Double dissociation of egocentric and allocentric space following medial prefrontal and parietal cortex lesions in the rat.

Animals with medial prefrontal cortex or parietal cortex lesions and sham-operated and non-operated controls were tested for the acquisition of an adjacent arm task that accentuated the importance of egocentric spatial lateralization and a cheese board task that accentuated the importance of allocentric spatial localization. Results indicated that relative to controls, animals with medial prefrontal cortex lesions are impaired on the adjacent arm task but displayed facilitation on the cheese board task. In contrast, relative to controls, rats with parietal cortex lesions are impaired on the cheese board task but show no impairment on the adjacent arm task. The data suggest a double dissociation of function between medial prefrontal cortex and parietal cortex in terms of coding of egocentric versus allocentric spatial information. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Stimulus perseveration and choice behavior in rats with septal lesions.

Conducted 3 experiments to test a total of 56 Sprague-Dawley rats with lesions in the septal area and 45 controls for spontaneous-alternation behavior under various stimulus conditions. Ss with septal lesions exhibited perseveration to olfactory and visual cues presented either alone or in conjunction. This behavior was largely independent of response or spatial contingencies. Placement of the olfactory and visual cues in opposition eliminated the perseverative responding of these Ss. Normal controls exhibited the expected spontaneous-alternation behavior which was largely independent of the olfactory and visual contingencies. Results are discussed in terms of the role of the septum in the utilization of stimulus cues. (28 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Retrograde amnesia for spatial information: a dissociation between intra and extramaze cues following hippocampus lesions in rats

Several recent studies have shown a flat retrograde amnesia for spatial information following lesions to the hippocampus in rats and mice. However, the results of the present investigation demonstrate that in rats that presurgically learned a spatial reference memory task based on extramaze cues, a temporally graded retrograde amnesia is evident following lesions to the hippocampus (1, 16, 32 or 64 days after learning) if two conditions are met. First, that a wide range of retention intervals is used, and second, that independent groups of rats are tested, not a single group that learns different spatial discrimination tasks at different times (expt 1). The results of expt 2 show that the hippocampus does not serve as a consolidating mechanism when the spatial task learned presurgically is based on intramaze cues. Taken together, these results indicate that the hippocampus is critical for the storage and/or retrieval of spatial reference information that was learned up to 1 month before hippocampus damage; however, in the absence of the hippocampus, efficient retention can still occur provided that the spatial knowledge was learned in a simple associative manner.     

Further evidence of dissociation between reactivity and visual evoked response following septal lesions in rats.

Used a more sensitive method than that of a previous study by J. Schwartzbaum, C. Kreinick, and M. Levine (see record 1972-30527-001) for behavioral reactivity to discrete series of photic stimuli, to allow closer examination of relationships between reactivity and averaged visual evoked responses (VERs) recorded at the cortex. 12 male Holtzman rats served as Ss. Septal lesions markedly impaired habituation of behavioral reactivity to flashes but facilitated development of the VER. The elaboration of VERs, particularly late components, is normally associated with habituation of behavioral reactivity to the stimuli. This lesion-induced dissociation was also confirmed through correlational analysis of the relationship between VERs and activity. It is concluded that septal lesions, in effect, attenuate the normal relationship between motoric activity and sensory-evoked response. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Allocentric spatial and tactile memory impairments in rats with dorsal caudate lesions are affected by preoperative behavioral training.

Rats with caudate lesions and pretrained for 36 trials demonstrated impaired performance on the "reference memory" or invariant aspect of a 12-arm maze and normal performance on the "working memory" or variable aspect of the maze. Rats with caudate lesions and no pretraining were also impaired on an invariant tactile discrimination in a T maze, but they were not impaired on the variable goal-arm choice of the T maze. More extensive preoperative training ameliorated behavioral deficits of rats with caudate lesions in the T maze and radial arm maze. Results showed that behavioral impairment after damage to the caudate is not restricted to egocentric tasks as previously suggested, but the caudate seems to be involved in the initial acquisition that is invariant over many trials. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Social behavior of rats with chronic prefrontal lesions.

