Distinct roles for striatal subregions in mediating response processing revealed by focal excitotoxic lesions.

This study examined the relative roles of distinct striatal areas in response processing. Rats were trained on a reaction time task that enabled performance on each side of the rat's body to be assessed independently. Rats then received unilateral lesions of the whole dorsal striatum or restricted medial or lateral lesions. Both medial and lateral lesions induced a response bias in contralateral space, but this bias was less severe in rats with medial lesions. Medial striatal lesions led to an increase in premature responses. Lateral striatal lesions produced an increase in late responses. It is suggested that the lateral striatum mediates the selection of responses, and the medial striatum acts to influence inhibitory control over responding. Discrete striatal areas are thus functionally dissociable, but both have a crucial role in the organization of responding in space. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Associative learning in neonatal rats revealed by cardiac response patterns.

Tested whether heart rate (HR) responses could measure learning in infant rats and assessed the effects of odor-temperature pairings on HR. In Exp I, the 15 infant rat pups (3-4 days of age) that received a single pairing of a novel odor (CS) with illness later responded to the CS with sustained accelerations in HR; a different novel odor evoked deceleratory HR responses. The 29 control pups responded to the CS and the 2nd novel odor with cardiac deceleration. In Exp II with 73 Ss, those that received 3 pairings of a novel odor with a cold (10°C) temperature reinforcement displayed a similar pattern of HR responses, i.e., acceleration to the CS and deceleration to the novel odor. The authors conclude that cardiac response patterns are a useful measure of learning in infant mammals. The directional modulations of HR found in the present experiments correspond to previous interpretations of "orienting" and "defensive" reactions derived from studies of HR responses in humans. (28 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Evidence of strategic effects in the modulation of orienting of attention

Two models of visual orienting of attention are frequently described. Voluntary orienting is usually induced by central cues that direct subjects' attention to a given location in the visual space. Automatic orienting is provoked by presentation of peripheral cues. It is shown that automatic orienting induces greater attentional costs and benefits, and is less under a subject's control (Jonides 1981). Furthermore, it is not similarly affected by factors such as signal eccentricity (Umiltà et al. 1991). The present experiment was undertaken to investigate how sensitive automatic orienting produced by peripheral cues is to voluntary modulations of attention. In experiment 1, subjects facing situations daily in which attentional requirements are high, were compared to non-practiced ones. In experiment 2, other groups of practiced subjects facing high or low attentional-demanding situations were tested. In both experiments, subjects were asked to respond to signals, presented in rapid succession, in one of two possible locations in space, on each side of central fixation point. The cue signal automatically oriented attention to one of the two locations in which a first stimulus was presented with 100% probability; 100 ms after the first response (RT1), a second response signal (RT2) was delivered either in the same location (valid condition) or in the opposite location (invalid condition). Four cue probabilities were manipulated for this second stimulus: 100%/0%, 80%/20%, 50%/50%, and 20%/80%. Two eccentricities of 3 degrees and 6 degrees were tested. RT2 data demonstrated that (1) there was no eccentricity effect; (2) the higher the cue probability, the greater were the attentional costs; (3) the attentional effects were smaller in the practiced subjects who faced attention-demanding situations daily, than in the other groups. Put together, these data suggest that automatic orienting of attention can be modulated by voluntary attentional processes, according to cue probability. Furthermore, experienced subjects seem to be able to better distribute their attentional resources in space, with increased task requirements. The adoption of an optimal criterion might lead to the use of a cost minimizing strategy.     

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)     

Pretraining effects on performance of rats with hippocampal lesions.

Investigated the role of pretraining factors in the overresponding observed on differential-reinforcement-of-low-rate (DRL) schedules following hippocampal lesions. 24 Long-Evans hooded rats divided into unoperated Ss and Ss with large or small hippocampal lesions were given 10 or 20 days of continuous reinforcement (CRF) pretraining before exposure to a DRL 20-sec schedule. Either large lesions or extended CRF pretraining resulted in only a transient elevation in response rates, while the unique combination of a large lesion and extended pretraining was required for persistent overresponding on DRL. It is concluded that the overresponding produced by hippocampal damage is not solely a function of loss of hippocampal tissue but depends upon unique training conditions for its appearance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Strength of the orienting response during inhibitory conditioning.

