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Relationship between hippocampal EEG, novelty, and frustration in the rat
BEHAVIORALBIOLOGY, 11,561-568 (1974), Abstract No. 3276
Relationship Between Hippocampal EEG, Novelty, a n d F r u s t r a t i o n in the R a t
RANDALL A. KIMSEY, 1 ROBERT S. DYER, and HERBERT L. PETRI
Department of Psychology, Towson State College, Baltimore, Maryland 21204 In a single alternation runway task, rat hippocampal EEG's changed with learning. At the goal cup, EEG frequencies varied depending upon whether a trial was reinforced or nonreinforced. Frequencies of 7.5-8.5 Hz accompanied nonreinforced trials while lower frequency less synchronized activity accompanied reinforced trials. These EEG patterns did not appear closely related to novelty or frustrative nonreward.
Gross electrical recordings from the dorsal hippocampus have been classified into three types: (a) rhythmical slow activity (RSA), commonly referred to as theta and characterized by highly synchronized waves between about 6 and 12 Hz in the rat; (b)Large amplitude irregular activity (LIA), characterized by high amplitude, low synchrony, and usually lower frequency waves than RSA; and (c) small amplitude irregular activity (SIA), characterized by apparent suppressions of hippocampal electrical activity for short (1-2 sec) bursts of time (Vanderwolf, 1971). The behavioral significance of these different types of activity, especially RSA, is a matter of some disagreement. The occurrence of RSA has alternatively been correlated with attention to meaningful stimuli in the environment (Grasty~n, Liss~ik, Madar~isz, and Donhoffer, 1959), initiation of skeletal movements (Klemm, 1970), and implicated in memory consolidation and recall during learning (Elazar and Adey, 1967). Vanderwolf (1971) hypothesizes that RSA occurs only during specifically voluntary movements and that changes in RSA related to learning really represent changes in voluntary movement coincident with efficient performance of the task. LIA is presumed by Vanderwolf to correlate with automatic behaviors, such as eating and drinking.
1Address: Department of Psychology, University of Delaware, Newark, Delaware, 19711. 561
562
KIMSEY, DYER AND PETRI
Within those occasions on which lISA is present, attempts have been made to relate the frequency of RSA to specific behaviors. One such attempt by Gray and Ball (1970) suggests that RSA between 7.5 and 8.5 Hz occurs when an animal is frustrated, which they define as the omission of anticipated reward. Gray and Bali's experiments do not rule out the possibility that occurrence of 7.5-8.5 Hz RSA is related to novelty, which presumably is present when an expected reward is omitted. Single alternation is a task in which rats can discriminate trials to be reinforced ("expected" reward) from nonreinforced trials ("expected" nonreward) as indicated by slower running speeds on normally nonreinforced trials (Tyler, Wortz, and Bitterman, 1953). In the present experiment a single alternation task was used to test Gray's hypothesis by providing occasions for "unexpected" reward as well as "unexpected" nonreward. Both conditions are presumably equally novel, but by Gray's definition only the latter should be frustrating. Additionally an attempt was made to further evaluate Vanderwolfs hypothesis by examining RSA while the task was being learned. The results suggest that (i) novelty does not necessarily produce RSA of 7.5-8.5 Hz, (ii) RSA of 7.5-8.5 Hz may occur in situations not covered by Gray's definition of frustration, !and (iii) the relationship between hippocampal EEG, and both voluntary movement and automatic movement may change as a function of learning a single alternation task.
METHOD
Subjects Subjects were 7 naive male Sprague-Dawley rats weighing 350-500 g at the beginning of the experiment.
Apparatus Training occurred in a 1.68 m straight alley divided by manually operated side opening doors into a 0.20 m startbox, 1.20 m alley and 0.28 m goalbox. Photobeams which controlled a digital elapsed time counter were placed 18 cm from each door in the alley to register maximum running speed to the nearest 0.01 sec. An additional photobeam was placed over the watercup in the goalbox, and all three beams triggered deflections on a second polygraph channel to correlate EEG with location in the alley. Cue lights (Chicago Miniature #1829) were located 25 cm above the startbox and goalbox floors.
