Effects of scopolamine and hippocampal lesions on negative patterning discrimination performance in rats.

Rats were trained in operant chambers to perform an appetitive negative patterning successive discrimination. They were required to respond to the left in response to a tone or click and right to a tone-click compound. Scopolamine and methyl scopolamine impaired performance accuracy and increased response latency and response omissions. Subsequent hippocampal aspiration lesions initially impaired accuracy, which later improved. Lesions decreased response latencies. Finally, the effects of scopolamine and methyl scopolamine were shown to be similar in lesioned and control rats, suggesting that the hippocampus is not involved in the actions of these drugs on this task. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Role of interference in retention by rats with hippocampal lesions.

Studied involvement of the hippocampus in memory in 22 male albino Sprague-Dawley rats by employing a retention task with and without interpolated activity. Ss with extensive damage to hippocampus were able to relearn a preoperatively acquired single-alternation task with savings and to perform the single alternation with relatively long delays at a level similar to that of control Ss. However, hippocampals were more affected than normals by an interpolated activity that interferes with retention. The finding of normal retention combined with increased susceptibility to interference supports the view that the memory impairment in Ss with damage to hippocampus may be due to an excess of interference among stored information. (28 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Selective cytotoxic lesions of the hippocampal formation and DRL performance in rats.

32 male Sprague-Dawley rats were given injections of ibotenic acid that made lesions of neurons throughout the hippocampus (CHC), lesions restricted to area CA3 (CA3), or lesions restricted to the subiculum (SUB), or they were sham-operated (SO). Ss were trained to leverpress on a differential reinforcement of low rates (DRL) schedule. Their performance efficiency was evaluated in 3 experiments. Overall results indicate that acquisition of DRL 12 sec was only slightly impaired by any of the lesions. Increasing the DRL requirement to 18 sec did not affect asymptotic efficiency of responding in the SO, CA3, or SUB group, but it markedly reduced efficiency in the CHC group. Administration of scopolamine reduced efficiency to the same extent in Ss in all surgical treatment groups. It is concluded that hippocampal lesions made with ibotenic acid resemble conventional hippocampal lesions in their behavioral effects on DRL performance. Furthermore, behavioral effects of scopolamine administration do not depend on disruption of activity of cholinoceptive cells in the hippocampal formation, and DRL schedules, although highly sensitive to septohippocampal system disruption, discriminate more between the extent than the location of lesions in the system. (34 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ventrolateral prefrontal cortex lesions in rats impair the acquisition and retention of a tactile-olfactory configural task.

Rats with aspirative lesions of the ventrolateral frontal cortex were tested on acquisition and postsurgical retention of an associative learning task that required that they learn a tactile–olfactory configural discrimination. The task required that they pull up a string to obtain attached food and that they identify the correct string using a compound of string size and odor. The rats were not impaired in initial learning or reversal of the olfactory elements of the discrimination. They were impaired in acquisition and retention of the compound, and their deficit was proportional to lesion size. The results confirm that the ventrolateral frontal cortex is involved in processing of olfactory information and imply that the prefrontal cortex is involved in at least certain types of cross-modal configural associative learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Selective dysgranular retrosplenial cortex lesions in rats disrupt allocentric performance of the radial-arm maze task.

The present study provides the 1st report on the effects of selective lesions of the dysgranular portion of the retrosplenial cortex in rats. Excitotoxic lesions of the dysgranular area were sufficient to impair behavior in the radial-arm maze by biasing the strategy used to solve the task. In particular, rats with dysgranular retrosplenial lesions were less reliant on distal visual cues to control performance of a working memory task in the radial-arm maze. Instead, they were more reliant on using a motor turning strategy to solve the task. This change in strategy is consistent with anatomical data showing that the dysgranular region is the primary recipient of visual inputs to the rat retrosplenial cortex. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Fornix lesions can facilitate acquisition of the transverse patterning task: a challenge for "configural" theories of hippocampal function