Investigated the strength of the orienting response to a light in 3 inhibitory conditioning experiments, using 72 male Sprague-Dawley rats. In Exp I, the occurrence of the light was negatively correlated with food delivery; this procedure resulted in a decline in the strength of the orienting response. A more rapid decline in the strength of this response was observed in Ss receiving the light and food presented randomly or the light presented alone. In the remaining experiments, a discrimination procedure was used in which the light was presented, nonreinforced, simultaneously with a tone. On reinforced trials, the tone was presented alone and was followed either directly by food (Exp II) or by a clicker that signaled food (Exp III). The results are smiliar to those of Exp I. It is concluded that the strength of the orienting response to a light may reflect the amount of attention or central processing that it receives, which itself is determined by the accuracy with which its immediate consequences are predicted. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Comparisons of behavioral effects of hippocampal and prefrontal cortex lesions in the rat.

5 groups of 5 male Wistar rats each, with aspiration lesions of dorsomedial frontal cortex, ventrolateral frontal cortex, hippocampus, or posterior cortex, or with sham operations, were tested in 5 behavioral situations: emotionality assessment, serial spatial reversals, 70:30 spatial probability, differential reinforcement of low rates (DRL), and barpress extinction. Ss with posterocortical lesions did not differ from operated controls on any task. The effects of lesions in the 2 anatomically defined frontal subfields were clearly dissociated on spatial reversals, spatial probability, and DRL. Lesions in either subfield produced a significant increase in emotionality relative to controls, and neither lesion affected barpress extinction. Results suggest that both frontal subfields may be functionally related to the hippocampus but in different ways. (31 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effects of neurotoxic hippocampal lesions on two effects of context after fear extinction.

Three conditioned suppression experiments with rats examined the role of the hippocampus in 2 effects of context after extinction. Reinstatement is the context-specific recovery of fear to an extinguished conditioned stimulus (CS) that occurs following independent presentations of the unconditioned stimulus (UCS), after extinction. Renewal is the recovery of fear when the CS is presented in the context in which it was conditioned, after extinction in a different context. Results indicated that neurotoxic lesions of the hippocampus, performed before conditioning, abolished reinstatement, which depends on context–UCS associations, but not renewal, which does not. This dissociation is not the result of differences in the recentness of context learning that ordinarily governs the 2 effects. The results suggest that the hippocampus is necessary for some, but not all, types of contextual learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The hamster hippocampal slice: II. Neuroendocrine modulation.

Studied effects of exposing golden hamster hippocampal slices to the gonadal steroids estradiol and testosterone and to delta-9-tetra-hydrocannabinol (THC). At 10–20M, estradiol and testosterone acted as facilitatory neuromodulators on hippocampal slices obtained from male and diestrous female hamsters, respectively. At 10–21M, THC facilitated responses in hippocampal slices from males. Implications for the use of the hamster in investigations of the biobehavioral role of steroid modulation of brain excitability are discussed. (14 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dissociations among the anxiolytic effects of septal, hippocampal, and amygdaloid lesions.

Fear reactions of rats given bilateral lesions to the septum, hippocampus, or amygdala were compared with those of rats given sham lesions, in 2 animal models of anxiety: the shock-probe burying test and the elevated plus-maze test. Septal lesions produced anxiolytic effects in both tests (i.e., an increase in open-arm activity and a decrease in burying), whereas hippocampal and amygdaloid lesions produced neither of these effects. On the other hand, hippocampal and amygdaloid lesions impaired rats' passive avoidance of the electrified shock-probe, whereas septal lesions did not. These dissociations suggest that limbic structures such as the septum, amygdala, and hippocampus exert parallel but distinct control over different fear reactions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pattern memory involves both elemental and configural processes: Evidence from the effects of hippocampal lesions.