Procedure Acquisition and Discrimination. Animals were gradually placed on a 23 1/2 hr water deprivation schedule over three days, during which time they were
HIPPOCAMPALEEG AND BEHAVIOR
563
handled daily for 10 min each. On the fourth day they were placed, three or four at a time, in the alley for a 15 rain adaptation period with no water available in the goalbox. On the fifth and sixth days each animal was confined to the goalbox for 10 rain with ad lib. water. Starting on the seventh day and continuing for four consecutive days, nine continuous reinforcement trials were run each day with 0.25 cc water delivered by a syringe to the watercup on each trial. Continuous reinforcement training was followed by 12 days of single alternation training, surgery, 5 days of recovery, and an additional 8 days of single alternation training. Nineteen trials were run each day, and the sessions always began and ended with a reinforcement. Each animal was placed in its home cage for the 15 sec intertrial interval at which time food was available. At the start of a trial the animal was placed in the startbox. If the trial was to be rewarded, the cue lights were turned "on" 1 sec later; if the trial was nonrewarded the cue lights were turned "off" 1 sec later. The door to the alley was opened 5 sec after placing the animal in the startbox, and the rat was removed 5 sec after arrival at the goal box. Total time for a session was 15-18 rain/animal. All animals were given 1/2 hr ad lib. water after their daily session. Surgery. Hippocampal electrode placements were identical to those specified by Gray et aI. (1972). Under 40 mg/kg Nembutal anesthesia and 0.2rag atropine sulfate, two 130tim insulated stainless steel wires were implanted, one in the right and one in the left posterior dorsal hippocampus. With the skull in a horizontal position, each electrode was placed 6 mm posterior to bregma, and 2 rnm lateral to the midline. The left and right electrodes were lowered to a depth of 4.5 mm and 3.5 mm respectively from the skull surface. A 0-80 stainless-steel screw placed over the frontal sinus was used to ground the animal and three other screws were positioned on the skull to anchor the acrylic. The electrodes were then attached to an Amphenol connector which was subsequently cemented to the rat's skull. Five days of postoperative recovery followed, during which daily injections of 0.15 cc of ampicillin trihydrate (Polyflex) was administered intramuscularly. Recording. Artifact free recording was obtained using a source follower attached to the recording plug and Microdot mininoise cable, which was suspended and counterbalanced for freedom of movement and connected to a Grass 7B polygraph (Filters set at 3 Hz to coincide with Gray's lower setting and 35 Hz.). On the fifth day following surgery, baseline EEG recordings were taken in the home cage. Recordings of two rewarded and two nonrewarded trials were taken for each animal on both the 14th and 20th day of single alternation. On recorded trials the entire EEG was evaluated from the time the animal was placed in the startbox until the time it was removed from the goalbox, with the exception that the < 0.5 sec between the second photobeam in the alley and the photobeam at the goalcup were not analyzed. EEG wave frequencies were computed by counting all waves above 150/aV for an entire segment of behavior
564
KIMSEY, DYER AND PETRI
and dividing by the elapsed time. Recording cables were attached on all trials during test sessions to avoid the possibility of their association with a change in the reward conditions. On each day of test trials, recordings were made before (baseline) as well as during actual test trials. Test Trials. Five additional days of single alternation training followed the initial 20 days of single alternation training. During these 5 days, one of the normally rewarded trials was not rewarded ("unexpected" nonreward) and one of the normally nonrewarded trials was rewarded ("unexpected" reward). One of these test trials was administered during the first half of the daily session and one during the second, but the actual trial was varied from day to day such that the "unexpected" nonreward trial occurring during one half of the session one day would be replaced by an "unexpected" reward trial on the next day. Histology. Following termination o f the experiment, the rats were perfused with saline followea by formalin, their brains frozen and 120/am sections taken in either the coronal or sagittal plane. Sections were stained with a cresyl violet technique and electrode placements verified. Statistics. All differences between latencies and EEG frequencies for the different conditions were tested using the Wilcoxon matched-pairs signed-ranks test, and all P values reported are two-tailed (Siegel, 1956). The pairs were not simply 5 pairs of data obtained from the 5 animals under different conditions. The Wilcoxon test only requires that pairs be matched, and does not exclude the possibility that a number of pairs may be obtained from the same animal. For example, during training the matches were formed by sequentially pairing each reinforced trial with its succeeding nonreinforced trial for both latency and EEG data. In all cases, at least 45 pairs were involved in the analyses.
