Removal of the amygdala plus subjacent cortex disrupts the retention of both intramodal and cross modal associative memories in monkeys.

Naive rhesus monkeys (Macaca mulatta) were trained preoperatively in an automated test apparatus on an auditory–visual (crossmodal) conditional task or on a visual–visual (intramodal) conditional task that involved learning a fixed set of stimulus–stimulus associations or paired associates. After having learned their respective tasks, each monkey received bilateral removal of the amygdala plus subjacent cortex. The 2 experimental groups showed equally poor retention of the stimulus–stimulus associations and subsequently relearned their respective crossmodal and intramodal associations at the same rate. These data argue against the idea that the amygdala is specialized for crossmodal associations. Instead, the data indicate that the amygdala and/or its underlying cortex play a more generalized role in stimulus–stimulus associative memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Interaction of ventral and orbital prefrontal cortex with inferotemporal cortex in conditional visuomotor learning.

Five rhesus monkeys (Macaca mulatta) were trained to learn novel conditional visuomotor associations, to perform this task with familiar stimuli, and to perform a visual matching-to-sample task with the same familiar stimuli. Removal of the orbital and ventral prefrontal cortex (PFv+o) in 1 hemisphere and inferotemporal cortex (IT) in the other, thus completing a surgical disconnection of these 2 regions, yielded an impairment on all 3 tasks. Addition of a premotor cortex lesion to the hemisphere containing the PFv+o lesion did not worsen the impairments. The results indicate that PFv+o interacts with IT in both the learning and retention of conditional visuomotor associations. In addition to those associations, which might be considered lower order rules for choosing a response, frontotemporal interaction also appears to be important for higher order rules, such as those involved in the matching task. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Discrimination learning set in Rhesus monkeys.

The rate of acquisition of discrimination learning set in rhesus monkeys is related to amount of within-problem learning difficulty, and amount of separation between stimuli and respones loci. Experimentally naive monkeys have a weak tendency to approach novel stimuli, but because of generalization from the positive to the negative stimulus within a problem, experimentally sophisticated monkeys tend to approach familiar negative stimuli rather than new stimuli. Early in training there are more errors following a first-trial error than following a correct first-trial response, but later this trend is reversed. All of the data can be accounted for by Hull-Spence theory, with a small number of assumptions added. (79 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Protein kinase Mzeta maintains fear memory in the amygdala but not in the hippocampus.

Recent work on the long-term stability of memory and synaptic plasticity has identified a potentially critical role for protein kinase Mzeta (PKMζ). PKMζ is a constitutively active, atypical isoform of protein kinase C that is believed to maintain long term potentiation at hippocampal synapses in vitro. In behaving animals, local inhibition of PKMζ disrupts spatial memory in the hippocampus and conditioned taste aversion memory in the insular cortex. The role of PKMζ in context fear memory is less clear. This study examined the role of PKMζ in amygdala and hippocampal neurons following a standard fear conditioning protocol. The results indicate that PKMζ inhibition in the amygdala, but not in the hippocampus, can disrupt fear memory. This suggests that PKMζ may only maintain select forms of memory in specific brain structures and does not participate in a universal memory storage mechanism. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The role of ventral and orbital prefrontal cortex in conditional visuomotor learning and strategy use in rhesus monkeys (Macaca mulatta).

[Correction Notice: An erratum for this article was reported in Vol 115(6) of Behavioral Neuroscience (see record 2007-17010-001). In Figure 1 (p. 974), the extent of the intended lesions in the sections 32 and 28 mm from the interaural plane was misprinted. The correctly printed figure is shown in the erratum.] Four rhesus monkeys (Macaca mulatta) were trained to learn novel sets of visuomotor associations in 50 trials or less, within single test sessions. After bilateral ablation of the orbital and ventral prefrontal cortex, the monkeys lost the ability to learn these associations within a session, although they could learn them when given several daily sessions. Thus, relatively slow, across-session visuomotor learning depends on neither the ventral nor orbital prefrontal cortex, but rapid, within-session learning does. The ablations also eliminated at least 2 response strategies, repeat-stay and lose-shift, which might account, in part, for the deficit in rapid learning. The deficit is unlikely to result from a failure of visual discriminative ability or working memory: The monkeys could discriminate similar stimulus material within a session, and reducing the working memory load did not improve within-session learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Role of stimulus ambiguity in conditional learning.

