Brain Research
Bulletin,
Vol.
3,
pp. 265-270.
Printed in the U.S.A.
Enhanced Passive Avoidance Learning and Appetitive T-Maze Learning with Post-Trial Rewarding Hypothalamic Stimulation JOSEPH
P. HUSTON
AND CORNELIA
C. MUELLER
Institute of Psychology, University of Diisseldorf, Lab. Comp. and Physiol. Psychol., Diisseldorf, West Germany and Institute ofPharmacology, University of Ziirich, Ziirich, Switzerland (Received
16 January
1978)
HUSTON, J. P. AND C. C. MUELLER. Enhanced passive avoidance learning and appetitive T-maze learning with post-trial hypothalamic stimulation. BRAIN RES. BULL. 3(3) 265-270, 1978. - Experiments were carried out to investigate the effects of post-trial reinforcing stimulation of the lateral hypothalamus on learning in rats. The reinforcing stimulation was always presented for a duration of 20-30 set (0.2 set on/O.8 set off), and was administered either immediately, 30 set delayed or 300 SW delayed after exposure to the learning situation. In Experiment 1 post-trial stimulation led to improved passive avoidance learning of an alcove-avoidance task when presented 30 set compared to immediately after the footshock. In Experiment 2 reversal learning of a one-way shuttle-box avoidance task was facilitated by 30 set delayed, but not 300 set delayed post-trial reinforcing stimulation. In Experiment 3 appetitive left-right discrimination was investigated using a T-maze task. Thirty set delayed post-trial reinforcing stimulation presented contingent on errors facilitated learning of this task. Together, the 3 studies provide further support for the hypothesis that reinforcers directly influence labile memory processes (such as short-term memory) and thereby improve learning.
rewarding
Passive avoidance Facilitation of learning Memory Self-stimulation Hypothalamic stimulation
Discrimination learning
Reinforcement
thalamic stimulation facilitated avoidance learning in a shuttle-box task [ 91. The experiments reported below were carried out: (a) to provide further tests of the hypothesis that post-trial reinforcing stimulation facilitates learning, (b) to examine the possibility of a time-dependent effect of the reinforcing stimulation on memory processes, and (c) to use different learning siutations, including a conventional passive avoidance situation as well as an appetitive learning task, to investigate the generality of the facilitating effect of the post-trial reinforcing stimulation.
SEVERAL studies have demonstrated that post-trial reinforcement can improve learning of an avoidance response. The first evidence came from a study [5] with mice showing that 1 min access to food provided between 20 and 50 set after the footshock in a step-down avoidance trial improved the performance of this avoidance response; i.e., the mice remained up on the platform longer 24 hr later. This result is counterintuitive from the standpoint of conventional consideration of the nature of positive reinforcers. Common sense would dictate that the reinforcer, if anything, should attenuate the effect of the preceding punishment, and cause the animal to step off the platform sooner instead of later, and therefore, to exhibit inferior rather than superior performance. This result, therefore, provided supporting evidence for a theory of reinforcement [4, 5, 61, which assumes that reinforcers in the operant conditioning situation strengthen behavior by a direct facilitative action on immediate memory traces; i.e., by preventing the trace from fading or being disrupted. It follows that the reinforcer presented during any period of iabile (i.e., immediate and short-term) memory processing, such as, during the post-trial period for an avoidance learning trial, should have a similar effect, and consequently facilitate learning. This theory received additional support when it was first shown that post-trial reinforcing hypo-
EXPERIMENT
1: ALCOVE-AVOIDANCE
The present study was undertaken to examine the effects of post-trial reinforcement on avoidance learning in rats by the use of a conventional passive avoidance paradigm. The passive avoidance task used was the twocompartment test developed by Kurtz and Pearl [8] and BureS and BureSova [ 11. It takes advantage of the fact that rats spend most of their time inside a small box in favor of a large adjoining box. The rats learn to avoid the preferred small box after experiencing in it inescapable electrical footshock. 265
Copyright
0 1978 ANKHO
International
Inc.-0361-9230/78/0303-0265$00.75
HUSTON
266