RESULTS AND DISCUSSION Two animals were eliminated following surgery; one because of a broken ground lead, and the other for failure to run and hypersensitivity to handling. Discrimination of the single alternation schedule was not apparent in the running speed data for rewarded and nonrewarded trials on the 14th day (X rewarded latency = 0.86 sec; X nonrewarded latency = 0.90 sec; Z = 0.12, P > .10) but was apparent on the 20th day (X rewarded latency = 0.87 sec; nonrewarded latency = 2.0 sec; Z = 4.33, P < .001; Fig. 1A). Before the single alternation schedule has been discriminated by the rat, it might be argued that occurrences of reward and nonreward are occasionally novel. In the simplest case, the rat is reinforced on the first trial, and when reinforcement does not occur on the second trial the situation might be construed as novel. Further, it might be argued that repeated occurrences of these "novel" events would eventually reduce their novelty. However, once the schedule has been accurately
HIPPOCAMPALEEG AND BEHAVIOR
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Fig. 1. (A)Mean running latencies during the 20 days of single alternation acquisition. Five days elapsed between acquisition days 12-14, during which electrode implantations and postsurgical recovery occurred. (B) Mean EEG frequencies for the three sections of the runway during rewarded and nonrewarded trials before (day 14) and after (day 20) discrimination of the single alternation schedule was evident. Abbreviations; AL-alley; GC-go alcup, NR -nonrewarded trials; R-rewarded trials; SB-startb ox, discriminated (i.e., day 20) by the rat, it seems reasonable to presume that "unexpected" events again become novel. RSA occurred in the startbox at all times, and as Gray and Ball report (1970), was of a frequency between 7.5 and 8.5 Hz (X = 7.9). As found by both Gray and Vanderwolf, RSA frequency increased as the animals ran down the runway (X = 9.1), and was significantly greater than the startbox frequency (Z = 6.99, P < .001). There were no reliable differences in frequency of RSA in either the startbox or runway between reinforced and nonreinforced trials, either before or after learning (all F s > . 10). The only significant differences in EEG frequency between reinforced and nonreinforced trials occurred at the watercup. According to Vanderwolf, LIA should accompany the consummatory behavior which occurs on all reinforced trials, and this should represent a difference from all nonreinforced trials. Although this qualitative difference in EEG predicted by Vanderwolf was found in the present study, it was possible to evaluate frequency independent of waveform rhythmicity. Differences in EEG frequency between reinforced and nonreinforced trials were significant both before learning (day 14; Z = 2.84, P < . 0 0 5 ) and after learning (day 20; Z = 3.87, P < .001). Frequency differences between reinforced trials before and after learning, and between nonreinforced trials before and after learning were not significant (all P's > . 10; Fig. 2B). Since the test trial phase of the experiment introduced a potentially disrupting influence upon the task, it is important to demonstrate that during the five test days a difference between the latencies of reinforced and nonreinforced trials still existed. Statistical analysis showed this latency difference to be significant (Z = 4.37, P <2.001 ; Fig. 2C).
566
KIMSEY, DYER AND PETRI
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Fig. 2. (A) Sagittal section of rat hippocampal formation showing placement of both recording electrodes (2 mm lateral from midline, 6 mm posterior to bregma).-left electrode placement (4.5 mm below skull); *-right electrode placement (3.5 mm below skull). Drawing modified from K6nig and Klippel (1963). (B) Representative EEG records from rat No. 2 on day 5 of test trials. (C) Mean running latencies during the five test days. (D) Mean EEG frequency during test trials under four reward conditions in the three sections of the runway. Abbreviations; AL-alley; EX-NR-expected nonreward; EX-R-expected reward; FH-fimbria hippocampi; GC-goalcup; GD-gyrus dentatus; HI-hippocampus; LIA-large irregular activity; RSA-rhythmic slow activity; S-subiculum; SB-startbox; SH-sulcus hippocampi; UN-EX NR-unexpected nonreward; UN-EX R-unexpected reward.