Configural theories of hippocampal function predict that hippocampal dysfunction should impair acquisition of the transverse patterning task, which involves the concurrent solution of three discrimination problems: A+ versus B-; B+ versus C-; and C+ versus A-. The present study tested this prediction in rats using computer-graphic stimuli presented on a touchscreen. Experiment 1 assessed the effects of fornix lesions when the three problems were introduced sequentially (phase 1: A+ vs B-; phase 2: A+ vs B-, B+ vs C-; phase 3: A+ vs B-, B+ vs C-, C+ vs A-). Fornix lesions significantly facilitated acquisition of the complete transverse patterning task (phase 3) but had no effect on the number of sessions or errors required to attain criterion during phase 1 or phase 2. In experiment 2, in which all three problems were presented concurrently from the outset of training, fornix-lesioned animals outperformed control animals during the seventh block of acquisition trials and were not impaired during any stage of acquisition. Importantly, these same animals were significantly impaired on two allocentric spatial tasks: T-maze alternation (experiments 1 and 2) and the Morris Swim Task (experiment 1). These results contradict the predictions of configural theories of hippocampal function and cast doubt on the popular notion that spatial learning is a special case of configural learning.     

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)     

Gustatory parabrachial lesions disrupt taste-guided quinine responsiveness in rats.

This study examined the effects of electrophysiologically placed electrolytic lesions in the gustatory zone of the parabrachial nuclei (PBN) on the rat's taste-guided unconditioned licking of quinine hydrochloride during repeated 10-sec trials. Concentration–response functions measured in water-deprived rats before and after surgery significantly shifted to the right as a result of the bilaterally placed lesions. These same rats were tested on their ability to acquire a lithium chloride (LiCl)-based conditioned taste aversion (CTA) to 0.1 M sucrose. Although the largest lesions severely affected performance in both tasks, there was only a modest correlation (r?=?–.447) between the extent of the lesion-induced shift in the quinine concentration–response curves and the degree of sucrose intake suppression after the first CTA conditioning trial. Thus, PBN lesions can disrupt performance on both tasks, but it appears that the neural processes governing unconditioned responsiveness to quinine may be to some extent dissociable from those subserving acquisition of a sucrose–LiCl-based CTA. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Bilateral cerebellar lesions disrupt conditioned eyelid responses in unrestrained rats.

Electromyographic eyelid responses in unrestrained rats were classically conditioned in a Pavlovian delay paradigm by using a tone conditioned stimulus (CS) and periorbital shock unconditioned stimulus (US). After eyelid conditioning was complete, bilateral electrolytic lesions were made in the dentate-interpositus region of the cerebellar nuclei. Initial eyelid conditioning was reliable and very similar to that previously observed in the rabbit, although the asymptotic eyelid responses contained a short-latency startle response in addition to the usual conditioned and unconditioned responses (CR and UR). Substantial decrements in CRs were observed in 13 of the 14 rats with accurately placed lesions. In contrast, startle responses and URs were unaffected. Results replicate the effects of cerebellar lesions on eyelid CRs in the rabbit and suggest that the anatomical basis of eyelid conditioning in both species is similar. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Chorda tympani transection and selective desalivation differentially disrupt two-lever salt discrimination performance in rats

Water-restricted rats were trained to press 1 of 2 levers if a sampled stimulus was NaCl and the other lever if the stimulus was KCl (0.05, 0.1, or 0.2 M). Responses were reinforced with water. After training, the average rate of correct responses was 90%. Performance was unchanged following sham surgery. Chorda tympani (CT) transection reduced average discrimination performance to 67.7% correct, and extirpation of the sublingual and submaxillary salivary glands reduced average performance to 80% correct. Although selective desalivation moderately reduced discriminability, a disrupted salivary environment does not explain the effects of CT transection. More likely, the discrimination deficit in CT-transected rats reflects a loss of critical taste input conveyed by the CT about salts.     

Effects of transplantation of fetal hippocampal or hindbrain tissue into the brains of adult rats with hippocampal lesions on water maze acquisition.