Method Male Sprague-Dawley (Tierspital Zurich) albino rats, weighing 210-350 g, were implanted with bipolar 0.2 mm dia. stainless steel electrodes (Plastic Products Co.) into the lateral hypothalamus (using coordinates: AP 5.4; H -2.6; L 1.5 ; [ 101 ). A total of 46 animals showed self-stimulation for reinforcing 0.2 set trains of 100 Hz sine-wave stimulation. The optimal current level for self-stimulation was roughly determined for each animal, and ranged from 14-42 MA, rms. The rats were kept two per cage on a 12 hr light/12 hr dark cycle, with continuous access to food and water. The experiments were performed during the light phase of the cycle. The apparatus consisted of a big box (50 x 50 x 35 cm) which was separated by means of a black guillotine door from an adjoining small box (21 x 13 x 16 cm). Both chambers had electrifiable grid floors (6 mm dia. stainless steel bars, spaced 13 mm apart). The small box had black walls and a removable metal cover, whereas the large box was grey and illuminated by overhead fluorescent room lights. The animals were given three successive daily baseline trials of 5 min duration each. They were placed onto the grid floor of the big box, and the entries and time spent in the little preferred box were recorded. They were then assigned to three groups: two experimental groups (each with 15 rats) received 30 set of reinforcing stimulation (0.2 set on/O.8 set off) commencing either immediately or 30 set after administration of the footshock in the small chamber. A control group (16 rats) was handled exactly like the 30 set delayed post-trial stimulation group, but was not administered electrical brain stimulation. During the learning trials the following procedure was repeated three times at 48 hr intervals: the rats were placed into the small box with the guillotine door and the cover closed. Then a 1 mA inescapable scrambled footshock of 3 set duration was administered, followed by either immediate, 30 set delayed, or sham stimulation, according
I
Acquisition
to the group assignment. The post-trial treatments were administered in a cylindrical container (34 cm dia./37 cm high). Twenty-four hours later the rats were retested in the same manner as during the baseline trials; i.e., they were placed into the big chamber, and entries and time spent in the small chamber were recorded for 5 min. Next, to test for possible differences in resistance to extinction between the three groups, six additional extinction trials (one 5 min trial per day) were administered. Results In order to test for possible differences in learning between the three groups, the number of successful learners were compared. The criterion for successful learning in avoiding the small box was arbitrarily taken to be 0 set spent in the little box. Comparison of numbers of learners revealed that the experimental group that received 30 set delayed post-trial reinforcing stimulation showed significantly superior learning in comparison to the control group (p
Bulletin,
Vol.
3,
pp. 265-270.
Printed in the U.S.A.
Enhanced Passive Avoidance Learning and Appetitive T-Maze Learning with Post-Trial Rewarding Hypothalamic Stimulation JOSEPH
P. HUSTON
AND CORNELIA
C. MUELLER
Institute of Psychology, University of Diisseldorf, Lab. Comp. and Physiol. Psychol., Diisseldorf, West Germany and Institute ofPharmacology, University of Ziirich, Ziirich, Switzerland (Received
16 January
1978)
HUSTON, J. P. AND C. C. MUELLER. Enhanced passive avoidance learning and appetitive T-maze learning with post-trial hypothalamic stimulation. BRAIN RES. BULL. 3(3) 265-270, 1978. - Experiments were carried out to investigate the effects of post-trial reinforcing stimulation of the lateral hypothalamus on learning in rats. The reinforcing stimulation was always presented for a duration of 20-30 set (0.2 set on/O.8 set off), and was administered either immediately, 30 set delayed or 300 SW delayed after exposure to the learning situation. In Experiment 1 post-trial stimulation led to improved passive avoidance learning of an alcove-avoidance task when presented 30 set compared to immediately after the footshock. In Experiment 2 reversal learning of a one-way shuttle-box avoidance task was facilitated by 30 set delayed, but not 300 set delayed post-trial reinforcing stimulation. In Experiment 3 appetitive left-right discrimination was investigated using a T-maze task. Thirty set delayed post-trial reinforcing stimulation presented contingent on errors facilitated learning of this task. Together, the 3 studies provide further support for the hypothesis that reinforcers directly influence labile memory processes (such as short-term memory) and thereby improve learning.
rewarding
Passive avoidance Facilitation of learning Memory Self-stimulation Hypothalamic stimulation
Discrimination learning
Reinforcement
thalamic stimulation facilitated avoidance learning in a shuttle-box task [ 91. The experiments reported below were carried out: (a) to provide further tests of the hypothesis that post-trial reinforcing stimulation facilitates learning, (b) to examine the possibility of a time-dependent effect of the reinforcing stimulation on memory processes, and (c) to use different learning siutations, including a conventional passive avoidance situation as well as an appetitive learning task, to investigate the generality of the facilitating effect of the post-trial reinforcing stimulation.