The formation of an integrated memory for a pattern of stimulation could be based on the elements of that pattern becoming directly linked to one another, or by each of the elements becoming linked to a shared separate configural representation. These 2 accounts have proven difficult to discriminate between. Here, rats received exposure to four patterns of stimulation, each consisting of an auditory stimulus, a visual context, and a time of day; and we examined whether pre-training lesions to the hippocampus influenced memory for the patterns. These lesions abolished pattern memory that required configural processes (Experiments 1A and 1B) but had no effect on pattern memory that could be supported by elemental processes (Experiment 2). This dissociation provides support for the views that elemental and configural processes ordinarily support pattern memory and that rats with lesions to the hippocampus are left reliant on elemental processes. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

The strength of the orienting response during Pavlovian conditioning.

Exp I, with 8 male hooded-Lister rats, demonstrated that the orienting response toward a light that signaled food declined in strength during conditioning but was temporarily restored during extinction. In Exp II, using 24 male Sprague-Dawley rats, the light was paired immediately with the UCS; but in Exps III and IV (40 male Sprague-Dawley rats), it signaled a tone that in turn signaled the UCS. Exps II–IV showed that continuous reinforcement resulted in a decline in the strength of light orientation. Under conditions of partial reinforcement, orientation to the light was sustained. Exp V, with 32 male Sprague-Dawley rats, demonstrated that the decline in light orientation with a continuous reinforcement procedure was retarded either by preexposing the light for a number of trials prior to conditioning or by intermixing reinforced light trials with nonreinforced presentations of a tone. Reversing the reinforcement contingency associated with the tone restored orientation to the light. (34 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Heart-rate change as a component of the orienting response.

Both Sokolov and the Laceys have proposed that autonomic feedback to central neural structures amplifies or reduces the effects of stimulation. Lacey and Lacey distinguished between the effects of feedback from the cardiovascular system and from other autonomic systems and suggested, specifically, that heart-rate (HR) acceleration should be associated with stimulus "rejection" and HR deceleration with stimulus enhancement. This appeared to be contradicted by evidence that HR increased with the orienting reflex whose function, according to Sokolov, is the enhancement of stimulus reception. However, when studies using simple "nonsignal" stimuli were reviewed, it was found that the criteria identifying an orienting reflex were satisfied by responses of HR deceleration and that instances of HR acceleration probably reflected a "defense," "startle," or "acoustic-cardiac" response. (2 p. ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differential effects of contextual change on latent inhibition and on the habituation of an orienting response.

In Exp I, using 20 female hooded Lister rats, the habituation of the orienting response (OR) shown by Ss to a discrete visual stimulus (a 10-sec light) in a given training context (A) was monitored. Dishabituation occurred, in that the OR returned to its initial level, when the light was presented in a different and novel context (B). In Exp II, 24 female rats received 2 sessions/day, one in each of the 2 contexts. For experimental Ss, the light was presented in Context A until the OR habituated. In the test phase, the light was presented in Context B, but the OR was not restored, suggesting that the dishabituation seen in Exp I depended on the absolute novelty of Context B. In Exp III, Ss from Exp II were required to form a light–food association in both contexts. Slow learning was observed in Ss trained with the familiar light in Context A, but learning proceeded normally with the familiar light in Context B. Thus, a context change that failed to produce dishabituation was enough to prevent the occurrence of a latent inhibition effect. (35 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

"The effects of neurotoxic hippocampal lesions on two effects of context after fear extinction": Errata.