Studied the social behavior of adult male Wistar albino rats in 6 experiments following medial frontal (n = 20) or orbital frontal (n = 14) lesions. 34 Ss served as controls. While both lesion groups showed transient increases in emotionality, only the Ss with orbital frontal lesions showed changes in social behavior. They were more aggressive in male-male aggression and shock-induced aggression but failed to differ from controls on tests of gregariousness, territorial aggression, and predatory aggression. Data may provide support for C. M. Leonard's (1969) suggestion that the orbital frontal cortex of rats and monkeys is homologous. (27 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Normal conditioning inhibition and extinction of freezing and fear-potentiated startle following electrolytic lesions of medial prefrontal cortex in rats.

The authors investigated the role of medial prefrontal cortex (mPFC) in the inhibition of conditioned fear in rats using both Pavlovian extinction and conditioned inhibition paradigms. In Experiment 1, lesions of ventral mPFC did not interfere with conditioned inhibition of the fear-potentiated startle response. In Experiment 2, lesions made after acquisition of fear conditioning did not retard extinction of fear to a visual conditioned stimulus (CS) and did not impair "reinstatement" of fear after unsignaled presentations of the unconditioned stimulus. In Experiment 3, lesions made before fear conditioning did not retard extinction of fear-potentiated startle or freezing to an auditory CS. In both Experiments 2 and 3, extinction of fear to contextual cues was also unaffected by the lesions. These results indicate that ventral mPFC is not essential for the inhibition of fear under a variety of circumstances. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Intact spatial learning in both young and aged rats following selective removal of hippocampal cholinergic input.

Studies using the selective cholinergic immunotoxin 192 IgG-saporin have demonstrated that lesions of the cholinergic input to the hippocampus from the medial septum/vertical limb of the diagonal band (MS/VDB) do not disrupt spatial learning in the water maze in young rats. However, age-related deficits in spatial learning correlate with the integrity of cholinergic neurons in the MS/VDB, suggesting that these neurons may be more crucial for spatial learning in aged rats. To investigate this hypothesis directly, we selectively lesioned these neurons in aged rats that demonstrated relatively intact spatial learning in an initial screening as well as in a comparison set of young rats. Intact and lesioned rats of both ages rapidly acquired a new place discrimination in a different spatial environment. These results indicate that the cholinergic input to the hippocampus is not differentially involved in spatial learning in aged rats. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Medial prefrontal lesions in the rat and spatial navigation: Evidence for impaired planning.

Rats with medial prefrontal cortical lesions were tested in a modified water maze navigation task. In Stage 1, the rats were trained to locate a hidden platform from a single start location. They were then subjected to a series of trials during which a second start position was used (Stage 2). In Stage 3, the rats had to navigate to a new goal location from the 2 experienced start positions. Stage 4 required the rats to navigate to the same goal as in Stage 3, starting from 4 distinct positions. Finally, a single probe trial with no platform was conducted. Rats with prefrontal lesions were impaired only during Stage 4. This deficit was specific to the 2 start positions newly introduced during this stage, suggesting a dysfunction of planning processes. This impairment might result from a working memory deficit, precluding the animal from forming an adequate representation of the whole course of movements required to reach the platform. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Olfactory learning and memory impairments following lesions to the hippocampus and perirhinal-entorhinal cortex.

The role of the hippocampus and perirhinal-entorhinal cortex was examined in an olfactory discrimination paradigm. Small neurotoxic lesions of the hippocampus (21% tissue damage) yielded relatively unimpaired olfactory retention across brief (30 s), intermediate (approximately 5 min), and 24-hr delays, whereas impairments were noted at 5-day retention intervals. Larger hippocampal lesions (63% tissue damage) spared memory at intermediate delays, with no impact at 8-day retention intervals. Aspiration lesions directed at the perirhinal-entorhinal cortex produced a variable performance pattern, with impairments noted at intermediate, 24-hr, and 5-day delays. Results suggest the hippocampus is not specifically involved in retaining olfactory information, with additional consideration given to the relationship between lesion size and memory impairment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Double dissociation of effects on learning of medial versus lateral hyperstriatal lesions in pigeons.