Three experiments using rats and the conditioned emotional response procedure examined the notion that when a conditioned stimulus (CS) is paired with a reinforcer (US), that CS must be ambiguous if the CS–US association is to become the target of conditional control. CS ambiguity was manipulated by varying whether the CS had been preexposed prior to conditioning. In Experiments 1 and 2, it was demonstrated that a cue that accompanied pairings of a CS and shock acquired conditional control over the CS–shock association when that CS had been preexposed, but not when it was novel. The measure of conditional control in Experiments 1 and 2 was the ability of the (conditional) cue to enhance responding to the target CS. Experiment 3 used a blocking procedure to show that this enhancement reflected an amplification of the target CS's effective associative strength. These findings extend existing knowledge of the conditions required for conditional cue formation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perirhinal cortex lesions impair simultaneous but not serial feature-positive discrimination learning.

The role of the perirhinal cortex in discriminative eyeblink conditioning was examined by means of feature-positive discrimination procedures with simultaneous (A-/XA+) and serial (A-/X→A+) stimulus compounds. Lesions of the perirhinal cortex severely impaired acquisition of simultaneous feature-positive discrimination but produced no impairment in serial feature-positive discrimination. The results suggest that the perirhinal cortex plays a role in discriminative eyeblink conditioning by resolving ambiguity in discriminations with overlapping stimulus elements. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Role of the amygdala complex in early olfactory associative learning.

Although olfactory associative conditioning in newborn rats produces marked structural and functional changes in the olfactory bulb, recent evidence suggests that extrabulbar circuits must be involved in storing these early memories. The present experiments examined the role of the amygdala complex on early olfactory learning. Bilateral amygdala lesions or sham lesions were performed on Postnatal Day (PN) 5. On PN6, pups were trained in a standard classical conditioning paradigm associating odor with tactile stimulation. Behavioral testing on PN7 revealed that amygdala lesions blocked odor preferences but had no effect on conditioned behavioral activation. Similar sized neocortical lesions did not impair odor preferences. Importantly, amygdala lesion effects on learned odor preferences could be reversed by extensive overtraining. These results suggest that the amygdala complex plays a critical role in modulating associative learning as early as the 1st postnatal week in the rat. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Taste avoidance, but not aversion, learning in rats lacking gustatory cortex.

Control rats rapidly learned to avoid drinking either a sucrose solution (Exp 1) or an NaCl solution (Exp 2) when the taste was paired with illness. These rats also produced aversive reactivity to each of these solutions in a taste reactivity test. Rats that lacked gustatory cortex (GC) learned to avoid drinking sucrose and NaCl, albeit at a slower rate than control rats. GC rats failed to display aversive reactivity to these tastes. The GC rats did show normal aversive reactivity to a strong quinine HCl solution during additional tests. It is suggested that the avoidance developed by GC rats did not entail a palatability shift of the conditional stimulus as it did in control rats. This altered learning strategy may account for the consistent learning deficits found in GC rats trained to avoid tastes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Comparison of emotional responses in monkeys with rhinal cortex or amygdala lesions.

Four emotionally arousing stimuli were used to probe the behavior of monkeys with bilateral ablations of the entorhinal and perirhinal cortex. The monkeys' behavioral changes were then contrasted with those observed earlier (M. Meunier, J. Bachevalier, E. A. Murray, L. Málková, & M. Mishkin, 1999) in monkeys with either neurotoxic or aspiration lesions of the neighboring amygdala. Rhinal cortex ablations yielded several subtle behavioral changes but none of them resembled any of the disorders typically seen after amygdalectomies. The changes produced by rhinal damage took mainly the form of heightened defensiveness and attenuated submission and approach responses, that is, just the opposite of some of the most distinctive symptoms following amygdala damage. These findings raise the possibility that the rhinal cortex and amygdala have distinct, interactive functions in normal behavioral adaptation to affective stimuli. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The rat prelimbic cortex mediates inhibitory response control but not the consolidation of instrumental learning.

The potential role of the prelimbic cortex of the rat in the acquisition of instrumental responding is currently uncertain. In addition, modeling the acquisition of Pavlovian and spatial conditioning tasks has suggested that the process of acquisition can, for certain forms of learning, be step like and consequently misrepresented in averaged group curves. Here, the authors report an experiment investigating the potential involvement of the prelimbic cortex in instrumental acquisition, in which the authors used the control data to model individual acquisition curves mathematically. The authors show that instrumental acquisition under fixed interval schedules was a gradual process extending over 4 instrumental sessions that is well represented in averaged group curves. Postsession infusion of a protein synthesis inhibitor into the prelimbic cortex did not affect any measure of acquisition, showing that during acquisition the prelimbic cortex does not mediate postsession consolidation of instrumental learning. However, inactivation of the prelimbic cortex increased responding, suggesting that the prelimbic cortex mediates a form of inhibitory response control. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Role of reinforcement in discrimination learning set in monkeys.