Reports an error in the original article by R. J. Frohardt et al (Behavioral Neuroscience, 2000 [Apr], Vol 114[2], 227-240). On page 229, there is an error in the Method section. The second full sentence on that page should read: Neurotoxic lesions of hippocampus were produced by injections of a mixture of 5.0 μg ibotenic acid and 5.0 μg NMDA per 0.5 ml of normal saline. (The following abstract of this article originally appeared in record 2000-15286-001): Three conditioned suppression experiments with rats examined the role of the hippocampus in 2 effects of context after extinction. Reinstatement is the context-specific recovery of fear to an extinguished conditioned stimulus (CS) that occurs following independent presentations of the unconditioned stimulus (UCS), after extinction. Renewal is the recovery of fear when the CS is presented in the context in which it was conditioned, after extinction in a different context. Results indicated that neurotoxic lesions of the hippocampus, performed before conditioning, abolished reinstatement, which depends on context-UCS associations, but not renewal, which does not. This dissociation is not the result of differences in the recentness of context learning that ordinarily governs the two effects… (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)     

Haloperidol reinstates latent inhibition impaired by hippocampal lesions: Data and theory.

The effect of haloperidol administration on the impairment of latent inhibition produced by aspirative lesions of the hippocampus was examined in the rat eyeblink response preparation. During the preexposure phase, rats with hippocampal or control lesions were either exposed to a tone or allowed to sit in the training apparatus. During the conditioning phase, the tone was paired with an airpuff to the eye after the rats were injected with either saline or haloperidol. Although saline-injected rats with hippocampal lesions did not show latent inhibition, the phenomenon was reinstated in rats that received haloperidol injections. A possible locus of the interaction between hippocampal lesions and haloperidol is the nucleus accumbens. The reported data are well described by a neural network model of classical conditioning. This study contributes to the understanding of the neurophysiology of latent inhibition as well as the neuropsychological bases of schizophrenia. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Defensive behavior and hippocampal cell proliferation: Differential modulation by naltrexone during stress.

The present study investigated the role of endogenous opioids in the expression of defensive behaviors (DBs) and the suppression of cell proliferation (CP) in the dentate gyrus (DG) induced by exposure to predator odor, trimethyl thiazoline (TMT). Adult male rats were injected with either naltrexone (an opioid antagonist, 5 mg/kg) or saline 30 min before exposure to either TMT or a control odor. Behavior was scored for the first 15 min of odor exposure. Bromodeoxyuridine (BrdU, 200 mg/kg) was then injected, and the rats were perfused 1 hr later. Exposure to TMT increased the expression of DBs and suppressed the number of proliferating cells in the DG. Pretreatment with naltrexone attenuated the effects of TMT on DB expression but did not attenuate the effects of TMT on CP. In addition, naltrexone administration suppressed CP in the absence of TMT. These results demonstrate a dissociation between DBs and regulation of CP in the DG. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Schedule-induced polydipsia in rats: Adrenocortical and hippocampal modulation.

Onset of schedule-induced polydipsia (SIP) is related to adrenal gland weight. In 4 experiments with 43 Sprague-Dawley rats, adrenalectomy, but not demedullation, hastened the emergence of SIP, and exogenous corticosterone administration tended to reverse this effect. Hippocampal lesions were followed by a rapid and uniform release of SIP. None of the above manipulations influenced normal (home-cage) drinking. A synthesis of present findings with the literature suggests that the hippocampus and the adrenal cortex interact and that the equilibrium established within this system is reflected, for any particular rat, in its adjunctive behavior. (48 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Skin-conductance orienting response in chronic schizophrenics: The role of neuroleptics.

The primary aim of this study was to determine whether there is an association between neuroleptic treatment and skin-conductance orienting response (SCOR) nonresponding in chronic schizophrenics. In a design adapted to this purpose, we were unable to demonstrate a relationship between neuroleptics and nonresponding. Although inability to prove the null hypothesis precludes a claim that neuroleptic treatment and SCOR nonresponding are unrelated, internal evidence and prior studies strongly suggest that such a dissociation exists in most chronic schizophrenic nonresponders. We also found stable nonspecific and tonic skin conductance activity differences between SCOR "responders" and "nonresponders" on three occasions of testing. We interpret our results as bearing on state and trait issues in chronic schizophrenics. (PsycINFO Database Record (c) 2010 APA, all rights reserved)