HIPPOCAMPALEEG AND BEHAVIOR
567
During the test trial phase there were no differences in EEG frequency between any of the conditions at the startbox. In the alley, no differences in frequency occurred between the two conditions in which reward was expected, nor was there a difference between the two conditions in which nonreward was expected (all P's > .10). Consequently the data from the two expected reward conditions was pooled and compared to the pooled data from the two expected nonreward conditions. This comparison was significant (Z = 3.47, P < .001), indicating that either (i) learning affects EEG frequency in the alley, or (ii) as Vanderwolf might predict, vigor of response, measured here by differences in latency, could account for the observed differences in EEG frequency (Fig. 2D). Although similar EEG differences occurred between the two conditions on day 20, that difference was not significant. The failure to find significance on day 20 may be attributed to either the relatively smaller amount of data from which the day 20 comparison was made, or to the fact that further learning may have been necessary for the difference to fully develop. Grasty~n et al. (1959) report that novelty is accompanied by desynchronization and decreased amplitude of the hippocampal EEG (SIA). If novelty had been the important variable in this experiment, then EEG frequencies at the watercup for the "unexpected" reward and "unexpected" nonreward conditions should both reflect the SIA pattern, but should be different from the conditions in which reward and nonreward are both "expected" and do in fact occur. It was shown that "unexpected" reward and "unexpected" nonreward do differ from each other (Z = 4.37, P < .001). Thus, if the Grasty~n et al. analysis is accurate, then it may be possible that the response to novelty can be masked by other hippocampal responses. As predicted by Gray, the "unexpected" nonreward conditions produced RSA between 7.5 and 8.5 (X = 7.9). However on trials when reinforcement would not normally have occurred, and in fact did not occur, similar frequencies were observed (X = 8.0). The difference between the frequencies in these two conditions was not significant (Z = . 7 1 ; P > .10). The "unexpected" reward trials were accompanied by a mean LIA of 6.4 Hz, which was not significantly different from the mean LIA of 6.6 Hz found at the watercup on those trials when reward was both "expected" and occurred (Z = .46;P > .10; Figs. 2B and 2D). If frustration is the omission of anticipated reward, and if this is mirrored by RSA of 7.5-8.5 Hz, then trials on which reward is neither anticipated, nor occurs cannot be construed as frustrating and should not be accompanied by 7.5-8.5 Hz. In our experiment RSA of this frequency does accompany anticipated nonreward. Thus, as Vanderwolf would predict, EEG activity at the watercup may be explained by the presence or absence of automatic behaviors associated with reward. These test trial results thus suggest that (i) either Gray's definition of frustration must be reevaluated to include anticipated nonreward as frustrating; or (ii) RSA of 7.5-8.5 Hz may correlate with behaviors other than those which are frustrating.
