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Behavioral encephalization in the bullhead embryo and its neuroanatomical correlates
Author(s) -
Armstrong Philip B.,
Higgins Don C.
Publication year - 1971
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.901430307
Subject(s) - mauthner cell , hindbrain , biology , midbrain , neuroscience , retina , tectum , anatomy , optic tract , central nervous system , fishery , fish <actinopterygii>
Abstract Three physiological phases can be recognized in the encephali‐zation of motor control in the developing bullhead. These are in succession 1. the spinal phase, 2. the hindbrain phase and 3. the optic‐midbrain phase. During the spinal phase motility is limited to lateral flexions of the trunk and tail by the contractions of the somitic muscle. The flexions become amplified as additional somites participate in this activity. There is no evidence of any encephalic control. Random undulatory swimming characterizes the hindbrain phase. It emerges with the maturation of the Mauthner cell and its labyrinthine afferents. In the optic‐midbrain phase there is a superposition of a visual control on swimming, a control which comes on with the differentiation of the rods and cones of the eye and their projection by way of the optic tectum and the tecto‐bulbar tracts to the Mauthner cells. The response in this phase is directed, a negative phototaxis for a major share of this phase. However, toward the end of this phase the photomechanical properties of the retina come into play providing an adaptive mechanism in which the response, negative or positive, is determined by the photomechanical state of the retina. Thus the retina, an exteroceptor, serves as an analyzer. The photic response in the advanced embryos can be predicted if the adaptive state of the photomechanical apparatus is known. It is suggested that the spinal and hindbrain activities result from endogenous neural activating mechanisms. Spontaneous firing in the labyrinth transmitted to the Mauthner cells may spark the random swimming characteristic of the hindbrain phase. This provides an activity base for the directed optic responses. The Mauthner cells thus receive input from both the labyrinth and the retina, a case of heterogenous summation. The random motor activities in the spinal and hindbrain phases do not appear to have survival value. The optic midbrain responses are reactions to an environmental situation and appear to have survival value or “purpose.”

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