurons, a significant aspect of neural evolution is a “parcellation” (segregation-isolation) process that involves the loss of selected connections by the new aggregates. A similar process occurs during ontogenetic development. These findings suggest that in many neuronal systems axons do not invade unknown territories during evolutionary or ontogenetic development but follow in their ancestors' paths to their ancestral targets; if the connection is later lost, it reflects the specialization of the circuitry. The pattern of interspecific variability suggests (1) that overlap of circuits is a more common feature in primitive (generalized) than in specialized brain organizations and (2) that most projections, such as the retinal, thalamotelencephalic, corticotectal, and tectal efferent ones, were bilateral in the primitive condition. Specialization of these systems in some vertebrate groups has involved the selective loss of connections, resulting in greater isolation of functions. The parcellation process may also play an important role in cell diversification. The parcellation process as described here is thought to be one of several underlying mechanisms of evolutionary and ontogenetic differentiation.
ISSN:0140-525X
1469-1825
DOI:10.1017/S0140525X00018379