568
KIMSEY, DYER AND PETRI REFERENCES
Elazar, A. and Adey, W. R, (1967). Spectral analysis of low-frequency components in the electrical activity of the hippocampus during learning. Electroencephalogr. Clin. Neurophysiol. 23, 225-240. Grasty~n, E., Lissak, K., Madar~sz, I. and Donhoffer, H. (1959). Hippocampal electrical activity during the development of conditional reflexes. Electroencephalogr. Clin. Neurophysiol. 11,409-430. Gray, J. A., Araujo-Sllva, M. T. and Quint~o, L. (1972). Resistance to extinction after partial reinforcement training with blocking of the hippocampal theta rhythm by septal stimulation. Physiol. Behav. 8, 497-502. Gray, J. A. and Ball, G. G. (1970). Frequency-specific relations between hippocampal theta rhythm, behavior and amobarbital action. Science. 168, 1246-1248. Klemm, W. R. (1970). Correlation of hippocampal theta rhythm, movements and brainstem reticular formation activity. Commun. Behav. Biol. 5, 147-151. K6nig, J. F. R. and Kfippel, R. A. (1963). "The Rat Brain," Baltimore: William and Wilkins. Siegel, S. (1956). "Nonparametric Statistics for the Behavioral Sciences," New York: McGraw-Hill. Tyler, D. W., Wortz, E. C. and Bitterman, M, E. (1953). The effect of random and alternating partial reinforcement on resistance to extinction in the rat. Amer. J. Psychol. 66, 57-66. Vanderwolf, C. H. (1971). Limbic-diencephafic mechanisms of voluntary movement. Psychol. Rev. 78, 83-113. Whishaw, I. Q. and Vanderwolf, C. H. (1973). Hippocampal EEG and behavior: changes in amplitude and frequency of RSA (theta rhythm) associated with spontaneous and learned movement patterns in rats and cats. Behav. Biol. 8, 461-484.
Relationship Between Hippocampal EEG, Novelty, a n d F r u s t r a t i o n in the R a t
RANDALL A. KIMSEY, 1 ROBERT S. DYER, and HERBERT L. PETRI
Department of Psychology, Towson State College, Baltimore, Maryland 21204 In a single alternation runway task, rat hippocampal EEG's changed with learning. At the goal cup, EEG frequencies varied depending upon whether a trial was reinforced or nonreinforced. Frequencies of 7.5-8.5 Hz accompanied nonreinforced trials while lower frequency less synchronized activity accompanied reinforced trials. These EEG patterns did not appear closely related to novelty or frustrative nonreward.
Gross electrical recordings from the dorsal hippocampus have been classified into three types: (a) rhythmical slow activity (RSA), commonly referred to as theta and characterized by highly synchronized waves between about 6 and 12 Hz in the rat; (b)Large amplitude irregular activity (LIA), characterized by high amplitude, low synchrony, and usually lower frequency waves than RSA; and (c) small amplitude irregular activity (SIA), characterized by apparent suppressions of hippocampal electrical activity for short (1-2 sec) bursts of time (Vanderwolf, 1971). The behavioral significance of these different types of activity, especially RSA, is a matter of some disagreement. The occurrence of RSA has alternatively been correlated with attention to meaningful stimuli in the environment (Grasty~n, Liss~ik, Madar~isz, and Donhoffer, 1959), initiation of skeletal movements (Klemm, 1970), and implicated in memory consolidation and recall during learning (Elazar and Adey, 1967). Vanderwolf (1971) hypothesizes that RSA occurs only during specifically voluntary movements and that changes in RSA related to learning really represent changes in voluntary movement coincident with efficient performance of the task. LIA is presumed by Vanderwolf to correlate with automatic behaviors, such as eating and drinking.
1Address: Department of Psychology, University of Delaware, Newark, Delaware, 19711. 561
562
KIMSEY, DYER AND PETRI
Within those occasions on which lISA is present, attempts have been made to relate the frequency of RSA to specific behaviors. One such attempt by Gray and Ball (1970) suggests that RSA between 7.5 and 8.5 Hz occurs when an animal is frustrated, which they define as the omission of anticipated reward. Gray and Bali's experiments do not rule out the possibility that occurrence of 7.5-8.5 Hz RSA is related to novelty, which presumably is present when an expected reward is omitted. Single alternation is a task in which rats can discriminate trials to be reinforced ("expected" reward) from nonreinforced trials ("expected" nonreward) as indicated by slower running speeds on normally nonreinforced trials (Tyler, Wortz, and Bitterman, 1953). In the present experiment a single alternation task was used to test Gray's hypothesis by providing occasions for "unexpected" reward as well as "unexpected" nonreward. Both conditions are presumably equally novel, but by Gray's definition only the latter should be frustrating. Additionally an attempt was made to further evaluate Vanderwolfs hypothesis by examining RSA while the task was being learned. The results suggest that (i) novelty does not necessarily produce RSA of 7.5-8.5 Hz, (ii) RSA of 7.5-8.5 Hz may occur in situations not covered by Gray's definition of frustration, !and (iii) the relationship between hippocampal EEG, and both voluntary movement and automatic movement may change as a function of learning a single alternation task.
