558
M. V. L. BENNETT
( Black-Cleworth, 1970; Mohres, 1957; Moller, 1970). In Gymnotus cessations appear to be involved in aggressive interactions between individuals ( Black-Cleworth, 1970; Westby and Box, 1970). Recent field
studies show that changes in organ discharge frequency are involved in
courtship behavior of several gymnotids ( C. Hopkins, unpublished data).
Positive reinforcement by feeding has been used by Lissmann and
Machin to establish sensitivity to conductivity differences and electric
stimuli in Gymnarchus (1958) and to electric stimuli in the catfish
Clarias ( 1963). Avoidance conditioning in which acceleration of organ
discharge is the conditioned response has been carried out using a
conductance change as the conditional stimulus and strong electric shock
as the aversive stimulus (Bennett, 1968b; cf. Mandriota et al., 1968).
A few experiments indicate that as would be expected the components
of the electrosensory system mediate the behavioral responses to electric
stimuli. In gymnotids section of the posterior branch of the anterior lateral
line that innervates the electroreceptors in the posterior of the body
abolishes the response to conductors placed posteriorly, but conductors
near the head region are still avoided (Bennett and Grundfest, 1959).
Unilateral section of this nerve reduces sensitivity on the affected side
and causes all responses to be toward that side, indicating that the
responses that do occur are mediated by the intact contralateral nerve.
Section of the posterior lateral line nerves, which contain only mechanoreceptive fibers, has no effect on the avoidance response. Similar results
have been obtained by cutting the appropriate nerves in catfish and
dogfish ( Dijkgraaf, 1968; Dijkgraaf and Kalmijn, 1963).
Simple energy considerations indicate that the electric organ discharge
is necessary for the detection of conductance changes. As noted above,
electric fish do not give the unconditional response of acceleration of
discharge rate if a conductance change is restricted to the periods between organ discharges.
E. Thresholds for Receptor and Behavioral Responses
Granted that the electroreceptors mediate the behavioral responses, it
may then be asked whether the observed behavioral thresholds can be
explained in terms of the receptor thresholds. The comparison is difficult to make because of differences in the methods by which the two
types of experiment have been carried out. Nonetheless, from considerations of receptor thresholds and the effects of accessory structures, a
preliminary evaluation can be made (Table 11).
In the skate the threshold field for cardiac acceleration is about 0.01
M. V. L. BENNETT
( Black-Cleworth, 1970; Mohres, 1957; Moller, 1970). In Gymnotus cessations appear to be involved in aggressive interactions between individuals ( Black-Cleworth, 1970; Westby and Box, 1970). Recent field
studies show that changes in organ discharge frequency are involved in
courtship behavior of several gymnotids ( C. Hopkins, unpublished data).
Positive reinforcement by feeding has been used by Lissmann and
Machin to establish sensitivity to conductivity differences and electric
stimuli in Gymnarchus (1958) and to electric stimuli in the catfish
Clarias ( 1963). Avoidance conditioning in which acceleration of organ
discharge is the conditioned response has been carried out using a
conductance change as the conditional stimulus and strong electric shock
as the aversive stimulus (Bennett, 1968b; cf. Mandriota et al., 1968).
A few experiments indicate that as would be expected the components
of the electrosensory system mediate the behavioral responses to electric
stimuli. In gymnotids section of the posterior branch of the anterior lateral
line that innervates the electroreceptors in the posterior of the body
abolishes the response to conductors placed posteriorly, but conductors
near the head region are still avoided (Bennett and Grundfest, 1959).
Unilateral section of this nerve reduces sensitivity on the affected side
and causes all responses to be toward that side, indicating that the
responses that do occur are mediated by the intact contralateral nerve.
Section of the posterior lateral line nerves, which contain only mechanoreceptive fibers, has no effect on the avoidance response. Similar results
have been obtained by cutting the appropriate nerves in catfish and
dogfish ( Dijkgraaf, 1968; Dijkgraaf and Kalmijn, 1963).
Simple energy considerations indicate that the electric organ discharge
is necessary for the detection of conductance changes. As noted above,
electric fish do not give the unconditional response of acceleration of
discharge rate if a conductance change is restricted to the periods between organ discharges.
E. Thresholds for Receptor and Behavioral Responses
Granted that the electroreceptors mediate the behavioral responses, it
may then be asked whether the observed behavioral thresholds can be
explained in terms of the receptor thresholds. The comparison is difficult to make because of differences in the methods by which the two
types of experiment have been carried out. Nonetheless, from considerations of receptor thresholds and the effects of accessory structures, a
preliminary evaluation can be made (Table 11).
In the skate the threshold field for cardiac acceleration is about 0.01