Analyzes the major theoretical explanations of learning-set (LS) formation in monkeys after reviewing empirical research on the role of reinforcement in LS formation. Studies showing that a reward can function to decrease as well as increase the probability of choosing an object cast doubt upon theories based on an automatic strengthening function of reward. Hypothesis or strategy selection theories avoid this problem by assuming hypotheses, rather than responses, are subject to reinforcement principles, but hypothesis theories are at best incomplete in their treatment of retention. A theory which assumes that LS formation results from between-problem stimulus generalization of feedback from expected rewards is consistent both with retention studies and with experiments on the function of reward in LS, suggesting that LS formation need not be considered a complex abstractive process. (94 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pretraining NMDA receptor blockade in the basolateral complex, but not the central nucleus, of the amygdala prevents savings of the conditional fear.

The acquisition of conditional freezing is abolished by N-methyl-D-aspartate (NMDA) receptor antagonism in the basolateral complex of the amygdala (BLA) during fear conditioning, suggesting that memory formation is prevented. The present study examined whether there is residual memory, or "savings," for fear conditioning in rats trained under amygdaloid NMDA receptor blockade. Rats infused with D,L-2-amino-5-phosphonovalerate (APV) into the BLA or central nucleus of the amygdala (CEA) during fear conditioning did not acquire either auditory or contextual fear conditioning. However, savings of conditional fear was exhibited by rats infused with APV into the CEA but not the BLA. These results suggest that both the BLA and CEA play a critical role in the acquisition of conditional fear but that the BLA is able to process and retain some aspects of aversive memories in the absence of the CEA. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Contributions of the entorhinal cortex, amygdala and hippocampus to human memory

Recent studies have indicated that, in the monkey, the rhinal cortex (consisting of the entorhinal and perirhinal cortices) is more important to visual recognition memory than the hippocampus or amygdala. The present study investigated the role of the entorhinal cortex in humans using memory scores from surgical epilepsy patients classified according to their mesial temporal lobe pathology. The temporal lobe removals included 4-5 cm of neocortex, amygdala, rhinal cortex and 2-3 cm of the hippocampus and parahippocampal gyrus. Compared to autopsied control subjects, all of the patients showed significant gliosis in the amygdala, but they differed as to whether or not there were entorhinal and/or hippocampal abnormalities. Both preoperatively and one or more years postoperatively, the patients performed tests of verbal recall (Wechsler Memory Scale Logical Memory), visual recall (Rey Figure), verbal recognition and visual recognition (Warrington Recognition Memory Test: Words and Faces, respectively). Preoperatively, patients with hippocampal pathology showed deficits in visual recall. Postoperatively, a significant drop in verbal and visual recall was seen only for patients who lost intact hippocampal tissue, irrespective of the condition of the excised entorhinal cortex. Together, the results argue that the hippocampus is more important than the entorhinal cortex for the recall of newly learned information.     

"The role of ventral and orbital prefrontal cortex in conditional visuomotor learning and strategy use in rhesus monkeys (Macaca mulatto)": Correction to Bussey et al (2001).

Reports an error in The role of ventral and orbital prefrontal cortex in conditional visuomotor learning and strategy use in rhesus monkeys (Macaca mulatta). by Timothy J. Bussey, Steven P. Wise and Elisabeth A. Murray (Behavioral Neuroscience, 2001[Oct], Vol 115[5], 971-982). In Figure 1 (p. 974), the extent of the intended lesions in the sections 32 and 28 mm from the interaural plane was misprinted. The correctly printed figure is shown in the erratum. (The following abstract of the original article appeared in record 2001-18882-001.) Four rhesus monkeys (Macaca mulatta) were trained to learn novel sets of visuomotor associations in 50 trials or less, within single test sessions. After bilateral ablation of the orbital and ventral prefrontal cortex, the monkeys lost the ability to learn these associations within a session, although they could learn them when given several daily sessions. Thus, relatively slow, across-session visuomotor learning depends on neither the ventral nor orbital prefrontal cortex, but rapid, within-session learning does. The ablations also eliminated at least 2 response strategies, repeat-stay and lose-shift, which might account, in part, for the deficit in rapid learning. The deficit is unlikely to result from a failure of visual discriminative ability or working memory: The monkeys could discriminate similar stimulus material within a session, and reducing the working memory load did not improve within-session learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Neural substrates of crossmodal association memory in monkeys: The amygdala versus the anterior rhinal cortex.

