1. ANATOMY AND PHYSIOLOGY OF THE CENTRAL NERVOUS S Y S m M
53
were free swimming (Clark et aZ., 1960). Electrodes were chronically implanted in the cerebellum of the animals and were attached to
a stimulator via flexible wires. The results of cerebellar stimulation of
these teleost fish varied with the strength and duration of stimulus.
In general, stimulation was immediately followed by a more-or-less rapid
motion which usually involved the turning of the head or tail or both.
The direction of turning following stimulation was toward the side contralateral to the electrical stimulus. Stimulation of areas near the midline,
especially in the anterior half of the corpus cerebelli resulted in a pattern
described as a typical response “stimulus-rebound.” The fish turned
toward the side stimulated (ipsiversive) only to reverse the direction to
the contralateral side following the cessation of stimulation (Clark
et aZ., 1960).
The magnitude of response increased with increasing stimulus amplitude. With mild stimulation there might be gentle bending of the tail or
body or both; increased strength of stimulus resulted in increased speeds
of reaction. During rapid movement of the body, the fins and eyes were
set in positions which were appropriate to the initial response but returned to a mirror image pattern when stiniulus-rebound occurred. It
was often found that different stimulus thresholds would give two conipletely opposite responses from the same site of stimulation. Thus, an
ipsilateral response at 0.45 mA would result in an ipsiversive turning
with an indication of rebound reversal of direction at termination. A
stronger stimulus of 0.5 mA to the same area produced turning to the
side contralateral to the original effect. In many areas of the cerebellum
it appeared that there was a topical response pattern, so that as depth
changed with microelectrode advance, subsequent stimulations could
reverse the direction of turning. These differences in depth were often
only a fraction of a millimeter (Clark et al., 1960). The turning
motion of the fish was not always in one plane. In addition to the simple
horizontal turning there was often movement with a rolling component
and a combination of rolling and turning, which often produced a
spiral motion. Upward and downward motions were also produced by
stimulation.
Stimulation also resulted in retraction of the barbels of the catfish.
In addition, most animals demonstrated coordinated eye movements in
the direction of turning or rotation and often retraction or extrusion of
the eyeball from the orbit. One case of stimulus evoked nystagmus was
observed (Clark et al., 19.60). Long aftereffects, like the seizures
elicited in mammals, have not been observed in the fish following cerebellar stimulation. However, prolonged effects of other types were
elicited from stimulation of other parts of the catfish brain, such as
53
were free swimming (Clark et aZ., 1960). Electrodes were chronically implanted in the cerebellum of the animals and were attached to
a stimulator via flexible wires. The results of cerebellar stimulation of
these teleost fish varied with the strength and duration of stimulus.
In general, stimulation was immediately followed by a more-or-less rapid
motion which usually involved the turning of the head or tail or both.
The direction of turning following stimulation was toward the side contralateral to the electrical stimulus. Stimulation of areas near the midline,
especially in the anterior half of the corpus cerebelli resulted in a pattern
described as a typical response “stimulus-rebound.” The fish turned
toward the side stimulated (ipsiversive) only to reverse the direction to
the contralateral side following the cessation of stimulation (Clark
et aZ., 1960).
The magnitude of response increased with increasing stimulus amplitude. With mild stimulation there might be gentle bending of the tail or
body or both; increased strength of stimulus resulted in increased speeds
of reaction. During rapid movement of the body, the fins and eyes were
set in positions which were appropriate to the initial response but returned to a mirror image pattern when stiniulus-rebound occurred. It
was often found that different stimulus thresholds would give two conipletely opposite responses from the same site of stimulation. Thus, an
ipsilateral response at 0.45 mA would result in an ipsiversive turning
with an indication of rebound reversal of direction at termination. A
stronger stimulus of 0.5 mA to the same area produced turning to the
side contralateral to the original effect. In many areas of the cerebellum
it appeared that there was a topical response pattern, so that as depth
changed with microelectrode advance, subsequent stimulations could
reverse the direction of turning. These differences in depth were often
only a fraction of a millimeter (Clark et al., 1960). The turning
motion of the fish was not always in one plane. In addition to the simple
horizontal turning there was often movement with a rolling component
and a combination of rolling and turning, which often produced a
spiral motion. Upward and downward motions were also produced by
stimulation.
Stimulation also resulted in retraction of the barbels of the catfish.
In addition, most animals demonstrated coordinated eye movements in
the direction of turning or rotation and often retraction or extrusion of
the eyeball from the orbit. One case of stimulus evoked nystagmus was
observed (Clark et al., 19.60). Long aftereffects, like the seizures
elicited in mammals, have not been observed in the fish following cerebellar stimulation. However, prolonged effects of other types were
elicited from stimulation of other parts of the catfish brain, such as