Three experiments examined the effects of medial and lateral hyperstriatal lesions in two groups of pigeons. In Experiment 1, both hyperstriatal groups were impaired, relative to unoperated and operated control groups, in postoperative performance of preoperatively acquired serial reversal of both spatial and visual discriminations. The deficits of the two hyperstriatal groups appeared both quantitatively and qualitatively similar. Experiment 2 found that performance of spatial reversals was disrupted in the medial, but not in the lateral, hyperstriatal group by a long intertrial interval. Experiment 3 found that acquisition of simultaneous matching-to-sample was disrupted by lateral, but not by medial, hyperstriatal lesions; the lateral group also showed a lower rate of response to the sample stimulus than any of the other groups. Implications of these findings for current theories of hyperstriatal function are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pilocarpine and physostigmine attenuate spatial memory impairments produced by lesions of the nucleus basalis magnocellularis.

Three experiments, with 63 male Long-Evans rats, investigated the effects of bilateral ibotenic acid-induced lesions of the nucleus basalis magnocellularis (NBM) on the acquisition and retention of several spatial memory tasks. Maintenance of spatial memory in a food-search task was impaired following NBM lesions. Acquisition of spontaneous alternation and reinforced alternation in a T-maze, but not the acquisition of a position habit, was also significantly impaired in Ss with these lesions. In several of the tasks, there was evidence of some learning in the lesioned Ss after substantial training, although they were significantly deficient when compared with controls. Intraperitoneal administration of the cholinergic agonists physostigmine sulfate (0.5 mg/kg) or pilocarpine nitrate (3 mg/kg) prior to behavioral testing resulted in a rapid and significant improvement in the performance of the lesioned Ss. Lesions significantly reduced the activity of choline acetyltransferase in the anterior and the posterior neocortex but not the hippocampus. Results indicate that the cholinergic projections originating in the NBM are involved in the learning and memory of spatial tasks. (48 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Defensive behaviors in rats following septal and septal-amygdala lesions.

Results of 2 experiments, utilizing 88 male albino Wistar rats, indicated that septal damage produced hyperdefensiveness rather than attack behavior or general hyperreactivity. Further division of this group indicated that damage to sites anterior and ventral to the septal area, sites previously implicated in the "septal syndrome," produced maximal effect on these behaviors. When amygdala lesions were combined with septal damage, enhanced defensive responding was almost eliminated. Results also indicate that amygdaloid mechanisms are involved in the regulation of conspecific defensive behaviors. (19 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Medial septal lesions disrupt spatial mapping ability in rats.

Rats with lesions of the medial septum were more likely to begin swimming in the wrong direction, swim farther, and, therefore, require more time to find a platform hidden in a Morris water tank than were control rats. Although the performance of the rats with medial septal lesions did improve over trials, their asymptotic performance also failed to equal that of the controls. Movement of the platform to a new position in the tank disrupted the performance of both groups, and, again, the rats with medial septal lesions were slower to locate the moved platform. However, this deficit was completely eliminated when a visual cue indicating the location of the moved platform was introduced. We suggest that these data indicate that damage to the septo-hippocampal cholinergic projection system produces a deficit in the formation or utilization of a spatial map (reference memory) that represents the location of a place with respect to the surrounding distal cues. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dissociation of spatial discrimination deficits following frontal and parietal lesions in monkeys.

Gave 40 rhesus monkeys dorsolateral prefrontal, posterior parietal, or inferotemporal lesions. 4 additional Ss served as unoperated controls. Ss then received 2 forms of spatial discrimination training, based on body position ("egocentric" cues) and on the position of an external referent ("allocentric" cues), respectively. On the former, a place discrimination reversal, frontal Ss were impaired but not parietals. On the latter, a landmark discrimination reversal, parietal Ss were impaired but not frontals; this result was also obtained on a test involving distance discrimination without reversal. Finally, the inferotemporals but not the frontals or parietals were impaired on a nonspatial object discrimination reversal. Results suggest that the 2 modes of spatial orientation, egocentric and allocentric, are related to frontal and parietal mechanisms, respectively. (18 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Selective memory impairments produced by transient lidocaine-induced lesions of the nucleus accumbens in rats.

Reversible lidocaine-induced lesions of the nucleus accumbens (NAC) impaired performance on the spatial win-stay, but not on the cued win-stay, radial arm maze task. Pretraining lesions on the former task did not affect foraging for 4 pellets during either the training or test phases. In contrast, lesions given prior to the test phase significantly disrupted retrieval of 4 pellets on the 8-arm maze. Comparable deficits also were observed in rats trained to forage for 4 pellets on an 8-arm maze without prior win-shift experience. State-dependent drug effects were ruled out by replicating the disruptive effects of lidocaine infusions into the NAC on spatial win-shift performance in rats receiving this treatment prior to both training and test phases. These results suggest that the NAC may interact with the hippocampus to guide foraging behavior requiring memory of previous spatial locations on a maze. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Radio-frequency lesions of the thalamus produce delayed-nonmatching-to-sample impairments comparable to pyrithiamine-induced encephalopathy in rats.