Rats were given bilateral aspiration lesions of the hippocampus. Some of these rats then received bilateral transplants of fetal hippocampal or dorsal ventricular ridge tissue that was dissected from embryonic rat brains at 16 or 17 days of gestation. The remaining rats with hippocampal lesions did not receive fetal brain transplants. Rats with neocortical aspiration lesions, but without transplants, and rats without brain damage were also included in the study. All of the rats were trained to find a submerged platform in a Morris water maze. Rats with the fetal brain transplants were more impaired in some measures of maze learning than were rats with hippocampal lesions only. The results indicate that transplants of fetal brain tissue are not always associated with recovery of behavioral function after brain damage and may even increase a lesion-induced behavioral impairment in tasks that require complex cognitive functioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Anxiolytic effects of cytotoxic hippocampal lesions in rats.

Rats with cytotoxic lesions of the hippocampus were given 3 anxiety tests: social interaction with a novel rat, the elevated zero-maze (a modification of the plus-maze), and hyponeophagia (eating familiar and novel foods in a novel place). Marked anxiolytic effects were seen in the social interaction and hyponeophagia tests, but not on the zero-maze. These results confirm and extend previous experiments that used traditional lesion techniques. The zero-maze result was consistent with other experiments using the plus-maze, in which intrahippocampal administrations of pharmacological agents were not anxiolytic, although variability in ethological tests may also be a factor. As the hyponeophagia test used an elevated apparatus, as in the zero- and plus-mazes, the lack of a lesion effect in the zero-maze was unlikely to have been due to an inability to relieve height-induced anxiety. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Selective hippocampal lesions: Differential effects on performance by rats of a spatial task with preoperative versus postoperative training.

102 male Sprague-Dawley rats with selective lesions involving different hippocampal cell fields and/or projections either learned a complex spatial maze postoperatively or were trained preoperatively and tested after the operations. Following damage to anterdorsal CA1 cells and the alveus, acquisition was impaired, but performance was normal when the task was learned preoperatively; postoperative acquisition and performance of the preoperatively learned task were impaired in animals with fimbrial lesions. Data suggest that the CA1 cell field and the projections to the subiculum play an important role in the acquisition of new spatial information but that these connections are not necessary for the utilization of spatial information learned preoperatively. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Preoperative differential housing and dorsal hippocampal lesions in rats.

The resemblance between the effects of social isolation and of hippocampal lesions (HCLs) in rats led to a study that investigated whether rats socially isolated at weaning rather than grouped counterparts show less behavioral change after sustaining dorsal HCLs when adults. Ss were 8 grouped male Lister rats with HCLs, 8 grouped male controls, 8 isolated male with HCLs, and 8 isolated controls. In socially reared Ss, HCLs produced increased ambulation and object contact in an open field, reduced passive avoidance in a runway task, and produced faster acquisition of active avoidance in a shuttlebox, but there were no such differences in isolation-reared Ss. Ambulation and object contact in isolates were intermediate to those of HCL Ss and intact group-housed Ss, and the behavior of isolates during passive and active avoidance training was generally similar to that of grouped Ss with HCLs. The introduction of a distractor during approach training in an alley reduced running speeds more in Ss with HCLs than in controls. The significant interactions between housing and lesion state suggest that neural pathways associated with the hippocampal formation may mediate some behavioral effects of differential housing. (41 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Olfactory discrimination in rats with anterior amygdala lesions.

In Exp I, 12 male rats with posterior lateral olfactory tract/anterior amygdala lesions or with control neocortical lesions were tested for retention of a preoperatively learned odor detection task and for learning on new odor discrimination problems. All Ss had perfect or near-perfect retention of the detection task, and there were no discernible differences between groups in learning on the new odor discrimination problems. In Exp II, an intensity-difference threshold for olfaction was determined in 4 male Long-Evans rats before and after similar lesions. There were no apparent differences between pre- and postoperative performances on this psychophysical test. Results indicate that lateral olfactory tract projections to the amygdala and posterior olfactory cortex are not essential for normal performance on simple olfactory discrimination tasks, although the more caudal projections of the olfactory bulb play an important role in the arousal and maintenance of certain species-typical behaviors. (21 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Septal lesions in rats produce reversal deficits in a simultaneous visual discrimination.

