1. ANATOMY AND PHYSIOLOGY O F THE CENTRAL NERVOUS SYSTEM
21
( Kaplan and Aronson, 1967). After the animals had learned the response,
the olfactory bulbs were ablated. Removal of olfactory bulbs before or
after conditioning had no effect on the animal's ability to make the
conditioned avoidance response ( Aronson and Kaplan, 1963; Kaplan
and Aronson, 1967). Following telencephalic ablation there was no
obvious sensory or motor deficit. However, there was a marked decline
in performance. The ablation resulted in a rapid drop in the percentage
of avoidances and an increase in latency to avoidance. Forebrain-lesioned
fish exhibited varying degrees of improvement with continued training;
however, the preoperative level of performance was not attained after
ablation. If the telencephalon was removed prior to training, the forebrain-ablated fish were unable to learn the avoidance response ( Aronson
and Kaplan, 1963; Aronson, 1967; Kaplan and Aronson, 1967).
Goldfish were also trained to avoid shock after the onset of the conditioned stimulus (light) by swimming through an area which was
previously covered by a partition (Hainsworth et al., 1967). The animals
were then returned to the starting box with a net (one-way conditioned
avoidance). Normal and sham-operated animals showed no significant
differences in learning. In contrast, forebrain removal resulted in marked
impairment of acquisition of the avoidance response. Following acquisition of the response, forebrainless fish exhibited rapid extinction leading
to the conclusion that this type of learning in forebrainless fish is an
unstable association. If the animals were trained and then the telencephalon removed, the operation resulted in a complete loss of the
previously learned avoidance response ( Hainsworth et al., 1967). Ilowever, unlike Tilapia (Kaplan and Aronson, 1967) the forebrainless goldfish did eventually relearn the avoidance response to preoperative levels.
The animals required as many trials to relearn the problem without the
telencephalon as they did with the telencephalon. Removal of the forebrain resulted in the complete loss of the previously learned response
since the animals demonstrated no savings from previous training when
compared with the performance of previously naive forebrainless subjects ( Hainsworth et al., 1967). Fish spontaneously recovered the ability
to acquire and retain a conditioned avoidance response if sufficient time
was allowed after forebrain removal before subsequent retraining. These
data indicate that removal of the telencephalon results in the loss of
ability to acquire instrumental conditioning, greatly impairs or prevents
the acquisition of instrumental avoidance conditioning, abolishes the
retention of a previously learned response, and greatly reduces the
resistance to extinction ( Hainsworth et al., 1967). The specific and
permanent deficits found in the forebrainless goldfish in this series of
experiments suggest that in fish the telencephalon subserves complex
21
( Kaplan and Aronson, 1967). After the animals had learned the response,
the olfactory bulbs were ablated. Removal of olfactory bulbs before or
after conditioning had no effect on the animal's ability to make the
conditioned avoidance response ( Aronson and Kaplan, 1963; Kaplan
and Aronson, 1967). Following telencephalic ablation there was no
obvious sensory or motor deficit. However, there was a marked decline
in performance. The ablation resulted in a rapid drop in the percentage
of avoidances and an increase in latency to avoidance. Forebrain-lesioned
fish exhibited varying degrees of improvement with continued training;
however, the preoperative level of performance was not attained after
ablation. If the telencephalon was removed prior to training, the forebrain-ablated fish were unable to learn the avoidance response ( Aronson
and Kaplan, 1963; Aronson, 1967; Kaplan and Aronson, 1967).
Goldfish were also trained to avoid shock after the onset of the conditioned stimulus (light) by swimming through an area which was
previously covered by a partition (Hainsworth et al., 1967). The animals
were then returned to the starting box with a net (one-way conditioned
avoidance). Normal and sham-operated animals showed no significant
differences in learning. In contrast, forebrain removal resulted in marked
impairment of acquisition of the avoidance response. Following acquisition of the response, forebrainless fish exhibited rapid extinction leading
to the conclusion that this type of learning in forebrainless fish is an
unstable association. If the animals were trained and then the telencephalon removed, the operation resulted in a complete loss of the
previously learned avoidance response ( Hainsworth et al., 1967). Ilowever, unlike Tilapia (Kaplan and Aronson, 1967) the forebrainless goldfish did eventually relearn the avoidance response to preoperative levels.
The animals required as many trials to relearn the problem without the
telencephalon as they did with the telencephalon. Removal of the forebrain resulted in the complete loss of the previously learned response
since the animals demonstrated no savings from previous training when
compared with the performance of previously naive forebrainless subjects ( Hainsworth et al., 1967). Fish spontaneously recovered the ability
to acquire and retain a conditioned avoidance response if sufficient time
was allowed after forebrain removal before subsequent retraining. These
data indicate that removal of the telencephalon results in the loss of
ability to acquire instrumental conditioning, greatly impairs or prevents
the acquisition of instrumental avoidance conditioning, abolishes the
retention of a previously learned response, and greatly reduces the
resistance to extinction ( Hainsworth et al., 1967). The specific and
permanent deficits found in the forebrainless goldfish in this series of
experiments suggest that in fish the telencephalon subserves complex