SEVERAL studies have demonstrated that post-trial reinforcement can improve learning of an avoidance response. The first evidence came from a study [5] with mice showing that 1 min access to food provided between 20 and 50 set after the footshock in a step-down avoidance trial improved the performance of this avoidance response; i.e., the mice remained up on the platform longer 24 hr later. This result is counterintuitive from the standpoint of conventional consideration of the nature of positive reinforcers. Common sense would dictate that the reinforcer, if anything, should attenuate the effect of the preceding punishment, and cause the animal to step off the platform sooner instead of later, and therefore, to exhibit inferior rather than superior performance. This result, therefore, provided supporting evidence for a theory of reinforcement [4, 5, 61, which assumes that reinforcers in the operant conditioning situation strengthen behavior by a direct facilitative action on immediate memory traces; i.e., by preventing the trace from fading or being disrupted. It follows that the reinforcer presented during any period of iabile (i.e., immediate and short-term) memory processing, such as, during the post-trial period for an avoidance learning trial, should have a similar effect, and consequently facilitate learning. This theory received additional support when it was first shown that post-trial reinforcing hypo-
EXPERIMENT
1: ALCOVE-AVOIDANCE
The present study was undertaken to examine the effects of post-trial reinforcement on avoidance learning in rats by the use of a conventional passive avoidance paradigm. The passive avoidance task used was the twocompartment test developed by Kurtz and Pearl [8] and BureS and BureSova [ 11. It takes advantage of the fact that rats spend most of their time inside a small box in favor of a large adjoining box. The rats learn to avoid the preferred small box after experiencing in it inescapable electrical footshock. 265
Copyright
0 1978 ANKHO
International
Inc.-0361-9230/78/0303-0265$00.75
HUSTON
266
Method Male Sprague-Dawley (Tierspital Zurich) albino rats, weighing 210-350 g, were implanted with bipolar 0.2 mm dia. stainless steel electrodes (Plastic Products Co.) into the lateral hypothalamus (using coordinates: AP 5.4; H -2.6; L 1.5 ; [ 101 ). A total of 46 animals showed self-stimulation for reinforcing 0.2 set trains of 100 Hz sine-wave stimulation. The optimal current level for self-stimulation was roughly determined for each animal, and ranged from 14-42 MA, rms. The rats were kept two per cage on a 12 hr light/12 hr dark cycle, with continuous access to food and water. The experiments were performed during the light phase of the cycle. The apparatus consisted of a big box (50 x 50 x 35 cm) which was separated by means of a black guillotine door from an adjoining small box (21 x 13 x 16 cm). Both chambers had electrifiable grid floors (6 mm dia. stainless steel bars, spaced 13 mm apart). The small box had black walls and a removable metal cover, whereas the large box was grey and illuminated by overhead fluorescent room lights. The animals were given three successive daily baseline trials of 5 min duration each. They were placed onto the grid floor of the big box, and the entries and time spent in the little preferred box were recorded. They were then assigned to three groups: two experimental groups (each with 15 rats) received 30 set of reinforcing stimulation (0.2 set on/O.8 set off) commencing either immediately or 30 set after administration of the footshock in the small chamber. A control group (16 rats) was handled exactly like the 30 set delayed post-trial stimulation group, but was not administered electrical brain stimulation. During the learning trials the following procedure was repeated three times at 48 hr intervals: the rats were placed into the small box with the guillotine door and the cover closed. Then a 1 mA inescapable scrambled footshock of 3 set duration was administered, followed by either immediate, 30 set delayed, or sham stimulation, according
I
Acquisition
to the group assignment. The post-trial treatments were administered in a cylindrical container (34 cm dia./37 cm high). Twenty-four hours later the rats were retested in the same manner as during the baseline trials; i.e., they were placed into the big chamber, and entries and time spent in the small chamber were recorded for 5 min. Next, to test for possible differences in resistance to extinction between the three groups, six additional extinction trials (one 5 min trial per day) were administered. Results In order to test for possible differences in learning between the three groups, the number of successful learners were compared. The criterion for successful learning in avoiding the small box was arbitrarily taken to be 0 set spent in the little box. Comparison of numbers of learners revealed that the experimental group that received 30 set delayed post-trial reinforcing stimulation showed significantly superior learning in comparison to the control group (p