Trained 54 rats with septal lesions and their operated controls on a 2-choice simultaneous brightness discrimination problem and its reversal using a correction procedure in a maze with 4 sequential choice points. Rats with septal lesions were deficient in the reversal of this brightness discrimination. However, this deficit was seen only in a measure of repeated errors and was considerably altered by forced preexposure to selected cues involved in discrimination. Thus, perseveration was seen, as measured by repeated errors, even though rats with lesions reached criterion in the same number of trials as operated controls. Findings emphasize the critical nature of stimulus conditions, response measures, and the history of the animal in determining the effects of brain damage on behavior. (37 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Consequences of serial cortical, hippocampal, and thalamic lesions and of different lengths of overtraining on the acquisition and retention of learning tasks.

The ability of the rat brain to acquire or to retain specific learning tasks was tested under conditions of multiple lesions and widely varying amounts of practice in 53 male young adult rats. Ss were randomly assigned to 1 of 4 groups in which lesions were made in 2 of 3 structural complexes (the medial prefrontal and cingulate cortex, the anterior and mediodorsal thalamus, and the dorsal and ventral hippocampus) or in all 3 before acquisition of the 2 learning tasks (Groups 1–4), or they were assigned to 1 of 3 groups in which lesions of all 3 structural complexes were made following the acquisition of the 2 learning tasks (Groups 5–7). Results question the assumption that serial lesions with intermittent training between lesions have beneficial effects and emphasize the importance of task practice (i.e., behavioral experience). It is argued that prolonged training will lead to a widely distributed storage of information within the brain. The process of wide diffusion of information will, however, be disturbed (or at least retarded) by lesions made shortly after task acquisition or task reacquisition (as was the case for Ss of Group 5). (159 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Reversible lesions of the red nucleus during acquisition and retention of a classically conditioned behavior in rabbits.

Previous lesion, recording, and stimulation studies implicated the cerebellum and its associated brain-stem circuitry as essentially involved in classical conditioning of discrete, somatic muscle responses. A prior study of interpositus cooling showed that the formation of memory was prevented. The present study assesses the red nucleus (RN) for its role in the plasticity associated with learning and memory by using local cooling as a reversible lesion technique. A cooling probe was implanted lateral to the RN. Recording electrodes were implanted in the right RN and the left interpositus nucleus (IPN). Animals were trained for 6 days with the cooling probe activated. No behavioral CRs developed, and multiple unit recordings related to learning did not develop in the RN. However, a learning related model did develop in the IPN. After 5 days of training while cooling, animals were given 5 days of normal training (cooling probe inactive) to assess retention. Substantial savings were evident when normal training was given. CRs appeared quickly on the 1st day of normal training, and multiple unit models were present in both RN and IPN. Results support the idea that the red nucleus is a necessary efferent for the memory trace formed in the cerebellum. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Lesions of the middle cerebellar peduncle disrupt acquisition and retention of the rabbit's classically conditioned nictitating membrane response.

Rabbits were classically conditioned to emit a nictitating membrane response (NMR) to either a light or tone conditioned stimulus (CS) paired with an eye shock unconditioned stimulus (UCS). They then received lesions of the middle cerebellar peduncle (MCP) or served as unoperated controls. Following surgery, they were given separate presentations of tone, light, and vibratory CSs, each paired with the eye shock UCS. In this way, conditioned responses (CR) to the previously trained light or tone served as a test of retention, whereas CRs to the remaining two conditioned stimuli (tone and vibratory or light and vibratory) served as a test of acquisition. The results of the study revealed that rabbits with complete lesions of the MCP showed disrupted acquisition and retention of the conditioned NMR to all stimuli, rabbits with partial MCP lesions also showed disrupted acquisition and retention to all CSs, but to a lesser degree, and animals with lesions that missed the MCP and unoperated controls both showed normal acquisition and retention of the conditioned NMR. (PsycINFO Database Record (c) 2010 APA, all rights reserved)