METHOD
Subjects Subjects were 7 naive male Sprague-Dawley rats weighing 350-500 g at the beginning of the experiment.
Apparatus Training occurred in a 1.68 m straight alley divided by manually operated side opening doors into a 0.20 m startbox, 1.20 m alley and 0.28 m goalbox. Photobeams which controlled a digital elapsed time counter were placed 18 cm from each door in the alley to register maximum running speed to the nearest 0.01 sec. An additional photobeam was placed over the watercup in the goalbox, and all three beams triggered deflections on a second polygraph channel to correlate EEG with location in the alley. Cue lights (Chicago Miniature #1829) were located 25 cm above the startbox and goalbox floors.
Procedure Acquisition and Discrimination. Animals were gradually placed on a 23 1/2 hr water deprivation schedule over three days, during which time they were
HIPPOCAMPALEEG AND BEHAVIOR
563
handled daily for 10 min each. On the fourth day they were placed, three or four at a time, in the alley for a 15 rain adaptation period with no water available in the goalbox. On the fifth and sixth days each animal was confined to the goalbox for 10 rain with ad lib. water. Starting on the seventh day and continuing for four consecutive days, nine continuous reinforcement trials were run each day with 0.25 cc water delivered by a syringe to the watercup on each trial. Continuous reinforcement training was followed by 12 days of single alternation training, surgery, 5 days of recovery, and an additional 8 days of single alternation training. Nineteen trials were run each day, and the sessions always began and ended with a reinforcement. Each animal was placed in its home cage for the 15 sec intertrial interval at which time food was available. At the start of a trial the animal was placed in the startbox. If the trial was to be rewarded, the cue lights were turned "on" 1 sec later; if the trial was nonrewarded the cue lights were turned "off" 1 sec later. The door to the alley was opened 5 sec after placing the animal in the startbox, and the rat was removed 5 sec after arrival at the goal box. Total time for a session was 15-18 rain/animal. All animals were given 1/2 hr ad lib. water after their daily session. Surgery. Hippocampal electrode placements were identical to those specified by Gray et aI. (1972). Under 40 mg/kg Nembutal anesthesia and 0.2rag atropine sulfate, two 130tim insulated stainless steel wires were implanted, one in the right and one in the left posterior dorsal hippocampus. With the skull in a horizontal position, each electrode was placed 6 mm posterior to bregma, and 2 rnm lateral to the midline. The left and right electrodes were lowered to a depth of 4.5 mm and 3.5 mm respectively from the skull surface. A 0-80 stainless-steel screw placed over the frontal sinus was used to ground the animal and three other screws were positioned on the skull to anchor the acrylic. The electrodes were then attached to an Amphenol connector which was subsequently cemented to the rat's skull. Five days of postoperative recovery followed, during which daily injections of 0.15 cc of ampicillin trihydrate (Polyflex) was administered intramuscularly. Recording. Artifact free recording was obtained using a source follower attached to the recording plug and Microdot mininoise cable, which was suspended and counterbalanced for freedom of movement and connected to a Grass 7B polygraph (Filters set at 3 Hz to coincide with Gray's lower setting and 35 Hz.). On the fifth day following surgery, baseline EEG recordings were taken in the home cage. Recordings of two rewarded and two nonrewarded trials were taken for each animal on both the 14th and 20th day of single alternation. On recorded trials the entire EEG was evaluated from the time the animal was placed in the startbox until the time it was removed from the goalbox, with the exception that the < 0.5 sec between the second photobeam in the alley and the photobeam at the goalcup were not analyzed. EEG wave frequencies were computed by counting all waves above 150/aV for an entire segment of behavior
564
KIMSEY, DYER AND PETRI