Rats were trained and matched on a delayed-nonmatching-to-sample (DNMTS) task and randomly assigned to treatment. In Exp 1, radio-frequency (RF) lesions were aimed at lateral portions of the internal medullary lamina (L-IML), midline thalamus (MT), mammillary bodies (MB), and the combination of MT and MB. In Exp 2, RF lesions were aimed at the fornix. After recovery, DNMTS was retrained at retention intervals of 3.0–28.0 sec, the critical retention level for 75% DNMTS accuracy was determined by a staircase procedure, and spontaneous exploration was observed in an open field. L-IML lesions produced significant deficits on DNMTS and exploratory behavior that were comparable to deficits on the same tasks in rats recovered from pyrithiamine-induced thiamine deficiency. Fornix lesions produced significant DNMTS deficits that were substantially smaller than for the L-IML group. The MT, MB, and MT?+?MB treatments had no significant effect on DNMTS. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Memory impairments following lesions to the mammillary region of the rat

The contribution of the mammillary region to learning and memory was investigated. It was demonstrated that lesions of this region impair performance on tasks that require memory for spatial information but that the deficit depends both on the amount of damage within the region and the difficulty of the task. A dissociation in the effect of such lesions on performance of comparable spatial and non-spatial memory tasks was shown. In contrast to the deficits observed on spatial memory tasks, the acquisition and retention of a complex non-spatial memory task was not impaired after extensive damage to the mammillary region. Such lesions also did not impair performance in a conditioned taste aversion task. These experiments suggest that the mammillary region may be selectively involved in spatial learning and memory.     

Functional consequences of embryonic neocortex transplanted to rats with prefrontal cortex lesions.

In four experiments, we reexamined the recent report by Labbe, Firl, Mufson, and Stein (1983) that fetal cortical tissue transplanted to an aspirative prefrontal cortical cavity in rats can ameliorate the learning impairments induced by the aspirative lesions. Healthy surviving grafts from young (E16) embryonic donors had no immediate effects on the rats' impairments in T-maze alternation, spatial navigation in the Morris swimming pool task, or locomotor activity, and they produced even greater impairments than the lesions alone when all three tests were conducted after longer (3–5 month) survival periods. Grafts taken from older (E21) donors did produce a short-lasting improvement in the T-maze alternation performance, replicating the previous report. However, this effect was not seen in the other two behavioral tests; the grafts survived poorly, and the beneficial effect was no longer apparent in the long-term tests. It is concluded that (a) functional benefits of embryonic cortical grafts are dependent on a precise combination of conditions rather than being a general phenomenon, and (b) the short-lasting recovery in delayed alternation performance is attributable to diffuse influences of the embryonic tissue on the lesioned host brain rather than to a reconnection of damaged circuitries. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differential effects of prefrontal lesions and combined prefrontal and limbic lesions on subsequent learning performance in the cat.

15 cats were given lesions in either the prefrontal cortex alone (n?=?7) or in the prefrontal cortex, anterior thalamus, mamillary bodies, and subiculum (n?=?8) before being tested in the acquisition of visual-reversal, delayed-alternation, and 2-way active-avoidance tasks. Lesioned Ss were compared to 6 unoperated and 4 sham-operated controls. As an extension of E. Irle and H. J. Markowitsch's (see record 1984-19842-001) study, in which triple limbic lesions failed to impair learning behavior of cats, the present study examined the effects of a lesion in the 4th brain structure (in addition to the original triple lesions). Results indicate that, compared with controls, Ss with prefrontal lesions were impaired in the acquisition of the avoidance task. In contrast, Ss with combined lesions were unimpaired in the acquisition of the visual-reversal task, facilitated in the acquisition of the avoidance task, but impaired in the acquisition of the delayed-alternation task. The superior performance Ss with combined lesions is interpreted as due to a lesion-induced functional shift acting on intact brain structures which, prior to massive limbic lesions, remained inhibited. (56 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)