Nine rhesus monkeys were trained on visual, tactual, and crossmodal (tactual–visual) versions of delayed nonmatching-to-sample (DNMS). They then received bilateral aspiration lesions of the anterior rhinal cortex or bilateral excitotoxic lesions of the amygdala or were retained as unoperated controls. Monkeys with anterior rhinal cortex lesions displayed a persistent deficit on crossmodal DNMS as well as a deficit on tactual DNMS. In contrast, monkeys with amygdala lesions exhibited only a transient impairment on crossmodal DNMS, and their difficulty appeared to be related to inadvertent damage to the anterior rhinal cortex. The present findings support the idea that the rhinal cortex is important for the formation and retrieval of stimulus–stimulus associations across sensory modalities. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Place navigation in rats with unilateral tetrodotoxin inactivation of the dorsal hippocampus: Place but not procedural learning can be lateralized to one hippocampus.

Lateralization of the Morris water maze task was examined by injecting 5 ng of tetrodotoxin (TTX) into 1 dorsal hippocampus (HPC) of chronically cannulated rats (n?=?20). The task, acquired (A) during unilateral HPC block, was retrieved (R) during TTX blockade of the ipsi- (I) or contralateral (C) HPC. Escape latencies (in seconds) at 3 levels of acquisition and in the 1st 4-trial block of I or C retrieval suggest lateralization was absent after the 1st block (A?=?49, I?=?40, C?=?44), partial after training to an efficient search strategy (A?=?6, I?=?9, C?=?14), and complete after overtraining to goal-directed escape (A?=?4, I?=?4, C?=?12), as further indicated by comparisons of A vs R behavior and probe trials. The analyses also indicate that (1) HPC contributes to the acquisition but is unnecessary for retrieval of the procedural engram, (2) overtrained learning with 1 HPC or intact brain is similar, and (3) there is no left–right hemispheric specialization for place learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Goal-directed responding is sensitive to lesions to the prelimbic cortex or basolateral nucleus of the amygdala but not to their disconnection.

The current view of instrumental conditioning indicates that performance in the early stage of training is maintained by a representation of the outcome, as indexed by its sensitivity to changes in the value of the reward. In the present study, the authors tested the effects of a disconnection of the prelimbic cortex (PL) and the basolateral nucleus of the amygdale (BLA), using an asymmetric lesion procedure, to determine whether these structures interact sequentially as part of a corticolimbic system. In marked contrast to the effects of bilateral lesions of the PL or the BLA, which both altered rats' sensitivity to outcome devaluation, the disconnection of these 2 brain areas was without an effect on outcome devaluation. These results demonstrate that the PL and the BLA mediate different aspects of outcome representation in goal-directed responding. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The amygdala is necessary for the expression of conditioned but not unconditioned analgesia.

Lesions of the basolateral region and central nucleus of the amygdala prevent conditioned analgesia (F. A. Helmstetter, 1992). In general, these regions of the amygdala are more critically involved in the expression of conditioned reactions to aversive events than in the mediation of unconditioned reactions. The impact of amygdala lesions on both conditioned and unconditioned analgesia was explored in Sprague-Dawley rats. The lesions completely prevented the expression of conditioned analgesia, but had no effect on unconditioned analgesia. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Phencyclidine injections into the dorsal hippocampus disrupt long- but not short-term memory within a spatial learning task

Since the hippocampus is likely to be a major site of phencyclidine (PCP) action, the effects of various doses of PCP (1.8, 18 or 36 nM) as well as 3.6 nM MK-801 or saline injected directly into the dentate gyrus of the hippocampus was tested for acquisition of a spatial navigation task (dry land version of a water maze) using a paradigm that assesses short term memory based on learning within a day and long term memory based on learning between days. Results indicated that relative to saline or 1.8 nM PCP injected rats, rats with 18 or 36 nM PCP or 3.6 nM MK-801 injections were impaired in acquisition of the task as measured by increased distances traveled to find the food location between days but not within days. In additional experiments 36 nM PCP or 3.6 nM MK-801 did not produce any deficits in the acquisition of an object discrimination task. It is suggested that PCP through its blocking action of the NMDA receptor in the dentate gyrus or CA1 region of the dorsal hippocampus mediates the consolidation of new spatial location information.