and dividing by the elapsed time. Recording cables were attached on all trials during test sessions to avoid the possibility of their association with a change in the reward conditions. On each day of test trials, recordings were made before (baseline) as well as during actual test trials. Test Trials. Five additional days of single alternation training followed the initial 20 days of single alternation training. During these 5 days, one of the normally rewarded trials was not rewarded ("unexpected" nonreward) and one of the normally nonrewarded trials was rewarded ("unexpected" reward). One of these test trials was administered during the first half of the daily session and one during the second, but the actual trial was varied from day to day such that the "unexpected" nonreward trial occurring during one half of the session one day would be replaced by an "unexpected" reward trial on the next day. Histology. Following termination o f the experiment, the rats were perfused with saline followea by formalin, their brains frozen and 120/am sections taken in either the coronal or sagittal plane. Sections were stained with a cresyl violet technique and electrode placements verified. Statistics. All differences between latencies and EEG frequencies for the different conditions were tested using the Wilcoxon matched-pairs signed-ranks test, and all P values reported are two-tailed (Siegel, 1956). The pairs were not simply 5 pairs of data obtained from the 5 animals under different conditions. The Wilcoxon test only requires that pairs be matched, and does not exclude the possibility that a number of pairs may be obtained from the same animal. For example, during training the matches were formed by sequentially pairing each reinforced trial with its succeeding nonreinforced trial for both latency and EEG data. In all cases, at least 45 pairs were involved in the analyses.
RESULTS AND DISCUSSION Two animals were eliminated following surgery; one because of a broken ground lead, and the other for failure to run and hypersensitivity to handling. Discrimination of the single alternation schedule was not apparent in the running speed data for rewarded and nonrewarded trials on the 14th day (X rewarded latency = 0.86 sec; X nonrewarded latency = 0.90 sec; Z = 0.12, P > .10) but was apparent on the 20th day (X rewarded latency = 0.87 sec; nonrewarded latency = 2.0 sec; Z = 4.33, P < .001; Fig. 1A). Before the single alternation schedule has been discriminated by the rat, it might be argued that occurrences of reward and nonreward are occasionally novel. In the simplest case, the rat is reinforced on the first trial, and when reinforcement does not occur on the second trial the situation might be construed as novel. Further, it might be argued that repeated occurrences of these "novel" events would eventually reduce their novelty. However, once the schedule has been accurately
HIPPOCAMPALEEG AND BEHAVIOR
565
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Fig. 1. (A)Mean running latencies during the 20 days of single alternation acquisition. Five days elapsed between acquisition days 12-14, during which electrode implantations and postsurgical recovery occurred. (B) Mean EEG frequencies for the three sections of the runway during rewarded and nonrewarded trials before (day 14) and after (day 20) discrimination of the single alternation schedule was evident. Abbreviations; AL-alley; GC-go alcup, NR -nonrewarded trials; R-rewarded trials; SB-startb ox, discriminated (i.e., day 20) by the rat, it seems reasonable to presume that "unexpected" events again become novel. RSA occurred in the startbox at all times, and as Gray and Ball report (1970), was of a frequency between 7.5 and 8.5 Hz (X = 7.9). As found by both Gray and Vanderwolf, RSA frequency increased as the animals ran down the runway (X = 9.1), and was significantly greater than the startbox frequency (Z = 6.99, P < .001). There were no reliable differences in frequency of RSA in either the startbox or runway between reinforced and nonreinforced trials, either before or after learning (all F s > . 10). The only significant differences in EEG frequency between reinforced and nonreinforced trials occurred at the watercup. According to Vanderwolf, LIA should accompany the consummatory behavior which occurs on all reinforced trials, and this should represent a difference from all nonreinforced trials. Although this qualitative difference in EEG predicted by Vanderwolf was found in the present study, it was possible to evaluate frequency independent of waveform rhythmicity. Differences in EEG frequency between reinforced and nonreinforced trials were significant both before learning (day 14; Z = 2.84, P < . 0 0 5 ) and after learning (day 20; Z = 3.87, P < .001). Frequency differences between reinforced trials before and after learning, and between nonreinforced trials before and after learning were not significant (all P's > . 10; Fig. 2B). Since the test trial phase of the experiment introduced a potentially disrupting influence upon the task, it is important to demonstrate that during the five test days a difference between the latencies of reinforced and nonreinforced trials still existed. Statistical analysis showed this latency difference to be significant (Z = 4.37, P <2.001 ; Fig. 2C).
