1. ANATOMY AND PHYSIOLOGY OF THE CENTRAL NERVOUS SYSTEM
17
Gorbman, 1967) there is a system of efferent nerve fibers in the olfactory
tract derived from the telencephalon proper. The cell bodies of these
efferent neurons were activated both by ipsi- and contralateral stimulation of the olfactory tract and demonstrated long periods of suppressed
excitability when single pulses of electrical stimulation were applied to
the opposite tract (Doving and Gemne, 1966). It is also interesting to
note that the spontaneous activity of the second-order neurons in the
olfactory bulb were inhibited by touch stimuli to the skin. There is then
a possibility of extraolfactory influences ascending from lower brain
centers that can influence olfactory bulb activity. In addition, the secondorder neurons of the olfactory system could be affected by physiological
stimulation of the olfactory epithelium with various solutions. After
transecting the olfactory tract recordings could be taken from single
units in the olfactory bulb for several hours (Doving and Gemne, 1966).
Using a large variety of olfactory stimuli it was found that 30% of the
stimuli produced increased activity in the second-order neurons of the
olfactory bulb and approximately 20% caused inhibition of the spontaneous discharge of these units. Approximately half of the stimulating
solutions failed to produce any change in the discharge rate. These data
demonstrate the influence of rhinencephalic centers of the telencephalon
as well as the diencephalic preoptic area upon the discharge rate of the
olfactory bulb and thus central control of periphery.
The rate of olfactory bulb discharge can develop a differential discharge pattern (Hara et al., 1965; Ueda et al., 1967). Neurons in the
olfactory bulb of Pacific coho and Chinook salmon, 0. kisutch and 0.
tslzawytscha, responded differentially to water from the pool in which
it was known the animals would spawn and to water from different
watersheds. High amplitude responses were recorded from home pond
water infused into the nasal cavity but not to water from different
breeding ponds. Weaker responses could be evoked in the olfactory bulb
by waters traversed by the spawning salmon when swimming toward the
spawning site. Water was taken from a branch of the stream that passed
by the spawning site or from water above the spawning site (Ueda
et al., 1967). This is remarkable since the adult pacific salmon had not
been exposed to these precise olfactory stimuli for many years. Therefore, the response appears to be “imprinted in the central nervous
system of the young salmon (neuronal imprinting).
D. Electroencephalography of the Telencephalon
The EEGs of the telencephdlon of several species of sharks (Hodgson et al., 1967) and bony fishes have been recorded. Recordings from
17
Gorbman, 1967) there is a system of efferent nerve fibers in the olfactory
tract derived from the telencephalon proper. The cell bodies of these
efferent neurons were activated both by ipsi- and contralateral stimulation of the olfactory tract and demonstrated long periods of suppressed
excitability when single pulses of electrical stimulation were applied to
the opposite tract (Doving and Gemne, 1966). It is also interesting to
note that the spontaneous activity of the second-order neurons in the
olfactory bulb were inhibited by touch stimuli to the skin. There is then
a possibility of extraolfactory influences ascending from lower brain
centers that can influence olfactory bulb activity. In addition, the secondorder neurons of the olfactory system could be affected by physiological
stimulation of the olfactory epithelium with various solutions. After
transecting the olfactory tract recordings could be taken from single
units in the olfactory bulb for several hours (Doving and Gemne, 1966).
Using a large variety of olfactory stimuli it was found that 30% of the
stimuli produced increased activity in the second-order neurons of the
olfactory bulb and approximately 20% caused inhibition of the spontaneous discharge of these units. Approximately half of the stimulating
solutions failed to produce any change in the discharge rate. These data
demonstrate the influence of rhinencephalic centers of the telencephalon
as well as the diencephalic preoptic area upon the discharge rate of the
olfactory bulb and thus central control of periphery.
The rate of olfactory bulb discharge can develop a differential discharge pattern (Hara et al., 1965; Ueda et al., 1967). Neurons in the
olfactory bulb of Pacific coho and Chinook salmon, 0. kisutch and 0.
tslzawytscha, responded differentially to water from the pool in which
it was known the animals would spawn and to water from different
watersheds. High amplitude responses were recorded from home pond
water infused into the nasal cavity but not to water from different
breeding ponds. Weaker responses could be evoked in the olfactory bulb
by waters traversed by the spawning salmon when swimming toward the
spawning site. Water was taken from a branch of the stream that passed
by the spawning site or from water above the spawning site (Ueda
et al., 1967). This is remarkable since the adult pacific salmon had not
been exposed to these precise olfactory stimuli for many years. Therefore, the response appears to be “imprinted in the central nervous
system of the young salmon (neuronal imprinting).
D. Electroencephalography of the Telencephalon
The EEGs of the telencephdlon of several species of sharks (Hodgson et al., 1967) and bony fishes have been recorded. Recordings from