566
KIMSEY, DYER AND PETRI
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Fig. 2. (A) Sagittal section of rat hippocampal formation showing placement of both recording electrodes (2 mm lateral from midline, 6 mm posterior to bregma).-left electrode placement (4.5 mm below skull); *-right electrode placement (3.5 mm below skull). Drawing modified from K6nig and Klippel (1963). (B) Representative EEG records from rat No. 2 on day 5 of test trials. (C) Mean running latencies during the five test days. (D) Mean EEG frequency during test trials under four reward conditions in the three sections of the runway. Abbreviations; AL-alley; EX-NR-expected nonreward; EX-R-expected reward; FH-fimbria hippocampi; GC-goalcup; GD-gyrus dentatus; HI-hippocampus; LIA-large irregular activity; RSA-rhythmic slow activity; S-subiculum; SB-startbox; SH-sulcus hippocampi; UN-EX NR-unexpected nonreward; UN-EX R-unexpected reward.
HIPPOCAMPALEEG AND BEHAVIOR
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During the test trial phase there were no differences in EEG frequency between any of the conditions at the startbox. In the alley, no differences in frequency occurred between the two conditions in which reward was expected, nor was there a difference between the two conditions in which nonreward was expected (all P's > .10). Consequently the data from the two expected reward conditions was pooled and compared to the pooled data from the two expected nonreward conditions. This comparison was significant (Z = 3.47, P < .001), indicating that either (i) learning affects EEG frequency in the alley, or (ii) as Vanderwolf might predict, vigor of response, measured here by differences in latency, could account for the observed differences in EEG frequency (Fig. 2D). Although similar EEG differences occurred between the two conditions on day 20, that difference was not significant. The failure to find significance on day 20 may be attributed to either the relatively smaller amount of data from which the day 20 comparison was made, or to the fact that further learning may have been necessary for the difference to fully develop. Grasty~n et al. (1959) report that novelty is accompanied by desynchronization and decreased amplitude of the hippocampal EEG (SIA). If novelty had been the important variable in this experiment, then EEG frequencies at the watercup for the "unexpected" reward and "unexpected" nonreward conditions should both reflect the SIA pattern, but should be different from the conditions in which reward and nonreward are both "expected" and do in fact occur. It was shown that "unexpected" reward and "unexpected" nonreward do differ from each other (Z = 4.37, P < .001). Thus, if the Grasty~n et al. analysis is accurate, then it may be possible that the response to novelty can be masked by other hippocampal responses. As predicted by Gray, the "unexpected" nonreward conditions produced RSA between 7.5 and 8.5 (X = 7.9). However on trials when reinforcement would not normally have occurred, and in fact did not occur, similar frequencies were observed (X = 8.0). The difference between the frequencies in these two conditions was not significant (Z = . 7 1 ; P > .10). The "unexpected" reward trials were accompanied by a mean LIA of 6.4 Hz, which was not significantly different from the mean LIA of 6.6 Hz found at the watercup on those trials when reward was both "expected" and occurred (Z = .46;P > .10; Figs. 2B and 2D). If frustration is the omission of anticipated reward, and if this is mirrored by RSA of 7.5-8.5 Hz, then trials on which reward is neither anticipated, nor occurs cannot be construed as frustrating and should not be accompanied by 7.5-8.5 Hz. In our experiment RSA of this frequency does accompany anticipated nonreward. Thus, as Vanderwolf would predict, EEG activity at the watercup may be explained by the presence or absence of automatic behaviors associated with reward. These test trial results thus suggest that (i) either Gray's definition of frustration must be reevaluated to include anticipated nonreward as frustrating; or (ii) RSA of 7.5-8.5 Hz may correlate with behaviors other than those which are frustrating.
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KIMSEY, DYER AND PETRI REFERENCES
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